More About Blood and the Heart

I don't really have much more to say about blood, apart from a couple more points about blood clotting and blood groups. I don't really have a lot more to say about the heart, either, except talk about cardiovascular disease.

Blood Clotting

In my previous post about blood, I mentioned that platelets are responsible for blood clotting but I didn't go into too much detail. I'm still not going to go into too much detail, but I will go into more detail than I did last time ;)

For most small tears to blood vessels, not too much has to be done. First of all, the muscles in the walls of the blood vessels constrict to reduce blood loss, and then platelets stick to the rough surface caused by damage (normally the internal walls of blood vessels are smooth, but not when damaged). As more and more platelets are attracted to the injury, the platelets begin to stick to each other and form a plug which reduces blood loss further. Next the platelets release substances that prolong the constriction of the damaged vessels until they heal themselves.

If the damage is much worse, then coagulation (a.k.a. blood clotting) is necessary. Many reactions take place involving a large number of chemical substances in the plasma called clotting factors. These result in the formation of threads of insoluble protein, which trap the cells in the blood, forming a clot. The threads hold the clot in position, before a slower process called clot retraction takes place, in which the threads contract, becoming denser and stronger and pulling the edges of the blood vessels together. While this happens, a fluid called serum is squeezed out. After this, the clot dries and forms a scab which protects the wound from infections.

There are several factors that stop blood from forming clots in undamaged vessels. First of all, as mentioned before, undamaged blood vessels have smooth walls that platelets can't stick to. Secondly, the plasma also contains anticlotting factors.

Blood Groups

I'm sure you've all heard of the ABO and Rhesus blood group systems, right? Well, here I'm going to explain how they work.

Basically your red blood cells (erythrocytes) may or may not contain specific antigens which determine your blood group. Antigens are substances that can stimulate the formation of antibodies, and the antigens on your red blood cells can consist of either antigen A only, antigen B only, both antigens A and B, or neither antigen. This corresponds to blood groups A, B, AB and O, respectively.

Meanwhile, your plasma contains the antibodies that react against the antigens that you don't have- for example, if you have group A blood (i.e. your red blood cells only have antigen A), you will have anti-B antibodies. Similarly, group B blood has anti-A antibodies. Type AB blood doesn't have any antibodies, while type O blood has both anti-A and anti-B antibodies.

You can't receive blood that contains antigens that your antibodies are going to attack, otherwise the donated blood will clump and disintegrate. For example, if someone has group B blood, with anti-A antibodies in the plasma, receiving A or AB blood will just result in a lot of cells clumping together before disintegrating. Type AB is probably the best off in this regard- their blood has no anti-A or anti-B antibodies, so they can receive blood from any other blood group! Type O, on the other hand, can only receive type O blood (since type O has both anti-A and anti-B antibodies), but thankfully type O is the most common type of blood (followed by type A, then type B, then type AB). Generally attempts are made to give the patient blood of the same type, but if that fails then, unless the patient is O negative (more on the Rhesus +/- system in a bit), another compatible type is given.

One thing that I don't really understand is why it isn't a problem the other way. As in, if someone has type AB blood and they receive type O, why don't the anti-A and anti-B antibodies in the donated blood react with the A and B antigens in the patient's blood? Could someone please answer this for me?

Now we're onto the Rhesus system! As well as the antigens listed above, there are also Rh antigens which might also appear on our red blood cells! If you have the antigens, you're Rh positive; if not, you're Rh negative. If you're Rh negative, your body will most likely produce anti-Rh antibodies when confronted with Rh positive blood. This is fine the first time, but subsequent exposures will cause your newly-created antibodies to spring into action.

This can also be a bit of a problem during pregnancy, if an Rh-negative woman gives birth to multiple Rh-positive children. The first child will cause the mother's body to produce anti-Rh antibodies; a second Rh-positive child might have its blood cells attacked by these antibodies. This can be prevented or managed through several medical interventions, including Rh immune-globulin injections. (See http://kidshealth.org/parent/pregnancy_center/your_pregnancy/rh.html for more info.)

Transfusions

Determining the patient's blood type is necessary for transfusions. As stated above, attempts are made to get the best match possible, or at the very least a compatible blood type. Another kind of transfusion is an autologous transfusion where the patient's own blood is used, which carries fewer risks, but obviously has a lot of drawbacks (for example, they are pretty much only used for non-emergency surgeries that are planned in advance, so they know when to collect your blood).

Aside from whole blood transfusions, there are several other kinds of transfusions, including red cell concentrates (the red cells are separated out, but the concentrate may also include platelets and leucocytes), plasma, platelet concentrates, cryoprecipitate (it's what you get if you freeze the plasma and let the other bits thaw out. Contains substances necessary for blood clotting) and immunoglobulins (contain antibodies against particular diseases).

Cardiovascular Diseases

Cardiovascular diseases, or heart diseases, come in many different varieties. Many of them are related to arteriosclerosis, which is a "hardening of the arteries." One type of arteriosclerosis, atherosclerosis (which looks too similar to "arteriosclerosis" IMO, which might be why I keep mixing the two up), is caused by the deposition of fatty substances onto the artery walls which creates fatty deposits known as plaques, which then cause fibrous tissue to develop, which results in the deposition of salts, which results in hard, calcified areas. These hard, calcified areas then cause obstructions and result in the artery walls losing their elasticity. 

One treatment for atherosclerosis is balloon angioplasty. First the patient is given drugs that help to dissolve clots, and then a tube with a tiny balloon at the tip is inserted. When the balloon is inflated, the artery expands, loosening the plaque from the wall.

Bypass surgery can be used to treat more severe cases where the blockage is leaving the patient at risk of a heart attack. Veins are taken and placed on the outside of the heart to allow the circulatory system to bypass those arteries affected by atherosclerosis.

Arteriosclerosis can lead to several other heart cardiovascular diseases:

• Coronary heart disease is a result of atherosclerosis in the coronary arteries (arteries that supply blood to the heart- see my post on the circulatory system). The obstructing plaques restrict the supply of blood to the heart muscle, so there might not be enough oxygen supply to the heart, particularly during exercise.
• Angina is pain in the chest that normally occurs during physical activity. It is normally called by atherosclerosis of the coronary arteries. Normally, the pain subsides during rest and there is no damage to the heart muscle, so people with angina can still lead relatively normal lives.
• A heart attack, or myocardial infraction, is a result of a complete stop in blood flow to a part of the heart muscle. A severe obstruction in the coronary arteries is usually the cause- sometimes this is due to plaque, or it might be due to a blood clot (clots can form on the rough surface caused by plaque). As oxygen supply is halted, the muscle in that area dies, resulting in sudden and severe chest pain. If only a small area is affected, it can heal- firstly, scar tissue forms, and then arterial branches develop to supply blood. Heart attacks, can, however, have very adverse effects: if it is severe enough to disturb the normal beat of the heart, cardiac arrest, where the heart pumps little to no blood, may occur. This can result in death within minutes.
  If someone is displaying the signs of a heart attack, you should get them to hospital immediately. Symptoms include chest pain, pain radiating to the left arm, shoulder, neck or jaw, sweating, breathlessness, faintness and palpitations.
• A stroke occurs when atherosclerosis affects the cerebral arteries (arteries supplying the brain with blood). This causes part of the brain tissue to die. Aside from blocked arteries, another cause of a stroke is cerebral haemorrhage, where bleeding occurs at a weak point in one of the arteries. Strokes range from mild to severe, some allowing people to continue leading normal lives, others resulting in death.
• A transient ischaemic attack (TIA) is like a stroke, but shorter, with less severe symptoms. They do not cause any permanent damage, but people who have a TIA should seek treatment as a TIA shares the same causes as other cardiovascular diseases (i.e. if you have a TIA, you're at more risk of stroke etc.)
• Peripheral vascular diseases are cardiovascular diseases affecting the limbs. One type of peripheral vascular disease is arteriosclerosis in the limb arteries, slowing blood supply to a limb. Other types of peripheral vascular disease include phlebitis (inflammation of a vein) which may cause blood clots, or varicose veins (enlarged and lengthened veins which cannot carry blood back to the heart efficiently, potentially resulting in the accumulation of blood in lower limbs).

Aside from these diseases, there are many other kinds of heart diseases. One other is congestive heart failure, or simply "heart failure," which is where the heart is too weak to pump sufficient amounts of blood. This could be due to excessive alcohol consumption, a heart attack, or an infection.

Now that we know what types of heart disease there are, let's look at factors that influence your risk at getting a heart disease so that you can avoid some of them! (Granted, there are some that you can't avoid, for example those related to gender and age, but lifestyle changes can go a long way.)

• Age: Incidence of atherosclerosis increases with age.
• Gender: Men are more likely to suffer from cardiovascular diseases at a younger age than women are (women rarely suffer from cardiovascular diseases until around 45 years old).
• Blood cholesterol: Blood cholesterol, a measure of the fat content of the blood, can be controlled via saturated fat intake and exercise levels. Higher blood cholesterol puts you more at risk of heart disease.
• Blood pressure: Smoking, high alcohol consumption and high salt consumption are all factors that can lead to hypertension, or high blood pressure. High blood pressure is another risk factor for heart disease.
• Weight: Being overweight is another risk factor for heart disease, as there is more strain on the heart and lungs.
• Smoking: Smoking constricts blood vessels, causing hypertension. Also, the CO in smoke combines with haemoglobin, reducing the capacity of the blood to carry oxygen. Not a good combination.
• Alcohol: Consuming too much can lead to hypertension or heart muscle weakness.
• Heredity: If you have a family member with cardiovascular disease, you might be at greater risk.

So, basically, if you want the best chance at avoiding cardiovascular diseases, reduce your saturated fat and salt intake, get in a decent amount of exercise, don't smoke and don't drink excessively. Oh, and choose your parents wisely. (Not that you can. Oops.)

Next up: the respiratory system! When I can be bothered to get off the computer and do some study, that is.

Blood

Following on from yesterday's post about the circulatory system, today I'm going to talk about blood!

Blood actually has quite a lot of stuff in it for a humble red liquid that spurts out every time we get cut or scratched. 55% of our blood is plasma, which is mainly water (91%), but also has proteins (7%) and other substances (the stuff that's being transported to and from the cells) dissolved in it. The other 45% of our blood is made up of the cells in it, namely erythrocytes (red blood cells), leucocytes (white blood cells) and thrombocytes (platelets).

Blood helps maintain the internal environment of the body (for some reason the word "homeostasis" comes to mind here, but I don't know whether it's applicable in this context). It not only does this through carrying nutrients to the cells and removing their wastes, but it also maintains the pH of bodily fluids, distributes heat, maintains water content and ion concentration of bodily fluids, and protects against diseases.

Let's take a look at all of the components in blood (as listed above) and how they help to achieve these functions:

Plasma

• Water (91%)- solvent for all of the other substances contained in plasma.
• Proteins (7%)- Proteins in the plasma are known as plasma proteins, and consist of albumins (like those in egg whites), globulins (some can act as antibodies when fighting diseases) and fibrinogen (involved in blood clotting). These proteins are what makes the blood sticky.
• Ions- including sodium (Na+), potassium (K+), calcium (Ca2+), chloride (Cl-) and bicarbonate (HCO3-). Ions and proteins combined contribute to the osmotic pressure of the blood, encouraging more water to diffuse into the blood (see my earlier post about diffusion and osmosis for more info on how this works).
• Other substances- include nutrients dissolved from food, dissolved gases (oxygen and carbon dioxide), hormones, waste products from cells, etc. Proportion of these substances depend on what part of the body you're looking at, among other factors.

Formed Elements

These are basically the cells suspended in the plasma- the aforementioned red and white blood cells, as well as platelets.

Erythrocytes (a.k.a. red blood cells)

FACT FILE

• Unique features: No nucleus, contains haemoglobin
• Colour: Red (obviously)
• Shape: Circular and biconcave (i.e. each side has a concave surface), due to having no nucleus.
• Size: Very small- roughly 7.5 micrometres in diameter.
• Number: In men- about 5.4 million per cubic millimetre. In women- about 4.8 million per cubic millimetre. (We have roughly 4-6L of blood in our bodies, so just imagine how many cells we have in total- or you can calculate it yourself, if you're in that way inclined.)
• Where formed: Red bone marrow (in adults, this is the marrow of bones such as ribs, vertebrae and pelvis) at the rate of around 2 million per second!
• Lifespan: Roughly 120 days, after which the cell membrane becomes fragile due to having no nucleus.
• Main function: Transport oxygen to the cells

How is the main function of this type of cell performed? Although red blood cells are initially formed with nuclei, the nucleus is removed as the cells mature. This makes the cells biconcave in shape, while still leaving plenty of room for haemoglobin. Haemoglobin is required for carrying oxygen around the blood. It's made up of a protein called globin, combined with four haem groups, each containing an iron atom which can combine with an atom of oxygen. The combination of haemoglobin and oxygen is facilitated by the large surface area of the red blood cells, which provides more room for oxygen to diffuse inside. When the iron combines with oxygen, haemoglobin turns red. Each red blood cell can hold up to 300 million molecules of haemoglobin, making red blood cells very red indeed.

Other fun facts about this type of cell: Aging blood cells are destroyed in the liver and spleen. Iron atoms and some other parts of haemoglobin are reused, while other parts, like the bile pigments, get excreted (see my second post on the digestive system). Two million red blood cells are destroyed every second. Two million more are produced in the red bone marrow each second in order to maintain the number of red blood cells. That's a lot of cells being destroyed and created!

What happens if you don't have enough of this type of cell? Anaemia is a condition where the number of red blood cells or the concentration of haemoglobin is reduced. This results in inadequate oxygen supply to the tissues, which then results in a myriad of symptoms including fatigue and intolerance to cold. Anaemia has a variety of different causes, including loss of too much blood, iron deficiency, B12 deficiency (B12 is needed for the normal development of erythrocytes), destruction or inhibition of red bone marrow, or genetic conditions. Some of these types of anaemia have special names- for example, sickle cell anaemia is a genetic condition resulting in deformed red blood cells, and pernicious anaemia is anaemia caused by inadequate B12.

Leucocytes (a.k.a. white blood cells)

FACT FILE

• Unique features: Can shape-change and can engulf bacteria, dead cells and so on. Granular leucocytes, or granulocytes, have granules suspended in the cell contents and their nuclei are "lobed" (that is, they have several lobes connected by thin filaments rather than just being one massive lobe). Agranular leucocytes consist of monocytes and lymphocytes, which do not have granules (hence the name) and usually have spherical nuclei.
• Colour: Hmm... let me think about this one... ... ... ... ... they're white.
• Shape: Can change shape, allowing them to slide through small spaces between the cells of the walls of capillaries etc.
• Size: Larger than erythrocytes- roughly 9-14 micrometres in diameter
• Number: 5000 to 10 000 per cubic millimetre.
• Where formed: Some (granulocytes and monocytes) are formed in the red bone marrow. Another type, lymphocytes, are formed in organs such as the spleen, tonsils, thymus gland and lymph nodes.
• Lifespan: A few days. During infection, they may only live for a few hours. This is because engulfing so much crap takes the life out of them (to be more scientific, "the substances taken in interfere with normal cell functioning").
• Main function: Defend the body against invading microorganisms, remove dead or injured cells

How is the main function of this type of cell performed? Their ability to change shape allows them to get around and engulf bacteria, dead cells, cell fragments, and so on. This is known as phagocytosis.

Other fun facts about this type of cell: Although white blood cells are necessary, too many isn't necessarily a good thing, as can be seen in leukaemia, where so many abnormal white blood cells are produced that they fill the red blood marrow, inhibiting the production of red blood cells. This can lead to anaemia.

Thrombocytes (a.k.a. platelets)

• Unique features: No nucleus.
• Colour: ?
• Shape: ?
• Size: Extremely small- only around 2.5 micrometres in diameter, roughly a third of that of an erythrocyte
• Number: 250 000 - 400 000 per cubic millimetre
• Where formed: Red bone marrow, at rate of around 200 billion a day!
• Lifespan: Around 7 days
• Main function: Form blood clots when blood vessels are damaged.

How is the main function of this type of cell performed? According to http://www.med.illinois.edu/hematology/PtClotInfo.htm platelets have several functions during the clotting process, including sticking to the injured blood vessel as well as other platelets to form a "plug," and providing molecules required for the reactions that take place during clotting.

Now that we're pretty much done looking at the blood, let's look at body fluid in general and how it moves between the blood plasma and the tissues.

There are many different names for different kinds of fluid in the body:

• Intracellular fluid: Fluid inside cells.
• Extracellular fluid: Fluid outside the cells. This is broken down into two categories: tissue fluid and plasma. Extracellular fluid moves between the tissues and the blood, carrying stuff with it.
• Tissue fluid (also known as interstitial fluid or intercellular fluid): fluid found between cells in the tissues.

Extracellular fluid mainly passes back and forth via diffusion. Since capillary walls are thin, many substances can diffuse through them (with the exception of larger molecules, such as proteins), due to concentration differences. Additionally, the relatively high pressure at the arterial end of the capillaries forces some fluid out (except for, of course, the stuff that's too big to go through, like the proteins).

Once substances have passed into the tissue fluid, they can be absorbed by cells via several methods, one of which is diffusion. Cells also use similar methods to get rid of their wastes.

The veins of capillaries have relatively low pressure, as the narrowness of the capillaries resists blood flow. Also, the amount of proteins left in there create a high osmotic pressure, which causes much of the tissue fluid to return to the capillaries.

Another great thing about capillaries being so small and so restrictive of blood flow is that the slower flow provides more time and more opportunities for substances to diffuse back and forth.

Now, another thing about fluid for ya. Not all of the fluid that diffuses into the tissue cells diffuses back into the capillaries. To stop the tissues from becoming all bloated, the lymph system kicks in to save the day!

The lymph capillaries begin in the tissues (remember the lacteals from the villi in the small intestine? They're lymph capillaries) before joining up to form larger vessels, called lymphatic vessels, which then join up to become even bigger lymphatic vessels, and so on, until they eventually join into the thoracic duct and the right lymphatic duct which then open up into the subclavian veins which bring blood to the heart from the arms. Lymph nodes, located along the lymphatic vessels, remove bacteria and foreign particles from the lymph (essentially the fluid inside the lymphatic system that used to be tissue fluid. In fact the only difference between lymph and tissue fluid is its location).

The lymphatic system is comprised of the above vessels as well as three organs known as lymphoid organs- the tonsils, thymus and spleen. Lymph vessels are kind of like veins in that contractions of skeletal muscles can move the lymph along (helpful since, unlike the circulatory system, the lymph system has no pump), and in that they have valves to ensure that the lymph only moves in one direction. They are, however, more permeable than veins and other blood vessels (including the capillaries), allowing proteins and other relatively large particles to pass into the lymph capillaries. The lymphoid organs and the lymph node are involved in specific immune responses which help overcome infections.

And that's pretty much it from me on this topic. I'm going to rest now. Maybe have some churros. I dunno.

The Circulatory System

Yesterday I spoke about the digestive system, which absorbs nutrients into the body. Today I'm going to speak about the system that transports these nutrients (as well as oxygen and probably some other substances as well) throughout the body- the circulatory system!

Fortunately, the circulatory system doesn't have such a wide variety of organs to talk about, so this should be done relatively quickly. (Note the emphasis on the word "relatively.")

Basically the circulatory system is made up of:

• the heart;
• arteries and arterioles (very small arteries);
• veins and venules (very small veins); and
• capillaries.

In a nutshell, the arteries take the blood away from the heart. The arteries then branch out into smaller arteries in arterioles, which then branch out into capillaries, which take blood to each individual cell. Then the capillaries join up to venules, which then join up to larger and larger veins, before arriving back in the other side of the heart to start the process again. (The two sides of the heart send the blood to different parts of the body, as we shall soon see.)

Let's first take a look at the heart, since the heart is after all what drives the blood through all of those arteries and veins and capillaries.

The heart is located in the middle of the chest, between the lungs. Sometimes it feels like your heart is a bit more over to the left, but that's only because the left side beats harder than the right side- more on that later.

The heart is made up of four main chambers, two on each side. The two halves are separated by a wall called the septum, and the entire heart is surrounded by a membrane called the pericardium which holds the heart in place and prevents it from overbeating while still giving it some freedom to move while beating. The wall of the heart is made up of cardiac muscle (protip: words containing cardi-, cardia- or cardio- are all related to the heart).

Each side of the heart has an atrium and a ventricle. The atrium is the first chamber that the blood enters after entering the heart through the veins. It has relatively thin walls as the atrium doesn't need a lot of muscle to hold that low-pressure blood coming in from the veins. Next the blood flows to the ventricle, which has thick muscular walls which pump the blood out of the heart and to other parts of the body. Between the two chambers is a valve called the atrioventricular valve which allows blood to flow from atrium to ventricle, but not the other way. These valves consist of flaps as well as fibrous chords, or chordae tendinae. The flaps swing shut when the ventricle contracts due to blood pressure (I think), and the chordae tendinae prevent the flaps from swinging too far. Once the blood leaves the ventricle, the valve at the bottom of each artery, called the semilunar valve, which consists of three cusps, hold any blood that tries to flow back, preventing backflow.

Now that we've looked at what each side of the heart has in common, let's take a look at what's different about each side of the heart. IMO, the main difference lies in where each side pumps the blood.

The left side of the heart receives blood from the lungs and delivers blood to all over the body (except for the lungs). The circulation of blood through the body is known as systemic circulation.

The right side of the heart, on the other hand, receives blood from all over the body (except for the lungs), and delivers it to the lungs. The flow of blood through the lungs is then known as pulmonary circulation (pulmo = lungs).

Let's see how this fundamental difference relates to other differences between the two sides of the heart:

• Since the left side pumps all over the body, while the right side only pumps to the lungs, the left ventricle's muscular wall is much thicker and stronger than the right ventricle's muscular wall in order to pump blood more forcibly. This increased force required to pump blood on the left side is why, if you put your hand on your chest, your left side feels like it's beating harder than your right side.
• The names of the arteries and veins leading into and out of each side of the heart are different.
  On the left side, the vein that flows in from the lungs is called the pulmonary vein. The artery that flows to the body is called the aorta. It's the main artery in the body IIRC, and it splits into many other arteries, some of the main ones being the carotid arteries (to head and neck), the coronary artery (to the heart itself), the subclavian arteries (to the arms), the hepatic artery (to the liver. Also has a branch going to the stomach), the mesenteric artery (to the intestines), the renal arteries (to the kidneys) and the femoral arteries (which take blood to the legs).
  On the right side, on the other hand, there are two veins flowing in from the body: the superior vena cava (from the upper body) and the inferior vena cava (from the lower body). The artery flowing out towards the lungs is called the pulmonary artery, which splits into the left and right pulmonary arteries (one for each lung obviously).
• The left side's atrioventricular valve has two cusps, and is called the bicuspid valve. The right side's atrioventricular valve has three cusps, and is called the tricuspid valve. I don't know why one side has more cusps than the other. Maybe it's because the left side has more muscle to hold the blood in the ventricle?

Oh and a fun fact for you: since the blood gets pumped by the heart twice in each circuit, this type of circulation is known as double circulation. This keeps the blood moving rapidly and stops the blood from losing too much pressure.

Anyway now that I've done talking about all the bits and pieces of the heart, let's see how the heart does its job!

The heartbeat also goes by a more fancy name (just like everything in human biology)- the cardiac cycle. It consists of a sequence of events:

1. For a short time (roughly 0.4 seconds), the atria and ventricles are in diastole- that is to say, the heart muscles are relaxed, allowing the blood to flow into the atria and ventricles (the atrioventricular valves are open at this point).
2. Atrial systole occurs, lasting roughly 0.1 seconds. During this phase, the atrium contracts (that's what's meant by "systole," by the way), forcing blood into the ventricles. Meanwhile, the ventricle stays relaxed, ready to receive the blood rushing in.
3. Ventricular systole then occurs, lasting roughly 0.3 seconds. This forces blood into the arteries (aorta on left side, pulmonary artery on right side).

Although all this beating is happening in the heart, why can we feel a pulse when we put our fingers on particular points on our bodies (such as our wrists or our neck)? This is a question I'll answer very shortly.

Blood Vessels

The heart is very important and all, but equally important are the tubes that take the blood to where it's needed. I'm referring, of course, to arteries, veins and capillaries. Let's have a closer look at what each kind of blood vessel does, and how it serves its function.

Once the blood leaves the heart, it's pumped into arteries, which are branched into smaller arteries, which are branched into very small arteries called arterioles, which then supply blood to the capillaries. Arteries and arterioles have thick, strong walls complete with smooth muscle to help the arteries stretch and relax in order to maintain blood pressure as the blood is pumped through. (Take note that this stretching and relaxing does NOT force the blood along, but rather just maintains the pressure.) The expansion and contracting of the arteries occurs in time with your heartbeat, giving you the ability to feel your pulse at certain points on your body. Other great aspects of having this kind of muscle is that the stretching gives the arteries some flexibility when being assaulted with relatively high pressure blood pumped out from the heart, and that the contracting and relaxing can manipulate the diameter of arteries, which can serve to either reduce or increase blood flow to particular organs, depending on the needs of each organ. These muscles also help regulate blood flow through the capillaries. Speaking of which...

Capillaries are microscopic blood vessels which form complex networks, allowing them to carry blood to nearly every body cell. Their walls are only one cell thick, just like villi, making it easier for things to pass in and out of them. Once blood has gone through the capillaries, it goes through the...

Venules, which are small veins (like how arterioles are small arteries), which later join up to larger and larger veins. Veins carry blood back to the heart. The walls of veins are much thinner than those of arteries, since the blood flowing through them isn't high pressure any more- blood loses a lot of pressure during its journey through the capillaries. Instead, the low pressure causes backflow to be a possible problem- but fear not! Many veins have several valves that prevent backflow of blood.

But if the blood is such low pressure, when does the pressure ever increase enough for any of the valves to open? you may ask. Well, when you move around, your muscles contract, squeezing your veins and providing the pressure required to push your blood along. Due to the valves, the blood can only go in one direction.

There's also more stuff about heart sounds and how those blood pressure monitors and electrocardiograph things work. I'm not going to go into these today, as I'm already quite tired, but maybe at some other point. Or not. I really don't know.

If you really want me to add this stuff though, please let me know. If you're even reading this, that is.

Digestion and Absorption of Food- Part 2

In my last post I said that Part 2 would cover the intestines, which is true, but first I'm going to quickly talk about the liver and the pancreas.

The Pancreas

The pancreas is just beneath the stomach, in the curve of the duodenum (the duodenum is the first C-shaped curve of the small intestine. If you don't understand, just Google it so I don't have to plagiarise someone else's picture, or *shudder* go through the effort of drawing my own diagram :P). The pancreas contains cells that secrete pancreatic juice as well as other cells which secrete the hormones insulin and glucagon, which regulate sugar levels in the blood.

Pancreatic juice is important for digestion as it contains digestive enzymes, including pancreatic amylase which breaks down starch into disaccharides, particularly maltose; trypsin (a.k.a. pancreatic protease- one way to remember this one is that "protease" sounds kinda like "protein") which breaks down proteins into smaller peptide chains; ribonuclease and deoxyribonuclease, which break down RNA and DNA, respectively; and pancreatic lipases (remember, fatty acids are a kind of lipid), which break down fats into fatty acids and glycerol.

One other important attribute of pancreatic juice is that it is slightly basic with a pH of 8. This helps neutralise any HCl that might still be in the chyme from the stomach (as I said in my last post, the chyme is basically the mixture that you get after everything's been digested in the stomach).

Pancreatic juice enters the aforementioned duodenum (beginning of small intestine) via two ducts: first it goes through the pancreatic duct, which is then joined by the common bile duct, which then enters the duodenum.

The Liver

The liver is a rather large organ. It lies just below the diaphragm on the right side of the body. One thing unique about the liver is that it receives blood from two different sources: through a hepatic artery and a hepatic portal vein. (FYI, "hepa-" is a prefix that generally refers to anything to do with the liver.) The hepatic artery, which branches from the aorta (the main artery in the body), carries highly oxygenated blood to the liver. The hepatic portal vein, which passes through the capillaries of the stomach and intestines before going through the liver, takes nutrients from the alimentary canal to the liver.

The liver has a lot of functions- in fact, if my quick Google search is anything to go by, it has over 500 known functions! Fortunately, you don't have to learn about all of them for now. Here's a list of just a few of the functions of the liver:

• Blood glucose regulation: The hepatic portal vein carries glucose to the liver, which is then either used to provide energy to the liver, converted into glycogen, or converted into fat. Glycogen is basically the form in which carbohydrates are stored as an energy reserve for the body. Glycogen can be converted back into glucose and back again to maintain healthy blood glucose levels.
• Deamination: Converts excess amino acids to carbohydrates (since excess amino acids can't be stored). In the deamination process, the -NH2 amine group is removed and converted to ammonia (NH3) which is then converted to urea, which is removed by the blood by the kidneys before being excreted in urine.
• Fat conversion: Fat produced from excess glucose can be transported by the blood to fat storage tissues. Between meals, fat storage tissues release fatty acids into the blood, which are converted by the liver into substances to be used as energy sources for tissues.
• Plasma protein production: The liver produces proteins that can be found in the liquid portion of the blood, otherwise known as plasma.
• Production of blood-clotting factors: Stuff that's required to clot blood is also produced in the liver.
• Storage: The liver stores a variety of different substances, including but not limited to glycogen, iron and vitamins A and D.
• Toxin breakdown: Toxic substances, both those naturally produced in the body and those from external sources, are broken down into harmless substances in the liver.
• Hormone inactivation: Pretty self-explanatory. Some hormones can be inactivated in the liver.
• Heat production: The liver does a helluva lot of stuff, and many of those chemical processes produce heat. Thus the liver also helps to maintain constant body temperature.

Now aside from the above, why else is the liver important to the digestive system? That's because...

• the liver produces bile, which contains both bile salts and bile pigments, among other things. Bile salts are necessary for the mechanical digestion of fat, as they emulsify the fat (i.e. turn it into separate components that can't be mixed back together). This increases the surface area on which enzymes can break them down further. Bile pigments, however, aren't so useful. They're just the end result of red blood cells breaking down, and have no digestive function.
• Bile first travels from the liver to the gallbladder, a sac on the outside of the liver, where it is stored and concentrated before travelling to the duodenum via the common bile duct (the same duct that pancreatic juice travels through right before it gets to the duodenum). After being used in the intestines, the bile salts are nearly all reabsorbed into the blood to be reused, while the bile pigments just get pooped out later on.

Now that the liver and the pancreas are out of the way, it's now time to talk about...

The Small Intestine

The small intestine is only "small" in terms of diameter as compared to the large intestine. In reality, it's pretty long- around 6m. The first part, the aforementioned duodenum, is about 25cm long on its own- and that's just the top bit that goes from the stomach and circles around the pancreas in a sort of C shape before you get to the main part of the small intestine! It's the longest part of the alimentary canal, and it is where both digestion and absorption of food molecules takes place.

As if it wasn't already long enough, the inside of the small intestine has several modifications to increase its surface area and make it even better at digestion. (See Reaction Rates for a tiny bit more info on why increased surface area should make reactions more efficient.) In the small intestine, the mucosa and submucosa are not smooth, but rather have many small folds that extend into the interior. Additionally, the mucosa also has small bristle-like projections called villi (singular: villus), which are each about 1mm long, and these villi in turn have small projections called microvilli (and the whole idea of small bristles having even smaller bristles attached to them just reminds me of a certain other picture that I saw on the Internet). All these projections further increase the surface area of the insides of the small intestine.

The mucosa of the intestines, just like the stomach, contains glands that produce useful digestive juices. This time, it's not HCl-containing gastric juice, but rather intestinal juice. Other juices used in the small intestine are those produced in the liver and pancreas (namely bile and pancreatic juice, respectively). The intestinal juice, like pancreatic juice, contains many enzymes. After the pancreatic amylase in the pancreatic juice breaks down starch into disaccharides, the enzymes in the intestinal juice break it down further into monosaccharides. Each disaccharide requires a specific enzyme. To work out which enzyme you need, just take the name of the disaccharide and substitute an "a" in for the "o"- e.g. lactase breaks down lactose and sucrase breaks down sucrose. Enzymes in the intestinal juice can also further break down proteins and lipids. Proteins are broken down via peptidases (it breaks down the small peptides formed after the pancreatic protease has broken down longer chains) and lipids are broken down via lipases.

Aside from chucking a whole lot of digestive juices in, how else does the small intestine digest food? Well, you see, the circular muscle fibres alternately contract and relax in a movement called segmentation, which moves food back and forth, allowing it all to mix well. Let me explain:

Basically, the small intestine contracts at evenly spaced intervals along its length, creating small compartments. Then the middle of each "compartment" contracts, and each originally contracted muscle relaxes. This creates compartments in different places, and the food in the original compartments is sloshed around into the new compartments. Here is a terrible Paint diagram that might help you understand:

Once food has been digested enough, the small intestine begins its next job: absorbing the food! Each villus only has one layer of cells on its surface, allowing the digested food to diffuse into the blood capillaries in the villus, which surround a lymph capillary, called a lacteal. (According to InnerBody.com, a lymph capillary's primary function is to drain fluids from the tissues around it.) Some foods enter the blood capillaries, while others enter the lacteals. Aside from using diffusion to absorb food, another method of absorption is active transport, where the villi use energy to forcibly absorb nutrients against a concentration gradient (i.e. bring them from a place with a lower concentration of those nutrients to a place with a higher concentration).

Here's a quick run-down on how foods are absorbed:

• Monosaccharides- active transport. Enter blood capillaries
• Amino acids- active transport. Enter blood capillaries
• Fatty acids and glycerol- diffusion. Once in the villi, fatty acids and glycerol recombine to form triglycerides (each glycerol molecule is combined with three fatty acid molecules), before being coated with protein and entering lacteals as tiny droplets called chylomicrons.
• Fat-soluble vitamins- absorbed with the fatty acids and glycerol. Water-soluble vitamins- absorbed via diffusion into blood capillaries.
• Water- osmosis into the cells of the villi.

Food absorbed in blood capillaries then goes to the liver via the hepatic portal vein, where it's either removed for processing or retained in the blood to be carried to other body cells. Food absorbed into the lacteals are eventually emptied into the blood through veins in the upper part of the chest after being carried around by the lymph system.

Food left unabsorbed, on the other hand, continues on to...

The Large Intestine

The large intestine is only a quarter of the length of the small intestine, but it's thicker in diameter. It begins with a 6cm pouch called the caecum, which ends in the appendix. The other end of the caecum joins the colon, which has 3 parts: first is the ascending colon (which goes up), then the transverse colon (which goes from the person's right to their left), and finally the descending colon (which goes down towards the rectum and anus). Surrounding the anal opening is a circular muscle known as the anal sphincter which basically controls when you do a number 2.

The large intestine has no villi and secretes no enzymes, though it does contain bacteria, some of which break down many of the remaining organic compounds into simpler substances, releasing CO2 (carbon dioxide), methane (CH4) and hydrogen sulfide (H2S). (The book doesn't say anything but I wouldn't be surprised if this is where farts come from.) Some other bacteria produce vitamins, which are then absorbed through the walls of the large intestine into the blood. Other things that are absorbed into the blood from the large intestine include water and minerals. The absorption of water makes your poo more solid. If not enough water is absorbed, you'll end up with diarrhoea- more on this later.

The lining of the large intestine contains glandular cells which secrete a large amount of mucus. Despite this, stuff in the large intestine moves fairly slowly, taking 18 to 24 hours to pass through the colon (and remember, it's only covering a roughly 1.5m distance as opposed to the roughly 6m distance in the small intestines). Eventually peristalsis pushes it all the way to the rectum. When the outside anal sphincter relaxes and the rectum contracts (the former is voluntary, the second is automatic when the rectum is full), the body finally gets to eliminate waste in a process known as defecation. The result of this, as you well know, is a nice little pile of faeces containing all the crap (if you'll pardon the pun) that didn't get digested, such as cellulose, bacteria, bile pigments etc.

What Can Go Wrong?

Now we've covered the basics of the whole digestive system, we're going to look at a few common disorders of the alimentary canal. Make sure you're sitting down, and don't read this when eating!

Vomiting- The diaphragm and abdomen contract, forcing the stomach contents into the oesophagus and out through the mouth. Has many causes, from dizziness to sickness that causes irritation of the stomach.

Ulcers- Can occur in the walls of the stomach, duodenum or oesophagus. Usually result from pepsin and acid eroding part of the mucosa. If severe, can bleed or even make a hole right through the wall of the alimentary canal. Caused by the bacterium helicobacter pylori.

Indigestion- Has many causes, including eating too much or excessive production of HCl.

Constipation- Dry, hard faeces which are difficult to eliminate. This happens when the stuff in the large intestine moves slower than usual. Could be caused by a lack of roughage in the diet (roughage is the stuff that can't be digested but promotes the movement of food), lack of exercise or emotional problems.

Diarrhoea- An irritation in one or both of the intestines increase peristalsis, making the food move through so quickly that not enough water is absorbed, resulting in watery faeces. Can be caused by bacterial or viral infections.

Appendicitis- Inflammation of the appendix. One possible cause is blockage of the appendix by faecal matter or a foreign body, but there could be other causes.

Whew. That was a lot. I'm going to take a break now! TTFN!

Digestion and Absorption of Food- Part 1

In my past few posts regarding human bio, we've looked at different kinds of nutrients and why they are essential for our bodies. Today I'm going to talk about how these nutrients are actually broken up and absorbed into our bodies so that we can benefit from them. Since there is a lot to talk about here, I'm going to break this up into two posts. This one will cover the mouth down to the stomach.

Digestion involves both mechanical and chemical processes- that is, there are ways that food is torn apart by some physical means (e.g. chewing), and there are also chemical reactions that occur that break down the food molecules into smaller ones that can be absorbed by the body. Digestion is actually kinda complex which is why loads of organs are involved in the process. Most of these organs lie in the alimentary canal- the tube running from the mouth to the anus- including the pharynx, oesophagus, stomach and intestines. There are other organs that don't lie in this canal, but are considered to be part of the digestive system all the same, most notably the liver and the pancreas.

A basic run-down of how the digestive system works is this: you eat food, your body breaks it down through various processes across various organs, the food is then absorbed into your body, and then anything that can't be absorbed becomes bodily waste. Let's look at all of the various organs involved in order to get a closer look at how this works:

The Mouth

The mouth is where it all begins, because that's where the food generally goes in the first place (unless of course you have some serious illness that prevents you from doing so and you have to get nutrients via IV or something instead). Both physical and chemical digestion occurs here: physical via chomping on stuff with your teeth, and chemical via the chemicals in your saliva.

We have four kinds of teeth: incisors, canines, premolars and molars. They all serve different purposes- chisel-shaped incisors are for biting or cutting, conical canines are used for tearing and ripping into your food, and premolars and molars are used for crushing and grinding due to the shape of their crowns. The cusps on the crowns of molars fit into the depressions of the crowns of the molars on the opposite side creating sets of mini mortars and pestles.

Teeth have several different parts to them. The three main parts of teeth are the crown, the neck and the roots. The crown is the bit that's visible, the roots are the one or two long thin bits that extend into the sockets in the bones of your jaws, and the neck is between them. The outer layer of the tooth on the crown side is enamel. It's the hardest substance in the body and it's used to protect your teeth. My friend had a tooth that naturally didn't have any enamel, and she had to have it extracted because it was just too hard for her to eat anything without pain. The outer layer of the tooth on the root side is not enamel, but a different substance called cementum, which, true to its name (which looks like "cement" with two extra letters on the end), it helps to anchor the roots of the teeth to the jaw bone. Underneath the enamel and cementum is a thick layer called dentine, which comprises much of the tooth and is hard and bone-like. Underneath all of these layers of protection is a pulp cavity which contains nerves, blood vessels and a soft tissue called pulp (hence "pulp cavity").

Oh and a fun fact for you: baby teeth are also called deciduous teeth. Kinda like deciduous trees, except while a deciduous tree only loses its leaves for a few months before growing them all back, deciduous teeth don't grow back.

Now that I've rambled on about the technicalities of the tools needed for physical digestion, let's look at the tool required for chemical digestion: saliva! It's secreted into the mouth by three pairs of salivary glands. (I would normally make some crude joke about the unimaginative name here, but considering that there is so much stuff to just remember in human bio, I'm going to just be grateful that it's easy to remember.) It contains mucus, which not only lubricates the mouth but also helps to hold the food together in a lump, or bolus, for swallowing; a digestive enzyme called salivary amylase which breaks down starch (a carbohydrate, remember?) into smaller units (I don't think they get broken down fully into monosaccharides here, just into shorter chains than what they originally were); and antibodies, which kill many of the bacteria in your food. When food is dissolved, the taste receptors can be stimulated so you can taste just how nice- or not- your food is!

Once the food has been turned into a bolus by your saliva and your tongue, your tongue then pushes it into...

The Pharynx

The pharynx is a cavity in the back of the mouth. The pharynx doesn't really do much in the digestive process, but the food has to pass through here before it gets to the next part of the alimentary canal- the oesophagus!

Oh and one thing awesome about the human body is that it has a safety plan neatly worked out so that food won't get into your lungs or come out through your nose (unless you start laughing, of course. So try and keep a straight face when eating, even if people are telling jokes that are so bad that they're funny). Basically, when food is in the pharynx, a flap of tissue closes off the opening to the trachea (windpipe), and the soft palate (the back of the roof of the mouth) closes off the opening to the nasal cavity. It's not foolproof, but it does the job most of the time.

The Oesophagus

The oesophagus is about 23-25cm long, and has four layers (actually, the rest of the alimentary canal also has four layers which are the same or similar to those of the oesophagus).

The innermost layer is called the inner mucosa. It secretes mucus which lubricates the oesophagus and makes it easier for the food to move through.

The next layer is called the submucosa, which contains glands and connective tissue. Within the connective tissue are other things that connect different parts of the body- blood vessels, lymph vessels and nerves.

The third layer is consists of several different muscles. In the oesophagus (and presumably most other parts of the alimentary canal), there are only two: circular muscle (muscle fibres are arranged in a circle around the alimentary canal) and longitudinal muscle (muscle fibres are arranged along the length of the alimentary canal). When the bolus enters the oesophagus, the circular muscle contracts behind it. Then the next band of circular muscle contracts, pushing the bolus along, and so on and so forth. This "wave of constriction" which causes the food to move down the alimentary is also known as peristalsis. (If that explanation doesn't make much sense to you, imagine that you're trying to squeeze the last little bit of toothpaste out from the bottom of the tube. To do so, you would squeeze the end tightly, and then gradually move your fingers towards the opening at the end, squeezing as you go. The constricting action caused by your fingers causes the toothpaste to move towards the opening. Peristalsis is kinda the same, except muscles are causing constriction, forcing a bolus to move along.)

The outermost layer is called the serosa. It's made out of connective tissue.

The oesophagus passes through the diaphragm before opening out into...

The Stomach

The stomach has four layers, just like the oesophagus, but there are some differences:

1. The mucosa here specialises in secreting gastric juice. The mucosa has narrow "pits" known as gastric pits, which contain gastric glands (which are the glands actually responsible for secreting the gastric juice). Gastric juice contains HCl (hydrochloric acid), mucus and digestive enzymes.
2. Unlike the rest of the alimentary canal, the muscle layer contains a third kind of muscle: an oblique muscle layer. Having more layers means that the stomach has more different ways in which it can churn the food, mixing it with the gastric juice and turning it into a soupy liquid called chyme.

Since I'm in the mood for making lists at the moment, here are some more. First up is a list of two fun facts about the mucosa that didn't fit above:

1. When the stomach is empty, it's all folded up in "large, longitudinal folds"; when the stomach is full with food, the folds smooth out.
2. The mucosa can cover itself in a protective layer of mucus to stop the stomach from digesting itself.

Second is a list of enzymes and other important chemicals in the stomach:

1. Pepsin (gastric protease)- breaks proteins and other long chains of amino acids down into shorter chains (a.k.a. polypeptides). It's secreted in an inactive form called pepsinogen so that the protein won't be digested in the lining of the stomach. It is inactive in alkaline surroundings and requires contact with HCl to activate.
2. Hydrochloric acid kills many of the bacteria that enter the stomach.
3. Rennin is an enzyme only found in the gastric juice of infants. It makes milk proteins coagulate (i.e. makes something turn from liquid to something solid or semi-solid), allowing the stomach more time to break down the milk proteins- necessary for infants as that's all they eat. Rennin isn't in the gastric juice of adults, so don't try living off milk and milk alone.

Third is a quick run-down of what's happening in the stomach when you're digesting stuff. Or at least, this is what I think the process is. Please let me know if anything's in the wrong order, because something probably is:

1. Food enters stomach from oesophagus.
2. Folds of the mucosa smooth out as the stomach fills with food.
3. Gastric glands secrete gastric juice.
4. Stomach muscles move in various ways, churning around the food and gastric juice and turning it all into chyme; the stomach mucosa becomes protected by a layer of mucus.
5. Pepsinogen in the gastric juice is activated by the HCl to become pepsin.
6. Enzymes get to work- pepsin breaks down amino acids, HCl kills bacteria, other enzymes do whatever it is that they're doing
7. 2-8 hours later, the stomach contents are pushed out into the next part of the alimentary canal- the duodenum (basically the top bit of the small intestine). First to leave are the high-carb foods, followed by high-protein foods, and last but not least are the foods higher in fat.

Oh and one last bit- through all of that churning, you might expect something to leak out of the stomach early, but that doesn't generally happen. This is because the lower end of the stomach has a thick circular muscle called the pyloric sphincter which stops the contents of your stomach from leaving prematurely (not to be confused with the anal sphincter, which stops the contents of your rectum from leaving prematurely).

Next up: small and large intestines!

Dietary Problems

Following on from yesterday's post on food and diet, today I'm going to talk about dietary problems, or what happens if you have too much or too little of any of the essential nutrients. I'm going to go one nutrient at a time, and then add a couple more points at the end about various related topics (food additives, alcohol etc.)

Sugar

Although sugar is not super duper harmful, or at least not as harmful as it was once thought to be, many foods high in sugar lack essential nutrients, so eating too many sugary foods can cause you to gain some deficiencies. Sugar can also aggravate certain illnesses, such as diabetes. Oh, and it probably isn't good for your teeth either.

Fibre

Fibre (which is a polysaccharide carbohydrate) has both soluble and insoluble components. Soluble forms, including pectins and mucilage, can be found in fruit and oat bran, and can help to reduce blood cholesterol or control blood sugar in diabetics. Insoluble fibre, which is mostly cellulose (as I mentioned in the aforementioned Food and Diet post), can be found in wholemeal bread, bran cereals and leafy and stringy vegetables, and is required to prevent disorders of the alimentary canal (which I *think* basically just means all the parts of the body that food passes through when being digested).

Fats

We've probably all had the whole "too much fat is bad" lesson drilled into us. Aside from making you grow fat, why else is fat bad?

Consuming fat may contribute to high blood cholesterol. Animal foods contain the lipid cholesterol. Hence, these saturated fats, which come from pork, lamb, beef, milk, butter, cheese and eggs, cause a rise in blood cholesterol, which can lead to cardiovascular disease such as coronary heart disease, stroke and atherosclerosis (hardening and narrowing of the arteries- yay, I FINALLY found out what 动脉硬化 is translated into English!). Don't get me wrong, though- cholesterol is necessary for the body's cell membranes, for hormones produced by the adrenal glands and for some other purposes, but too much can be a bad thing.

Not all fats are bad, however. Polyunsaturated fats, abundant in vegetable oils, as well as in fish and poultry, can actually lower your blood cholesterol. If you consume fewer saturated fatty acids, and more polyunsaturated fatty acids, your body will synthesise less cholesterol from dietary fat. Hence, if you want to control your blood cholesterol levels, substitute foods with saturated fats for those with polyunsaturated fats.

I should now probably give a quick explanation on what "saturated" and "polyunsaturated" actually mean. As Chemistry students should know, "saturated" means that every carbon atom in the molecule is joined to as many hydrogen atoms as it can handle. "Unsaturated" means that there are double or triple bonds somewhere that could take more hydrogen atoms. Monounsaturated means that there's only one double bond, while polyunsaturated means that there are multiple double bonds. This is all covered in my post on the Basics of Organic Chemistry.

Vitamins and Minerals

Vitamins and minerals are pretty essential for the human body. If you're deficient in something, you could end up with a nasty disease- for example, deficiency in calcium could cause rickets or osteoporosis, a deficiency in iron could cause anaemia, a deficiency in Vitamin C could result in scurvy, and so on. A healthy, balanced diet should contain all of the vitamins and minerals you need, though, so you can relax without having to worry about taking supplements. In fact, some vitamins and minerals can actually have toxic effects if you consume too much (way more than you'd get in your diet, so you can still relax).

Salt

Too much salt can result in high blood pressure (hypertension), which can result in strokes. You don't need much salt in your diet- you're probably getting enough from what you're eating without extra salt. You can reduce intake by choosing less salty foods and by not adding extra salt.

Alcohol

Although a little bit of alcohol has been shown to be beneficial, reducing the risk of heart attacks or strokes, you still shouldn't have too much. It's recommended that everyone has at least 2 alcohol-free days a week. Alcohol produces 29 kJ of energy per gram, which is less energy per gram than fatty acids, but more per gram than proteins or carbohydrates. Hence alcohol can also provide you with extra calories that you may or may not need, and if it's the latter, then you're going to end up with some extra fat. Drinking too much alcohol can also lead to other health problems all over the body: liver cirrhosis, cancers, ulcers, heart disease, high blood pressure, brain damage, foetal alcohol syndrome and so on.

Food Additives

Many processed foods have additives. Additives come in many different varieties and have many different functions, including adding flavour or colour, preserving the food, sweetening it, altering the texture, and so on. Also, there might be other things unintentionally added to the food, such as insecticides. Obviously food regulations on additives and food production are quite strict, but due to consumer concern more and more foods are made with fewer or no additives, as you can see from the many bottles and packages on supermarket shelves proudly declaring themselves to contain "NO ADDED PRESERVATIVES" or "NO ADDITIVES."

Take-away Foods

Why is fast food considered unhealthy? Well, they often have too much of some nutrients, namely saturated fat, and not enough of others, such as fibre and vitamins A and C. Fast food is still okay to eat occasionally, but if you eat it all the time you will probably begin to lack certain nutrients and suffer the ill effects of too much saturated fat (which can result in high cholesterol as I said above).

Other random points to make

The rest of this chapter covers food and the media, as well as eating disorders.

The media is good at providing information about food. It's also very good at providing misinformation about food. Hence just make sure to view everything with a critical eye (and "a pinch of salt"... sorry, couldn't resist slipping a pun in there). Make sure to look at the reliability of the source (i.e. who wrote it, is there any bias involved etc.) and how credible the information is. If the diet in question looks too extreme, it probably is.

Oh and be careful about food labelling. There are some very interesting facts in this book, such as that the word "light" can refer to a food being light in colour and not reduced fat, and that "no added sugar" or "no added salt" just means that they haven't put more salt in than they really need, but there could've been a lot of sugar or salt in there to begin with. Sometimes manufacturers get around food labelling laws by deliberately misspelling words- for example, only products containing fruit can use the word "fruit" in its name, which is why you end up with stuff like Froot Loops, which doesn't contain fruit, but it doesn't have to because they didn't spell it right. (I remember writing "I ate Froot Loops for breakfast" in the "diary" thingy that I had to do back in year 3, and the teacher marked it wrong. Good times...)

Now for eating disorders. This book only covers anorexia and bulimia, though there are others, such as binge eating disorder. "Orthorexia," an obsession with eating the "right" foods, is also considered to be an eating disorder by some, but it hasn't been officially included in the DSM (Diagnostic and Statistical Manual of Mental Disorders) as of yet. Anyway anorexia is an eating disorder characterised by restricted food intake, sometimes to the point where sufferers become extremely thin or even die of starvation. Bulimia, on the other hand, is characterised by binge-eating followed by purging methods to gain control. These purging methods can range from self-induced vomiting to using laxatives, all of which can have consequences for the sufferer's physical health. There are lots and lots of reasons why eating disorders may develop. The media is often blamed but I have an extremely strong hunch that the media is generally not the primary cause for most people, but rather other life stressors. In any case, if you're suffering from an eating disorder, or know someone who is, get help as soon as you're able. After all, life has enough challenges already- you don't need an obsession with food adding to it.

And that's all from me for today! Coming next is some info on how food is digested and absorbed from the body! It looks like quite a long, detailed chapter (with lots of highlighting from the two people who used this book before me), so I might take two days, and not one, to cover this chapter. Anyway, I'll cross that bridge when I come to it. Bye for now!

Organic Chemistry- Some New Functional Groups

I've been procrastinating over writing this post for a while because of the damned diagrams. Especially those Hs. Damn those Hs.

Anyway, Organic Chemistry this year pretty much follows on from last year, but now we have some new functional groups to deal with: alcohols, aldehydes, ketones, carboxylic acids, esters and amines. I think I've got them all. It sounds like a lot, but it hopefully won't feel like a lot when you're actually learning it, because they're all somewhat related to each other (and not only by the fact that they're all organic compounds).

If you need a refresher from last year, check out these two blog posts:

• Basics of Organic Chemistry- covers alkanes, alkenes, alkynes, the cyclic compounds, aromatic compounds, basic reactions (combustion, addition, substitution) and naming very basic compounds.
• Naming and Drawing Organic Compounds- provides a worked example for naming a more complex organic compound, and another worked example for drawing an organic compound.

Right. Enough procrastination from me. Time to deal with our first functional group, which you're probably already reasonably familiar with already: the alcohols!

The alcohol that you're probably most familiar with would be ethanol, which is found in alcoholic drinks and is not to be confused with methanol. Its prefix eth- indicates that it has two carbon atoms, which it does. And, since it's an alcohol, it contains the alcohol functional group: an -OH group.

Methanol is pretty similar, but it only has one C atom and therefore less C atoms too. It also shares the -OH group, just like every other alcohol.

Alcohols have a special kind of secondary classification system, whereby you can classify them into primary, secondary or tertiary, depending on how many C atoms are attached to the same C atom as the -OH group. Yup, sounds confusing, but let me explain.

In the above picture, the -OH group is attached to the second carbon atom. This second carbon atom is only attached to one other carbon atom. Hence, ethanol is a primary alcohol. (I assume that methanol is also a primary alcohol, even though the C atom isn't attached to any other C atoms.)

Now for a secondary alcohol!

Meet propan-2-ol: prop- because it has 3 carbon atoms, -ol becase it has an alcohol group, and 2 because the alcohol group is attached to the second carbon on the chain. Here the -OH group is attached to carbon atom no. 2, which is attached to two others- no. 1 and no. 3- making this a secondary alcohol.

And now for a tertiary alcohol! (Don't worry, it won't go any further than this, since carbon can only form four bonds.)

This here is 2-methylpropan-2-ol. It's basically just propan-2-ol with a methyl group attached to the second carbon. As you can see, that poor little carbon in the middle is squashed by C atoms on 3 sides, its last bond being reserved exclusively for that OH group. Hence this is a tertiary alcohol.

Just a quick note on naming here: Naming for alcohols works pretty much the same way it has for the previous types of hydrocarbons covered so far. The main difference is that you have to add -ol on the end this time. Also, when numbering, the -OH is always given its lowest possible number, just like how the double bond of an alkene was always given the lowest possible number. For example, if you have a molecule with 8 carbons, and you have two chlorine atoms attached to the second and third carbons and the -OH group attached to the seventh, then you'd end up with 6,7-dichlorooctan-2-ol, NOT 2,3-dichlorooctan-7-ol. In other words, the functional group ALWAYS takes precedence over the other stuff when it comes to assigning numbers.

Now, what happens if you get, say, a double bond and an -OH group? I don't know. I think that one takes precedence over the other, so one becomes the suffix and the other just gets delegated to being another random thing attached to the main chain. Actually, I think in this case the double bond wins out, so the molecule name would have an -ene ending and then the -OH group becomes hydroxy- or something to that effect.

Anyway. Back to the different kinds of alcohols. You're probably asking the number one question at this point: WHY DOES THIS MATTER? Indeed, why does it matter?

It matters because the three different types of alcohols can undergo different reactions (or, rather, the same reaction) to produce different types of chemicals. Apart from combustion, and possibly substitution, it's also possible to oxidise alcohols. Well, in any case, it's possible to oxidise primary and secondary alcohols- tertiary alcohols cannot react in this way.

One of the definitions of oxidation is the addition of oxygen. Another definition is the removal of hydrogen. It's the latter definition that's important here. In a primary alcohol, the carbon that the -OH is attached to loses one hydrogen. In addition, the H on the -OH is removed. This paves the way for an =O group to form, and a new organic compound known as an aldehyde. This is ethanal, which you get initially when ethanol oxidises:

Note that I said initially. I said this because, if the reaction is allowed to continue (i.e. you don't distill off or somehow collect the aldehyde as soon as it's formed), the aldehyde then becomes a carboxylic acid via the addition of oxygen:

The above molecule is ethanoic acid. Does it sound familiar? It should, if you've been studying chemistry all these years. It's also known as acetic acid, and if you get rid of the H on the -OH group and turn it into a negative ion, then it becomes the ethanoate ion. Ethanoic acid is also found in vinegar and is responsible for its smell (I think...).

Naming aldehydes and carboxylic acids is the same as naming any other molecule thus far, except that aldehydes end in "-al" and carboxylic acids end in "-oic acid." If you have trouble remembering this, just remember that aldehydes start with "al" and that our good old friend ethanoic acid is a carboxylic acid that ends in "-oic acid." Also, you don't have to worry about providing a number for the aldehyde or carboxylic acid group, since these groups are always on the end of a carbon chain due to having being derived from a primary alcohol.

I can't be bothered writing sample reactions for these, since they're the same as redox reactions (go read my post on Redox Equations if you need to brush up on this). Permanganate and dichromate solutions are still pretty common here. Sometimes heat is needed too.

Secondary alcohols can undergo a similar reaction to produce a ketone, which is like an aldehyde but the =O group's not on the end. It's given a different name because ketones have different properties and undergo different reactions. For one thing, they cannot undergo further oxidation.

This is propan-2-one, or propanone for short (remember, ketone groups cannot be on the ends of molecules, otherwise they'd be aldehydes):

Again, naming conventions are the same, but this time names end in -one.

I'm wondering whether to talk next about the reactions of alcohols with reactive metals or to talk about the formation of esters. Eh, I'll talk about reactive metals.

Y'know how, when water reacts with an alkali (Group I) metal, there's a really violent reaction in which the metal's consumed? No? Then watch this video:

In these reactions, a metal dissolves in water to produce the metal ion, hydroxide ions and hydrogen gas.

K _(s) + 2H₂O _(l) à K⁺_(aq) + 2OH^-_(aq) + H_{2 (g)}

Now let's rewrite the equations in a slightly different manner in order to pave the way to understanding how this applies to alcohols:

K _(s) + 2H-OH _(l) à K⁺_(aq) + 2H-O^-_(aq) + H_{2 (g)}

Now let’s consider how alcohols can be represented by the general formula R-OH, where R is a hydrocarbon chain, and substitute this into the equation: 

K _(s) + 2R-OH _(l) à K⁺_(aq) + 2R-O^-_(aq) + H_{2 (g)}

Hence, the reaction of an alcohol with an alkali metal results in a metal ion, an alkoxide ion (names end in -oxide, e.g. ethoxide ion, pentoxide ion etc.) and hydrogen gas.

Now back to esterification!

Esterification is the production of esters. Esters are formed when alcohols and carboxylic acids are mixed under the presence of a catalyst such as sulfuric acid. They often smell quite fruity and, indeed, they're often found in fruits. When the alcohol and carboxylic acid react, one loses an H atom while the other loses its -OH group. I can't remember which one loses which, but it's not important at this stage.

After losing all these atoms, the compounds then join together to form an ester:

Meet methyl ethanoate. (I chose this one because it has relatively few atoms but has two different chain lengths.) This ester was formed from the reaction between methanol and ethanoic acid. The methyl part comes from methanol and the ethanoate part comes from ethanoic acid. In fact it's kinda like a methyl group joining to an ethanoate ion, but not. Or maybe it is? I don't know.

All ester names are two words long. The part that is derived from the alcohol is given the -yl ending while the part that is derived from the carboxylic acid is given the -oate ending, just like the negative carboxylate ions of these acids.

Wait. I haven't talked about carboxylate ions yet. Silly me. Those carboxylic acids are called carboxylic acids for a reason- they can react as acids, losing a proton (i.e. an H+ ion) in order to form a conjugate base. Carboxylate ions are essentially the conjugate bases of carboxylic acids- they're carboxylic acids with one less H and a -1 charge. Naming follows normal conventions but end in "-oate ion."

Another way to remember which part has the -yl and which part has the -oate is that -oate is longer and the -oate side also has an =O group, or, to be kinda crass (I think I used that word correctly...?), the side that has more crap on it gets the longer name.

I'm not sure how to name esters if they have branches. I'm not sure if I've really encountered any in my textbooks. There was one that I did remember encountering but the question even specifically said that naming it was "beyond the scope of this course" or something like that.

Last but not least, I'm finally up to talking about the last functional group covered in the course: the amines! Amines are pretty simple. Basically, they're any compound with the -NH2 group. Like alcohols, they are also classified into primary and secondary, but, unlike alcohols, the classification works differently. I'm not sure how the classification system here works, because we've only covered primary amines in class. Let's just say that most if not all of the amines you're gonna see this year will be primary amines.

Amino acids, those things that you hear about in biology, are a bit different. They're amino acids, you see, so they have an amine group and an acid group! How exciting. w00t. Now, one thing really funky about amino acids is that the -NH2 amine end is capable of forming a positive -NH3+ ion, while the -COOH carboxylic acid end is capable of forming a negative -COO- ion... AND BOTH ENDS CAN DO THIS AT THE SAME TIME!! Yes, you can have an ion that is both positive AND negative! This is called a zwitterion (pronounced "zwitter ion"). As zwitterions, amino acids can form ionic compounds (the positive end of one bonds with the negative ion of another) and thus take up many characteristics of ionic compounds such as high melting and boiling point.

Oh and having both a basic -NH2 end and an acidic -COOH end means that amino acids are not just zwitterions, they are also amphoteric (acidic or basic depending on the situation)! It'll become an acid in a basic solution by losing a hydrogen ion on its carboxylic acid end (leaving behind a -COO- ion- the -NH2 group stays neutral), or a base in an acidic solution by gaining a hydrogen ion on the amine end (resulting in a -NH3+ ion- the -COOH group stays neutral). In a neutral solution, the amino acids take up their zwitterion form. This amphoteric nature of amino acids makes them good buffers.

One last bit of terminology for you- if the -COOH group and the -NH2 group are attached to the same carbon atom, and that carbon atom is at the end of the chain, the amino acid is called an alpha-amino acid. (Replace "alpha" with the Greek letter.)

That's pretty much it from me. Yay! I've finally gotten this post out to the world after having it sit around in draft form for the past five months or so! If you want to know a bit more about how organic chemistry relates to human bio, you can check out my new post at http://year11misadventures.blogspot.com.au/2014/08/diffusion-osmosis-enzymes-and-organic.html. Have a nice day! :D