Some more notes on the respiratory system

As I promised in my last post, here are some notes on the respiratory system.

1. Define the pleural space anatomically.

The pleural space is the area between the parietal pleura and the visceral pleura (the connective tissue lining the chest wall and lungs, respectively). It is filled with a lubricating fluid to allow the lungs to expand and contract.

2. Would tracheostomy help in the case of a severe asthma attack? If so, why? If not, why not?

Tracheostomy would not help in the case of an asthma attack. A tracheostomy is an operation which allows patients with blocked larynxes to breathe by inserting a tube lower down in the trachea, allowing air to bypass the larynx. Asthma, however, affects the smooth muscles near the alveoli, which is far past the area bypassed by a tracheostomy.

3. What muscles are involved in respiration during severe exertion? How is that different from respiration at rest?

During severe exertion, the accessory muscles of respiration are also involved (as opposed to only the diaphragm being involved as during rest). These muscles include the external and internal intercostal muscles, the sternocleidomastoid muscle, the scalene muscles and the rectus abdominus.

4. What is a pneumothorax? Describe the events that occur in the chest after a gunshot wound that creates a hole in the chest wall.

A pneumothorax is a loss of the vacuum in the pleural cavity following a tear in the visercal and/or parietal pleura. This loss of vacuum causes the lung to collapse.

After a gunshot wound causing damage to the parietal pleura and probably the visceral pleura as well, air rushes into the pleural cavity, causing a loss in vacuum. The decreased pressure causes the lung to collapse, which in turn stops gas exchange in the lung.

Some more notes on the cardiovascular system

It's been a rather long time since I last posted.

I don't really have that much to say, since it's been holidays and I've been on gap year and all. A couple of months ago I got Understanding the Human Body: An Introduction to Anatomy and Physiology as a gift of sorts, but you know what holiday mode is like- I watched some of the lectures but then didn't keep up with it for a while. Well, now that uni is about to start, I finally got the motivation to do so, and to answer some of the chapter questions in the book. Here goes...

1. Describe the route of blood flow, starting at the entry into the left atrium through its return to the left atrium.

Blood flows from the left atrium into the left ventricle, where it is pumped into the aorta for transport around the body. The aorta branches off into arteries supplying various parts of the body with blood, which then branch out into smaller and smaller arteries, which eventually branch out into arterioles, which then branch out further into capillaries which are only thick enough for one red blood cell to pass through at a time. The capillaries eventually combine into small venules, which combine to form larger and larger venules until you get veins, which get progressively larger and larger until you get to the level of the superior and inferior vena cava. Blood flows through these very large veins into the right atrium.

Blood then flows from the right atrium into the right ventricle, where it is pumped into the pulmonary arteries. These arteries also divide into smaller and smaller vessels until the capillary beds in the lungs. The vessels then get larger and larger, progressing through the venule and vein stages, eventually getting to the pulmonary vein, which brings blood back to the left atrium.

2. Define the physical borders of the mediastinum.

The mediastinum is essentially the space between the lungs in the chest cavity. It is also the heart's enclosure.

The tough fibrous tissue that covers the heart is called the pericardium, and is made up of two layers with a lubricating fluid between them. The outer layer of the pericardium is called the parietal pericardium. The inner layer is called the visceral pericardium and is very thin and can be torn easily.

The heart wall itself also has several layers. The outer layer, the epicardium, is essentially also the visceral pericardium. The middle layer is quite muscular, and is called the myocardium, or heart muscle. The inner layer is known as the endocardium. This inner layer also extends into the vessels, where it lines the vessels and is called the endothelium. (The endocardium and endothelium are pretty much the same- the name just changes depending on the location.)

3. Describe the events during the phases of the cardiac cycle.

The first phase of the cardiac cycle is relaxation, where both the atria and ventricles are in diastole (i.e. their muscles are relaxed, allowing atria and ventricles to expand). Blood fills the atria on both sides, and when the pressure is high enough, the mitral and tricuspid valves open, marking the start of the second phase of the cardiac cycle.

During the second phase of the cardiac cycle, the ventricles fill. At first, they fill passively due to the opening of the valves. After that, atrial systole (contraction of the atria) occurs, pushing any blood remaining in the atria into the ventricles. Throughout this phase, the atrioventricular valves (i.e. the mitral and tricuspid valves) remain open, while the semilunar valves (i.e. those leading into the pulmonary artery and aorta) remain closed.

The third and final phase of the cardiac cycle is ejection, where the atrioventricular valves close (all valves are closed for a fraction of a second), the aortic and pulmonary semilunar valves open, and the blood is ejected out into the main arteries. The aortic and pulmonary valves then close in order to start the cycle all over again.

4. Define cardiac output. What is stroke volume, and how does it affect cardiac output? What is the cardiac output in a man with a stroke volume of 90 mL and a heart rate of 85 beats per minute?

Cardiac output is the volume of blood pumped out per minute in millilitres. Stroke volume is the volume of blood (in mL) pumped out per beat, and a higher or lower stroke volume will obviously cause an increase or decrease in cardiac output.

e.g. In a man with stroke volume 90 mL and heart rate 85bpm

Cardiac output = 90 x 85 = 7 650

5. How is the portal circulation different from a systemic capillary bed?

The portal circulation, such as in the liver and surrounding organs, is different in that venous systems feed into each other (i.e. veins are going into other veins, rather than arteries going to veins). Also instead of progressively getting bigger or progressively getting smaller, the vessels may get bigger then smaller than bigger again.

6. How is blood shunted from one organ system to another?

Blood is shunted from one organ system to another via the constriction of vessels, which is in turn controlled by the brain.

7. Define shock.

Shock is a state in which the body cannot maintain sufficient cardiac output to carry out its fnctions effectively.

8. What are the three stages of shock, and which (if any) are treatable?

The first stage of shock is compensated non-progressive shock, in which no permanent damage or cell death occurs. Only transient fainting is experienced by the patient, who generally recovers naturally.

The second stage of shock is decompensated progressive shock, in which cells are injured. It can be treated, but not without medical assistance.

The third stage of shock is irreversible shock, in which organs are damaged, the blood becomes acidic and the patient dies within hours. It is untreatable.

That's it for now on the cardiovascular system. Later on I'll put up a couple more notes regarding the respiratory system.