Following on from yesterday's post, here's some more notes on the digestive system! By the way, I think I've worked out what the biliary tree is- it appears to refer to the system of bile ducts running down from the liver since they kinda look like a tree.
These questions are (in my opinion) harder than previous questions that I've addressed, so answers to these might not be 100% accurate. Please correct me if you find anything wrong :)
1. Describe the structure of the portal circulation of the liver. Why is this complicated anatomy a necessary evolution of the digestive system?
In the portal circulation of the liver, rather than veins becoming progressively larger as they approach the heart, veins branch out back into capillaries before merging to become veins again. Additionally, if I remember correctly, some arterial blood is mixed with the venous blood in this portal system. The complex bed of capillaries allows for a greater number of hepatocytes (liver cells) to become intertwined with blood vessels, which in turn allows for a greater exchange of nutrients.
2. Trace the route of venous blood in the colon as it enters the inferior mesenteric vein until it comes into the right heart.
The inferior mesenteric vein, along with several other veins such as the superior mesenteric vein, the splenic vein, the gastric veins and the oesophageal veins, all drain into the portal vein. The portal vein enters the liver, and then branches off into capillaries to allow exchanges to take place before returning to the central (portal) veins. Blood then travels through the hepatic veins into the inferior vena cava which leads back to the right side of the heart.
3. Name three hormones secreted by the enteroendocrine glands of the small intestine and describe their target organs and effects.
The enteroendocrine glands of the small intestines secrete several different enzymes, each with somewhat different functions. Some help to slow down the passage of food through the pylorus so that the intestines do not get "overwhelmed," while others stimulate the movement of the intestines.
One hormone is GIP, or gastric inhibitory peptide. It acts on the stomach to inhibit gastric secretion and slow stomach emptying. It also acts on the pancreas to stimulate insulin release, preparing the body for the absorption of glucose.
Another hormone is secretin, which acts on the pancreas, liver and gallbladder to increase the amount of bicarbonate in pancreatic juice. Bicarbonate ions are basic, and hence the rise in bicarbonate increases the pH and neutralises the stomach acid. Secretin, like GIP, also inhibits gastric juice secretion.
A third hormone is CCK, or cholecystokinin. CCK also acts on the pancreas, liver and gallbladder. Functions include increasing bile secretion, stimulating emptying of the gallbladder and providing feelings of satiety.
4. What are the major causes of obstructive jaundice? Which one would you choose to have, if you had a choice? Which would be your last choice?
This is a topic that I'm really not very clear on. Additionally, this is a bloody weird question. If I had a choice, pretty sure I'd choose not to have any kind of obstructive jaundice...?
Anyway as far as I know, obstructive jaundice is basically when the bile ducts get clogged up and all the bile salts back up, making your skin yellow and causing a whole host of other health problems. Some of the major causes of this are gallbladder stones and pancreatic cancer. Obviously if I had to choose between them, I'd choose the stones over the cancer.
The gallbladder is a vestigial organ (that is, it's basically a remnant of some organ passed down to us through evolution) and doesn't always empty that well, resulting in stones forming from the bile salts that have remained in there for too long. Gallbladder stones can be removed and in fact the entire gallbladder can be removed without too many problems.
Pancreatic cancer, on the other hand, is a whole other ball game. The mortality rate is quite high and we don't have effective treatments for it yet. There is surgery that can be done, however the surgery itself has quite a high mortality rate (30-40%), and the survival rate after 5 years is only around 2%. Even more unfortunate is that we still don't know how this cancer can be prevented. Let's hope researchers find something soon to help patients and families affected by this terrible disease :(
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