The Endocrine System

Now we've moved onto the endocrine system! This system is a bit different to the other systems that we've talked about- organs in the endocrine system appear to be grouped together not because they work together but because they send their messages to the rest of the body in the same way. Organs in the endocrine system use the endocrine (!) system of signalling, which is through hormones sent via the blood (as opposed to exocrine in which the chemicals and stuff are dumped into the cavities of organs or onto body surfaces or paracrine in which the stuff diffuses through the interstitial fluid).

Without further ado, here are some notes:

1. How does the venous portal capillary system function in the anterior pituitary gland? Why is this necessary?

There is a small portal system (i.e. veins go to smaller capillaries which go back to being veins again) between the hypothalamus and the anterior pituitary gland. If I remember correctly, this is called the hypophyseal portal system (hypophysis = pituitary). This portal system, with its smaller vessels, allow the hormones to travel in a more concentrated form than they would be in if the vessels had gotten larger as veins normally do. This, in turn, makes communication between the hypothalamus and pituitary more effective.

2. Describe the differences between endocrine control and nervous system control of bodily functions.

While both systems play roles in signalling and communication, there are also several very important differences. One of the main differences is that, while the nervous system uses an electric current to send messages, the endocrine system uses chemical messengers called hormones. The nervous system signalling is therefore much faster than the endocrine system. On the other hand, the effects of the nervous system tend to be much shorter lived than the effects of the endocrine system, which can linger for a long time.

3. Define and describe the differences between exocrine and endocrine glands. In what category is the pancreas?

I kinda already explained this in the introduction, but let me quickly explain again. In an exocrine gland, products are secreted directly into the lumen (cavity) of organs or onto a body surface, such as the skin. In an endocrine gland, on the other hand, products are secreted into the bloodstream to be carried around the body.

The pancreas exists in both categories. 99% of the mass of the pancreas is devoted to its exocrine function, which is the secretion of bile into the duodenum. The remaining 1% of the pancreas is devoted to its endocrine function, which is the secretion of hormones, most notably insulin and glucagon, into the blood where they can regulate blood glucose levels.

4. List as many symptoms as possible in a diabetic patient who has forgotten to eat after taking a normal dose of insulin.

This is the sort of question where I would probably be best off asking a friend of mine who has diabetes, but I don't want to look overly nosy so I'm going to try and answer this question by myself. If a diabetic patient takes insulin, the insulin works to decrease blood glucose levels by increasing the speed of diffusion of glucose into cells, conversion of glucose into glycogen and synthesis of proteins and fatty acids while decreasing the rate of glucose synthesis. If the patient does not eat, they might have an overall net decrease in blood glucose levels. Since glucose is an important form of energy, a patient might go into shock or even into a coma from low blood glucose levels.

5. Describe the function of the thyroid gland.

The thyroid gland secretes hormones that regulate many chemical reactions that take place within the body. These include reactions related to oxygen uptake, body temperature control and the synthesis of molecules in cells.

6. What is a negative feedback mechanism? Describe one such system in detail.

A negative feedback mechanism is a mechanism in which an organ sends out a message to produce a product, and that product sends a message back to the organ to stop producing more. Negative feedback is important for regulating homeostasis. One example of negative feedback is that of glucagon, the hormone in the pancreas that stimulates glucose production. Glucose production, triggered by the release of glucagon, is stimulated by low blood sugar. When enough glucose is produced, the pancreas secretes less glucagon. In this way, blood sugar levels can be maintained. (Glucagon also works closely with insulin, which has the opposite effect on blood sugar levels.)

7. What is a goiter? What is exophthalmos? Are they related? If so, how? If not, why not?

Goiter is a word that basically means "thyroid enlargement." Goiter is not a disease on its own, it's just the name of a symptom that could be triggered by a disease or some other condition such as iodine deficiency. Exophthalmos, on the other hand, is a completely different symptom. It refers to a bulging of the eyes caused by fat deposition behind the eyes. While these symptoms are very different, they do have one thing in common: they can both be caused by Graves' disease. In Graves' disease, patients have antibodies that mimic TSH (thyroid-stimulating hormone) and thus the thyroid becomes overstimulated (a condition known as hyperthyroidism).