B11 Hormonal coordination

B11.1 Principles of hormonal control

The endocrine system is a second coordination and control system made up of glands secreting hormones directly into the blood, carrying it to the target organs, where it takes effect by triggering a response in the cell when the receptors on the cell membrane pick up the hormone. Hormonal effects are slower but longer-lasting than the nervous system.

The pituitary gland secretes a variety of different hormones into the blood in response to changes in body conditions: ADH, which affects the amount of urine made by the kidney; FSH, which stimulates the ovaries to make oestrogen; and TSH, which stimulates the thyroid to make thyroxine controlling metabolic rate. The pituitary gland also makes growth hormone and stimulates the testes to make sperm and testerone.

The pancreas control blood glucose levels, the adrenal glands prepare the body for stressful situations, the ovaries control the development of the female secondary sexual characteristics and is involved in the menstrual cycle; and the testes control the development of the male secondary sexual characteristics and is involved in the production of sperm.

B11.2 Control of blood glucose levels

The body responds to blood glucose level changes so cells have a constant supply of glucose for respiration.

The pancreas monitor and control this with two hormones. When blood glucose rises, the pancreas make insulin which allows glucose to move to the cells. Insulin also controls the storage of glycogen in the liver and muscles. Glycogen can be converted to glucose anytime, and when glycogen stores are full excess glucose is converted to lipids (fats) and stored.

When blood glucose falls, the pancreas makes glucagon which breaks down glycogen to glucose to release it back into the blood. The pancreas keeps blood glucose constant using negative feedback control, switching between the two.

Type 1 diabetes is when the pancreas makes little, if any, insulin so blood glucose may skyrocket, and the kidneys excrete glucose in the urine. More urine is made and you are thirsty more often. You have less energy and lose weight. Type 1 may be genetic and usually starts in young people. Type 2 usually starts in older people and is caused by obesity or lack of exercise, or genetically. The pancreas make less insulin than necessary or the body cells don't respond to insulin.

B11.3 Treating diabetes

Treating Type 1 diabetes may include replacement insulin before meals as an injection into the blood. Regular meals are needed, as well as exercise and a certain amount of carbohydrates. Doctors can transplant the pancreas but it is risky and difficult, and medicine must be exchanged. Pancreatic cells making insulin can also be transplanted. There is also genetic engineering, or producing insulin secreting cells from embryonic stem cells, but there are rejection issues and ethical issues. More research is needed.

For Type 2, it can be treated by losing weight, a balanced diet, exercise, certain drugs, or like Type 1, insulin injections.

B11.4 Role of negative feedback

Negative feedback systems work…