Insulin is a hormone, that means it is a chemical secreted into the blood by an endocrine organ and carried around the body to a target organ. Insulin helps to control the amount of glucose dissolved in the blood. Insulin prevents the blood sugar level from rising too high. It is also necessary to have insulin in your blood for respiration to take place. Without insulin cells can only get energy from fat and this causes serious problems. The control of blood sugar level is a homeostatic mechanism.
How Insulin Works:
Insulin is secreted by the Islets of Langerhans which are special groups of cells in the pancreas. The Islets (little islands) are endocrine organs.
If you have a large carbohydrate meal, the level of glucose in the blood will start to rise as your digestive system turns all the starch and sugars in your food into glucose.
If you have not had a meal for several hours your blood sugar level will fall because your cells use up the glucose in aerobic respiration.
When your blood sugar level rises, the Islets of Langerhans secrete MORE insulin.
When your blood sugar level falls, the Islets of Langerhans secrete LESS insulin.
The main target organ for insulin is the liver. It is the liver which removes glucose from the blood by turning it into glycogen.
All other tissues in your body need insulin to help then respire glucose, so in a way they are also target organs.
If you eat, and eat, and eat, and eat, never mind how little exercise; there will come a time when there is no more room for glycogen in your liver. High levels of insulin will make you start to turn the excess glucose into FAT. Please balance your diet!!!!!
When you fast for more than two days, your liver will run out of glycogen, so you will have to use fat and protein to get energy.
When your blood sugar level falls too low, not only does the pancreas make less insulin, but another endocrine gland, the adrenal gland, starts to make adrenalin and glucocorticoids.
Adrenalin and glucocorticoids are hormones which have the opposite effect to insulin, i.e. they help to raise blood sugar level.
The hypothalamus detects the conditions in your blood. It measures many things including blood sugar level. The hypothalamus is connected to the pituitary gland which is yet another endocrine gland.
Negative feedback is the special mechanism for turning the hormones off after they have done their job. So when your blood sugar level drops, the amount of insulin produced also falls, and when your blood sugar level has risen back to normal, the amount of adrenalin and glucocorticoids falls.
Hormone: this is a chemical secreted directly into the blood by an endocrine organ, it carries a message to a target organ. A hormone is a chemical messenger.
Endocrine Organ: this is an organ which secretes a chemical messenger or hormone directly into the blood. (c.f. an exocrine organ.) Endocrine organs make hormones.
Target Organ: this is any organ which is affected by a hormone. Almost every organ in the body is affected by one or more hormones. Target organs ar controlled by hormones.
Hypothalamus: this is a region at the base of the brain which monitors the conditions of your blood. It measures how much water, salts, bicarbonate ions and sugar is present; it also measures blood temperature. The hypothalamus helps to control the pituitary gland.
Pituitary Gland: this is the Master Endocrine Gland. It secretes hormones which control other endocrine glands.
Homeostasis: this is the mechanism for keeping your internal conditions constant. Blood sugar control is one example of homeostasis/a homeostatic mechanism. The other important ones are: osmoregulation, & thermoregulation.
Negative feedback: this is exactly the opposite of positive feedback! Another page in this Web Site to explain it. It is a switching off mechanism.