HORMONES IN ANIMALS (ENDOCRINE SYSTEM)
- Electrical impulses can instruct only a few tissues to prepare for an activity. Therefore, animals have another method of control and coordination called the Endocrine System.
- It includes endocrine glands and their secretions called hormones (chemical signals). These can reach all cells and provide wide-ranging changes. For example, adrenal glands secrete adrenaline.
- Adrenaline prepares the body to cope with emergency situations. For example, when encountering a scary animal, such as a squirrel, the body prepares to fight or run away, requiring more energy.
- Though fighting and running are different, both require some common preparations.
- Adrenaline is secreted into the blood and carried to different body parts, resulting in the following events:
- Heart beats faster to supply more oxygen to muscles.
- Blood to the digestive system and skin is reduced by contracting muscles around small arteries in these organs, diverting blood to skeletal muscles.
- Breathing rate increases due to the contraction of the diaphragm and rib muscles.
- These responses prepare the body to deal with the situation (fighting or running).
- The timing and amount of hormone released are regulated by feedback mechanisms. For example, if the blood sugar level increases, it is detected by cells of the pancreas, which produce more insulin. As the blood sugar level falls, insulin secretion is reduced.
SOME IMPORTANT HORMONES AND THEIR FUNCTIONS
| Endocrine Gland | Hormone | Functions & Other Info |
|---|---|---|
| Hypothalamus | Releasing hormones | Stimulates pituitary gland to release hormones. For example, growth hormone releasing factor stimulates the pituitary gland to release GH. |
| Pituitary gland | Growth hormone (GH) |
Stimulates growth and development of the body. Dwarfism: Deficiency of GH in childhood. Gigantism: Overproduction of GH in childhood. |
| Thyroid gland | Thyroxine |
Regulates carbohydrate, protein, and fat metabolism for balanced growth. Iodine is essential for the synthesis of thyroxine. Iodised salts provide iodine. Deficiency of iodine causes goitre. Swollen neck is the main symptom. |
| Pancreas | Insulin |
Regulates blood sugar level. Deficiency of insulin causes diabetes (sugar level increases). Such patients are given insulin injections. |
| Adrenal gland | Adrenaline | Prepares the body to cope with emergency situations. |
| Testes (in male) | Testosterone | Changes during puberty. Development of male sex organs, behaviour, etc. |
| Ovaries (in female) | Oestrogen | Changes during puberty. Development of female sex organs, regulates menstrual cycle, etc. |