Control and Coordination

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• Summary

The hormones in animals are produced by the endocrine glands, and they too play an important
role in control and coordination.

Hormones are chemical substances that control and coordinate activities of living organisms and also their growth.

Features and functions of hormones:

1. They are secreted by the endocrine glands and are called ‘chemical messengers’.
2. They are poured directly into the blood-stream as endocrine glands have no ducts of their own (ductless glands).
3. They usually have their effect at sites different from the sites where they are made. They act on specific areas called target organs.
4. Hormones coordinate body activities and growth.
5. They are released in minute quantities.

The endocrine system is composed of several endocrine glands. A ductless gland is called endocrine gland. The endocrine gland secretes its product directly into the bloodstream. Hormones are produced by the endocrine glands. The hormone is mainly composed of protein.

The various endocrine glands in humans are hypothalamus, pineal gland, pituitary gland, thyroid gland, parathyroid glands, thymus, pancreas, adrenal glands, ovary (in female) and testis (in males).

The pituitary gland: The pituitary gland produces hormones that regulate many of the other endocrine glands.

Hypothalamus: The hypothalamus makes hormones that control the pituitary gland. In addition, it makes hormones that are stored in the pituitary gland.

Pineal gland: The pineal gland releases melatonin, which is involved in rhythmic activities, such as daily sleep-wake cycles.

Thyroid: The thyroid produces thyroxine, which regulates metabolism.

Parathyroid glands: Parathyroid hormone regulates the level of calcium in the blood.

Pancreas: The pancreas produces insulin and glucagon, which regulate the level of glucose in the blood.

Thymus: The thymus releases thymosin, which stimulates T cell development.

Adrenal glands: The adrenal glands release epinephrine and norepinephrine, which help the body deal with stress.

Pancreas: The pancreas produces insulin and glucagon, which regulate the level of glucose in the blood.

Ovary: The ovaries produce estrogen and progesterone. Estrogen is required for the development of secondary sex characteristics and for the development of eggs. Progesterone prepares the uterus for a fertilized egg.

Testis: The testes produce testosterone which is responsible for sperm production and the development of male secondary sex characteristics.