This weblog on hormones is specially designed for students of FOLA MODEL COLLEGE, FELELE IBADAN. The main objective is simply to use this page as a supplement to normal class work. Teachers and students from other secondary schools within Nigeria and worldwide should feel free to use materials within this page.
HORMONES IN MAMMALS
Hormones are organic substances secreted from certain restricted areas of the body called endocrine glands and conveyed in the blood to regulate functions of tissues and organs (target cells) elsewhere in the body. The endocrine system combines with the nervous system to aid the animal in coordination of its various parts.
Only target cells are sensitive to hormones and respond to their secretions.Usually, response occurs in the form of a change in the metabolic activities of the responding cells, tissues or organs.
Hormones are basically secreted from the pituitary gland(master endocrine gland), thyroid and parathyroid gland, pancreas and adrenal gland. Likewise, the female and male gonads secretes certain forms of hormones.
Hormones are organic substances secreted from certain restricted areas of the body called endocrine glands and conveyed in the blood to regulate functions of tissues and organs (target cells) elsewhere in the body. The endocrine system combines with the nervous system to aid the animal in coordination of its various parts.
Only target cells are sensitive to hormones and respond to their secretions.Usually, response occurs in the form of a change in the metabolic activities of the responding cells, tissues or organs.
Hormones are basically secreted from the pituitary gland(master endocrine gland), thyroid and parathyroid gland, pancreas and adrenal gland. Likewise, the female and male gonads secretes certain forms of hormones.
THE PITUITARY GLAND
This is also known as the master endocrine gland because it secretes several hormones some of which has a profound effect on the thyroid and the adrenal glands. Other hormones from the pituitary gland affect the gonads. Some of the hormones secreted by the pituitary gland control the reabsorbtion of water and salts in the Kidney
The posterior pituitary stores and releases the hormone oxytocin and antidiuretic hormone (ADH). ADH is also known as vasopressin. While oxytocin facilitates the contraction of uterine wall during childbirth and promotes the flow of milk from the mammary gland, ADH controls the reabsorbtion of water in the kidney tubules.
The anterior region of the pituitary gland produces growth hormones.Over secretion of these hormones may lead to gigantism. While undersecretion of the same hormone may lead to dwarfism. A condition known as acromegally results if the secretion of growth hormone increases suddenly after adult life.
The anterior pituitary also secretes the hormone prolactin. This is responsible for the secretion of milk in a woman after birth. Some hormones from the pituitary gland are also concerned with the regulation of the reproductive cycles in men and women. If the pituitary gland is removed early in the life of an animal, the animal will stop growing.
THE THYROID GLAND AND PARATHYROID GLAND
These are located in front of the trachea in the neck.The thyroid gland produces the hormone thyroxine.Thyroxine is an amino acid which contains the substance iodine. Thyroxine controls the rate of growth, mental and physical development of young animals.
In adults thyroxine speed up body metabolism and aerobic respiration. If it happens that an animal fail to produce sufficient thyroxine, the animal becomes overweight, sluggish and may not reach the adult weight.
In young ones, an insufficient production of thyroxine could result in poor physical and mental development - this condition is known as cretinism.
Excessive production of the hormone in adults results in voracious appetite.The animal instead of increasing in weight grows thin. Supposing a man lives on a diet with a deficiency of iodine, the thyroid gland will fail to produce enough thyroxine. As a result , the gland increases in size in an effort to produce thyroxine. As a result, the gland increases in size in an effort to produce thyroxine.This results in GOITRE, a disease with a peculiar swelling in the neck.
The parathyroid gland produces parathyroid hormone. This hormone controls the metabolism of calcium and phosphate ion. Thje nervous system, bones and muscles require an abundance of these substances to perform their functions effectively.
THE PANCREAS
The pancreas could be found within the loop of the duodenum. The normal control of the amount of glucose in the blood depends upon the hormone insulin. This is secreted by special cells within the pancreas called islets of langerhans. Insulin aids the process of conversion of sugar to glycogen in the liver. It also aids the oxidation of glucose in the muscles.
Another hormone secreted by the islets of langerhans is called glucagon.This is responsible for the reconversion of glycogen to glucose
ADRENAL GLAND
This consist of an outer region called the cortex and a central area called the medulla. The adrenal gland is situated above the kidney. The cortex produces hormones which are collectively refferred to as corticosterones.These hormones control the salt and water balance in the body as a result of the fact that they control and regulate the absorbtion of these substances in the kidney tubules.
The central area called the medulla secretes the hormone known as adrenaline(epinephrine). Adrenaline is secreted as a result of fear, danger,pain and anger. Under these conditions, adrenaline causes the acceleration of the heart beat, constriction of blood vessels and a marked increase in metabolic rate. Adrenaline also induces the liver to convert glycogen to glucose.
OVARIES (FEMALE GONAD)
The ovaries secretes the hormones called oestrogen and progesterone.Oestrogen is responsible for the development of female secondary sexual characters. These include smooth hairless skin, pubic hairs, rounded bodies and the preparation of the wall of the uterus for the reception of fertilised egg. Progesterone facilitates the proper development of the embryo during pregnancy.
