ROLE OF HORMONES IN HUMANS

AT THE END OF THE CLASS, STUDENTS WILL BE ABLE TO:At the end of the class students are able to : State what a hormone is. State what the endocrine system is State why the endocrine system is necessary State the physiological processes not directly regulated by the nervous system Describe how the endocrine system complements the nervous system Label the main glands of the endocrine system

Name the main hormones produced by each endocrine gland State the functions of the hormones involved in some physiological processes Describe briefly how the secretion of hormone is regulated Describe briefly coordination involving both the nervous system and endocrine system in a fight or flight situation. State the effects of hormonal imbalance State the use of hormones in medicine.

ROLE OF HORMONES IN HUMANS

Besides nervous system, there is another coordinating system. It is called THE ENDOCRINE SYSTEM. It controls the bodys activities by releasing chemicals called hormones. Hormones are CHEMICALS IN THE BLOODSTREAM THAT CAN REGULATE THE ACTIVITIES OF ORGANS AND TISSUES.

Role of the Endocrine System

. Made up of endocrine glands. . Endocrine system does not have ducts. . Endocrine glands produce and release hormones directly into the bloodstream. . The blood then carries the hormones throughout the body to target cells. In this way, the hormones can regulate activities in tissues and organs situated far from the glands. . The bodys responses to hormones are slower and longer-lasting than the responses to nerve impulses.

. Certain physiological processes which involve hormones, such as the menstrual cycle and the development of secondary sex characteristics, cannot be directly regulated by the nervous system. . Hence the endocrine system complements the nervous system in carrying out various body processes.

Endocrine Glands and Hormones

. The major glands of the endocrine system include the pituitary gland, thyroid gland, adrenal glands, pancreas and gonads (testes and ovaries). The pituitary gland is controlled by the hypothalamus in the brain. It secretes several hormones that directly regulate many body functions and control the activities of other endocrine glands. . Table shows the main hormones produced by each endocrine gland and their functions.

human nervous systemThe pituitary gland is often called the master endocrine gland - because it controls other endocrine glands such as the thyroid gland, testes and ovaries.The functions of hormones fall into three main categories: -(a) Reproduction(b) Growth(c) HomeostasisHormones involved in reproduction include the follicle-stimulating hormone, luteinising hormone, oestrogen, progesterone and androgen.

Hormones which CONTROL GROWTH include the growth hormones and thyroxine.Hormones INVOLVED IN HOMEOSTASIS include antidiuretic hormone, insulin, glucagon and adrenaline.

THE REGULATION OF SECRETION OF A HORMONEBY ANOTHER HORMONESecretion of THYROXINE will be increased when it is stimulated by the THYROID-STIMULATING HORMONE (TSH) produced by the pituitary gland. A fall in the level of thyroxine stimulate pituitary gland to secrete more TSR, which stimulates the thyroid gland to secrete more thyroxine. When level of thyroxine has gone too high, pituitary gland stop producing TSH. Less thyroxine will be secreted NEGATIVE FEEDBACK MECHANISM

(b) By the level of certain substances

Insulin and glucagon produced by the pancreas to control the blood glucose level. Secretion of these hormones controlled by the blood glucose level. More insulin will be secreted when the blood glucose level is high, and more glucagon will be secreted when the blood glucose level is low.

(c) By the nervous system Secretion of some hormones is initiated by nerve impulses. Example, secretion of adrenaline increased when the adrenal glands receive nerve impulses from the sympathetic nervous system. This will be discussed in the next subtopic.

Coordination involving both thenervous system and the endocrine system

Both the nervous system and endocrine system are important in controlling and coordinating body functions. These two systems are not independent of each other. In fact, they often interact with each other in carrying out their functions.Sometimes, one is faced with a critical situation, example a robber in the park. Such a situation calls for immediate and appropriate actions. It is called a fight or flight situation. That person has to decide whether to confront the robber (fight) or to run away (flight).

Under such a critical condition, the nervous system and the endocrine system will work hand in hand to save the persons life.The nervous system which controls the involuntary actions in critical situations is called the sympathetic nervous system. The sympathetic nervous system has a sympathetic nerve which links to the adrenal glands. When nerve impulses arrive at the adrenal glands, the adrenal glands will secrete adrenaline.

Impulses from the sympathetic nervous system, together with adrenaline, initiate the following responses:An increase in breathing rate, so as to bring more oxygen into the body. The conversion of glycogen to glucose in the liver.An increase in heartbeat, so as to pump and transport oxygen and glucose more rapidly to body cells.Constriction of arterioles of the skin and digestive system, but dilation of arterioles of muscles and brain, so that more blood is pumped to the muscles and the brain. This is to enable the brain to make a quick decision and the muscles to act accordingly.(e) Increase in energy production.Increase in blood pressure. Dilation of pupils to allow more light to enter the eyes.

THE EFFECTS OF HORMONAL IMBALANCE

Imbalance of thyroxine(a) Some diseases are associated with an imbalance of thyroxine, caused by an improper functioning of the thyroid gland. The thyroid gland may be secreting too little of thyroxine, (a condition known as hypothyroidism), or it may be secreting too much of thyroxine (hyperthyroidism).The functions of thyroxine are to control growth and the rate of metabolism.Hypothyroidism in a child can result in retarded growth, both physically and mentally. The condition is called cretinism.

On the other hand, hyperthyroidism during a childs growth can result in gigantism.In an adult, hypothyroidism results in myxoedema. A myxoedema patient has a low metabolic rate, is sensitive to cold, lethargic and tends to be overweight.Hyperthyroidism in an adult results in the opposite conditions: a high metabolic rate, feeling hot, over-activeness both physically and mentally, insomnia and tendency to lose weight.

Very often, an imbalance in thyroxine is manifested in a swelling in the neck called goitre. It is caused by the swelling of the thyroid gland.Simple goitre is caused by insufficient secretion of thyroxine, while exophthalmic goitre (goitre accompanied by protruding eyes) is caused by an excess of thyroxine.Since iodine is one of the components of thyroxine, hypothyroidism is sometimes due to a lack of iodine in ones diet. Iodine can be obtained from seafood such as fish and seaweed.

Imbalance of growth hormoneThe growth hormone is important for the growth of muscles and bones during childhood and adolescence. In fact, the growth hormone works together with thyroxine to stimulate growth.Under-secretion of growth hormone during childhood results in dwarfism. However, there is no mental retardation in this case as in cretinism.Excessive secretion of growth hormone, on the other hand, results in gigantism.