THE ENDOCRINE THE ENDOCRINE SYSTEM 2SYSTEM 2

THE HORMONESTHE HORMONES

Hormones produced by the Hormones produced by the hypothalamushypothalamus

The secretion of hormones from the The secretion of hormones from the anterior pituitaryanterior pituitary is controlled by is controlled by the production of hormones by the the production of hormones by the hypothalamus.hypothalamus.

Although there are a number of Although there are a number of

different hormones they can be split different hormones they can be split into two main types: into two main types:

ANTERIOR PITUITARYANTERIOR PITUITARY

• hormones that tell the pituitary to hormones that tell the pituitary to switch on production of a hormone (a switch on production of a hormone (a releasing releasing hormonehormone); and ); and

• hormones that tell the pituitary to hormones that tell the pituitary to switch off production of a hormone switch off production of a hormone (an (an inhibiting inhibiting hormonehormone). ).

Posterior pituitaryPosterior pituitary

The hormones secreted by the The hormones secreted by the posterior pituitaryposterior pituitary are produced in are produced in the hypothalamus and then passed the hypothalamus and then passed down a tube between the down a tube between the hypothalamus and the pituitary (the hypothalamus and the pituitary (the pituitary stalk) when they are then pituitary stalk) when they are then secreted into the blood.secreted into the blood.

ALCOHOL CONSUMPTIONALCOHOL CONSUMPTION

Alcohol interferes with the release at Alcohol interferes with the release at ADH from the pituitary gland. ADH from the pituitary gland. Therefore, drinking alcohol leads to Therefore, drinking alcohol leads to an increase in the urine produced and an increase in the urine produced and so a person will need to urinate more so a person will need to urinate more frequently. Drinking a great deal of frequently. Drinking a great deal of alcohol can lead to dehydration, alcohol can lead to dehydration, which is largely responsible for the which is largely responsible for the headache the following morning.headache the following morning.

The Pineal GlandThe Pineal Gland

The pineal gland is situated in the brain and The pineal gland is situated in the brain and releases a hormone called releases a hormone called melatonin.melatonin. More More melatonin is releasedmelatonin is released when a person is in when a person is in darkness and this results in sleepiness. In darkness and this results in sleepiness. In bright sunlight less melatonin is produced, bright sunlight less melatonin is produced, so there is a lack of sleepiness. During sleep so there is a lack of sleepiness. During sleep the melatonin level is high and then the melatonin level is high and then decreases to a low level again before decreases to a low level again before awakening. Thus melatonin helps to control awakening. Thus melatonin helps to control body rhythms.body rhythms.

The ThyroidThe Thyroid

The thyroid is made up of two lobes and The thyroid is made up of two lobes and is found in front of the throat, just below is found in front of the throat, just below the voice box. It produces the hormones the voice box. It produces the hormones thyroxine, triiodothyronine and thyroxine, triiodothyronine and calcitionin. Iodine calcitionin. Iodine is needed by the is needed by the thyroid to produce these hormones. The thyroid to produce these hormones. The body obtains iodine from the food we body obtains iodine from the food we eat. Lack of iodine causes the thyroid eat. Lack of iodine causes the thyroid gland to enlarge, a condition known as gland to enlarge, a condition known as goitregoitre..

The ThyroidThe Thyroid

ThyroxineThyroxine and and triiodothyroninetriiodothyronine control the control the body’s metabolism and affects all tissues of the body’s metabolism and affects all tissues of the body. body.

It is the sum of all the chemical processes going It is the sum of all the chemical processes going on inside the body, especially the conversion of on inside the body, especially the conversion of glucose into energy by the cells — in other words, glucose into energy by the cells — in other words, the burning of calories to provide energy for the the burning of calories to provide energy for the body. Thyroxine helps to control how energetic a body. Thyroxine helps to control how energetic a person is by stimulating cells to burn more or less person is by stimulating cells to burn more or less glucose as needed. glucose as needed.

Calcitionin helps in the regulation of calcium and Calcitionin helps in the regulation of calcium and phosphorus levels in the body phosphorus levels in the body

The ParathyroidsThe Parathyroids The four tiny parathyroid glands can he found The four tiny parathyroid glands can he found

embedded on the back of the thyroid gland. embedded on the back of the thyroid gland. They produce the hormone They produce the hormone parathormoneparathormone

The Parathyroids are sensitive to the levels of The Parathyroids are sensitive to the levels of calcium in the blood. Calcium is important as calcium in the blood. Calcium is important as it is needed for muscle contraction it is needed for muscle contraction transmission of nerve impulses and blood transmission of nerve impulses and blood clotting. The main function of parathormone clotting. The main function of parathormone is to control calcium levels in the blood to is to control calcium levels in the blood to maintain normal limits. If calcium levels are maintain normal limits. If calcium levels are low, parathormone will cause calcium to be low, parathormone will cause calcium to be taken from bones.taken from bones.

The ThymusThe Thymus The thymus gland is situated in the The thymus gland is situated in the

thorax behind the sternum. It is made thorax behind the sternum. It is made up of lymphoid tissue and in an infant it up of lymphoid tissue and in an infant it is large, but after puberty it begins to is large, but after puberty it begins to waste away. The thymus is thought to waste away. The thymus is thought to act as a brake on sexual development act as a brake on sexual development until puberty. It releases hormones, one until puberty. It releases hormones, one of which is called of which is called thymosin. thymosin. Thymosin Thymosin is involved with the production of is involved with the production of lymphocytes, which help fight against lymphocytes, which help fight against viruses and other infections in the viruses and other infections in the body.body.

The adrenal GlandsThe adrenal Glands

The adrenal glands are foundThe adrenal glands are found onon top top of each kidney They are made of two of each kidney They are made of two parts, the cortex and the medulla parts, the cortex and the medulla The Cortex is the outside and the The Cortex is the outside and the medulla the inner part of the gland medulla the inner part of the gland

Adrenal CortexAdrenal Cortex

The adrenal Cortex is essential to life and The adrenal Cortex is essential to life and plays an important role in states of stress. plays an important role in states of stress. It is known that the adrenal cortex It is known that the adrenal cortex releases over 50 hormones. All of these releases over 50 hormones. All of these hormones are steroids and are produced hormones are steroids and are produced from a fatty substance called from a fatty substance called cholesterol.cholesterol. They are grouped into three Categories, They are grouped into three Categories, sex corticoids glucocorticoids and mineral sex corticoids glucocorticoids and mineral corticoids according to the type of action corticoids according to the type of action they are involved in.they are involved in.

Sex CorticoidsSex Corticoids

Sex corticoids help control the Sex corticoids help control the changes in males and females during changes in males and females during puberty. The female sex hormones puberty. The female sex hormones oestrogen and male hormones oestrogen and male hormones androgens are produced in small androgens are produced in small amounts from this gland.amounts from this gland.

GlucocorticoidsGlucocorticoids

The glucocorticoids help regulate nutrient The glucocorticoids help regulate nutrient levels within the blood. One main levels within the blood. One main glucocorticoid is called glucocorticoid is called cortisolcortisol, also , also known as hydrocortisone. Adrenalin is known as hydrocortisone. Adrenalin is quickly released from the adrenal medulla quickly released from the adrenal medulla whenever danger threatens. Cortisol is whenever danger threatens. Cortisol is released a little while later and prepares released a little while later and prepares the body for the after-effects of danger. the body for the after-effects of danger. Cortisol helps reduce the feelings of pain, Cortisol helps reduce the feelings of pain, which is why people who are severely which is why people who are severely injured may feel no pain until some time injured may feel no pain until some time later.later.

Mineral corticoidsMineral corticoids

Mineral corticoids help to maintain the right Mineral corticoids help to maintain the right balance of the minerals such as sodium balance of the minerals such as sodium (salt) and potassium in the body. One of the (salt) and potassium in the body. One of the mineral corticoids is called mineral corticoids is called aldosteronealdosterone and and is released if sodium levels drop in the body, is released if sodium levels drop in the body, e.g. through sweating a lot. e.g. through sweating a lot.

Oversecretion of aldosterone causes Oversecretion of aldosterone causes increased levels of sodium, which can lead increased levels of sodium, which can lead to fluid retention (oedema).to fluid retention (oedema).

Adrenal medullaAdrenal medulla

The adrenal medulla produces hormones called The adrenal medulla produces hormones called adrenalinadrenalin and and noradrenalinnoradrenalin, which together prepare the body for , which together prepare the body for action, known as the fight or flight response. action, known as the fight or flight response.

In response to stress, such as being chased by a mad cow, In response to stress, such as being chased by a mad cow, the hypothalamus sends a message via sympathetic nerves the hypothalamus sends a message via sympathetic nerves to the adrenal glands. Adrenalin is released and is to the adrenal glands. Adrenalin is released and is distributed quickly by the blood.distributed quickly by the blood.

Noradrenalin is a neurotransmitter of the sympathetic Noradrenalin is a neurotransmitter of the sympathetic nervous system and exerts the same effects as adrenalin in nervous system and exerts the same effects as adrenalin in preparation for fight or flight.preparation for fight or flight.

The PancreasThe Pancreas To maintain the balance of sugar in the blood the To maintain the balance of sugar in the blood the

islets of Langerhans islets of Langerhans in the pancreas release in the pancreas release hormones. The islets of Langerhans are sensitive hormones. The islets of Langerhans are sensitive to sugar levels in the body.to sugar levels in the body.

One of the hormones calledOne of the hormones called insulin insulin is released is released when the blood sugar levels are too high. Insulin when the blood sugar levels are too high. Insulin causes the liver and muscles to store glucose in causes the liver and muscles to store glucose in the form of glycogen. (Lots of glucose molecules the form of glycogen. (Lots of glucose molecules joined together). This helps to bring the blood joined together). This helps to bring the blood sugar levels down.sugar levels down.

If sugarIf sugar levels are too low in the blood a hormone levels are too low in the blood a hormone called called glucagon glucagon is released by the islets of is released by the islets of Langerhans. It causes the liver and muscles to Langerhans. It causes the liver and muscles to release glucose into the bloodstream to help release glucose into the bloodstream to help restore blood sugar levels.restore blood sugar levels.

The ovariesThe ovaries

The ovaries are a pair of almond-The ovaries are a pair of almond-shaped organs found within the pelvis, shaped organs found within the pelvis, one on either side of the womb. They one on either side of the womb. They produce the female hormones produce the female hormones oestrogen oestrogen and and progesteroneprogesterone, which , which are responsible for all female are responsible for all female secondary sexual characteristics such secondary sexual characteristics such as breasts, a female body shape and as breasts, a female body shape and ova (egg) production.ova (egg) production.

Menstrual cycleMenstrual cycle

• During a menstrual During a menstrual cycle, cycle, oestrogen oestrogen causes the lining of causes the lining of the uterus to the uterus to thicken and grow. thicken and grow. It also stimulates It also stimulates the release of an the release of an egg from the egg from the ovary.ovary.

• Progesterone Progesterone maintains the maintains the lining of the uterus. lining of the uterus. When the levels of When the levels of progesterone fall, progesterone fall, the lining then the lining then breaks down and is breaks down and is shed in the shed in the menstrual flow.menstrual flow.

The TestesThe Testes

Testes are found in the groin area of the Testes are found in the groin area of the male in a sac called the scrotum. male in a sac called the scrotum.

The testes produce the hormone The testes produce the hormone testosteronetestosterone, which is responsible for all , which is responsible for all male secondary sexual characteristics at male secondary sexual characteristics at puberty, such as, the voice breaking (deep puberty, such as, the voice breaking (deep voice) and muscle development, facial, voice) and muscle development, facial, pubic, axillary, abdominal and chest hair. pubic, axillary, abdominal and chest hair. The testes also contain fine tubes in which The testes also contain fine tubes in which sperm are produced when stimulated by sperm are produced when stimulated by follicle stimulating hormone.follicle stimulating hormone.

THE ENDTHE END