THE ENDOCRINE SYSTEM

THE FUNCTIONS: To maintain homeostasis,balancing the external and internal environments. To do this by production of hormones or chemical messengers. By utilising hormones to control and regulate developmental changes from birth through childhood, to adolescence, to sexual maturity, to pregnancy and nourishment of children, through to menopause and death.

The system The activities of this system require the cooperation of the cardio vascular and nervous systems. Hormones are carried by plasma proteins in the circulation. They are transported from the pituitary gland in the brain largely as trigger hormones to target organs around the body. They are also transported from organs to other areas as locally produced hormones. The nervous system and the endocrine system work together to carry messages, however the actions of the nervous system take place very quickly and their affects can pass rapidly, whereas the affects of the endocrine system may last longer.

The Anatomy This consists of organs, ductless glands and parts of the brain. The brain has two main players which are the hypothalamus which receives messages by a feed back system about which hormones are needed around the body and the Pituitary gland which lies beneath it. The pituitary is instructed by the hypothalamus on which hormones to produce and to release. The pituitary has two parts, an anterior which produces upwards of 6 trigger hormones and a posterior which stores and produces 2 hormones. Hormones travel to target organs which include : Thyroid and adrenal glands, ovaries, testes, breasts uterus, skin, bones and kidneys. In addition, the pineal gland positioned further towards the back of the brain produces its own hormone called melatonin which regulates sexual development and the Circadian rhythms of the body.

What are hormones ? 1.Hormones are described as the chemical messengers of the body. 2.Some are formed from proteins and glyco proteins. 3.Some are formed from steroids. They are engaged in the regulation of the body and its systems, the maintenance and control of genetic sequential growth patterns, use of energy and general homeostasis.

The physiology Hormones regulate :metabolism, rates of growth, sexual development, birth, nurturing and feeding of children, pigmentation of the skin, urine production, activation of fight or flight responses, balance of electrolytes ( sodium and potassium ),balance of fluids. They are either trigger hormones which travel to an organ or set of tissues to stimulate that target organ to produce other hormones or they travel to the target organ and carry out an action immediately.

Examples of Anterior lobe hormones : Adrenocorticotropic which travels to the cortex of the adrenal glands and stimulates production of cortisol. Thyroid stimulating hormone which travels to the thyroid gland and stimulates production of thyroxin and calcitonin Follicle stimulating hormone which travels to the ovaries and results in the production of oestrogen. Prolactin which travels to the breast and stimulates production of milk. Melanocyte stimulating hormone which travels to the skin and stimulates melanocytes to produce pigment. Human Growth Hormone which stimulates growth of tissues of all kinds and in adults works to maintain our systems at functional levels.

The Pituitary Gland

The Role of Sex hormones In girls the ovaries are stimulated by two hormones : 1. Follicle stimulating 2. Luteinising. These are known as Gonadotrophins The uterus, fallopian tubes and ovaries mature. Ovulation and the menstrual cycle begin. Growth of pubic and axillary hair. Breasts develop. Height increases and pelvis widens. Subcutaneous fat layer increases. In boys: The same gonadotrophins are produced but luteinising is called interstitial stimulating hormone. This stimulates the testes to produce testosterone. There is growth of muscle and bone with height increase and a broadening of the chest. The voice breaks and the larynx enlarges. Sexual organs develop with the testes producing testosterone and sperm. Pubic hair grows as well as facial, axillary and chest hai r. At puberty, many changes take place in young people, mostly because hormone levels are rising and changing rapidly.

Some diseases and disorders Cushings Syndrome :Hyper production of the hormones from the cortex of the adrenal glands effecting sex, growth and salt balance This will cause muscle weakness, high blood pressure, redistribution of fat, osteoporosis and changes in the shape of the face. The opposite extreme or Hypo production to this can cause Addisons Syndrome. Polycystic Ovarian syndrome :Cause unknown ; effects are irregular menstruation due to over stimulation of ovaries by luteinising hormone. Multiple growth of ovarian cysts causing scar tissue. High levels of testosterone leading to growth of body hair, sufferers are prone to weight gain and infertility. Diabetes Melitus: Type 1: Inability of the pancreas to produce insulin. This means high levels of glucose in the blood, excessive thirst and frequent urination. Sufferers have to inject themselves with insulin. Type 2:The body cells become insulin resistant and the pancreas may not produce enough. This can usually be controlled by careful diet.