Hormones have a central role to play in regulating body function
Introduction
All hormones in the body play a central role in the body, and quite a few of them regulate body function and help keep homeostasis. One gland that makes and stores important hormones is the Thyroid gland, which is located at the lower part of the neck, below the Adams apple and is wrapped around the trachea. The hormones it produces and stores help regulate heart rate, blood pressure, body temperature and the rate at which food is converted to energy. The two most important thyroid hormones are thyroxine and triiodothyronine. The thyroid gland also makes the hormone calcitonin, which is involved in calcium metabolism and stimulating bone cells to add calcium to bone. The production of thyroid hormones is controlled by another hormone called thyroid stimulating hormone (TSH). This is made by an endocrine gland in the brain called the pituitary gland.
The thyroid gland can become overactive (hyperthyroidism) or underactive (hypothyroidism). Hypothyroidism usually develops gradually. The symptoms are mild some of the symptoms are, tiredness, dry skin, thinning hair, sore muscles, weakness, depression, weight gain and a slow heart rate.
The most common cause of hypothyroidism is autoimmune thyroiditis, this is an autoimmune disease, which is caused by antibodies attacking the body, rather than attacking foreign bodies like bacteria. The Antibodies destroy the thyroid gland cells and this prevents the thyroid gland from working properly. Hypothyroidism can be treated with a thyroxine replacement medicine, called levothyroxine.
Hyperthyroidism
The thyroid gland is overactive and produces excess thyroid hormones; Graves’ disease is the most common cause of hyperthyroidism. It’s is another autoimmune disease. In Graves’ disease, the antibodies mimic the activity of TSH, causing the thyroid gland to produce too much thyroid hormone, leading to the symptoms of hyperthyroidism some of the symptoms are, shaking, being hot and sweating more than usual, losing weight, having increased appetite, tiredness, muscle weakness, palpitations and shortness of breath. Medical treatment of hyperthyroidism can be anti-thyroid medicines such as carbimazole and propylthiouracil, to reduce the production of thyroid hormones. However, over time anti-thyroid medicines can lead to hypothyroidism.
Blood glucose
Controlled by hormones; these hormones are controlled by the pancreas. The pancreas has glucose receptor cells, which monitor the concentration of glucose in the blood, and it also has endocrine cells (called the islets of Langerhans), which secrete hormones. The alpha cells in the islets secrete the hormone glucagon, while the beta cells in the islets secrete the hormone insulin. In a healthy person blood glucose levels should be 80-120mg.100cm-?. Insulin is secreted when blood glucose levels are high to make it fall and glucagon is secreted when blood glucose is low to make it rise. As shown in the diagram:
The most common disorders involving blood glucose and the hormones are diabetes type 1 and type 2;
Type 1 insulin dependent diabetes mellitus (IDDM) is caused by a lack of insulin either by a faulty insulin gene so there is no functioning insulin or by an autoimmune attack on the beta islets cells that produce the insulin so there are no cells left to produce it. This type of diabetes mainly occurs in children and young adults, onset is usually sudden. The main Symptoms of this are fatigue and copias quantities of urine which contains glucose. If this goes undiagnosed and treated then a coma may result from hyperglycaemic or hypoglycaemic, hyperglycaemia is where too much blood glucose is in the body, there is no insulin so no removal of the glucose from blood, the kidney then cant reabsorb all the glucose and the glucose in the urine takes water with it by osmosis, cells also can’t take the glucose in the blood up quick enough so start using fats and proteins in respiration, all this causes Dehydration, loss of vital salts and low blood pH which results in a coma.
Hypoglycaemia
Where there is not enough blood glucose, and no glycogen stores in liver because of the lack of insulin, glucagon has nothing to act on and blood glucose is too low to supply respiring cells which results in a coma. The treatment for type 1 is diet and insulin injections.
Type 2 none insulin dependent diabetes mellitus (NIDDM) is caused by a resistance to insulin and usually comes later on in life, a contributing factor to type 2 is also obesity, treatment is diet and exercise, tablet that increase cell sensitivity to insulin and in extreme cases insulin injections.
Additional glands that make hormones are the adrenal glands (also called suprarenal glands), these are small glands located on top of both kidneys. The adrenal glands work with the hypothalamus and pituitary gland. Both adrenal glands are composed of two parts that have different functions and structures. The outer part is the cortex and is essential to life, where as the inner part is the medulla and is not essential to life. The adrenal cortex makes three groups of steroid hormones from cholesterol, collectively called adrenocorticocoids these are, glucocorticoids, minerslocorticoids and sex hormones (androgens). The medulla is completely surrounded by the cortex, and it is part of the sympathetic division of the autonomic nervous system. It is stimulated by its extensive sympathetic nerve supply to produce the hormones adrenaline (epinephrine) and noradrenaline (norepinephrine).
One of the main disorders of the adrenal cortex is hypersecretion of glucocorticoids or Cushing’s syndrome, symptoms of this syndrome include; weight gain and fatty deposits, skin changes, depression, brittle bones, muscle weakness, headaches and high blood pressure. Cushing’s syndrome can be caused by an over use of a steroid medication or by a tumour that causes your body to produce more cortisol. Treatments for these causes could be reducing the dose of steroid medication or for tumours surgery, radiotherapy or chemotherapy. With the adrenal medulla the main disorder is hormone secreting tumours, which cause excess adrenaline and noradrenaline, the symptoms of which are; hypertension, weight loss, nervousness, headaches excessive sweating, hyperglycaemia and glycosuria.
Kidneys
Important functions to do within the body, there functions are; the formation of urine, filtration and selective reabsorption. Each kidney is associated with a different group of structures, the right kidney is associated with; the right adrenal gland, the right lobe of the liver, the duodenum, the hepatic flexure of the colon, the diaphragm and the muscles of the posterior abdominal wall. The left kidney is associated with; the left adrenal gland, the spleen, stomach, pancreas, jejunum, the splenic flexure of the colon, the diaphragm and the muscles of the posterior abdominal wall. The kidney is extremely flexible in its working. It excretes large amount of hypotonic urine when water intake is very high, while it excretes small amount of hypertonic urine when water is deficient and needs to be conserved. This is very useful in Osmoregulation.
Osmoregulation
control of the levels of water and mineral salts in the blood. The water potential of the blood must be regulated to prevent loss or gain of water from cells. Blood water homeostasis is controlled by the hypothalamus. It contains osmosreceptor cells, which can detect changes in the water potential of the blood passing through the brain. In response, the hypothalamus controls the sensation of thirst, and it also secretes the hormone ADH (antidiuretic hormone). ADH is stored in the pituitary gland, and its target cells are the endothelial cells of the collecting ducts of the kidney nephrons. These cells are unusual in that water molecules can only cross their membranes via water channels called aquaporins, rather than through the lipid bilayer. ADH causes these water channels to open.
All these hormones that have been mentioned are working to help keep homeostasis. Homeostasis is the maintenance of a constant internal environment and is important because it results in our cells being bathed in tissue fluid which has the correct amount of water, mineral salts, glucose and temperature, a great deal of the hormone system is dedicated to homeostasis. Temperature homeostasis is controlled by the thermoregulatory centre in the hypothalamus. It receives input from two sets of thermoreceptors: receptors in the hypothalamus itself monitor the temperature of the blood as it passes through the brain (the core temperature), and receptors in the skin monitor the external temperature. Both pieces of information are needed so that the body can make appropriate adjustments. As stated previously Blood glucose concentration is controlled by the pancreas. The pancreas has glucose receptor cells, which monitor the concentration of glucose in the blood, and it also has endocrine cells (called the islets of Langerhans), which secrete hormones.
Homeostasis
Controlled by our nervous and endocrine systems. The endocrine system is all the glands that secrete hormones (proteins or steroids) some glands that have been mentioned and a lot more that haven’t, the main glands are; Thyroid, Pituitary, Pancreas, Adrenal, Hypothalamus, Testes and Ovaries.
The endocrine system relies on negative feedback to maintain control.
This works as shown in the diagram, Negative feedback means that whenever a change occurs in a system, the change automatically causes a corrective mechanism to start, which reverses the original change and brings the system back to normal. It also means that the bigger then change the bigger the corrective mechanism.
Bibliography
- Bupa (2011) [Online] Available at: www.bupa.co.uk (02/04/2011)
- MedicineNet (2011) [Online] Available at www.medterms.com (01/04/2011)
- Scott, D. (2004) [Online] Available at www.biologymad.com (02/04/2011)
- Tutorvista (2010) [Online] Available at www.tutorvista.co.uk (02/04/2011)
- University of Maryland Medical Centre (2010) [Online] Available at www.umm.edu/endocrin/adrengl.htm (02/04/2011)
- Waugh, A. And Grant, A. (2006) Anatomy and Physiology in Health and Illness. 10th edn: Elsevier Limited.
