The Endocrine System

The endocrine system is a self-regulating system made up of glands that generate hormones that control the body's metabolism, the way tissues work, how body cells excrete waste, how cells develop and grow, and how cells reproduce. The body's endocrine system reacts to biochemical stimuli by secreting hormones into the bloodstream, which are subsequently carried to the organs that need them. In contrast to the nervous system, the target organs respond very slowly and may take up to weeks to produce the desired alteration. Some of the glands making up the Endocrine system include the Pineal gland, Pituitary gland, Thyroid gland, Adrenal gland, and Thymus gland, Pancreas, Parathyroids, Testes and the Ovary (Thornton, Taylor, and Mulligan 187).

The primary function of the Endocrine system is to regulate body processes by the use of hormones to maintain homeostasis in the body. When homeostatic functions are working properly, it means that the body’s osmotic pressure is at the optimum level. It also means that other body systems such as the excretion system and the digestive system are functioning at their optimum level.

Hormones

A hormone is a chemical substance that is secreted by another cell and which, regulates the metabolism of other cells in the body. Some common examples of hormones include Insulin, Glucagon, and Thyroid hormones. Hormones exhibit a unifying characteristic in their specificity to distinct target cells in the body. Each hormone has a specific action center in the body cells. A target cell is therefore a specific cell that is particularly affected by a hormone. A target cell contains certain protein receptors on its plasma membrane thus allowing the hormone to bind on to it. The higher number of protein receptors a target organ has, the greater the effects that the hormone has on the target cell. If the number of protein receptors is low, then the effects by the hormones on the target cells will be negligible or will result in Endocrine dysfunction.

Another factor influencing the target cell activation is the affinity of the protein receptors.. The affinity of the protein receptors to the hormone is crucial. A high affinity is favorable and results in the proper functioning of the hormone in the target cell whereas a low affinity means that the protein receptors are not strong enough to bind to the hormones. The concentration of the hormones also influences the proper functioning of the hormones in their target cells. In some situations, the target cells will form more protein receptors following subsequent increase in the amount of hormones secreted. This is called up-regulation. However, in some cases the exposure of the target cells to a high concentration of hormones leads to loss of receptors in the target cells. This is called down-regulation.

Other hormones may also inhibit the action of specific hormones. A good example is the inhibiting action of progesterone to the production of estrogen in the uterus. Estrogen however does the opposite to the production of progesterone by stimulating more production of progesterone in the body.

Lipophilic and Hydrophilic hormones

Steroid hormones are lipophilic. This means that they are soluble in lipids thus they can easily penetrate the plasma membrane. The cell membrane allows the passage of steroid hormones because it is partly made of lipids. Steroid hormones are not soluble in water due to their lipid nature. They do not in blood plasma but are transported to their target cells by protein carriers. When they get to the target cells, they easily diffuse through the cell membrane and enter the cytoplasm of their target cells. The steroid hormones then move on to bind with the nucleus. Another example of a lipophilic hormone is Thyroxin.

Hormones that are soluble in water but are insoluble in lipids are called Hydrophilic hormones. These hormones cannot penetrate the cell membrane of their respective target cells. They therefore adopt a mechanism commonly referred to as the ‘second messenger system.’ The hormones bind to the receptor proteins which are located outside the plasma membrane of the target cells. After binding to the receptor proteins, there is a subsequent increase in the concentration of the ‘second messengers’ located within the cytoplasm of the target cells. The hormone can therefore perform its function within the target cell but very briefly since the connection only lasts a very short time. An example of a hormone that depends on this mechanism is Epinephrine.

The Pineal

It is a very small endocrine gland located in the brain. It is part of the epithalamus. It is grey in color. It is also referred to as epiphysis. It consists of interstitial cells and pinealocytes. The main hormone the Pineal produces is Melatonin. Melatonin is produced mostly at night. It functions in the Central Nervous System by helping to modulate sleep patterns in human beings. The production of Melatonin is stimulated by darkness and subsequently inhibited by light. Studies have also proved that pineal hormones can also act as tumor suppressors.

In rodents, it has been proven that pineal glands affect the secretion of sex hormones: Follicle Stimulating Hormone and Luteinizing Hormone.

The Thyroid

The Thyroid gland is located in the neck. It is found below the larynx. It is also one of the largest endocrine organs. The Thyroid gland is responsible for the synthesis and secretion of the hormones Thyroxine and Triiodothyronine. These Thyroid hormones are essential throughout the life of a human being. In children, these hormones are secreted into growing cells to further stimulate growth and development. They also function in the nervou7s system by stimulating its development and proper functioning. Therefore if there is a shortage in the secretion of the Thyroid hormones in children, it leads to stunted growth and mental retardation. This results in cretinism in children. Also Iodine is quite necessary for the production of these thyroid hormones. A deficiency of iodine in the body means a subsequent decrease in the Thyroid hormones resulting in a disease called Goiter characterized by the swelling of the Thyroid gland.

The Thyroid hormones work on almost all cells in the body. They function to increase the Basal Metabolic Rate of the body. They are also responsible for the regulation of food substances in the body such as carbohydrates, proteins and fat. In animals, more so amphibians, the thyroid hormones are needed to stimulate the development of the larvae into adults. The thyroid gland also regulates the level of Calcium ions in the blood by secretion of Calcitonin.

Anterior Pituitary Gland

The anterior pituitary gland is located in the barain. Many of the hormones produced by the Anterior pituitary gland stimulate growth in their target cells. It synthesizes and secretes the growth hormone Somatotropin which, stimulate the growth of the muscles and bones. It also produces Corticotrophin hormone which stimulates the adrenal cortex to produce corticosteroid which regulate the level of glucose in the human body. Thyroid-stimulating hormone stimulates the thyroid gland to produce more thyroxine. The Anterior pituitary gland is responsible for the secretion of Luteinizing hormone which stimulates the formation of the corpus luteum in females which brings about ovulation. In males, it is responsible for stimulating the testes to produce testosterone. Testosterone is needed for the development of secondary sexual characteristics in males and the production of sperm.

It also produces the Follicle Stimulating Hormone responsible for the production of sperms in males and the development of follicles in the ovary of females. Prolactin is also secreted and it stimulates the production of milk from the mammary glands. The Melanocyte stimulating hormone stimulates the synthesis of the melanin pigment on human beings (Depleweski 365).

Posterior Pituitary Gland

It is located in the brain next to the hypothalamus. It functions mainly to regulate homeostatic functions in the body such as blood-sugar level and water retention thus its main target organs are the kidneys. It produces Anti diuretic hormone which works, in the kidney to regulate the amount of water leaving the body. If the body has little amount of water, ADH functions to reduce the amount of water leaving the body through urination. Consumption of alcohol inhibits the proper functioning of Anti diuretic hormone.

Oxytocin is also produced by the posterior pituitary gland. It functions in the smooth muscles of the mammary gland of a female (Zouboulis 34). It stimulates the contraction of the smooth muscles to release milk from the mammary glands. Oxytocin stimulates the contraction of the uterine walls of females during child birth.

Parathyroid

The parathyroid glands are attached to the thyroid gland in the neck region. They function mainly to regulate the Calcium ions in the body. The gland produces a hormone referred to as Parathyroid hormone. It functions to correct either over secretion of calcium ions in the body or under secretion of calcium ions in the blood. This is important because it maintains the proper functioning of organs such as the heart and body systems such as the Central Nervous System.

The PTH functions in the bone cells by stimulating the osteoclasts to dissolve the calcium phosphate crystals found in the bones. It also stimulates the kidney to reabsorb calcium ions from urine.

Thymus

It is a ductless gland found beneath the sternum in the upper mediastinum. It produces the hormone thymosin. It is within the thymus that lymphocytes grow to maturity. The lymphocytes serve an immunological function in the body. They protect the body from infections and certain viruses. Thymosin stimulates the development of the T cells. On maturity, the T cells migrate to the lymph nodes where they serve as the body’s immunity. The thymus gland is only active until puberty.

Pancreas

It is located next to the stomach and is attached to the duodenum by a duct. The islets of Langerhan in the pancreas produce insulin. Insulin regulates the amount of glucose in the blood. In the case of excess glucose in the blood, insulin is secreted to stimulate the uptake of the excess glucose into the muscles for storage. It also acts in the liver by stimulating the conversion of excess glucose to glycogen for storage. Glucagon is also produced by the pancreas in response to a deficiency of glucose in the body. It serves to stimulate the conversion of glycogen in the liver to blood glucose. It also oxidizes proteins and fats in the body to glucose.

Ovary

It is found in the female reproductive system and its main function is to produce ova. They secrete estrogen which is responsible for the onset of secondary sexual characteristics. They also ensure the development of the female reproductive organs. Progesterone in coordination with estrogen brings about the menstrual cycle monthly. Progesterone prepares the uterus for implantation by stimulating the healing of the endometrium after menstruation. The corpus luteum produces the hormone Relaxin which relaxes the cervix and pelvic ligaments for parturition.

Testes

It is found in the male reproductive system enclosed in the scrotum. It functions to produce testosterone hormone responsible for the onset of secondary sexual characteristics in males. It also controls the functioning of the reproductive organs. It enhances libido and is also key to the production of sperms by spermatogenesis. Oestradiol is also produced by the testes with the function of preventing cell death of male sex cells through apoptosis.







Diabetes

There are two different types of Diabetes: Type 1 and Type 2. Type 1 diabetes is often diagnosed in children. It is characterized by production of very little or no insulin since the body’s immune system destroys insulin producing-cells in the pancreas. Without insulin in the body cells, the cells shrink and starve. The high level of blood sugar that keeps on building up turns toxic and damages major organs such as the heart, kidney and liver. This can eventually lead to coma and death. A person suffering from Diabetes loses a considerable amount of weight due to cell starvation. It is important for the person to be injected with insulin shots at aregular basis. The person should also eat foods with a low sugar level.

Type 2 Diabetes is often diagnosed in people over 30 years of age. The person manufactures insulin but the body cells are resistant to it and do not use it properly. It is called insulin resistance. The pancreas then makes more insulin to try to get the insulin into the cells but it leads to a bigger build up of glucose in the blood stream. People suffering from Diabetes 2 often suffer from high blood pressure. It mostly affects people who are obese. Its symptoms are fatigue and frequent urination. It can be treated by keeping fit and eating healthy. If not treated, it can lead to death of the person.







Work Cited

Depleweski. D. Rosenfield. Role of hormones in pilosebaceous unit development. June 2000. p. 363-367. Print.

Thornton MJ, Taylor AH, and Mulligan K. Estrogen receptor b in the predominant estrogen receptor in human scalp skin. 2003. P. 181-190. Print.

Zouboulis. C. Christos. The Human Skin as a Hormone, target and endocrine gland. Department of Dermatology, Charite University Medicine Berlin, Campus Benjamin Franklin, Berlin, Germany. March 2004. Print.