The Endocrine System

The endocrine system has the major function of secreting animal hormones that are used as chemical signals secreted into the extracellular fluid carried by the circulatory system. Hormones are the functional unit and endocrine glands or ductless glands secrete them. Neuro-secretory cells are nerve cells that secrete hormones into the blood. Hormone system sometimes are part of a feedback loop that could be either negative or positive. Negative loops cause the initial response to cease once the hormone is released and positive loops promote further responses and secretion.

Feedback Loops Example

Hormones travel in pathways, and a signal transduction pathway is the series of bindings and changes to a hormone or signal through receptors and cellular proteins into a specific response.

Some major organs or glands in this system are the hypothalamus, pituitary gland, thyroid, parathyroid, pancreas, adrenal, gonads, and the pineal gland. The hypothalamus secretes hormones that regulate the pituitary gland. The pituitary gland controls growth hormones as well as metabolism, milk production, ova and sperm, retention of water in kidneys, and contraction of the uterus and mammary glands. the thyroid gland maintains the metabolic processes and the parathyroid regulates blood calcium levels. Adrenal glands regulate blood glucose, epinephrine, nor-epinephrine, and re-absorption of Sodium and Potassium excretion in kidneys. Gonads, the testes and ovaries, are steroid controls of androgen and estrogen as well as sperm and uterine lining growth. The pineal gland is tasked with maintaining light/dark or biological cycles/rhythms.

Pancreas Diagram

The pancreas is the major endocrinal gland. The tissues and glands that secrete into ducts are exocrine. The islets of Langerhans are groups of endocrinal cells that are everywhere in the exocrine tissue. Each islet has alpha cells that produce glucagon, a hormone; and beta cells produce insulin. These two hormones are antagonistic meaning they regulate glucose concentration from going into extreme levels. Glucose is very important in bodily processes because it is used in cellular respiration to create ATP energy and a carbon source in other molecules. Metabolic balance is based on glucose concentrations in blood. Insulin lowers glucose levels and glucogen when glucose is low in blood.

Insulin stimulates all body cells except the brain’s to take up glucose and slows glycogen breakdown in the liver to lower blood sugar concentrations. Once excess glucose is cleared form the blood, glycogen immediately begins glucogen breakdown or hydrolysis to make glucose again.

If the pancreas does not fulfill its tasks then many issues occur. Diabetes is when insulin is deficient or tissues do not respond well to insulin, and therefore blood glucose keeps rising. The amount of glucose cannot be absorbed by the kidneys. Type 1 diabetes is when the immune system destroys beta cells in the pancreas and this destroys a person’s insulin production ability, and occurs in children. Type 2 diabetes is caused by an insulin deficiency or a lower responsiveness of target tissue caused by insulin receptor failure. Lack of exercise, an unhealthy diet, and genetics cause this type.

Thank you and stay tuned for the next and last system essay!

Written By: Neil 7/24/2019


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