Endocrine 3

• The adrenal glands are located on top of the kidneys and are separated into two portions: the adrenal cortex and the adrenal medulla
• The adrenal cortex secretes mineralocorticoids such as aldosterone, glucocorticoids such as cortisol and gonadocorticoids (sex hormones) VS the adrenal medulla which secretes epinephrine and norepinephrine
• Mineralocorticoids play an important role in regulating how mineral salts are processed in the body. Aldosterone is the most important mineralocorticoid in the body with the main function and maintaining sodium homeostasis in the blood (by increasing sodium reabsorption in kidneys)
• Aldosterone is controlled by the RAAs system:

  1. BP drops and the juxtaglomerular apparatus secretes renin into the blood
  2. Renin causes angiotensinogen to be converted to angiotensin 1
  3. Angiotensin 1 circulates to the lungs and angiotensin 2 is formed due to the ACE enzyme
  4. Angiotensin 2 circulates to the adrenal cortex and stimulates the secretion of aldosterone
  5. Aldosterone causes increased reabsorption of sodium which causes increased water retention
• Glucocorticoids regulate glucose and metabolism
• Cortisol function

  • Increase rate of protein breakdown in muscle fibers (provide amino acids for ATP)
  • stimulates liver formation of glucose
  • Increase rate of triglycerides breakdown in adipose tissue
  • Anti-inflammatory effects
  • Depress immune response
• Glucocorticoid secretion is part of the long stress hormone and can lead to immune dysfunction
• Glucocorticoid secretion is controlled mainly by negative feedback mechanisms that involve ACTH from the anterior pituitary gland
• Gonadocorticoids are masculinizing hormones such as testosterone. They stimulate growth of armpit and pubic hair as well as contribute to adolescent growth spIrt. Female androgens contribute to libido and are converted to estrogen (feminizing hormone)
• The adrenal medulla is composed of cells innervated by sympathetic nerve fibers. When the sympathetic nervous system is activated (short stress response) the cells secrete catecholamine (epinephrine) directly into the blood
• Epinephrine is released in stressful situations or exercice. It results in increased heart rate and force of contraction, increased blood pressure, increased blood flow to the heart, liver, skeletal muscle and adipose tissue and it dilates the airways
• Adrenal gland disorders:

  • Hypersecretion of cortisol is called Cushing’s syndrome
  • Hyposecretion of glucocorticoids and aldosterone is called Addison’s disease and results in vomiting, weight loss, muscle weakness, decreased sodium in blood, decreased heart rate and bronzed skin
• The pancreas is composed of both endocrine and exocrine tissue. The endocrine portion is made up of scattered tiny islands of cells called Islets of Langerhans
• Each pancreatic islet contains a combination of four primary types of endocrine cells which each secrete a different hormone:

  • alpha cells secrete glucagon
  • beta cells secrete insulin
  • delta cells secrete somatostatin
  • pancreatic polypeptide cells secrete pancreatic polypeptide
• Glucagon tends to increase blood glucose levels by stimulating the conversion of glycogen to glucose in liver cells
• Insulin tends to promote the movement of glucose out of the blood and into the tissue cells when blood sugar is high
• Pancreatic islet disorder is diabetes, which is the most common endocrine disorder. It is caused by an inability to either produce or use insulin depending on diabetes type (1 or 2)
• Type 1 diabetes is when the insulin level in the body is low because the person’s own immune system destroys the pancreatic beta cells. No insulin an no uptake of glucose leads to hyperglycemia. Treatment is insulin replacement therapy
• Type 2 diabetes is when the insulin level in the body is normal but target cells become less sensitive to it. Treatment is a lifestyle change or medication to stimulate even more insulin secretion.
• Hyperinsulinism most often results when a diabetic injects too much insulin which results in hypoglycemia and can lead to insulin shock
• The gonads are the primary sex organs in the male (testes) and female (ovaries)
• The interstitial cells found in areas between the seminiferous tubules produce testosterone, an androgen responsible for male sexual characteristics and sperm production. Its secretion is regulated principally by LH and FSH levels in the blood.
• Ovaries produce two hormones under the control of FSH and LH: estrogen, responsible for development and maintenance of female sexual characteristics such as breast development and the menstrual cycle, and progesterone, which maintains the lining of the uterus necessary for pregnancy
• The placenta is a temporary endocrine glands which forms on the lining of the uterus between the circulatory systems of the mother and fetus
• The placenta produces human chorionic gonadotropin (hCG). It is only present when pregnant and stimulates development and hormone secretion by maternal ovarian tissues
• The placenta also produces additional estrogen and progesterone during pregnancy as well as other hormones like human placental lactogen (responsible for milk production) and relaxin (relaxation of uterus)
• The thymus is a gland just beneath the sternum. It atrophies from puberty to adulthood until is becomes fat and fibrous tissue. It secretes thymosin and thymopoietin
• Thymosin and thymopoietin have a crucial role in the development of the immune system. They stimulate the production of T-cells (special lymphocytes involved in the immune response)
• The mucous lining of the GI produces gastrin, secretin and cholecystokinin (CCK) which have important roles in coordinating the secretory and motor activities involved in the digestive process
• Gastrin stimulates secretion of gastric juice rich in pepsin and HCL. It is only secreted when food is present in the stomach
• Secretin inhibits gastric secretion and stimulates the secretion of pancreatic juice and ejection of bile
• CCK has an opposite action to gastrin. It raises pH of gastric juice and ejects bile and secretion of pancretaic juice
• The heart has a secondary endocrine role due to some hormone producing cells in its wall. The principal hormone produced by these cells is called atrial natriuretic hormone (ANH). It works opposite to aldosterone.
• Atrial cells increase secretion of ANH in response to abnormally high blood volume or BP. It functions by promoting the removal of sodium from the body by means of urine. Water loss results in a decrease of blood volume, resulting in a decrease of BP.