Adrenal Glands.docx
Transcript
Before we look at the key components of the body’s response to stress, we need to review the adrenal glands. Please go back to your anatomy and physiology notes and review the adrenal glands, the anatomy, the hormones and their function. These retroperitoneal glands are comprised of three main layer...
Before we look at the key components of the body’s response to stress, we need to review the adrenal glands. Please go back to your anatomy and physiology notes and review the adrenal glands, the anatomy, the hormones and their function. These retroperitoneal glands are comprised of three main layers: The outer layer is the capsule. This is a touch, fibrous capsule enclosed in fat for protection. The adrenal cortex forms the bulk of the gland and accounts for 80-90% of the gland. This layer has three divisions or zones. Lastly the inner most layer is the adrenal medulla, which is more like a knot of nervous tissue and is part of the sympathetic nervous system accounting for 10-20% of the gland. The adrenal cortex has three layers. Zona Glomerulosa: We will start with the outermost layer, which is the Zona glomerulosa. This produces primarily aldosterone. 95% of the mineralocortecoid produced is in the form of aldosterone. This is key for regulating sodium and potassium secretion and retention. Aldosterone is a key component of the renin, angiotensin, aldosterone pathway for volume and blood pressure control. Aldosterone plays a role with the pH balance, as it facilitates the excretion of hydrogen ions. If someone has too much aldosterone excreted called aldosteronism, it is usually related to the neoplasms. The person will present clinically with hypertension and edema due to the high sodium. A decrease in potassium and if enough will cause muscle weakness, paralysis. If too little aldosterone is secreted, it can lead to hypotension. Dehydration can be common, decreased sodium, increased potassium and potential weight loss. Zona Fasciculata: The middle layer of the adrenal cortex is the Zona fasciculata – primarily cortisol. 95% of the gluco-corticoid is secreted in the form of cortisol. Others include cortisone, and corticosterone. Cortisol is released with ACTH stimulation and there is negative feedback with increased cortisol levels. Cortisol, also known as hydrocortisone is the major stress hormone and it is a glucocorticoid. It is important to understand that cortisol is secreted during periods of stress and it is essential for our survival. Cortisol has many physiological facts and some of the main ones are it increases blood glucose, both by decreasing peripheral uptake and promoting gluconeogenesis. It acts synergistically with glucagon and epinephrine, and the overall affect is greater than the sum of the individual hormones. It decreases insulin sensitivity. This should help with the understanding of why well controlled diabetes are harder to control in the hospital setting and their control often improves when they go home. It increases protein synthesis in the lives, but actually promotes the catabolism in the muscles. Cortisol promotes lipolysis in the extremities and although the mechanism is unclear, there seems to be an important acute and long term effects on the fatty acid metabolism. In the acute stage cortisol promotes the breakdown of fatty acids to be used as a source for energy. However in the long term with sustained cortisol levels, the body starts to redistribute fat or promote lipogenesis in the face and trunk area. Clinically this is seen as the fat pad at the back of the neck or the buffalo hump, moon face or increased visual abdominal fat. These findings are commonly referred to as Cushingoid signs. It provides an anti-inflammatory effect. Research is starting to show that this happens at a cellular level with anti-inflammatory effects but may be linked to increased autoimmune responses. Increased levels are linked to decreasing levels of Interleukin 1, Interleukin 2, Interleukin 6 and tumor necrosis factor alpha all pro-inflammatory cortisol. Cortisol also has a key immuno- suppressive role, causing the T helper 2 shift and increasing humoral immunity. Remembering the 2 sub-population of the T helper cells, part of the T helper 2. T helper 1 cells provide more help for cell medicated immunity, where T helper 2 provides more help for humoral immunity, and ideally both sub-sets should be in balance. Cortisol acts to suppress the activity of T helper 1 cells, leading to a decrease in the cellular immunity and promotes the activity of T helper 2 cells, leading to an increase in humoral immunity and increases the anti-inflammatory response. This change in balance ultimately leading to the increased T helper 2 cells and their activity is called the T helper 2 shift. Please see the next point about cortisol affects to look at what happens when you have insufficient cortisol level or excessive cortisol levels. So if too little cortisol is secreted often in conjunction with too little mineralocorticoid, this is called adrenal insufficiency or Addison’s disease. Essentially the availability of cortisol is decreased, limiting the required hormonal effects. Conversely if too much cortisol is secreted from the adrenal cortex, or more commonly caused by excessive corticosteroid medication administration, this is called Cushing’s disease. The patient could present with hyperglycemic, sometimes referred to as steroid diabetes. They would also have hypertension edema. Poor wound healing susceptibility for infections. Also they would have the Cushingoid signs. The buffalo hump, and the moon face. Zona Reticularis: The inner most layer of the adrenal cortex is the Zona reticularis. It is here that Gonadocorticoids are made. They are considered by weak androgens. Primarily DHEA or dehydroepiandrosterone and DHEA sulphate can be converted to testosterone or in females, estrogen. If too much DHEA is secreted, especially in females, it can lead to an increase virilisation or hirsutism, that is facial hair. Often is seen with PCOS, polycystic ovarian syndrome. Adrenal Medulla: In the middle of the adrenal gland is the adrenal medulla. This is made up of chromaffins cells also called pheochromocytes. It has a rich blood supply and a rich nerve supply. Epinephrine is secreted approximately ten times more potent than norepinephrine more potent for the heart and metabolic activities. Norepinephrine is secreted, although the medulla is a minor source of norepinephrine. It has key links to the autonomic nervous system, the fight or flight component. One side note, a pheochromocytoma is a neuroendocrine tumour, which secretes excessive catecholamines.
