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Lecture

The adrenal glands

9 Pages
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Department
Physiology
Course Code
PSL201Y1
Professor
Christopher Perumalla

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Description
Primary Endocrine organs Pineal gland Hypothalamus Pituitary gland Thyroid gland Parathyroid glands Thymus Adrenal gland Pancreas Ovaries (female) Testes (male) Secondary Endocrine organs Heart Stomach Liver Kidney Small intestine Skin Primary Endocrine organs Pineal gland Hypothalamus Pituitary gland Thyroid gland Parathyroid glands Thymus Adrenal gland Pancreas Ovaries (female) Testes (male) Secondary Endocrine organs Heart Stomach Liver Kidney Small intestine SkinThe adrenal glands The adrenal glands are pair structures that sit above each kidney. Both the adrenal glands and the kidneys are located in a potential space called the retroperitoneum that lies deep within the abdominal cavity. Although it appears as if the adrenal glands are attached to the kidney, they have their own blood supply. Each adrenal gland consists of an outer layered portion called the cortex which constitutes of 80%The Adrenal Glands Adrenal Capsule Cortex Zona glomerulosa A Adrenal medulla Zona fasciculata Cortex Adrenal gland Zona reticularis Kidney Medulla Adrenal medulla (a) (b) Cortex secretes adrenocorticoids: mineralocorticoids, glucocorticoids, sex hormones The Adrenal Glands Adrenal Capsule Cortex Zona glomerulosa A Adrenal medulla Zona fasciculata Cortex Adrenal gland Zona reticularis Kidney Medulla Adrenal medulla (a) (b) Cortex secretes adrenocorticoids: mineralocorticoids, glucocorticoids, sex hormonesof the glands’ total mass. The other area is the inner core called the adrenal medulla. The cortex and the medulla operate as two distinct glands in one, as they are structurally and functionally distinct. The adrenal cortex secretes a number of hormones that are collectively called adrenal corticoids named for their origin of release and their chemical class. They are all of the steroid family. The adrenal corticoids include three families of hormones: he mineralcorticoids, the glucocorticoids and the sex hormones. The adrenal medulla is formed of chromaffin cells which secrete a family of hormones known as the catecholamines. The adrenal gland has a thin outer shell called the capsule and beneath this, the three layers of adrenal cortex. The outer one is called the zona glamerulosa, the middle layer is the zona fasciculate and the inner one is the zona reticularis. In the inner core of the gland we see the chromaffin cells of the adrenomedulla. Adrenal cortex hormones The adrenal corticoids include three families of hormones: he mineralcorticoids, the glucocorticoids and the sex hormones. Mineralcorticoids These hormones are synthesized and secreted from the outermost layer of the cortex called the zona glamerulosa. Chief among these hormones is called the aldosterone.  Glucocorticoids Glucocorticoids are synthesized and secreted by the two inner layers of the cortex: the zona fasciculata and the zona reticularis. The most important glucocorticoid is called the cortisol.  Sex hormones The sex hormones are also synthesized and secreted by the two inner layers of the cortex: the zona fasciculata and the zona reticularis. The most important sex hormones are the androgens. Aldosterone Aldosterone is synthesized by the outer layer of the adrenal cortex, the zone glamerulosa. The aldosterone controls the osmolarity of the outer fluid by its ability to stimulate the reabsorption of sodium at the kidneys. It controls our plasma osmolarity. This is performed at two levels of the kidney tubule. This sodium reabsorption is coupled with potassium secretion. Aldosteron also plays a role in blood pressure regulation. The aldosterone in response to a signal is secreted and arrives by the circulation to its target cell, the principal cell. The aldosterone is a hydrophobic molecule and so uses cyclosopic receptors. The binding forces the sodium and potassium channels to open, the synthesis of new sodium and potassium channels and the synthesis and insertion of more sodium and potassium pumps. These events provide channels through which sodium can move from the tubular filtrate to the circulation and channels for potassium to move from the circulation to the tubular filtrate.Aldosterone Actions Na freely filtered atglomerulus:70% reabsorbed atproximal tubule (non-regulated) 30% reabsorbed at distal tubule, collecting duct(regulated) Lumen of late distal Basolateral Peritubular Peritubular tubule or collecting duct membrane fluid capillary Principal cell Apical membrane Cytosolic Na receptor Aldosterone Na Na Na Na Na Tubular fluid Plasma Na reabsorption: filtrated ncipal cell Mitubularfluid plaana (tubularfluid) K secretion: plasma Nvritubularfluid. urincipal cell te (tubular fluid Aldosterone Actions Na freely filtered atglomerulus:70% reabsorbed atproximal tubule (non-regulated) 30% reabsorbed at distal tubule, collecting duct(regulated) Lumen of late distal Basolateral Peritubular Peritubular tubule or collecting duct membrane fluid capillary Principal cell Apical membrane Cytosolic Na receptor Aldosterone Na Na Na Na Na Tubular fluid Plasma Na reabsorption: filtrated ncipal cell Mitubularfluid plaana (tubularfluid) K secretion: plasma Nvritubularfluid. urincipal cell te (tubular fluidAt very low circulation of aldosterone. The number of sodium and potassium channels in both membranes would be relatively low while in high circulation of aldosterone, the number of these channels would be much higher. Aldosterone is also involved in blood circulation through its participation in the rennin-angiotesin-aldosterone system. Increased plasma sodium levels is associated with retention of water and elevated blood pressure. A decrease in blood pressure or volume is sensed by barrel receptors, pressure sensitive receptors. This results in activation of the sympathetic nervous system which acts as a primary stimuli for the release of renin. Renin is released from specialized cells in the kidney. Release in Renin is translated to a relative increase in angiotensin 2 levels. Angiotensin will work to restore normal blood pressure through 5 different means. Through the stimulation of the sympathetic nervous system, through its own receptors, through the release of aldosterone, through the reabsorption of sodium and through the stimulation of release ofRenin-angiotensin-aldosterone system Sympathetic activity Na Kidney Lungs Tubular Na Surface of pulmonary reabsorption and K and renal endothelium: cretion, H,o retention Ho- ex ACE COrtev Aldosterone Angiotensinogen Angiotensin I Angiotensin ll Renin Decrease in renal perfusion Arteriolar Juxtaglomerular vasoconstriction. apparatus) Increase in blood pressure ADH
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