Aldosterone Mechanism of Action

welcome to another path of video in this video we'll be talking about aldosterone aldosterone is an important hormone in the regulation of blood pressure and blood volume by increasing sodium reabsorption by the kidneys it is secreted from the zona glomerulosa of the adrenal cortex the zona glomerulosa cells use cholesterol to make aldosterone and other mineral corticoids and since aldosterone is hydrophobic it needs to be transported in the blood bound to albumin aldosterone is released under conditions of low blood pressure secretion of aldosterone will increase when levels of angiotensin ii or potassium in the blood and

extracellular fluid increase it will decrease when sodium ion concentration in the extracellular fluid increases as aldosterone is hydrophobic it diffuses into the principal epithelial cells of the late distal tubules and cortical collecting tubules and in the cytoplasm of the cell will bind with the mineral corticoid receptor to form an L dosterone receptor complex this complex then diffuses into the nucleus of the cell once inside the nucleus of the cell it up regulates the transcription of certain segments of DNA into mRNA the mRNA leaves the nucleus through nuclear pores and in the cytoplasm is translated on

ribosomes into proteins that allow for more sodium reabsorption and potassium and hydrogen secretion in particular it increases the formation of sodium potassium pumps on the basolateral membrane of principal cells it also increases the expression of epithelial sodium channels or enak on the apical membrane of principal cells the action of enak and sodium potassium pumps allow for movement of sodium from the filtrate back into the renal capillaries so less sodium is lost in the urine sodium attracts water therefore the end effect of aldosterone is to increase saram levels of sodium and to increase the fluid volume

in the vasculature to increase blood pressure as opposed to the reabsorption of sodium principal cells secrete potassium potassium comes into the cell because of the sodium potassium pump because of its high intracellular concentration it will then diffuse out through potassium channels on the apical membrane and enter the filtrate of the tubular lumen aldosterone will also increase the activity of the hydrogen potassium pump on the apical membrane of type a intercalated cells this action causes more hydrogen secretion and therefore alkalosis in some individuals a tumor can form in the zona glomerulosa cells this is usually a

single benign tumor that will secrete large amounts of aldosterone this condition is called primary aldosterone ism or Kahn syndrome the patient will experience hypokalemia mild metabolic alkalosis a modest increase in ECF and blood volume and most often high blood pressure interestingly however edema is not often present with primary aldosterone ism because an increase in fluid volume stimulates the release of atrial natriuretic hormone from the atria which causes loss of sodium and water the patient will also experience a four to six million Quillen per liter increase in sodium levels in the blood the low levels of

extracellular potassium will change the resting potential of neurons making them more hyperpolarized and can result in muscle weakness an important diagnostic feature of primary aldosterone ism is a decrease in plasma renin levels this comes from the fact that high blood volume will suppress the release of renin by the kidneys surgical removal of the tumor is the most common treatment before surgery it is necessary to manage the hypertension and hypokalemia another option for treatment is an aldosterone antagonist like spironolactone this drug will bind to the mineral corticoid receptor and block it and therefore prevent the effects

of high levels of aldosterone what would you expect to see in an individual with primary aldosterone ISM looking at the chart below use arrows to describe what would increase or decrease pause the video now and then resume it once you have determined your answers secondary aldosterone ism refers to causes of high aldosterone levels that are due to an extra adrenal stimulus this most often occurs where Wrentham production increases which in turn causes angiotensin ii levels to rise which will increase aldosterone what would cause Renan to increase anytime there is a decrease in circulating blood volume

due to conditions like shock dehydration or liver failure with liver failure there is a decrease in blood colloid osmotic pressure because the liver is not making sufficient amounts of albumin there are also conditions that result in less delivery of blood to the kidneys that will increase aldosterone levels examples of this are renal artery stenosis and heart failure renin secreting tumors can also bring about secondary aldosterone ISM you