SAQ EXAM QUESTIONS Flashcards
What effects would a fall in cardiac output have on the renal system, describe the sequence of events (6 points).
A fall in cardiac output will cause a decrease in blood pressure and a fall in relative blood volume. In the afferent arterioles of the kidney, there are juxtaglomerular cells which release renin. Juxtaglomerular cells have baroreceptors which can detect a fall in blood pressure. Renin is then released when a decrease in blood volume is detected. When blood pressure falls, the circulating fluid in the afferent arterioles, the glomerulus, and the proximal convoluting tubule, is slower, this mean that there is more time to reabsorb Na+ into the body.
Once it reaches the distal convoluting tubule , there is less Na+. This trudgers renin release. In the distal convoluting tubule there are macula dense cells, these measure the concentration of sodium. The distal convoluting tubule and the afferent arterioles are in close proximity (connected by connective tissue). This means that when the macula dense cells detect a fall in sodium concentration, it stimulates the juxtaglomerular cell to release renin.
Renin is then released into the systemic circulation. In the liver there is angiotensinogen which is an inactive and stored form. The liver then releases this into the bloodstream where it meets renin. Renin is an enzyme so: Renin + Angiotensinogen = Angiotensin I.
Angiotensin I is then released into the systemic circulation where it travels to the lungs. The lungs produce Angiotensin Converting Enzyme (ACE) where it converts angiotensin I into angiotensin II.
Angiotensin II is a generalised vasoconstrictor, this will constrict the arterioles causing blood to back up, increasing blood pressure.
Angiotensin II will also constrict the afferent arterioles causing blood to back up, this will increase the GFR (Glomerular Filtration Rate) and cause Na+ in to the distal convoluting tubule.
Angiotensin II will then travel to the adrenal cortex where it stimulates aldosterone. Aldosterone will then travel to the distal convoluting tubule and stimulate the reabsorption of Na+ in the body. H20 follows Na+, and therefore increases the blood pressure and increases the blood volume.
Angiotensin II will then travel to the posterior pituitary gland where it stimulates the release of anti diuretic hormone (ADH). This travels to the distal convoluting tubule stimulated the reabsorption of water into the body. This increases the blood volume and increases the blood pressure.
