Urinary System Quiz

A: Aldosterone is produced in the adrenal cortex (not the kidneys). The kidneys, along with the skin and liver contribute to producing calcitriol.

A: In normally functioning kidneys, approximately two thirds of the water filtered by the glomerular capillaries is reabsorbed in the proximal tubule. Although dehydration increases ADH levels and water reabsorption by the distal tubules, collecting tubules, and collecting ducts, and this action contributes importantly to decreased water excretion in dehydration, the total amount of water that remains in these tubular segments is small compared with the amount of water in the proximal tubules.

A: Cortical nephrons are situated almost entirely within the cortex, while the far less numerous juxtamedullary nephrons have their glomeruli adjacent to the medulla and extend their loop of Henle into the medulla.

B: Not to be confused with the urethra through which urine exits the body.

C: Afferent (incoming) arteriole enters the glomerulus; the efferent arteriole leaves the glomerulus.

D: Filtration due to the pressure difference between the capillary blood and fluid in the Bowman’s capsule.

B: Urea (a waste product) is lipid soluble, so it can passively move out of the filtrate into the tubule cells. It is secreted back into the filtrate to effect its excretion.

B: Hilum is the name of the point of attachment between an organ and its supply services.

A: Only the cortex contains glomeruli.

A: Water does not pass through the ascending limb. However, solutes (Na+ and Cl-) do pass through.

D: The efferent (outgoing) arteriole has a smaller diameter than the afferent arteriole; hence, the glomerulus is a high-pressure area. This aids the movement of dissolved substances through the filtration membrane.

C: A rise in blood pH means it is getting more alkaline. That means there is too much bicarbonate in the blood. To counter this, some bicarbonate ions are secreted into the filtrate, while some hydrogen ions are absorbed from the filtrate into the tubule cells to decrease the pH.

A: Excessive secretion of ADH increases water reabsorption by the renal collecting tubules, which reduces extracellular fluid sodium concentration (hyponatremia). Restriction of fluid intake, excessive aldosterone secretion, or administration of hypertonic 3% NaCl solution would all cause increased plasma sodium concentration (hypernatremia), whereas administration of 0.9% NaCl (an isotonic solution) would cause no major changes in plasma osmolarity.

A: The cortex is superficial to the medulla. All glomeruli are in the cortex. The medulla has the collecting ducts.

B: The afferent arteriole carries blood into the glomerulus so must be first. The efferent arteriole carries blood away from the glomerulus. The peritubular capillaries then arise.

C: High urine flow occurs in type 1 diabetes because the filtered load of glucose exceeds the renal threshold, resulting in an increase in glucose concentration in the tubule, which decreases the osmotic driving force for water reabsorption. Increased urine flow reduces extracellular fluid volume and stimulates the release of ADH.

D: Renin is an enzyme that catalyses the reaction that forms angiotensin I from angiotensinogen.

A: All other substances are passively reabsorbed.

B: ADH, from the posterior pituitary, would allow more water to be reclaimed from the filtrate so that plasma osmotic pressure does not increase further._x000D__x000D_The anterior pituitary gland does not release ADH._x000D__x000D_Renin and its effects do not promote diuresis.

D: The tubules and collecting ducts extend into the medulla, but all glomeruli are in the cortex.

B: The descending limb is permeable to water so water flows out of the tubule decreasing filtrate volume. The ascending limb is impermeable to water, so its volume does not change, however, sodium, potassium and chloride ions are reabsorbed which decreases the concentration of the filtrate.

C: The ascending limb. Hence, volume of filtrate does not change as it passes through the ascending limb.

B: Excess aldosterone increases sodium reabsorption and potassium secretion by the principal cells of the collecting tubules, causing sodium retention, increased blood pressure, and decreased renin secretion while increasing excretion of potassium and tending to decrease plasma potassium concentration._x000D__x000D_Excess aldosterone also causes a shift of potassium from the extracellular fluid into the cells, further reducing plasma potassium concentration. Aldosterone excess also stimulates hydrogen ion secretion and bicarbonate reabsorption by the intercalated cells and tends to increase plasma pH (alkalosis). Therefore the classic manifestations of excess aldosterone secretion are hypokalemia, hypertension, alkalosis, and low renin levels.

C: Constricting the afferent arteriole will decrease the volume of blood entering the glomerulus and hence the blood pressure in it. All other choices will result in an increase in pressure within the glomerulus.

D: Dehydration due to water deprivation decreases extracellular fluid volume, which in turn increases renin secretion and decreases plasma atrial natriuretic peptide. Dehydration also increases the plasma sodium concentration, which stimulates the secretion of ADH. The increased ADH increases water permeability in the collecting ducts. The ascending limb of the loop of Henle is relatively impermeable to water, and this low permeability is not altered by water deprivation or increased levels of ADH.