Renal System

The descending and ascending limbs should be between the PCT and DCT, while the collecting duct is last.

100 ml/3 hr. is a low rate of urine production, indicating dehydration. Hence, the urine will be concentrated as the body is conserving water, and its SG will be high.

High hydrostatic pressure facilitates filtration and pores in the capillary walls (fenestrae) allow easy passage.

ADH, from the posterior pituitary, would allow more water to be reclaimed from the filtrate so that plasma osmotic pressure does not increase further. Renin and its effects do not promote diuresis.

Increased permeability of the collecting duct means that more water will be reclaimed from the filtrate. Angiotensin II stimulates thirst. ANP diminishes thirst and increases sodium secretion at the kidneys.

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

Efferent means outgoing.

The efferent and afferent arterioles flow out from and into, respectively, the glomerulus, so the glomerulus is misplaced. In choice C, the afferent arteriole should precede the peritubular capillaries.

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

Juxtamedullary nephrons have a capillary bed known as the vasa recta which descends into the kidney medulla. As it does so, the concentration of the contained blood increases to 1200 mosmol/L.