Kidney structure and function 3

Question 1

Describe how ultrafiltration produces glomerular filtrate.

Answer 1

Ultrafiltration is due to hydrostatic pressure as the afferent arterioles are wider than the efferent arterioles; Small molecules; Pass through the pores in the capillaries and the projections of the podocytes; They also Pass through basement membrane which acts as filter; Protein too large to go through so stays behind;

Question 2

Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin (high blood glucose)

Answer 2

There is a high concentration of glucose in blood; High concentration in tubule, in the filtrate; Reabsorbed by facilitated diffusion and active transport; This process requires proteins carriers; If these are working at maximum rate they are saturated; So not all glucose is reabsorbed, some is lost in urine;

Question 3

Explain how a lack of insulin affects reabsorption of water in the kidneys of a person who does not secrete insulin (high blood glucose). /
Explain why a person with diabetes produces more urine.

Answer 3

High concentration of glucose in blood, high concentration in tubule and filtrate, not all can be reabsorbed into the blood, glucose in filtrate lowers the water potential of the filtrate. There is a lower water potential in the filtrate, so there is not a concentration gradient with the interstitial space. Glucose and water remains in the filtrate and passes down the collecting duct to be passed out of the body.

Question 4

Some desert mammals have long loops of Henle and secrete large amounts of antidiuretic hormone (ADH). Explain how these two features are adaptations to living in desert conditions.

Answer 4

Due to the longer loop of Henle more water is reabsorbed here from the filtrate, back into the blood, via osmosis. This happens because in the ascending limb, more sodium ions can be actively transported into the interstitial space, creating a higher concentration gradient, so more water can be reabsorbed into the interstitial space in the descending limb. The ADH acts on the collecting duct, and makes it more permeable to water, causing more to be reabsorbed by osmosis from the collecting duct.

Question 5

Why does a thicker medulla cause an increase in reabsorption of water?

Answer 5

A thicker medulla means a longer loop of Henle.

Question 6

Some drugs to treat blood pressure work by increasing the volume of urine produced. How does this treat high blood pressure?

Answer 6

Less water is reabsorbed. The volume of the blood decreases. This reduces the pressure.