The urinary system

Question 1

Describe the physiological process of filtration with reference to the nephron?

Answer 1

• Takes place in the semipermeable walls of the glomerular capillaries and glomerular capsule.
• Blood flows through the afferent arteriole (wider) into the glomerulus and leaves through efferent arteriole (narrower)
• Resistance to blood flow is created due to the size difference of arterioles.
• The glomerular filtrate contains water, ions, glucose, amino acids, and other small molecules that can pass through the filtration barrier.
• Large molecules like proteins are usually retained in the bloodstream because they are too large to pass through the filtration barrier.

Question 2

Describe the physiological process of reabsorption with reference to the nephron?

Answer 2

• Occurs in proximal convoluted tubule (PCT), loop of Henle, distal convoluted tubule (DCT), and collecting ducts.
• The majority of reabsorption occurs in the PCT - sodium ions, glucose, amino acids, and water are reabsorbed into peritubular capillaries
• Loop of Henle - Descending loop water reabsorbed and Na+ diffuses in. Ascending loop Na+ reabsorbed (active transport) and water stays in

Question 3

Describe the physiological process of secretion with reference to the nephron

Answer 3

The descending loop of henle Na+ diffuses in to encourage reabsorption of water. In the ascending loop Na+ is reabsorbed (active transport) water stays in.

Question 4

Outline the actions of antidiuretic hormone in the kidney

Answer 4

• Secreted by the posterior pituitary
• Increases the permeability of the distal convoluted tubules and collecting ducts to water, increasing water reabsorption
• Osmoreceptors in the hypothalamus monitor the water content of the blood, and ADH secretion is adjusted accordingly

Question 5

Outline the actions of aldosterone in the kidney

Answer 5

• Secreted by the adrenal cortex
• Increases the reabsorption of sodium and water

Question 6

Identify the importance of the kidney in pH regulation

Answer 6

The kidneys regulate pH levels by excreting hydrogen ions and reabsorbing bicarbonate ions. This helps maintain the body’s acid-base balance.

Question 7

Explain the role of the kidney in the elimination of nitrogenous waste

Answer 7

Nitrogenous waste such as urea and creatinine are eliminated through filtration, reabsorption and secretion.
This process helps maintain proper balance of nitrogenous compounds in the body, preventing their accumulation, which could be harmful.

Question 8

Describe the renin-angiotensinogen mechanism and its function in the body

Answer 8

• Cells in the kidney release an enzyme called renin into the bloodstream
• Renin cleaves angiotensinogen to produce angiotensin I (inactive)
• Conversion occurs in the lungs, where an enzyme called angiotensin-converting enzyme (ACE) cleaves angiotensin I to form angiotensin II
• Angiotensin II aimed at increasing blood pressure and maintaining fluid balance
• Vasoconstriction which increases blood pressure and stimulates the release of aldosterone from the adrenal glands.
• Aldosterone promotes the reabsorption of sodium and water in the kidneys, increasing blood volume.