水分調節（滲透調節）：練習題

Which of the following descriptions regarding the dialysis machine (kidney machine) used for patients with kidney failure is correct?

When blood water potential drops below normal, what happens to the osmoreceptors in the hypothalamus?

Which of the following best explains how the loop of Henle maintains a high solute concentration in the tissue fluid of the renal medulla?

In a healthy human, at which part of the nephron is glucose almost completely reabsorbed back into the blood?

In the context of dialysis, how is the dialysis fluid (dialysate) formulated to ensure that metabolic wastes like urea are removed from the patient's blood?

State the role of ultrafiltration in the process of urine formation within the nephron.

The diagram below shows the renal corpuscle of a human nephron. Explain how the structural difference between vessel \(X\) and vessel \(Y\) is significant for the formation of glomerular filtrate.

Explain the detailed physiological responses, involving both endocrine and renal mechanisms, that occur when a person experiences prolonged severe dehydration, focusing on how the body restores its water balance.

When a person consumes a large amount of salty snacks without drinking water, the water potential of the blood changes.

(a) State the change in the blood water potential and identify the receptor that detects this change. (2 marks)

(b) Describe the role of the pituitary gland and antidiuretic hormone (ADH) in restoring the water potential to a normal level. (3 marks)

The table below provides data on the concentration of various substances in the blood plasma and the urine of a healthy human subject:

Substance | Concentration in Plasma (g/100 cm⁳) | Concentration in Urine (g/100 cm⁳)
Proteins | 7.50 | 0.00
Glucose | 0.10 | 0.00
Urea | 0.03 | 1.95
Inorganic salts | 0.72 | 1.55

(a) Explain why proteins are absent from the urine despite being present in high concentrations in the blood plasma. (1 mark)

(b) Describe the process of selective reabsorption of glucose and explain why its concentration in the urine is normally zero in a healthy individual. (2 marks)

(c) Using the concept of water potential gradients, explain how the loop of Henle and antidiuretic hormone (ADH) facilitate the production of urine with a urea concentration much higher than that of the plasma. (3 marks)

(d) In some medical conditions, glucose is not fully reabsorbed. Explain how the presence of glucose in the kidney tubules would affect the volume of water reabsorbed into the blood. (2 marks)