Bowman's capsule glomerulus proximal tubule descending limb loop of Henle ascending limb distal tubule collecting duct blood in blood out urine Fig. 1 shows...
Question 1 Report
Fig. 1 shows a cross-section of a kidney nephron used in a teaching laboratory. A student follows the path of fluid from the glomerulus to the collecting duct. Table 1 gives concentrations in the filtrate and in the blood leaving the nephron.
| Substance | Filtrate at start / g dm-3 | Blood leaving nephron / g dm-3 |
|---|---|---|
| Glucose | 1.0 | 1.0 |
| Urea | 0.30 | 0.05 |
(a) What process forces small molecules from blood into the nephron at the glomerulus? [1]
(b) Describe what happens to glucose in a healthy kidney. [1]
(c) Give one reason why blood leaving the nephron has less urea than the filtrate at the start. [2]
A paramedic gives an athlete an intravenous saline drip after prolonged vomiting. Fig. 1 shows the bag connected to a vein in the athlete’s arm. The saline contains sodium chloride at a concentration close to that of blood plasma.
(a) What is the main purpose of giving saline in this situation? [1]
(b) Describe what could happen to red blood cells if pure water were used instead of saline. [1]
(c) Explain why a saline concentration close to that of blood prevents this change. [2]
Answer Details
Kidney and nephron
(a) Small molecules are forced from the blood into the nephron by filtration, also called ultrafiltration. [1]
(b) In a healthy kidney, all glucose is selectively reabsorbed into the blood. [1]
(c) Urea remains in the tubule fluid rather than being fully reabsorbed. It is then removed from the body in urine, so blood leaving the nephron has less urea. [2]
Saline drip
(a) Saline replaces lost water and ions and restores blood volume. [1]
(b) If pure water were used, red blood cells would gain water, swell, and may burst. [1]
(c) Saline close to blood-plasma concentration has a similar water concentration to the cell contents. There is therefore no net osmosis, preventing red blood cells from swelling. [2]
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