Higher Nephron Structure and Dialysis vs Transplant
Part of Water Regulation — GCSE Biology
This higher tier covers Higher Nephron Structure and Dialysis vs Transplant within Water Regulation for GCSE Biology. Topic 7: Water Regulation It is section 8 of 11 in this topic. This section is most useful once the core foundation idea is secure, because it adds the detail that pushes answers higher.
Topic position
Section 8 of 11
Practice
15 questions
Recall
20 flashcards
Higher Nephron Structure and Dialysis vs Transplant
Detailed nephron structure: Blood enters the glomerulus (a knot of capillaries inside the Bowman's capsule) under high pressure. Small molecules — water, glucose, urea, mineral ions — are forced through the capillary walls into the Bowman's capsule (ultrafiltration). Large molecules such as proteins and blood cells remain in the blood. As filtrate travels along the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct, useful substances are selectively reabsorbed. The loop of Henle creates an osmotic gradient that allows concentration of urine.
Kidney failure treatments — comparison:
| Feature | Dialysis | Transplant |
|---|---|---|
| Permanence | Ongoing (3x/week, 4h sessions) | Long-term solution |
| Lifestyle impact | Very restricting | Near-normal life possible |
| Risks | Infection, cardiovascular strain | Rejection, immunosuppressant side effects |
| Availability | Widely available | Limited by donor availability |
Quick Check: A person goes for a long run on a hot day and does not drink any water. Explain, in terms of ADH, what happens to their urine concentration and why.
Running causes sweating, which removes water from the blood. Blood water concentration falls. Osmoreceptors in the hypothalamus detect this fall. The pituitary gland releases more ADH into the blood. ADH travels to the kidneys and increases the permeability of the collecting duct. More water is reabsorbed back into the blood. Less water remains in the urine, so a smaller volume of more concentrated (darker) urine is produced. This is negative feedback — the response (reabsorbing water) opposes the original change (falling blood water concentration).
Quick Check: A student claims: "If the kidneys stop producing ADH, you would become dehydrated." Evaluate this statement.
The statement contains an error: the kidneys do not produce ADH — the hypothalamus produces it and the pituitary gland releases it. However, the consequence described is roughly correct. If ADH were absent, the collecting duct would remain impermeable to water. Water would not be reabsorbed, so large volumes of very dilute urine would be produced (a condition called diabetes insipidus). Losing excessive water in urine would cause dehydration. The student has the right effect but has misidentified the source of ADH.
Quick Check: Compare and contrast kidney dialysis and a kidney transplant as treatments for kidney failure. In your answer, consider effectiveness, lifestyle impact, and risks.
Both treatments allow patients with kidney failure to survive, but differ significantly. Dialysis filters waste from blood using a machine (typically 3 times per week, each session 4 hours), is a continuous commitment with strict dietary restrictions, and carries risks of infection and cardiovascular strain. A kidney transplant offers a long-term solution that restores near-normal kidney function, removes the need for regular dialysis sessions, and greatly improves quality of life. However, transplants carry the risk of organ rejection; patients must take immunosuppressant drugs for life, which increase susceptibility to infection. Availability is also limited by the shortage of suitable donor organs, whereas dialysis is widely accessible.