Brainlag PlusHow the kidneys balance water and remove urea, ADH, dialysis and transplants, auxin and tropisms, and the seedling growth required practical.
The kidneys
Excess amino acids are broken down in the liver into ammonia, which becomes urea.
The kidneys filter the blood, then selectively reabsorb all the glucose, the ions the body needs and the right amount of water. Urea, excess ions and excess water leave as urine. Protein molecules are too large to be filtered.
Higher: when the blood is too concentrated, the pituitary releases more ADH, which makes the kidney tubules more permeable, so more water is reabsorbed and the urine is small in volume and concentrated. This is negative feedback.
Kidney failure is treated by dialysis (blood flows past a partially permeable membrane and urea diffuses out into dialysis fluid, several hours, several times a week) or by a transplant (a donor kidney with a close tissue match; immunosuppressant drugs for life to stop rejection).
Glucose is filtered out and then all reabsorbed. Protein is never filtered.
The rest of this lesson and its 13 practice questions are in Plus.
Screen 1 of 4, free to read.
- 13 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards