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Kidneys, excretion and water balance

Homeostasis and response • Hormonal coordination in humans

Key concepts

What you'll likely be quizzed about

  • Anti-diuretic hormone (ADH) is produced by the pituitary gland and acts on the kidneys, altering the permeability of collecting ducts and tubules.
  • Increased ADH levels make kidney tubules more permeable to water, leading to greater water reabsorption back into the bloodstream and a reduction in urine volume, resulting in more concentrated urine.
  • Conversely, reduced ADH levels lead to less permeable tubules, resulting in a larger volume of dilute urine.
  • This feedback mechanism regulates blood water concentration.

Flashcards

Test your knowledge with interactive flashcards

List two major disadvantages of kidney transplant.

Click to reveal answer

Risk of immune rejection and the limited availability of donor organs.

Key notes

Important points to keep in mind

ADH level controls water reabsorption; more ADH results in more water reabsorbed.

Filtration allows small solutes into nephron; selective reabsorption recovers essential molecules.

Urea forms in the liver from ammonia after deamination and is excreted through kidneys.

Water loss occurs via urine, sweat, and exhaled air; amounts vary based on activity and environment.

Hypertonic plasma causes cell shrinkage; hypotonic plasma causes cell swelling.

Dialysis clears urea and restores ion balance but requires repeated treatments.

Transplant offers potential cure but involves rejection risks and lifelong medication.

Interpretative tip: expect glucose to be fully reabsorbed, urea to be removed, and ion levels to vary.

Nephrons function as renal units where filtration and reabsorption occur.

Homeostatic water control uses negative feedback mechanisms involving osmoreceptors and ADH.

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