Slide 1
The kidneys filter fluid, then change what remains
The kidneys make urine by filtering blood and then modifying the filtered fluid. Much of what first enters the filter returns to the blood.
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Each kidney contains many nephrons, the working units that combine a filter with a tubule. This arrangement prevents the body from losing useful substances simply because they are small enough to cross the first barrier.
Slide 2
The glomerular barrier normally retains cells and large proteins
A glomerulus is a cluster of small blood vessels. Its filtration barrier normally retains blood cells and most large proteins.
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Pressure drives fluid across the barrier into a collecting space. Water and small dissolved substances enter together, so the first filtrate contains useful molecules as well as potential waste.
Slide 3
Tubules return useful material and water to the blood
Along the tubule, a small tube in the kidney’s working unit, water and needed substances move back toward the blood.
This reabsorption makes the final urine very different from the first filtered fluid.
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Secretion adds selected substances from blood to tubular fluid. The two directions of movement allow the kidney to regulate composition rather than behave like a simple kitchen sieve.
Slide 4
This selective work helps balance salts and acidity
Kidneys help regulate water, salts and acidity. Their work supports the electrical and chemical conditions needed by nerves and muscles.
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The kidneys also participate in hormonal systems: they help regulate blood pressure, support red-cell production and contribute to bone health. Urine formation is one part of a wider physiological role.
Slide 5
Blood and urine leave by different routes
Blood returns to the circulation through renal veins. Urine follows a separate route through the ureters into the bladder.
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The bladder stores urine before it leaves through the urethra. Distinguishing the urinary tubes from the blood vessels helps explain why a blocked drainage route and damaged filtering tissue are different problems.
Sources
- Your Kidneys & How They Work
NIDDK, NIH
- Physiology of Urine Formation
OpenStax, Rice University