School project #2: kidneys

Hi there!

My second school project post will be about the kidneys! I will tell about the function and how they look under the microscope with a HE stain and an EVG stain.

Almost everyone knows that one of the important tasks of the kidneys is to filter the blood to keep the composition constant, but how does that go exactly? I’ll explain the anatomy of the kidneys first, so you can understand how it filters the blood and maneuvers the urine out of the body.

Anatomy of the kidney

Macroscopy of the kidney (from the outside in) :

  • The outside of the kidney: a smooth brown layer of tissue with fatty tissue on top.
  • The cortex: in the cortex are the Malpighian corpuscles. The Malpighian corpsules contain glomerular capillaries that are rolled up into a ball, and are encapsulated bij the Bowman’s capsule. The plasma is filtered out of the blood and go through the Bowman’s capsule to the loop of Henle, where a big part of the water and other useful substances are reabsorbed. The waste is transferred to the pelvis and is then called urine.
  • The medulla (marrow): in the medulla are the loops of Henle, collection tubes and 10 to 20 renal pyramids.
    The renal pyramids are round parts of the marrow where the loops of Henle are, where a big part of the water and other useful substances are reabsorbed into the bloodstream. The filtered plasma is then called urine.
  • The renal pelvis: the pelvis contains calyces and is a gathering place for urine.


The route of urine

The blood enters the kidneys in the renal artery, wich brances of in capillaries that go trough the entire kidney. The blood is filtered when it flows through the nephrons in the Bowman’s capsule in the cortex.

The blood is filtered under pressure in a way that the blood cells and proteins don’t go out of the blood, and the blood plasma goes trough the filter and in the loops of Henle. The loops of Henle then come together in the pelvis, where the urine enters the ureter. The ureter ends in the bladder, where the urine is then collected and discharged.

The kidney under the microscope (HE stain)

*note: these preperations are contaminated, as you can see on both pictures. This may be caused by unclean glass containers where the stains are preserved in, or late taping.

The kidney under the microscope (EVG stain)

These preperations are all small pieces of tissue from the cortex. The cortex is mainly connective tussue, transfer tubes and Malpighian corpuscles. You can recognise the Malpighian corpuscles by the round shape and the capsule around it. The Malpighian corpuscles are often darker than the surrounding tissue.

How do the stains work?

  • The HE stain contains hematoxylin and eosin. The hematoxylin stains the nuclei purple, and the eosin stains the cytoplasm a pink hue.
  • The EVG stain contains hematoxylin, picric acid and fuchsin. This stain dyes collagen red, the nuclei brown and sarcoplasm yellow.

And that’s it! I hope that I explained it well.

See you in the next post!




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