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Pl. II · Renal corpuscle

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Pl. II · FAM. NEPHRONIDAE

Corpusculum fenestratum var. cyathi

the sieve in a cup  ·  renal corpuscle

The plate

The specimen, drawn

Pl. II

Hand-drawn field-guide plate in coloured pencil: a bird’s nest fungus, its fluted cup drawn in warm brown with a tangled ball of pale peridioles sitting loose inside and a clear gap all the way around them. Below, a schematic of the renal corpuscle showing the glomerular tuft, the capsular space, the simple squamous parietal layer of Bowman’s capsule, the afferent arteriole entering wider than the efferent arteriole leaving, and the urinary pole opening into the proximal tubule. A circular inset at ×1000 shows the filtration barrier in section: a fenestrated capillary, the fused basement membrane, and a podocyte with its foot processes and filtration slits.

The fungus as it was drawn, with the corpuscle below it and the filtration barrier in the circle.

Habitat & range

Where it lives

Body map

Body map: a figure drawn with a broken pencil outline and cross-hatch fill, with four numbered markers over the kidney region. A key beneath reads: 1 the cortex — the outer rim only; 2 never the medulla, not one; 3 about a million in each kidney; 4 and every one drains inward. A closing line reads, all of them in the outer third.

Cortex only. A million of them in each kidney, and never one in the medulla.

Range

  • Cortex only, never medulla — about a million per kidney, 200 µm across.
  • Two poles: the vascular pole where the arterioles enter and leave, the urinary pole where the tubule begins.
  • Filters roughly 125 mL a minute, which comes to 180 litres a day.
  • The only capillary bed in the body with an arteriole at both ends.

Collection record

  • Add your slide numbers here.

Niche

What it does for a living

It is a sieve run at high pressure, and it does not choose. Three layers — fenestrated endothelium, fused basement membrane, podocyte slit diaphragms — sort by size and by charge, and by nothing else. Anything smaller than about 70 kDa goes through; albumin is just over the line and is also negative, so it is turned away twice. Net filtration pressure is only about 10 mmHg, which sounds small until you remember it runs every minute of your life. An arteriole at both ends is what lets the kidney hold its filtration rate steady while the blood pressure moves around it.

field collected specimen

How to know it on sight

  • A ball of capillaries sitting in a cup, with a clear space all the way around it. Once you have seen the gap you cannot unsee it.
  • The parietal layer of Bowman’s capsule is simple squamous — a thin dark line around the outside.
  • The visceral layer is podocytes wrapped onto the capillaries; at this power they are just the nuclei sitting on the tuft.
  • At the vascular pole, two arterioles — and the afferent is wider than the efferent. That difference is the pressure.
Histological slide of a kidney’s renal corpuscle, with a centered glomerulus surrounded by Bowman’s capsule. The staining reveals cell nuclei as dark purple dots amidst pink cytoplasm, against a nearly white interstitial background. The composition is tightly framed to emphasize the cell structures.

Specimen 1

High-magnification light micrograph of a glomerulus. The glomerulus appears as a central, tightly packed cluster of cells and capillaries, stained in eosinophilic pink. The nuclei are stained darker, in basophilic purple. The periphery shows the Bowman’s capsule, and the surrounding tissue shows renal tubules, also in varying shades of pink, with cell nuclei.

Start with the gap. Trace the capsular space all the way round before you look at anything else.

Specimen 2

Histological micrograph of a kidney glomerulus, stained with eosin. The glomerulus is centered, a well-defined circular shape with granular texture from capillaries and cells. Renal tubules surround it, forming pink to red stained rings and interconnected shapes.

The tuft at higher power. The dark dots on it are podocyte and endothelial nuclei, not separate cells sitting on top.

Specimen 3

Micrograph of kidney glomerulus (Slide 205) with fenestrated capillaries. Tissue stained with hematoxylin and eosin (H&E). Round glomeruli show clusters of red-stained cells and blue nuclei. Surrounding tissue includes tubules and capillaries, also stained with red and blue.

Fenestrated capillaries in the tuft. You cannot resolve a window at this power — but you can see how much blood is in there.

The filtration barrier in cross-section: rounded podocyte foot processes on top with narrow slits between them, a continuous basement membrane in the middle, and a capillary wall with small windows below.

People keep calling her by the wrong name

Look-alikes

Two plates. One is a thing that is not a corpuscle, and one is a corpuscle that has stopped working.

A cluster of cut tubules

Micrograph of kidney tissue displaying tubular structures lined by simple cuboidal epithelium. The cells manifest as circular or elliptical forms with centrally positioned, round, blue-stained nuclei. The cytoplasm appears pinkish. The tubules are closely packed, creating a densely cellular composition across the frame.
Cut tubules — packed together, but with no capsule and no space.

Round profiles packed together can look like a tuft at low power. There is no capsule and no space around them — that is the whole test.

A corpuscle in disease

Left: a normal glomerulus on H&E from the site’s slide 209. Right: two microscope fields of an amyloid deposit, one stained salmon-red with Congo red and one glowing apple-green on a dark field under polarized light.
A damaged corpuscle — the space filled and the tuft swollen to meet the capsule.

A normal glomerulus beside an amyloid deposit — salmon-red on Congo red, apple-green under polarised light. This is the slide that explains Stina’s proteinuria.

Examine it yourself

The virtual slide

Go to a named Renal Corpuscle view and find the vascular pole — the side where two vessels come and go rather than one tubule leaving. Then measure the two arterioles against each other by eye and decide which one is the afferent.

Virtual slide courtesy of Histology Guide.

YOur missions

Field Notes for Future Missions

Mission 1: label the filter

Mission 2: quick check

Field notes

Why this organism

A bird’s nest fungus is a cup with a tangled ball sitting loose inside it and a clear space all the way around — which is the renal corpuscle, structurally, with nothing left out. The fungus earns its place for a second reason: the cup is a splash-cup, and the whole arrangement exists to make water arriving under pressure do a job. That is the corpuscle’s entire argument.

Next · Pl. III

Tubulus villosus var. callistemonis

the greedy one · proximal convoluted tubule.

Continue to Pl. III →

In the wild  ·  photograph to come.

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