Organ histology: urinary, endocrine, reproductive and skin
Introduced| English | Meaning |
|---|---|
| nephron/ˈnefrɒn/ | A microscopic kidney unit that filters blood plasma and modifies the resulting fluid through reabsorption and secretion. |
| brush border | brush border |
| fenestrated capillaries | Capillaries with pores in their endothelium, as in the kidney and endocrine glands. |
| keratinised stratified squamous epithelium | keratinised stratified squamous epithelium |
| dermis | dermis |
Three machines in a biopsy
- The kidney's tubules, the endocrine glands' blood supply and the skin's layered armour are each recognisable histological machines.
- Together they cover urine, hormones and the body's barrier, and their diseases are read in biopsies every day.
The nephron's segments
- The nephron 肾单位 starts with the glomerulus, a tuft of leaky capillaries inside Bowman's capsule. Then: proximal tubule (cuboidal, with a brush border), loop of Henle, distal tubule (cuboidal, no brush border), collecting duct (pale cuboidal to columnar cells).
- The loop's thin limbs are flat squamous; its thick ascending limb is cuboidal and packed with mitochondria.
Put the parts of the nephron in the order the filtrate passes through them.
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Filter, reabsorb in bulk, build the salt gradient, adjust, then fine-tune water.
Epithelium predicts function
- The proximal tubule takes back about 65% of the filtrate, so it needs area: a brush border 刷状缘 of microvilli. The thin limbs let water and ions move passively, with almost no machinery.
- The thick limb pumps salt out (hence its mitochondria), and the collecting duct fine-tunes water under hormone control.
Why does the proximal tubule have a brush border?
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Bulk reabsorption needs area, and microvilli multiply the cell's surface.
The kidneys filter 180 L a day. If the proximal tubule takes back 65%, how many litres a day is that?
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180 × 0.65 = 117 L a day, which is why the proximal tubule is the most heavily built segment.
Endocrine glands
- Endocrine cells sit in cords or follicles wrapped in fenestrated capillaries 有孔毛细血管: capillaries with pores.
- Hormones go straight into the blood, so there are no ducts; that is what "endocrine" means.
What feature is shared by endocrine glands?
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Hormones enter the blood by the shortest path; pores in the capillaries make that path short.
Skin
- The epidermis is keratinised stratified squamous epithelium 复层扁平角化上皮 on the dermis 真皮, which carries the vessels, nerves and glands.
- The epidermis renews itself about every four weeks, from a basal layer of dividing cells on the basement membrane.
The epidermis is replaced about every four weeks.
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Basal cells divide and move up, flatten and fill with keratin before they flake off.
Worked example: where is this biopsy from?
- A field shows a tuft of capillaries inside a capsule, next to a tubule with a fuzzy, brightly stained brush border.
- Glomerulus plus proximal tubule means renal cortex. The pairing names the region without a map.
Match each appearance to the nephron part.
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Each segment wears its job, so one high-power field names it.
Worked example: the burn
- (Fictional burn) Where the epidermis has died, the barrier is gone: fluid is lost and infection follows quickly.
- Healing depends on how much basement membrane, and how many hair follicles and glands, survive: they are where new epidermis grows from. One layer's survival decides the outcome.
Three common slips
- All tubules look alike. The differences between segments are the whole point.
- Endocrine glands with ducts. Endocrine cells release into capillaries; glands with ducts are exocrine.
- "The dermis is just connective tissue." It is the vascular, sensory and structural half of the skin.
Recap
- Brush border = proximal tubule; flat = thin limbs; cuboidal with mitochondria = thick limb; pale columnar = collecting duct.
- Endocrine cells sit on fenestrated capillaries, with no ducts.
- Skin: keratinised stratified squamous over a vascular dermis, renewed about every four weeks.