Kidney and endocrine histology
Kidney, urinary tract, reproductive, skin and endocrine histology
Histology of the nephron and filtration barrier, urothelium, testis, ovary, endometrium, cervix, skin and endocrine glands for FCPS Part 1. Each structure is linked to what it does, so podocyte effacement, renin release, endometrial shedding and steroid-cell organelles make sense.
Steroid cells versus protein cells
Cells that make steroids (adrenal cortex, Leydig cells, corpus luteum, theca interna) are packed with smooth endoplasmic reticulum, mitochondria with tubular cristae and lipid droplets, because cholesterol is processed in these organelles. Cells that make proteins (pancreatic acini, plasma cells, osteoblasts, chief cells) are rich in rough ER and Golgi. Steroid cells store little hormone and secrete as they make it.
Glomerular filtration barrier
| Layer | Barrier |
|---|---|
| Fenestrated endothelium | Blocks cells; negative glycocalyx |
| Glomerular basement membrane | Type IV collagen and negatively charged heparan sulphate: size and charge barrier, so albumin (negative) is held back |
| Podocytes | Foot processes interdigitate, leaving filtration slits bridged by slit diaphragms (nephrin) |
- Effacement (flattening) of podocyte foot processes loses the slit barrier, causing heavy proteinuria: the only EM finding in minimal change disease, the commonest nephrotic syndrome in children.
- Disease by layer: Goodpasture has linear IgG along the GBM (anti-type IV collagen) with lung haemorrhage; Alport syndrome shows a split, basket-weave GBM with deafness and eye changes; subepithelial humps occur in post-streptococcal GN.
- Mesangial cells support capillary loops, contract and phagocytose.
- Afferent arteriole feeds the glomerulus; the efferent arteriole drains it and forms the peritubular capillaries (and vasa recta).
Tubule
| Part | Histology | Job |
|---|---|---|
| Parietal Bowman capsule | Simple squamous | Encloses filtrate |
| PCT | Cuboidal with tall brush border, many mitochondria, eosinophilic | Reabsorbs about two-thirds of filtrate |
| Thin limbs | Simple squamous | Water and passive salt movement |
| Thick ascending limb, DCT | Cuboidal, no brush border, many mitochondria | Active NaCl transport |
| Macula densa | Crowded tall cells of the distal tubule at the hilum | Senses NaCl delivery |
| Juxtaglomerular cells | Modified smooth muscle in the afferent arteriole | Secrete renin |
| Collecting duct | Cuboidal to columnar | Principal cells (Na⁺, K⁺, water via aquaporin-2); intercalated cells (H⁺ or HCO₃⁻) |
Urinary tract
- Urothelium (transitional) lines the renal pelvis, ureters, bladder and proximal urethra; umbrella cells with uroplakin plaques make it impermeable and stretchable. Because the same field lines the whole tract, bladder urothelial cancer can be multifocal and the upper tracts must be imaged. Squamous carcinoma arises from metaplasia (stones, catheters, schistosomiasis).
- Ureter: inner longitudinal and outer circular muscle, with an extra outer longitudinal layer in the lower third.
Testis and male tract
- Sertoli cells: tall cells resting on the basement membrane; tight junctions between them form the blood–testis barrier; FSH receptors; make androgen-binding protein, inhibin and AMH; nurse and phagocytose.
- Germ cells mature from spermatogonia at the base to spermatozoa near the lumen.
- Leydig cells in the interstitium: testosterone under LH; smooth ER; Reinke crystals.
- Sperm gain motility and are stored in the epididymis (mainly the tail) and proximal vas. Epididymis: pseudostratified with stereocilia; vas deferens: thick three-layered muscle.
- Prostate: tubuloalveolar glands with two cell layers (secretory and basal), corpora amylacea, fibromuscular stroma. Seminal vesicles: highly folded mucosa.
Ovary
- Cortex with follicles: primordial, primary, secondary (antrum), mature (Graafian). The zona pellucida is the PAS-positive acellular glycoprotein ring round the oocyte.
- Corpus luteum: luteinised granulosa and theca cells; secretes mainly progesterone (with oestrogen); maintained by LH, then by hCG if pregnancy occurs; otherwise becomes the corpus albicans.
Endometrium
| Layer | Blood supply | Fate |
|---|---|---|
| Stratum functionalis | Spiral (coiled) arteries, sensitive to progesterone withdrawal | Shed at menstruation |
| Stratum basalis | Straight (basal) arteries | Retained; regenerates the functionalis |
- Proliferative phase (oestrogen): straight tubular glands with mitoses, growing stroma.
- Secretory phase (progesterone after ovulation): coiled glands with subnuclear vacuoles (early), luminal secretion and stromal oedema (mid), predecidual change (late).
- Falling progesterone constricts the spiral arteries, the functionalis becomes ischaemic and is shed.
- Endometrial hyperplasia comes from unopposed oestrogen (anovulation, obesity, tamoxifen); endometrial cancer is part of Lynch syndrome (mismatch repair genes) with colon cancer.
- Cervix: endocervix simple columnar mucus-secreting; ectocervix stratified squamous; CIN arises in the transformation zone. Vagina: non-keratinised stratified squamous rich in glycogen, no glands.
- Uterine tube: ciliated and secretory (peg) cells; highly folded in the ampulla.
Skin
- Epidermis from deep to surface: basale (stem cells, melanocytes, Merkel cells), spinosum (desmosomes; Langerhans cells with Birbeck granules present antigen), granulosum (keratohyalin), lucidum (thick skin only), corneum. The epidermis is the main barrier to water loss.
- Dermis: papillary (loose, Meissner corpuscles for light touch) and reticular (dense irregular, Pacinian corpuscles deeper for vibration).
| Gland | Secretion type | Site and control |
|---|---|---|
| Eccrine sweat | Merocrine | Whole body; sympathetic cholinergic |
| Apocrine sweat | Apocrine (classically) | Axilla, groin, areola; into hair follicles; active after puberty |
| Sebaceous | Holocrine | With hair follicles; androgen-driven |
Endocrine glands
| Gland | Histology |
|---|---|
| Thyroid | Follicles of cuboidal cells around colloid (thyroglobulin); C cells (calcitonin) between follicles |
| Parathyroid | Chief cells (PTH), oxyphil cells, fat increasing with age |
| Adrenal cortex | Glomerulosa (aldosterone), fasciculata (cortisol; widest, foamy lipid-laden columns), reticularis (androgens) |
| Adrenal medulla | Chromaffin cells (adrenaline, noradrenaline), from neural crest |
| Pancreatic islets | β insulin, α glucagon, δ cells somatostatin (inhibits insulin and glucagon), PP cells |
| Pituitary | Anterior: acidophils (GH, prolactin), basophils (ACTH, TSH, FSH, LH), chromophobes; posterior: axons, pituicytes, Herring bodies |
- Glomerulosa control: aldosterone secretion is driven mainly by angiotensin II and plasma K⁺, with ACTH only a minor role. Long-term prednisolone suppresses ACTH, so the fasciculata and reticularis atrophy while the glomerulosa is preserved. Secondary adrenal insufficiency therefore rarely causes hyperkalaemia.
Remember Steroid cells are full of smooth ER; protein-secreting cells are full of rough ER.
Exam trap Juxtaglomerular cells in the afferent arteriole secrete renin; the macula densa senses NaCl.
Exam trap The functionalis (spiral arteries) is shed; the basalis (straight arteries) remains.
How FCPS asks about this
- Organelle abundant in Leydig and adrenal cortical cells: smooth ER (steroid synthesis).
- Cells forming filtration slits and effect of effacement: podocytes; proteinuria (minimal change disease).
- Layer shed at menstruation and its arteries: stratum functionalis; spiral arteries.
- Zone preserved after long-term steroids: zona glomerulosa, driven by angiotensin II and K⁺.
- Islet cells secreting somatostatin: delta cells.
- Main product of the corpus luteum and what maintains it: progesterone; LH, then hCG in pregnancy.
- Blood–testis barrier: tight junctions between Sertoli cells; sperm stored in the epididymis.
Test yourself on this topic
5 of the 31 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
Which part of the breast gives rise to most breast carcinomas, including both ductal and lobular types?
Answer: Terminal duct lobular unit
The functional unit of the breast is the terminal duct lobular unit (TDLU): a terminal duct and the cluster of acini (ductules) it drains, within specialised loose intralobular stroma. Most epithelial lesions, including fibroadenoma, fibrocystic change and both ductal and lobular carcinomas, arise here. The names ductal and lobular describe the pattern of growth, not the site of origin. Large ducts more often give rise to intraductal papillomas.
Terminal duct lobular unit
- Terminal duct + acini
- Origin of most carcinomas
- Ductal and lobular: pattern, not site
- Large ducts: papillomas
Remember Most breast cancers start in the TDLU.
Exam trap Bloody nipple discharge from a single duct is most often an intraductal papilloma, but cancer must be excluded.
Why the other options are wrong
- Lactiferous sinus Typical site of intraductal papilloma, not most cancers.
- Major lactiferous duct Large ducts are a less common origin.
- Nipple epidermis Paget disease of the nipple reflects underlying carcinoma spreading up.
- Interlobular stroma Stroma gives rise to phyllodes tumours and sarcomas.
Which histological feature identifies the proximal convoluted tubule on a kidney section?
Answer: Cuboidal with brush border
The proximal convoluted tubule reabsorbs about two-thirds of filtered sodium and water and nearly all glucose and amino acids, so its cuboidal cells have a dense apical brush border (increasing surface area), basal infoldings packed with mitochondria (energy for Na-K-ATPase) and deeply eosinophilic cytoplasm; the lumen often looks fuzzy. The distal convoluted tubule has smaller, paler cells without a prominent brush border and a clearer lumen; the macula densa is part of the distal tubule next to the glomerulus. The thin limb of the loop of Henle is lined by simple squamous epithelium. The PCT is the segment most vulnerable to ischaemic and toxic acute tubular necrosis.
Kidney tubule histology
- PCT: brush border, mitochondria, pink
- Thin limb: squamous
- DCT: paler, no brush border, clear lumen
- Macula densa: DCT next to glomerulus
- PCT most vulnerable to ATN
Remember Brush border = busy proximal tubule.
Why the other options are wrong
- Flat squamous cells Thin limb of loop of Henle.
- Ciliated tall columnar cells Not in tubules.
- Transitional epithelium Pelvis and ureter.
- No microvilli, clear lumen Distal tubule features.
After removal of a parathyroid adenoma in a woman with renal stones and hypercalcaemia, which cells are identified as the main source of parathyroid hormone?
Answer: Parathyroid chief cells
The parathyroid glands contain chief cells, which are small, numerous and secrete parathyroid hormone, and larger oxyphil cells with eosinophilic, mitochondria-rich cytoplasm whose function is uncertain. Fat cells increase with age. Most parathyroid adenomas are composed mainly of chief cells. C cells in the thyroid secrete calcitonin, which lowers calcium.
Parathyroid
- Chief cells secrete PTH
- Oxyphil cells: pink, many mitochondria
- Fat increases with age
- Adenomas: mostly chief cells
Remember Chief cells are in charge of calcium.
Exam trap Do not confuse parathyroid chief cells with gastric chief cells, which secrete pepsinogen.
Why the other options are wrong
- Oxyphil cells Increase with age; not the main hormone source.
- Parafollicular C cells Thyroid cells that secrete calcitonin.
- Follicular cells Thyroid cells that make T4 and T3.
- Chromaffin cells Adrenal medulla cells that make catecholamines.
A specimen from an orchidectomy contains a highly coiled tube in cross-section, lined by tall pseudostratified columnar cells with long stereocilia, surrounded by a thin layer of smooth muscle, with sperm in the lumen. Which structure is this?
Answer: Epididymis
The epididymis is a single, highly coiled duct, so a section shows many profiles of the same tube. It is lined by tall pseudostratified columnar epithelium with stereocilia, which absorb fluid and help concentrate sperm, and it has a thin circular smooth muscle coat. The vas deferens has the same lining but a very thick three-layered muscular wall and a star-shaped lumen. Seminiferous tubules contain germ cells and Sertoli cells.
Epididymis
- Coiled duct: many profiles
- Pseudostratified with stereocilia
- Thin smooth muscle
- Sperm mature and store here
Remember Thin muscle: epididymis; thick muscle: vas.
Exam trap Stereocilia are absorptive microvilli; they do not propel sperm.
Why the other options are wrong
- Vas deferens Has a much thicker three-layered muscle wall.
- Seminiferous tubule Lined by germ cells and Sertoli cells, not stereocilia.
- Rete testis Lined by low cuboidal epithelium.
- Prostatic urethra Lined by urothelium.
A 30-year-old woman with Hashimoto thyroiditis develops well-defined, milk-white patches on her hands and around her mouth. A skin biopsy of a patch is taken. Which of the following findings is expected?
Answer: Absent melanocytes in the basal layer
Melanocytes sit in the basal layer of the epidermis and pass melanin to surrounding keratinocytes. In vitiligo, an autoimmune attack, mainly by cytotoxic T cells, destroys the melanocytes, so the patches have no pigment cells at all. Vitiligo is linked with other autoimmune diseases such as Hashimoto thyroiditis, type 1 diabetes and pernicious anaemia. In albinism the melanocytes are present in normal numbers but cannot make melanin.
Vitiligo
- Melanocytes in basal layer
- Autoimmune T-cell destruction
- Patches have no melanocytes
- Linked to thyroid autoimmunity
Remember Vitiligo: cells gone; albinism: cells there, no pigment.
Exam trap Pale patches with fine scale on the trunk are more likely pityriasis versicolor than vitiligo.
Why the other options are wrong
- Melanocytes present but lacking tyrosinase That is oculocutaneous albinism, which is generalised from birth.
- Melanin trapped in dermal macrophages Dermal melanin in macrophages is post-inflammatory pigmentation.
- Fungal hyphae in the stratum corneum That is pityriasis versicolor, which gives scaly hypopigmented patches.
- Loss of Langerhans cells in the spinous layer Langerhans cells are antigen-presenting cells; they do not make pigment.
Where this sits in the CPSP syllabus
- Paper 1: General and special histology, Kidney, urinary and reproductive histology; skin and endocrine glands
- Surgery & Allied, Paper 2: Histology for surgery, Kidney, urinary and reproductive histology; skin and endocrine glands
- Medicine & Allied, Paper 2: Histology: liver, pancreas, spleen, kidney, brain, gut, Kidney, urinary and reproductive histology; skin and endocrine glands
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