Histology of the urinary tract Dr Stuart Brown
Histology of the urinary tract Dr Stuart Brown Histopathologist stuart. brown@sth. nhs. uk
Outline Kidneys Ureters Bladder Urethra
Kidney - surface anatomy Retroperitoneal Between T 12 and L 3 Right lower than left
Kidney - gross anatomy Three distinct structures Cortex Medulla Pelvis
A quick look at the different areas in the kidney
Cortex
Medullary Ray
Medullary Rays
Medulla
Pelvis
The kidney’s blood supply Abdominal aorta Renal artery at L 1 Anterior & posterior division Interlobar artery Arcuate artery (corticomedullary) Interlobular artery Afferent arteriole
Renal microvasculature
A lobulated kidney
A brief history of the kidney Pre 550 M 2 germ layers Cell surface transport No vascular system
Mesoderm and the Cambrian explosion 550 M 3 germ layers Mesoderm
Protonephridia in basal Chordates Salty marine environment Blood hypo-osmotic to environment Body gains salt and loses water by osmosis Aglomerular pronephridium excretes nitrogen without the loss of excess water
Freshwater, ammonia and the glomerulus Freshwater environment Blood hyperosmotic to environment Body gains water and loses salt by osmosis Glomeruli cause loss of greater volumes of fluid and help flush out ammonia
Land the loop of Henle 150 M - Land based life Limited access to water Need to conserve water Loop of Henle Concentrates urine
The kidney show us a map of our evolutionary heritage
Renal structure – the nephron There are millions of nephrons in the cortex and medulla Cortex Prox / Dist. convoluted tubules Renal corpuscles Medulla Loop of Henle Collecting ducts Pelvis Receives the collecting ducts
The nephron in gross anatomy
The nephron - the basic unit of the kidney Renal Corpuscle Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct
Renal corpuscle A filter Tuft of convoluted capillaries with fenestrated walls Glomerular basement membrane Lined by podocytes Supported by mesangial cells Encased in Bowman’s capsule
Glomerulus
Glomerulus
Glomerular filter
Glomerular basement membrane
Podocytes
Review of ultrafiltration Form of barrier Mechanical barrier Repulsive negative charge Capillary fenestration + GBM + + Podocyte slit membrane + +
Juxtaglomerular apparatus 2 Components: 1. Afferent arteriole 2. Distal convoluted tubule 1. Afferent arteriole Contributes Granular cells Secrete renin in response to: Systemic blood pressure
Juxtaglomerular apparatus 2. Distal convoluted tubule Contributes the Macula Densa Patch of closely packed endothelial cells along tubule Senses Na. Cl concentration and regulates tubuloglomerular feedback
JGA
Proximal convoluted tubule Cuboidal epithelium Round central/basal nuclei Brush border of microvilli at apical end Many mitochondria so appears eosinophilic Reabsorption of Na. Cl, proteins, polypeptides, amino acids, glucose
Proximal convoluted tubule EM Lysosomes in the PCT are involved in degradation of small protein molecules reabsorbed from the urinary space
Loop of Henle Descending and ascending limbs Both with thick and thin segments Thin – simple squamous Thick – low cuboidal Supplied by a rich vasa recta
Tamm-Horsfall Protein Produced in the thick ascending tubule Low levels in urine associated with calculi Mutations associated with renal failure Absence associated with severe infection
Loop of Henle and vasa recta Afferent arteriole (from renal corpuscle) Peritubular capillaries Descends into medulla Vasa recta Renal veins Inferior Vena Cava
Distal convoluted tubule Low cuboidal epithelium Scanty microvilli Numerous mitochondria Regulates acid base by Secreting H+ and absorbing HCO 3 - (via cellular carbonic anhydrase) Regulates Na level by exchanging Na for K
Collecting duct Cuboidal epithelium Principal cells Respond to aldosterone Reabsorbing Na Secreting K Also respond to ADH Inserting Aquaporin 2 Intercalated cells Exchange H+ for HCO 3 -
Collecting Duct
Aquaporin 2
Renal pelvis Transitional epithelium (urothelium) Transmits filtrate from nephron to ureter
Urothelium AKA Transitional epithelium About 5 cells thick Changes shape and stretches
Urothelium Surface layer – large dome-shaped umbrella cells Intermediate layer - note nuclear orientation Basal layer – cuboidal cells
Urothelium The umbrella cells are large and cover several underlying intermediate cells. They have tight junctions at their surface
Tight Junctions - Zonula Occludens Prevent liquid movement around cells Composed of Claudins And Occludins Anchored to Actin in the cytoskeleton
Ureters Transitional epithelium Spiral muscular tube Inner “longitudinal” Outer “circular” (different to GI arrangement) No serosa Loose adventitia
Bladder Transitional epithelium Lamina propria Muscularis Mucosa Submucosa Muscularis Propria Subserosa and Serosa Functional valve prevents reflux into ureter
Urethra Different anatomy in males and females Two sphincters Internal sphincter composed of smooth muscle from the bladder External sphincter composed of skeletal muscle from the pelvic floor
Urethra - female 4 -5 cm long Proximally transitional epithelium Distally squamous epithelium Paraurethral and periurethral glands open into the urethra
Urethra - male 20 cm long 3 parts 1. Prostatic urethra 2. Membranous urethra Transitional epithelium 3. Penile urethra Pseudostratified epithelium proximally Stratified squamous epithelium distally
Summary The kidney has a complicated histology reflecting its complicated function and our evolutionary history The renal pelvis, ureter, bladder and urethra all have the same transitional epithelium Transitional epithelium is unique to the urinary tract
Quiz time!
Q 1. A 5 year old child has nephrotic syndrome. A renal biopsy shows normal glomeruli. Electron microscopy shows this following appearance: What is the abnormality here?
Q 2. An adult has nephrotic syndrome. A renal biopsy shows the following appearance. What is the abnormality here?
Q 2. A silver stain of the tissue demonstrates the following: What is the diagnosis?
Q 3. Another adult has nephrotic syndrome. A renal biopsy shows the following appearance. What is the abnormality here?
Q 3. A silver stain of the tissue demonstrates the following: What is the diagnosis?
Q 4. Another adult is coughing up blood and has blood in their urine. They have antibodies to the glomerular basement membrane. This is their kidney biopsy: What is the diagnosis?
Do you have any questions?
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