Histology of the kidney Ákos Lukást MD., Ph.D (lukats.akos@med.semmelweis-univ.hu)

Renal lobes (10-18) Medulla: pyramid (papilla), medullary rays Cortex: cortical labyrinths, columns of Bertini (renal columns)

Functional unit: nephron Cca. 1.000.000 per kidney

Parts of the nephron: Renal corpuscules (filtration): -Bowman’s capsules -Glomeruli 2. Tubules renales (modification): -Proximal convoluted and straight tubules -Loop of Henle -Distal convoluted and straight tubule Collecting duct

Histological vs. Physiological descriptions Alternative names -Proximal convoluted - proximal tubule - Proximal straight – thick descending limb of loop of Henle -Loop of Henle – thin ascending and descending limb -Distal straight – thick ascending limb of loop of Henle Distal convoluted – distal tubule Histological vs. Physiological descriptions

- Subcapsular - Cortical - Juxtamedullary Medullary rays

cortex medulla lobule Medullary rays: Proximal and distal straight tubules, Collecting ducts cortex Cortical labyrinths: Renal corpuscules, Proximal and distal convoluted tubules medulla

cortex medulla lobule Arcuate artery and vein Interlobular artery and vein

1. Arteria interlobularis 2. Arteriola afferens 3. Glomerulus 4. Arteriola efferens

Peritubular capillaries Vasa recta (countercurrent exchange – to maintain the osmotic gradient)

Vasa recta

Bowman’s capsule: Parietal layer: simple squamous epithelum Visceral layer: podocytes Glomerulus: capillaries Vascular pole: - Vas afferens (inflow) - Vas efferens (outflow) Urinary pole Cca. 180 liters of filtrate produced each day 99% is reabsorbed!

Podocytes Primary (P1) and secondary (P2) interdigitating processes Endothelial cells also fenestrated – true filtration barrier is the basal membrane

Pressure gradient due to the smaller diameter of the efferent arteriole (filtration pressure) Generally: Small molecules whose diameter is smaller than 40 000 (max 70 000) Daltons (E.g. water, sugar, ions, amino acids, ammonia, urea, etc) filtrated into Bowman’s capsule. Filtration is also dependent on charge (basal membrane has a – charge!)

350 nm töltés barrier fizikalis filter töltés-barrier podokalixin lamina densa lamina rara 350 nm töltés barrier fizikalis filter töltés-barrier podokalixin

The juxtaglomerular apparatus 1. Macula densa (Distal convoluted tubule, modified epithelium to detect sodium levels in DCT - chemoreceptor) 2. juxtaglomerular cells in afferent arteriole (renin secretion) Extraglomerular mesangial cells Function: tubuloglomerular feedback regulation of perfusion of the kidneys regulation of blood pressure

JUXTAGLOMERULAR APPARATUS ACE inhibitors!

Proximal and distal tubules

Proximal and distal tubules EMI

Cortex Outer medulla

P P D P D P

Loop of Henle, collecting ducts

LH D CD LH D CD

dp CM area cribrosa

Outer medulla: Proximal str. Distal str. Collecting duct capillaries Middle medulla: Distal str. Collecting duct Loop of Henle capillaries Inner medulla: Collecting duct Loop of Henle capillaries