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LSS Urinary System

Alexandra Burke-Smith

Loop of Henle  

The loop can be divided into the descending and ascending limb The descending limb is thinner, and highly permeable to water (which is passively reabsorbed between the squamous epithelium) o There are few mitochondria in the descending limb as ions are not actively transported The ascending limb is thicker and more involved in ion transport, therefore contains many more mitochondria. o Consists of a cuboidal epithelium with few microvilli, but is impermeable to water o Again, the Na/K pump on the basal membrane creates a concentration + electrical gradient, which drives the symporter on the apical membrane. This symporter transports 1 Na, 1 K and 2 Cl ions into the cell (making the inside of the cell negative compared to the outside) o However, there is also a K+ channel on the apical membrane which allows K+ to leak into the lumen along its concentration gradient. However this exaggerates the electrical gradient thus driving paracellular movement of the cations Na, K, Ca + Mg o Loop diuretics block the Na/K/Cl co-transporter On leaving the loop, 85% water + 90% of Na and K have been reabsorbed. However the fact that the ascending limb is impermeable to water means the tubular fluid is also hypo-osmolar compared to the plasma

Distal convoluted tubule (proximal end) 

   

Consists of a cuboidal epithelium with few mitochondria, complex basolateral membrane interdigitations with Na/K pumps + numerous mitochondria Na+ dependent uptake of Cl occurs (by co-transporter) Ca2+ entry into cell – from tubular fluid driven by electrochemical gradient + from plasma (by Na+/Ca antiporter) Thiazides = diuretics which target the Ca2+ channels  knock on effect on plasma calcium There is also a specialisation of the DCT where it meets the glomerulus = macula densa (forms part of juxtaglomerular apparatus) – detects changes in the [Na] of the tubular fluid filtrate

The Distal DCT + Cortical Collecting duct    

“fine” tuning of the filtrate in order to maintain homeostasis (plasma osmolarity, pH etc) occurs here Regulation is under hormonal control (aldosterone + ADH/Vasopressin) Consist of two types of cells: principle cells + intercalated cells The principle cells of the DCT are under the control of aldosterone, whereas the principle cells of the cortical collecting duct are under the control of ADH/Vasopressin


Alex's Urinary  

Alex's Urinary