  The Body Fluids and Kidneys Lecture 16 KEEP OFF YOUR MOBILE PHONES kidney.lecture 5b 17 February 2019 KEEP OFF YOUR MOBILE PHONES The Body Fluids and Kidneys Lecture 16   dr.rashid mahmood

Water Reabsorption Passive / Osmosis Mainly coupled to Sodium Reabsorption Water channels made up of proteins called: AQUAPORINS Paracellular + Transcellular

Water Reabsorption contd…….. Proximal Tubule High Permeability Solvent Drag Distal Tubule ↓ Permeability i. Tighter junctions ii. ↓ Surface Area Ascending Loop of Henle Almost Zero Permeability More Distal Parts ADH

Reabsorption of Urea & Chloride

Proximal Tubule

Reabsorption in First half of Proximal tubule Active Transport: 1. Primary Active Transport Sodium( Sodium-Potassium ATPase) 2. Secondary Active Transport (Co-Transport) Glucose, Amino Acids, Organic Acids Passive Transport: Water, Urea? Chloride ?

Reabsorption in Second half of Proximal tubule Active Transport: 1. Primary Active Transport Sodium( Sodium-Potassium ATPase) 2. Secondary Active Transport (Co-Transport) Chloride Passive Transport: Water, Glucose, Amino Acids ? Urea reabsorption and secretion

Secretion in Proximal tubule Counter Transport H+ Organic Acids + Bases e.g. Bile Salts Oxalate Urate Catecholamines Drugs Toxins PAH (Para-Amino- Hippuric Acid)

Reabsorption of various solutes in proximal tubule

Reabsorption in Loop of Henle 20% Urea reabsorbed Back in Thin Ascending Limb

Reabsorption in Loop of Henle Thin descending segment Structure Thin epithelial membrane No brush border Few mitochondria Function Highly Permeable to water Almost all water absorbed in Loop of Henle is absorbed here →↑osmolarity Moderately permeable to most solutes, including Sodium and Urea No active transport

Reabsorption in Loop of Henle Thin ascending segment Structure (Same as descending limb) Thin epithelial membrane No brush border Few mitochondria Function Impermeable to water Permeable to NaCl No active transport Urea is reabsorbed back Juxta -medullary nephrons

Reabsorption in Loop of Henle Thick ascending segment Structure Thick epithelial cells Function Na+-K+ ATPase in basolateral membrane i) Active reabsorption of Na+, K+, Cl- (about 20-25% of filtered load) (Secondary active transport) (1-Sodium, 2-chloride, 1-Potassium co-transporter) ii) Reabsorption of Ca++, HCO3--, Mg++ 2. Paracellular reabsorption of Ca++, K+, Mg++, Na+ 3. Na+ -H+ Counter-transport 4. Impermeable to water →↓osmolarity (dilute tubular fluid) Loop diuretics

Reabsorption in Loop of Henle 20% Water Reabsorbed in Loop of Henle 25% Sodium Reabsorbed in Loop of Henle some Passive Reabsorption of Urea No Water Reabsorption in Ascending Limb No Active Transport in Thin Limb

Transport in Thick Ascending Loop of Henle

NaCl transport in thick ascending limb of loop of Henle

Reabsorption in Distal Convoluted Tubule Juxta Glomerular Apparatus Early Distal Tubule Almost same as Thick Ascending Loop of Henle (5% sodium reabsorption in early DCT) Diluting Segment

Reabsorption in Distal Convoluted Tubule water Aldosterone Aldosterone H+ ATPase

Mechanism of Na+ Reabsorption in Distal Convoluted Tubule Early Late K+ sparing diuretics

Reabsorption in Second Half of Distal Convoluted Tubule Water Reabsorbed from both cells in the presence of ADH (Anti-Diuretic Hormone) Impermeable to urea Na+ reabsorption and K+ secretion under influence of Aldosterone Active secretion of H+

Cortical Collecting Tubule Same as second Half of Distal Collecting Tubule

Medullary Collecting Duct

Tubular processing in Medullary Collecting Duct Structure Cuboid Smooth surface Few mitochondria Function Reabsorption of 10% of water and sodium Final site of processing of urine ADH Permeable to urea H+ secretion

Summary Contd…

Summary (ADH present)