Renal System L33 PDF

L33- RENAL SYSTEM Dr.Pugazhandhi Bakthavatchalam Assistant Professor of Anatomy and Physiology, AUACAS, American University of Antigua  LEARNING OUTCOMES 2 At the end of this session the student would be able to:  Functions of renal tubules, reabsorption, secretion, concentra...

L33- RENAL SYSTEM Dr.Pugazhandhi Bakthavatchalam Assistant Professor of Anatomy and Physiology, AUACAS, American University of Antigua  LEARNING OUTCOMES 2 At the end of this session the student would be able to:  Functions of renal tubules, reabsorption, secretion, concentration, acidification.  Mechanism of reabsorption, substances reabsorbed across the PCT, descending and ascending, collecting ducts. 24-Oct-24 Juxtamedullary nephrons vs Cortical nephrons Urine Formation Preview Mechanisms of tubular transport:  Active transport: i. Primary active transport: e.g. Na-K-pump, H+-pump ii. Secondary active transport : e.g. Na-K-2Cl co-transport, glucose-sodium co-transport, amino acid-sodium co-transport.  Passive transport: i. Simple diffusion e.g. Cl, HCO3-, urea. ii. Facilitated diffusion glucose at the basal border.  Osmosis.  Thus the molecules moves through ion channels, transporters, pumps & exchangers.  Pinocytosis/ exocytosis.  Primary Active transport Carrier, direct source of Energy ATP, against electrochemical gradient High Examples: conc  Sodium potassium ATPase,  Hydrogen ATPase,  Hydrogen potassium ATPase, and  Calcium ATPase. Na transport through PCT  Secondary active transport  The secondary active transport does not require energy directly from ATP.  The direct source of the energy is that liberated by the simultaneous facilitated diffusion of another transported substance down its own electrochemical gradient.  The electrochemical gradient for Na is maintained by Na/K pump..  Osmosis  Transport of solutes out of the tubules by either primary or secondary active transport, makes their concentration inside the cells to decrease while increase in the renal interstitium. This creates a concentration difference that causes osmosis of water in the same direction that the solutes are transported, from the tubular lumen to the renal interstitium.  Water reabsorption is mainly coupled to sodium.  Permeability differs through the nephron.  Route: Paracellular via tight junctions  Effect of ADH (Distal & collecting tubules).  Renal tubular reabsorption through PCT  Solute reaborption in the proximal tubule is isosmotic (water follows solute somatically and tubular fluid osmolality remains similar to that of plasma= equal amount of solute and water are reabsorbed).  65%-70% of water and sodium reabsorption occurs in the proximal tubule  90% of bicarbonate, calcium, K+  100% of glucose & amino acids.  Secretion: organic acids and bases such as bile salts, oxalate, urate, and catecholamines, certain drugs, such as penicillin and salicylates,  Proximal tubules: coarse adjustment.  Distal tubules: fine adjustment (hormonal control).  Loop of Henle 11  Responsible for producing a concentrated urine by forming a concentration gradient within the medulla of kidney.  When ADH is present, water is reabsorbed and urine is concentrated.  Counter-current multiplier. Absorption through loop of Henle:  Descending limb: is water permeable and allow absorption of 25% of filtered H2O. It is impermeable to Na-CL.  Thin ascending limb: is impermeable to H2O, but permeable to Na-Cl, where they are absorbed passively in this part.  Thick ascending limb: is impermeable to H2O. Na-K-2Cl co-transport occur in this part. By the end of ascending limb of loop, the tubular fluid becomes hypo-osmolar to plasma.  Distal convoluted tubule and collecting ducts 14  What happens here depends on hormonal control:  Aldosterone affects Na+ and K+  ADH – facultative water reabsorption  Parathyroid hormone – increases Ca++ reabsorption.  Fine adjustment of tubular filtrate takes place here according to body needs.  The first portion of DCT forms part of JGA, that provides feedback control of GFR and RBF of the same nephron.  The next early portion has the same characteristics as ascending limb of Henle that is impermeable to water but absorbs solutes. So it is called the diluting segment & the osmotic pressure of the fluid ~ 100 mOsm/L. Late distal tubule& collecting tubules  Have similar functional characteristics.  Composed of two types of cells:  a. Principal cells: absorb Na+& H2O and secrete K+  b. Intercalated cells: absorb K+ & secrete H+  Impermeable to Urea.  water permeability under ADH  Secretion of K+ and reabsorption of Na+ controlled by aldosterone. Cell types of the nephron Medullary collecting ducts  Reabsorb