Urinary System - Elsalanty.pdf

Introduction to Urinary System  Objectives 1. List the different components of the nephron and the main function(s) of each 2. Describe the structure of the glomerulus 3. Define glomerular filtration, renal reabsorption, and renal secretion 4. Describe the juxtaglomeru...

Introduction to Urinary System  Objectives 1. List the different components of the nephron and the main function(s) of each 2. Describe the structure of the glomerulus 3. Define glomerular filtration, renal reabsorption, and renal secretion 4. Describe the juxtaglomerular apparatus and its main function 5. Define the significance of the glomerular basement membrane its epithelial and endothelial sides Posterior View Afferent arteriole → Glomerular Capillaries → Initial filtration into the urinary space (Bowman’s capsule)  Glomerular Filtration The first step in urine formation Passive diffusion of ions and molecules and water from the glomerular capillaries to the bowman’s urine capsule 125 mL/min  Glomerulus and Bowman’s Capsule Glomerular filtration goes through the wall of the glomerular capillary, basement membrane and the visceral layer of Bowman’s capsule Stevens & Lowe, Human Histology, 2nd edition, Glomerular Basement Membrane Important barrier between blood and urine. Location of glomerular filtration.  Glomerular Basement Membrane Urine Physical and electric barrier Particles > 10 nm and negatively charge ptns > 69 BLOOD kDa cannot cross  GFR Control Diameter of Afferent and Efferent arterioles Diameter of glomerular capillaries Mesangial cells: – In between glomerular capillaries – Contractile (control capillary size) – Angiotensin II (Contract → Vasoconstriction → - GFR) – ANP receptors (Relax → Vasodilation → +GFR) After Filtration Initial urine (Bowman’s capsule) has too much water, as well as valuable molecules, such as glucose, amino acids, electrolytes, etc Some harmful molecules could not be filtered through the glomerulus Therefore, the filtered urine needs to be adjusted after filtration This adjustment takes place between the tubules (urine) and peritubular capillaries (blood)  The Nephron is the structural and functional unit of the kidney Exchange happens between two fluid circuits: Blood and Urine  The walls of the renal tubules adjust the urine content: Reabsorption: important molecules are returned to “peritubular” Filtration of the plasma by glomerular capillaries → capillaries initial urine Secretion: molecules initially missed get pushed from peritubular capillaries into the urine  Blood: Abdominal Aorta → Renal Artery →→ Afferent Arterioles → Glomerulus → Efferent Arterioles → Peritubular Capillaries →→ Renal Vein → IVC Urine: Bowman’s capsule → PCT → Loop of Henle → DCT → Collecting tubules & ducts → Calyx  Tubular Reabsorption Active/passive process of returning solutes and water back from the nephron (PCT, DCT, LH, or CT) into the blood (Peritubular capillaries) Most of reabsorption is automated (cannot be controlled externally), occurring in the PCT Some reabsorption in the DCT and collecting duct can be controlled (e.g. by aldosterone, a circulating hormone)  Tubular Secretion Active/passive process of pushing material from the peritubular capillaries into the nephron (PCT, DCT, LH, or CT) Proximal Convoluted Tubule Reabsorbs all the glucose, amino acids, small proteins & 80% of the sodium chloride & water Exchanges the hydrogen ions from the interstitium for bicarbonate ions from the filtrate (Hydrogen goes into the urine, bicarb stays in the body) Secretion of organic wastes such as creatinine and urea Automatic (cannot be controlled), Numerous ATPase pumps for active transport Added function: activation of vitamin D  Urine amount and composition are adjusted, based on the body’s specific needs: Preserve or remove water In the next segments Control the amount of salt in the Salt (Na, K, Cl, Ca) blood (which determines blood of the osmolarity → volume → blood pressure) Water Hydrogen nephron Finalize hydrogen (acid) content → pH Get rid of any remaining ammonia or other toxins Distal Convoluted Tubules (DCT) Similar in structure to PCT Aldosterone → sodium reabsorption → Diluted urine When adjustments ADH (water preserving hormone), need to still be made H2O follows Na+ → Scanty, more concentrated urine Secretion of potassium, ammonium & hydrogen ions into the filtrate Contributes to blood pressure control  The Juxtaglomerular Apparatus How the kidney controls blood pressure Macula Densa Cells Wall of distal convoluted tubule Monitor osmolarity & fluid volume in DCT Juxtaglomerular Cells Primarily in wall of the afferent arteriole Synthesize renin This system is a major regulator of blood pressure through the Angiotensin / aldosterone pathway Collecting Ducts ADH → reabsorb more H2O → further concentration of urine The Way Out Renal Calyx (minor → major) Renal Pelvis Ureters Urinary Bladder Urethra Summary of the Nephron Glomerulus: Initial filtration PCT: Automatic reabsorption and secretion Loop of Henle: Adjusting osmolarity DCT: Adjustable reabsorption Collecting Ducts: Adjustable reabsorption Functions of the Kidney A - controlling ACID-base balance. W - controlling WATER balance. E - maintaining ELECTROLYTE balance. T - removing TOXINS and waste products from the body. B - controlling BLOOD PRESSURE. E - producing the hormone ERYTHROPOIETIN D - activating vitamin D