Renal Physiology PDF

RENAL PHYSIOLOGY Kidney Clean Blood UREA Shabby Blood  Renal Physiology Outline The Kidneys – Anatomy of the urinary system and overview of renal processes – Filtration GFR Regulation Calculate glom...

RENAL PHYSIOLOGY Kidney Clean Blood UREA Shabby Blood  Renal Physiology Outline The Kidneys – Anatomy of the urinary system and overview of renal processes – Filtration GFR Regulation Calculate glomerular filtration rate Calculate renal blood flow – Absorption, secretion, and excretion Calculate renal threshold for a substance Fluid and Electrolyte Balance – Urine Concentration – Water, sodium, potassium balance Learning Objectives  The Urinary System Excretes – metabolic end products – drugs, and many other exogenous compounds (xenobiotics). Regulates – many essential substances: (Na+, K+, H+, Ca++, Mg++, Cl-, HCO3-, HPO4-2, H2O) – Osmolarity – pH – arterial blood pressure Secretes – Secrete Renin, erythropoietin, and actives Vitamin D. Figure 19-1a  Anatomy: The Kidney Cortex: Outer area – Outer cortical region – Inner juxtamedullary region Medulla: Inner area – Renal pyramids Calyces: – Minor: Papillae extend – Major: Converge to form pelvis Figure 19-1c  Anatomy: Nephron Functional Unit of the Kidney Two types: Cortical (85%) – Re-absorption – Peritubular capillaries Juxtamedullary – Concentrate urine – Vasa recta and peritubular capillaries A nephron = Corpuscle + A renal tubule of 50 mm in length Bowman’s capsule Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct  Overview of Renal Processes Urinary excretion of a substance depends on its filtration, reabsorption, and secretion Peritubular capillaries Distal tubule Efferent arteriole Glomerulus Afferent arteriole Proximal Bowman’s tubule capsule Collecting = Filtration: blood to lumen Loop duct = Reabsorption: lumen to blood of To renal Henle vein = Secretion: blood to lumen To bladder and external environment For all substances: Excretion = Filtration – Reabsorption + Secretion Renal Processes: Filtration Glomerular Filtration Rate (GFR): Amount of plasma filtered from the glomeruli into Bowman’s space per unit time In the average adult human, the glomerular filtration rate (GFR) is 125 Your entire ml/min, or 180 L/day. plasma can be filtered ~60 times/day  Renal Processes: Filtration Renal Corpuscle = Glomerulus + Bowman’s capsule Glomerulus: capillary network Bowman’s capsule: Beginning of tubule – Parietal & visceral epithelium  Renal Processes: Filtration Filtration Barrier Fenestrated capillary epithelium Basement membrane (also called basal lamina) Pores formed by Podocytes Resulting filtrate = protein-free dialysate of plasma  Factors that Affect GFR Forces favoring filtration – PH - glomerular capillary hydrostatic pressure PH Primary mechanism for Forces opposing Primary physiological mechanism regulation of GFR filtration – Pfluid - Bowman’s hydrostatic pressure – π - colloid osmotic force Net glomerular filtration pressure = PH - PBS – π GFR = Kf x (PH - PBS – π) (Kf: Filtration coefficient ml/min/mmHg) Glomerular Capillary Hydrostatic Pressure (PH) Primary mechanism for physiological regulation of GFR – increase in glomerular hydrostatic pressure, causing an increase in GFR. 3 variables influencing PH: 1. Arterial pressure; however, this is buffered by autoregulation (more later). 2. Afferent arteriolar resistance. 3. Efferent arteriolar resistance.  Variables influencing PH 1. Arterial pressure; buffered by autoregulation 2. Afferent arteriolar resistance 3. Efferent arteriolar resistance Q: What happens to capillary blood pressure, GFR, and Renal Blood Flow when the afferent arteriole dilates? Figure 19-8a  Autoregulation of GFR Achieved over a wide range of blood pressures How is this accomplished? Myogenic response (blood vessel itself) Tubuloglomerular feedback (Juxtaglomerular apparatus) Hormones and autonomic neurons Figure 19-7  Autoregulation of GFR Myogenic response – Similar to autoregulation in other systemic arterioles – ↑ renal BP  constriction of afferent arteriole (and vice versa) Tubuloglomerular feedback – Paracrine control – ↑ GFR (increased NaCl sensed by macula densa)  constriction of afferent arteriole Hormones and autonomic neurons Eg., Renin-angiotensin system  Juxtaglomerular Apparatus - A feedback mechanism Macula densa cells Osmoreceptors (modified epithelial cells) in distal tubule Granular cells (aka. Juxtaglomerular cell) Modified smooth muscle of afferent arteriole Secrete Renin Mesangial cells Contractile->regulate glomerular filtration  Tubuloglomerular Feedback Glomerulus Distal tubule 1 GFR increases. Efferent arteriole 2 Flow through tubule increases. Bowman’s capsule 3 Flow past macula densa increases. 4 Macula densa 1 5 Granular cells 4 Paracrine from macula Afferent arteriole densa to afferent arteriole 2 3 Proximal 5 Afferent arteriole constricts. tubule Resistance in afferent arteriole increases. Collecting duct Hydrostatic pressure in glomerulus decreases. Loop of GFR decreases. Henle Figure 19-10, steps 1–5 (4 of 4)  Question Adenosine causes vasoconstriction and NO causes vasodilation. When GFR increases, Macula densa will release which paracrine as part of the TGF response: A. Adenosine B. NO  Autoregulation of GFR Myogenic response – Similar to autoregulation in other systemic arterioles – ↑ renal BP  constriction of afferent arteriole (and vice versa) Tubuloglomerular feedback – Paracrine control – ↑ GFR (increased NaCl sensed by macula densa)  constriction of afferent arteriole Hormones and autonomic neurons Eg., Renin-angiotensin system  Renin-angiotensin mechanisms Renin released when – blood pressure drops – sympathetic innervation – osmolarity of the tubular fluid is too low (through macula densa) Angiotensin II restore blood pressure – Arterioles vasoconstrict – Aldosterone secretion – CNS (thirst and ADH release)