Lecture 19 PDF - Kidney Function

About This Chapter 19.1 Functions of the Kidneys 19.2 Anatomy of the Urinary System 19.3 Overview of Kidney Function 19.4 Filtration Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 19.1 Functions of the Kidneys When ECF volume decreases, blood pressure too 1. Regu...

About This Chapter 19.1 Functions of the Kidneys 19.2 Anatomy of the Urinary System 19.3 Overview of Kidney Function 19.4 Filtration Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 19.1 Functions of the Kidneys When ECF volume decreases, blood pressure too 1. Regulation of extracellular fluid volume and blood pressure 2. Regulation of osmolarity to maintain it to 290 mOsM balancing dietary intake with urinary loss is the major ion involved in regulation of ECF volume and osmolarity 3. Maintenance of ion balance Sodium Potassium and calcium concentration closely regulated too If ECF too acidic, kidneys remove H+ and converse HCO3- (buffer) 4. Homeostatic regulation of pH If too alkaline, opposite 5. Excretion of wastes like creatinine, urea, urobilinogen (yellow color), saccharin, benzoate cytokine regulating RBC synthesis 6. Production of hormones Erythropoietine: Renin: regulates production of hormones involved in sodium balance and blood pressure homeostasis Renal enzymes: conversion of vitamin D3 into a hormone that regulates CA2+ balance Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.1(a-b) Anatomy summary (a) Urinary system, (b) Structure of the Kidney Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.1(c-d) Anatomy summary Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.1(e-f,h) Anatomy summary Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.1(g-h) Anatomy summary Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 19.2 Overview of Kidney function • Kidneys filter, reabsorb, and secrete • Filtration – Fluid from blood into the lumen of the nephron – Occurs at renal corpuscle – Filtered plasma is called filtrate – excreted unless reabsorbed • Reabsorption – Materials in the filtrate are passed back into the blood – Occurs with peritubular capillaries • Secretion – Material from blood into lumen of tubule selective process that usually uses membrane proteins – Occurs with peritubular capillaries more to move molecules across the tubule epithelium Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Nephron Modifies Fluid Volume and Osmolarity • Filtrate is almost identical plasma at the renal corpuscle – • About 70% of filtrate is reabsorbed by the proximal tubules – – • More solute is reabsorbed than water, diluted 18 L/day remains, 100 mOsm Distal tubule and collecting duct – – • Solutes and water 54 L/day remains, 300 mOsm Filtrate in the loop of Henle – – • 180 L/day, 300 mOsm Some reabsorption and secretion 1.5 L/day remains, 100 – 1200 mOsm depending on hydration state Amount excreted = amount filtered – amount reabsorbed + amount secreted Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.2 Nephron Function (1 of 2) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.2 Nephron Function (2 of 2) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.3 Solute movement through the nephron Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 19.4 Filtration • Filtration fraction – % renal flow that filters into the tubule • The renal corpuscle contains filtration barriers • Filtration occurs in the renal corpuscle – Glomerular capillary endothelium pores that allow most components of plasma to filter through ▪ Fenestrated capillaries large endothelium ▪ Glycocalyx lattice-like layer of glycoproteins lining luminal surface of capillary and pores acellular layer of extracellular matrix that separates capillary endothelium from of Bowman’s capsule – Basement membrane epithelium negatively charged glycoproteins, collagen, and other proteins —> exclude most plasma proteins from fluid that filters through it – Epithelium of Bowman’s capsule ▪ Podocytes specialized cells that surround each glomerular capillary foot processes wrap around glomerural capillaries and long cytoplasmic with one another, leaving narrow filtration slits extensions that – Foot processes and filtration slits interlace closed by a slit diaphragm extend from the main body cell lie between and around glomerular capillaries, creating a support structure for tuft of capillaries, filtration by altering surface area of filtration slits + secrete cytokines associated with ▪ Mesangial cellsinfluence immune and inflammatory processes Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.4 The filtration fraction Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.5(a-b) The renal corpuscle Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.5(c-d) The renal corpuscle Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Capillary Pressure Causes Filtration (1 of 2) • Three pressures influence glomerular filtration 1. Capillary blood pressure (PH) ▪ Hydrostatic pressure ( ~ 55 mm Hg) forces fluid through leaky endothelium capillary blood pressure = 55 mm Hg and favours filtration Bowman’s capsule ▪ Favors filtration into Pressure decreases as blood moves through capillaries, it remains higher than opposing pressures glomerular capillaries higher than that of the fluid in 2. Capillary colloid osmotic pressure (π) inside Bowman’s capsule pressure gradient ▪ Due to proteins in plasma ▪ ~ 30 mm Hg ▪ Opposes filtration (pulls fluid back to plasma) favors fluid movement back into capillaries 3. Capsule fluid pressure (Pfluid) ▪ Hydrostatic pressure inside Bowman’s capsule ( ~ 15 mm Hg) ▪ Opposes filtration fluid filtering out of capillaries must displace fluid already in capsule lumen • Net pressure = PH – π – Pfluid = 10 mm Hg into Bowman’s capsule Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Capillary Pressure Causes Filtration (2 of 2) • Glomerular Filtration Rate (GFR) – volume of fluid filtered per unit time – Influenced by ▪ Net filtration pressure – ▪ Renal blood flow and blood pressure Filtration coefficient – Surface areas of glomerular capillaries available for filtration – Permeability of filtration slits • GFR is relatively constant • GFR is controlled primarily by regulating blood flow through the renal arterioles – Increased resistance in afferent arteriole, decreases GFR – Increased resistance in efferent arteriole, increases GFR – Decreased resistance in afferent arteriole, increases GFR – Decreased resistance in efferent arteriole, decreases GFR Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.6(a) Glomerular Filtration Rate Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.6(b) Glomerular Filtration Rate Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.6(c-e) Glomerular Filtration Rate Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved GFR Is Subject to Autoregulation a decrease in GFR helps body conserve blood volume Vasoconstriction, after depolarization, increases resistance to flow, so blood flow through arteriole diminishes, which decrease filtration pressure in glomerulus Since vasodilation is not as effective as vasoconstriction bc afferent arteriole fairly relaxed, when blood pressure < 80 mm Hg, GFR decreases • Myogenic response – Intrinsic ability of vascular smooth muscle to respond to pressure changes – Similar to autoregulation in other systemic arterioles with depolarization and Ca2+ • Tubuloglomerular feedback – Paracrine control local pathway in which fluid flow through tubule influences GFR tubule and When NaCl delivery past the macula – Juxtaglomerular apparatus where arteriolar walls are dense increases as a result of together increased GFR, the macula dense cells paracrine message to ▪ Macula densa cells detect NaCl in the filtrate send neighbouring afferent arteriole The afferent arteriole constricts, increasing resistance and decreasing ▪ Granular cells secrete enzyme renin GFR • Hormones and autonomic neurons also influence GFR – By changing resistance in arterioles – By altering the filtration coefficient Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.7(a-b) The juxtaglomerular apparatus Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 19.7(c) The juxtaglomerular apparatus Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Key words kidneys, ureter, urinary bladder, urethra, micturition, renal arteries, renal veins, cortex, medulla, nephron, juxtamedullary nephron, cortical nephron, afferent arteriole, glomerulus, efferent arteriole, peritubular capillaries, vasa recta, Bowman’s capsule, renal corpuscle, proximal tubule, loop of Henle, descending limb, ascending limb, distal tubule, collecting duct, renal pelvis, urine, juxtaglomerular apparatus, filtration, filtrate, excretion, reabsorption, secretion, filtration barriers, glomerular capillaries, fenestrated capillaries, podocytes, foot processes, filtration slits, mesangial cells, hydrostatic pressure (PH), colloid osmotic pressure (π), fluid pressure (Pfluid),glomerular filtration rate (GFR), myogenic response, tubuloglomerular feedback, macula densa, granular cells. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved