Chapter 26

Anatomy and Physiology, Sixth Edition Rod R. Seeley Idaho State University Trent D. Stephens Idaho State University Philip Tate Phoenix College

Chapter 26 Lecture Outline* *See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.

26-1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 26

Urinary System

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Urinary System Functions • Filtering of blood • Regulation of – – – –

blood volume concentration of blood solutes pH of extracellular fluid blood cell synthesis

• Synthesis of Vitamin D 26-3

Urinary System Anatomy

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Location and External Anatomy of Kidneys • Location – Lie behind peritoneum on posterior abdominal wall on either side of vertebral column – Lumbar vertebrae and rib cage partially protect – Right kidney slightly lower than left

• External Anatomy – Renal capsule • Surrounds each kidney

– Perirenal fat • Engulfs renal capsule and acts as cushioning

– Renal fascia • Anchors kidneys to abdominal wall

– Hilum • Renal artery and nerves enter and renal vein and ureter exit kidneys 26-5

Internal Anatomy of Kidneys • Cortex: Outer area – Renal columns

• Medulla: Inner area – Renal pyramids

• Calyces – Major: Converge to form pelvis – Minor: Papillae extend

• Nephron: Functional unit of kidney – Juxtamedullary – Cortical 26-6

The Nephron

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Histology of the Nephron

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Internal Anatomy of Kidneys • Renal corpuscle – Bowman’s capsule • Parietal layer • Visceral layer

– Glomerulus • Network of capillaries

• Arterioles – Afferent • Blood to glomerulus

– Efferent

• Tubules – Proximal (convoluted) tubule – Loops of Henle • Descending limb • Ascending limb

– Distal (convoluted) tubules

• Collecting ducts

• Drains 26-9

Renal Corpuscle

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Kidney Blood Flow

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Ureters and Urinary Bladder • Ureters – Tubes through which urine flows from kidneys to urinary bladder

• Urinary bladder – Stores urine

• Urethra – Transports urine from bladder to outside of body – Difference in length between males and females – Sphincters • Internal urinary • External urinary 26-12

Ureters and Urinary Bladder

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Urine Formation

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Filtration • Filtration – Renal filtrate • Plasma minus blood cells and blood proteins • Most (99%) reabsorbed

• Filtration membrane – Fenestrated endothelium, basement membrane and pores formed by podocytes

• Filtration pressure – Responsible for filtrate formation – Glomerular capillary pressure (GCP) minus capsule pressure (CP) minus colloid osmotic pressure (COP) – Changes caused by glomerular capillary pressure

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Filtration Pressure

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Tubular Reabsorption • Reabsorption – Passive transport – Active transport – Cotransport

• Specialization of tubule segments

• Substances transported – Active transport moves Na+ across nephron wall – Other ions and molecules moved by cotransport – Passive transport moves water, urea, lipid-soluble, nonpolar compounds 26-17

Reabsorption in Proximal Nephron

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Reabsorption in Loop of Henle

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Reabsorption in Loop of Henle

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Tubular Secretion • Substances enter proximal or distal tubules and collecting ducts • H+, K+ and some substances not produced in body are secreted by countertransport mechanisms

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Secretion of Hydrogen and Potassium

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Urine Production • In Proximal tubules – Na+ and other substances removed – Water follows passively – Filtrate volume reduced

• In descending limb of loop of Henle – Water exits passively, solute enters – Filtrate volume reduced 15%

• In ascending limb of loop of Henle – Na+, Cl-, K+ transported out of filtrate – Water remains

• In distal tubules and collecting ducts – Water movement out regulated by ADH • If absent, water not reabsorbed and dilute urine produced • If ADH present, water moves out, concentrated urine produced 26-23

Filtrate and Medullary Concentration Gradient

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Medullary Concentration and Urea Cycling

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Urine Concentration Mechanism • When large volume of water consumed – Eliminate excess without losing large amounts of electrolytes – Response is kidneys produce large volume of dilute urine

• When drinking water not available – Kidneys produce small volume of concentrated urine – Removes waste and prevents rapid dehydration

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Urine Concentrating Mechanism

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Hormonal Mechanisms • ADH

• Renin

– Secreted by posterior – Produced by kidneys, pituitary causes production of – Increases water angiotensin II permeability in distal • Atrial natriuretic tubules and collecting ducts

• Aldosterone – Produced in adrenal cortex – Affects Na+ and Cltransport in nephron and collecting ducts

hormone

– Produced by heart when blood pressure increases • Inhibits ADH production • Reduces ability of kidney to concentrate urine 26-28

Effect of ADH on Nephron

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Aldosterone Effect on Distal Tubule

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Autoregulation and Sympathetic Stimulation • Autoregulation – Involves changes in degree of constriction in afferent arterioles – As systemic BP increased, afferent arterioles constrict and prevent increase in renal blood flow

• Sympathetic stimulation – Constricts small arteries and afferent arterioles – Decreases renal blood flow

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Clearance and Tubular Load • Plasma clearance – Volume of plasma cleared of a specific substance each minute – Used to estimate GFR – Used to calculate renal plasma flow – Used to determine which drugs or other substances excreted by kidney

• Tubular load – Total amount of substance that passes through filtration membrane into nephrons each minute – Normally glucose is almost completed reabsorbed

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Tubular Maximum • Tubular maximum – Maximum rate at which a substance can be actively absorbed – Each substance has its own tubular maximum

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Urine Flow and Micturition Reflex • Urine flow – Hydrostatic pressure forces urine through nephron – Peristalsis moves urine through ureters

• Micturition reflex – Stretch of urinary bladder stimulates reflex causing bladder to contract, inhibiting urinary sphincters – Higher brain centers can stimulate or inhibit reflex

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Micturition Reflex

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Effects of Aging on Kidneys • Gradual decrease in size of kidney – Decrease in kidney size leads to decrease in renal blood flow

• Decrease in number of functional nephrons • Decrease in renin secretion and vitamin D synthesis • Decline in ability of nephron to secrete and absorb 26-36

Kidney Dialysis

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