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Anatomy and Physiology, Sixth Edition

Rod R. SeeleyIdaho State UniversityTrent D. StephensIdaho State UniversityPhilip TatePhoenix College

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

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

Chapter 26

Lecture Outline*

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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

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Urinary System Anatomy

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Location and External Anatomyof 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

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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

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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• Drains

• Tubules– Proximal

(convoluted) tubule– Loops of Henle

• Descending limb• Ascending limb

– Distal (convoluted) tubules

• Collecting ducts

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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

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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

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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

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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

– Secreted by posterior pituitary

– Increases water permeability in distal tubules and collecting ducts

• Aldosterone– Produced in adrenal

cortex– Affects Na+ and Cl-

transport in nephron and collecting ducts

• Renin– Produced by kidneys,

causes production of angiotensin II

• Atrial natriuretic hormone– Produced by heart

when blood pressure increases• Inhibits ADH

production• Reduces ability of

kidney to concentrate urine

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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

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Kidney Dialysis

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