Chapter 26Chapter 26

Urinary SystemUrinary System

Urinary System Urinary System FunctionsFunctions

FilteringFiltering of blood of blood RegulationRegulation of of

blood volumeblood volume concentration of blood solutesconcentration of blood solutes pH of extracellular fluidpH of extracellular fluid blood cell synthesisblood cell synthesis

SynthesisSynthesis of Vitamin D of Vitamin D

Urinary System Urinary System Anatomy:Anatomy:

Location and External Location and External AnatomyAnatomy

of Kidneysof Kidneys LocationLocation

Lie behind Lie behind peritoneum on peritoneum on posterior abdominal posterior abdominal wall on either side wall on either side of vertebral columnof vertebral column

Lumbar vertebrae Lumbar vertebrae and rib cage and rib cage partially protectpartially protect

Right kidney Right kidney slightly lower than slightly lower than leftleft

External AnatomyExternal Anatomy Renal capsuleRenal capsule

Surrounds each kidneySurrounds each kidney Perirenal fatPerirenal fat

Engulfs renal capsule Engulfs renal capsule and acts as cushioningand acts as cushioning

Renal fasciaRenal fascia Anchors kidneys to Anchors kidneys to

abdominal wallabdominal wall HilumHilum

Renal artery and nerves Renal artery and nerves enter and renal vein and enter and renal vein and ureter exit kidneysureter exit kidneys

Internal Anatomy of Internal Anatomy of Kidneys:Kidneys:

CortexCortex: Outer area: Outer area Renal columnsRenal columns

MedullaMedulla: Inner area: Inner area Renal pyramidsRenal pyramids

CalycesCalyces Major: Converge to Major: Converge to

form pelvisform pelvis Minor: Papillae Minor: Papillae

extendextend

NephronNephron:: Functional unit of Functional unit of kidneykidney JuxtamedullaryJuxtamedullary CorticalCortical

The The Nephron:Nephron:

Histology of the Histology of the NephronNephron

Internal Anatomy of Internal Anatomy of KidneysKidneys

Renal corpuscleRenal corpuscle Bowman’s capsuleBowman’s capsule

Parietal layerParietal layer Visceral layerVisceral layer

GlomerulusGlomerulus Network of Network of

capillariescapillaries

ArteriolesArterioles AfferentAfferent

Blood to glomerulusBlood to glomerulus EfferentEfferent

DrainsDrains

TubulesTubules Proximal Proximal

(convoluted) tubule(convoluted) tubule Loops of HenleLoops of Henle

Descending limbDescending limb Ascending limbAscending limb

Distal (convoluted) Distal (convoluted) tubulestubules

Collecting ductsCollecting ducts

Renal CorpuscleRenal Corpuscle

Kidney Blood Flow: Kidney Blood Flow:

Ureters and Urinary Ureters and Urinary BladderBladder

UretersUreters Tubes through Tubes through

which urine flows which urine flows from kidneys to from kidneys to urinary bladderurinary bladder

Urinary bladderUrinary bladder Stores urineStores urine

UrethraUrethra Transports urine Transports urine

from bladder to from bladder to outside of bodyoutside of body

Difference in Difference in length between length between males and femalesmales and females

SphinctersSphincters Internal urinaryInternal urinary External urinary External urinary

Ureters and Urinary Ureters and Urinary BladderBladder

Urine FormationUrine Formation

FiltrationFiltration

FiltrationFiltration Renal filtrateRenal filtrate

Plasma minus blood Plasma minus blood cells and blood proteinscells and blood proteins

Most (Most (99%)99%) reabsorbed reabsorbed

Filtration membraneFiltration membrane Fenestrated Fenestrated

endothelium, endothelium, basement membrane basement membrane and pores formed by and pores formed by podocytespodocytes

Filtration pressureFiltration pressure Responsible for Responsible for

filtrate formationfiltrate formation Glomerular capillary Glomerular capillary

pressure (pressure (GCPGCP) ) minus capsule minus capsule pressure (pressure (CPCP) minus ) minus colloid osmotic colloid osmotic pressure (pressure (COPCOP))

Changes caused by Changes caused by glomerular capillary glomerular capillary pressurepressure

Filtration PressureFiltration Pressure

Tubular ReabsorptionTubular Reabsorption

ReabsorptionReabsorption Passive transportPassive transport Active transportActive transport Cotransport Cotransport

SpecializationSpecialization of of tubule segmentstubule segments

Substances Substances transportedtransported Active transport Active transport

moves moves NaNa++ across across nephron wallnephron wall

Other ions and Other ions and molecules moved by molecules moved by cotransportcotransport

Passive transport Passive transport moves water, urea, moves water, urea, lipid-soluble, lipid-soluble, nonpolar compoundsnonpolar compounds

Reabsorption in Proximal Reabsorption in Proximal Nephron:Nephron:

Reabsorption in Loop of Reabsorption in Loop of HenleHenle

Reabsorption in Loop of Reabsorption in Loop of HenleHenle

Tubular SecretionTubular Secretion

Substances enter proximal or distal Substances enter proximal or distal tubules and collecting ductstubules and collecting ducts

HH++, K, K++ and some substances not and some substances not produced in body are secreted by produced in body are secreted by countertransport mechanismscountertransport mechanisms

Secretion of Hydrogen Secretion of Hydrogen and Potassiumand Potassium

Urine ProductionUrine Production

In Proximal tubulesIn Proximal tubules NaNa++ and other and other

substances removedsubstances removed Water follows Water follows

passivelypassively Filtrate volume Filtrate volume

reducedreduced In descending limb In descending limb

of loop of Henleof loop of Henle Water exits passively, Water exits passively,

solute enterssolute enters Filtrate volume Filtrate volume

reduced reduced 15%15%

In ascending limb of In ascending limb of loop of Henleloop of Henle NaNa++, Cl, Cl--, K, K++ transported transported

out of filtrateout of filtrate Water remainsWater remains

In distal tubules In distal tubules and collecting ductsand collecting ducts Water movement out Water movement out

regulated by regulated by ADHADH If absent, water not If absent, water not

reabsorbed and dilute reabsorbed and dilute urine producedurine produced

If If ADHADH present, water present, water moves out, concentrated moves out, concentrated urine producedurine produced

Filtrate and Medullary Filtrate and Medullary Concentration GradientConcentration Gradient

Medullary Medullary Concentration and Concentration and

Urea CyclingUrea Cycling

Urine Concentration Urine Concentration MechanismMechanism

When large volume When large volume of water consumedof water consumed Eliminate excess Eliminate excess

without losing large without losing large amounts of amounts of electrolyteselectrolytes

Response is kidneys Response is kidneys produce large produce large volume of dilute volume of dilute urineurine

When drinking When drinking water not availablewater not available Kidneys produce Kidneys produce

small volume of small volume of concentrated urineconcentrated urine

Removes waste and Removes waste and prevents rapid prevents rapid dehydrationdehydration

Urine Concentrating Urine Concentrating Mechanism I:Mechanism I:

Urine Concentrating Urine Concentrating Mechanism II:Mechanism II:

Hormonal MechanismsHormonal Mechanisms ADHADH

Secreted by posterior Secreted by posterior pituitarypituitary

Increases water Increases water permeability in distal permeability in distal tubules and collecting tubules and collecting ductsducts

AldosteroneAldosterone Produced in adrenal Produced in adrenal

cortexcortex Affects Affects NaNa++ and and ClCl--

transport in nephron transport in nephron and collecting ductsand collecting ducts

ReninRenin Produced by kidneys, Produced by kidneys,

causes production of causes production of angiotensin IIangiotensin II

Atrial natriuretic Atrial natriuretic hormonehormone Produced by heart Produced by heart

when blood pressure when blood pressure increasesincreases

Inhibits ADH productionInhibits ADH production Reduces ability of Reduces ability of

kidney to concentrate kidney to concentrate urineurine

Effect of ADH on Effect of ADH on NephronNephron

Aldosterone Effect on Aldosterone Effect on Distal TubuleDistal Tubule

Autoregulation and Autoregulation and Sympathetic Sympathetic StimulationStimulation

AutoregulationAutoregulation Involves changes in Involves changes in

degree of degree of constriction in constriction in afferent arteriolesafferent arterioles

As systemic As systemic BPBP increased, afferent increased, afferent arterioles constrict arterioles constrict and prevent and prevent increase in renal increase in renal blood flowblood flow

Sympathetic Sympathetic stimulationstimulation Constricts small arteries Constricts small arteries

and afferent arteriolesand afferent arterioles Decreases renal blood Decreases renal blood

flowflow

Clearance and Tubular Clearance and Tubular LoadLoad

Plasma clearancePlasma clearance Volume of plasma Volume of plasma

cleared of a specific cleared of a specific substance each substance each minuteminute

Used to estimate Used to estimate GFRGFR

Used to calculate Used to calculate renal plasma flowrenal plasma flow

Used to determine Used to determine which drugs or other which drugs or other substances excreted substances excreted by kidneyby kidney

Tubular loadTubular load Total amount of Total amount of

substance that substance that passes through passes through filtration membrane filtration membrane into nephrons each into nephrons each minuteminute

Normally glucose is Normally glucose is almost completed almost completed reabsorbedreabsorbed

Tubular MaximumTubular Maximum

Tubular Tubular maximummaximum Maximum rate at Maximum rate at

which a substance which a substance can be actively can be actively absorbedabsorbed

Each substance Each substance has its own has its own tubular maximumtubular maximum

Urine Flow and Urine Flow and Micturition ReflexMicturition Reflex

Urine flowUrine flow Hydrostatic Hydrostatic

pressure forces pressure forces urine through urine through nephronnephron

Peristalsis moves Peristalsis moves urine through urine through uretersureters

Micturition reflexMicturition reflex Stretch of urinary Stretch of urinary

bladder stimulates bladder stimulates reflex causing reflex causing bladder to contract, bladder to contract, inhibiting urinary inhibiting urinary sphincterssphincters

Higher brain Higher brain centers can centers can stimulate or inhibit stimulate or inhibit reflex reflex

Micturition ReflexMicturition Reflex

Effects of Aging on Effects of Aging on KidneysKidneys

Gradual decrease in size of kidneyGradual decrease in size of kidney Decrease in kidney size leads to Decrease in kidney size leads to

decrease in renal blood flowdecrease in renal blood flow Decrease in number of functional Decrease in number of functional

nephronsnephrons Decrease in renin secretion and Decrease in renin secretion and

vitamin D synthesisvitamin D synthesis Decline in ability of nephron to Decline in ability of nephron to

secrete and absorbsecrete and absorb

Kidney DialysisKidney Dialysis