The Urinary SystemThe Urinary System

Chapter 15Chapter 15

Functions of the Urinary SystemFunctions of the Urinary System Elimination of waste productsElimination of waste products

Nitrogenous wastesNitrogenous wastes ToxinsToxins DrugsDrugs

Regulate aspects of homeostasisRegulate aspects of homeostasis Water balanceWater balance ElectrolytesElectrolytes Acid-base balance in the bloodAcid-base balance in the blood Blood pressureBlood pressure Red blood cell productionRed blood cell production Activation of vitamin DActivation of vitamin D

Organs of the Urinary systemOrgans of the Urinary system

KidneysKidneysUretersUretersUrinary bladderUrinary bladderUrethraUrethra

Location of the KidneysLocation of the Kidneys

Kidney is located against Kidney is located against dorsal body wall in the dorsal body wall in the bodybody

Kidneys extend from TKidneys extend from T1212

to Lto L33

The right kidney is slightly The right kidney is slightly lower than the leftlower than the left

Features and Structure of KidneyFeatures and Structure of Kidney Is dark red kidney-bean shapedIs dark red kidney-bean shaped

12 cm long, 6 cm wide, 3 cm thick12 cm long, 6 cm wide, 3 cm thick

Has medial indentationHas medial indentation called called Renal hilumRenal hilum

Several structures enter or exit Several structures enter or exit the kidney (ureters, renal blood the kidney (ureters, renal blood vessels, and nerves) at vessels, and nerves) at hilumhilum

An adrenal gland sits atop each An adrenal gland sits atop each kidneykidney

Coverings of the KidneysCoverings of the Kidneys Three layers of supportive tissue Three layers of supportive tissue

surround each kidney:surround each kidney:

Fibrous capsuleFibrous capsule Transparent fibrous capsule Transparent fibrous capsule

surrounds each kidneysurrounds each kidney

Perirenal fat capsulePerirenal fat capsule Surrounds the kidney and Surrounds the kidney and

cushions against blowscushions against blows

Renal fasciaRenal fascia Outermost capsule that helps Outermost capsule that helps

hold the kidney in place hold the kidney in place against the muscles of the against the muscles of the trunk walltrunk wall

Regions of the KidneyRegions of the Kidney

Cortex –Cortex – the light colored, the light colored, outer region outer region

Medulla –Medulla – Reddish brown Reddish brown areaarea

Has cone-shaped Has cone-shaped medullary (renal) medullary (renal) pyramids separated by pyramids separated by renal columnsrenal columns

Renal pelvis –Renal pelvis – Medial to Medial to the hilusthe hilus

Flat basin like cavityFlat basin like cavity

Regions of the KidneyRegions of the Kidney

Calyces –Calyces – large branches large branches of the of the renal pelvisrenal pelvis

Collect urine draining from Collect urine draining from tips of tips of pyramidspyramids

Empty urine into the Empty urine into the renal renal pelvispelvis

Urine flows through the Urine flows through the renal pelvis to ureter and renal pelvis to ureter and then to the bladderthen to the bladder

Blood Flow in the KidneysBlood Flow in the Kidneys Kidneys continuously cleanse Kidneys continuously cleanse

the bloodthe blood One-quarter of the total blood One-quarter of the total blood

supply of the body passes supply of the body passes through the kidneys each minutethrough the kidneys each minute

Renal artery provides each Renal artery provides each kidney with arterial blood supplykidney with arterial blood supply

Venous blood drain from kidney Venous blood drain from kidney takes place via Renal veintakes place via Renal vein

NephronNephron Each kidney contains more Each kidney contains more

than a million tiny structures – than a million tiny structures – NephronsNephrons

Nephrons -Nephrons - The structural and The structural and functional units of the kidneysfunctional units of the kidneys

Responsible for forming urineResponsible for forming urine

Main structures of the nephronMain structures of the nephron

GlomerulusGlomerulus Renal tubuleRenal tubule

GlomerulusGlomerulus Is a knot of capillariesIs a knot of capillaries

Attached to Attached to arterioles on both sides arterioles on both sides (maintains (maintains high pressure)high pressure)

Large afferent Large afferent arteriolearteriole

Narrow efferent Narrow efferent arteriolearteriole

GlomerulusGlomerulus Capillaries are covered Capillaries are covered

with with Octopus –like cells called Octopus –like cells called

podocytes podocytes Forms porous membrane Forms porous membrane

around glomerulusaround glomerulus

Cup-shaped, First part of Cup-shaped, First part of renal tubule surrounds the renal tubule surrounds the glomerulus known as glomerulus known as Glomerular (Glomerular (Bowman’sBowman’s) ) capsulecapsule

NephronNephron Renal TubuleRenal Tubule

Renal tubule extends from Renal tubule extends from glomerular capsule and ends glomerular capsule and ends at the collecting ductat the collecting duct

Proximal convoluted Proximal convoluted tubule (PCT)tubule (PCT)

Loop of HenleLoop of Henle

Distal convoluted tubule Distal convoluted tubule (DCT)(DCT)

Types of NephronsTypes of Nephrons Cortical nephronsCortical nephrons

Located entirely in the Located entirely in the cortexcortex

Includes most Includes most nephronsnephrons

Juxtamedullary nephronsJuxtamedullary nephrons Found at the boundary Found at the boundary

of the cortex and of the cortex and medullamedulla

Collecting DuctCollecting Duct

Receives urine from Receives urine from many nephronsmany nephrons

Run through the Run through the medullary pyramidsmedullary pyramids

Deliver urine into the Deliver urine into the calyces and renal calyces and renal pelvispelvis

Each and every Nephron is associated Each and every Nephron is associated with two capillary bedswith two capillary bedsGlomerulusGlomerulusPeritubular capillary bedPeritubular capillary bed

Nephron AnatomyNephron Anatomy

GlomerulusGlomerulus Glomerulus is fed and drained by Glomerulus is fed and drained by

arteriolesarterioles

Afferent arteriole—Afferent arteriole— arises from a arises from a cortical radiate artery and feeds the cortical radiate artery and feeds the glomerulusglomerulus

Efferent arteriole—Efferent arteriole— receives blood receives blood that has passed through the that has passed through the glomerulusglomerulus

Specialized for filtrationSpecialized for filtration

BP in glomerular capillaries is much BP in glomerular capillaries is much higher than other capillarieshigher than other capillaries

High pressure forces fluid and solutes High pressure forces fluid and solutes (smaller than proteins) out of blood and (smaller than proteins) out of blood and into the glomerular capsuleinto the glomerular capsule

Most of the filtrate from renal tubule is Most of the filtrate from renal tubule is absorbed by peritubular capillary beds absorbed by peritubular capillary beds and returned to bloodand returned to blood

Peritubular CapillariesPeritubular Capillaries

Arise from Arise from efferent arterioleefferent arteriole of of the glomerulus, which drains the glomerulus, which drains the glomerulusthe glomerulus

low pressure capillarieslow pressure capillaries

Adapted for absorption instead Adapted for absorption instead of filtrationof filtration

Cling close to the renal tubule to Cling close to the renal tubule to reabsorb (reclaim) some solutes reabsorb (reclaim) some solutes and waterand water

Drains into the veinsDrains into the veins

Urine Formation ProcessesUrine Formation Processes

Three processes:Three processes:Glomerular FiltrationGlomerular FiltrationTubular ReabsorptionTubular ReabsorptionTubular SecretionTubular Secretion

Glomerular FiltrationGlomerular Filtration Nonselective passive processNonselective passive process

Fluid passes from blood into Fluid passes from blood into glomerular capsule (part of glomerular capsule (part of renal tubule)renal tubule)

Fluid (Water and solutes smaller Fluid (Water and solutes smaller than proteins) than proteins) are forced through capillary are forced through capillary

wallswalls

Blood cells and proteins cannot Blood cells and proteins cannot pass out to the capillariespass out to the capillaries

Filtrate is collected in the Filtrate is collected in the glomerular capsule glomerular capsule

and leaves via the renal tubuleand leaves via the renal tubule

Tubular ReabsorptionTubular Reabsorption Besides wastes and excess ions ,Filtrate Besides wastes and excess ions ,Filtrate

contains many useful substances, which is contains many useful substances, which is returned to blood via absorptionreturned to blood via absorption

Reabsorption begins when filtrate enters Reabsorption begins when filtrate enters proximal convoluted tubule from glomerulusproximal convoluted tubule from glomerulus

The peritubular capillaries reabsorb useful The peritubular capillaries reabsorb useful substancessubstances WaterWater GlucoseGlucose Amino acidsAmino acids IonsIons

Some reabsorption is passive, most is activeSome reabsorption is passive, most is active

Most reabsorption occurs in the proximal Most reabsorption occurs in the proximal convoluted tubuleconvoluted tubule

Materials not reabsorbedMaterials not reabsorbedNitrogenous waste productsNitrogenous waste products

Urea—Urea— protein breakdown protein breakdownUric acid—Uric acid— nucleic acid breakdown nucleic acid breakdownCreatinine—Creatinine— associated with creatine metabolism associated with creatine metabolism

in musclesin muscles

Excreted through the urineExcreted through the urine

ReabsorptionReabsorption

Tubular SecretionTubular Secretion

Some materials move from Some materials move from the peritubular capillaries the peritubular capillaries

into the renal tubules filtrate into the renal tubules filtrate to be eliminated in urine, to be eliminated in urine, such assuch as

Hydrogen and potassium Hydrogen and potassium ionsions

CreatinineCreatinine

Materials left in the renal Materials left in the renal tubule move toward the tubule move toward the ureterureter

Characteristics of UrineCharacteristics of Urine In 24 hours, about 1.0 to 1.8 liters of urine are producedIn 24 hours, about 1.0 to 1.8 liters of urine are produced

Yellow color due to the pigment urochrome (from the destruction Yellow color due to the pigment urochrome (from the destruction of hemoglobin) and solutesof hemoglobin) and solutes

SterileSterile

Slightly aromaticSlightly aromatic

Normal pH of around 6Normal pH of around 6

Specific gravity of 1.001 to 1.035Specific gravity of 1.001 to 1.035

Solutes normally found in urineSolutes normally found in urineSodium and potassium ionsSodium and potassium ionsUrea, uric acid, creatinineUrea, uric acid, creatinineAmmoniaAmmoniaBicarbonate ionsBicarbonate ions

Characteristics of UrineCharacteristics of Urine

Solutes NOT normally found in urineSolutes NOT normally found in urineGlucoseGlucoseBlood proteinsBlood proteinsRed blood cellsRed blood cellsHemoglobinHemoglobinWhite blood cells (pus)White blood cells (pus)BileBile

Characteristics of UrineCharacteristics of Urine

UretersUreters Slender tubes attaching the Slender tubes attaching the

kidney to the bladderkidney to the bladder Superior end of ureter is Superior end of ureter is

continuous with the renal pelviscontinuous with the renal pelvis Enter the posterior aspect of Enter the posterior aspect of

the bladderthe bladder

Ureters are passageways that Ureters are passageways that carry urine from kidneys to bladdercarry urine from kidneys to bladder

Propel urine into bladder by Propel urine into bladder by Peristalsis aids Peristalsis aids

Urinary BladderUrinary Bladder Smooth, collapsible, muscular sacSmooth, collapsible, muscular sac Temporarily stores urineTemporarily stores urine Trigone – three openingsTrigone – three openings

Two from the uretersTwo from the ureters One to the urethraOne to the urethra

Urinary Bladder WallUrinary Bladder Wall Bladder wall contains three layers Bladder wall contains three layers

of smooth muscle, collectively of smooth muscle, collectively known as known as detrusor muscledetrusor muscle

And its mucosa is made of And its mucosa is made of transitional epitheliumtransitional epithelium

Suited for urine storageSuited for urine storage

When bladder is empty it When bladder is empty it collapses and thrown into foldscollapses and thrown into folds

Bladder can expand significantly Bladder can expand significantly without increasing internal without increasing internal pressurepressure

Urinary Bladder CapacityUrinary Bladder Capacity

A moderately full A moderately full bladder is about 5 bladder is about 5 inches long and holds inches long and holds about 500 mL of urineabout 500 mL of urine

Capable of holding Capable of holding twice that amount of twice that amount of urineurine

UrethraUrethra Thin-walled tube that carries urine from the bladder to the outside of Thin-walled tube that carries urine from the bladder to the outside of

the body by peristalsisthe body by peristalsis Release of urine is controlled by two sphinctersRelease of urine is controlled by two sphincters

Internal urethral sphincter Internal urethral sphincter Involuntary and made of smooth muscleInvoluntary and made of smooth muscle

External urethral sphincterExternal urethral sphincter Voluntary and made of skeletal muscleVoluntary and made of skeletal muscle

Urethra Gender DifferencesUrethra Gender Differences LengthLength

Females – 3–4 cm (1 inch)Females – 3–4 cm (1 inch) Males – 20 cm (8 inches)Males – 20 cm (8 inches)

LocationLocation Females – along wall of the vaginaFemales – along wall of the vagina Males – through the prostate and penisMales – through the prostate and penis

FunctionFunction Females – only carries urineFemales – only carries urine Males – carries urine and is a passageway for sperm Males – carries urine and is a passageway for sperm

cellscells

Micturition (Voiding)Micturition (Voiding)

Is the act of emptying the bladderIs the act of emptying the bladder

Two sphincters, internal and external sphincter control Two sphincters, internal and external sphincter control the flow of urinethe flow of urine

When volume of bladder reaches around 200 mlWhen volume of bladder reaches around 200 ml

Bladder stretches and activates stretch receptorsBladder stretches and activates stretch receptors

Then impulses transmitted to spinal cordThen impulses transmitted to spinal cord

Micturition (Voiding)Micturition (Voiding)

And then back to bladder via Pelvic splanchnic nerves And then back to bladder via Pelvic splanchnic nerves

Pelvic splanchnic nerves initiate bladder to go into reflex Pelvic splanchnic nerves initiate bladder to go into reflex contractionscontractions

Urine is forced past the internal urethra sphincter and the Urine is forced past the internal urethra sphincter and the person feels the urge to voidperson feels the urge to void

The external urethral sphincter must be voluntarily The external urethral sphincter must be voluntarily relaxed to voidrelaxed to void

Kidneys have four roles in maintaining blood Kidneys have four roles in maintaining blood compositioncomposition

Excretion of nitrogen-containing wastesExcretion of nitrogen-containing wastes

Maintaining water balance of the bloodMaintaining water balance of the blood

Maintaining electrolyte balance of the bloodMaintaining electrolyte balance of the blood

Ensuring proper blood pHEnsuring proper blood pH

Fluid, Electrolyte, and Acid-Base BalanceFluid, Electrolyte, and Acid-Base Balance

Distribution of Body FluidDistribution of Body Fluid Normal amount of water in the Normal amount of water in the

human bodyhuman body Young adult females – 50%Young adult females – 50% Young adult males – 60%Young adult males – 60% Babies – 75%Babies – 75% Old age – 45%Old age – 45%

Intracellular fluidIntracellular fluid (inside cells) - (inside cells) -2/3 of body fluid2/3 of body fluid

Extracellular fluidExtracellular fluid (outside (outside cells)cells) Interstitial fluidInterstitial fluid Blood plasmaBlood plasma

Maintaining Water BalanceMaintaining Water Balance Water intake must equal water Water intake must equal water

outputoutput

Sources for water intakeSources for water intake Ingested foods and fluidsIngested foods and fluids Water produced from metabolic Water produced from metabolic

processesprocesses Thirst mechanism is the driving Thirst mechanism is the driving

force for water intakeforce for water intake

Sources for water outputSources for water output Vaporization out of the lungsVaporization out of the lungs Lost in perspirationLost in perspiration Leaves the body in the fecesLeaves the body in the feces Urine productionUrine production

Maintaining Water BalanceMaintaining Water Balance

Dilute urine is produced if water intake is Dilute urine is produced if water intake is excessiveexcessive

Less urine (concentrated) is produced if large Less urine (concentrated) is produced if large amounts of water are lostamounts of water are lost

Proper concentrations of various electrolytes Proper concentrations of various electrolytes must be present in both intracellular and must be present in both intracellular and extracellular fluidsextracellular fluids

The Link Between Water and SaltThe Link Between Water and Salt

Electrolytes: Na+, K+ Electrolytes: Na+, K+ Changes in electrolyte balance Changes in electrolyte balance

causes water to move from one compartment causes water to move from one compartment to anotherto another

Alters blood volume and blood pressureAlters blood volume and blood pressureCan impair the activity of cellsCan impair the activity of cells

Regulation of Water and Electrolyte Regulation of Water and Electrolyte Reabsorption: ADH and AldosteroneReabsorption: ADH and Aldosterone

Cells in the Cells in the kidneyskidneys and and hypothalamushypothalamus are active monitorsare active monitors

When the blood pressure and volume When the blood pressure and volume decreasedecrease

Kidney releases renin Kidney releases renin Renin acts on angiotansiogenRenin acts on angiotansiogen

to form angiotensin Ito form angiotensin I Angiotensin I is further broken toAngiotensin I is further broken to

Angiotensin IIAngiotensin II

Angiotensin II stimulates Angiotensin II stimulates VasoconstrictionVasoconstriction Release of hormones ADH and Release of hormones ADH and

aldosteronealdosterone Stimulates hypothalamus thirst Stimulates hypothalamus thirst

center to drink watercenter to drink water

Antidiuretic hormone Antidiuretic hormone (ADH) release(ADH) release

Stimulates body to Stimulates body to retain waterretain water By the kidneysBy the kidneys Increases fluid volumeIncreases fluid volume Increases blood Increases blood

pressurepressure Thus brings blood Thus brings blood

pressure and volume pressure and volume togethertogether

In addition it takes the In addition it takes the help of aldosteronehelp of aldosterone

Aldosterone regulates Aldosterone regulates sodium ion content of sodium ion content of extracellular fluidextracellular fluid

Triggered by the Triggered by the rennin-angiotensin rennin-angiotensin mechanismmechanism

Increases Na+ Increases Na+ retentionretention

Increases fluid Increases fluid retentionretention

Increases blood Increases blood volumevolume

Maintaining Acid-Base Balance Maintaining Acid-Base Balance in Bloodin Blood

Blood pH must remain between 7.35 and Blood pH must remain between 7.35 and 7.45 to maintain homeostasis7.45 to maintain homeostasis

Alkalosis – pH above 7.45Alkalosis – pH above 7.45Acidosis – pH below 7.35Acidosis – pH below 7.35

Maintaining Acid-Base Balance Maintaining Acid-Base Balance in Bloodin Blood

Most acid-base balance is maintained by Most acid-base balance is maintained by the kidneysthe kidneys

Other acid-base controlling systemsOther acid-base controlling systemsBlood buffersBlood buffersRespirationRespiration

Molecules react to prevent dramatic changes in Molecules react to prevent dramatic changes in hydrogen ion (H+) concentrationshydrogen ion (H+) concentrations

Bind to H+ when pH dropsBind to H+ when pH dropsRelease H+ when pH risesRelease H+ when pH rises

Blood BuffersBlood Buffers

Blood BuffersBlood Buffers Acids are proton (H+) donorsAcids are proton (H+) donors

Strong acids dissociate completely Strong acids dissociate completely and liberate all of their H+ in waterand liberate all of their H+ in water

Cause large change in pHCause large change in pH Weak acids, such as carbonic Weak acids, such as carbonic

acid, dissociate only partiallyacid, dissociate only partially Less effect on solution`s pHLess effect on solution`s pH Play imp. role in buffer systemPlay imp. role in buffer system

Bases are proton (H+) acceptorsBases are proton (H+) acceptors Strong bases dissociate easily in Strong bases dissociate easily in

water and tie up H+ water and tie up H+

Weak bases, such as bicarbonate Weak bases, such as bicarbonate ion and ammonia, are slower to ion and ammonia, are slower to accept H+accept H+

Three major chemical buffer systemsThree major chemical buffer systems

Bicarbonate buffer systemBicarbonate buffer systemPhosphate buffer systemPhosphate buffer systemProtein buffer systemProtein buffer system

Blood BuffersBlood Buffers

Mixture of carbonic acid (HMixture of carbonic acid (H22CO3) and sodium CO3) and sodium bicarbonate (NaHCObicarbonate (NaHCO33))

Bicarbonate ions (HCOBicarbonate ions (HCO33––) react with strong acids to ) react with strong acids to

change them to weak acidschange them to weak acids

HCl + NaHCOHCl + NaHCO33 H H22COCO33 + NaCl + NaCl

strong acid weak base weak acid saltstrong acid weak base weak acid salt

Bicarbonate Buffer SystemBicarbonate Buffer System

Carbonic acid dissociates in the presence of a strong Carbonic acid dissociates in the presence of a strong base to form a weak base and waterbase to form a weak base and water

NaOH + H2CONaOH + H2CO33 NaHCO NaHCO33 + H + H22OO

strong base weak acid weak base waterstrong base weak acid weak base water

Bicarbonate Buffer SystemBicarbonate Buffer System

Carbon dioxide in the blood is converted to bicarbonate ion and Carbon dioxide in the blood is converted to bicarbonate ion and transported in the plasmatransported in the plasma

Increase in carbon dioxide produces more carbonic acidIncrease in carbon dioxide produces more carbonic acid

And Increases in hydrogen ion concentration produces more And Increases in hydrogen ion concentration produces more carbonic acidcarbonic acid

Excess hydrogen ion can be blown off with the release of carbon Excess hydrogen ion can be blown off with the release of carbon dioxide from the lungs by increasing the breathing ratedioxide from the lungs by increasing the breathing rate

COCO22 + H + H22O HO H22COCO3 3 H H++ + HCO + HCO33--

Respiratory rate can rise and fall depending on changing blood pHRespiratory rate can rise and fall depending on changing blood pH

Respiratory System Controls of Respiratory System Controls of Acid-Base BalanceAcid-Base Balance

Excrete bicarbonate ions if neededExcrete bicarbonate ions if needed

Conserve (reabsorb) or generate new bicarbonate ions if neededConserve (reabsorb) or generate new bicarbonate ions if needed

When blood pH risesWhen blood pH rises

Bicarbonate ions are excreted Bicarbonate ions are excreted Hydrogen ions are retained by kidney tubulesHydrogen ions are retained by kidney tubules

When blood pH fallsWhen blood pH falls

Bicarbonate ions are reabsorbedBicarbonate ions are reabsorbed Hydrogen ions are secretedHydrogen ions are secreted

Urine pH varies from 4.5 to 8.0Urine pH varies from 4.5 to 8.0

Renal Mechanisms of Acid-Base BalanceRenal Mechanisms of Acid-Base Balance

Developmental Aspects of the Urinary Developmental Aspects of the Urinary SystemSystem

Functional kidneys are developed by the third monthFunctional kidneys are developed by the third month

Urinary system of a newbornUrinary system of a newborn Bladder is smallBladder is small Urine cannot be concentratedUrine cannot be concentrated

Control of the voluntary urethral sphincter does not start Control of the voluntary urethral sphincter does not start until age 18 monthsuntil age 18 months

Urinary infections are the only common problems before Urinary infections are the only common problems before old ageold age

There is a progressive decline in urinary functionThere is a progressive decline in urinary function

The bladder shrinks with agingThe bladder shrinks with aging