Kidney FunctionsKidney Functions Filter 200 liters of blood daily, allowing Filter 200 liters of blood daily, allowing

toxins, metabolic wastes, and excess ions to toxins, metabolic wastes, and excess ions to leave the body in urineleave the body in urine

Regulate volume and chemical makeup of the Regulate volume and chemical makeup of the bloodblood

Maintain the proper balance between water Maintain the proper balance between water and salts, and acids and basesand salts, and acids and bases

Other Renal FunctionsOther Renal Functions Gluconeogenesis during prolonged fastingGluconeogenesis during prolonged fasting Production of rennin to help regulate blood Production of rennin to help regulate blood

pressure and erythropoietin to stimulate RBC pressure and erythropoietin to stimulate RBC productionproduction

Activation of vitamin DActivation of vitamin D

Other Urinary System OrgansOther Urinary System Organs Urinary bladder – provides a temporary Urinary bladder – provides a temporary

storage reservoir for urinestorage reservoir for urine Paired ureters – transport urine from the Paired ureters – transport urine from the

kidneys to the bladderkidneys to the bladder Urethra – transports urine from the bladder out Urethra – transports urine from the bladder out

of the bodyof the body

Kidney Location and External Kidney Location and External AnatomyAnatomy

The kidneys lie in a retroperitoneal position in The kidneys lie in a retroperitoneal position in the superior lumbar regionthe superior lumbar region

The right kidney is lower than the left because The right kidney is lower than the left because it is crowded by the liverit is crowded by the liver

The lateral surface is convex; the medial The lateral surface is convex; the medial surface is concavesurface is concave

The renal hilus leads to the renal sinusThe renal hilus leads to the renal sinus Ureters, renal blood vessels, lymphatics, and Ureters, renal blood vessels, lymphatics, and

nerves enter and exit at the hilusnerves enter and exit at the hilus

Layers of Tissue Supporting the Layers of Tissue Supporting the KidneyKidney

Renal capsule – fibrous capsule that prevents Renal capsule – fibrous capsule that prevents kidney infectionkidney infection

Adipose capsule – fatty mass that cushions the Adipose capsule – fatty mass that cushions the kidney and helps attach it to the body wallkidney and helps attach it to the body wall

Renal fascia – outer layer of dense fibrous Renal fascia – outer layer of dense fibrous connective tissue that anchors the kidneyconnective tissue that anchors the kidney

Internal Anatomy (Frontal Internal Anatomy (Frontal Section)Section)

Cortex – the light colored, granular superficial Cortex – the light colored, granular superficial regionregion

Medulla – exhibits cone-shaped medullary Medulla – exhibits cone-shaped medullary (renal) pyramids separated by columns(renal) pyramids separated by columns The medullary pyramid and its surrounding The medullary pyramid and its surrounding

capsule constitute a lobecapsule constitute a lobe Renal pelvis – flat funnel shaped tube lateral to Renal pelvis – flat funnel shaped tube lateral to

the hilus within the renal sinusthe hilus within the renal sinus

Internal AnatomyInternal Anatomy Major calyces – large branches of the renal Major calyces – large branches of the renal

pelvispelvis Collect urine draining from papillae Collect urine draining from papillae Empty urine into the pelvisEmpty urine into the pelvis

Urine flows through the pelvis and ureters to Urine flows through the pelvis and ureters to the bladderthe bladder

Blood and Nerve SupplyBlood and Nerve Supply Approximately one-fourth (1200 ml) of Approximately one-fourth (1200 ml) of

systemic cardiac output flows through the systemic cardiac output flows through the kidneys each minutekidneys each minute

Arterial flow into and venous flow out of the Arterial flow into and venous flow out of the kidneys follow similar pathskidneys follow similar paths

The nerve supply is via the renal plexusThe nerve supply is via the renal plexus

Renal Vascular PathwayRenal Vascular Pathway

Figure 25.3c

The NephronThe Nephron Nephrons are the structural and functional Nephrons are the structural and functional

units that form urine, consisting of:units that form urine, consisting of: Glomerulus – a tuft of capillaries associated with a Glomerulus – a tuft of capillaries associated with a

renal tubulerenal tubule Glomerular (Bowman’s) capsule – blind, cup-Glomerular (Bowman’s) capsule – blind, cup-

shaped end of a renal tubule that completely shaped end of a renal tubule that completely surrounds the glomerulussurrounds the glomerulus

The NephronThe Nephron Renal corpuscle – the glomerulus and its Renal corpuscle – the glomerulus and its

Bowman’s capsuleBowman’s capsule Glomerular endothelium – fenestrated epithelium Glomerular endothelium – fenestrated epithelium

that allows solute-rich, virtually protein-free that allows solute-rich, virtually protein-free filtrate to pass from the blood into the glomerular filtrate to pass from the blood into the glomerular capsulecapsule

Anatomy of the Glomerular Anatomy of the Glomerular CapsuleCapsule

The external parietal layer is a structural layerThe external parietal layer is a structural layer The visceral layer consists of modified, The visceral layer consists of modified,

branching epithelial podocytesbranching epithelial podocytes Extensions of the octopus-like podocytes Extensions of the octopus-like podocytes

terminate in foot processesterminate in foot processes Filtration slits – openings between the foot Filtration slits – openings between the foot

processes that allow filtrate to pass into the processes that allow filtrate to pass into the capsular spacecapsular space

Renal TubuleRenal Tubule Proximal convoluted tubule (PCT) – Proximal convoluted tubule (PCT) –

composed of cuboidal cells with numerous composed of cuboidal cells with numerous microvilli and mitochondriamicrovilli and mitochondria Reabsorbs water and solutes from filtrate and Reabsorbs water and solutes from filtrate and

secretes substances into itsecretes substances into it

Renal TubuleRenal Tubule Loop of Henle – a hairpin-shaped loop of the Loop of Henle – a hairpin-shaped loop of the

renal tubulerenal tubule Proximal part is similar to the proximal convoluted Proximal part is similar to the proximal convoluted

tubuletubule Proximal part is followed by the thin segment Proximal part is followed by the thin segment

(simple squamous cells) and the thick segment (simple squamous cells) and the thick segment (cuboidal to columnar cells)(cuboidal to columnar cells)

Distal convoluted tubule (DCT) – cuboidal Distal convoluted tubule (DCT) – cuboidal cells without microvilli that function more in cells without microvilli that function more in secretion than reabsorptionsecretion than reabsorption

Connecting TubulesConnecting Tubules The distal portion of the distal convoluted The distal portion of the distal convoluted

tubule nearer to the collecting ductstubule nearer to the collecting ducts

Connecting TubulesConnecting Tubules Two important cell types are found hereTwo important cell types are found here

Intercalated cellsIntercalated cells Cuboidal cells with microvilli Cuboidal cells with microvilli Function in maintaining the acid-base balance of the Function in maintaining the acid-base balance of the

bodybody Principal cellsPrincipal cells

Cuboidal cells without microvilliCuboidal cells without microvilli Help maintain the body’s water and salt balanceHelp maintain the body’s water and salt balance

NephronsNephrons Cortical nephrons – 85% of nephrons; located Cortical nephrons – 85% of nephrons; located

in the cortexin the cortex Juxtamedullary nephrons:Juxtamedullary nephrons:

Are located at the cortex-medulla junctionAre located at the cortex-medulla junction Have loops of Henle that deeply invade the Have loops of Henle that deeply invade the

medulla medulla Have extensive thin segmentsHave extensive thin segments Are involved in the production of concentrated Are involved in the production of concentrated

urineurine

Capillary Beds of the NephronCapillary Beds of the Nephron Every nephron has two capillary bedsEvery nephron has two capillary beds

Glomerulus Glomerulus Peritubular capillariesPeritubular capillaries

Each glomerulus is: Each glomerulus is: Fed by an afferent arteriole Fed by an afferent arteriole Drained by an efferent arterioleDrained by an efferent arteriole

Capillary Beds of the NephronCapillary Beds of the Nephron Blood pressure in the glomerulus is high Blood pressure in the glomerulus is high

because:because: Arterioles are high-resistance vesselsArterioles are high-resistance vessels Afferent arterioles have larger diameters than Afferent arterioles have larger diameters than

efferent arteriolesefferent arterioles Fluids and solutes are forced out of the blood Fluids and solutes are forced out of the blood

throughout the entire length of the glomerulusthroughout the entire length of the glomerulus

Capillary BedsCapillary Beds Peritubular beds are low-pressure, porous Peritubular beds are low-pressure, porous

capillaries adapted for absorption that: capillaries adapted for absorption that: Arise from efferent arteriolesArise from efferent arterioles Cling to adjacent renal tubulesCling to adjacent renal tubules Empty into the renal venous systemEmpty into the renal venous system

Vasa recta – long, straight efferent arterioles of Vasa recta – long, straight efferent arterioles of juxtamedullary nephrons juxtamedullary nephrons

Vascular Resistance in Vascular Resistance in MicrocirculationMicrocirculation

Afferent and efferent arterioles offer high Afferent and efferent arterioles offer high resistance to blood flowresistance to blood flow

Blood pressure declines from 95mm Hg in Blood pressure declines from 95mm Hg in renal arteries to 8 mm Hg in renal veinsrenal arteries to 8 mm Hg in renal veins

Vascular Resistance in Vascular Resistance in MicrocirculationMicrocirculation

Resistance in afferent arterioles:Resistance in afferent arterioles: Protects glomeruli from fluctuations in systemic Protects glomeruli from fluctuations in systemic

blood pressureblood pressure Resistance in efferent arterioles:Resistance in efferent arterioles:

Reinforces high glomerular pressureReinforces high glomerular pressure Reduces hydrostatic pressure in peritubular Reduces hydrostatic pressure in peritubular

capillaries capillaries

Juxtaglomerular Apparatus Juxtaglomerular Apparatus (JGA)(JGA)

Where the distal tubule lies against the afferent Where the distal tubule lies against the afferent (sometimes efferent) arteriole(sometimes efferent) arteriole

Arteriole walls have juxtaglomerular (JG) cellsArteriole walls have juxtaglomerular (JG) cells Enlarged, smooth muscle cells Enlarged, smooth muscle cells Have secretory granules containing reninHave secretory granules containing renin Act as mechanoreceptorsAct as mechanoreceptors

Juxtaglomerular Apparatus Juxtaglomerular Apparatus (JGA)(JGA)

Macula densaMacula densa Tall, closely packed distal tubule cells Tall, closely packed distal tubule cells Lie adjacent to JG cells Lie adjacent to JG cells Function as chemoreceptors or osmoreceptorsFunction as chemoreceptors or osmoreceptors

Mesanglial cells: Mesanglial cells: Have phagocytic and contractile propertiesHave phagocytic and contractile properties Influence capillary filtrationInfluence capillary filtration

Filtration MembraneFiltration Membrane Filter that lies between the blood and the Filter that lies between the blood and the

interior of the glomerular capsuleinterior of the glomerular capsule It is composed of three layersIt is composed of three layers

Fenestrated endothelium of the glomerular Fenestrated endothelium of the glomerular capillariescapillaries

Visceral membrane of the glomerular capsule Visceral membrane of the glomerular capsule (podocytes)(podocytes)

Basement membrane composed of fused basal Basement membrane composed of fused basal laminae of the other layerslaminae of the other layers

Mechanisms of Urine FormationMechanisms of Urine Formation The kidneys filter the body’s entire plasma The kidneys filter the body’s entire plasma

volume 60 times each dayvolume 60 times each day The filtrate:The filtrate:

Contains all plasma components except proteinContains all plasma components except protein Loses water, nutrients, and essential ions to Loses water, nutrients, and essential ions to

become urinebecome urine The urine contains metabolic wastes and The urine contains metabolic wastes and

unneeded substancesunneeded substances

Mechanisms of Urine FormationMechanisms of Urine Formation Urine formation Urine formation

and adjustment of and adjustment of blood composition blood composition involves three involves three major processes major processes Glomerular Glomerular

filtrationfiltration Tubular Tubular

reabsorptionreabsorption SecretionSecretion

Figure 25.8

Glomerular FiltrationGlomerular Filtration Principles of fluid dynamics that account for Principles of fluid dynamics that account for

tissue fluid in all capillary beds apply to the tissue fluid in all capillary beds apply to the glomerulus as wellglomerulus as well

The glomerulus is more efficient than other The glomerulus is more efficient than other capillary beds because:capillary beds because: Its filtration membrane is more permeableIts filtration membrane is more permeable Glomerular blood pressure is higher Glomerular blood pressure is higher It has a higher net filtration pressureIt has a higher net filtration pressure

Plasma proteins are not filtered and are used to Plasma proteins are not filtered and are used to maintain pressure of the bloodmaintain pressure of the blood

Net Filtration Pressure (NFP)Net Filtration Pressure (NFP)

The pressure responsible for filtrate formationThe pressure responsible for filtrate formation NFP equals the glomerular hydrostatic NFP equals the glomerular hydrostatic

pressure (HPpressure (HPgg) minus the oncotic pressure of ) minus the oncotic pressure of glomerular blood (OPglomerular blood (OPgg) combined with the ) combined with the capsular hydrostatic pressure (HPcapsular hydrostatic pressure (HPcc))

NFP = HPg – (OPg + HPc)

Glomerular Filtration Rate Glomerular Filtration Rate (GFR)(GFR)

The total amount of filtrate formed per minute The total amount of filtrate formed per minute by the kidneysby the kidneys

Factors governing filtration rate at the Factors governing filtration rate at the capillary bed are:capillary bed are: Total surface area available for filtrationTotal surface area available for filtration Filtration membrane permeabilityFiltration membrane permeability Net filtration pressureNet filtration pressure

Glomerular Filtration Rate Glomerular Filtration Rate (GFR)(GFR)

GFR is directly proportional to the NFPGFR is directly proportional to the NFP Changes in GFR normally result from changes Changes in GFR normally result from changes

in glomerular blood pressurein glomerular blood pressure

Regulation of Glomerular Regulation of Glomerular FiltrationFiltration

If the GFR is too high:If the GFR is too high: Needed substances cannot be reabsorbed quickly Needed substances cannot be reabsorbed quickly

enough and are lost in the urineenough and are lost in the urine If the GFR is too low:If the GFR is too low:

Everything is reabsorbed, including wastes that are Everything is reabsorbed, including wastes that are normally disposed ofnormally disposed of

Regulation of Glomerular Regulation of Glomerular FiltrationFiltration

Three mechanisms control the GFR Three mechanisms control the GFR Renal autoregulation (intrinsic system)Renal autoregulation (intrinsic system) Neural controlsNeural controls Hormonal mechanism (the renin-angiotensin Hormonal mechanism (the renin-angiotensin

system)system)

Intrinsic ControlsIntrinsic Controls Under normal conditions, renal autoregulation Under normal conditions, renal autoregulation

maintains a nearly constant glomerular maintains a nearly constant glomerular filtration ratefiltration rate

Autoregulation entails two types of controlAutoregulation entails two types of control Myogenic – responds to changes in pressure in the Myogenic – responds to changes in pressure in the

renal blood vesselsrenal blood vessels Flow-dependent tubuloglomerular feedback – Flow-dependent tubuloglomerular feedback –

senses changes in the juxtaglomerular apparatussenses changes in the juxtaglomerular apparatus

Extrinsic ControlsExtrinsic Controls When the sympathetic nervous system is at When the sympathetic nervous system is at

rest:rest: Renal blood vessels are maximally dilatedRenal blood vessels are maximally dilated Autoregulation mechanisms prevailAutoregulation mechanisms prevail

Extrinsic ControlsExtrinsic Controls Under stress:Under stress:

Norepinephrine is released by the sympathetic Norepinephrine is released by the sympathetic nervous systemnervous system

Epinephrine is released by the adrenal medulla Epinephrine is released by the adrenal medulla Afferent arterioles constrict and filtration is Afferent arterioles constrict and filtration is

inhibited inhibited The sympathetic nervous system also The sympathetic nervous system also

stimulates the renin-angiotensin mechanismstimulates the renin-angiotensin mechanism

Renin-Angiotensin MechanismRenin-Angiotensin Mechanism Is triggered when the JG cells release reninIs triggered when the JG cells release renin Renin acts on angiotensinogen to release Renin acts on angiotensinogen to release

angiotensin I angiotensin I Angiotensin I is converted to angiotensin II Angiotensin I is converted to angiotensin II Angiotensin II: Angiotensin II:

Causes mean arterial pressure to rise Causes mean arterial pressure to rise Stimulates the adrenal cortex to release aldosterone Stimulates the adrenal cortex to release aldosterone

As a result, both systemic and glomerular As a result, both systemic and glomerular hydrostatic pressure risehydrostatic pressure rise

Renin ReleaseRenin Release Renin release is triggered by:Renin release is triggered by:

Reduced stretch of the granular JG cellsReduced stretch of the granular JG cells Stimulation of the JG cells by activated macula Stimulation of the JG cells by activated macula

densa cellsdensa cells Direct stimulation of the JG cells via Direct stimulation of the JG cells via 11-adrenergic -adrenergic

receptors by renal nervesreceptors by renal nerves Angiotensin IIAngiotensin II