Chapter 14Chapter 14
The Urinary SystemThe Urinary System
V. Pag. 511-557
VI. Pag. 501-545
Functions of the KidneysWater balance and control of osmolarityin body fluids
Regulation of electrolyte concentration
Maintain acid-base balance by regulating H+ and HCO3
- urinary output
Excretion of waste products (urea, creatinine)
Excretion of drug products
Production of erythropoietin (to stimulate red blood formation)
Renin production to control salt conservation
Cardiac Output/Kidney
On average, 20 to 25 percent of the cardiac output passes through the pair of kidneys each minute. Therefore, over a very short time span the entire blood volume of the body passes through the kidneys for control of its chemical composition.
Each minute, the remaining 75 to 80 percent of the cardiac output is pumped from the heart to the other tissues of the body. This blood supplies cells with their metabolic needs (oxygen, glucose, etc.).
Organs of the Urinary System
Urinary system:1) Urine forming organ-
kidneys
2) Urine storage/release structures: urinary bladder, ureter, urethra
Functional Unit of Kidneys: NephronThere are two regions in the
kidneys:1) Renal cortex2) Renal Medulla
Each nephron consist of two areas:
1) Vascular componenta) Glomerulusb) Afferent/efferent arterioles
2) Tubular componenta) Bowman’s capsuleb) Proximal tubulec) Loop of Henled) Distal tubulee) Collecting tubule
Vascular and Tubular Components of the Nephron
Proximal tubule Distaltubule Collecting
duct
Bowman’scapsule
Glomerulus
CortexMedulla
Loop of Henle
To renalpelvis Overview of Functions of Parts of a Nephron
Peritubularcapillaries
Vein
Artery
Afferentarteriole
Efferentarteriole
Juxtaglomerularapparatus
Juxtamedullary vs. Cortical Nephrons
Proximaltubule
Distaltubule
Distaltubule Glomerulus
Bowman’scapsule
Proximaltubule
Loop of Henle
Other nephrons emptying intothe same collecting duct
Collectingduct
Ascendinglimb ofloop ofHenle
To renalpelvis
Vasa recta
Descendinglimb ofloop ofHenle
Medulla
Cortex
Juxtamedullary vs. Cortical Nephrons
Juxtamedullary Nephron(20 %)
Cortical Nephron(80 %)
Glomerulus located in inner layer of cortex
Glomerulus located in outer layer of cortex
Peritubular capillaries form a straight vessel (or vasa recta)
that runs along the loop of Henle
Branched peritubular capillaries surround loop
of Henle
Involved in the formation of very concentrated urine
Renal Processes
The kidneys regulate the composition of the ECF through three processes that occur in the nephrons. As a result of these three processes we have urine formation and excretion.
These processes are:
1) Glomerular filtration (~20%)
2) Tubular reabsorption
3) Tubular secretion (~80%)
Renal Processes
Glomerular Filtration
Tubular reabsorption
Tubular secretion
Glomerulus & Bowman’s capsule
Proximal tubules & loop of Henle
Involved in the formation of very
concentrated urine
Distal & collecting tubules
Filter 20% of blood plasma
Filter 80% of blood plasma
Sequence of Blood and Fluid Flow
180 L/day 178.5 L/day 1.5L/day
Glomerular FiltrationAfferent arteriole Efferent arteriole
Glomerulus
Bowman’scapsule
Lumen ofBowman’scapsule
Outer layer ofBowman’s capsule
Inner layerof Bowman’s capsule(podocytes)
Proximal convoluted tubule
Lumen ofglomerularcapillary
Endothelialcell
•Basement•membrane
Podocytefoot process
Blood Plasma is Filtered Through Three Layers :
1) Capillaries’ endothelial cells2) Basement membrane - collagen & glycoproteins3) Epithelial cells (podocytes) in Bowman’s capsule
Podocytefoot process
Filtrationslit
Basementmembrane
Capillarypore
(see next slide)
Podocytefoot process
Filtrationslit
•Basement•membrane
Capillarypore
Endothelialcell
Lumen of glomerularcapillary
Lumen ofBowman’s capsule
Forces Driving Glomerular FiltrationThe glomerular filtration rate develops by the interaction of several pressures.
Capillary blood pressure (CBP~55 mm Hg) due to differences in diameter of afferent and efferent arterioles
Plasma osmotic pressure (POP~30 mm Hg)
Bowman’s capsule hydrostatic pressure (HP~15 mm Hg)
Net filtration pressure ~10 mm Hg
CBP
POP HP
Influence of Total Peripheral Resistance on Mean Arterial Pressure
Capillary blood pressure (except kidneys)
Capillary blood pressure in kidneys
11 mm Hg(ultrafiltration)
Interstitial fluid
From arteriole To venule
-9 mm Hg(reabsorption)
Initial lymphaticvessel
Blood capillary
Glomerular capillary
blood pressure(55)
Plasmaosmotic pressure
(30)
Bowman’s capsulehydrostatic pressure
(15)
Differences in the driving forces driving glomerular filtration in kidneys and capillary
filtration in other organs
Glomerular Filtration Rate (GFR)
Net Filtration P= Blood plasma P –(Osmotic P + Hydrostatic P)= 10 mm Hg
Osmotic P: can change as a result of albuminuria, increased albumin filtration
Hydrostatic P: can increase due to urinary tract obstruction (kidney stones)
CBP (55)
POP(30)
HP(15)
Glomerular Filtration Rate (GFR)GFR = K x Net Filtration Pressure
Net Filtration Pressure is mainly determined by Capillary Blood Plasma (CBP)
Where: K is filtration coefficient, proportional to filtration area. Notice K is not a constant because filtration area can change as a result of podocyte contraction
CBP
POP HP
•Glomerular•basement•membrane
•Glomerular•capillary lumen
•Glomerular•capillary•loop
•Podocyte foot processes •Filtration•slit
•Bowman’s•capsule•lumen
Capillary Blood Pressure is the Critical Factor Driving Glomerular Filtration
Regulation of GFR:1) Intrinsic Factors (Autoregulation):
acting at the level of the kidneys to autoregulate GFR within MAP of 80-180 mm Hg
a) Myogenic activity of vascular tissue
b) Activity of the juxtaglomerularapparatus
2) Extrinsic Factor: Sympathetic Stimulation
Slide 12
Fig. 14.11aPage 521
Vasoconstriction(decreases blood flowinto the glomerulus)
Afferent arteriole
Glomerulus
Efferent arteriole
Glomerularcapillaryblood pressure
Net filtrationpressure
GFR
When mean arterial pressure increase
Afferent arteriole
Glomerulus
Efferent arteriole
Glomerularcapillaryblood pressure
Net filtrationpressure
GFR
Vasodilation(increases blood flowinto the glomerulus)
When mean arterial pressure decrease
Juxtaglomerular ApparatusMacula dense cells can detect changes in flow rate and
release vasoactive substances (vasoconstrictors and vasodilators) that alter capillary blood flow.
Pressure sensorsSecrete reninSense changes in
flow rateSecrete vasoactive
substances
Juxtaglomerular Apparatus Regulates GFR
Slide 16
Figure 14.13Page 523
Arterial blood pressure
Driving pressure into glomerulus
Glomerular capillary pressure
GFR
Rate of fluid flowthrough tubules
Stimulation of macula densa cellsto release vasoactive chemicals
Chemicals released that induceafferent arteriolar vasoconstriction
Blood flow into glomerulus
Glomerular capillary pressureto normal
GFR to normal
Regulation of GFR by Baroreceptor Reflex and Sympathetic Activity
The idea here is toincrease blood volume when drop in blood pressure occurs
Slide 17
Short-termadjustment for
Arterial blood pressure
Long-termadjustment for
Arterialblood pressure
Detection by aorticarch and carotid sinusbaroreceptors
Cardiacoutput
Totalperipheralresistance
Sympathetic activity
Generalizedarteriolar vasoconstriction
Afferent arteriolarvasoconstriction
Glomerular capillaryblood pressure
GFR
Urine volume
Conservation of fluid and salt
Arterial blood pressure
Figure 14.14Page 523
Glomerular filtration rate (GFR) can be regulated by changes in the filtration
coefficient (K)
GFR = Kf x net filtration pressure
Podocytefoot process
Filtrationslit
Basementmembrane
Capillarypore
(see next slide)
Podocytefoot process
Filtrationslit
•Basement•membrane
Capillarypore
Endothelialcell
Lumen of glomerularcapillary
Lumen ofBowman’s capsule
Sequence of Blood and Fluid Flow
Renal Processes-ReabsorptionThe kidneys regulate the
composition of the ECF through three processes that occur in the nephrons. As a result of these three processes urine is formed and excreted
These processes are:1) Glomerular filtration (~20%)
2) Tubular reabsorption- allows the recovery of Na+, Cl-, H2O, glucose, amino acids and other substances
3) Tubular secretion (~80%)
Barriers for Tubular ReabsorptionTrans-epithelial Transport
Transepitheliar TransportPassive reabsorption - mov. of substances down concentration or osmotic gradient (Cl-, H2O, urea)Active reabsorption - requires energy for transport
of Na+, glucose, amino acids
Na+ ReabsorptionNa+/K+ APTase in basolateral membrane
generate a Na+ gradient
© Brooks/Cole - Thomson Learning
Basolateral membrane
Regional Differences in Tubular Na+
ReabsorptionNa+ reabsorption takes place in:1) proximal tubules (67%) drives
reabsorption of glucose, AA and Cl-
2) ascending loop of Henle (25%) produce urine of varying concentrations
3) distal/collecting tubules (8%) subject to hormonal control
Notice: Na+ reabsorption does not occur in descending loop of Henle. In descending loop of Henle water reabsorption takes place
No Na+
reabsorption
Regional Differences in Tubular Na+
Reabsorption
No Na+reabsorption
In proximal tubule, Na+ reabsorption occurs independently of Na+
load (total amount of Na+ not Na+
concentration)
In distal tubules, Na+ reabsorption is controlled by aldosterone
Renin-Angiotensin-Aldosterone Regulates Na+ Reabsorption
Aldosterone acting on distal/collecting tubules, drives the insertion of new Na+ channels and Na+/K+ ATPases in tubular cells
Slide 23
Figure 14.19Page 529
NaCl / ECF volume /
Arterial blood pressure
Liver Kidney Lungs Adrenalcortex Kidney
H2Oconserved
Na+ (and CI–)osmotically holdmore H2O in ECF
Na+ (and CI–)conserved
Na+ reabsorptionby kidney tubules( CI–
reabsorptionfollows passively)
Vasopressin Thirst Arteriolarvasoconstriction
H2O reabsorptionby kidney tubules
Fluid intake
ReninAngiotensin-convertingenzyme
Angiotensinogen Angiotensin I Angiotensin II Aldosterone
Aldosterone FunctionAldosterone stimulates Na+ reabsorption by
promoting the insertion of new Na+ channels in the luminal membrane and additional Na+/K+
ATPase carriers in the basolateral membrane
© Brooks/Cole - Thomson Learning
Granular Cells in JuxtaglomerularApparatus Release Renin
1) Macula densa cells sense changes inNaCl/ECF volume and induce the release of renin by granular cell
2) Granular cells sense changes in blood pressure and release renin
3) Drop in blood pressure activate sympathetic NS, that triggers stimulation of granular cells and renin release
Other Functions of the Renin-Angiotensin-Aldosterone System
Slide 23
Figure 14.19Page 529
NaCl / ECF volume /
Arterial blood pressure
Liver Kidney Lungs Adrenalcortex Kidney
H2Oconserved
Na+ (and CI–)osmotically holdmore H2O in ECF
Na+ (and CI–)conserved
Na+ reabsorptionby kidney tubules( CI–
reabsorptionfollows passively)
Vasopressin Thirst Arteriolarvasoconstriction
H2O reabsorptionby kidney tubules
Fluid intake
ReninAngiotensin-convertingenzyme
Angiotensinogen Angiotensin I Angiotensin II Aldosterone
Water conservation
Arteriolar vasoconstriction
Water/fluid intake
Vasopressin release is controlled by ECF volume, MAP, and aldosterone
Slide 11
Figure 18.10Page 684
Paraventricularnucleus
Neurosecretoryneurons
Supraopticnucleus
Hypothalamic–posteriorpituitary stalk
Hypothalamus
Anteriorpituitary
Posterior pituitary
Systemicarterial inflow
Systemicvenous outflow
= Vasopressin
= Oxytocin
Vasopressin-releasing cells
Vasopressin (or antidiuretic hormone) stimulate H2O retention in distal/collecting tubules
Atrial Natriuretic Peptide (ANP) Inhibits Na+ Reabsorption
ANP is released by myocardial cells when they sense an increase in NaCl/ ECF volume
Slide 24
Helps correct Helps correctNaCl / ECF volume /Arterial blood pressure
Cardiacatria
Atrial natriuretic peptide
Na+ reabsorptionby kidney tubules
Salt-conservingrenin-angiotensin-aldosterone system
Smooth muscleof afferent arterioles
Sympatheticnervous system
Afferentarteriolarvasodilation
Cardiacoutput
Totalperipheralresistance
Na+ excretionin urine
H2O excretionin urine
GFR
Na+ and H2O filtered
Arterial bloodpressure
Figure 14.20Page 530
ANP inhibits renin and Aldosterone secretion, & Na+ reabsorption
Vasodilation
Active Transport of Glucose and Amino Acids Is Driven by the Na+ Gradient
Transport of glucose/ amino acids (AA) occurs only in proximal tubules by specialized cotransport systems
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Glucose, AA
Na+
Regional Differences in Tubular Glucose Reabsorption
Slide 4
Figure 14.3Page 514
Proximal tubule Distaltubule Collecting
duct
Bowman’scapsule
Glomerulus
CortexMedulla
Loop of Henle
To renalpelvis Overview of Functions of Parts of a Nephron
Peritubularcapillaries
Vein
Artery
Afferentarteriole
Efferentarteriole
Juxtaglomerularapparatus
Glucosereabsorption takes place in:
1) proximal tubules
Passive Cl- Reabsorption is Driven by Na+ Gradient
© Brooks/Cole - Thomson Learning
Cl-
Passive Reabsorption of WaterWater molecules pass through aquaporins or water channels
High osmolarity in interstitial fluid (created by active Na+ transport) drives water movement
The number of waterchannels in distal/collectingtubules is controlled byvasopressin
Passive Urea Reabsorption is Driven by Na+ Gradient
Urea is a waste product formed by the breakdown of proteins
Not all Actively Reabsorbed Substances Are Equally Regulated by
KidneysCarrier saturation limits
transport of a substance in tubules- tubular maximum
If concentration of substance in tubules goes above tubular maximumexcretion will take place-renal threshold
Kidneys do not regulate glucose plasma levels= role of endocrine sys. and liver
Kidneys regulate PO43-
plasma levels
[Glucose] 125 mg
[PO43- ]
300 mg
Renal Processes-SecretionThe kidneys regulate the composition
of the ECF through three processes that occur in the nephrons. As a result of these three processes urine is formed and excreted.
These processes are:
1) Glomerular filtration (~20%)
2) Tubular reabsorption
3) Tubular secretion (~80%) involved in the transepithelial movement of K+, H+ and organic ions
Sequence of Blood and Fluid Flow
Tubular secretion allowsthe movement of K+, H+, organic cations and anions intothe tubules from the blood by transepithelial transport
K+ SecretionK+ ions move out of peritubular capillaries along the
nephron but they are only secreted in distal/collecting tubules because K+ channels are located
in the luminal membrane
K+ SecretionIn proximal tubules K+ ions move back into the interstitial
fluid because K+ channels are found only in the basolateral membrane
© Brooks/Cole - Thomson Learning
K+
Increased K+ Concentration Stimulates Aldosterone Release
Increased K+
concentration in extracellular space can result in changes in resting membrane potential.
K+-induced aldosterone release increases K+ secretion
Transport Processes in Nephron
Glomerular filtrationNa+ K+ Glucose AAUrea Cl- H+ Water
Proximal tubules reabsorptionActive Na+ Glucose AA
Passive Urea Cl-
Water channels always open
Descending loop of HenleH2O reabsorption
No active Na+
Ascending loop of HenleActive Na+
No H2O transport
Distal/collecting tubules Reabsorption:
Active Na+ regulated by aldosterone
Passive Urea Cl-
Water channels only open in response to vasopressin
Secretion:K+ H+ organic ions
Why there is no secretion of K+ in proximal tubules?
Vertical Osmotic GradientIs generated because different parts of the loop of Henle have
different permeabilities to NaCl and water. It allows the kidneys to secrete urine of varying concentrations
Renal medulla
Renal cortex
Factors that Induce Formation of Vertical Osmotic Gradient
Proximaltubule
Distaltubule
DistaltubuleGlomerulus
Bowman’scapsule
Proximaltubule
Loop of Henle
Other nephrons emptying intothe same collecting duct
Collectingduct
Ascendinglimb ofloop ofHenle
To renalpelvis
Vasa recta
Descendinglimb ofloop ofHenle
Medulla
Cortex
Anatomical1) Loop of Henle in
juxtamedullary nephrons go deep into renal medulla
2) Vasa recta and loop of Henle flow in parallel
Physiological1) Different permeabilities of
ascending and descending loop of Henle to Na+ and H2O
http://www.cellphys.ubc.ca/undergrad_files/301KKurine_anim.htmhttp://www.colorado.edu/kines/Class/IPHY3430-200/13urinar.html
Descending loop of Henle-Permeable to water-Does not reabsorb NaCl
Ascending loop of Henle-Impermeable to water-Actively reabsorb NaCl
Permeability to NaCl and Water in Loop of Henle
Functional Consequence of Differential Permeabilities in Loop of Henle:
Countercurrent System
High osmolarity in interstitial fluid of renal medulla can be used to control urine concentration by vasopressin
Functional Significance of Countercurrent System
Regulation of Urine Concentration by Vasopressin
Fromproximaltubule
Filtrate has concentrationof 100 mosm/liter as itenters distal andcollecting tubules
In the face of water deficit: vasopressin stimulates water movement out of distal/collecting tubules
Collectingtubule
Loop ofHenle
Medulla
Cortex
Distal tubule
Concentration ofurine may be upto 1,200 mosm/literas it leavescollecting tubule
= permeability to H2Oincreased by vasopressin
= passive diffusion of H2O
= active transport of NaCl
= portions of tubule impermeable to H2O
*
*
*
*
Fromproximaltubule
Filtrate has concentrationof 100 mosm/liter as itenters distal andcollecting tubules
In the face of water excess: vasopressin secretion decreases and excess water is removed in urine
Collectingtubule
Loop ofHenle
Medulla
Cortex
Distal tubule
Concentration ofurine may be as lowas 100 mosm/literas it leavescollecting tubule
= permeability to H2Oincreased by vasopressin
= passive diffusion of H2O
= active transport of NaCl
= portions of tubule impermeable to H2O
*
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter27/animation__micturition_reflex.htmlhttp://camel2.conncoll.edu/academics/zoology/courses/zoo202/Excretory/micturition.html
MicturationEmptying of the Bladder
Slide 3
Female Male
Urethra
Externalurethralorifice
Ureter
Smoothmuscleof bladderwall
Ureteralopenings
Internalsphincter
Pelvicdiaphragm
Externalsphincter
Prostate gland(an accessorysex gland)
Bulbourethralglands(accessorysex glands)
Externalurethralorifice
Urethra
Figure 14.2Page 513
Bladder consist of inner layer of epithelial tissue and outer layer of smooth muscle innervated by parasympathetic NS
Emptying of bladder requires opening of internal sphincter (smooth muscle) and external sphincter (skeletal muscle)
http://camel2.conncoll.edu/academics/zoology/courses/zoo202/Excretory/micturition.html
MicturationIs driven by the micturation reflex (a spinal reflex) and voluntary
control
Slide 49
Figure 14.32Page 552
Reflex control Voluntary controlBladder fills
Stretch receptors
Parasympathetic nerve
Bladder
Bladder contracts
Internal urethralsphincter mechanicallyopens when bladdercontracts
Cerebral cortex
Motor neuron toexternal sphincter
External urethralsphincter openswhen motor neuronis inhibited
External urethralsphincter remainsclosed when motorneuron is stimulated
No urinationUrination
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