urinary system. topics & objectives 1. kidney anatomy function 2. glomerular filtration 3....
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Urinary System
Topics & Objectives
1. Kidney• Anatomy• Function
2. Glomerular filtration
3. Tubular reabsorption & secretion
4. Urine excretion & plasma clearance
Kidney Functions:
Ultimately regulate ECF volume (receive ~ 20% of cardiac output!)
1. Maintain H2O balance in the body
2. Maintain osmolarity
3. Regulation of ECF ions• Na+, Cl-, K+, H+, etc.
4. Maintain plasma volume & acid-base balance
5. Excretion of end products and foreign compounds
6. Producing EPO & renin
Figure 14.1Page 513
Renalvein
Inferiorvena cava
Urinarybladder
Urethra
Ureter
Aorta
Kidney
Renalartery
Ureter
Renalpelvis
Renalpyramid
Renalcortex
Renalmedulla
Nephrons
• ~ 1 million within kidney Functional unit for urine
formation
• Arrangement comprises renal cortex & renal medulla
• Each nephron composed of:1. Vascular component
2. Tubular component
CortexMedulla
Figure 14.3Page 514
CortexMedulla
Proximal tubule
Juxtaglomerularapparatus
Efferentarteriole
Afferentarteriole
Bowman’scapsule
Glomerulus
Distaltubule Collecting
duct
To renalpelvis
Loop of Henle
Peritubularcapillaries
Vascular Component: Glomerulus
• Location for H2O and solute filtration from blood
Arterioles• Afferent: to glomerular
capillaries• Efferent: drains
capillariesNo O2 extraction!
Peritubular capillaries• Supply renal tissue
Efferentarteriole
Afferentarteriole
Glomerulus
Peritubularcapillaries
Tubular Component: Bowman’s capsule
• Collects fluid from glomerulus
Fluid travels to:1. Proximal tubule2. Loop of Henle3. Passes through
juxtaglomerular apparatus Vascular/tubular component
4. Distal tubule
Proximal tubule
Juxtaglomerularapparatus
Bowman’scapsule
Distaltubule
Loop of Henle
Cortical nephron
Juxtamedullary nephron
Urine Formation
1. Glomerular filtration (protein-free)• ~ 20% of the plasma (1st step of urine formation)• ~ 50 gallons each day (PV ~ 65x/day)
2. Tubular reabsorption• Of the 50 gallons filtered, about 98% reabsorbed
3. Tubular secretion• ~ 80% of the plasma into the peritubular
capillaries
GF
Figure 14.6Page 516
80% of the plasmathat enters theglomerulus is not filteredand leaves throughthe efferent arteriole.20% of the
plasma thatenters theglomerulusis filtered.
Urine excretion(eliminatedfrom the body)
To venous system(conservedfor the body)
Peritubularcapillary
Kidneytubule(entire length,uncoiled)
Bowman’scapsule
Glomerulus
Afferentarteriole
Efferentarteriole
TR
TS
Glomerularcapillaries
Efferentarteriole
Peritubularcapillaries
Venousblood
UrineTubule (from proximal tubule to collecting duct)
Bowman’scapsule
Filtratepathway
Bloodpathway
Glomerularfiltration
Tubularreabsorption
Tubularsecretion
Figure 14.7Page 517
Glomerular Filtration
Figure 14.8 (1)Page 518
Glomerulus
Bowman’scapsule
Proximal convoluted tubule
Afferent arteriole Efferent arteriole
Glomerular capillary
Basementmembrane
Glomerular Filtration
Figure 14.8 (3)
Page 518
Endothelialcell
Lumen of glomerularcapillary
Lumen ofBowman’s capsule
Basementmembrane
pores
podocytes
Glomerular Filtration (cont.):
Occurs through pressure gradients…
1. Capillary blood pressure (~55mmHg) Favors filtration
2. Plasma osmotic pressure (~30mmHg) Caused by distribution of plasma proteins across
glomerular membrane Cannot cross into Bowman’s capsule
3. Bowman’s capsule hydrostatic pressure (~15mmHG) Pressure by the fluid
All three pressures determine filtration rate!
1) Changes in BP
2) Osmotic pressure
3) Hydrostatic pressure
Look at Table 14.1!
GFR Regulation1. Autoregulation
• Prevents spontaneous changes in GFR Vasoconstriction & vasodilation
a. Myogenic mechanism – response to stretchb. Tubuloglomerular feedback mechanism
2. Extrinsic sympathetic control• Long-term regulation of arterial BP
Sympathetic nervous system (no parasympathetic activity)
• Baroreceptor reflex
GFR autoregulation
1. Alterations in arteriolar afferent & efferent blood pressures
Afferent arteriole
Glomerulus
Efferent arteriole
Glomerularcapillaryblood pressure
Net filtrationpressure
Arterial blood pressure(increases blood flow into the glomerulus)
GFRFigure 14.10Page 520
Vasoconstriction(decreases blood flowinto the glomerulus)
Afferent arteriole
Glomerulus
Efferent arteriole
Net filtrationpressure
Glomerularcapillaryblood pressure
GFR
GFR autoregulation (cont.)
Afferent arteriole
Glomerulus
Efferent arteriole
Net filtrationpressure
Glomerularcapillaryblood pressure
GFR
Vasodilation(increases blood flowinto the glomerulus)
GFR autoregulation
1. Smooth muscle cells within afferent arterioleGranular cells – secretory
capabilities
2. Tubular cells (macula densa)Detect changes in the rate
of fluid passing through tubuleBring about
vasoconstriction or vasodilation
Efferentarteriole
Distaltubule
Bowman’scapsule
Afferentarteriole
GFR Autoregulation – Tubuloglomerular feedback
Efferentarteriole
Smoothmusclecell
Maculadensa
Distaltubule
Afferentarteriole
Granular cells
Podocyte
Glomerularcapillaries
Lumen ofBowman’scapsule
Endothelialcell
Arterial blood pressure
Driving pressure into glomerulus
Glomerular capillary pressure
GFR
Rate of fluid flow through tubules
Stimulation of macula densa cells to release vasoactive chemicals
Chemicals released that induce afferent arteriolar vasoconstriction
Blood flow into glomerulus
Glomerular capillary pressure to normal
GFR to normal
Extrinsic Control – Baroreceptors
Response to decreased BP• Sympathetically induced vasoconstriction• Afferent arterioles (sympathetically innervated)
Response to increased BP• Sympathetic stimulation decreases
Short-termadjustment for
Arterial blood pressure
Long-termadjustment for
Arterialblood pressure
Detection by aortic arch and carotid sinus baroreceptors
Cardiac output
Total peripheral resistance
Sympathetic activity
Generalized arteriolar vasoconstriction
Afferent arteriolar vasoconstriction
Glomerular capillary blood pressure
GFR
Urine volume
Conservation of fluid and salt
Arterial blood pressure
Tubular Reabsorption
GF
Figure 14.6Page 516
Peritubularcapillary
Bowman’scapsule
Glomerulus
Afferentarteriole
Efferentarteriole
TR
Tubular reabsorption: Ultimately attempting to maintain body’s
internal environment• Proper composition & volume
Filtered substance reabsorbed
Filtered substance excreted
Water 99 1
Sodium 99.5 0.5
Glucose 100 0
Urea (waste product) 50 50
Phenol (waste product) 0 100
Table 14.2
Tubularlumen
Tubularepithelial cell
Peritubularcapillary
Plasma
Tightjunction
4) Interstitialfluid
Material must pass through the cells (5 steps)
Figure 14.17Page 526
1) Luminalmembrane
5) Capillary wall
3) Basolateralmembrane
2) Cytosol
Transepithelial transport
Passive & Active Reabsorption
1. Passive: all steps follow electrochemical or osmotic gradients
2. Active: any one of the steps requiring energy• Sodium (80% of kidney’s total energy
requirement) ~ 67% in proximal tubule ~ 25% in loop of Henle ~ 8% in distal and collecting tubules
• Glucose• Phosphate
Constant percentage of Na+ reabsorption
Lumen Tubular cell Interstitial fluidPeritubularcapillary
Figure 14.18Page 527
Na+ pumped out against concentration gradient• Creates higher concentration in interstitial fluid &
allows for passive diffusion back into lumen
Diffusion
Diffusion
Na+
channelActive transport
BasolateralNa+– K+ ATPasecarrier
Distal tubule (~ 8% of total reabsorption) is hormonally regulated
• Related to total Na+ load in bodyChanges in ECF affect
osmotic pressuresex: Increased Na+ in ECF
causes increased H2O in ECF
• Ultimately regulates blood pressureRenin-angiotensin-
aldosterone system ↑Atrial natriuretic peptide ↓
Distaltubule
Granular cells release renin• In response to fall of NaCl/ ECF volume/ BP• Recognized by intrarenal baroreceptors
Sympathetic response to secrete more renin
• Ultimately trying to increase plasma volume
Within juxtaglomerular apparatus…
Figure 14.19Page 529
Liver Kidney LungsAdrenalcortex
Kidney
H2Oconserved
Na+ (and CI–)osmotically holdmore H2O in ECF
Na+ (and CI–)conserved
Vasopressin Thirst Arteriolarvasoconstriction
H2O reabsorption
by kidney tubules Fluid intake
NaCl / ECF volume /
Arterial blood pressure
Na+ reabsorption by kidney tubules ( CI– reabsorptionfollows passively)
Renin
Angiotensin-convertingenzyme
Angiotensinogen Angiotensin I Angiotensin II Aldosterone
Helps correct Helps correct
Cardiacatria
Atrial natriuretic peptide
Na+ reabsorptionby kidney tubules
Salt-conservingrenin-angiotensin-aldosterone system
Smooth muscleof afferent arterioles
Sympatheticnervous system
Afferentarteriolarvasodilation
Na+ excretion in urine
H2O excretion in urine
Na+ and H2O filtered
GFR
Cardiacoutput
Totalperipheralresistance
Arterial bloodpressure
NaCl / ECF volume /Arterial blood pressure
Figure 14.20Page 530
Inhibits aldosterone & renin secretion
Glucose and amino acid reabsorption• Na+ dependent secondary active transport
Co-transporters that do not require energy
• Maximal reabsorption rate depends on substance
No energyrequired
Cotransport carrier
No energyrequired Glucose
carrierBasolateralborder
Energyrequired
Na+–K+ pump
Blood vessel
Luminal border
Phosphate & Calcium reabsorption• Dependent upon total body content• Regulated by kidneys
Hormonally (parathyroid hormone)
Na+ reabsorption responsible for passive reabsorption of Cl-, H2O, and urea
Lumen Proximal tubular cell Peritubular capillaryInterstitial fluid
H2O (passive) reabsorption
• 80% in proximal tubules & loops of Henle
Figure 14.22Page 533
Osmosis
Osmosis
Hydrostaticpressure
Waterchannel
Glomerulus
Bowman’scapsule
Beginning ofproximaltubule
End ofproximaltubule
= Urea molecules
Peritubularcapillary
Urea (passive) reabsorption• Waste product of
protein• Becomes
increasingly concentrated
Na+ (active)
H2O (osmosis)
Na+ (active)
H2O (osmosis)
Passive diffusionof urea down itsconcentration gradient
44 mloffiltrate
125 mloffiltrate
Figure 14.23
Page 534
Tubular Secretion
Figure 14.6Page 516
Afferentarteriole
Efferentarteriole
Glomerulus
Bowman’scapsule
Kidneytubule(entire length,uncoiled)
Peritubularcapillary
GF
TS
Tubular secretion:
Hydrogen ions (H+)• Acid-base regulation throughout the body
Potassium (K+)• Early reabsorption into tubules not regulated• Secretion in distal tubules regulated
Na+-K+ pumpAldosterone
Organic anions & cations• Foreign compounds, chemical messengers
Renin
Angiotensin I
Angiotensin IIPlasma K+
Aldosterone
Tubular K+ secretion
Urinary K+ excretion
Tubular Na+ reabsorption
Urinary Na+ excretion
Na+/ ECF volume/arterial pressure
Figure 14.25Page 536
Aldosterone - dual regulation
1) Na+ & K+
Plasma Clearance
Fig. 14.26a Page 539
Glomerulus
Tubule
Peritubularcapillary
Inurine
Substance:
1) Filtered
2) NOT reabsorbed
3) NOT secreted
All filtered plasma is
cleared of substance
Substance:
1) Filtered
2) NOT secreted
3) Completely reabsorbed
None of filtered plasma is
cleared of substance
Substance:
1) Filtered
2) NOT secreted
3) Partially reabsorbed
Portion of filtered plasma is
cleared of substance
Substance:
1) Filtered
2) Secreted
3) NOT reabsorbed
ALL of filtered plasma is
cleared of substance
Regulation of plasma H2O
Fluids & solutes• Normal balance in body fluids called isotonic
300 mosm/liter
• HypotonicToo much H2O compared to solute (osmolality < 300)
• HypertonicToo little H2O compared to solute (osmolality > 300)
Osmotic gradient maintained in interstitial fluid of medulla• Dependent upon hydration levels
Descending limbof loop of Henleof juxtamedullarynephron
Medullaryinterstitial fluid
Fromproximaltubule
Todistaltubule
Medullaryinterstitial fluid
Ascending limbof loop of Henleof juxtamedullarynephron
Initial scene
Fig. 14.28a (2)Page 542
Step 1
Fromproximaltubule
Todistaltubule
Step 2
Step 3
Fromproximaltubule
Todistaltubule
Step 4
Step 5
Step 6 and on
Fromproximaltubule
Todistaltubule
Tubularlumenfiltrate Distal tubular cell
Peritubularcapillaryplasma
Waterchannel
Figure 14.29
Page 544
Further regulation Vasopressin
• Anti-diuretic hormone from hypothalamus
Increases permeability ofluminal membrane to H2Oby inserting newwater channels