1. Regulating total water volume and total solute concentration in water
Kidney Functions
Regulating total water volume and total solute concentration in water
Regulating ECF ion concentrations
Ensuring long-term acid-base balance
Removal of metabolic wastes, toxins, drugs
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2. Activation of vitamin D
Kidney Functions
Endocrine functions
Renin - regulation of blood pressure
Erythropoietin - regulation of RBC production
Activation of vitamin D
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3. Kidneys - major excretory organs
Urinary System Organs
Kidneys - major excretory organs
Ureters - transport urine from kidneys to urinary bladder
Urinary bladder - temporary storage reservoir for urine
Urethra transports urine out of body
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4. Figure 25.1 The urinary system.
Hepatic veins (cut)
Esophagus (cut)
Inferior vena cava
Renal artery
Adrenal gland
Renal hilum
Aorta
Renal vein
Kidney
Iliac crest
Ureter
Rectum (cut)
Uterus (part of female
reproductive system)
Urinary
bladder
Urethra
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5. Internal Anatomy Renal cortex Renal medulla
Granular-appearing superficial region
Renal medulla
Composed of cone-shaped medullary (renal) pyramids
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6. Figure 25.4a Blood vessels of the kidney.
Cortical radiate
vein
Cortical radiate
artery
Arcuate vein
Arcuate artery
Interlobar vein
Interlobar artery
Segmental arteries
Renal vein
Renal artery
Renal pelvis
Ureter
Renal medulla
Renal cortex
Frontal section illustrating major blood vessels
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7. Structural and functional units that form urine
Nephrons
Structural and functional units that form urine
> 1 million per kidney
Two main parts
Renal corpuscle
Renal tubule
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8. Two parts of renal corpuscle
Glomerulus
Tuft of capillaries; fenestrated endothelium  highly porous  allows filtrate formation
Glomerular capsule (Bowman's capsule)
Cup-shaped, hollow structure surrounding glomerulus
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9. Figure 25.5 Location and structure of nephrons.
Renal cortex
Renal medulla
Renal pelvis
Glomerular capsule: parietal layer
Basement
membrane
Ureter
Podocyte
Kidney
Fenestrated endothelium
of the glomerulus
Renal corpuscle
• Glomerular capsule
Glomerular capsule: visceral layer
• Glomerulus
Distal
convoluted
tubule
Apical
microvilli
Mitochondria
Highly infolded basolateral
membrane
Proximal
convoluted
tubule
Proximal convoluted tubule cells
Cortex
Apical side
Medulla
Basolateral side
Thick
segment
Thin segment
Distal convoluted tubule cells
Nephron loop
• Descending limb
• Ascending limb
Nephron loop (thin-segment) cells
Collecting
duct
Principal
cell
Intercalated cell
Collecting duct cells
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10. Renal Tubule Three parts Proximal convoluted tubule Nephron loop
Proximal  closest to renal corpuscle
Nephron loop
Distal convoluted tubule
Distal  farthest from renal corpuscle -> Collecting duct
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11. Proximal convoluted tubule (PCT)
Renal Tubule
Proximal convoluted tubule (PCT)
Cuboidal cells with dense microvilli (brush border  surface area); large mitochondria
Functions in reabsorption and secretion
Confined to cortex
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12. Renal Tubule Nephron loop Descending and ascending limbs
Distal descending limb = descending thin limb; simple squamous epithelium
Thick ascending limb
Cuboidal to columnar cells; thin in some nephrons
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13. Distal convoluted tubule (DCT)
Renal Tubule
Distal convoluted tubule (DCT)
Cuboidal cells with very few microvilli
Function more in secretion than reabsorption
Confined to cortex
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14. Receive filtrate from many nephrons Two cell types
Collecting Ducts
Receive filtrate from many nephrons
Two cell types
Principal cells
Sparse, short microvilli
Maintain water and Na+ balance
Intercalated cells
Cuboidal cells; abundant microvilli; two types
A and B; both help maintain acid-base balance of blood
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15. Cortical nephrons—85% of nephrons; almost entirely in cortex
Classes of Nephrons
Cortical nephrons—85% of nephrons; almost entirely in cortex
Juxtamedullary nephrons
Long nephron loops deeply invade medulla
Important in production of concentrated urine
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16. Figure 25.7a Blood vessels of cortical and juxtamedullary nephrons.
Cortical nephron
Juxtamedullary nephron
• Short nephron loop
• Glomerulus further from the cortex-medulla junction
• Efferent arteriole supplies peritubular capillaries
• Long nephron loop
• Glomerulus closer to the cortex-medulla junction
• Efferent arteriole supplies vasa recta
Renal
corpuscle
Glomerulus
(capillaries)
Efferent
arteriole
Cortical radiate vein
Cortical radiate artery
Glomerular
capsule
Afferent arteriole
Collecting duct
Proximal
convoluted
tubule
Distal convoluted tubule
Afferent
arteriole
Efferent
arteriole
Peritubular
capillaries
Ascending
limb of
nephron loop
Cortex-medulla
junction
Arcuate vein
Kidney
Arcuate artery
Vasa recta
Nephron loop
Descending
limb of
nephron loop
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17. Nephron Capillary Beds
Renal tubule associated with two capillary beds
Glomerulus
Peritubular capillaries
Juxtamedullary nephron associated with
Vasa recta
Important in regulation of rate of filtrate formation and blood pressure
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18. Nephron Capillary Beds
Glomerulus - specialized for filtration
Different from other capillary beds – fed and drained by arteriole
Afferent arteriole  glomerulus  efferent arteriole
Blood pressure in glomerulus high because
Afferent arterioles larger in diameter than efferent arterioles
Arterioles are high-resistance vessels
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19. Nephron Capillary Beds
Peritubular capillaries
Low-pressure, porous capillaries adapted for absorption of water and solutes
Arise from efferent arterioles
Cling to adjacent renal tubules in cortex
Empty into venules
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20. Juxtaglomerular Complex (JGC)
Two important cell type:
Macula densa, granular cells,
Macula densa:
Tall, closely packed cells of ascending limb
Chemoreceptors; sense NaCl content of filtrate
Granular cells (juxtaglomerular, or JG cells)
Enlarged, smooth muscle cells of arteriole
Secretory granules contain enzyme renin
Mechanoreceptors; sense blood pressure in afferent arteriole
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21. Juxtaglomerular Complex (JGC)
Granular cells (juxtaglomerular, or JG cells)
Enlarged, smooth muscle cells of arteriole
Secretory granules contain enzyme renin
Mechanoreceptors; sense blood pressure in afferent arteriole
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22. Figure 25.8 Juxtaglomerular complex (JGC) of a nephron.
capsule
Glomerulus
Foot
processes
of podocytes
Efferent
arteriole
Parietal layer
of glomerular
capsule
Podocyte cell body
(visceral layer)
Capsular
space
Afferent
arteriole
Red blood cell
Efferent
arteriole
Proximal
tubule cell
Juxtaglomerular
complex •
Macula densa
cells
of the ascending
limb of nephron loop
Lumens of
glomerular
capillaries
• Extraglomerular
mesangial cells
• Granular
cells
Endothelial cell
of glomerular
capillary
Afferent
arteriole
Glomerular mesangial
cells
Juxtaglomerular complex
Renal corpuscle
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23. Kidney Physiology: Mechanisms of Urine Formation
Three processes in urine formation and adjustment of blood composition
Glomerular filtration
Tubular reabsorption
Tubular secretion
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24. Kidney Physiology: Mechanisms of Urine Formation
Glomerular filtration – produces cell- and protein-free filtrate
Tubular reabsorption
Selectively returns 99% of substances from filtrate to blood in renal tubules and collecting ducts
Tubular secretion
Selectively moves substances from blood to filtrate in renal tubules and collecting ducts
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25. Kidney Physiology: Mechanisms of Urine Formation
Filtrate (produced by glomerular filtration)
Blood plasma minus proteins
Urine
<1% of original filtrate
Contains metabolic wastes and unneeded substances
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26. To cortical radiate vein Glomerular filtration
Figure A schematic, uncoiled nephron showing the three major renal processes that adjust plasma composition.
Afferent
arteriole
Glomerular
capillaries
Efferent arteriole
Cortical
radiate
artery
Glomerular capsule 1
Renal tubule and
collecting duct
containing filtrate
Peritubular
capillary 2 3
To cortical radiate vein
Three major
renal processes:
Urine 1
Glomerular filtration 2
Tubular reabsorption 3
Tubular secretion
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27. Glomerular Filtration
Passive process
No metabolic energy required
Hydrostatic pressure forces fluids and solutes through filtration membrane
No reabsorption into capillaries of glomerulus
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28. The Filtration Membrane
Porous membrane between blood and interior of glomerular capsule
Water, solutes smaller than plasma proteins pass; normally no cells pass
Three layers
Fenestrated endothelium of glomerular capillaries
Basement membrane (fused basal laminae of two other layers)
Foot processes of podocytes with filtration slits; slit diaphragms repel macromolecules
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29. Figure 25.10a The filtration membrane.
Glomerular
capsular space
Efferent
arteriole
Cytoplasmic extensions
of podocytes
Filtration slits
Podocyte
cell body
Afferent
arteriole
Proximal
convoluted
tubule
Glomerular
capillary covered by
podocytes that form
the visceral layer of
glomerular capsule
Parietal layer
of glomerular
capsule
Fenestrations
(pores)
Glomerular capillaries and the
visceral layer of the glomerular
capsule
Glomerular
capillary endothelium
(podocyte covering
and basement
membrane removed)
Foot
processes
of podocyte
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30. Figure 25.10c The filtration membrane.
• Capillary endothelium
Capillary
• Basement membrane
• Foot processes of podocyte
of glomerular capsule
Filtration
slit
Slit
diaphragm
Plasma
Filtrate
in capsular
space
Foot
processes
of podocyte
Fenestration
(pore)
Three layers of the filtration membrane
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31. The Filtration Membrane
Macromolecules "stuck" in filtration membrane
Allows molecules smaller than 3 nm to pass
Water, glucose, amino acids, nitrogenous wastes
Plasma proteins remain in blood  maintains colloid osmotic pressure  prevents loss of all water to capsular space
Proteins in filtrate indicate membrane problem
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32. Pressures That Affect Filtration
Outward pressures promote filtrate formation
Hydrostatic pressure in glomerular capillaries = Glomerular blood pressure
Chief force pushing water, solutes out of blood
Quite high – 55 mm Hg (most capillary beds ~ 26 mm Hg)
Because efferent arteriole is high resistance vessel with diameter smaller than afferent arteriole
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33. Pressures That Affect Filtration
Inward forces inhibiting filtrate formation
Hydrostatic pressure in capsular space (HPcs)
Pressure of filtrate in capsule – 15 mm Hg
Colloid osmotic pressure in capillaries (OPgc)
"Pull" of proteins in blood – 30 mm Hg
Sum of forces  Net filtration pressure (NFP)
55 mm Hg forcing out; 45 mm Hg opposing = net outward force of 10 mm Hg
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34. Net Filtration Pressure (NFP)
Pressure responsible for filtrate formation (10 mm Hg)
Main controllable factor determining glomerular filtration rate (GFR)
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35. Figure 25.11 Forces determining net filtration pressure (NFP).
Glomerular
capsule
Efferent
arteriole
HPgc = 55 mm Hg
OPgc = 30 mm Hg
Afferent
arteriole
HPcs = 15 mm Hg
NFP = Net filtration pressure
= outward pressures – inward pressures
= (HPgc) – (HPcs + OPgc)
= (55) – ( )
= 10 mm Hg
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36. Regulation of Glomerular Filtration
Volume of filtrate formed per minute by both kidneys (normal = 120–125 ml/min)
Constant GFR allows kidneys to make filtrate and maintain extracellular homeostasis
Goal of intrinsic controls - maintain GFR in kidney
GFR affects systemic blood pressure
 GFR  urine output   blood pressure, and vice versa
Goal of extrinsic controls - maintain systemic blood pressure
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37. Regulation of Glomerular Filtration
Intrinsic controls (renal autoregulation)
Act locally within kidney to maintain GFR
Extrinsic controls
Nervous and endocrine mechanisms that maintain blood pressure; can negatively affect kidney function
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38. Two types of renal autoregulation
Intrinsic Controls
Two types of renal autoregulation
Myogenic mechanism
Tubuloglomerular feedback mechanism
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39. Intrinsic Controls: Myogenic Mechanism
Smooth muscle contracts when stretched
 BP  muscle stretch  constriction of afferent arterioles  restricts blood flow into glomerulus
Protects glomeruli from damaging high BP
 BP  dilation of afferent arterioles
Both help maintain normal GFR despite normal fluctuations in blood pressure
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40. Intrinsic Controls: Tubuloglomerular Feedback Mechanism
Flow-dependent mechanism directed by macula densa cells; respond to filtrate NaCl concentration
If GFR  filtrate flow rate   reabsorption time  high filtrate NaCl levels  constriction of afferent arteriole   NFP & GFR  more time for NaCl reabsorption
Opposite for  GFR
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41. Extrinsic Controls: Renin-Angiotensin Mechanism
Triggered when the granular cells of the JGA release renin
angiotensinogen (a plasma globulin)
resin 
angiotensin I
angiotensin converting enzyme (ACE) 
angiotensin II
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42. Effects of Angiotensin II
Constricts arteriolar smooth muscle, causing MAP to rise
Stimulates the reabsorption of Na+
Acts directly on the renal tubules
Triggers adrenal cortex to release aldosterone
Stimulates the hypothalamus to release ADH and activates the thirst center
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43. Effects of Angiotensin II
Constricts efferent arterioles, decreasing peritubular capillary hydrostatic pressure and increasing fluid reabsorption
Causes glomerular mesangial cells to contract, decreasing the surface area available for filtration
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44. Extrinsic Controls: Renin-Angiotensin Mechanism
Triggers for renin release by granular cells
Reduced stretch of granular cells (MAP below 80 mm Hg)
Stimulation of the granular cells by activated macula densa cells
Direct stimulation of granular cells via 1-adrenergic receptors by renal nerves
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45. afferent arterioles; GFR peripheral resistance
SYSTEMIC BLOOD PRESSURE
(–)
Blood pressure in
afferent arterioles; GFR
GFR
Granular cells of
juxtaglomerular
apparatus of kidney
Baroreceptors in
blood vessels of
systemic circulation
Release
Stretch of smooth
muscle in walls of
afferent arterioles
Filtrate flow and
NaCl in ascending
limb of Henle’s loop
(+)
(+)
Renin
(+)
Sympathetic
nervous system
Catalyzes cascade
resulting in conversion
Targets
Vasodilation of
afferent arterioles
Angiotensinogen
Angiotensin II
(+)
(+)
Macula densa cells
of JG apparatus
of kidney
(+)
Adrenal cortex
Systemic arterioles
Releases
Aldosterone
Vasoconstriction;
peripheral resistance
Release of vasoactive
chemical inhibited
Targets
Kidney tubules
Vasodilation of
afferent arterioles
Na+ reabsorption;
water follows
(+)
Stimulates
(–)
Inhibits
Increase
Decrease
GFR
Blood volume
Systemic
blood pressure
Myogenic mechanism
of autoregulation
Tubuloglomerular
mechanism of
autoregulation
Hormonal (renin-angiotensin)
mechanism
Neural controls
Intrinsic mechanisms directly regulate GFR despite
moderate changes in blood pressure (between 80
and 180 mm Hg mean arterial pressure).
Extrinsic mechanisms indirectly regulate GFR
by maintaining systemic blood pressure, which
drives filtration in the kidneys.
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Figure 25.12

46. Extrinsic Controls: Sympathetic Nervous System
Under normal conditions at rest
Renal blood vessels dilated
Renal autoregulation mechanisms prevail
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47. Extrinsic Controls: Sympathetic Nervous System
If extracellular fluid volume extremely low (blood pressure low)
Norepinephrine released by sympathetic nervous system; epinephrine released by adrenal medulla 
Systemic vasoconstriction  increased blood pressure
Constriction of afferent arterioles   GFR  increased blood volume and pressure
© 2013 Pearson Education, Inc.