1. 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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2. Kidney Functions Eliminate Wastes- toxins, nitrogenous waste, drugs
Homeostasis- H2O balance, electrolytes, Acid-base balance, RBC production, activation of vitamin D

3. 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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4. Kidney Functions Endocrine functions Activation of vitamin D
Renin - regulation of blood pressure
Erythropoietin - regulation of RBC production
Activation of vitamin D
Gluconeogenesis during prolonged fasting
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5. Internal anatomy of kidney
Urine flow: Renal pyramid  minor calyx  major calyx  renal pelvis  ureter
Renal
hilum
Renal cortex
Renal medulla
Major calyx
Papilla of
pyramid
Renal pelvis
Minor calyx
Ureter
Renal pyramid in
renal medulla
Renal column
Fibrous capsule
Photograph of right kidney, frontal section
Diagrammatic view

6. Urine Flow from the Collecting Duct to Outside the Body
Cortical collecting duct through the Renal Cortex
Medullary collecting duct
Minor and Major calyx/ Calyces
Renal Pelvis
Ureter
Bladder- hollow muscular organ
Internal urethral sphincter
External urethral sphincter
Urethral tube
Urethra- opening

8. Proximal Convoluted Tubule (PCT)
Glomerulus/
Glomerular Capillaries
Distal Convoluted Tubule (DCT)
Bowman’s capsule/space
Descending loop of Henle
Juxtaglomerular apparatus (JGA)/ Macula densa
Thick ascending loop of Henle
Efferent arteriole
Afferent arteriole
Thin ascending loop of Henle
Collecting Duct

9. Three major renal processes controlling blood 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
Tubular reabsorption
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Tubular secretion

10. Processes of the Nephron

11. Reabsorptive Capabilities of Renal Tubules and Collecting Ducts
PCT
Site of most reabsorption
All nutrients, e.g., glucose and amino acids
65% of Na+ and water
Many ions
~ All uric acid; ½ urea (later secreted back into filtrate)
Nephron loop
Descending limb - H2O can leave; solutes cannot
Ascending limb – H2O cannot leave; solutes can
Thin segment – passive Na+ movement
Thick segment – Na+-K+-2Cl- symporter and Na+-H+ antiporter; some passes by paracellular route
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12. Tubular Reabsorption: transcellular and paracellular
Transport across the basolateral membrane. (Often involves the lateral intercellular spaces because membrane transporters transport ions into these spaces.) 3
Paracellular route:
Transcellular route:
• Movement through leaky
tight junctions, particularly in
the PCT.
• Movement through the inter-
stitial fluid and into the
capillary.
Transport across the apical membrane. 1
Diffusion through the cytosol. 2
Movement through the inter-
stitial fluid and into the capillary. 4
Filtrate
in tubule
lumen
Tubule cell
Interstitial fluid
Peri-
tubular
capillary
Tight junction
Lateral
intercellular
space 3 4 1 2 3 4
H2O and
solutes
Transcellular
route
Capillary
endothelial
cell
Apical
membrane
Paracellular route
H2O and
solutes
Basolateral
membranes

13. Figure 25.14 Reabsorption by PCT cells.
Slide 1
At the basolateral membrane, Na+ is pumped into the interstitial space by the Na+-K+ ATPase. Active Na+ transport
creates concentration gradients that drive: 1 2
“Downhill” Na+ entry at the
apical membrane.
Reabsorption of organic nutrients and certain ions by cotransport at the apical membrane. 3
Filtrate
in tubule
lumen
Nucleus
Interstitial
fluid
Peri-
tubular
capillary
Tubule cell 4
Reabsorption of water by osmosis through
aquaporins. Water reabsorption increases the concentration of the
solutes that are left behind. These solutes can then be reabsorbed as they move down their gradients: 2
Glucose
Amino
acids
Some
ions
Vitamins 1 3 4 5
Lipid-soluble substances diffuse by the transcellular route.
Lipid-
soluble
substances 5
Various
Ions
and urea 6 6
Various ions (e.g., Cl−, Ca2+, K+) and urea diffuse by the paracellular route.
Tight junction
Paracellular
route
Primary active transport
Transport protein
Secondary active transport
Ion channel
Passive transport (diffusion)
Aquaporin
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14. Blood flow through Kidneys

15. Figure 25.17 Mechanism for forming dilute or concentrated urine.
If we were so overhydrated we had no ADH...
If we were so dehydrated we had maximal ADH...
Osmolality of extracellular fluids
Osmolality of extracellular fluids
ADH release from posterior pituitary
ADH release from posterior pituitary
Number of aquaporins (H2O channels) in collecting duct
Number of aquaporins (H2O channels) in collecting duct
H2O reabsorption from collecting duct
H2O reabsorption from collecting duct
Large volume of dilute urine
Small volume of concentrated urine
Collecting
duct
Collecting duct
Descending limb
of nephron loop
300
Descending limb
of nephron loop
300
100
100
150
DCT
100
DCT
300
Cortex
Cortex
300
100
300
300
100
300
300
400
600
400
Osmolality of interstitial fluid (mOsm)
600
600
400
Osmolality of interstitial fluid (mOsm)
600
600
100
Outer
medulla
Outer
medulla
Urea
900
700
900
900
700
900
900
Urea
Urea
Inner
medulla
Inner
medulla
1200
100
1200
1200
1200
1200
Large volume
of dilute urine
Small volume of
concentrated urine
Urea contributes to
the osmotic gradient. ADH increases its recycling.
Active transport
Passive transport

16. Reabsorptive Capabilities of Renal Tubules and Collecting Ducts
DCT and collecting duct
Reabsorption hormonally regulated
Antidiuretic hormone (ADH) – Water
Aldosterone – Na+ (therefore water)
Atrial natriuretic peptide (ANP) – Na+
PTH – Ca2+
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17. Reabsorptive Capabilities of Renal Tubules and Collecting Ducts
Antidiuretic hormone (ADH)
Released by posterior pituitary gland
Causes principal cells of collecting ducts to insert aquaporins in apical membranes  water reabsorption
As ADH levels increase  increased water reabsorption
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18. Reabsorptive Capabilities of Renal Tubules and Collecting Ducts
Aldosterone
Targets collecting ducts (principal cells) and distal DCT
Increases Na+ and K+ channels, and Na+-K+ ATPases for Na+ reabsorption; water follows
Increase Na+ reabsorption & water retention
Functions – increase blood pressure; decrease K+ levels
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19. Regulation of Glomerular Filtration
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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20. 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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21. 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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22. 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
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