1. THE URINARY SYSTEM– b III. Physiology … - Urine IV. Other Organs:
THE URINARY SYSTEM– b III. Physiology … Urine IV. Other Organs: Ureters, Bladder, & Urethra

2. B. Step 2: Tubular Reabsorption (figure 25.14)
1. Introduction
Selective process moving substances from filtrate to blood; mostly via active transport & diffusion
a. Nutrients & water: absorbed automatically
b. Ions and 10% water: regulated; depends on body homeostasis
c. Location: Primarily in PCT, DCT, Collect. Ducts
Three major
renal processes:
Afferent arteriole
Efferent arteriole
Glomerular capsule
Rest of renal tubule
containing filtrate
Peritubular
capillary
Tubule Cells
2. Tubular reabsorption
Tubule Cells
Interstial Fluid
Lumen
Peritubular Capillary

3. REVIEW SECONDARY ACTIVE TRANSPORT
d. Methods: Primary & Secondary Active Transport
Extracellular fluid
Glucose
Na+-glucose
symport
transporter
loading
glucose from
ECF
Na+-glucose
symport transporter
releasing glucose
into the cytoplasm
Na+-K+
pump
Na diffuses
Cytoplasm 1
The Primary Active Transport
stores energy by creating a
steep concentration gradient for
Na+ . 2
As Na+ diffuses back using a
cotransporter protein, the protein also moves glucose against its concentration gradient
REVIEW SECONDARY ACTIVE TRANSPORT
Figure 3.11 step 2

4. Peritubular Capillaries
B. Step 2: Tubular Reasorption … 2. Sodium Reabsorption via active transport
Importance: Its active transport provides energy to move other items by secondary active transport
Peritubular Capillaries
Lumen of Tube
Interstial fluid
Kidney Tube Cell 2

5. 3. Reabsorption of Nutrients, Water, & ions
Via Secondary Active Transport
a. sodium diffuses in for step 2 and energy generated causes:
Cotransport via Secondary Active Transport: Nutrients, Vitamins, some ions form Low to High
Then diffuse to peritubular capillaries 3
Transport Maximum (Tm) = maximum transport capacity due to Limited number of protein carriers/channels
When saturated, excess is excreted in urine
Lumen of Tube
Kidney Tube Cell
Peritubular Capillaries 2 3
Glucose
Amino A.
Vitamins
Ions (some)
1 sign of diabetes = glucose and ketones in urine

6. 3. Reabsorption of Nutrients, Water, & Ions …
Passive
c. Osmosis of H2O, passively
i) Most H2O diffuses out of Tubules: H2O diffusion gradient created by movement of Na+-- osmosis occurs from filtrate  peritubular capillaries
ii) Collecting Duct: have control of remaining 25% water via ADH 4
Lumen of Tube
Peritubular Capillaries
Kidney Tube Cell 4

7. 3. Reabsorption of H2O, Nutrients, & Ions …
d. Passive Tubular Reabsorption 5 and 6
As water diffused out of filtrate, solute concen. Increases to create diffusion gradient
Ions (Ca+,Mg+2, and Cl-) diffuse; filtrate   peritubular cap
Lipid-soluble substances & urea diffuse out of filtrate to  peritubular capillaries
Peritubular Capillaries
Lumen of Tube
Kidney Tube Cell 4
Lipids
5-6
Urea ions(some)

8. 4. Reabsorptive Capabilities
a. PCT - site of most reabsorption
65% of Na+ and water
All nutrients &Small proteins
b. Loop of Henle
Descending limb: H2O
Ascending limb: Na+, K+
c. DCT and collecting duct - hormonally regulated
Water (ADH) in collecting duct
Na+ (aldosterone)
HCO3- (for blood pH)

9. ADH inserts aquaporins
4. Reabsorptive Capabilities of the Tubules and Collecting Ducts d. Mechanism of Aldosterone
Na+ K+
Targets collecting ducts (principal cells) and distal DCT
Promotes synthesis of Na+ and K+ channels and Pumps
Result: Na+ reabsorbed, K+ secreted; water follows Na+
e) Mechanism of ADH
ADH inserts aquaporins
(H2O channels)  allows triggers H2O to diffuse out of the
Collecting Ducts
H2O
DCT
Regulated by
aldosterone:
Na+
aquaporin K+
H2O
Collecting Duct

10. C. Step 3: Tubular Secretion
Blood or Tubule cells → tubule lumen
Functions:
Disposes of drugs, metabolites
Eliminates wastes (urea/uric acid)
Rids body of excess K+
Helps Control blood pH (via H+ or HCO3–)
Locations:
Prox. CT mostly
Collecting Duct
Dist. CT
Afferent arteriole
Three major
renal processes:
Glomerular filtration
Tubular reabsorption
Tubular secretion
Urine

11. D. Regulation of Urine Concentration and Volume
1. Basic Concepts
Kidney must maintain constant solute concentration: of body fluids = 300 mOsmo
How– Countercurrent mechanism: parallel portions of a tube connected by a hairpin turn  maximum transfer of substances
c. Loop of Henle ascending and descending limbs create NaCl/H2O gradient in interstitial fluid
Cortex
Medulla

12. 2. Mechanism: Countercurrent in Loop and Vasa Recta
i) Descending Limb
Permeable to H2O
Not to NaCl
ii) Ascending Limb
Permeable to NaCl via active transport
Not to H2O
H2O
H2O
iii) Vasa Recta maintains medulla gradient while removing water and solutes to blood.
NET RESULT: filtrate more dilute at Dist CT (100) than interstial fluid & blood (300)
Interstial fluid

13. 3. Formation of Dilute or Concentrated Urine
a) DILUTE URINE
Filtrate is already dilute at top of DCT
Absence of ADH = no aquaporins
then collecting tubule impermeable to H2O
Medullary gradient not used
Active transport
Passive transport
Collecting duct
Descending limb
of loop of Henle
DCT
Cortex
NaCI
H2O
NaCI
Outer
medulla
NaCI
H2O
Urea
Inner
medulla
Large volume
of dilute urine
(a) Absence of ADH

14. b) Formation of Concentrated Urine
ADH inserts aquaporins  triggers H2O diffusion out of collecting ducts (reabsorption)
medullary osmotic gradient of loop creates the lower concentration for H2O diffusion
Almost all the H2O reabsorbed (remaining 25%)
Overall: then up to 99% of H2O in filtrate reabsorbed
Active transport
Passive transport
Collecting duct
H2O
Descending limb
of loop of Henle
H2O
DCT
Cortex
H2O
NaCI
H2O
H2O
NaCI
Outer
medulla
H2O
NaCI
Urea
H2O
H2O
Urea
Inner
medulla
H2O
Small volume of
concentrated urine
(b) Maximal ADH

15. E. Renal Clearance = volume of plasma cleared of a known substance (test substance like inulin) in a given time
Used to identify kidney disease
RC = GFR = 125 ml/min When substance is neither reabsorbed nor secreted
If RC < 125 ml/min,
the substance is being reabsorbed
At RC = 0,
substance is completely reabsorbed
If RC > 125 ml/min,
the substance is being secreted

16. III. Urine Color Odor pH Specific Gravity Chemical Composition Water
Nitrogen Wastes: Urea,
Solutes: Na+, K+, phosphate, sulfate
Other Nitrogen Wastes: Uric Acid, Creatinine
Variable: Ca+2, Mg+2, Bi-carbonate
ABNORMAL SUBSTANCES

17. IV. The other Organs A. Ureters direct flow to Bladder
B. Bladder emptied out by urethra
Urination (micturition) is controlled by voluntary
external sphincter
This holds up to 1 liter!
Figure 15.6
(a) Female.

18. Figure 25.21a Structure of the urinary bladder and Urethra.
Peritoneum
Ureter
In males, urethra also part of reproductive system
Urethra = passage for urine and semen in men
Rugae
Detrusor muscle
Adventitia
Ureteric orifices
Trigone of bladder
Bladder neck
Internal urethral sphincter
Prostate
Prostatic urethra
Urogenital diaphragm
External urethral sphincter
Urethra
Spongy urethra
Erectile tissue of penis
External urethral orifice
(b) Male. The long male urethra has three
regions: prostatic, membranous and spongy.

19. END OF PPT
Review Questions

20. Participating…
The outermost layer of the kidney is known as the ________ while the core is called the ____________. Kidneys are considered _______________ because they are found on the dorsal wall of the abdominal cavity behind the peritoneum.
What 2 hormones are secreted by the kidneys?
cortex
medulla
retroperitoneal
Renin and EPO

21. Participating…
The functional unit of the kidney is known as the __________ . The three steps of urine formation are: 1. ______________, 2. ______________, and 3. ___________.
What cells of the JG apparatus release renin?
nephron
filtration
reabsorption
secretion
granular

22. Participating…
What are 3 things that trigger renin release by the granular cells? Low levels of NaCl ions indicates ______ flow rates in the nephron and are detected by ______ _______ cells of the J-G apparatus which signal the _________ arteriole to _________.
Very low b.p.; low filtrate flow; sympathetic stimulation
low
macula densa
afferent
dilate

23. Participating…
The __________ _________ developed in the long loops of Henle allows the body to produce __________ urine. Aldosterone targets the collecting tubules and the ______ ; it promotes ____ (and thus H2O) reabsorption by stimulating the production of what?
countercurrent multiplier
concentrated
DCT
Na+
Na+ and K+ channels and Na-K pumps

24. peripheral resistance
SYSTEMIC BLOOD PRESSURE
(–)
Granular cells of
juxtaglomerular
apparatus of kidney
Baroreceptors in
blood vessels of
systemic circulation
Release
(+)
(+)
Renin
(+)
Sympathetic
nervous system
Catalyzes cascade
resulting in conversion
Angiotensinogen
Angiotensin II
(+)
(+)
(+)
Adrenal cortex
Systemic arterioles
Releases
Aldosterone
Vasoconstriction;
peripheral resistance
Targets
Kidney tubules
Na+ reabsorption;
water follows
(+)
Stimulates
(–)
Inhibits
Increase
Decrease
Blood volume
Systemic
blood pressure
Hormonal (renin-angiotensin)
mechanism
Neural controls
Extrinsic mechanisms indirectly regulate GFR
by maintaining systemic blood pressure, which
drives filtration in the kidneys.