Urinary Physiology

1
Urinary Physiology
2
Emphases

• Review of the 3 phases of urine formation
• Intrinsic regulation of kidney function
• Extrinsic regulation for ECF homeostasis plasma
  volume, plasma osmolarity, electrolyte pH
  balance

3
Urinary System Anatomy Review
Pg. 600
Figure 19-1 Anatomy Summary The Urinary System
4
Review 3 Phases of Urine Formation
Pg. 604
Figure 19-3 The excretion of a substance depends
on the amount that was filtered, reabsorbed, and
secreted
Filtration depends on permeability, surface area,
and the pressure gradient.
Explain why filtration is the most important
(rate-limiting) step in urine formation, i.e.
what happens if filtration is below normal?
5
Review Nephron Structure Function
Figure 19-2 Filtration, reabsorption, secretion,
and excretion
Pg. 603
80 of the energy expended by kidneys is used in
secondary active transport. Where does this
occur along the nephron? Why does it occur?
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The Glomerulus Bowman's Capsule Blood
Filtration
Pg. 605
Can permeability and surface area change at the
glomerulus? Approximately how much filtrate is
produced per day?
How do podocytes help regulate GFR? How is the
function of mesangial cells different than that
of podocytes?
Figure 19-4 Structure of the renal corpuscle
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Glomerular Filtration
Pg. 607
What kinds of materials enter the filtrate at
this stage of urine formation? Glomerular
filtration is a passive process. What 4 basic
factors influence overall net GFR at the
kidneys? Describe how blood flow into and out of
the glomerulus might be regulated to control the
filtration pressure gradient.
Figure 19-6 Filtration pressure in the renal
corpuscle
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Controlling Filtration Pressure (GFR) Extrinsic
Regulation
Pg. 608

• Sympathetic Innervation
• NE at alpha-adrenergic receptors, on both
  afferent and efferent arterioles
• Decrease in systemic BP --gt SNS activation and
  vasoconstriction of esp. afferent arteriole
• Increase in systemic BP --gt decreased SNS and
  vasodilation of arterioles
• Endocrine System
• Angiotensin II (activated by the RAA system
  pg. 134 packet)
• Atrial Natriuretic Peptide (ANP)

What will this do to GFR and urine output? How
does this help BP?
What is the target tissue for this potent
vasoconstrictor, and what would the effect be on
GFR and urine output?
( Beta 1 receptors are on tubule cells)
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Atrial Natriuretic Peptide (ANP)
Pg. 639
Why is sodium so important in the regulation of
ECF volume?
(inhibits sympathetic output from CV center)
(causes afferent arterial vasodilation and
relaxes mesangial cells)
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Autoregulation of GFR (Intrinsic Regulation)
Pg. 609
What solute(s) normally found in urine are
monitored by macula densa cells?

• Myogenic stretch (afferent a.)
• Tubuloglomerular feedback

What do these cells release?
Figure 19-9 The juxtaglomerular apparatus
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Renin-Angiotensin-Aldosterone System
(also decreases GFR to conserve H2O)
(Page 134 of course packet see also Figure 20-13
on pg. 637)
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Tubular Reabsorption 10 Active Transport
Pg. 610
Define obligatory water reabsorption. How is it
different from facultative water reabsorption?
Whats this?
Figure 19-11 Sodium reabsorption in the proximal
tubule
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Reabsorption Secondary Active Transport
Pg. 611
In addition to glucose, what other solutes are
absorbed by secondary active transport?
Figure 19-12 Sodium-linked glucose reabsorption
in the proximal tubule
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Chemical Buffering of Metabolic Acids
Pg. 646
Complete the following buffer pairs H2CO3
______ ______ K2HPO4 NaH2PO4 ______ Hb-H
______ ______ R-COO- R-NH3 ______ Where are
these buffers normally found in the body?
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Tubular SecretionFrom Peritubular Blood Vessels
ECF
Compensation in acidosis with conservation of base
How is electrical balance maintained? See the
details on pp. 650 651 and pg. 135 in your
course packet
80-90 of HCO3- is recovered this
way.
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Body Water Balance
Pg. 628

• Drinking eating provides water
• Kidney conserves water so that output intake

Figure 20-2 Water balance in the body
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Nephron H2O conservation Overview
Pg. 629
Figure 20-4 Osmolarity changes as fluid flows
through the nephron
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Urine Osmolarity Regulation Collecting Duct
Pg. 630
Figure 20-5 Water movement in the collecting
duct in the presence and absence of vasopressin
19
Formation of Water Pores Mechanism of
Vasopressin Action
Pg. 631
Figure 20-6 The mechanism of action of
vasopressin
20
Water Reabsorption in Descending Loop of Henle
Pg. 634

• Countercurrent multiplier exchange
• Medullary osmotic gradient
• H2O?ECF?vasa recta vessels

Figure 20-10 Countercurrent exchange in the
medulla of the kidney