Chapter 20

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THIRD EDITION
HUMAN PHYSIOLOGY
AN INTEGRATED APPROACH
Dee Unglaub Silverthorn, Ph.D.
Chapter 20
Integrative Physiology II:
Fluid and Electrolyte Balance
PowerPoint® Lecture Slide Presentation by
Dr. Howard D. Booth, Professor of Biology, Eastern Michigan University
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Body Water Balance
Urine concentration:
Dilute: 300 mOsM
Concentrated: 1200 mOsM
Figure 20-3: Role of the kidneys in water balance
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What is “put back” and where in the nephron.
• Proximal tubule
• Glucose (those carriers) & Na+ (Primary active
transport) urea (passive transport)
• Loop of Henle
• H2O and ions ( Na+, K+ & Cl-)
• Distal tubule
• Na+ & H2O
• Collecting duct
• H2O, Na+ & urea (again)
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Overview: starts off isosmotic 300 mOsM (saltiness)
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Figure 20-4: Osmolarity changes as fluid flows through the nephron
VASOPRESSIN:
If we NEED water, we can get it from the collecting duct!
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Vasopressin (a.k.a. ADH) regulates urine OsM:
Let’s make concentrated uring part I
Figure 20-5: Water movement in the collecting duct in the presence and absence of vasopressin
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Formation of Water Pores:
Mechanism of Vasopressin Action
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Figure 20-7: Factors affecting vasopressin release
Countercurrent exchanger. Loop of Henle
Let’s make concentrated uring part II
• Medullary osmotic
gradient; more salty
Collecting duct
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Figure 20-10: Countercurrent exchange in the medulla of the kidney
• The players:
• Loop of Henle
• Descending/ascending
• vasa recta
• Ions: which ones?
• H2O
• Why is it,
countercurrent?
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• Key facts:
• 1. descending LOH is
water permeable,
ascending LOH is NOT.
• 2. Ascending LOH
actively pumps out ions.
• 3. water goes to where
the most stuff is!!!
• 4. vasa recta removes
water so it doesn’t dilute
the medullary gradient.
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SODIUM BALANCE:
• What happens to the body’s OsM after eating
salty fries? Increase/decrease
• This triggers two responses; can you guess?
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• Vassopressin and thirst; both decrease OsM, but
raise blood pressure.
• To lower blood pressure our kidneys excrete
sodium.
• How does excreting sodium lower BP?
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• WATER GOES TO WHERE THE MOST STUFF
IS.
• When sodium leaves, water follows, decreasing
ECF volume, and BP.
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Sodium Balance: Intake & Excretion
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Figure 20-11: Homeostatic responses to eating salt
• Sodium is regulated by aldosterone from the
adrenal cortex.
• Aldosterone is actually secreted in response to
blood pressure, blood volume and OsM.
• More aldosterone: more sodium reabsorption.
• Aldosterone target: principal cell (P cell) of the
distal tubule & collecting duct.
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Mechanism of Na+ Selective Reabsorption in
Collecting Duct
!water does not follow!
Vassopressin must be present
Figure 20-12: Aldosterone action in principal cells
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How does aldosterone get released?
RAAS: renin-angiotensin-aldosterone-system
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Figure 20-13: The renin-angiotensin-aldosterone pathway
Artial Natruretic Peptide: Regulates Na+ & H2O
Excretion
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Figure 20-15: Atrial natriuretic peptide
Potassium Balance:
Critical for Excitable Heart & Nervous Tissues
• Hypokalemia – low [K+] in ECF, Hyperkalemia high [K+]
• Reabsorbed in Ascending Loop, secreted in
Collecting duct
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Potassium Balance:
Critical for Excitable Heart & Nervous Tissues
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Figure 20-4: Osmolarity changes as fluid flows through the nephron
Potassium Balance:
Critical for Excitable Heart & Nervous Tissues
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 20-12: Aldosterone action in principal cells
THIRD EDITION
HUMAN PHYSIOLOGY
AN INTEGRATED APPROACH
Dee Unglaub Silverthorn, Ph.D.
Chapter 20, part B
Integrative Physiology II:
acid-base balance
PowerPoint® Lecture Slide Presentation by
Dr. Howard D. Booth, Professor of Biology, Eastern Michigan University
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Acid/Base Homeostasis
• Acidosis:  plasma pH
• Protein damage
• CNS depression
• Alkalosis:  plasma pH
• Hyperexcitability
• CNS & heart
• Buffers: HCO3- & proteins
• H+ input: diet & metabolic
• H+ output: lungs & kidney
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• Neutral pH is 7.0
• Biological pH is 7.4
• Determined based upon
H+ concentration.
Acid/Base Homeostasis: Overview
Figure 20-18: Hydrogen balance in the body
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• Low pH – acidosis – nervous tissue becomes less
exciteable – respiratory centers shut down.
• High pH – alkalosis – neurons become
hyperexciteable – twitching, numbness – tetenay
and paralyzed respiratory muscles.
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pH homeostasis depends on 3 things:
• 1. buffers
• 2. the lungs
• 3. the kidneys
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Buffer systems
• Bicarbonate, phosphate ions, and proteins (Hb)
• Buffers prevent significant changes in pH by
binding or releasing H+
CO2 + H2O
H2CO3
carbonic anhydrase
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H+ + HCO3-
• What will drive the equation to the right?
• What will drive the equation to the left?
CO2 + H2O
H2CO3
H+ + HCO3-
carbonic anhydrase
How can ventilation compensate for pH disturbances? Pg. 647.
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Acidosis prevention at the Proximal Tubule:
H+ excreted, bicarbonate reabsorption.
1. Na+ - H+ antiport activity
2. Glutamine metabolism
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Figure 20-21: Proximal tubule secretion and reabsorption of filtered HCO3-
Kidney Hydrogen Ion Balancing: Collecting Duct
• Type A Intercalated cells excrete H+ absorb
HCO3• Type B intercalated cells absorb H+ secrete HCO3-
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Kidney Hydrogen Ion Balancing: Collecting Duct
The polarity of the two cells is reversed with the transport
proteins on opposite sides.
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Figure 20-22: Role of the intercalated cell in acidosis and alkalosis
Acid-base disturbances: respiratory or metabolic
• Respiratory acidosis –
• hypoventilation & CO2 retention.
• COPD- loss of alveolar tissue
• Metabolic acidosis
• Metabolic acids increase protons
• Lactic acid from anaerobic metabolism burn sugar not oxygen.
• Respiratory alkalosis
• Hyperventilation rids CO2
• Hysterical hyperventilation
• Renal compensation can occur
• Metabolic alkalosis
• Vomiting stomach acids and taking bicarbonate-containing
antacids.
• Respiratory compensation takes place rapidly.
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