Chapter 20b

Chapter 20b

Integrative Physiology II:

Fluid and Electrolyte Balance

Potassium Balance

• Regulatory mechanisms keep plasma potassium in narrow range• Aldosterone plays a critical role

• Hypokalemia • Muscle weakness and failure of respiratory

muscles and the heart• Hyperkalemia • Can lead to cardiac arrhythmias

• Causes include kidney disease, diarrhea, and diuretics

Behavioral Mechanisms

• Drinking replaces fluid loss• Low sodium stimulates salt appetite• Avoidance behaviors help prevent

dehydration• Desert animals avoid the heat

Disturbances in Volume and Osmolarity

Figure 20-16

Volume and Osmolarity

Table 20-1 (1 of 3)


Table 20-1 (2 of 3)


Table 20-1 (3 of 3)

Blood volume/Blood pressure

Osmolarityaccompanied by

osmolarity inhibits

CVCC +

Para-sympathetic

outputSympathetic

output

Heart

ForceRate

Cardiacoutput

Vasoconstriction

Peripheralresistance

Distalnephron

Vasopressinrelease from

posterior pituitary

Arterioles

Volume H2Oreabsorption

++

H2Ointake

Thirst

+

+

Volumeconserved

DEHYDRATION

CARDIOVASCULARMECHANISMS

RENIN-ANGIOTENSINSYSTEM

RENALMECHANISMS

HYPOTHALAMICMECHANISMS

Carotid and aorticbaroreceptors

Hypothalamicosmoreceptors

Osmolarity

andBloodpressure

Granularcells

GFRFlow atmacula densa

+

++

+

+

Angiotensinogen ANG I

ACE

ANG II

Aldosterone

Na+

reabsorption

Distalnephron

+

Hypothalamus

Adrenalcortex

Atrial volumereceptors; Carotid

and aorticbaroreceptors

Renin


• Homeostatic compensation for severe dehydration

Figure 20-17


Figure 20-17 (5 of 6)



osmolarity inhibits

CVCC +

Para-sympathetic

outputSympathetic

output

Vasoconstriction


Distalnephron


posterior pituitary

Arterioles


+

H2Ointake

Thirst

+

Volumeconserved

DEHYDRATION


RENALMECHANISMS

Osmolarity

andBloodpressure

Granularcells


+

++

+

+


ACE

ANG II

Aldosterone

Na+

reabsorption

Distalnephron

+

Adrenalcortex

Renin


Figure 20-17 (6 of 6)



osmolarity inhibits

CVCC +

Para-sympathetic

outputSympathetic

output

Heart

ForceRate

Cardiacoutput

Vasoconstriction


Distalnephron


posterior pituitary

Arterioles


++

H2Ointake

Thirst

+

+

Volumeconserved

DEHYDRATION

CARDIOVASCULARMECHANISMS


RENALMECHANISMS

HYPOTHALAMICMECHANISMS

Carotid and aorticbaroreceptors

Hypothalamicosmoreceptors

Osmolarity

andBloodpressure

Granularcells


+

++

+

+


ACE

ANG II

Aldosterone

Na+

reabsorption

Distalnephron

+

Hypothalamus

Adrenalcortex

Atrial volumereceptors; Carotid

and aorticbaroreceptors

Renin

Acid-Base Balance

• Normal pH of plasma is 7.38–7.42• H+ concentration is closely regulated• Changes can alter tertiary structure of proteins

• Abnormal pH affects the nervous system• Acidosis: neurons become less excitable and

CNS depression• Alkalosis: hyperexcitable

• pH disturbances • Associated with K+ disturbances

Acid-Base Balance

• Hydrogen ion and pH balance in the body

Figure 20-18

Fatty acidsAmino acids

CO2 (+ H2O)Lactic acidKetoacids

CO2 (+ H2O)

H+ input

H+ output

Plasma pH7.38–7.42

Buffers:• HCO3

– in extracellular fluid• Proteins, hemoglobin, phosphates in cells• Phosphates, ammonia in urine

H+

Acid and Base Input

• Acid• Organic acids • Diet and intermediates

• Under extraordinary conditions • Metabolic organic acid production can increase• Ketoacids • Diabetes

• Production of CO2 • Acid production

• Base• Few dietary sources of bases

pH Homeostasis

• Buffers• Moderate changes in pH• Combines with or releases H+

• Cellular proteins, phosphate ions, and hemoglobin• Ventilation

• Rapid response• 75% of disturbances

• Renal regulation • Slowest of the three mechanisms• Directly excreting or reabsorbing H+

• Indirectly by change in the rate at which HCO3– buffer is

reabsorbed or excreted

pH Disturbances

• The reflex pathway for respiratory compensation of metabolic acidosis

Figure 20-19

Respiratorycontrol centers

in themedulla

Plasma H+

( pH)Plasma

PCO2

Carotid and aorticchemoreceptors

Centralchemoreceptors

PlasmaPCO2

Plasma H+

( pH)

by Law of Mass Action

by Law of Mass Action

Action potentials in somaticmotor neurons

Muscles of ventilation

Rate and depth of breathing

Neg

ativ

e fe

edba

ck

Negative feedback

Sensory neuron Interneuron

pH Disturbances

• Overview of renal compensation for acidosis

Figure 20-20

CO2 + H2O

Carbonic Anhydrase

Nephroncells

AcidosispH = H+

HCO3–

reabsorbed

HCO3– buffer

added toextracellular

fluid

Amino acids + H+

NH4+

H+ + HCO3–H+

secreted

H+

HPO42–

filtered

H2PO4–

Excretedin urine

Blood

Renal Compensation: Transporters

• Apical Na+-H+ exchanger (NHE)• Basolateral Na+-HCO3

– symport• H+-ATPase• H+-K+-ATPase• Na+-NH4

+ antiport

Renal Compensation

• Proximal tubule H+ secretion and the reabsorption of filtered HCO3

–

Figure 20-21

8

5

7

6

32

4

1

Na+-H+ antiportsecretes H+.

H+ in filtrate combineswith filtered HCO3

– toform CO2.

CO2 diffuses into celland combines with waterto form H+ and HCO3

–.

H+ is secreted againand excreted.

HCO3– is reabsorbed.

Glutamine is metabolizedto ammonium ion and HCO3

–.

NH4+ is secreted and

excreted.

HCO3– is reabsorbed.

Peritubularcapillary

Interstitialfluid

Reabsorbed

Filtration

Glomerulus

HCO3–

H+ + HCO3–

HCO3–

CO2 + H2O

Na+

Secreted H+

Na+

H+

Na+

HCO3–

Na+

Bowman’scapsule

H2O + CO2

Filtered HCO3– + H+

Na+

CACA

Na+ Na+ Na+

KG HCO3–

Glutamine

NH4+ HCO3

–Secreted H+ and NH4+

will be excreted

Proximal tubule cell

1

2

3

4

5

6

7

8

Intercalated Cells

• Type A intercalated cells function in acidosis

Figure 20-22a

Intercalated Cells

• Type B intercalated cells function in alkalosis

Figure 20-22b

Acid-Base Balance

Table 20-2

Summary

• Fluid and electrolyte homeostasis• Water balance• Vasopressin, aquaporin, osmoreceptors,

countercurrent multiplier, and vasa recta• Sodium balance• Aldosterone, principal cells, ANG I and II, renin,

angiotensinogen, ACE, and ANP• Potassium balance• Hyperkalemia and hypokalemia

Summary

• Behavioral mechanisms• Integrated control of volume and osmolarity• Acid-base balance• Buffers, ventilation, and kidney• Acidosis and alkalosis• Intercalated cells

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Chapter 20b