Fluid and Acid–Base Balance

Human Physiology – From Cells to Systems | 9e Lauralee Sherwood Body Defenses Chapter 15

Homeostasis

• control of ECF volume (salt)

• control of ECF osmolarity (water)

• maintain acid-base balance by removing or retaining H+ (acid) and bicarbonate (base)

Positive balance

Positive or negative balance?

gains exceed losses

Negative balance

Positive or negative balance?

losses exceed gains

Water

What is the most abundant component of the body?

ICF and ECF

Body water is distributed between what two compartments?

salt

Control of ECF volume is done through:

1/3

Portion of H2O in this compartment:

Plasma & interstitial fluid

2/3

Portion of H2O in this compartment:

ICF compartment

blood vessel walls

Barrier between plasma and interstitial fluid

cellular plasma membranes

Barrier between ECF and ICF

salt

Maintaining ______ balance is of primary important in the long-term regulation of ECF volume.

Water

Maintaining ______ balance is of primary importance in regulating ECF osmolarity.

Baroreceptor reflex

alters cardiac output and total peripheral resistance

kidneys; thirst

Long-term regulation of blood pressurre rests with the ______ and the _______ mechanism, which control urinary output and fluid intake.

equal

To maintain salt balance at a set level, salt input must ________ salt output.

T

T or F?
Humans typically consume salt in excess of needs.

Osmolarity of a fluid

Measure of the concentration of the individual solute particles dissolved in it

Na+, Cl-, and K+

What 3 ions are responsible for ECF and ICF osmolarity?

Hypertonic

insufficient H2O intake or excessive H2O loss

• dehydration

• H2O moves out of cells by osmosis into the more concentrated ECF

Hypotonic

Renal failure or rapid H2O ingestion

• overhydration

• syndrome of inappropriate vasopressin secretion

• excess free H2O retention dilutes the ECF

hypertonicity

Cells shrink as H2O leaves in:

Vasopressin

control of free H2O balance is important in regulating ECF osmolarity

Acids

What liberates free hydrogen ions?

Bases

What accepts free hydrogen ions?

H+

Fluctuations in _______:

alter nerve, enzyme, and K+ activity

• small changes have dramatic effects on normal cell function

Henderson-Hasselbalch

pH = pKa + log ([A⁻]/[HA])

proteins

most plentiful buffers of body fluids

• contain both acidic and basic groups that can give up or take up H+

Hemoglobin

Buffers the H+ generated from metabolically produced CO2 in transit between the tissues and the lungs

Respiratory

This system regulates H+ by controlling the rate of CO2 removal

• able to alter pulmonary ventilation and excretion of H+-generating CO2

respiratory

Which system serves as the second line of defense against changes in H+?

kidneys

What structure is a powerful third line of defense against changes in H+?

Respiratory

Respiratory or Metabolic acidosis?

arises from an increase in CO2

• kidneys most important in compensating for

• causes:

  • flung disease, depression of respiratory center by drugs or disease, nerve or muscle disorders, or even holding one’s breath

Metabolic

Respiratory or Metabolic acidosis?

fall in HCO3-

• causes:

  • severe diarrhea, diabetes mellitus, strenuous exercise, and uremic acidosis

CO2, H2O, H2CO3, H+, HCO3-

Acid/base metabolism in the body is regulated by this chemical equation:

_____ + _____ ↔ _____ ↔ _____ + ______

pH range

Which range?

7.35 - 7.45

1. pH range

2. CO2 range

3. HCO3- range

CO2 range

Which range?

35 - 45

1. pH range

2. CO2 range

3. HCO3- range

HCO3- range

Which range?

21- 28

1. pH range

2. CO2 range

3. HCO3- range

Respiratory alkalosis

pH ≥ 7.45

HCO3- ≥ 28 

(Opposite of metabolic)

Respiratory acidosis

pH ≤ 7.35

HCO3- ≤ 21

CO2 ~ 45

(Opposite of metabolic)