Chap 27 Student 3

8/11/2019 Chap 27 Student 3

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Chapter 27

Homeostasis of Fluids,

Electrolytes, and Acids-

Bases

I. Body Fluids

A. General Comments

1. water makes up 5580% of total adult body mass

2. water is exchanged continuously through different

body compartments via:

a.

b.

c.

d.

3. composition of water and salts is maintained by

kidneys primarily

Total body

mass (female)

(a) Distribution of body solids and fluids in average lean, adult female and male (b) Exchange of water among body

fluid compartments

Total body

mass (male)

45%

Solids

40%

Solids

55%

Fluids

60%

Fluids

2/3

Intracellular

fluid (ICF)

80%

Interstitial

fluid

1/3

Extracellular

fluid (ECF)20% Plasma

Blood capillary

Tissue

cells

Total body

fluid

Extracellular

fluid

I. Body Fluids

B. Fluid Compartments

1. intracellularall fluid inside cells; about 2/3 of all

body fluid


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2. extracellular fluidall fluid outside cell membranes

a. about 1/3 of all body fluid

b. is found between cells

c. is a combination of:

i. blood plasma

ii.iii.

iv.

v.

vi.

Metabolic water

(200 mL)

Ingested

foods

(700 mL)

Ingested

liquids

(1600 mL)

WATER GAIN

GI tract (100 mL)

Skin

(600 mL)

Kidneys

(1500 mL)

WATER LOSS

2500

2000

1500

1000

500

Volume of

water (mL)

Lungs

(300 mL)

C. Fluid Balance: fluid intake usually equals fluid loss on a

daily basis

B. Fluid Balance

1. regulated by feedback loops involving

a. hormones

--angiotensin II

--aldosterone

--ADH

--atrial natriuretic peptide

b. kidneys

--

--


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Dehydration

Decreased

flow of saliva

Increased blood

osmolarity

Decreased

blood volume

Dry mouth

and

pharynx

Stimulates

osmoreceptors in

hypothalamus

Decreased

blood

pressure

Increased renin

release by

juxtaglomerularcells of kidneys

Increased

angiotensin II

formation

Stimulates

thirst center in

hypothalamus

Increases thirst

Increases water intake

Increases body

water to normal

level and relieves

dehydration

Increased intake of NaCl

Increased plasma concentrations

of Na+and Cl

Increased osmosis of waterfrom intracellular fluid tointerstitial fluid to plasma

Increased blood volume

Increased stretching

of atria of heart

Increased release ofatrial natriuretic peptide

Decreased release of renin

by juxtaglomerular cells

Decreased formation ofangiotensin II

Reduced reabsorption ofNaCl by kidneys

Increased loss of Na+andClin urine (natriuresis)

Increased glomerular

filtration rate

Decreased release

of aldosterone

Increased loss of water inurine by osmosis

Decreased blood volume

Excessive blood loss, sweating,vomiting, or diarrhea coupled with

intake of plain water

Decreased Na+concentration ofinterstitial fluid and plasma

(hyponatremia)

Decreased osmolarity of interstitialfluid and plasma

Osmosis of water from interstitialfluid into intracellular fluid

Water intoxication (cells swell)

Convulsions, coma, and possibledeath


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142

Key:

Blood plasma

Interstitial fluid

Intracellular fluid

Extracellular

fluids

Na+ K+ Ca2+ Mg2+ Cl HCO3 HPO4

2+

(organic)SO4

2 Proteinanions

175

150

125

100

75

50

25

0

mEq/liter

145

104 4

140

53 0.2 2 2

35

100

117

3

2427

15

2 2

100

1 1

20 20

50

2

II. Electrolytessalts - most of the solutes in body fluids

--Ions form when electrolytes dissolve and dissociate.

A. Functions of ions:

1. determine how water will move between

fluid compartments

Extracellular

fluid

Cytosol

Extracellular fluid Plasma membrane Cytosol

Phosphate ion

Protein

Potassium ion

2 K+

ADP

ATP

3 Na+Na+/K+ATPaseNa+leak channelK+leak channel

Chloride ion

Sodium ion

Resting

membrane

potential

2. carry electrical currentallow membrane potentials


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3. act as cofactors contribute to enzyme function

Carbonic anhydrase

zinc

4. help maintain acid-base balance

a. acidcompound that releases H+into solution

b. basecompound that binds H+and takes it out

of solution (usually OH-)

III. Acid-Base Balance

Purpose: prevent protein (enzyme) denaturation

Three mechanisms:

A. Chemical buffers

*buffer

Example:


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B. Respiration - increase rate and depth of breathing

more CO2exhaled level of carbonic acid in blood is

reduced ________________

respiratory compensation:

C. Kidney Excretion of H+or HCO3-

renal compensation:

Some stimulusdisrupts

homeostasis by

Blood pH(increase in H+concentration)

Receptors

Control center

Effectors

Return to homeostasiswhen response bringsblood pH or H +concentration back tonormal

As less H2CO3forms andfewer H+are present,blood pH increases (H +concentration decreases)

Diaphragmcontracts moreforcefully andfrequently so

more CO2isexhaled

Inspiratory area inmedulla oblongata

Centralchemo-receptorsinmedullaoblongata

Decreasing

Nerve impulses

Nerve impulses

Input

Output

Peripheralchemorece

ptors inaortic andcarotid

bodies

Fluid

in tubule

lumen

Intercalated cell

in collecting duct

Absorbed into

peritubular capillary

H+

ATPCA

CO2+ H2O

H2CO3

ADP

H++ HCO3

Cl Cl

HCO3 HCO3

(new)

(a) Secretion of H+

Key:

Proton pump (H+ATPase) in apical

membrane

HCO3/Clantiporter in

basolateral membrane

Diffusion

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Chap 27 Student 3