CHAPTER 27 FLUID, ELECTROLYTE, AND ACID-BASE HOMEOSTASIS

I.BODY FLUIDS

A. Intracellular and extracellular fluid compartments

Total body water 40 liters (70kg adult)

0______________________________________________________________40

Extracellular (ECF)

15 liters

_______________ Plasma

Interstitial 3 liters RBCs

12 liters 2 liters

25 Liters

Intracellular (ICF)

1. Plasma membrane regulates concentrations of substances in each compartment.

2. Extracellular also includes lymph, secretions, CSF

3. Water is universal solvent

B.Electrolytes

1.solutes dissolved in water

2.ionize or dissociate into cations and anions

a.Na major extracellular cation

b.K major intracellular cation

c.Cl major extracellular anion

d.phosphate major intracellular anion

e.Ca intracellular concentrations kept low

(1)higher extracellularly

C.Nonelectrolytes

1.do not dissociate in water

2.example: glucose

D.Water

1.metabolic water

a.produced by cellular respiration WHERE?

2.Thirst

a.decrease in plasma volume stimulates

thirst center

b.dry mouth due to less water to make saliva

3.Loss of water

a.obligatory

(1)lungs

(2)skin

(3)feces

(4)urine

4.dehydration

a.water loss exceeds intake

5.edema

a.accumulation of fluid in interstitium

II.Electrolyte balance

A.refers to salt balance

B.loss

1.perspiration

2.feces

3.urine

C.most are sodium salts

1.NaCl

2.Sodium bicarbonate

D.Sodium

1.major role in electrolyte balance

2.kidney function

3.ECF Na concentrations remain constant

a.water shifts to maintain homeostasis

4.transport of many substances linked to Na

5.Hormonal control

a.aldosterone

(1)low sodium or high potassium signals

(2)from adrenal cortex

(3)effects kidney tubules

(4)increases Na reabsorption

(5)increases K secretion

(6)stimulates synthesis of more Na transporters

b.renin/angiotensin

(1)vasoconstriction

(2)stimulates aldosterone secretion

c.Antidiuretic hormone (ADH)

(1)high ADH great reabsorption of water

(a)concentrated urine output

(2)low ADH very little reabsorption of water

(a)dilute urine

d.Atrial Natriuretic factor (ANF)

(1)reduces BP and blood volume

(2)inhibits mechanisms to reabsorb Na

(3)signal is stretch receptor in atrium

e.estrogen

(1)stimulates Na reabsorption

f.glucocorticoids

(1)increase GFR

(2)stimulate Na reabsorption

E.Potassium

1.pH regulation

a.shifts of H ions balance with K shifts in

opposite direction

b.High K increases intracellular volume

c.signals secretion of K at tubules

2.hormone regulation

a.aldosterone

F.Calcium

1.tightly regulation ion

2.role in signalling,blood clotting, as salts in bones

3.hormonal regulation

a.Parathyroid hormone (PTH)

(1)to increase blood levels

(a)absorption at GI

(b)bone release

(c)reabsorption in kidneys

(d)stimulates phosphate excretion

b.calcitonin

(1)calcium deposits enhanced to bone

G.Chloride

1.follows Na

III.ACID-BASE BALANCE

A.Biochemical activities of cell influenced by pH

1.necessary to keep pH in normal physiological range

2.buffers

a.resist fluctuations in pH

3.alkalosis - increase in pH of body fluids

4.acidosis - decrease in pH of body fluids

5.acid - donates proton

6.base - proton acceptor

B.Buffer systems

1.Bicarbonate buffer system

a.carbonic acid (H₂CO₃)

b.sodium bicarbonate (NaHCO₃)

c.add acid: HCl + NaHCO₃-> H₂CO₃ + NaCl

d.add Base: NaOH+ H₂CO₃ -> NaHCO₃ + H₂O

e.important in respiratory regulation

(1)CO₂+H₂O<->H₂CO₃<->H + HCO₃^-

2.phosphate buffer system

a.not as important

b.components are sodium salts of

(1) dihydrogen phosphate (acid)

(2) monohydrogen phosphate (base)

3.Proteins act as buffers

a.COOH group donate

b.R-NH₂ can accept (NH₃)

C.Renal regulation

1.buffer systems tie up acids/bases but must eliminate

2.regulates

a.H ion secretion

b.Bicarbonate ion (HCO₃) reabsorption

3.In urine

a.phophate buffer system

b.ammonium buffer

(1)NH₃ from deamination

(2)picks up H to make NH₄

4.metabolic acidosis, alkalosis

a.disorders associated with acids/bases

eliminated by kidney

b.compensate by respiratory controls

5.respiratory acidosis, alkalosis

a.acidosis - not being able to clear CO₂

b.alkalosis - blowing off too much CO₂

c.compensation by kidneys to correct pH