Fluid Balance (Ch. 26 Part I)

Question 1

List the factors that determine body water content and describe the effect of each factor.

Answer 1

Body fat & bone mass (inverse relationship), skeletal muscle (direct relationship), infants have about 73%, men 60%, women 50%, elderly 45%
~40L of water

Question 2

List the body’s fluid compartments and describe the relative fluid volume

Answer 2

Intracellular Fluid (ICF) - 25L and 
Extracellular Fluid (ECF) - total 15L - plasma (3L) and interstitial fluid (12L) including CSF, vitreous/aqueous fluid, synovial fluid, serous fluid, GI secretions, b/w cell, lymph

Question 3

Differentiate electrolytes and non-electrolytes.

Answer 3

non-electrolytes do not dissociate in water, ie glucose, urea, creatinine, lipids; no charged particles are made,
electrolytes do dissociate, ie NaCl breaks apart into + and -, acids and bases dissociate into H+ and OH-, contribute more to osmotic pressure and drive movement of water because dissociates

Question 4

Explain electrolytes and non-electrolytes’ different osmotic effects in solution.

Question 5

Describe the movement of fluids among the body’s compartments.

Answer 5

due to osmotic and hydrostatic pressures, substances move across cell membrane, water is 2-way, ions move selectively into or out, nutrients, wastes, gases have unidirectional flow

Question 6

List the routes by which water enters and exits the body.

Answer 6

60% beverage + 30% food + 10% metabolic water = 2500 mL intake + output,

72% sensible water loss (feces, urine, sweat) and body can control that, but 28% insensible via skin and lungs

Question 7

Describe the thirst mechanism in detail.

Answer 7

hypothalamic osmoreceptors detect ECF osmolality increases, that means water volume dropping, hypothalamic thirst center initiates sensation, drink water, water moistens mouth and stretches stomach and duodenum, thirst center inhibited;

water volume drops, conserve salivary glands, saliva production decreases, dry mouth detected by sensory afferent fibers that communicate to thirst center;

low body water volume causes decrease in blood plasma volume, blood pressure decreases, granular cells detect it (macula densa cells, stretch, direct innervation) and RAAS activated → angiotensin II → activate thirst center → drink water → raise blood volume → raise blood pressure

Question 8

Describe the hormonal controls of water output in the urine.

Answer 8

(focus on ADH)

what triggers release? loss of water from body (drops in BP in increased osmolarity)

what does ADH do? travels to collecting duct and stims insertion of aquaporins in collecting duct, puts urea -→ medulla, increases urea recycling and increasing effects of [] gradient allowing us to further concentrate urine

Question 9

Explain the causes and consequences of dehydration

Answer 9

dehydration - loss of ECF → concentrated with high osmotic pressure → water moves into ECF → cell crenates → hypovolemic shock because low blood volume = low perfusion of organs

treatment is hypotonic saline to move fluid back into cells

Question 10

describe the relative solute composition of the ECF and ICF

Answer 10

ECFs are plasma and IS fluid, very similar (except protein content of blood plasma), Major cation: Na+, Major anion: Cl–

ICF contains even more soluble proteins than in blood plasma, Low Na+ & Cl– Major cation: K+, Major anion: HPO42–,

Question 11

solute

Answer 11

substance dissolved in water

Question 12

list angiotensin II’s effects, including on thirst

Question 13

ADH

Answer 13

what triggers release? loss of water from body (drops in BP in increased osmolarity)

where is it released from? posterior pituitary gland

detected in hypothalamus

what does ADH do? travels to collecting duct and stims insertion of aquaporins in collecting duct, puts urea → medulla, increases urea recycling and increasing effects of [] gradient allowing us to further concentrate urine

Question 14

hyponatremia

Answer 14

low plasma Na+ associated with hypotonic hydration

Question 15

why is hypotonic hydration treated with hypertonic saline?

Answer 15

hypotonic hydration: more water than solutes

hypertonic saline has more solutes than water, increase osmolarity of ECF - to pull water back out of cells

Question 16

less ADH means ___ urine output

Answer 16

higher volume, less concentrated, dilute

Question 17

Explain the causes and consequences of hypotonic hydration.

Answer 17

too much water in ECF = lower [solute], less osmotic pressure, water moves into cells, hyponatremia → net osmosis of water into tissue cells → cells swell and burst, swelling of brain and spinal cord, treated with hypertonic saline so that ECF more concentrated to reverse flow of water

Question 18

more ADH

Answer 18

concentrated, low volume

Question 19

edema

Answer 19

causes include spikes in BP in capillary bed, lymphatic blockage, hypoproteinemia [protein] in blood causes low osmotic pressure in blood and things don’t move from cells to blood, note that it’s interstitial fluid not intercellular fluid, harder for stuff from blood to get to cells and vice versa because increased distance → damage to tissues

Question 20

arrange following from smallest Volume of Water Lost Each Day to greatest

Answer 20

feces, sweat, insensible (lungs and skin), urine