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BIO 241: Anatomy & Physiology II > Fluids > Flashcards

Flashcards in Fluids Deck (23)
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What % of the body is made up of fluids?

By body weight:
- 40% solids
- 60% fluids

Of Fluids:
Intracellular fluid (67%)
Extracellular fluid (33%)

Of the ECF:
interstitial fluid (80%)
plasma (20%)
other fluids
- lymph, cerebral spinal fluid, synovial fluid


How are fluids in constant motion?

Semi-permeable* membranes separate the fluid compartments.

Fluids are in constant motion between the 3 compartments.
- Blood vessels, Interstitial Fluid, Tissue Fluid


What does fluid balance mean?

water balance, and it implies
electrolyte balance as well – the two are inseparable.


What is the primary mechanism by which water moves from one compartment to the next?



What controls osmosis and therefore fluid balance?

Driven by solute concentration


What factors affect how much of total body weight is made up of water?

age – newborn = 75%, lean adult man = 60%, old age = 45%

body size – obese = as little as 45%, very lean as much as 75%

gender – lean adult man = 60%, lean adult women = 50%


How much water is gained/lost every day?

2500 mL/day


How is water gained every day?

Preformed water - the water you take in through food and drink every day

metabolic water
- forming water from muscle formation (dehydration rxn)
O2 final electron acceptor crates H2O


How is water lost every day?

sensible water loss:
- Urine

- Feces
- Expired Air
- Cutaneous transpiration: Evaporation of water through the skin
- Sweat


Go through the mechanism of Dehydration, Thirst, Rehydration.

- causes increased Blood Osmolarity → ADH Secretion
- causes Reduced Blood Pressure → Renin Secretion → Angiotensin II

- ADH+Angiotensin II Stimulates hypothalamic thirst center
- Thirst center reduces salivation → dry mouth → sense of thirst

- Ingestion of water → rehydrates blood


How does ADH regulate fluid output?

Dehydrated → Increased blood osmolarity →
stimulation of hypothalamic osmoreceptors →
secretion of ADH from posterior pituitary gland → increased thirst+water reabsorption →


How does aldosterone regulate fluid output?

Dehydration/ decreased blood pressure →
increased angiotensin II →
increased aldosterone →
increased Na+ reabsorption →
increased water reabsorption →


How does Atrial Natriuretic Peptide regulate fluid output?

increased blood volume →
stretch of right atrium →
secretion of ANP →
decreased Na+ reabsorption →
decreased water reabsorption →
decreased blood volume


What is the difference between electrolytes and non-electrolytes?

Electrolytes have a greater effect on osmosis than do nonelectrolytes.

Just as important, once the electrolyte dissociates, its component ions attract other ions of the opposite charge, creating an electrochemical gradient that then adds to the osmotic effect.


What are the functions of electrolytes?

Essential minerals
- coenzymes, establish membrane potentials, Ca+ for muscle function, Fe2+ for hemoglobin

Exert osmotic influences

Help maintain acid-base balance

Carry electrical current


How does Exchange of water between plasma and interstitial fluid occurs across capillary membranes occur?


vesicular transport (transcytosis)

bulk flow (majority of movement)


Bulk flow is dependent upon which four pressures that determine the net filtration pressure (NFP)?

= +10 mmHg net filtration
= - 9 mmHg net reabsorption


How is water exchanged across cell membranes?

Based on osmosis
Different ionic compositions in the compartments
Net flow = zero
Na+ and K+ have the greatest effects


What is the normal body fluid pH?

pH = 7.35 – 7.45


How is the normal body fluid pH maintained?

buffer systems – strong acids or bases converted to weaker ones

respiratory compensation – exhalation of carbon dioxide

renal compensation – kidney excretion of hydrogen ions


What are buffer systems? How do the different mechanisms maintain body fluid pH?

Strong acids or bases converted to weaker ones

bicarbonate system is found everywhere in body

phosphate system is found inside of cells (lots of phosphate from nucleic acids - RNA, DNA, ATP)
- loses proton when pH getting too high
- gains proton when pH getting to low (H2PO4-)

Protein system (found in blood plasma - plasma proteins - and inside of cells)
- amino acids gain lose protons based on the pH of the solution
- interstitial fluid doesn’t contain alot of proteins


How does respiratory compensation maintain body fluid pH?

exhalation of carbon dioxide

effects of hyperventilation

CO2 + H2O ← H2CO3 ← H+ + HCO3-

effects of hypoventilation

CO2 + H2O → H2CO3 → H+ + HCO3-


How does renal compensation maintain body fluid pH?

Kidney excretion of hydrogen ions

most permanent because H+ are directly eliminated from the body
- slow – hours to days to take effect

(eg. working out, accumulation of lactic acid) Metabolic acidosis vs. respiratory acidosis (Hypoventilation)

(taking tums) Metabolic alkalosis vs. respiratory alkalosis (Hyperventilation)