Fluids Flashcards
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?
osmosis
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
insensible
- Feces
- Expired Air
- Cutaneous transpiration: Evaporation of water through the skin
- Sweat
Go through the mechanism of Dehydration, Thirst, Rehydration.
DEHYDRATION
- causes increased Blood Osmolarity → ADH Secretion
- causes Reduced Blood Pressure → Renin Secretion → Angiotensin II
THIRST
- ADH+Angiotensin II Stimulates hypothalamic thirst center
- Thirst center reduces salivation → dry mouth → sense of thirst
REHYDRATION
- 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 →
rehydration
How does aldosterone regulate fluid output?
Dehydration/ decreased blood pressure → increased angiotensin II → increased aldosterone → increased Na+ reabsorption → increased water reabsorption → rehydration
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?
Osmosis/diffusion
vesicular transport (transcytosis)
bulk flow (majority of movement)
Bulk flow is dependent upon which four pressures that determine the net filtration pressure (NFP)?
NFP = (BHP + IFOP) – (BCOP + IFHP)
= +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- Alkalosis
effects of hypoventilation
CO2 + H2O → H2CO3 → H+ + HCO3- Acidosis
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)
