fluid compartments #fluids

Intracellular fluid

fluid within our cells

2/3 total vol

Extracellular fluid

fluid outside cell

• intersititial fluid (IF) - surrounds cell

• blood plasma - extracellular fluid within blood vessel

ICF composition

K+, Mg2+ cations, phosphate anions, negatively charged proteins

ECF composition

Na+, calcium cations, chloride ions, bicarbonate anions

water movement is result of osmolarity changes

1. water enters blood

2. plasma osmolality decreases and blood plasma becomes hypotonic to the ICF

3. water moves from blood into intersititial fluid

4. from interstitial fluid to inside cell (intracellular fluid)

If ECF is hypotonic, ICF must be hypertonic

If ECF is hypertonic, ICF must be hypotonic

fluid movement if dehydrated

• plasma osmolality increases and blood plasma becomes hypertonic

• water moves from inside cell to interstitial fluid

• from interstitial fluid to blood

fluid balance

when fluid intake = fluid output

fluid intake

addition of water to the body

major way to increase body fluid

Ingested (preformed) water

water absorbed from food and drink

Metabolic water

water produced daily from aerobic cellular respiration

(sweating)

fluid output

loss of water from body

must equal fluid intake (homeostasis)

ways of fluid loss

breathing, sweating, transpiration, defecation, urination

Sensible water loss

measurable

water lost in feces and urine

Insensible water loss

not measurable

fluids lost in expired air

Obligatory water loss

loss of water that occurs regardless of hydration state

includes sensible and insensible water loss

Facultative water loss

controlled water loss by regulating urine output

fluid imbalance: 5 categories

1. volume depletion

2. volume excess

3. dehydration

4. hypotonic hydration

5. fluid sequestration

fluid imbalance w constant osmolarity

occurs when isotonic fluid is lost or gaines

volume depletion

isotonic fluid loss > isotonic fluid gain

ex. hemorrhage, vomiting, diarrhea, hyposecretion of aldosterone

No change in osmolarity, no net movement of water

volume excess

isotonic fluid gain > isotonic fluid loss

ex. renal failure or hypersecretion of aldosterone

No change in osmolarity, no net movement of water

fluid imbalance with changes in osmolarity

fluid loss that is not isotonic

dehydration

water loss is greater than the loss of solutes > blood plasma becomes hypertonic

water shifts from the cells into interstitial fluids and blood plasma

ex. alcohol intake, sweating, hyposecretion of ADH, dec. water intake

net movement of water based in solute concentration in either the ECF or ICF

hypotonic hydration

the loss of solutes and water with only replacement of water (no solutes present). leading to hypotonic blood plasma

cells could possible swell and rupture

net movement of water based in solute concentration in either the ECF or ICF

fluid sequestration

total body fluid is normal but distributed abnormally

edema

accumulation of fluid in the interstitial space around cells

when fluid intake is greater than fluid output

• inc. blood volume and BP

• dec. plasma osmolarity

when fluid intake is less than fluid output

• dec. blood volume and BP

• inc. plasma osmolarity

regulating fluid intake

through activation or inhibition of thirst center

thirst center

hypothalamus

stimuli to turn on thirst center

1. decreased blood volume and BP

• causes renin release from the kidney and creation of Ang II

• Ang II stimulates thirst center

2. increased blood osmolarity

• activation of thirst center and release ADH (also stimulates thirst center)

• most common stimuli

3. decreased salivary secretion

   causes mucous membranes dry

   signal sent from mucous membranes to thirst center

stimuli to turn off thirst center

occurs when fluid intake is greater than fluid output

how to turn off thirst center

1. inc. BP

   kidneys stop renin and Ang II production

   thirst center stimulation stops

2. dec. blood osmolarity

   in response to inc. fluid intake

   ADH secretion and thirst center stops

3. Inc. salivary secretions

   mucous membranes are moist > thirst center signals decrease

4. Distensions of stomach

   signal sent to the hypothalamus to inhibit thirst center

Ang II, aldosterone, and ADH

work together to dec. urine output to maintain BV and BP

non-electrolytes

• molecules that don’t dissolve in solution bc theyre covalently bonded

• organic molecules (glucose, urea)

electrolyte

dissociate in solution forming cations and anions

(na+, K+, Cl-)

able to conduct electrical current

Sodium (Na+)

99% in ECF, 1% in ICF

principal cation in ECF

Sodium balance

gradients are maintained by NA+/K+ pumps

• obtained through diet

• lost in urine, feces, or sweat

• regulated by hormones (aldosterone, ADH, ANP)

Na+ role

• most important electrolyte

• determining blood plasma osmolarity and regulating fluid balance

• exerts greatest osmotic pressure in ECF

retention of Na+

inc. BV and BPl

loss of Na+

dec. BV and BP

Hypernatremia

Na+ concentration above normal lvls

Hyponatremia

Na+ concentration below normal lvls

potassium percentage

98% in ICF, 2% in ECF

function of potassium

exerts intracellular osmotic pressure, heart rhythm contrl, and neuromuscular activities

potassium imbalance

• lost lethal electrolyte imbalance (causes heart irregularities)

potassium distribution

controlled by Na+/K+ pump and leaky channels that allow K+ out of cell

potassium shift

changes in K+ lvls cause shift in K+ between ECF and ICF

if blood K+ lvls inc., H+ exits the ECF → interstitial fluid → ICF, while K+ exits the ICF → IF → ECF (blood)

if blood K+ lvls dec., H+ exits the ICF → interstitial fluid → ECF (blood) → IF → ICF (cell)

hyperkalemia

elevated K+ lvls in the blood plasma

hypokalemia

decreased K+ lvls in the blood plasma

Chloride ion (Cl-)

associated with Na+

follows Na+ by electrostatic interactions

most abundant anion in ECF

hyperchloremia

inc. blood chloride lvls.

hypochloremia

de. blood chloride lvls.

Calcium ion (Ca2+)

most abundant electrolyte in bone and teeth

needed for muscle contraction and neurotransmitter release

hypercalcemia

inc. blood calcium lvls.

hypocalcemia

decreased blood calcium lvls

Phosphate ion (PO3-4)

most abundant anion in ICF

85% stores in bone and teeth as calcium phosphate

regulated by many of same mechanisms as Ca2+

Magnesium ion (Mg2+)

primarily within the bone or within cells

2nd most abundant cation in ICF

assists in Na+/K+ pump