65-75% TBW

~40% TBW

40-50% less water in fat vs muscle

60-40-20 Rule

Water moves freely by diffusion through the lipid bilayer cell membrane through aquaporins, a water channel protein. Ions balance is mediated by ion channels or transporters. Under normal condition, Na+ is responsible for the osmotic balance of the ECF space; K+ for osmotic balance of the ICF space.

Na+ is responsible for the osmotic balance of the

K+ is responsible for osmotic balance of the

Milimoles of solute per liter of solvent (mmol/L)

Millimoles of solute particles per kg of solvent (mmol/kg)

275-295 mOsm/L

(Na+) x (2+10)

Facilities the outward movement of water from the space. Capillary hydrostatic pressure (BP) and Interstitial hydrostatic pressure.

Osmotically attracts water into the space (proteins, like albumin, globulins and fibrinogens). Capillary (plasma) oncotic pressure. Intersitital oncotic pressure.

How the presence of solutes (ions, nutrients, small proteins) changes fluid movement.

Forces favoring filtration - Forces opposing filtration

Capillary hydrostatic pressure (Pc) + Interstitial oncotic pressure (Pi)

Capillary oncotic pressure (pc) + Interstitial hydrostatic pressure (pi)

Substances can cross the capillaries in 3 ways

90% of extracellular cations, maintains balance extracellular fluid. Balance of this cation is main goal of osmosis. Normal: 135-145.

Cation maintains intracellular balance. Balance maintained by active transport. Responds to: acid/base imbalance, hyperglycemia, adrenergic antagonists/agonists, cell lysis. Normal: 3.5-5.5.

Drink too much water. Inadequate Na+ intake. Caused medications. Heart, kidney, liver problems. SIADH. Pure Na+ deficits: chronic, severe vomiting or diarrhea, burns, other causes of dehydration. Hormonal changes: Addisons.

SALT LOSS: Seizure, stupor, abdominal cramping, lethargic, diminished tendon reflexes, difficulty concentrating, loss of appetite and urine. Orthostatic hypotension, overactive bowel sounds. Shallow respirations (late). Spasms of muscles.

Severe vomiting, diarrhea, diabetic ketoacidosis, medications, CKD, dietary deficiency, overheating.

Weakness, fatigue, muscle cramps and twitching, hypotension, arrhythmia, polyuria, polydipsia.

CKD, uncontrolled DM, dehydration, severe bleeding, excessive K+ intake, medications.

Abdominal pain and diarrhea, heart symptoms, muscles symptoms, N/V.

Decreased perfusion, altered cell to cell interactions

Impaired O2 and metabolic diffusion, obstructed capillary flow and lymphatic drainage, altered cell to cell interactions, cerebral, myocardial, pulmonary, kidney interstitial edema, hepatic congestion, gut and tissue edema.

Excessive accumulation of fluid within interstitial spaces. Often problem in fluid distribution not fluid excess.

Produced in the hypothalamus and released from posterior pituitary. Increases water permeability in the distal tubule, collecting tubule, and collecting duct = water reabsorption (or decreased UOP). Without it leads to decreased water reabsorption and intravascular dehydration. Secreted in response to low intravascular volume. Osmoreceptors cause thirst sensation.

Secreted by adrenal cortex. Primary sites of action in the principle cells of the late distal tubules and cortical collecting tubules. Stimulates Na-K ATPase pump (regulates sodium reabsorption and K secretion). Secretion regulated by ATCH, Angiotensin II, and increased serum K levels. Major hormone responsible for K homeostasis.

Secreted in response to decreased blood volume. Constricts efferent arterioles to increase filtration rates and net tubular reabsorption. Directly stimulates Na reabsorption in the proximal tubules, loop of Henle, and distal tubules (stimulates Na/H+ exchange). Stimulates aldosterone release. Most powerful Na retaining hormone.

Produced by cells in the cardiac atria (ANP) and myoendocrine ventricular cells (BNP) when distended by increased intravascular volume. Inhibits Na and water reabsorption by the renal tubules, particularly the collecting ducts. Increases Na and water excretion in the urine. May contribute to cerebral salt wasting - produced by neurons in brain injury.

Cushing’s, increased Cortisol release, Conn’s Syndrome, increased Aldosterone, hypertonic solutions, corticosteroids, drinking too much water or loosing too much (Diabetes Insipidis, burns, etc)

FRIED: Fatigue, Restless and agitated, Increased reflexes (seizures/coma), Extreme thirst (BIG), Decreased urine, dry mucous membranes and skin.

Intravascular fluid compartment has ___ TBW (AKA blood plasma) and attributes to ___ and ____.

Interstital fluid compartment is ____ TBW (AKA fluid between cells, lymph, GI, spinal, eyes/synovial fluid) cause fluid shifts between ___ and ____ using the 4 Starking Forces.

Intracellular fluid compartment accounts for ___TBW (fluid inside the cell) and ___ shifts freely across PM through ____.

Increased capillary hydrostatic pressure

Decreased capillary oncotic pressure

Increased capillary permeability

Lymphatic obstruction

Common reasons someone’s TBW would not be 60%