Fluids Flashcards
What is the body water content of adults and infants?
a. Adults 50-60%
b. Infants 73% or more
Describe the total body water composition
a. Total body water volume
i. 40 L, 60% of body weight
b. Intracellular fluid (ICF)
i. 25 L, 40% of body weight
c. Extracellular fluid
i. Includes Interstitial Fluid and Plasma
ii. 15 L, 20% of body weight
iii. Interstitial Fluid (IF)
1. 12 L, 80% of ECF
iv. Plasma
1. 3 L, 20% of ECF
Describe fluid movement among compartments
a. Osmotic and hydrostatic pressures regulate continuous exchange and mixing of fluids
b. Water moves freely along osmotic gradients
c. OP is proportional to # particles, more particles, more pressure
Describe water balance of input and output
a. Water intake = water output (2500 ml/day)
b. Water intake: ingested foods and beverages, but small amount is Metabolic water (water of oxidation): water produced by cellular respiration
c. Water output: urine (60%), insensible water loss (lost through skin and lungs), perspiration, and feces
What maintains osmolality?
a. Osmolality is maintained by thirst center in hypothalamus - drinking water inhibits the thirst center
b. Rise in osmolality stimulates thirst and causes ADH release
Describe electrolyte balance
a. Electrolyte balance usually refers only to salt balance even though electrolytes also include acids, bases, and some proteins
b. Salts control fluid movements, provide minerals for excitability, secretory activity, and membrane permeability
c. Salts enter body by ingestion and metabolism and are lost via perspiration, feces, urine, vomit
Which cation is the most abundant in ECF?
Sodium
What is the central role of sodium in fluid and electrolyte balance?
a. Only cation exerting significant osmotic pressure
b. Changes in Na+ levels affects plasma volume, blood pressure, and ECF and IF volumes
What is sodium concentration versus sodium content?
a. Concentration of Na+
i. Determines osmolality of ECF and influences excitation of neurons and muscles
ii. Remains stable because of water shifts in and out of cells
b. Content of Na+
i. determines ECF volume and bp
Describe regulation of sodium
a. There are no known receptors that monitor Na+ levels in body fluids
b. Na+-water balance is linked to blood pressure and blood volume control mechanisms which regulate Na+ content
c. Influence of aldosterone and angiotensin II
i. Aldosterone plays biggest role in regulation of
Na+ by kidneys
ii. Regardless of aldosterone presence
iii. 65% of Na+ is reabsorbed in proximal tubules, and
25% is reclaimed in nephron loops; Na+ is never secreted into filtrate
Describe regulation of sodium balance (RAA mechanism)
a. R-A-A mechanism
i. Renin-angiotensin-aldosterone mechanism is main trigger for aldosterone release
ii. Kidney cells secrete renin in response to:
iii. Decreased filtrate NaCl concentration or decreased blood pressure
iv. Renin catalyzes production of angiotensin II
v. Prompts aldosterone release from adrenal cortex
vi. Results in increased Na+ reabsorption by kidney tubules
vii. Aldosterone brings about its effects slowly
(hours to days)
Describe regulation of sodium balance Natriuretic Peptide
a. Influence of atrial natriuretic peptide (ANP)
i. Released by atrial cells in response to stretch caused by increased blood pressure
ii. Effects
iii. Decreases blood pressure and blood volume
iv. Inhibits ADH, renin, and aldosterone production
v. Increases excretion of Na+ and water
vi. Promotes vasodilation
Describe regulation of sodium balance (female sex hormones)
a. Estrogens: increase NaCl reabsorption (water follows)
b. Leads to H2O retention during menstrual cycles and pregnancy
