Chapter 27: Fluid, Electrolyte, and Acid-Base Homeostasis Flashcards
What percentage of ECF is interstitial fluid?
80%
20 % of ECF is _____, the liquid portion of the blood
plasma
What does fluid balance refer to? What are the various body fluid compartments
When the required amounts of water and solutes are present and are correctly proportioned among the various compartments
Compartments:
- 45% solids, 55% fluids in females
- 40% solids, 60% fluids in males
2/3 of fluids is ICF, 1/3 is ECF (20% plasma, 80% ISF)
Why is fluid balance closely related to electrolytes?
The concentration of solutes in these fluids determines the direction of water movement and most solutes in body fluids are electrolytes
Describe the sources of body water gain and loss
Gain: ingestion and by metabolic synthesis (metabolic water) that is produced in the body mainly when levetrons are accepted by oxygen during aerobic respiration and to a smaller extend during dehydration synthesis reactions
Loss: GI tract, lungs, skin, and kidneys
Describe how body water gain is regulated
Body water gain is mainly regulated by the volume of water intake - the thirst centre in the hypothalamus governs the urge to drink
When water loss is greater than water gain, dehydration - a decrease in volume and an increase is osmolarity of body fluids - stimulates thirst
Describe how water and solute loss is regulated
The elimination of excess body water or solutes occurs mainly by control of their loss in urine
Hormonal changes regulate the urinary loss of Na and Cl which increases loss of water in urine by osmosis and turn decreases blood volume
The 3 most important hormones that relate the extend of renal Na and Cl reabsorption are:
- Angiotensin II: Stimulates secretion of aldosterone and reduces loss of water in urine.
- Aldosterone: promotes urinary reabsorption of Na and Cl, increasing water reabsorption via osmosis which reduces loss of water in urine.
- Antidiuretic hormone (ADH): promotes insertion of water-channel proteins (aquaporin-2) into apical membranes of principal cells in collecting ducts of kidneys. As a result, water permeability of these cells increases and more water is reabsorbed. Reducing loss of water in urine.
Define water intoxication
When a person steadily consumes water faster than the kidneys can excrete it (maximum urine flow is 15 mL/min) or when renal function is poor they can experience a state in which excessive body water causes cells to swell dangerously
Can result in convulsions, coma, and possible death
Why do solutions used for oral rehydration therapy contain a small amount of table salt (NaCl)?
If a solution used for oral rehydration therapy contains a small amount of salt, both the salt and water are absorbed in the GI tract, blood volume increases without a decrease in osmolarity, and water intoxication does not occur.
Compare the electrolyte composition of plasma, ISF, and ICF
Bood plasma contains many proteins anions, in contrast to ISF, which has very fetwhile allows only a few plasma proteins to leak out into the ISF
ECF (plasma & ISF) most abundant cation is Na+ and the most abundant anion is Cl, whereas ICF’s most abundant cation is K+ and anion are proteins and phosphates
Describe the function of sodium and explain how their concentrations are regulated
Na+ are the most abundant ions in ECF and plays a role in fluid and electrolyte balance because it accounts for ~1/2 of the osmolarity of ECF
It is also necessary for generation and conduction of APs
Na+ levels are controlled by:
aldosterone - increases renal absorption of Na+
ADH - release ceases which permits greater excretion of water in urine and restoration of normal Na+ levels
ANP - increases Na+ excretion by kidneys when levels are too high
Describe the function of potassium and explain how their concentrations are regulated
K+ plays a key role in establishing the resting membrane potential and in the depolarization phase of APs, also helps maintain normal ICF volume
Controlled mainly by adolsterone which when decreted stimulates principal cells of renal collecting ducts to secrete more K+ so it is secreted in urine, and the opposite effect to conserve K+
Describe the function of bicarbonate and explain how their concentrations are regulated
HCO3- increases as blood flows through systemic capillaries because to CO2 releases combines with water to form carbonic acid, which dissociates into H+ and HCO3-
The kidneys are the main regulators - intercalated cells of renal tubule can either form HCO3- and release it into blood when levels or low or release it into urine when levels are high
Describe the function of calcium and explain how their concentrations are regulated
Ca2+ is mainly an ECF cation which contributes to hardiness of bones & teeth, plays important roles in blood clotting, NT release, maintenance of muscle tone, and excitability of nercous and muscle tissue
Regulated by parathyroid hormone (PTH) which is released by Ca2+ levels are high which timualtes osteoclasts in bones to release more Ca2+; can also enhance reabsorption of Ca2_ from glomerular filtrate through renal rubella cells back into blood; increases calcitriol which increase Ca2+ absorption from food in GI tract
Calcitonin (released by thyroid glands) decreases Ca2+ levels
Describe the function of phosphate and explain how their concentrations are regulated
85% of P in adults is present as calcium phosphate salts, structural components of teeth and bone
They re important buffer of H+ both in body fluids and urine ad most are covalently bound to organic molecules
PTH and calcitriol also regulate the level of HPO42-
PTH stimulates reabsorption of bone ECM increasing P levels but it the kidneys it inhibits reabsorption levels to increase release in urine
Calcitrol promptes absorption of body P and Ca2+ from GI tract
