Ch. 27 - Homeostasis Flashcards
What are the 2 places that exchange between body fluids can occur?
- plasma membrane (b/t intracellular and IS fluid)
2. BV/capillary walls (b/t IS fluid and blood plasma)
How does the body gain water?
ingestion and metabolic synthesis
How does the body lose water?
- excreted by kidneys as urine
- eliminated by GI tract in feces
- evaporation as sweat/insensible perspiration
- exhaled from lungs as water vapour
What are 4 things that stimulate the thirst center in hypothalamus?
- increased blood osmolarity
- decreased blood vol
- decreased BP
- dry mouth
Which hormonal responses are triggered in response to thirst?
- RAA pathway to decrease blood osmolarity and increase BP/blood vol
- ADH to reabsorb more water
What are 3 hormones that regulate renal excretion of Na+ and Cl- ?
aldosterone, angiotensin II, ANP
How does the RAA pathway conserve water?
- angiotensin II increases Na+ reabsorption in PCT
- aldosterone increases Na+ reabsorption/K+ secretion in DCT/cd
- increased Na+/water reabsorption leads to increased BP/blood vol
How does the ANP pathway function in fluid regulation?
- ANP decreases Na+ reabsorption in PCT/CD, results in increased Na+ excretion
- increased urine/Na+/H2O secretion
- decreased BP/blood vol
If IS fluid increases in osmolarity…
…fluid will leave ICF and cells will shrink
If IS fluid decreases in osmolarity…
…fluid will move into ICF and cells will swell
What causes water intoxication? (decreased osmolarity of IS fluid)
- when water consumption is faster than kidney can excrete it
- hypersecretion of ADH
- dilutes [Na+] in plasma/IS fluid –> water moves into cells –> water causes cell swelling
How can you treat a patient with water intoxication?
saline solution
What are 4 functions of electrolytes in body fluids?
- control osmosis of water bt body compartments
- maintain acid-base balance
- carry electrical current, allowing for APs
- cofactors required for optimal activity of some enzymes
What is the major cation and anion in ECF?
Na+ ; Cl-
What is the major cation and anion in ICF?
K+; HPO4 (-2)
What does sodium retention lead to?
water retention; edema (abnormal accumulation of is fluid)
What can cause sodium retention?
- renal failure (cannot excrete Na+)
- hyperaldosteronism (excessive reabsorption of Na+)
What can cause excessive loss of sodium? (hypovolemia = low blood vol)
- inadequate secretion of aldosterone
- excessive intake of certain diuretics
What regulates Cl- levels?
- reabsorption indirectly due to Na+/Cl- symporters
- indirectly regulated by aldosterone
How is K+ regulated?
mainly by aldosterone through Na+/K+/Cl- pumps
- as Na+/Cl- are reabsorbed, K+ is being secreted (levels decrease)
Describe levels of bicarbonate ion in plasma acid-base buffer system
- increased levels in systemic capillaries due to increased CO2
- decreased levels in pulmonary capillaries as CO2 is exhaled
How are bicarbonate ion levels regulated?
by kidneys
- form more HCO3- if blood levels are too low
- excrete excess in urine if blood levels are too high
How are Ca2+ levels regulated?
- by PTH when blood Ca2+ levels are low (increases production of calcitriol!)
- by calcitonin when blood Ca2+ levels are high
What is the function of phosphate in body fluids?
- buffer of H+ in body fluids/urine
- buffers in blood
How are phosphate levels regulated?
- resorption of bone releases phosphate
- PTH: increases phosphate elimination in kidneys
- calcitriol: increases GI absorption of phosphate
How are magnesium levels regulated?
excreted by kidneys in urine in response to several stimuli
What is the normal range for plasma pH?
7.35-7.45
What are 3 major mechanisms to regulate pH?
- buffer systems in body fluids
- exhalation of CO2 (resp system)
- kidney excretion of H+ (urinary system)
What do most buffer systems consist of?
weak acid and a weak base (of that acid)
What is the function of buffer systems?
resist changes in pH (make [H+] constant)
- change the pH of solution but do not remove excess H+ from body
What are the 3 main buffer systems?
- protein buffer system
- carbonic acid-bicarbonate buffer system
- phosphate buffer system
Where are protein buffer systems found?
intracellular fluids, plasma
How do amino acids act as a buffer?
- contains at least 1 carboxyl group (-COOH) that acts as an acid and releases H+
- contains at least 1 amino group (-NH2) that acts as a base and combines with H+
How does the carbonic acid-bicarbonate buffer system work?
- HCO3- acts as weak base and takes in excess H+ before dissociating into H2O and CO2
- H2CO3 acts as a weak acid and dissociates into H+ and HCO3
How does the phosphate buffer system work?
- H2PO4- acts as a weak acid and releases H+ into a solution
- HPO4 (2-) acts as a weak base by absorbing H+
Increased rate and depth of breathing causes…
- more CO2 to be exhaled
- [H+] decreases
- increases blood pH (more alkaline)
Decreased rate and depth of breathing causes…
- less CO2 to be exhaled
- {H+] increases
- decreases blood pH (more acidic)
How does the kidney excrete H+?
- intercalated cells in CD and tubular cells in PCT play important role
- Na+/H+ antiporters and H+ pumps secrete H+ into tubular filtrate
How else does the kidney regulate pH?
- synthesize new bicarbonate and reabsorb filtered bicarbonate to keep blood levels high
What is acidosis?
blood pH below 7.35; causes depression of CNS through depression of synaptic transmission
What is alkalosis?
blood pH above 7.45; causes overexcitability of CNS through facilitation of synaptic transmission
What are disorders of blood PCO2?
respiratory acidosis and alkalosis
What are disorders of bicarbonate concentration?
metabolic acidosis and alkalosis
What are two methods of compensation for acid-base imbalances?
respiratory and renal
What is compensation?
physiological response to acid-base imbalance that attempts to normalize arterial pH
What is respiratory compensation?
hyperventilation or hypoventilation due to metabolic imbalance
What is renal compensation?
changes in secretion/reabsorption of H+ and HCO3- due to respiratory imbalance
What is respiratory acidosis?
elevation of PCO2 in arterial blood due to lack of CO2 removal
What are possible causes for resp acidosis?
emphysema, pulmonary edema, airway obstruction
What are treatment options for resp acidosis?
- ventilation therapy to increase CO2 exhalation
- IV administration of bicarbonate
How does renal compensation work in resp acidosis?
increases H+ secretion and bicarb reabsorption to increase blood pH
What is respiratory alkalosis?
arterial blood PCO2 is too low
What are possible causes for resp alkalosis?
hyperventilation due to high altitude, pulmonary disease, anxiety
What are treatment options for resp alkalosis?
rebreathe into paper bag; inhale air with higher than normal [CO2]
How does renal compensation function in resp alkalosis?
decrease H+ excretion and bicarb reabsorption to decrease blood pH
What is metabolic acidosis?
arterial blood [bicarb ion] is too low, decreasing blood pH
What are possible causes for metabolic acidosis?
- excessive loss of HCO3- through diarrhea/kidney dysfunction
- accumulation of acid (ketosis with dieting/diabetes)
- kidney failing to remove H+
How does respiratory compensation function in metabolic acidosis?
hyperventilation to get rid of CO2
What is possible treatment for metabolic acidosis?
IV administration of sodium bicarbonate
What is metabolic alkalosis?
arterial blood [bicarb ion] is too high, increasing blood pH
What are possible causes of metabolic alkalosis?
vomiting, gastric suctioning, excessive intake of alkaline (antacid) drugs
What is possible treatment for metabolic alkalosis?
fluid and electrolyte therapy
How does respiratory compensation function in metabolic alkalosis?
hypoventilation
