Structure and function of the kidney III Flashcards
What can you say about homeostatic regulation of BP and blood volume
integrated
response to low blood volume and low BP
volume receptors in atria and cartoid and aortic baroreceptors trigger homeostatic reflexes
CV: incr cardiac output
Behaviour: thirst causes incr water intake, incr ECF and ICF volume
Kidneys: conserve H2O to minimise further volume loss
Overall incr blood pressure
Response to high blood volume and BP
Volume receptors in atria, endocrine cells in atria and cartoid and aortic baroreceptors trigger homeostatic reflexes
CV: decr cardiac ouput, vasodilation
Kidneys: excrete salts and h2o in urine, decr in ECF and ICF volume
Overall decr BP
renin-angiotensin-aldosterone system
controls responses of the CV and renal systems to decreases in BP/volume
How does the renin-angiotensin aldosteone system work
- Increased blood K+ or decr Na+ cause adrenal cortex to incr secretion of aldosterone into circulation
- Kidneys detect decr BP and so incr secretion of renin into circulation- renin converts angiotensinogen (from teh liver) into angiotensin I. A converting enzyme converts angiotensin I to angiotensin II, causing contraction of blood vessels and incr BP
- Angiotensin II causes incr secretion of aldosterone, which affects the kidneys
- Aldosterone stimulation of kidneys causes Na+ retention,, K+ secretion and decr water loss
Angiotensin II
stimulus: low blood volume or pressure stimulates renin-induced production
at PCT
Effects: incr Na+, Cl- and water reabsorption–> incr BV
Angiotensin II
stimulus: low blood volume or pressure stimulates renin-induced production
Site: at PCT
Effects: incr Na+, Cl- and water reabsorption, which incr blood volume
Aldosterone
Stimulus: incr angiotensin II levels promotes release from adrenal cortex
Site: at collecting duct
Effects: incr K+ secretion and Na+, Cl- and water reabsorption, which incr blood volume
ADH
regulates reabsorption of water in the collecting duct
vasopressin
What happens with high plasma osmorality (incr Na+ intake or dehydration)
sensed by hypothalmic osmoreceptors, leading stimulation of thirst and release of ADH from the posterior pituitary.
Leads to increased water reabsorption by distal nephron
Feedback for low BP/
Hypothalamic nerve cells detect incr osmotic pressure
Baroreceptors detect decr BP.
ADH secreted whih leads to vasoconstriction of blood vessels and incr reabsorption in the kidney, less urine.
Leads to incr blood volume and pressure
How does ADH work
regulates reversible insertion of water pores in the apical membrane of cells in the collecting duct
- Vasopressin binds to membrane receptor on basolateral membrane of collecting duct epithelial cell
- Receptor activates cAMP second messenger system
- Cell inserts AQP2 water pores into apical membrane via vesicles carrying Aquaporin -2 water pores
- Water moves by osmosis into the blood
Atrial Natriuretic Peptide - main action
Decreases reabsorption of Na+ and water in the DCT an CCD (cortical collecting duct)
Heart full of fluid due to incr in blood volume, incr BP in right atrium, ANP secretion, leading to more Na+ secretion and more water loss. More urine so decr BP.
ANP-other actions
decr aldosterone secretion
decr ADH secretion
clearance of a solute
rate a which a solute disappears from the body by excretion/metabolism
Inulin
Freely filtered through the glomerelus, but is neither reabsorbed nor secreted.
Filtration and excretion are the same.
All inulin filtered in kidney is recovered in the urine and the following can be stated:
GFR= inulin clearance
100mL plasma cleared/min
(where GFR = 100)
Glucose clearance
All glucose that filters is reabsorbed
0 mL plasma cleared/min
Urea clearance
net reabsorption
If filtration is greater than excretion, there is net reabsorption.
If clearance is less than GFR, there is net reabsorption.
50mL plasma cleared/min
Penicillin clearance
net secretion
If excretion is greater than filtration, there is net secretion.
If clearance is greater than GFR, there is net secretion.
150mL plasma clearance/min
If clearance of a solute is zero
can conclude it’s been reabsorbed
If clearance less than GFR
can conclude net reabsorption
if clearance more than GFR
can conclude net secretion
H+ input
fatty acids and AAs in diet
CO2 and lactic acid from metabolism
Buffers
HCO3- in ECF
Proteins, haemoglobin, phosphates in cells
Phosphates, ammonia in urine
H+ output
Renal: H+, delayed response, long term
ventilation: CO2, rapid response, short term
What does acid base balance depend on
respiratory and renal systems
acidosis
pH too low
Kidney secretes H+ and reabsorbs HCO3- and K+
Alkalosis
pH too high
Kidney excretes K+ and HCO3- reabsorbs H+
