Endocrine Control of Body Fluid Volume Flashcards
Where does the distal tubule end?
the collecting ducts
How much of the ion loads are reabsorbed?
95%
what is the estimated residual load of NaCl?
700-1000mmol NaCl/day
What are the hormones that regulate ion and water balance?
ADH
Aldosterone
ANP
PTH
What is the effect of ADH?
increased water absorption
What is the effect of Aldosterone?
increase Na absorption
increase K/H secretion
What is the effect of ANP?
decrease Na absorption
What is the effect of PTH?
increase Ca absorption
decrease PO4
What does the distal tubule have a low permeability to?
water and urea
What does urea concentrated in the tubular fluid do?
establishes the osmotic gradient within the medulla
What are the two segments to the distal tubule?
early and late
What happens in the early distal tubule?
NKCC transport - Na Cl reabsorption
What happens in the late distal tubule?
Ca reabsorption
H secretion
Na reabsorption
K reabsorption
What is the collecting duct split into?
early and late
What is the early duct similar to?
the late distal tubule
What happens in late collecting duct?
a low ion permeability
permeability to water influenced by ADH
When in ADH released?
when APs lead to Ca dependent exocytosis
What is the half life of ADH?
10-15mins
Where is ADH produced?
paraventricular nuclei in hypothalamus
What does ADH do in the distal tubular cell?
increases permeability of the collecting duct by inserting aquaporins
What is the effect of ADH on urine?
high water permeability = hypertonic urine 1400mosmol/l
How does the tubular fluid equilibrate with the interstitium?
aquaporins
What is true in the collecting duct?
impermeable to water so no water reabsorption in presence of minimal ADH
What does ADH do to urine osmolarity, volume and total solute excretion?
increase osmolarity
decrease volume
What happens in water deficit?
hypothalamic osmoreceptors detect increase in osmolarity and decreased Arterial blood pressure
What is diabetes insipidus or nephrogenic diabetes insipidus?
hereditary disease with large volumes of dilute urine and constant thirst
What is the treatment for diabetes insipidus?
ADH replacement
What are some stimulants and inhibitory influences of ADH?
nicotine stimulates
alcohol, stretch receptors in upper GI inhibits
When is aldosterone secreted?
in response to rising K or falling Na in blood
activation of the renin-angiotensin system
What does Aldosterone do?
Na reabsorption and K secretion
Where is most K reabsorbed?
early regions of the nephron
What happens to K when aldosterone is absent?
rest is reabsorbed in distal tubule
What does an increase in K directly stimulate?
adrenal cortex
How does a decrease in plasma Na promote indirect secretion of aldosterone?
the juxtaglomerular apparatus
What does a decrease in NaCl, ECF and BP do?
stimulates release of renin from kidney which converts angiotensinogen to angiotensin I
What converts Angiotensin I to angiotensin II?
angiotensin converting enzyme
What does angiotensin II do?
stimulates adrenal cortex to produce aldosterone
stimulates thirst, ADH and arteriolar vasoconstriction
Na and Cl reabsorption
What are the steps in renin release from granular cells in JGA?
reduced pressure in afferent arterioles - more renin
macula densa cells sense the amount of NaCl in distal tubule - if reduced NaCl then renin released
increased sympathetic activity as a result of reduced BP - causes renin release
What can abnormal increases in RAA system?
hypertension
What are abnormal increased in RAA responsible for in congestive heart failure?
fluid retention
failing heart causes decreased CO and BP -> low BP stimulates RAA -> increases salt and water retention -> failing heart
What is the treatment for abnormal RAAS?
low salt diet, diuretics, ACE inhibitors
What is ANP?
a hormone from atrial muscle cells that is released when the cells are mechanically stretched due to increase in plasma volume
What does ANP promote?
excretion of Na and diuresis
What is micturation?
urination
What is urination governed by?
micturation reflex
voluntary control
How much can the bladder store?
250-400ml before the stretch receptors activate the micturation reflex
What does the micturation reflex do?
involuntary emptying of the bladder by simultaneous bladder contraction and opening of the internal and external urethral sphincters
How can micturation be voluntarily prevented?
by deliberate tightening of external sphincter and surrounding pelvic diaphragm
What stimulation causes the bladder to contract?
parasympathetic
