regulation of homeostasis by the kidney - fluid balance

Question 1

what does ADH do

Answer 1

CD impermeable to water but ADH can make it permeable
nonapeptide
vasopressin
half life 10-15 min
V2 receptors on basal membrane of principle cells in cd, inc camp = AP-2 water channels on apical surface
little conc urine

Question 2

why is ADH released

Answer 2

in response to changes in plasma osmolarity and effective circulating volume
detected by osmoreceptors and baroreceptors
eg dehydration inc plasma osmolarity, ORs in hypothalamus, trigger ADH release to reabs more water and promote water intake

Question 3

how does urea play a role in water reabsorption

Answer 3

freely filtered in g, reabs in PT but LOH/DT relatively impermeable to urea, urea can diffuse out of CD into medulla down conc gradient, adds to osmolarity of medullary interstitium

Question 4

how is plasma osmolarity controlled

Answer 4

osmoreceptors in hypothalamus
ADH - kidney - excretion of water
thirst - brain - water intake

Question 5

how is ECV controlled

Answer 5

baroreceptors (carotid sinus, aortic arch, renal afferent arteriole, atria of heart)
ADH, RAAS, ANP, SNS
short term - heart, BVs
long term - Na+ excretion

Question 6

what are central vascular sensors

Answer 6

baroreceptors
low pressure blood vol receptors
important
large systemic veins, cardiac atria, pulmonary vasculature

Question 7

what are high pressure arterial stretch receptors

Answer 7

less important baroreceptors
carotid sinus, aortic arch, renal afferent arteriole (the renal baroreceptor)
sensors also in CNS and liver - least important

Question 8

how is ECV controlled

Answer 8

mediated by BR stim
changes in ECV trigger 4 parallel effector pathways which act on kidney
RAAS
SNS
ADH release
ANP release
change renal haemodynamics and Na transport by renal tubule cells

Question 9

what is RAAS

Answer 9

renin (JGA) controls AngII
dec ECV stimulates renin release - dec renal perfusion pressure detected in afferent arteriole (renal baroreceptor)
dec Na conc in DT detected by macula dense cells (renal Na sensor)
brain BRs detects systemic BP drop to trigger SNS

Question 10

effects of AngII

Answer 10

inc SNS 
tubular Na, Cl reabs and K sec, H20 retention
aldosterone sec
vasoconstriction 
CD H20 abs

Question 11

what are the actions of AngII for

Answer 11

inc ECV
enhance Na transport in kidney
stimulation of aldosterone release from adrenal cortex
act on hypothalamus to stimulate thirst and ADH release into circulation

Question 12

other effects of AngII

Answer 12

vasoconstriction on renal and other systemic vessels
longer term effects
renal cell hypertrophy (more protein synthesis of Na transporter and channels)
?role in hypertension

Question 13

important actions of aldosterone

Answer 13

inc ECV
stimulates Na reabs (and K ex) in DT/CD
indirect neg FB on RAAS by inc ECV and lowering plasma K conc
important in conserving Na and water but also stopping K variation

Question 14

what is Atrial Natriuretic peptide

Answer 14

lower ECV
atrial myocytes synthesise and store it
inc ECV = atrial stretch = ANP release
promote natriuresis 
renal vasodilation - inc blood flow - inc GFR - Na excreted (MD, renin release reduced)
inhibit renin and oppose AngII