Kidney: Fluid Balance Flashcards
What can the kidneys control (5)?
Extracellular, specifically plasma, fluid volume- Effective circulating volume (ECV)
Body fluid osmolality by H2O and electrolyte control
The amount of ultrafiltrate produced in the glomeruli
The amount of H2O and electrolytes reabsorbed in the nephron and tubules
Fluid, electrolyte and H+ and HCO3- balance i.e. the amount gained minus the amount lost each day
Where is ultrafiltrate formed?
glomerulus
What rate is the ultrafiltrate formed at?
80-120ml/min
The countercurrent mechanism in the loop of Henle allows the nephron to control what features of urine?
- osmolality
- volume
ECV
Effective Circulating Volume
A decrease in ECV is combated by renal
Na+ retention
Renal Control of ECV:
- changes in ECV trigger 4 pathways
acting upon the kidney:
- effect
1) RAAS
2) Sympathetic Nervous System
3) Antidiuretic Hormone Release
(ADH)
4) ANP (atrial natriuretic peptide)
release
Together, these change renal haemodyanmics and Na+ transport by renal tubule cells
Apart from ADH, most pathways use changes in NA+ excretion to change ECV
Macula Densa sense
sodium delivery to the distal tubule
ECV regulation: RAAS:
insert diagram
2 types of baroreceptors are:
- central vascular sensors
- peripheral stretch receptors
Central vascular receptors are locates (3):
- large systemic veins
- cardiac atria
- pulmonary vasculature
Peripheral stretch receptors are located (3):
- carotid sinus
- aortic arch
- renal afferent arteriole
ECV Regulation: ADH:
- in response to
- receptors involved
- released by the posterior pituitary
gland in response to
***hyperosmolality and volume
depletion - *** antidiuretic effect tmediated by
V2 receptors acting on renal
collecting ducts (more permeable to
H2O) - also increases vascular resistance
mediated by V1 receptor
ECV Regulation: ADH:
insert
ECV Regulation: ANP: action:
- actions of ANP are all designed to
lower ECV - Atrial myocytes synthesize and store
ANP - increased ECV causes atrial stretch
which leads to ANP release into
blood - ANP promotes natriuresis (
increased Na+ and H2O excretion
from kidney) - causes renal vasodilatation so
increased blood flow leads to an
increase in GFR so more Na+ - more Na+ reaches the macula densa
so renin release by JGA is reduced,
hence effects of angiotensin II is
reduced - overall effect: inhibits actions of
renin and opposes effects of
Angiotensin II