Bioengineering 6000 CV Physiology
Kidney
Renin-Angiotensin System
• Renin, enzyme released from the granular cells
by
– reduced renal blood pressure
– reduced solute delivery to distal tubule
– sympathetic stimulation
• Angiotensin I, released from the kidneys by
– rise in Renin
• Angiotensin II, result of Angiotensin I cleavage by
– ACE
• Angiotensin II causes
– at low levels, constriction of efferent arterioles, raises
glomerular filtration
– at higher levels constriction of both efferent and afferent
arterioles, reduces glomerular filtration
– increase reabsorption of Na
+
(and water) in distal tubule
– release of aldosterone (adrenal cortex) and vasopressin
(pituitary) which increases reabsorption of Na
+
and water in
distal tubule
Bioengineering 6000 CV Physiology
Kidney
Proximal Tube Reabsorption
• 70% of salts reabsorbed
– Active pumping (via K/Na pump
on basolateral)
– Water and Cl
+
follow Na
+
passively (and perhaps co-
transport)
– Glucose and amino acids follow
in co-transport
– Other substances concentrated
in filtrate
• By loop of Henle
– 75% of filtrate reabsorbed
– Iso-osmotic with cells/plasma
(300 mosm/L)
– Phosphates, Ca
2+
, and other
electrolytes reabsorbed as
needed
Passive
cotransport
Passive
cotransport
Active transport
Channels
