BIOL 2420 Lecture Notes - Lecture 6: Macula Densa, Distal Convoluted Tubule, Afferent Arterioles
26 Apr 2018
School
Department
Course
Professor
Unit 8 – Lecture 6
The Renin-Angiotensin Pathway
- ANGII (angiotensin II) is the signal that usually controls aldosterone release from the
adrenal cortex
o One component of the renin-angiotensin system (RAS)
▪ This is a complex multistep pathways for maintaining blood pressure
- RAS pathway
o Begins when juxtaglomerular granular cells in the afferent arterioles of a nephron
secrete an enzyme called renin
o Renin converts an inactive plasma protein (angiotensinogen) into angiotensin I
(ANGI)
o When ANGI in the blood encounters an enzyme called angiotensin-converting
enzyme (ACE)
▪ ANGI is concerted into ANGII
▪ ACE is now know to take place on the endothelium of the blood vessels
throughout the body
o When ANGII in the blood reaches the adrenal gland, it causes synthesis and
release of aldosterone
o At the distal nephron, aldosterone initiates the intracellular reactions that cause
the tubule to reabsorb Na+
- Stimuli that begin the RAS pathway – all related directly or indirectly to low blood
pressure
1. Granular cells are directly sensitive to blood pressure
o Respond to low blood pressure in renal arterioles by secreting renin
2. Sympathetic neurons, activated by the cardiovascular control center when blood
pressure decreases, terminate on the granular cells and stimulate renin secretion
3. Paracrine feedback from the macula densa in the distal tubule to the granular cells
stimulates renin release
o When fluid flow through the distal tubule is relatively high, the macula densa cells
release paracrine signals that inhibit renin release
o When fluid flow in the distal tubule decreases, macula densa cells signal the
granular cells to secrete renin
- Sodium reabsorption does not directly raise low blood pressure, but retention of Na+
increases osmolarity, which stimulates thirst
o Fluid intake when the person drinks more water increases ECF volume
o When blood volume increases, blood pressure also increases
- The effects of the RAS pathway are not limited to aldosterone release
find more resources at oneclass.com
find more resources at oneclass.com
