Physiology 2130 Lecture Notes - Lecture 45: Macula Densa, Carotid Sinus, Juxtaglomerular Cell
1 May 2018
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Lecture 045 (GOOD)
Aldosterone
● Made by the adrenal gland
● A steroid hormone
○ Can enter in to all the cells
○ Only exert effect if the cell contains the correct
receptor
● Stimulated by
○ Angiotensin II
○ High K+ levels
○ Adrenal corticotropin hormone (ACTH)
● Increase sodium reabsorption in the collecting duct,
by:
○ Non-genomic fast effects
■ Existing channels and proteins are
moved
■ Increase of number of Na+ and K+ channels in the luminal membrane
● Cytosolic channels are exocytosed/inserted into the membrane
● Increased Na+ reabsorption
● Increase K+ secreted
■ Increase the activity of Na+/K+ ATPase
● Na+ is pumped into the interstitial space
● K+ is pumped into the cytosol
○ Genomic slow effects
■ Gene expression is changing
● Takes hours
■ Increase the expression of Na+ channels and Na+/K+ ATPase
● Enters into the nucleus and binds to promoter regions to increase
transcription
Regulation of Aldosterone
● Angiotensin II, high K+ levels, ACTH
● Most of this regulated by the release of renin
Regulation of Renin Release
● Juxtaglomerular cells (JG) release renin under specific circumstances
● Detection of low sodium:
○ Baroreceptors: respond to pressure changes
■ Low sodium means, low blood volume, low pressure
■ Carotid sinus baroreceptors directly reflex to the JG cells
■ JG cells are also intrarenal baroreceptors
○ Chemoreceptors: detect composition of chemical
■ Located within the macula densa cells
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■ Macula densa cells release paracrine factor
● Some stimulate renin release other inhibit renin release
● What activates the JC cells?
○ Sympathetic innervation from the carotid sinus
■ Release NE to trigger the JG cells (strong signal)
○ Intrarenal pressure (of the afferent arteriole)
○ Macula densa cells
■ Part of the tubule cells
■ Chemoreceptors that release factors
● What must happen for the JC cells to release renin?
○ Carotid sinus detect low blood pressure and release NE
■ Solitary tract nucleus has less excitation
■ Vasomotor activation of the sympathetic system
○ Less stretching of the afferent arterial
■ Intrarenal blood pressure is low
○ Macula densa cell detect low Na+ levels
■ release renin releasing factors
Macula Densa Function: Glomerular Filtration Rate (GFR) and Renin Release
● Macula Densa cells can sense NaCl content of the lumen
○ Due to the activity of the NKCC2 multi-porter
■ When the concentration of the salts change in the body it also changes in
the filtrate
● Tubuloglomerular feedback
○ Mechanism to protect itself, assumes that if Na+ or Cl- are high, the blood
pressure will also be high (due to a large blood volume)
■ Will react in a way to prevent bursting of the golmerous in case of high
blood pressure than then to maintain GFR
● Vasodilates
○ High levels of Na- and Cl- in the filtrate
■ The macula densa cells release ATP (paracrine factor)
■ ATP is cleaved to adenosine (outside of the macula densa cells)
■ Adenosine is a vasoconstrictor only at the afferent arteriole
● GFR decreases
○ Low levels of Na- and Cl- in the filtrate
■ The macula densa cells release NO (paracrine)
■ NO causes vasodilation
● GFR increases
Effects of the macula densa input on JC cells and renin release
● Assumption: Na+ and Cl- levels in the filtrate reflect the Na+ and Cl- levels in the body
● When Na+ and Cl- levels are high in the filtrate
○ The macula densa cells release ATP and ATP is cleaved to adenosine
■ Both ATP and adenosine bind to JC via purinergic receptors
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Can enter in to all the cells. Only exert effect if the cell contains the correct receptor. Increase sodium reabsorption in the collecting duct, by: Increase of number of na+ and k+ channels in the luminal membrane. Cytosolic channels are exocytosed/inserted into the membrane. Na+ is pumped into the interstitial space. Increase the expression of na+ channels and na+/k+ atpase. Enters into the nucleus and binds to promoter regions to increase transcription. Most of this regulated by the release of renin. Juxtaglomerular cells (jg) release renin under specific circumstances. Low sodium means, low blood volume, low pressure. Carotid sinus baroreceptors directly reflex to the jg cells. Some stimulate renin release other inhibit renin release. Release ne to trigger the jg cells (strong signal) Carotid sinus detect low blood pressure and release ne. Macula densa cell detect low na+ levels release renin releasing factors. Macula densa function: glomerular filtration rate (gfr) and renin release.
