Q. What triggers renin release? I know that it’s hypo-filtration of the juxtaglomerular apparatus (i.e. reduced fluid flow) but what is the actual trigger for renin release?
A. There are actually three different types of cells in the JGA: granular cells (which secrete renin), macula densa cells (which secrete a vasopressive substance that acts on the afferent glomerular arteriole) and mesangial cells (whose function is a little obscure).
Granular cells (also called juxtaglomerular cells) are little connective tissue cells surrounding glomerular arterioles. They secrete renin in response to three things: 1) beta-adrenergic stimulation, 2) decreased renal perfusion pressure (which is detected by the granular cells themselves) and 3) signals from the macula densa.
Macula densa cells are specialized cells within the wall of the distal tubule. They sense the salt content and the volume of fluid within the tubule (which is related to the glomerular filtration rate). If the salt content is high, or the volume of fluid is low, the macula densa cells do two things: 1) tell the granular cells to release renin, and 2) dilate the afferent arteriole of the glomerulus (by secreting a little vasopressive hormone).
Mesangial cells come in two types: those within the glomerulus (which provide structural support for the capillaries, and also secrete some hormones, like erythropoietin), and those outside the glomerulus (which are considered part of the juxtaglomerular apparatus). The two types are connected by gap junctions. The function of the extraglomerular cells is a bit obscure. They contract when they are stimulated by sympathetic nerves. In addition, they are located in between the macula densa and the afferent arteriole, so maybe they help these two structures communicate.
- viji said Very clear explanation. Thank you Dr Kristine!
- Kristine said Thanks, Meghan – I agree! It should be a primary concern, not an afterthought, and we need to...
- Meghan J said Thank you for this post. It’s a topic that is often added as an afterthought to medical schoo...
- Kristine said Thanks, Sumayya!
- sumayya roohi said mantle cell lymphoma is CD 5+.CD 23-, CD 79b+, FMC7 and cyclin D1 +
- Kristine said I would presume so – at least as long as it remained in the blood.
- Kristine said “Open” chromatin means that you can see through the chromatin – it appears fine, l...
- Kristine said Thanks, Julia!! So glad you found it and it was helpful
- mcray aboagye said Thanks
- ikondere julius said thanx so much
- Kristine said No – I’m sorry, we’re all sold out.
- Rachel Nicholson said Are these shirts still available?