Intro to renal histology
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Give me an overview of how urine is formed?
Urine is formed in the nephron, it drains through the medullary pyramids through an opening called renal papilla at the apex of renal pyramid into the renal pelvis and then into the urether which carries urine into the bladder
What is the MAlpighian corpuscle?
It is the same thing as renal corpuscle and it is basically the glomerualr tuft and the bowman's capsule.
How many nephrons per kidney are in the adult kidney and who are the exceptions?
There are up to 1 million but children born prematurely may have decreased numbers since new nephrons continue to form in the third trimester which could predispose them to disease and HTN later in life.
What is the function of the podocyte?
- structural support for capillary loops
- major component of filtration barrier
- synthesis and repair of glomerular basement membrane
- secretes VEGF to maintain healthy fenestrated endothelial cells.
What is the role of the mesangium?
- holds the glomerular capillary loops together due to having collagen 3-6 and other substances such as fibrilin, chondroitin, decron, ect
- plays a role in the contractile and secretory phenotype
- also has a role in the mononuclear phagocyte system
What makes up the glomerular basement membrane? Basics
- glycoproteins and proteoglycans
- Glycoproteins: type 4 collagen (in adults Alpha 3,4,5 and in children alpha 1,1,2 , laminin and entactin
- Proteoglycans: heparan sulfate, perlacan
Alport Syndrome cause
we all have type 4 collagen- alpha chains in the GBM but as after birth it switches from Alpha 1,1,2 to Alpha 3,4,5 and if this switch doesn't occur then there are diseases like alport syndrome because the GBM can't withstand the pressure of the blood passing through and there is escape of blood..
In humans what are the only alpha triple helix that can work?
In the gbm we have only 3 types of promoters that can form, a1,1,2 that occurs in children and then is changed at birth to a345 and then a5,5,6 can apparently also work
What is the function of the glomerular capillaries?
to form ultra-filtrate of plasma which is protein free and contains water, crystalloid Na, K, Cl, phosphate, glucose, aa and urea and is free of blood cells, colloid particles plasma proteins and lipids.
What are slit diaphram?
- They are proteins. They are made of extracellular domains of the proteins that reside in the cell membrane of adjacent podocyte foot processes and intertwine.
- Some of the proteins are: nephrin, podocin, p-cadherin, FAT1, Neph1 and 2 and CD2AP
What is the main composition of the renal cortex? of the renal medulla?
- The renal cortex is mostly made up of tubules and only 5% made up of glomeruli
- The renal medulla only has tubules (no glomeruli) but there is much more interstitial space.
How do cells look in each part of the nephron tubules?
- proximal tubule: columnar cell with brush border and infoldings on basal side due to the longitudinally arranged mitochondria.
- thin loop of hence: small flat cells with no brush border and few mitochondria throughout.
- Thick loop of henle: cuboidal cells, basolateral infoldings and mitochondria
- distal tubule: no brush border but there are mitochondria longitudinally arranged at the base
- collecting duct: no brush border and no basolateral foldings due to mito but there are tall columnar.
What is the function of the proximal tubule?
- reabsorption mostly but there is some secretion.
- S1 and S2 segments reabsorb most of the Na, Cl, K, water,, HCO3, glucose and amino acids and that is why there are is a brush border and basolateral membrane infoldings in order to increase surface area and the mitochondria help provide energy.
S3 segment is also necessary for the secretion of various ions, drugs, toxins into the lumen to be excreted and since it is not as prominent then there is less brush border, mito and basoletral foldings.
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