Anatomy and Cell Biology 3309 Lecture Notes - Lecture 10: Distal Convoluted Tubule, Proximal Tubule, Renal Corpuscle
15 May 2018
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Lecture 10 – Urine Passage
- Podocytes: cells involved in urinary filtration
o Part of the visceral layer of Bowmann’s capsule
o Adjacent to glomerular capillaries
o Layer continues to the vascular pore to become parietal layer of Bowmann’s capsule
- Fenestrated endothelium is part of the glomerular capillaries that form a basement
membrane that fuses with the basement membrane of the podocytes
- Minor/secondary foot processes of podocytes: pedicles
o Held together by filtration slit diaphragm made of nephrin → does not filter
anything, just ensures that podocytes are arranged in a way to allow for regulated
passage of material from capillary → urinary space
- Fluid is sent through the basement membrane and a lot of material will be filtered out to
create an ultrafiltrate within the urinary space
- Bases of filtration: CHARGE AND SIZE
The nephron
- Production of ultrafitrate
- Conservation of water, electrolytes and metabolites
- Removal of metabolic waste
- Approximately 1 million in each kidney
- Filtrate leaves urinary space and enters the proximal convoluted tubule → flows through
loop of Henle that enters the medulla and comes back to the cortex → distal convoluted
tubule → collecting tubule → medulla → out of the kidney
- Purpose: recovering things that has been filtered out (includes water, electrolytes, small
metabolites)
o At the end, what we excrete is metabolic waste
- Proximal tubule and distal convoluted tubule:
o Found together with renal corpuscle in the cortex
o Distal: well-recognizable lumen
o Proximal: small lumen or not even visible
- As filtrate leaves cortex and enters medulla, it travels through the loop of henle
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o THIN: epithelial cells are very squamous (like endothelial cells)
▪ Flat, thin cytoplasm
▪ Allow reabsorption of water and NaCl
o TS: thin segment
▪ Epithelial cells where the nuclei as prominent but cytoplasm is thin
o VR: vasa recta
▪ Capillaries running parallel to tubules to take in liquid that leaves epithelial
lined loop of Henle
- Collecting duct has ducts:
o Large cuboidal/low columnar ducts
o Have large lumen
- Epithelial cells are different
- Proximal convoluted tubule:
o Reabsorbs vitamins, small amino acids, glucose, water, ions, etc.
- Loop of Henle:
o Epithelium changes as it goes around the loop
o Descending limb: freely permeable to water
▪ Water leaves the tubule because the ascending limb and the distal tubule are
impermeable to water and actively pump out NaCl
▪ This creates a high concentration of NaCl outside the tubule
▪ Water follows the ions in the descending limb
o Regulated: must regulate how much water we excrete and retain in our blood
stream
o Water is reabsorbed into capillaries – it does not stay in the tissue
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- Aldosterone is produced by adrenal gland
o This regulates how much NaCl is reabsorbed from the nephron tubules
o This secondarily affects water reabsorption
- Final regulation is at the level of the collecting duct
o Collecting duct contains water channels that can be turned on and turned off
o This regulates the final volume of urine
o Water reabsorption is regulated by ADH (vasopressin)
o ADH regulates water reabsorption in the collecting duct
- Filtration efficiency is regulated by hormonal mechanisms
Juxtaglomerular apparatus
- Distal convoluted tubule that originated from renal corpuscle comes back to its origin at the
vascular pole
- There are many cells located at the vascular pole
- Cells are bunched together closely
- Nuclei are close together (shows up as a dense spot in an EM = macula densa)
- Macula densa cells are part of the distal convoluted tubule
o They measure the efficiency of NaCl reabsorption in that same part of the nephron
o Information is conveyed next to the afferent arteriole
- Afferent arteriole at the vascular pole has specialized smooth muscle cells within its wall
o Smooth muscle cells are both CONTRACTILE and SYNTHETIC
o They produce renin
o Renin is a signaling molecule that kicks off a cascade of events
- Signal transmission between macula densa and juxtaglomerular cells is by extraglomerular
mesangial cells
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Document Summary
Podocytes: cells involved in urinary filtration: part of the visceral layer of bowmann"s capsule, layer continues to the vascular pore to become parietal layer of bowmann"s capsule, adjacent to glomerular capillaries. Fenestrated endothelium is part of the glomerular capillaries that form a basement membrane that fuses with the basement membrane of the podocytes. Fluid is sent through the basement membrane and a lot of material will be filtered out to create an ultrafiltrate within the urinary space. Purpose: recovering things that has been filtered out (includes water, electrolytes, small metabolites: at the end, what we excrete is metabolic waste. Proximal tubule and distal convoluted tubule: found together with renal corpuscle in the cortex, distal: well-recognizable lumen, proximal: small lumen or not even visible. Collecting duct has ducts: lined loop of henle: large cuboidal/low columnar ducts, have large lumen. Proximal convoluted tubule: reabsorbs vitamins, small amino acids, glucose, water, ions, etc.
