Anatomy and Cell Biology 3309 Lecture Notes - Lecture 27: Distal Convoluted Tubule, Proximal Tubule, Connecting Tubule
2 May 2018
School
Department
Professor
Histology Lecture 9 – Semester 2
The Urinary System Part 2
- Juxtaglomerular apparatus: combination of different cells that regulate blood volume and blood
pressure
- Podocytes are part of the visceral layer of the Bowman’s capsule
o Adjacent to glomerular capillaries
o Layer continues at the vascular pole to become the parietal layer of Bowman’s capsule
- Urinary space in between that collects filtrate being sent into the proximal convoluted tubule
- REMEMBER HOW PODOCYTES ARE ORGANIZED AND HOW THEY RELATE TO THE CAPILLARIES
o Fenestrated endothelium, part of the glomerular capillary that forms a basement membrane
that fuses together with the BM of the podocyte
- Minor or secondary foot process of the podocyte – held together by filtration slit diaphragm made of
nephron
- Liquid or tissue fluid will be send through the BM (a lot of material will be filtered out) to create an
ultra filtrate in the urinary space
- IMPORTANT: THE BASIS OF FILTRATION = CHARGE + SIZE
- The filtration slit diaphragm does not filter anything
o It makes sure that the podocytes are arranged in a way to allow regulated passage of
material from the capillary into the urinary space
o Structural!
The Nephron
- The filtrate leaves the urinary space and enters the proximal convoluted tubule
- It flows through a loop like structure that enters the medulla, and comes back to the cortex = loop of
Henle
o Loop of Henle has a thick part (ascending and descending) and a thin part
find more resources at oneclass.com
find more resources at oneclass.com
- The filtrate enters the distal convoluted tubule and ascending into collecting tubules back into the
medulla and out of the kidney
- Purpose = to recover a lot of material that has been filtered out, including water, electrolytes and
some small metabolites
o At the end, what we excrete is metabolic waste
- How can we distinguish the different parts of the nephron histologically?
- Proximal convoluted tubule and distal convoluted tubule – found together with the renal corpuscle in
the cortex
o Two different cross sections of tubules that look different (in the cortex)
- Can distinguish both tubules by their lumen
o Distal convoluted tubule has a well recognizable lumen
o Proximal convoluted tubule lumen is fairly small or sometimes not even visible
- As the filtrate leaves the cortex it goes into the medulla, it travels through the loop of Henle
- Most prominent feature of the loop of Henle, is that some parts of it are thin
o The epithelial cells are very squamous (similar to endothelial cells)
▪ Attenuated – cytoplasm is thin
▪ Elongated nucleus
▪ Allows resorption of water and NaCl through the tubule
- TS = thin segment
o Epithelial cell where the nuclei are prominent but cytoplasm is very thin
- VR = vasa recta
o Capillaries run parallel to these tubules to take in liquid that leaves from the epithelial lined
loop of Henle into the capillaries
- Larger ducts in the medulla = collecting ducts
o Cuboidal to low columnar in shape
o Easy to identify
▪ Large lumen
- Distal convoluted tubule:
o Continue from macula
dense
o Short convoluted course
o Continue into collecting
tubule in medullary ray
find more resources at oneclass.com
find more resources at oneclass.com
- Why are these epithelial cells so different?
- Proximal convoluted tubule:
o Re-absorption of nutrients, vitamins, amino acids, glucose, small proteins, cations
▪ Most of the good stuff that we can use – including water, electrolytes, ions
- Filtrate goes through the loop of Henle
o Epithelium changes as it goes around the loop
▪ Descending down into the medulla = freely permeable to water. Water can easily
leave the tubule
▪ Ascending limb of the loop of Henle including the distal convoluted tubule =
impermeable to water
• Actively pumps out NaCl
• Creates a high concentration of NaCl right outside of the tubules due to
the NaCl gradient, water tries to equilibrate that and flows out of the tubule
at the descending limb of the loop of Henle
- Regulate how much water we excrete and we retain within our blood stream
o Water enters back into the blood stream; it does not stay in the tissue. Absorbed in the
capillaries to become part of our blood
o Two mechanisms:
▪ 1. Aldosterone – produced by the adrenal gland
• Regulates how much NaCl is being resorbed from the nephron Tubules
• Regulates NaCl reabsorption and secondarily, water reabsorption
▪ 2. ADH (vasopressin, antidiuretic hormone)
• Level of the collecting duct – permeability for water is ADH dependent
• Collecting duct has water channels within the epithelium that can be turned
on and turned off – therefore, collecting duct can regulate the final volume
of urine
o Regulated by ADH!
• Produced in the brain and regulates water reabsorption in the collecting
duct
- It is important that each nephron (filtration efficiency) can be regulated by these hormonal
mechanisms
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Juxtaglomerular apparatus: combination of different cells that regulate blood volume and blood pressure: adjacent to glomerular capillaries. Podocytes are part of the visceral layer of the bowman"s capsule: layer continues at the vascular pole to become the parietal layer of bowman"s capsule. Minor or secondary foot process of the podocyte held together by filtration slit diaphragm made of. Urinary space in between that collects filtrate being sent into the proximal convoluted tubule. Remember how podocytes are organized and how they relate to the capillaries nephron. Liquid or tissue fluid will be send through the bm (a lot of material will be filtered out) to create an ultra filtrate in the urinary space. Important: the basis of filtration = charge + size. The filtration slit diaphragm does not filter anything: fenestrated endothelium, part of the glomerular capillary that forms a basement membrane that fuses together with the bm of the podocyte.
