Physiology 3120 Lecture Notes - Lecture 39: Distal Convoluted Tubule, Renal Glucose Reabsorption, Peritubular Capillaries
15 May 2018
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Lecture 39 – Renal Handling
Tubule function
- Mutation or something not functioning in the tubule:
o Changes can be detected by calculating filtered load and looking at excretion rates
- Proximal tubule reabsorbs 65% of the volume of the filtrate that is produced
o First segment has a major role in the reabsorption of solvent and solute (items in
the filtrate)
o We reabsorb ALL of the glucose and amino acids, lots of water, (Na+, K+, Cl-)
o Proximal tubule is the only segment in the tubule length that has the capability of
absorbing glucose and amino acids
- Loop of Henle:
o Both the descending and ascending limb together reabsorb 20% volume
o The two limbs are different from one another
o Descending limb reabsorbs mostly water with a little bit of sodium
o Ascending limb does not reabsorb water – reabsorbs ions (Na+, K+, Cl-)
- Distal convoluted tubule and the collecting duct:
o Together they reabsorb 14% of the volume of the filtrate
o Distal tubule and collecting duct are different
o Distal convoluted tubule reabsorbs ions (Na+, K+, Cl-, Ca++)
▪ Calcium must be reabsorbed in the body so bones and teeth remain strong
o Collecting duct reabsorbs predominantly Na+ and water but reabsorption is variable
▪ There are hormones that act on the collecting duct which change how much
reabsorption occurs
▪ (other parts of the tubule are affected by hormones but the collecting duct is
majorly affected)
find more resources at oneclass.com
find more resources at oneclass.com
Tubule transport
- Tubule is a single layer of epithelial cells
o Epithelial cells sit on a basement membrane that faces the outside of the tube
o Basement membrane is a thin layer of extracellular matrix that adheres the
epithelial cells together
- Filtrate flows through the lumen
- Outside of the tubule is the interstitial space and then the capillary bed
o Peritubular capillaries: capillary beds that wrap around the corticol nephron
o Vasa recta: capillary beds that wrap around the juxtamedullary nephrons
- Epithelial cells are polarized and membranes act differently even though they are on the
same cell
o Apical/luminal: membrane of the epithelial cell that faces inside of the lumen
o Basolateral: membrane on the outside of the tube facing the basement membrane
- There are channels and transports:
o Channels: protein-lined pores where things go through by diffusion
o Transporters: protein carriers that facilitate diffusion – items must bind and change
conformation
- Channels and transporters on the apical membrane are different from the basolateral
membrane
- Because of the organization of the channels/transporters, we can change and specifically
move things across membranes for reabsorption or secretion
- Epithelial cells are held together by tight junctions (family of proteins)
o Some parts of the tubule are very tightly adhered together based on the type of tight
junction proteins
o Other parts are further apart allowing for some things to move in between the cells
- PARACELLULAR REABSORPTION: reabsorption that occurs in between tubule cells because
of a certain type of tight junction
- TRANSCELLULAR REBABSORPTION: reabsorption across membranes
o Solute must get out of the lumen across the apical/luminal membrane and across
the basolateral membrane
o Most substances in filtrate cannot pass through the membrane and require a
transporter or a channel to get across
o Ions, water, glucose and amino acids all require a transporter or channel to get
across membranes transcellular
o Secretion is generally transcellular as well
▪ Specific removal of items from capillaries in body
▪ Items cross basolateral membrane via channel or transporter and then
apical membrane into the lumen to then be excreted
- Majority of reabsorption is transcellular → selective process
find more resources at oneclass.com
find more resources at oneclass.com
Sodium reabsorption
- Ion that drives reabsorption throughout the whole tubule
- EXTRA important ion because it drives the majority of reabsorption along the entire tubule
o Concentration is favorable along the majority of the way
o Low inside cells and high outside of cells
- OUTSIDE OF TUBULE CELL FACES:
o Interstitial space (peritubular capillaries)
o Filtrate (inside the lumen) – derived from blood plasma
▪ Plasma has a high concentration of sodium and the sodium filters into the
tubule lumen = driver for ion movement and other solutes
o Sodium pairs up with many other solutes to move into cells
- 30x concentration gradient from filtrate to tubule cells
- Na+ would like to move into tubule cells along the whole length of the nephron tubule but it
requires transporters (protein lined pore/channel or carrier that allows movement across
membrane)
o It is an ion and it is charged and cannot just diffuse across the membrane
o Carrier: protein embedded in the membrane that recognizes, binds to and changes
conformation to move something across the membrane
Examples of transporters:
- 1. Sodium channels
o Protein lined pore that recognizes sodium – most simple mechanism
o E.g ENaC
o Sodium can pass through the channel in either direction if there is a concentration
gradient (can move into or out of cells)
o But there is favorable motion of sodium INTO cells
o ENac (simple channels) allow for sodium to move from the filtrate → tubule cells
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Mutation or something not functioning in the tubule: changes can be detected by calculating filtered load and looking at excretion rates. Tubule is a single layer of epithelial cells: epithelial cells sit on a basement membrane that faces the outside of the tube, basement membrane is a thin layer of extracellular matrix that adheres the epithelial cells together. Outside of the tubule is the interstitial space and then the capillary bed: peritubular capillaries: capillary beds that wrap around the corticol nephron, vasa recta: capillary beds that wrap around the juxtamedullary nephrons. There are channels and transports: channels: protein-lined pores where things go through by diffusion, transporters: protein carriers that facilitate diffusion items must bind and change conformation. Channels and transporters on the apical membrane are different from the basolateral membrane. Because of the organization of the channels/transporters, we can change and specifically move things across membranes for reabsorption or secretion.
