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Proximal tubular function (Part 1), n - Coggle Diagram
Proximal tubular function
(Part 1)
Reabsorbtion and secretion
(special for proximal tubule)
Reabsorb (outwards)
filtered glucose and amino acid
filtered Na+, K+, Ca2+, Cl-, HCO3-, water
Sodium reabsorbtion
2/3 (67%) of sodium is reabsorbed in
proximal convoluted tubule
.
25% in
thick ascending limb of Loop of Henle
8% in
distal convoluted tubule
and
collecting duct
Water reabsorbtion is always linked to Na reabsorbtion (isosmotic reabsorbtion)
In early proximal convoluted tubule
Na+ reabsorbed primarily with HCO3- and organic solute (glucoose, amino acid, phosphate, lactate, citrate)
Luminal membrane
Has multiple secondary active transport.
It transport solutes following transmembrane Na+ gradient.
Na+ move into cell
down
its electrochemical gradient.
Glucose, amino acid, lactate, citrate move into the cell
against
its electrochemical gradient
Counter transport: Na+H+ exchange
Potential difference:
In the lumen: negative
In the cell: positive
Negative charge created by:
Na+ glucose cotransport
Na+ amino acid cotransport
Na+H+ exchange > neutral charge
Basolateral membrane
Na+ is extruded from the cell into the blood by
Na+K+ ATPase
.
Glucose and other solute are extruded by
facilitated diffusion
In late proximal convoluted tubule
Na+ is reabsorbed primarily with Cl- (no organic solutes)
consequences of what happened in early proximal convoluted tubule
No glucose/ amino acid and little HCO3-
High Cl- concentration
High Cl- concentration? Why?
HCO3- has been preferentially reabsorbed in the early proximal tubule
Cl- is leaved behind
Water is reabsorbed isosmotically along with solute
Luminal membrane
Reabsorbed primarily NaCl (transcellularly and paracellularly)
High [Cl-] is the driving force
Transcellular component
Na+ transported into the cell via Na+H+ exchanger
Cl- transported into the cell via Cl-formate- anion exchanger
1 more item...
Paracellular component
Tight junctions are permeable to small solutes
[Cl-] gradient drive Cl- diffusion creating Cl- diffusion potential (lumen is more positive than blood)
Na+ reabsorption
Basolateral membrane
Na+ is extruded from the cell into the blood by Na+K+ ATPase
Cl- ion moves from the cell into the blood by diffusion
In midpoint of proximal convulated tubule
consequences of what happened in early proximal convoluted tubule
100% filtered glucose and amino acid is filtered
85% of the filtered HCO3- reabsorbed
Most of filtered phosphate, lactate, and citrate is reabsorbed
Na+ is extensively reabsorbed
Secrete (inwards)
Organic anions and cations
Nephron
Function:
to separate water, ions and small molecules from the blood
filter out wastes and toxins
return needed molecules to the blood
Type
corticol nephron
80-85%
renal corpuscle lies in the outer potion of renal cortex
have short nephron loops
lies mainly in cortex
penetrate only into the outer region of renal medulla
juxtamedullary nephron
15-20%
renal corpuscle lies deep in the cortex close to the medulla
have long nephron loops (extend into the deepest region of the medulla)
The main 3 processes
filtration
reabsorbtion
secretion
2 Parts
renal copuscle:
glomerulus
Bowman's capsule
renal tubule:
proximal convulated tubule
loop of Henle
distal convulated tubule
The formation of urine
Glomerular filtration (in renal corpuscle)
Tubular reabsorbtion (in renal tubule)
Tubular secretion
(in renal tubule)
Principle of tubular reabsorbtion and tubular secretion
Reabsorbtion
99% of filtered water is reabsorbed
Proximal convulated tubule makes the largest contribution
Solutes are reabsorbed by active an passive processes
Routes
Paracellular reabsorbtion
fluid leaks into cells in a passive process
tight junctions permit some reabsorbed substances to pass between cells into peritubular capillaries
Transcellular reabsorbtion
substance passes through route
*fluid in tubular lumen > apical membrane of a tubule cells > cytosol > basolateral membrane > interstitial fluid > peritubular capillaries
active transport
Secretion
Secreted substances
H+, K+, NH4+, creatinine, certain drugs
Outcome:
secretion of H+ help control blood pH
secrete other substances and eliminate them from the body in urine
Principal transport mechanism
different type of transport proteins are present in apical and basolateral membrane
Tight juction: prevent mixing of proteins in the apical and basolateral membrane compartments
reabsobtion of Na is important
