AfraTafreeh.com
Last edited: 11/21/2021
1. PROXIMAL CONVOLUTED TUBULE
Proximal Convoluted Tubule Medical Editor: Mariel Antoinette L. Perez
• There is [glucose] inside the cell
OUTLINE o Na+ helps glucose move against its
concentration gradient
I) GLOMERULAR FILTRATION
• When it gets into the cell, there are specific
II) OSMOLALITY
transporters on the basolateral membrane
III) PROXIMAL CONVOLUTED TUBULE
IV) LIPIDS that transports glucose out of the cell and into
V) SMALL PROTEINS the bloodstream
VI) METABOLIC ACIDOSIS
VII) APPENDIX
(ii) Sodium/AA Cotransporter
VIII) REVIEW QUESTIONS Transports Na+ inside the cell along with amino acids
IX) REFRENCES • [amino acids] inside the cell
Inside the cell, amino acids have specific
transporters that facilitate their diffusion out of the
I) GLOMERULAR FILTRATION tubular cell and into the blood
Watch the video on “Glomerular Filtration” first, if you (iii) Sodium-Lactate Cotransporter
haven’t yet!
Passive diffusion of sodium facilitates transport of lactate
In the glomerulus, the following were filtered
o Water Assuming normal physiological conditions, all (100%) of
o Electrolytes (Na+, K+, Cl–, Ca2+, Mg2+) the glucose, amino acids, and lactate get reabsorbed
o Nutrients (glucose, vitamins, amino acids) from the kidney tubules into the blood.
o Very, very small proteins (e.g., insulin) (3) How does bicarbonate (HCO3–) go into the cell?
II) OSMOLALITY CO2 + H2O H2CO3 H+ + HCO3–
o This reaction is catalyzed by the enzyme carbonic
Volume of particles per kilogram of solvent (mol/kg) anhydrase
Generally, in the glomerulus, the blood is 300 mosm o Carbon Dioxide (CO2)
o mosm = milliosmoles Can be found in our blood
We need to figure out how to get substances from kidney Can move into the cell and react with water to
tubule into the blood, or vice versa form sodium bicarbonate
o Sodium Bicarbonate (H2CO3)
III) PROXIMAL CONVOLUTED TUBULE Unstable; dissociates into a proton (H+) and
bicarbonate (HCO3–)
(A) TUBULAR SECRETION o What happens to the proton (H+)?
From blood into the kidney tubule Sodium-Hydrogen Antiporter
active process: requires ATP • Secondary Active Transport
o Adenosine Triphosphate • As Na+ moves through the channel to go in the
o “Energy currency of the cell” cell, it helps push H+ out
H combines with HCO3– outside of the cell
+
(B) TUBULAR REABSORPTION
• Resulting H2CO3 is converted by carbonic
from the kidney tubule into the blood anhydrase into CO2 and H2O
depending upon the chemicals being reabsorbed, it could o What happens to the bicarbonate (HCO3–)?
be active or passive Approximately 90% of HCO3– gets pushed into the blood
(1) Sodium-Potassium ATPase (4) Osmosis
Pumps 3 Na+ out of the cell and 2 K+ ions into the cell Sodium is very critical in the process
o Na+ and K+ move against their concentration gradient Obligatory Water Reabsorption
from an area of low concentration to an area of high o Water feels obliged to follow sodium
concentration For example, in the sodium-glucose channel
AfraTafreeh.com
Primary active transport • When sodium is coming in with the glucose,
o Requires ATP water feels obliged to follow sodium
o Water moves by the process of osmosis
97% of K in our bodies is inside the cell From the kidney tubules into the blood
What does it do inside the cell?
o [Na+] and [K+] About 65% of sodium is being reabsorbed
o Hence, 65% of water is also being reabsorbed
(2) Secondary Active Transport
(5) Paracellular Transport
Passive diffusion of one substance helps facilitate the
active transport of another substance How ions move in between the cell to the blood
Special transporter on cell membrane o Ca2+, Mg2+, K+, Cl–
Can transport two things at once inside the cell o Very little calcium and magnesium are reabsorbed in this area
About 50% of Cl– is reabsorbed via this mechanism
(i) Sodium-Glucose Cotransporter About 55% of K+ is reabsorbed via this mechanism
Na+
(6) Sodium-Chloride Symporter
• Since there’s [Na+] inside the cell, it’s moving
passively along its concentration gradient Moves sodium and chloride ions into the cell
Glucose o They are then pushed into the blood
PROXIMAL CONVOLUTED TUBULE RENAL PHYSIOLOGY: Note #2. 1 of 3
Last edited: 11/21/2021
1. PROXIMAL CONVOLUTED TUBULE
Proximal Convoluted Tubule Medical Editor: Mariel Antoinette L. Perez
• There is [glucose] inside the cell
OUTLINE o Na+ helps glucose move against its
concentration gradient
I) GLOMERULAR FILTRATION
• When it gets into the cell, there are specific
II) OSMOLALITY
transporters on the basolateral membrane
III) PROXIMAL CONVOLUTED TUBULE
IV) LIPIDS that transports glucose out of the cell and into
V) SMALL PROTEINS the bloodstream
VI) METABOLIC ACIDOSIS
VII) APPENDIX
(ii) Sodium/AA Cotransporter
VIII) REVIEW QUESTIONS Transports Na+ inside the cell along with amino acids
IX) REFRENCES • [amino acids] inside the cell
Inside the cell, amino acids have specific
transporters that facilitate their diffusion out of the
I) GLOMERULAR FILTRATION tubular cell and into the blood
Watch the video on “Glomerular Filtration” first, if you (iii) Sodium-Lactate Cotransporter
haven’t yet!
Passive diffusion of sodium facilitates transport of lactate
In the glomerulus, the following were filtered
o Water Assuming normal physiological conditions, all (100%) of
o Electrolytes (Na+, K+, Cl–, Ca2+, Mg2+) the glucose, amino acids, and lactate get reabsorbed
o Nutrients (glucose, vitamins, amino acids) from the kidney tubules into the blood.
o Very, very small proteins (e.g., insulin) (3) How does bicarbonate (HCO3–) go into the cell?
II) OSMOLALITY CO2 + H2O H2CO3 H+ + HCO3–
o This reaction is catalyzed by the enzyme carbonic
Volume of particles per kilogram of solvent (mol/kg) anhydrase
Generally, in the glomerulus, the blood is 300 mosm o Carbon Dioxide (CO2)
o mosm = milliosmoles Can be found in our blood
We need to figure out how to get substances from kidney Can move into the cell and react with water to
tubule into the blood, or vice versa form sodium bicarbonate
o Sodium Bicarbonate (H2CO3)
III) PROXIMAL CONVOLUTED TUBULE Unstable; dissociates into a proton (H+) and
bicarbonate (HCO3–)
(A) TUBULAR SECRETION o What happens to the proton (H+)?
From blood into the kidney tubule Sodium-Hydrogen Antiporter
active process: requires ATP • Secondary Active Transport
o Adenosine Triphosphate • As Na+ moves through the channel to go in the
o “Energy currency of the cell” cell, it helps push H+ out
H combines with HCO3– outside of the cell
+
(B) TUBULAR REABSORPTION
• Resulting H2CO3 is converted by carbonic
from the kidney tubule into the blood anhydrase into CO2 and H2O
depending upon the chemicals being reabsorbed, it could o What happens to the bicarbonate (HCO3–)?
be active or passive Approximately 90% of HCO3– gets pushed into the blood
(1) Sodium-Potassium ATPase (4) Osmosis
Pumps 3 Na+ out of the cell and 2 K+ ions into the cell Sodium is very critical in the process
o Na+ and K+ move against their concentration gradient Obligatory Water Reabsorption
from an area of low concentration to an area of high o Water feels obliged to follow sodium
concentration For example, in the sodium-glucose channel
AfraTafreeh.com
Primary active transport • When sodium is coming in with the glucose,
o Requires ATP water feels obliged to follow sodium
o Water moves by the process of osmosis
97% of K in our bodies is inside the cell From the kidney tubules into the blood
What does it do inside the cell?
o [Na+] and [K+] About 65% of sodium is being reabsorbed
o Hence, 65% of water is also being reabsorbed
(2) Secondary Active Transport
(5) Paracellular Transport
Passive diffusion of one substance helps facilitate the
active transport of another substance How ions move in between the cell to the blood
Special transporter on cell membrane o Ca2+, Mg2+, K+, Cl–
Can transport two things at once inside the cell o Very little calcium and magnesium are reabsorbed in this area
About 50% of Cl– is reabsorbed via this mechanism
(i) Sodium-Glucose Cotransporter About 55% of K+ is reabsorbed via this mechanism
Na+
(6) Sodium-Chloride Symporter
• Since there’s [Na+] inside the cell, it’s moving
passively along its concentration gradient Moves sodium and chloride ions into the cell
Glucose o They are then pushed into the blood
PROXIMAL CONVOLUTED TUBULE RENAL PHYSIOLOGY: Note #2. 1 of 3
