Acid-Base Balance Flashcards
(46 cards)
What is the definition of a body fluid buffer?
Molecule that helps to maintain pH within a normal range
What are the Buffers in our bodies?
- HCO3- (ECF)
- Phosphate and Proteins (ICF)
- main place for buffering in the body
How are acids and bases moved between ECF and ICF?
K+/H+ Exchanger which can go IN BOTH DIRECTIONS depending on needs of the body
In the case of Acidosis, what action would the K+/H+ Exchanger take?
- H+ is moved into the cell
2. K+ is moved into the ECF
In the case of Alkalosis, what action would the K+/H+ Exchanger take?
- H+ is moved into the ECF
2. K+ is moved into the cell
What effect does Hypoventilation have on the body’s acidity?
Hypoventilation=Acidosis
- Increase in CO2
- Decreases pH
What effect does Hyperventilation have on the body’s acidity?
Hyperventilation=Alkalosis
- Decreases in CO2
- Increases pH
Bicarbonate:
- Freely Filtered
- 24 mmol/L
- Filtered Load= 4320 mmol/day
- Virtually entirely REABSORBED
Simplified Overview of Renal Acid-Base Handling:
- Proximal Tubule: Kidneys reabsorb Bicarbonate and secrete NH4+
- Ascending Limb and Distal Tubule: Kidneys secrete either H+ or HCO3- to balance NET Input
What is the Proximal Tubule Mechanism for Bicarbonate Reabsorption?
- Inside of Proximal Tubule cells, H2O and CO2 come together to form H2CO3 (Carbonic Acid)
- Carbonic Anhydrase breaks down H2CO3 into H+ and HCO3-
- Na+/H+ Exchanger on Apical Membrane pumps H+ into the lumen and Na into the cell (NOTE: Angiotensin II can increase this exchange)
- H+ ion in the lumen combines with a filtered HCO3 to produce H2O and CO2 (Lose 1 filtered HCO3)
5A. Na/HCO3 Symporter on the Basolateral Membrane pumps Na and HCO3 out of the cell and into the Blood (Gain 1 blood HCO3)
OR
5B. Cl/HCO3 Antiporter on Basolateral Membrane pumps one HCO3 into the blood and Cl into the cell
IMPORTANT: This is the “effective” Reabsorption of an HCO3- molecule without moving it across the membranes
What are the Net results of Proximal Tubule Bicarbonate Reabsorption?
NO NET CHANGE IN PLASMA BICARBONATE
- Filtered Bicarbonate disappears (H2O and CO2)
- Bicarbonate produced inside cell enters blood
Does Bicarbonate reabsorption make Urine more acidic?
NO, the H+ ion that is secreted into the urine combines with HCO3 to produce CO2 AND H2O
What is the Distal Tubule Mechanism for Bicarbonate Reabsorption in ALPHA Intercalated Cells?
HCO3 REABSORPTION
- Inside of Distal Tubule cells, H2O and CO2 come together to form H2CO3 (Carbonic Acid)
- Carbonic Anhydrase breaks down H2CO3 into H+ and HCO3-
ENERGY IS REQUIRED TO PUMP H+ INTO THE URINE:
3A. Proton Pump on the Apical Membrane utilizes ATP to put H+ into Urine using Primary Active Transport
OR
3B. H+/K+ ATPase on the Apical Membrane pumps a H+ out into the Urine and a K+ into the cell - H+ pumped out of the cell combines with a Filtered HCO3 in the Urine to form H2O and CO2
- Cl/HCO3 Antiporter on Basolateral Membrane pumps one HCO3 into the blood and Cl into the cell
What is the Distal Tubule Mechanism for Bicarbonate Reabsorption in BETA Intercalated Cells?
HCO3 SECRETION
- Inside of Distal Tubule cells, H2O and CO2 come together to form H2CO3 (Carbonic Acid)
- Carbonic Anhydrase breaks down H2CO3 into H+ and HCO3-
ENERGY IS REQUIRED TO PUMP H+ INTO THE BLOOD:
3A. Proton Pump on the Basolateral Membrane utilizes ATP to put H+ into Blood (Primary Active Transport)
OR
3B. H+/K+ ATPase on the Basolateral Membrane pumps a H+ out into the Blood and a K+ into the cell - H+ pumped out of the cell and into the blood increasing pH
- Cl/HCO3 Antiporter on Apical Membrane secretes one HCO3 into the urine and takes a Cl into the cell
In the Distal Tubule, when would the BETA Intercalated Cells be ACTIVE while the ALPHA Intercalated Cells are INACTIVE?
During Alkalosis
What happens in a Base load situation?
You are loaded with base, so Bicarbonate excretion happens
What happens in an Acid load situation? Simplified
- The Acid load reduces the amount of Bicarb in the blood
- Kidney needs to replace lost Bicarb by generating NEW Bicarb
- H+ ions are secreted via NH4+ and Titratable Acids
Can a H+ ion be free flowing in the urine?
NO
What is the purpose of Titratable Acids and what is their mechanism?
Purpose: Excrete excess H+ and increase HCO3- concentration in the blood
- Inside of Distal Tubule cells, H2O and CO2 come together to form H2CO3 (Carbonic Acid)
- Carbonic Anhydrase breaks down H2CO3 into H+ and HCO3-
ENERGY IS REQUIRED TO PUMP H+ INTO THE URINE:
3A. Proton Pump on the Apical Membrane utilizes ATP to put H+ into Urine using Primary Active Transport
OR
3B. H+/K+ ATPase on the Apical Membrane pumps a H+ out into the Urine and a K+ into the cell - H+ pumped out of the cell combines with a Filtered HPO4 creating H2PO4
- H2PO4 Titratable Acid is excreted in the urine lowering blood H+ levels
- Cl/HCO3 Antiporter on Basolateral Membrane pumps NEW HCO3 into the blood and Cl into the cell
NET GAIN of 1 HCO3 in blood
Every Titratable Acid found in the Urine corresponds to…
Every Titratable Acid found in the Urine coincides to 1 NEW HCO3 put into the blood
What happens when the fixed amount of Titratable Acids in the body are all utilized?
By creating Ammonium
From what part of the Nephron are Titratable Acids secreted?
“TAD T”
Distal Tubule
From what part of the Nephron is Ammonium secreted?
“APT”
Proximal Tubule
What Amino Acid is the basis for creating Ammonium and where is it made?
- Glutamine
2. Made in the Liver by catabolism of proteins
