Acid-Base Balance Flashcards
Where do H+ ions come from?
Why is PH kept constant?
- Metabolism of Carbohydrates and Fat - produce CO2, which becomes Carbonic Acid - Volatile acid
Metabolism of Proteins - Sulphuric and Hydrochloric Acid - Non-volatile acids - Enzymes function at a specific PH and have many functions in the body. PH kept between 7.35 - 7.45.
What are the 3 systems that control PH?
What are the 3 buffering systems in the body and what are their equations?
- ICF/ECF Buffering systems
- Respiratory system - pCO2
- Kidney - [HCO3-]
1. Bicarbonate System: H+ + HCO3- ⇄ H2CO3 ⇄ CO2 + H2O 2. Phosphate System: H+ + HPO42- ⇄ H2PO4- 3. Protein Buffer System: H+ + Pr- ⇄ HPr
What are the logarithmic and non-logarithmic forms of the Henderson-Hasselbach equation?
[H+] = ( K1[CO2] ) / [HCO3–]
PH = pK + ( log10[HCO3-] ) / [CO2]
How do the kidneys control acid-base levels?
What are the Primary Renal mechanisms involved in this?
- Kidneys control the acid-base levels by excretion of acidic or basic urine
- Primary renal mechanisms involved are:
• Reabsorption/secretion of HC03-
• Formation of new HC03-
• Secretion of H+ into tubule, where they react with the buffer systems e.g. ammonium, phosphate, bicarbonate systems.
What occurs in the PCT cell in controlling [H+] and [HCO3-]?
LOOK AT DIAGRAM!!
85-90% of HC03- is reabsorbed and it has a huge capacity to secrete H+:
- CO2 reacts with water, catalysed by Carbonic Anhydrase/CA, to from carbonic acid, which then dissociates into HC03- and H+.
- Na+ moves into cell from lumen, providing energy for the secondary active transport of H+ into the filtrate using an Na/H Antiporter on the luminal membrane = acidifies urine.
- H+ is also actively transported from cell to filtrate using the H-ATPase pump - for every H+ that’s secreted, a HC03- is reabsorbed into the blood along with a Na+ via a Symporter on the basolateral membrane.
What occurs in the Late DCT/CD in controlling {H+} and [HCO3-]?
LOOK AT DIAGRAM!!
Occurs in intercalated cells:
• Luminal H-ATPase pump allows for even more H+ to be secreted against a large H+ gradient, since lots of it was secreted in the PCT.
• In the distal nephron, there’s a low [HC03-] and the H+ present can react with other buffer systems, like Phosphate and Ammonia.
Explain the role of the Phosphate system in the kidney?
LOOK AT DIAGRAM!!
- HPO42- buffers some of the H+ secreted
- Effective buffer as it has pKa=6.8, which is near pH of filtrate
- HC03- is actively moved into ECF via Cl-HC03 antiporter on basolateral membrane.
- H+ is actively moved into lumen via H-ATPase (aldosterone-sensitive) on luminal membrane - H+ reacts with HPO42-, instead of bicarbonate.
Explain the role of the Ammonia system in the kidney?
LOOK AT DIAGRAM!!
Epithelial cells produce α-ketoglutarate and NH3 from glutamine - uses Glutaminase:
- α-ketoglutarate → H2CO3 - dissociates into new bicarbonate and H+
- NH3 reacts with this H+ → NH4+
- NH4+ is secreted into lumen via NH4/Na antiporter on luminal membrane
*NH4+ in urine is elevated a lot during metabolic acidosis
What is the role of the respiratory system in PH control?
Central chemoreceptors in medulla - monitors plasma [H+] via the CSF indirectly:
• ↓blood PH = ↑Ventilation - remove more CO2.
What causes Metabolic Acidosis?
How do the ICF/ECF, Kidney, and Lungs work together to adjust this acid-base imbalance?
LOOK AT DIAGRAM!!
- Sepsis/shock, Diabetic Ketoacidosis, Diarrhoea
- ICF/ECF: doesn’t help compensate
Kidney: ↑H+ secretion, ↑NH4+ secretion, ↑HCO3- formation and reabsorption.
Lungs: ↑Ventilation = ↓pCO2
What causes Metabolic Alkalosis?
How do the ICF/ECF, Kidney, and Lungs work together to adjust this acid-base imbalance?
LOOK AT DIAGRAM!!
- Excessive Thiazide diuretic use, Vomiting, Alkaline antacids, Hypokalaemia
- ICF/ECF: doesn’t help compensate
Kidney: ↓H+ secretion, ↓NH4+ secretion, ↓HCO3- formation and reabsorption.
Lungs: ↓Ventilation = ↑pCO2
