BIOL125 Lecture Notes - Lecture 11: Airway Obstruction, Alkalosis, Metabolic Acidosis
BIOL week 11 LC pH Homeostasis
Basic Concepts:
- If [H+] increases, pH decreases
- Plasma pH = 7.4
- The pH of arterial blood must remain within 6.8-7.8
opH above 7.8 or below 6.8 is incompatible with life
- if pH changes protein structure, enzyme function, etc. get impacted/impaired
- even slightly altered pH has a major impact on protein structure and function, and
even slight pH changes may be lethal due to loss of protein function
Threats to pH balance
- As the result of physiological metabolism, the human body produces great quantities
of acidic products
- But this is ok; we are well-equipped to handle acid (H+) load
Pillars of pH Homeostasis
1. Buffer systems (instantaneous)
2. Respiratory control (1-3 minutes) ventilation
3. Renal control (hours – days) although it takes longer, it tends to have a more
sustained effect
What are (pH) buffers?
- Buffers can bind or release H+ can reduce changes of free H+ concentration
oBuffers resist changes in pH upon addition of small amounts of either an acid
or base
- Buffer solutions (buffers) stabilise pH
Buffer Systems in the Human Body
- We use the combination of several buffers
oProteins positive and negative systems create the potential for binding
oHaemoglobin
oPhosphate
- H2CO3/HCO3-
H2CO3/HCO3- Buffer System
- The single most important buffer system in the body to maintain the pH of blood
- HCO3- concentration of arterial blood = 24 mM (milimolar)
- pCO2 of arterial blood = 40 mmHg
- 20:1 (ratio of bicarbonate to CO2)
- The point here is that this is the pH buffer system that actually sets the plasma pH
(and all other buffer systems just help compensate for apparent changes). Further,
because the numerator and denominator can be independently set by the renal and
respiratory systems, respectively, any desired pH value could be set (at least in
theory)
- This is an open system the numerator and denominator can be changed
independently
- [HCO3-] is controlled by the kidneys
- pCO2 is controlled by the respiratory system
- This is the buffer system that actually sets the plasma pH
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