Learning objectives
- By the end of the session should be able to comprehend:
- Regulation of Hydrogen ion
- Production
- Elimination
- Concept of acid and a base
- Defense mechanisms
- Buffer and its types
Acid Base Balance
• Precise regulation of hydrogen ions
• Balance between intake, production and excretion of H+ ions is
maintained
• Optimum hydrogen ion balance is maintained for homeostasis
Introduction
• pH:
Measure of hydrogen ions,
Normal pH= 7.35-7.45
• pCO2 :
– Partial Pressure of CO2
: is the concentration of CO2
in the blood
– High pCO2
indicates acidosis and vice versa
• HCO3 or Bicarbonate:
– Measures the concentration of HCO3
ions only
– High values indicate alkalosis and vice versa
Introduction
• Acids: Liberate free H+
ions
– Strong Acid: Greater tendency to dissociate into free H+ & Anions e.g. HCl
– Weak Acid: Only less no of molecules dissociate in solution e.g.: H2 CO3
• Base: Accepts free H+ ions
– Strong Base: is able to bind H+
ions more readily than weak base
• K : Dissociation constant
– Every acid has constant degree of dissociation, when in solution
Dissociated ions [H+
] [(HCO-3
] = K
[H2 CO3
]
Undissociated Acid
Introduction
• Normal pH = 7.4
– pH of Arterial Blood = 7.45
– pH of Venous Blood = 7.35
• Normal Range = 6.8 – 8.0 Beyond which death occurs in seconds.
– Acidosis = Blood pH < 7.35 – Alkalosis = Blood pH > 7.45
• pH of ICF is lower than plasma i.e. 6.0 – 7.4
• pH of urine ranges between 4.5 – 8.0
• Extreme Acidic pH in body is of gastric Acid = 0.8
• As a result of metabolic processes ‘Acids’ are produced
• Daily production of H+ ions by metabolism or ingestion with food [e.g.
Citric Acid in oranges] = 80 mEq/L
• Types
i. Respiratory or Volatile acids; CO2
ii. Metabolic or fixed acids
• To maintain balance ‘acids’ are to be; “Excreted” or “Metabolized”
• Non-volatile acids (fixed acids), not excreted by lungs, but excreted by
kidneys
• Lungs regulate amount of CO2
in the blood
• Kidneys regulate the bicarbonate ions
• Both acidosis and alkalosis can be of two different types:
– Respiratory
– Metabolic
• Respiratory disturbances caused by various malfunctions of the
lungs.
• Metabolic disturbances are caused by metabolic disorders
which result in an excessive build up or loss of acids or bases
Defense Mechanisms
• Hydrogen ions in the body are regulated by Three Defense
Mechanisms:-
1
st defense: Chemical buffering
2
nd defense: Respiratory (alteration in arterial CO2)
3
rd defense: Renal (alteration in HCO-3 excretion)
Buffer
• A substance that can reversibly bind H+ ions
Buffer + H+ H Buffer
– If excess reaction shifts to the right
– If deficient reaction shifts to the left
• Normal H+ ions concentration in body = 0.00004mEq/L
– Can alter from 10nEq/L to 160nEq/L
• Daily intake or by metabolism = 80mEq/L
• Buffering system is needed to maintain the concentration
Buffer
- Chemical Buffer system:
– Responds within seconds
– Does not eliminate or add H+
from body
– Operates by binding or to tied up H+
till balance is reestablished.
14
a. In ECF:
• Mainly HCO-3/CO2 Buffer
system
• Plasma Proteins
• HPO–4/H2PO-4 Buffer system
b. In ICF:
• Proteins Mainly e.g.: Hb in
RBCs
• HPO–4/H2PO-4 Buffer
system
• Routes of excretion of acids
– Lungs
– Kidneys
- Respiratory Mechanisms:
– Responds within minutes
– Takes 6-12 hours to be fully effective
– Operates by excreting CO2 or (adding H2CO3/HCO-3)
- Renal Mechanisms:
• Responds slowly (effectively in 3-5 days)
• Eliminates excess Acids or Bases from body
• The most powerful mechanism
e.g. i. HCO3/CO2 Buffer system
ii. NH3/NH+
4 Buffer system
iii. HPO–4/H2PO4 Buffer system
Bicarbonate buffer system
• Consist of
– A weak acid
– A bicarbonate salt
CO2+ H2 O H2 CO3
• Slow reaction without carbonic anhydrase
• Present in walls of alveoli and renal tubules
H2 CO3 H++ HCO-3
• Second component
NaHCO3 Na + HCO-3