Download Chapter 1 A Perspective on Human Genetics

ACID BASE BALANCE
Dr.Mohammed Sharique Ahmed Quadri
Assistant professor physiology
Al Amaarefa College
Objectives
 Identify the normal range of pH values, and the
upper and lower limits compatible with life.
 Identify the role of kidney in regulation of acid
base balance
 Explains the mechanism of reabsorption of
HCO3- and secretion of H+ by nephron
 Describe the adjustments in filtered load and
HCO3 reabsorption (H+ secretion) by alterations
in systemic acid-base balance.
 Describe net acid excretion by the kidneys,
treatable acid, the importance of urinary buffers,
and the production and excretion of ammonium.
Acid-Base Balance
 Refers to precise regulation of free H+ concentration in body
fluids
 Acids
• Group of H+ containing substances that dissociate in
solution to release free H+ and anions(H2CO3)
 Bases
• Substance that can combine with free H+ and remove it
from solution(HCO3)
 pH
• Designation used to express the concentration of H+
• pH 7 – neutral
• pH less than 7 → acidic
• pH greater than 7 → basic
pH
Acid-Base Balance
 Arterial pH less than 6.8 or greater than 8.0 is
not compatible with life
 Acidosis
• Exists when blood pH falls below 7.35
 Alkalosis
• Occurs when blood pH is above 7.45
Acid-Base Balance
 Consequences of fluctuations in pH
• Changes in excitability of nerve and
muscle cells
• Marked influence on enzyme activity
• Changes influence K+ levels in body
The body produces more acids than
bases
 Sources of H+ in the body
• Acids taken with foods.
• Carbonic acid formation
CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3• Inorganic acids produced during breakdown of
nutrients( sulfuric acid & phosphoric acid )
• Organic acids resulting from intermediary
metabolism( lactic acid)
Lines of Defense Against pH Changes
 Chemical buffers :function almost immediately
(seconds to minutes).
 Respiratory mechanisms :take minutes to
hours.
 Renal mechanisms: may take hours to days.
First line of defense
Lines of Defense Against pH Changes
Buffer systems do not eliminate H+ from or add
them to the body but only keep them tied up until
balance can be reestablished by other mechanisms.
Buffer Systems in the Body
Bicarbonate: most important ECF buffer
H2O + CO2
H2CO3
H+ + HCO3Phosphate: important ICF and renal tubular buffer
HPO4-- + H+
H2PO4 Ammonia: important renal tubular buffer
NH3 + H+
NH4+
Proteins: important ICF and ECF buffers
Largest buffer store in the body
Albumins and globulins, such as Hb
Respiratory System
 Second line of defense again changes in pH
 Acts at a moderate speed
 Regulates pH by controlling rate of CO2 removal
Kidneys
 Third line of defense against change in
hydrogen ion concentration
 Kidneys require hours to days to compensate for
changes in body-fluid pH
 Control pH of body fluids by adjusting
• H+ excretion
• HCO3- excretion/ reabsorption
• Ammonia secretion
H+ secretion
 In luminal membrane
 H+ ATPase pump
 Na – H + Antiporter
Mechanism of HCO3- Reabsorption and
Na+ - H+ Exchange
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H+ secretion in Distal & Collecting Tubule
H+ secretion and excretion couples with
addition of HCO3 to plasma
Renal handling of H+ during acidosis and
alkalosis
 Under normal circumstances proximal tubular
cells and alpha intercalated cells promotes
• Net H+ secretion
• HCO3- reabsorption
 This pattern of activity adjusted when pH
deviates
Control of rate of tubular secretion & H+
reabsorption
Other Urinary Buffers
 the minimal urine pH is about 4.5.
 In order to excrete more H+, the acid must be
buffered in tubular lumen.
 H+ secreted into the tubular tubule and combines with
HPO4-2 or NH3.
 HPO4-2 + H+
 NH3 + H+
H2PO4-2
NH4+
Buffering of Secreted H+ by Filtered phosphate
(NaHPO4-) and Generation of “New” HCO3-
“New” HCO3-
Production and Secretion of NH4+ and HCO3- by
Proximal, Thick Loop of Henle, and Distal Tubules
H++NH3
“New” HCO3-
Acid-Base Imbalances
 Can arise from either respiratory dysfunction or
metabolic disturbances
 Deviations divided into four general categories
•
•
•
•
Respiratory acidosis
Respiratory alkalosis
Metabolic acidosis
Metabolic alkalosis
Respiratory Acidosis
 Result of abnormal CO2 retention arising from hypoventilation
 Possible causes
• Lung disease
• Depression of respiratory center by drugs or disease
• Nerve or muscle disorders that reduce respiratory muscle
activity
• Holding breath
Respiratory Acidosis
Compensations
Chemical buffers immediately take up
additional H+
Kidneys are most important in
compensating for respiratory acidosis
Respiratory Alkalosis
 Primarily due to excessive loss of CO2 from body as result of
hyperventilation
 Possible causes
• Fever
• Anxiety
• Aspirin poisoning
• Physiologic mechanisms at high altitude
Respiratory Alkalosis
Compensations
Chemical buffer systems liberate H+
If situation continues a few days, kidneys
compensate by conserving H+ and
excreting more HCO3-
Metabolic Acidosis
 Includes all types of acidosis other than those caused by
excess CO2 in body fluids
 Causes
• Severe diarrhea
• Diabetes mellitus
• Strenuous exercise
• Uremic acidosis

Metabolic Acidosis
Compensations
Buffers take up extra H+
Lungs blow off additional H+ generating CO2
Kidneys excrete more H+ and conserve more
HCO3-
Metabolic Alkalosis
 Reduction in plasma pH caused by relative deficiency of
noncarbonic acids
 Causes
• Vomiting
• Ingestion of alkaline drugs
Metabolic Alkalosis
Compensations
Chemical buffer systems immediately liberate H+
Ventilation is reduced
If condition persists for several days, kidneys
conserve H+ and excrete excess HCO3- in the urine
Summary of acid base abnormalities
References
 Human physiology by Lauralee Sherwood, seventh
edition
 Text book physiology by Guyton &Hall,11th edition
 Text book of physiology by Linda .s contanzo,third
edition