lab 9 regulating acid base balance A&P2

 Normal pH of body fluids

Arterial blood is 7.4

◦Venous blood and interstitial fluid is 7.35

◦Intracellular fluid is 7.0

 Alkalosis or alkalemia – arterial blood pH

rises above 7.45

 Acidosis or acidemia –

arterial pH drops below 7.35 (physiological acidosis)

 Concentration of hydrogen ions is regulated sequentially by:

◦Chemical buffer systems – act within seconds

◦The respiratory center in the brain stem acts to adjust RR up or down within 1à3 minutes

◦Renal mechanisms adjust excretion of H⁺ or HCO3^-, but this requires hours to days to change pH

 Strong acids – chemical buffer

all their H⁺ is dissociated completely in water

 Weak acids – chemical buffer

dissociate partially in water and are efficient at preventing pH changes

 Strong bases –

 chemical buffer

dissociate easily in water and quickly tie up H⁺

Weak bases –chemical buffer

accept H⁺ more slowly (e.g., HCO₃¯ and NH₃)

 Three major chemical buffer systems

Protein buffer system

Bicarbonate buffer system

Phosphate buffer system

protein buffer system

 Plasma and intracellular proteins are the body’s most plentiful and powerful buffers

 Some amino acids of proteins have:

Free organic acid groups (weak acids; aspartate)

◦Groups that act as weak bases (arginine or lysine)

 Amphoteric molecules

are protein molecules that can function as both a weak acid and a weak base

 Most influential in ICF –

75% of all buffering

bicarbonate buffer system

 A mixture of carbonic acid (H₂CO₃) and its salt, sodium bicarbonate (NaHCO₃) (potassium or magnesium bicarbonates work as well)

 If strong acid is added to bicarbonate buffer system

Hydrogen ions released combine with the bicarbonate ions and form carbonic acid (a weak acid)

◦The pH of the solution decreases only slightly

 If strong base is added: bicarbonate buffer system

◦It reacts with the carbonic acid to form sodium bicarbonate (a weak base)

◦The pH of the solution rises only slightly

 for the bicarbonate buffer system This system is the only important

ECF buffer

phosphate buffer system  Nearly identical to the bicarbonate system

true

for phosphate buffer system  Its components are:

◦Sodium salts of dihydrogen phosphate (H₂PO₄^-), a weak acid

◦Monohydrogen phosphate (HPO₄^2-), a weak base

phosphate buffer  This system is an effective buffer in

urine and intracellular fluid

physiological buffer system

 The respiratory system regulation of acid-base balance

 There is a reversible equilibrium between: for the physiological buffer system

◦Dissolved carbon dioxide and water

◦Carbonic acid and the hydrogen and bicarbonate ions

for physiological buffer system

 When hypercapnia or rising plasma H⁺ occurs:

◦Deeper and more rapid breathing expels more carbon dioxide

◦Hydrogen ion concentration is reduced

 for physiological buffer system

Alkalosis causes slower, more shallow breathing, causing

 

H⁺ to increase

for physiological buffer system

Respiratory system impairment causes

acid-base imbalance (respiratory acidosis or respiratory alkalosis)

 Chemical buffers can tie up excess acids or bases, but they

cannot eliminate them from the body

 The lungs can eliminate carbonic acid by

eliminating carbon dioxide

Only the kidneys ______of metabolic acids (phosphoric, uric, and lactic acids and ketones) and prevent metabolic acidosis

can rid the body

The ultimate acid/base regulatory organs are the

kidneys

 The most important renal mechanisms for regulating acid-base balance are:

Conserving (reabsorbing) or generating new bicarbonate ions

Excreting bicarbonate ions

Excreting H⁺ ions

 reabsorption of bicarbonate

Carbon dioxide combines with water in tubule cells, forming carbonic acid

 For each hydrogen ion secreted, a sodium ion (or maybe a potassium ion) and a bicarbonate ion are reabsorbed by the PCT cells

 Secreted hydrogen ions form carbonic acid; thus, bicarbonate disappears from filtrate at the same rate that it enters the peritubular capillary blood 

normal urine

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