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RESPIRATORY PHYSIOLOGY

Role of the Lungs in Acid-Base BaLar

A. Role ot Lungs and Kidneys in Acid-Base Balance

"Add Load"    ^Vol-'^lilt

Body

tissues

C. Acid-Base Paths

B. Metabolit Production of Acid and Alkali

Food Source	Add/ Alkali	Quantitv (mEq/day)
Carbohydrate Fat	]— CO,	15-20,000
Amino adds
S-containing	H2so41
Cationic	HCI U	—■100 (acid)
Anionie	Hcor J
Organie ions	HCO,-	60 (alkali)
Pbosphate	h2po4-	30 (acid)
Total		70 (acid)
1 mtq/k&/day of noiwolatile add production

Metabolic alkalosis and respiratory addosis

Metabolic alkalosis

Uncompensated respiratory addosis

Metabolic alkalosis

Metabolic addosis N /    ^a"^d "^Bpira,"^{y a,kabs}''

nal buffer linę

and respiratory addosis

Metabolic addosis and respiratory alkalosis

D. Acid-Base Disorders

Disorder	pH	1 ° Alteration	Defenso Merhanisms
Metabolic addosis		♦ 1 HCO,- 1	Buffers, | PC02, | NAL
Metabolic alkalosis	t	f 1 HCO," 1	Buffers, f PC02. | NAE
Respiratory addosis	♦	ł PCO,	8uffers & f NAL	J. Perkins
Respiratory alkalosis	♦	♦ PCO,	Buffers A | NAE	•-WNJ

Figurę 5.23 Acid-Base Baiancf_

Ą Both the lungs and kidneys participate in add-base balance.

R, Our diet and cellular metabolism add acid and alkali to our system. In a typical meat-containing diet. there is the addition ot acid to our body tluids. CO., (sometimes referred to as "volatile acid"), gen erated by carbohydrate and fat metabolism, is efficiently eliminated by the lungs and does not normally aftect acid-base balance. How-ever, tailure to excrete the CO., ran alter acid-base balance. Non-volatile add (e.g., lactic acid) is buffered by HCO,* in the extracellu-lar fluid. The kidneys ntust excrete this nonvolatile acid and repleitish the HCO/ used to neutralize these adds. The kidneys do this by excreting the acid anion with NH« (the kidneys also excrete H*. which also results in the addition HCO, to the cxtracdlular fluid (see Figurę 6.18). The lungs servc as a respiratory "buffer* that can respond quickly and remove large quantities ol volatile add {CO hypcrventilation. The kidneys take hours or days to respond to ar acid-base imbalance and do so largely by varying the amount ot NH.,' exc reted in the urine. C and D illustrate acid-base disorders resulting from alterations in the Pco, (respiratory disordersi or alt*. atir>ns in the IHCO./I (metabolic disorders). When an acid-base i -turbance occurs, intracellular (primarily protcins) and extracellula-(primarily HCO,') buffers minimize the change in body fluid pH i-addition, ihe lungs can adjust the Pco, to compensate for metabr disorders, and the kidneys can ad|ust net acid excretion lo coinpr sate for respiratory disorders. Notę: Net acid excretion (NAE) includes acid excreted with urinary buffers and as NH,', less any HCO,- lost in the urine.

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