THANG BANG ACID - BASE
3. SI/DIEU HOA THANG BANG ACID - BASE CUA CCf THE
Trong qua trinh chuyen hda, luon co stf tao thanh mot sd acid vo cd nhtf H2S04, H3P04, H2CO3..., mot sd acid htfu cd nhtf acid lactic, acid pyruvic, acid acetoacetic... Tong ltfdng ion H+
dtfdc tao thanh cd thd len de'n 100mEq/24gid. Tuy vay, pH ciia mau va cac dich cd thd vln ra't
on dinh chi giao dong trong mot gidi tan hep (7,4 ±0,05). Cd thd cd kha nang duy tri thang bang acid base nhtf vay chinh la nhcj mot cd chd didu hda ciia cac he dem kdt hdp vdi hoat dong sinh
ly ciia phoi va than.
3.1. Dieu hda thang bang acid base do tac dong ciia he dem
He dem cd tac dung didu hda nhanh chdng cac tac nhan gay ma't can bang noi mo vd
acid base.
Cd the chia he dem cua huyet ttfdng va dich gian bao thanh hai loai:
- He dem bicarbonat (H2C03 / HC03")
- He dem ngoai bicarbonat: bao gdmcac he dem khac.
Khi cd the nhan mot Itfdng acid manh (AH), 53% Itfdng acid manh do se ket hdp vdi ion
bicarbonat (HC03"), 47% ket hdp vdi cac anion cua he dem khac.
Khi cd the nhan mot ltfdng base manh, 53% ltfdng base do se ket hdp vdi acid carbonic
,phan con lai ket hdp vdi acid yeu cua cac he dem khac.
Do do, stf tang acid hay base khong lam anh htfdng de'n pH ciia cd the.
3.2. Dieu hoa thang bang acid - base do co* che sinh ly
3.2.1. Su* ho hap d phoi
C02 dtfdc tao thanh lien tuc trong td chtfc vdi toe do khoang 200ml/phut (lOmmol/phut).
Ttf td chtfc, C02 dtfdc van chuyen bdi mau de'n phoi, dao thai ra ngoai thong qua qua trinh trao ddi khi dphoi vdi tdc do bang vdi tdc do tao thanh dcac td chtfc. Cd the ngtfdi la mot he tho'ng md, trong do C02 vtfa dtfdc tao thanh lien tuc trong cac mo, vtfa dtfdc dao thai lien tuc bdi phoi.
Do dd, pC02 ciia mau va cac dich khong ddi va pH cQng gitf dtfdc gia tri on dinh. Vay phoi la cd quan thai trtf acid carbonic htfu hieu bang stf thd ra khi C02. Trung tarn ho ha'p d hanh tuy dieu
hoa pC02 va pH ciia mau theo cd che':
- Khi p C02 /mau tang, pHmau giam, tdc do ho ha'p tang.
- Khi p C02 / mau giam, pH mau tang, to'c do hd ha'p giam.
3.2.2. Su" bai tie't d than
•_•- Than dong vai tro quan trong trong stf dieu hda thang bang acid base ciia cd the. Cd che ciia stf dieu hda la duy tri ndng do sinh ly ciia ion bicarbonat (HC03") trong huye't ttfdng va dich
gian bao bang 3 qua trinh nhtf sau:
♦ Tai hap thu ion bicarbonat (HCO3) tf o'ng than
Trong dieu kien sinh ly binh thtfdng, ntfdc tieu khong chtfa HC03" vi toan bd ltfdng HCO3"
loc qua cau than dtfdc tai ha'p thu d o'ng than... Khi than bi tdn thtfdng ve chtfc nang tai hap thu HC03", se nhanh chdng din de'n tinh trang thieu hut HC03" va nhilm base chuyen hda.
Kha nang tai ha'p thu HC03" ciia te' bao than chiu anh htfdng ciia nhieu yeu to':
- pC02 ciia cd the tang lam tang hap thu HC03" d o'ng than va ngtfdc lai.
- Stf tai ha'p thu Na+ d o'ng than.
- Ndng do CI" va K+ trong mau giam cung gay tang tai ha'p thu HC03" d o'ng than.
Trtfdng hdp trong mau va dich ngoai te bao thtfa HC03", than se khong tai hap thu ma se bai xua't ion nay.
♦Tan tao bicarbonat
Cac ion H+ cua cac acid tao ra trong qua trinh chuyen hda dtfdc trung hoa bdi HC03" noi md. Ltfdng HC03" mat di nay se dtfdc bu lai bang stf tan tao HC03" trong te bao o'ng than.
, Ion HC03" dtfdc tao bdi phan tfng gitfa C02 sinh ra d te bao va ntfdc tao H2C03 Chat nay dtfdi tac dung ciia anhydrase carbonic phan ly thanh HC03" va H+. Ion HC03" dtfdc khuech tan vao mau, con H* se ke't hdp vdi NH3 (san pham chuyen hda d than) tao NH4+ dao thai ra ngoai
theo ntfdc tieu.
♦ Dao thai cac acid khong bay hoi ra ntftfc tieu
Cf ntfdc tieu.ngoai NH3,con cd muo'i phosphat (HP04)2", creatinin, urat ...la chat nhan H+
de tao thanh cac dang acid . Ngoai ra, trong ntfdc tieu con chtfa cac acid htfu cd ,san pham trung gian cua qua trinh chuyen hda. Tat ca cac dang acid nay dtfdc goi la acid khong bay hdi cda
ntfdc tieu.
4. ROI LOAN THANG BANG ACID - BASE
Tuy thuoc vao nguyen nhan, cac tinh trang ro'i loan thang bang acid-base dtfdc chia thanh
2 nhdm chinh:
4.1. Ro'i loan thang bang acid-base do nguyen nh£n ho hap
Gdm nhiem acid ho hap va nhiem base ho ha'p, cd lien quan trtfc tiep den stf thay ddi
pC02 cda mau.
4.1.1. Nhilm acid ho hS'p
Nhiem acid ho ha'p la trang thai hay qua trinh benh ly gay giam stf thong khi cda phe nang dan de'n tang pC02 trong mau dong mach (>45mmHg), vi du:viem phdi,khi thdng, phu phoi, tdn thtfdng trung tarn ho ha'p, liet cd hd ha'p, tac nghen dtfdng thd
Phan tfng cda cd the: huy dong he dem cda mau va dich the, tang tao HC03" cda than.
Ne'u nhilm acid hd ha'p keo dai, than tang dao thai ion If1" dtfdi dang NH4+ va cac acid khong
bay hdi.
4.1.2. Nhidm base ho hap
La trang thai hay qua trinh benh ly gay tang thdng khi phe nang dan de'n giam pC02 trong mau dong mach (< 35mmHg), vi du :trung tarn ho ha'p bi kich thich (viem nao) hay benh ve
phoi.
Phan tfng cda cd the: huy dong he thdng dem cda mau va dich noi bao va cham hdn la hoattiong.bu trtf cda than (giam stf tao thanh amoniac va tan tao HC03", tang dao thai HCO-Q.
4.2. Ro'i loan thang bang acid - base do nguyen nhSn chuyen hoa
Khi ndng do bicarbonat thay ddi do nhtfng cd che lien quan de'n chtfc nang cda than, he
tieu hda va stf chuyen hda d md se din de'n tinh trang nhiem acid chuyen hda va nhilm base
chuyen hda.
4.2.1. Nhilm acid chuydn hda
La qua trinh benh ly dan de'n tang acid khong bay hdi trong cd the hoac stf thieu hut HC03" trong mau va dich ngoai bao (ndng do HC03" <22 mEq/L)
Nguyen nhan:
- Mat ion HC03" do tieu chay keo dai.
- Suy than, ro'i loan chtfc nang o'ng than (giam kha nang dao thai cac acid chuyen hda nhtf acid lactic, ceton, giam kha nang tan tao HC03", giam tai ha'p thu HCO3").
- Ro'i loan chuyen hda gay tang stf tao thanh cac acid cetonic nhtf benh tieu dtfdng, ddi
keo dai.
4.2.2. Nhiem base chuyen hoa
La tinh trang benh ly dan den thie'u acid hoac thtfa HC03"d mau va dich ngoai bao (ndng
do bicarbonat > 26mEq/L).
Nguyen nhan:
- Ndn mtfa keo dai gay mat acid dich vi - Tang tan tao HC03"d te bao o'ng than.
- Giam CI" trong mau.
- Cac benh gay tang san xua't aldosterol do hau qua cda viec mat acid theo ntfdc tieu.
TAI LIEU DQC THEM
1. Bo mon Hda sinh-Trtfdng Dai hoc Y ha Noi. Hda sinh, NXB Y hoc Ha Noi, 2001.
2. Bo mon Hda sinh - Dai hoc Y dtfdc TPHCM, Hda sinh y hoc NXB Y hoc TP HCM 2003 3. Bo Y Te, Vu Khoa hoc va Dao tao, Hda sinh hoc, NXB Y hoc Ha Noi, 2005
4.R.K. Murray, D.K. Granner, V.W. Rodwell-Harper's Illustrated Biochemistry 27th edition-
Lange Medical Books/McGraw-Hill, 2006.
5. F. Percheron, R. Perles, M.J. Foglietti, Biochimie strucmrale et metabolique, Tome 1, Massonv1992.
6. P. Valdiguie, Biochimie clinique, EM Inter, 1993.
7. C.A. Burtis , E.R. Ashwood, D.e. Bruns - Tietz Textbook of Clinical Chemistry and Molecular Diagnostics 4th edition- Elsevier saunders, 2006.
CAU HOI TU LU0NG GIA Chon mot cau tra Itfi dung nh&'t
1. He dem chd yeu cua huyet ttfdng va dich gian bao la:
a. He dem bicarbonat
b. He dem phosphat c. He dem protein
d. He dem hemoglobin
2. Phoi cd vai tro quan trong trong stf dieu hda thang bang acid - base cda cd the thong qua tac
dong cda:
a. He dem hemoglobin va he dem phosphat b. He dem bicarbonat va he dem protein c. He dem hemoglobin va he dem bicarbonat d. He dem protein va he dem phospghat 3. He dem chu yeu cda dich trong td bao la:
a. He dem hemoglobin va he dem phosphat b. He dem bicarbonat va he dem protein c. He dem hemoglobin va he dem bicarbonat d. He dem protein va he dem phospghat