THANG BANG ACID - BASE
4. Neu dtfdc ynghia lam sang cda cac chat bat thtfdng trong ntfdc tieu
Trinh bay dtfdc nguyen ta*c va y nghia cac nghiem phap tham do chtfc nang
than. 6
5
1. THAN
^ Than gid* vai trd quan trong nhat trong viec bai xua't cac cha't cd hai hay khong can thiet ra ngoai cd the dtfdi dang ntfdc tieu. Than tham gia didu hda thang bang acid - base nhd vao stf tai tao ion bicarbonat va stf bai tiet ion amoni va hydro. Cac chtfc nang khac cda than la tham gia vao mot sd chuydn hda cac cha't (acid
hippuric, urocrom) va chtfc phan ndi tiet.
_ Hai than cda ngtfdi ldn nang khoang 300g (khoang 0,5% khdi ltfdng cd the) va mdi than dai khoang 12 cm. Hang ngay ltfdng mau di qua than la rat ldn (1.000 - 1.500 lit/24 gid), vdi 90% Itfdng mau di qua de loc va dao thai cac cha't, con 10%
de cung cap nang Itfdng cho than.
Ddn vi chtfc nang cda than la nephron. Mdi than co khoang ttf 1 den 1,5 trieu nephron. Mdi nephron bao gdm :
- Cau than: gdm mot bd mao dong mach hinh cau (quan cau than) dtfdc boc
bang tui 2 mang (boc Bowman).
-Ong than: gdm co o'ng Itfdn gan no'i vdi boc Bowman, quai Henle va o'ng Itfdn
xa. Ong Itfdn xa nd'i vdi 6'ng gdp va cuo'i cung la be than.
Tieu dpng mach
than di ra
Nhung chit 6u>uc loc qua c^u thin
-Nu6c
- Chit diengiai
- Glucose -Acid amin - UrS -Acid uric
-Creatinin NaCl—-
Ong thgn
Hinh 9.1. Ca'u tao cda nephron, ddn vi chtfc nang cda than.
1.1. Chtfc nang loc va bai tie't cua than
Cac chtfc nang chinh cda than bao gdm stf loc, tai ha'p thu va bai tie't. Than ket hdp nhtfng chtfc nang nay de duy tri va dieu hda can bang ndi mdi.
Stf hinh thanh ntfdc tieu la tdng hdp cda cac qua trinh : - Sieu loc xay ra d cau than.
- Tai ha'p thu va bai tiet xay ra d o'ng than.
1.1.1. Qua trinh sieu loc
Giai doan dau cda stf tao thanh ntfdc tieu la qua trinh sieu loc cda huyet
ttfdng d cau than. Mdi ngay cd khoang 180 lit ntfdc tidu ban dau dtfdc hinh thanh.
Ntfdc tieu ban dau cd thanh phan nhtf huye't ttfdng nhtfng khong cd cac protein co trong ltfdng phan ttf ldn hdn 70.000.
Qua trinh loc d cau than xay ra la nhd vao ap ltfc hieu dung Pf:
Pf = Pg-(Po + Pc)
Pg: ap sua't thdy tinh trong cau than (ap sua't mao dong mach day ntfdc ra bao
Bowman)
Po: ap sua't keo cda huye't ttfdng (hut ntfdc ttf bao Bowman vao mao mach) Pc: ap sua't thdy tinh trong bao Bowman (ngtfdc vdi stf hut ntfdc ttf bao Bowman
vao mao mach)
Gia tri binh thtfdng cda Pg = 50 mmHg, Po = 25 mmHg, Pc = 5 mmHg, Pf =
20 mmHg.
^ 1,1.2. Qua trinh tai hap thu
^ Qua trinh tai ha'p thu la qua trinh xay ra lien tuc d o'ng than. Cd nhidu mtfc
do hap thu :ha'p thu hoan toan, ha'p thu phin ldn, ha'p thu mot phin va khong dtfdc
tai hap thu. Nhtfng cha't ma hlu hdt dtfdc tai ha'p thu hoan toan khi ndn* do cda
chung trong huydt ttfdng la kha tha'p xua't hien trong ntfdc tidu khi ndng do trong huyet ttfdng dtren ngtfdng ha'p thu cua chiing. Creatinin la cha't dtfdc tai ha'p thu vdi
mot ltfdng rat nho vi cd ngtfdng ha'p thu tha'p.
1.1.2.1. Tai h£p thu hoan toan
Nhtfng chat cd ngtfdng hap thu cao nhtf glucose hau net dtfdc tai ha'p thu
hoan toan d o'ng than.
Ngtfdng tai ha'p thu cda glucose dthan la l,75g/iit. Mot sd ngtfdi cd ngtfdng
than giam se gay ra tinh trang dtfdng nieu (dai thao dtfdng do than)
1.1.2.2. Tai Mp thu hlu he't
99% ntfdc dtfdc tai ha'p thu, phan ldn d dng Itfdn gin. Stf tai ha'p thu ntfdc
thtfdng di kem vdi stftai ha'p thu natri va clo.
Cac chat dtfdc tai ha'pv thu hau net con bao gom kali 98%, phosphat 95%, bicarbonat tren 90% (chu ydu ddng Itfdn gin). Cac acid amin cung dtfdc tai ha'p thu
gin het d o'ng than.
1.1.2.3. Tai hfip thu phan ldn
Natri va clor la cac chat dtfdc tai ha'p thu phin ldn, chd yeu d o'ng Itfdn gan.
Stf tai ha'p thu natri thtfdng kem theo stf tai hap thu ntfdc va nhieu chat tan khac.
1.1.2.4. Tai hap thu mot phin
Cac chat nhtf ure, urat, vitamin C dtfdc tai ha'p thu khoang 50% tai dng
than.
1.1.2.5. Khdng tai ha'p thu
Cac chat dtfdc loc qua clu than nhtfng khong dtfdc tai hap thu d o'ng than la inulin, manitol va natri hyposulfid. Vi vay ngtfdi ta thtfdng do do thanh thai cua cac
chat nay de khao sat chtfc nang loc cda clu than.
1.1.3. Qua trinh bai tiet
Chtfc nang bai tie't cda than nham loai bd khoi cd the cac san pham chuyen hda cuo'i cung va bat ky nhffng chat vd cd dtf thtfa trong che do an. Bai tiet la qua
trinh cac chat ttf huye't ttfdng dtfdc te bao o'ng than tfao thai vao ntfdc tieu. - Cac san pham dtf thtfa dtfdc bai tiet bao gdm nhtfng hdp chat ure cd nitd khong phai la protein ; mot sd acid htfu cd, bao gdm ca acid amin, dtfdc bai tie't vdi
sd Itfdng nho. Cac chat nhtf kali, acid uric, creatinin, H+, NH4+ ... cQng dtfdc bai tie't
vao o'ng than khi ndng do trong mau cao.
Ngoai ra, cac chat dtfa vao cd the de dieu tri hay chan doan nhtf P.S.P (phenyl sulpho phtalein), acid para amino hippuric (P.H.A), penicillin... cung dtfdc
bai tie't d d'ng than.
Qua cac chtfc nang neu tren cda than, cd the thay rang ntfdc tieu cd dac
dtfdc hinh thanh thdng qua cac qua trinh sieu loc, tai hap thu va bai tiet. Day cQng
chinh la cd che dao thai cd chon loc cda than.
1.2. Chtfc nang dieu hoa thang bang acid - base
Than dong vai trd chinh trong viec duy tri thang bang acid - base thdng qua stf tai tao bicarbonat va bai tiet NH/ va H*. Ba cd chd chinh nhtf sau :
- Stf tai ha'p thu bicarbonat (90% xay ra d o'ng than) (hinh 9.2)
- Stftai tao lai bicarbonat bang each dao thai ion H+ dtfdi dang acid dinh ltfdng (acid dihydrophosphat) (hinh 9.3)
- Stftai tao lai bicarbonat bang each bai xua't NH4+ (hinh 9.4)
Mau Ong Itfdn gan Ntftfe tieu
CO. * CO, + CO,
H20 "* H,0 H,0 *" H,0
AC AC
H2C03
> H+ —• H2C03
HC03" <- HCO3 HCO
Na+ Na+ Na+
AC: Anhydrase carbonic
Hinh 9.2. Stf di chuyen ciia ion H+ d dng Itfdn gan.
Mau
CO,
H20
HC03- <-
Na+
Ong Itfdn xa
•* CO,
"* H20
AC
H2C03
HCO
Na+ <
Ntfdc tieu
2Na++HP0.2-
Na^
Na++ HT+HP04
AC: Anhydrase carbonic
Hinh 9.3. Stfbai tie't ion H+ d o'ng Itfdn xa.
Mau
C02 H20"
HCO, <•
Na+
Ong Itfdn xa
KhrJ amin ciia aa —• NH3 \
• CO
•* HiO —*-*
AC
H2C03 N,.
©
HCO,
Na+
4.' *?
Ntfdc tieu
>H+
NH3
-* • NH4+
AC: Anhydrase carbonic
Hinh 9.4. Stf tao thanh va bai tiet NH4+ d o'ng Itfdn xa.
1.3. Chtfc nang noi tiet ciia than
Chtfc nang ndi tie't cda than cd the dtfdc xem nhtf la chtfc nang nguyen phat vi than cung la mot cd quan noi tie't san xua't hormon, hoac dtfdc xem nhtf la chtfc nang thtf phat vi than la dich tac dong cda hormon dtfdc san huat hay hoat hda bdi
ndi khac. Them vao do, than la ndi thoai bidn cua cac hormon nhtf insulin va
aldosteron. Hai chtfc nang ndi tiet cda than la : , A
-Dilu hoa stf hang dinh noi moi, thang bling ntfdc, dien giai va huyet ap qua he
tho'ng renin-angiotensin va aldosteron
-TdV hdp ydu td tao hdng clu cua than (REF =Renal erythropoietic factor) giup chuydn'tidn cha't cua erythropoietin trong huydt ttfdng thanh erythropoietin
dang hoat dong.