Indlela Yokuthuthwa Kwe-Oxygen Yi-Hemoglobin
I-oksijini "iwuphethiloli" oyinhloko wamaseli ukuze akhiqize amandla ngokuphefumula kwamaseli. Kodwa-ke, i-oksijini ayikwazi ukuthuthwa ngobuningi ngokumane incibilike ku-plasma yegazi. Ukuncibilika kwe-oksijini ku-plasma kuphansi kakhulu, kudinga uhlelo lokuthutha olusebenza kahle kakhulu. Yilapho i-hemoglobin—iphrotheni eyinhloko kumaseli abomvu egazi—idlala khona indima ebalulekile. I-hemoglobin ivumela ukumuncwa kwe-oksijini emaphashini, ithuthwe ngemithambo yegazi, futhi ikhishwe ezicutshini njengoba kudingeka. Lesi sihloko sixoxa ngendlela yokuthuthwa kwe-oksijini yi-hemoglobin, okuhlanganisa isakhiwo sayo, izinqubo zokubopha nokukhulula i-oksijini, kanye nezici ezithonya ukuhambisana kwe-hemoglobin.
Isakhiwo se-Hemoglobin nokuthi Kungani Kubalulekile
I-Hemoglobin (Hb) iyiprotheni eyinkimbinkimbi etholakala kuma-erythrocyte (amangqamuzana abomvu egazi). Kubantu abadala, uhlobo oluvame kakhulu yi-hemoglobin A (HbA), eyakhiwa ngamaketanga amane e-globin: amaketanga amabili e-alpha (α) kanye namaketanga amabili e-beta (β). Iketanga ngalinye le-globin liphethe iqembu le-heme, ukuze i-molecule eyodwa ye-hemoglobin ibe namaketanga amane e-heme.
Iqembu le-heme liqukethe i-athomu yensimbi (i-Fe²⁺) enkabeni yalo. Le nsimbi ibopha ngqo ku-oxygen (O₂). Ngenxa yokuthi kune-heme ezine, i-molecule eyodwa ye-hemoglobin ingabopha ama-molecule e-oxygen afinyelela kwamane. Isakhiwo se-tetrameric se-hemoglobin asigcini nje ngokuba "yindawo yokwamukela" umoya-mpilo, kodwa futhi siyisihluthulelo sezakhiwo zayo zokubambisana: ukubopha umoya-mpilo ku-heme eyodwa kuthinta kalula ukuthi umoya-mpilo ubopha kanjani kwamanye ama-heme.
Isakhiwo se-hemoglobin singaba nezinguquko zokwakheka. Kalula nje, kunezimo ezimbili eziyinhloko: isimo se-T (sesikhathi), esine-affinity ephansi ye-oxygen, kanye nesimo se-R (esikhululekile), esine-affinity ephezulu. Ukuguquka kwe-T kuya ku-R kuyisisekelo sokubopha i-oxygen kahle emaphashini kanye nokukhululwa okuphumelelayo ezicutshini.
Ukubopha i-oksijini emaphashini
Emaphashini, ikakhulukazi kuma-capillary e-alveolar, ingcindezi engaphelele yomoya-mpilo (pO₂) iphezulu. Umoya-mpilo uyasakazeka usuka ku-alveoli uye egazini ngenxa yokuphakama kwengcindezi. Uma usungene kuma-erythrocyte, umoya-mpilo ubopha ngokubuyela emuva ku-iron (Fe²⁺) ku-heme ukuze wakhe i-oxyhemoglobin (HbO₂).
Lokhu kubopha akuyona inqubo elula "yokuvala". Lapho i-molecule eyodwa ye-O₂ ibophana, i-hemoglobin idlula kushintsho lokwakheka okwandisa ukusondelana kwayo endaweni elandelayo. Lesi yisimo sokusebenzisana okuhle. Ngenxa yalokho, ubudlelwano phakathi kokugcwala kwe-hemoglobin kanye ne-pO₂ buyi-sigmoidal (isimo se-S), kunokuba kube umugqa oqondile. Lesi simo se-sigmoidal senza i-hemoglobin isebenze kahle kakhulu: "ishaja" kalula kuma-pO₂ aphezulu (amaphaphu) futhi "ikhipha" kalula ukushaja kwayo kuma-pO₂ aphansi (izicubu).
Ngaphansi kwezimo ezijwayelekile, ku-alveolar pO₂ engaba ngu-100 mmHg, ukugcwala kwe-hemoglobin kufinyelela ku-97–99%. Lokhu kusho ukuthi izindawo eziningi zokubopha ku-hemoglobin zigcwele umoya-mpilo. Lokhu kubalulekile ukuqinisekisa umthamo omkhulu wokuthwala umoya-mpilo ngesikhathi somsebenzi.
Ukuthuthwa Kwe-Oxygen Ekujikelezeni Kwegazi
Ngemva kokuba amangqamuzana abomvu egazi ephumile emaphashini, igazi lemithambo yegazi lithwala umoya-mpilo kuwo wonke umzimba. Umoya-mpilo egazini ukhona ngezindlela ezimbili: uboshelwe ku-hemoglobin (ikakhulukazi) futhi uncibilike ku-plasma (kancane kakhulu). Ngokwemvelo, umoya-mpilo oncibilikile uhlala ubalulekile ngoba unquma i-pO₂ futhi ukhuthaza ukusabalala komoya-mpilo usuka egazini uye ezicutshini. Kodwa-ke, ngaphandle kwe-hemoglobin, okuqukethwe komoya-mpilo okuphelele egazini kuzokwehla kakhulu, njengoba i-plasma ngeke ikwazi ukuncibilikisa umoya-mpilo owanele.
I-hemoglobin isebenza njenge-"buffer" ye-oxygen. Ithatha umoya-mpilo uma ubuningi bese iwukhipha lapho izicubu ziwudinga. Le ndlela igcina ukuhlinzekwa komoya-mpilo okuzinzile naphezu kokushintshashintsha kwesidingo sezicubu.
Ukukhishwa Kwe-Oksijini Ezicutshini
Ezicutshini ezingaphandle, i-pO₂ iphansi kunasemaphashini ngoba umoya-mpilo usetshenziswa njalo ngamaseli ukukhiqiza i-ATP. Umoya-mpilo uyasabalala kusuka kuma-capillary uye oketshezini oluphakathi bese ungena emaseli. Njengoba umoya-mpilo oncibilikisiwe wehla, i-hemoglobin iyaphendula ngokukhulula umoya-mpilo oboshiwe ukuze kugcinwe ibhalansi.
Ukukhishwa komoya-mpilo kuthonywa isimo se-metabolic sezicubu. Izicubu ezisebenzayo (isib., imisipha ngesikhathi sokuzivocavoca) zikhiqiza i-CO₂ eningi, ama-ion e-hydrogen amaningi (ukwehlisa i-pH), kanye nokushisa, konke okukhuthaza i-hemoglobin ukuthi ikhiphe umoya-mpilo kalula. Lokhu kuqinisekisa ukuthi umoya-mpilo utholakala lapho udingeka khona kakhulu.
Ku-pO₂ yezicubu ezimaphakathi ezingaba ngu-40 mmHg, ukugcwala kwe-hemoglobin kwehla cishe ku-75%. Lokhu kusho ukuthi cishe u-25% womoya-mpilo "uthululwa" ezicutshini lapho ziphumule. Njengoba umsebenzi ukhula, i-pO₂ yezicubu ingancipha kakhulu, okuvumela i-hemoglobin ukuthi ikhiphe umoya-mpilo owengeziwe.
Umphumela weBohr: Indima ye-CO₂ kanye ne-pH
Enye yezindlela ezibaluleke kakhulu ekulawuleni ukukhishwa kwe-oxygen umphumela we-Bohr. Umphumela we-Bohr uchaza ukuthi ukwanda kwe-CO₂ kanye nokwehla kwe-pH (okune-acid eningi) kunciphisa ukusondelana kwe-hemoglobin ne-oxygen, okuguqula ijika lokuhlukanisa i-oxygen liye kwesokudla. Ngamanye amazwi, ku-pO₂ efanayo, i-hemoglobin izothwala i-oxygen encane futhi ikhulule okwengeziwe ezicutshini.
Ngokwekhemikhali, i-CO₂ ingasabela namanzi ukuze yakhe i-carbonic acid, bese ihlukana ibe yi-H⁺ kanye ne-bicarbonate (HCO₃⁻). I-H⁺ izobopha izingxenye ezithile ze-hemoglobin, iqinise isimo sayo se-T esiphansi. Ngaphezu kwalokho, enye i-CO₂ ingabopha ngqo kwi-hemoglobin ukuze yakhe i-carbaminohemoglobin, ephinde isekele ukukhishwa komoya-mpilo. Ngakho-ke, izicubu ezikhiqiza i-CO₂ eningi “zicela” umoya-mpilo owengeziwe ngokuzenzakalelayo ngezinguquko endaweni yamakhemikhali egazini.
Emaphashini, isimo siyashintsha: i-CO₂ iyakhishwa, i-pH iyakhuphuka, futhi i-hemoglobin iphinda ithole umoya-mpilo ohambisanayo, okwenza ikwazi ukubopha kalula.
Umphumela Wokushisa Nokusebenza Kwe-Metabolic
Izinga lokushisa liphinde lithinte ukuhambisana kwe-hemoglobin. Izinga lokushisa elikhuphukile—njengasemisipheni esebenzayo—livame ukuhambisa ijika lokuhlukana liye kwesokudla, okwenza kube lula nge-hemoglobin ukukhulula umoya-mpilo. Ngokuphambene nalokho, emazingeni okushisa aphansi, i-hemoglobin ivame ukubamba umoya-mpilo ngokuqinile. Lokhu kunegalelo ekusabalalisweni okukhulu komoya-mpilo ezicutshini ezisebenzayo nezifudumele.
Indima ye-2,3-BPG ekuGuquguqukeni
Amaseli abomvu egazi aqukethe i-molecule ebalulekile ebizwa ngokuthi i-2,3-bisphosphoglycerate (2,3-BPG), umkhiqizo ophuma ku-glycolysis. I-2,3-BPG ibopha i-hemoglobin engenawo umoya-mpilo (ephelelwe umoya-mpilo) futhi izinzise isimo sayo se-T, ngaleyo ndlela inciphise ukuzwelana kwayo nomoya-mpilo. Ngenxa yalokho, umoya-mpilo ukhishwa kalula ezicutshini.
Amazinga angu-2,3-BPG angakhuphuka ezimweni ezithile, njengokuphila ezindaweni eziphakeme, i-anemia, noma i-hypoxia engapheli. Ukwanda kwe-2,3-BPG kusiza umzimba ukuba uzivumelanise nezimo ngokukhuthaza ukukhishwa okukhulu komoya-mpilo ezicutshini naphezu kwe-pO₂ ephansi yendawo.
Ijika Lokuhlukaniswa Kwe-Oksijini: Ingqikithi Yokuqonda Indlela Ye-Hb
Ijika lokuhlukaniswa kwe-oxygen-hemoglobin libonisa ubudlelwano phakathi kwe-pO₂ kanye nokugcwala kwe-hemoglobin. Ukuma kwe-sigmoid kubonisa ukubambisana. Ingxenye "esicaba" ku-pO₂ ephezulu isiza ukugcina ukugcwala okuphezulu emaphashini ngisho nalapho i-pO₂ yehla kancane. Ingxenye "eqinile" ku-pO₂ ephakathi nendawo ephansi yenza ukukhishwa kwe-oxygen kuphendule kakhulu ezicutshini: ukwehla okuncane ku-pO₂ kungaholela ekukhishweni kwe-oxygen enkulu kakhulu.
Ukushintshela kwejika ngakwesokudla kubonisa ukuncipha kokusondelana (umoya-mpilo omningi ukhishwa), okubangelwa ukwanda kwe-CO₂, ukwehla kwe-pH, izinga lokushisa elikhuphukile, kanye nokwanda kwe-2,3-BPG. Ukushintshela kwesobunxele kubonisa ukwehla kokusondelana (umoya-mpilo awukhishwa kalula), isibonelo ngaphansi kwezimo ze-CO₂ ephansi, i-pH ephezulu, izinga lokushisa eliphansi, noma izinhlobo ezithile ze-hemoglobin.
Isiphetho
Indlela yokuthutha umoya-mpilo nge-hemoglobin iwumphumela womklamo osebenza kahle kakhulu womzimba. I-hemoglobin ibopha umoya-mpilo emaphashini ngokubambisana, iyithuthe ngokujikeleza kwegazi, bese iyikhipha iye ezicutshini njengoba kudingeka ukuze kulawulwe i-metabolism. Ukuzwela kwe-hemoglobin ku-pH, i-CO₂, izinga lokushisa, kanye ne-2,3-BPG kwenza ukusatshalaliswa komoya-mpilo kuhambisane nezimo: izicubu ezisebenzayo kakhulu zithola umoya-mpilo owengeziwe ngokuzenzakalelayo. Ukuqonda le ndlela kusiza ukuchaza izenzakalo eziningi zezokwelapha nezomzimba, kusukela ekusabeleni komzimba ekuzivocavoceni kuya ekuzivumelaniseni nezimo ezindaweni eziphakeme kanye nokuthuthwa komoya-mpilo okungasebenzi kahle ezifweni ezahlukahlukene.
