Placoid nplai yog cov yam ntxwv ntawm cov ntses pob txha tuag tawm kaum tawm, thiab qee qhov ntau pua txhiab xyoo dhau los. Txawm li cas los xij, nyob rau hauv peb lub sijhawm muaj cov neeg sawv cev ntawm lub ntiaj teb hauv qab dej, uas tseem muaj cov tawv nqaij zoo sib xws. Koj tuaj yeem kawm txog cov ntses twg tseem muaj cov nplais placoid, hais txog nws cov qauv, nrog rau lwm cov ntsiab lus nthuav tawm los ntawm kab lus no.
cov ntaub ntawv dav dav
Cov nplai ntawm cov ntses yog txheej txheej txheej tsim los ntawm cov pob txha daim hlau, muaj ob peb txheej, nrog rau cov khoom tshwj xeeb thiab cov ntaub so ntswg. Lawv cov qauv txiav txim siab qhov kev faib tawm uas muaj nyob hauv peb lub sijhawm. Muaj plaub hom kev ntsuas - cosmoid, elasmoid, ganoid thiab placoid. Nws yog hais txog lawv kawg uas peb yuav tham ntxiv.
Cov duab thiab qhov ntau thiab tsawg ntawm cov nplais
Placoid denticles yog cais lub khob zoo li tsim nrog lub hauv paus nthuav dav lossis hu ua basal phaj, uas yog raus rau hauv lub dermis. Ib qho nyuaj spike pib loj hlob los ntawm nws ntawm ib lub kaum ntse ntse. Los ntawmThaum nws loj hlob, nws tawg los ntawm epidermis thiab protrudes sab nraud. Cov hniav nrog lawv saum yog ib txwm qhia ntawm taub hau mus rau tus Tsov tus tw.
Feem ntau, qhov nruab nrab qhov loj ntawm cov flake tsis ntau tshaj 0.3 hli. Hauv qee hom sharks thiab rays, nws tuaj yeem loj hlob mus txog 4 hli. Nyob rau hauv cov ntaub ntawv no, lub teev yuav muaj ib tug complex qauv, txij li thaum nws twb yog ib tug multi-vertex tsim - qhov tshwm sim ntawm fusion ntawm ob peb cov hniav ib zaug. Nws yog cov qauv no uas muaj nyob rau hauv cov pob txha daim hlau ntawm cov pob txha ntses feem ntau.
Nyob rau hauv tsos, hom nplai ntawm cov ntses sib txawv yog sib txawv heev. Dissimilarity tuaj yeem yog ob qho tib si nyob rau hauv daim ntawv ntawm ib tug spike thiab nyob rau hauv nws lub hauv paus. Hauv qee hom ntses cartilaginous, cov nplai tsis muaj qhov taw qhia. Nws zoo li lub phaj dav dav nrog ob peb incisors raws ntug thiab peb los yog tsib qhov ntev ridges. Cov qauv ntawm lub hauv paus ntawm placoid nplai yog ntau haiv neeg; dhau li ntawd, nws cov duab kuj muaj nyob rau hauv lwm yam kev faib tawm. Nws ntug yog qee zaum du lossis nrog cov txheej txheem, nws tuaj yeem elongated lossis sib npaug.
Internal structure
Cov pob txha daim hlau nrog spikes tuaj yeem sib txawv ntawm ib leeg. Raws li rau cov qauv sab hauv ntawm placoid nplai, nws yog qhov zoo sib xws hauv txhua hom. Cov txheej txheej txheej tuaj yeem tsim los ntawm cov khoom siv ruaj khov durodentin lossis vitrodentin, nrog rau cov enamel tiag.
Lub hauv paus ntawm clove yog ib lub phaj tsim los ntawm cov pob txha ntawm tes. Nws lub cev yog ua los ntawm dentin. Nyob rau hauv nws yog lub pulp kab noj hniav. Los ntawm nws tob rau hauv lub dentinetawm tag nrho cov network ntawm branched tubules uas muaj cov hlab ntsha fibers thiab cov ntshav capillaries. Nyob rau hauv cov khaubncaws sab nraud povtseg ntawm lub dermis, txhua clove tuav strands ntawm collagen fibers uas originates nyob rau hauv cov pob txha cov ntaub so ntswg. Interestingly, nyob rau hauv tib neeg, tag nrho cov hniav nyob rau hauv lub puab tsaig yog tuav nyob rau hauv no txoj kev. Cov strands no hu ua Sharpei fibers (tom qab tus kws tshawb fawb uas tshawb pom thiab kawm lawv).
Kev txhim kho
Kev tsim cov placoid nplai pib nrog kev tsim cov denticles. Nws tshwm sim nyob rau hauv tus txheej txheem ntawm kev sib raug zoo ntawm ob yam - lub epidermis thiab dermis. Ua ntej, tus precursor ntawm cov hniav yog yug los nyob rau hauv cov ntaub so ntswg mos. Nws tseem tsis tuaj yeem txiav txim siab qhov twg yog cov enamel thiab qhov twg yog txheej dentin. Cov ntaub so ntswg ua nyuaj tsuas yog thaum lawv loj hlob mus rau qhov loj ntawm cov hniav tom ntej.
Cov txheej txheem kev loj hlob zoo li kev tsim thiab nws cov tawv tawv ntxiv txhais tau hais tias cov nplai ntawm hom no (thiab, tshwj xeeb, nws cov hniav), muaj qhov loj me, tsis tuaj yeem nce ntxiv. Nws paub tias kev loj hlob ntawm cov ntses txuas ntxiv mus thoob plaws nws lub neej. Tom qab ib lub sij hawm ntawm lub sij hawm, cov nplais pib hnav, thiab ib qho tshiab tshwm. Cov txheej txheem no yuav rov ua dua ob peb zaug hauv lub neej. Nrog rau txhua tiam neeg, cov cloves loj dua kom txog thaum lawv ncav cuag lawv qhov loj tshaj plaws. Yog hais tias lub cev tseem loj tuaj, ces qhov kev tso ntawm cov pob txha ntxiv pib. Nws muaj kev ruaj ntseg hais tias cov txheej txheem zoo li no hauv daim tawv nqaij yog cov yam ntxwv ntawm cov neeg sawv cev ntawm txhua hom pob txha mosntses.
Qhov chaw
Placoid nplai ntawm lub cev ntawm cov ntses tau faib tsis sib npaug. Nws tsis yog pawg nyob rau hauv ib qho kev qhia meej meej kab, tab sis vice versa - nws tshwm sim randomly, vim hais tias cov hniav tuaj yeem muab tso rau ob qho tib si ntawm ib cheeb tsam ntawm daim tawv nqaij, thiab hla nws tag nrho saum npoo.
Feem ntau muaj qee qhov kev ncua deb ntawm lawv, yog li lub npog tas li tsis muaj ntau. Raws li txoj cai, cov ntses zoo li "liab qab", tab sis tib lub sijhawm lawv cov tawv nqaij muaj qhov tshwj xeeb roughness. Qee lub sij hawm koj tuaj yeem soj ntsuam cov duab sib txawv kiag li, thaum qee cov nplai lean ntawm lwm tus, yog li npog tag nrho lub cev thiab tiv thaiv lawv tus tswv.
Functions
Raws li cov ntaub ntawv no, cov kws tshawb fawb tau xaus lus tias cov nplai placoid tsis tas yuav ua cov haujlwm uas lwm hom pob txha ua. Yog hais tias lawv ua si lub luag hauj lwm ntawm kev tiv thaiv cov qauv uas tsim ib tug haum haum thiab txhim khu kev qha plhaub nyob ib ncig ntawm lub mos mos lub cev ntawm cov ntses, ces qhov teeb meem yog txawv nrog placoid denticles. Lawv lub luag haujlwm tseem ceeb yog txiav los ntawm cov kwj dej uas ntws raws nws thaum lub sijhawm cov ntses ua luam dej. Hauv qhov no, micro-vortices tshwm sim, uas txo qis kev sib txhuam ntawm lub cev, yog li ua kom yooj yim rau nws txoj kev txav mus tom ntej.
Shark hniav thiab pob txha daim hlau
Placoid nplai ntawm cov ntses cartilaginous paub tias muaj ntau yam duab. Cov no tuaj yeem yog cov pob txha lossis cov pob txha daim hlau nrog cov ntug tsis sib xws thiab cov kab ntev ntev. Txhua hom shark muaj nws tus kheej zoo ntawm cov hniav thiab nplai. pob txha daim hlauyuav luag tag nrho lub cev ntawm ib tug predatory ntses yog them. Tsuas yog cov gill slits tseem muaj kev phom sij. Nws yog ib qho tseem ceeb uas nyob rau hauv feem ntau cov lus qhia kev nyab xeeb npaj rau divers, thaum muaj shark nres, nws raug nquahu kom tawm tsam ntawm qhov chaw tsis muaj kev tiv thaiv ntawm lub cev ntawm cov ntses. Cov kws tshaj lij hais tias qhov kev ua li no feem ntau pab kom ntshai tus neeg txhoj puab heev.
Nws kuj tseem nthuav tias cov nplai ntawm lub cev ntawm shark yuav luag ib txwm muaj tib yam li cov hniav. Tsis tas li ntawd, ob leeg ntawm lawv muaj cov qauv yuav luag zoo tib yam thiab muaj peev xwm tshwj xeeb los hloov kho tas li. Cov kws tshawb fawb tau ua pov thawj tias cov hniav shark yog hloov cov nplai placoid. Txawm li cas los xij, vim tias lawv ua haujlwm sib txawv, lawv kuj muaj qee qhov sib txawv ntawm qhov loj thiab cov qauv. Nyob rau hauv lub qhov ncauj kab noj hniav ntawm shark, cov nplai, nce loj, ua cov hniav. Nws kuj tuaj yeem hloov pauv, tsim lwm cov pob txha tawm ntawm daim tawv nqaij, piv txwv li, pom cov hniav hauv pylons lossis spines hauv katrans.
Lub cev ntawm shark, npog nrog nplai, tiv thaiv nws los ntawm kev cuam tshuam sab nraud thiab los ntawm cov hniav ntawm lwm cov tsiaj txhu. Yog tias koj khiav koj txhais tes raws li qhov ntxhib ntawm qhov taw qhia ntawm caudal fin mus rau lub taub hau, ces koj tuaj yeem tev tawm ntawm koj cov tawv nqaij mus rau qhov ntshav. Cov nplai ntawm cov tsiaj txhu muaj zog heev uas txawm tias rab riam tsis tuaj yeem ua rau nws puas tsuaj. Muaj qhov chaw ntawm lub cev ntawm shark uas daim tawv nqaij tuab heev. Nws yooj yim nqa mus txog 500 kg ib 1 cm².
