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Wat veroorsaak dat weefsels die verskillende vorme wat hulle doen manifesteer?

Wat veroorsaak dat weefsels die verskillende vorme wat hulle doen manifesteer?


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'n Hart (of enige ander orgaan) bestaan ​​uit 'n groep selle. Sover my kennis strek, hang die groei van 'n hart van seldeling af. Seldeling op sigself blyk egter nie te verklaar waarom hartselle gesamentlik die vorm van 'n hart manifesteer nie.

Wat veroorsaak dat weefsels die verskillende vorme wat hulle doen manifesteer?


Dit is 'n onderwerp van aktiewe navorsing. Al die selle in die sigoot is identies tot op 8-selstadium. By die volgende verdeling wat lei tot vorming van 16 selle word dit a genoem morula.

Die sigoot het totipotent selle wat beteken dat elke sel die vermoë het om op sigself tot volle organisme te ontwikkel as dit van die sigoot skei (dit is hoe 'n identiese tweeling gebore word).

Menslike sigote is totipotent tot ten minste 4-selstadium. By ander primate het eksperimente totipotensie getoon tot 16-selstadium.

Die totipotente selle onderskei in pluripotente selle en dan in verskeie afsonderlike selle wat aan verskillende sisteme behoort. Hierdie proses is baie kompleks en baie embriologiese faktore en chemikalieë kom ter sprake.

Die embrioniese faktore veroorsaak migrasie (genoem embriotaksis) en differensiasie van die embrioniese selle. Sommige van die faktore is soniese reier, wnt, insulien soos groeifaktore, Hox, ens ...

Verskillende faktore veroorsaak differensiasie in verskillende sellyne. Hierdie faktore veroorsaak ook dat die organe spesifieke vorm en struktuur verkry, dus word die hart as 'n hart gevorm en die lewer is gevorm as 'n lewer ensovoorts.

Sodra die selle in 'n spesifieke lyn differensieer, differensieer die stamselle van daardie streek gewoonlik na daardie spesifieke lyn as gevolg van die parakriene invloed in daardie lokus, al kan hierdie stamselle in ander sellyne differensieer wanneer dit toepaslik gestimuleer word (dus pluripotensie demonstreer). Derm stamselle sal dus differensieer in bekerselle, oppervlakepiteelselle, Enterochromaffienselle, ens ... wat in daardie lokus teenwoordig is.


Vir meer sien hier:

  1. http://www.sciencedirect.com/science/article/pii/S009286740800216X
  2. http://www.embryology.ch/anglais/iperiodembry/controle01.html
  3. https://www.bio.cmu.edu/labs/ettensohn/pdfs/dvg22746-2.pdf

Gangreen Simptome

Droë gangreen simptome sluit in:

  • Verskrompelde vel wat van blou na swart verander en uiteindelik afkom
  • Koue, gevoellose vel

Simptome van nat gangreen sluit in:

  • Swelling en pyn en voel onwel
  • Rooi, bruin, pers, blou, groen-swart of swart vel of sere met 'n ruikende afskeiding (etter)
  • 'n Krakende geluid wanneer jy op die geaffekteerde area druk
  • Dun, blink of haarlose vel
  • ’n Lyn tussen gesonde en beskadigde vel

Interne gangreen veroorsaak erge pyn in die aangetaste area. Byvoorbeeld, as jy gangreen in jou blindederm of kolon het, sal jy waarskynlik maagpyn hê. Inwendige gangreen kan ook koors veroorsaak.


Die belangrikste endokriene kliere

Geleë aan die basis van die brein, produseer die pituïtêre klier baie hormone wat ander organe reguleer. As gevolg hiervan word daar dikwels na die pituïtêre klier verwys as die "master" endokriene klier, alhoewel die term "sentrale" endokriene klier meer korrek is omdat hormoonvrystelling deur die pituïtêre primêr gereguleer word deur 'n breinstruktuur genaamd die hipotalamus, wat dien om die senuweestelsel met die endokriene stelsel te verbind. Die hipotalamus produseer hormone wat die vrystelling van pituïtêre hormone stimuleer of inhibeer. Die hipotalamus produseer ook antidiuretiese hormoon, wat die waterbalans in die liggaam reguleer deur urienvorming te inhibeer deur die

Hormone wat deur die hipofise vrygestel word, sluit in groeihormoon, wat tydens die kinderjare toeneem en die groei van spiere, been en ander weefsels stimuleer. Sporadiese uitbarstings in groeihormoon vrystelling lei dikwels tot vinnige groei "spurts" wat met adolessensie geassosieer word. Hiposekresie van groeihormoon kan dwergisme tot gevolg hê, terwyl hiperafskeiding van groeihormoon gigantisme en ander afwykings kan veroorsaak. Die hipofise produseer ook follikelstimulerende hormoon en luteïniserende hormoon, wat gameetproduksie en geslagsteroïedproduksie in manlike en vroulike voortplantingsorgane stimuleer, en prolaktien, wat melkvorming in die melkkliere stimuleer.

Geleë aangrensend aan die larinks , produseer die tiroïedklier hoofsaaklik tiroksien en trijodotironien, gesamentlik na verwys as tiroïedhormoon. Skildklierhormoon stimuleer groei van spiere en bene, koolhidraatmetabolisme en basale metaboliese tempo. Die produksie daarvan vereis jodium die gebrek aan dieetjodium veroorsaak goiter, 'n skildklier wat te vergroot is in 'n poging om te vergoed vir die tekort aan tiroïedhormoon.

Effekte van skildklierafwykings by kinders en volwassenes kan baie verskil. Byvoorbeeld, hiposekresie van tiroïedhormoon by babas veroorsaak aangebore hipotireose, 'n siekte wat gekenmerk word deur verstandelike gestremdheid en swak liggaamsgroei hiposekresie by volwassenes, veroorsaak miksoedeem, met simptome soos lusteloosheid , gewigstoename en droë vel. Omgekeerd veroorsaak hiperafskeiding van tiroïedhormoon by volwassenes Graves'-siekte, 'n toestand wat gekenmerk word deur gewigsverlies, senuweeagtigheid en dramatiese toenames in liggaamsmetabolisme. Die skildklier produseer ook kalsitonien, 'n hormoon wat kalsiumkonsentrasie in die bloed reguleer.

Die byniere is klein organe op die top van elke nier. Die buitenste lae selle in die bynier, genoem die bynierkorteks, produseer verskeie hormone wat reproduktiewe ontwikkeling mineraalbalans vet-, proteïen- en koolhidraatbalans en aanpassing by stres beïnvloed. Die binneste deel, genoem die byniermedulla, skei epinefrien en norepinefrien af, wat die simpatiese senuweestelsel en stimuleer die "veg-of-vlug" reaksie wat die liggaam help om stresvolle situasies, soos vrees, te hanteer.

Die pankreas produseer insulien en glukagon, wat op teenstrydige wyse funksioneer om bloedsuiker (glukose) konsentrasie te reguleer. Wanneer bloed glukose vlak styg, byvoorbeeld, na die eet van 'n suikerryke maaltyd—insulien verlaag dit deur glukoseberging in lewer- en spierselle te stimuleer, aangesien lang kettings glukose genoem word glikogeen . Omgekeerd, tussen maaltye, daal bloedglukosevlak. In reaksie hierop stel die pankreas glukagon vry, wat glikogeenafbreking en die daaropvolgende vrystelling van glukose in die bloedstroom stimuleer. Een van die mees gekarakteriseerde endokriene afwykings is diabetes mellitus, wat die gevolg is van hiposekresie van insulien of, meer algemeen, teikensel-onsensitiwiteit daarvoor.

Endokriene funksies van die gonades word in artikels oor die manlike en vroulike voortplantingstelsels aangespreek. Die geslagshormoon testosteroon reguleer spermproduksie by mans. Estrogeen en progesteroon beïnvloed eiers rypwording en vrystelling (ovulasie) en beheer die baarmoeder (menstruele) siklus by vroue.

Alhoewel die talle hormone wat deur menslike endokriene organe geproduseer word, 'n wye verskeidenheid aksies het, is die gemeenskaplike doel van alle hormone om orgaan-tot-orgaan-kommunikasie wat nodig is vir liggaamsfisiologie, te fasiliteer.


Weefselstruktuur en -komponente

Die struktuur van weefsels verskil volgens die tipe weefsel. Onthou dat weefsels 'n groep selle is wat bymekaar kom om 'n spesiale funksie vir die liggaam uit te voer daar kan verskillende tipes selle wees wat bymekaar kan kom om 'n spesiale funksie uit te voer. In sommige weefsels kan die selle soortgelyk wees en in sommige kan die selle verskil.

Wanneer selle bymekaar kom, doen hulle dit binne 'n beperkte ruimte wat die Ekstrasellulêre matriks of die Ekstrasellulêre ruimte. Jy kan die Ekstrasellulêre matriks of ruimte visualiseer as 'n gemeenskap wat baie huise en elke huis as 'n sel het (elke huis kan soortgelyk wees, maar hulle verrig spesiale funksies soos om sommige huise as kamers te gebruik om te slaap, ander huise word as winkels gebruik terwyl ander word as kantore gebruik). Die buitesellulêre ruimte is as die gemeenskap waar die huise op die grond gebou word. In weefsels hou die ekstrasellulêre matriks die verskillende tipes selle en bied 'n n bemagtigende omgewing vir die selle om hul funksies te verrig.

Die rede hoekom dit die genoem word ekstrasellulêre ruimte of matriks is omdat die ruimte buite die selle geleë is (ekstra sellulêre ruimte). Selfs binne die ekstrasellulêre ruimte is daar verskeie proteïene wat hierdie ruimte vorm. Dit sal bespreek word terwyl hierdie spasie in besonderhede beskryf word.

Daarom kan gesê word dat 'n weefsel 2 hoofkomponente het, die selle en die ekstrasellulêre matriks.


Wat veroorsaak veroudering?

Daar is min fisiese verskille tussen 'n groep eerstegraadse leerders. Maar as jy 65 jaar later na dieselfde groep kyk, is hul fisiese verskille meer as hul ooreenkomste. Sommige sal die toonbeeld van gesondheid wees, terwyl ander een of meer chroniese toestande sal bestuur. Sommige sal kragtig wees, terwyl ander lusteloos sal wees.

Soos ons ouer word, word ons fisies minder soos ons maats. Dit is omdat ons die som van ons lewenservarings is. Op die ouderdom van ses het daar nie te veel met ons liggame gebeur om ons radikaal van ons eweknieë te verskil nie. Maar teen middel- en oudag het ons dekades gehad om gewoontes te ontwikkel en in stand te hou wat 'n impak op ons gesondheid het, beide negatief en positief.

Die omgewing beïnvloed ook ons ​​gesondheid, insluitend waar ons werk en woon en hoeveel blootstelling ons aan aansteeklike siektes het. Veroudering is universeel, maar elkeen van ons ervaar dit op verskillende maniere.

Veroudering kan onvermydelik wees, maar die tempo van veroudering is nie. Waarom en hoe ons liggame verouder, is steeds grootliks 'n raaisel, hoewel ons elke jaar meer en meer leer. Wetenskaplikes hou egter vol dat chronologiese ouderdom min invloed het op biologiese ouderdom. Die aantal kerse op jou verjaardagkoek dien bloot as 'n merker van tyd dit sê min oor jou gesondheid.

Maar wat raak ons ​​meer – ons gene of ons lewenstyl? Vind uit op die volgende bladsy.

Oorsake van veroudering: Natuur of Koestering?

Die kompleksiteit van ouer word maak dit moeilik om vas te stel waarom een ​​persoon goed verouder terwyl 'n ander ouer lyk en optree as sy jare. Word goeie gesondheid en deursettingsvermoë oorgedra soos blou oë en blonde hare? Of is dit 'n produk van die omgewing, insluitend die kos wat jy eet, of jy aan skadelike chemikalieë of aansteeklike siektes blootgestel is, en hoeveel jy oefen? Albei speel beslis 'n rol, maar ons weet nog nie watter 'n kragtiger invloed het nie.

Gene is kragtige voorspellers van gesondheid en lang lewe sowel as siekte en dood, maar hulle is slegs deel van die storie. As jou ouers en grootouers tot ver in hul negentigs geleef het, is die kans groot dat jy dit ook sal doen - maar nie as jy jou liggaam langs die pad mishandel nie. (Wetenskaplikes sê egter dat alle genetiese weddenskappe af is sodra jy die ouderdom van 80 bereik het. Daarna het familiegeskiedenis min invloed op langlewendheid.)

En as jou pa jonk aan ’n hartaanval gesterf het of jou ma borskanker gehad het, is jy dalk geneties vatbaar vir daardie siektes. Wetenskaplikes op die Menslike Genoomprojek ontdek voortdurend meer genetiese determinante van chroniese en dodelike siektes.

Alhoewel gene gedeeltelik bepaal wie chroniese toestande sal ontwikkel wat die verouderingsproses verhaas, soos kanker en hartsiektes, is daar geen twyfel dat 'n gesonde leefstyl jou wapen is teen die gene wat jy behandel is nie, of jou as in die gat as jy het goeie gene.

’n Man wie se pa en broers in hul veertigs en vyftigs aan hartsiektes gesterf het, kan heel moontlik dieselfde lot vryspring deur gereeld te oefen en sy bloedcholesterolvlakke en liggaamsgewig in toom te hou. Aan die ander kant kan 'n man met geen genetiese aanleg vir hartsiektes beslis hartprobleme skep deur 'n hoë vet, slagaarverstoppende dieet te eet en 'n heeltemal sittende leefstyl te lei.

Gesonde lewe vertraag baie van die liggaamsveranderinge wat veroudering meebring. En dit is nooit te laat om op die pad na beter gesondheid te begin nie. Om 'n voedsame dieet te eet, gaan 'n lang pad om goeie gesondheid te verseker. Byvoorbeeld, om genoeg kalsium en vitamien D op enige ouderdom te kry, sal die aanvang en vordering van osteoporose vertraag, 'n beensiekte wat pyn, frakture, hospitalisasie en selfs dood by bejaardes veroorsaak.

As jy 'n roker is en jy stop enige tyd, verminder jy die kanse om 'n hartaanval te kry. En om te oefen of meer fisies aktief te raak, verbeter longfunksie en verlaag die risiko vir hartaanval, maak nie saak hoe oud jy is nie.

So deur watter veranderinge gaan jou selle, weefsels en liggaamstelsels deur soos jy ouer word? Op die volgende bladsy sal ons die biologiese proses van veroudering bespreek.

Verouderingsbiologie: Hoe verouder selle?

Selle, die mees basiese liggaamseenheid, is die middelpunt van enige bespreking oor veroudering. Jy het triljoene selle, en hulle is georganiseer in verskillende weefsels waaruit organe bestaan, soos jou brein, hart en vel.

Sommige selle, soos dié wat die spysverteringskanaal beklee, reproduseer voortdurend ander, soos die selle aan die binnekant van arteries, lê dormant maar is in staat om te repliseer in reaksie op besering. Nog ander, insluitend selle van die hart, senuwees en spiere, kan nie voortplant nie. Sommige van hierdie nie-reproduserende selle het kort lewensduur en moet voortdurend deur ander selle in die liggaam vervang word. (Rooi en witbloedselle is voorbeelde.)

Ander, soos hart- en senuweeselle, leef vir jare of selfs dekades. Met verloop van tyd oortref seldood selproduksie, wat ons met minder selle laat. As gevolg hiervan is ons minder in staat om slytasie op die liggaam te herstel, en ons immuunstelsel word in die gedrang gebring. Ons word meer vatbaar vir infeksies en minder vaardig om mutante selle te soek en te vernietig wat kankergewasse kan veroorsaak. Trouens, baie ouer volwassenes swig voor toestande wat hulle in hul jeug kon weerstaan ​​het.

Alhoewel seldood die basis is om die verouderingsproses te verstaan, is dit nie die enigste faktor nie. Die verouderingsproses is ongelooflik ingewikkeld, en dit is dikwels moeilik om te onderskei tussen veranderinge wat die gevolg is van die tyd wat aanstap en dié wat gepaard gaan met algemene mediese toestande, insluitend hoë bloeddruk en hartsiektes.

Veroudering is die onvermydelike afname in die liggaam se veerkragtigheid, wat uiteindelik lei tot kwynende kragte, beide geestelik en fisies. Sommige verouderingsveranderinge raak ons ​​almal. Byvoorbeeld, verminderde sig wat 'n leesbril noodsaak, word as normaal beskou, hoofsaaklik omdat dit almal raak wat lank genoeg lewe.

Aan die ander kant kan katarakte, wat formasies op die lens van die oog is wat jou sig vertroebel, voorkom word en word nie as deel van die verouderingsproses beskou nie, ten spyte van hul voorkoms by ouer mense. Om sake verder te bemoeilik, verouder organe teen verskillende spoed. Dis hoekom ’n 50-jarige dalk net so goed hoor as iemand wat twintig jaar jonger is, maar dalk artritis of hoë bloeddruk het.

Teorieë is volop oor die onderliggende oorsaak van veroudering. Sommige beweer dat veroudering vooraf in ons selle geprogrammeer is, terwyl ander beweer dat veroudering hoofsaaklik die gevolg is van omgewingskade aan ons selle. Alhoewel nie een van die teorieë die proses volledig kan verduidelik nie, help dit ons om beter te verstaan ​​hoe ons verouder. Op die volgende bladsy sal ons die gewildste verouderingsteorieë ondersoek.

Verouderingsteorieë: Gene vs. Leefstyle

Wat is daardie geluid? Volgens hierdie teorie is dit jou biologiese horlosie wat teen 'n voorafbepaalde tempo wegtik. Hierdie teorie sê dit DNA, die selle se genetiese materiaal, hou van dag een af ​​die sleutel tot jou beplande afsterwe. Terwyl hierdie verouderingsteorie op die oog af fatalisties lyk, onthou dat biologie nie die lot is nie. Jy kan nie jou gene verander nie, maar jy kan die gang van tyd vertraag met beter voeding en gereelde fisiese aktiwiteit.

Jou liggaam produseer hormone wat help om talle funksies te reguleer, insluitend groei en gedrag, voortplanting en immuunfunksie. In jou jeug is hormoonproduksie hoog, maar namate jy ouer word, daal hormoonvlakke, wat afname in die liggaam se vermoë veroorsaak om homself te herstel en om in topvorm te bly funksioneer.

Werkende selle produseer afval. Met verloop van tyd maak selle meer afval as waarvan hulle moontlik ontslae kan raak, wat hul vermoë om te funksioneer verwoesting kan saai en stadig tot hul dood kan lei. Lipofuscin, of ouderdomspigment, is een van die afvalprodukte wat hoofsaaklik in sommige senuwee- en hartspierselle voorkom. Lipofuscin bind vet en proteïene saam in die selle. Dit versamel met verloop van tyd en kan inmeng met selfunksie.

Die proteïen kollageen is die kern van hierdie teorie. Kollageen, soortgelyk aan die liggaam se gom, is een van die mees algemene proteïene wat die vel, bene, ligamente en senings uitmaak. Wanneer ons jonk is, is kollageen buigbaar. Maar met ouderdom word kollageen meer rigied, en dit krimp. Daarom is jou vel minder elasties as voorheen.

Afgesien van estetika, kan kruisbinding die vervoer van voedingstowwe in selle blokkeer, asook die verwydering van afvalprodukte belemmer. Vrye radikale is vernietigende plunderaars wat jou liggaam ronddwaal, gereed om op gesonde selle toe te slaan. Hulle word geproduseer as deel van die miljoene chemiese reaksies wat jou liggaam uitvoer om lewe te onderhou.

Jou liggaam maak dit ook in reaksie op omgewingsgifstowwe soos oormatige hoeveelhede onbeskermde sonlig en sigaretrook. Vrye radikale oksideer jou selle (dink roes metaal). As ongebalanseerde, vlugtige suurstofmolekules offer hulle gesonde selle op om hulself meer stabiel te maak.

Sodoende vernietig of verander vrye radikale DNA, die sel se genetiese bloudruk, en ontwrig baie ander selfunksies. Vrye radikale kan selle doodmaak as gevolg van hul plundering, of hulle kan aanleiding gee tot mutante selle wat kan lei tot chroniese toestande, insluitend kanker en hartsiektes. Gelukkig handhaaf die liggaam 'n gesofistikeerde verdedigingstelsel teen vrye radikale. Ongelukkig kwyn ons verdediging mettertyd, en selskade volg.

Hierdie teorie kan ook genoem word Die gebruik dit en verloor dit-teorie. Die idee is dat die gebruik, en oorbenutting, van jou organe hulle tot op die rand van vernietiging stoot. ’n Swak dieet, te veel alkohol en sigaretrook word vermoedelik natuurlike slytasie versnel. Met ouderdom is die liggaam minder in staat om homself te herstel.

Hoe vind slytasie plaas? Vrye radikale, wat sellulêre skade aanrig, kan skuldig wees. Soortgelyk aan die slytasie-idee, sê hierdie teorie dat jy met 'n sekere hoeveelheid energie gebore word. As jy " vinnig" leef, sterf jy jonk, want jy gebruik jou energiereserwes gouer. "Ontspanne mense" wat aan minder stres ly en die lewe makliker neem, sal langer lewe as hierdie teorie korrek sou blyk.

’n Sterk immuunstelsel is jou liggaam se belangrikste verdediging teen kieme en gifstowwe. Wit selle verswelg en vernietig potensiële plae soos bakterieë en virusse. En hulle vervaardig teenliggaampies, die "soldate" wat die bloedstroom patrolleer en enige stof wat hulle nie as die liggaam se eie herken nie, aanval en ontwapen.

Probleem is dat die immuunstelsel mettertyd minder doeltreffend word, en minder teenliggaampies word geproduseer, wat jou infeksierisiko verhoog. Wat meer is, die liggaam kan op homself draai deur teenliggaampies te produseer wat sy eie weefsel vernietig. Wanneer dit gebeur, is outo-immuun siekte, soos lupus en rumatoïede artritis, die gevolg.

Alhoewel ons steeds nie die proses van veroudering heeltemal verstaan ​​nie, weet ons nogal baie daarvan, soos ons gesien het. Om meer uit te vind oor die verouderingsproses, kyk na die skakels op die volgende bladsy.


Plantweefselkultuur: voordeel, struktuur, tipes en tegnieke

Plantweefselkultuur verwys breedweg na die in vitro-verbouing van plante, sade en verskeie dele van die plante (organe, embrio's, weefsels, enkelselle, protoplaste).

Die verbouingsproses word sonder uitsondering in 'n voedingstofkultuurmedium onder aseptiese toestande uitgevoer.

Plantselle het sekere voordele bo dierselle in kultuurstelsels. Anders as dierselle, behou hoogs volwasse en gedifferensieerde plantselle die vermoë van totipotensie, dit wil sê die vermoë om na meristematiese toestand te verander en in 'n hele plant te differensieer.

Voordele van plantweefselkultuur:

Plantweefselkultuur is een van die gebiede van biotegnologie wat die vinnigste groei vanweë die hoë potensiaal daarvan om verbeterde gewasse en sierplante te ontwikkel. Met die vooruitgang wat gemaak is in die weefselkultuurtegnologie, is dit nou moontlik om spesies van enige plant in die laboratorium te regenereer.

Om die doelwit te bereik om 'n nuwe plant of 'n plant met gewenste eienskappe te skep, word weefselkultuur dikwels met rekombinante DNS-tegnologie gekoppel. Die tegnieke van plantweefselkultuur het grootliks gehelp in die groen revolusie deur die oesopbrengs en kwaliteit te verbeter.

Die kennis verkry uit plantweefselkulture het bygedra tot ons begrip van metabolisme, groei, differensiasie en morfogenese van plantselle. Verder het ontwikkelings in weefselkultuur gehelp om verskeie patogeenvrye plante te produseer, behalwe die sintese van baie biologies belangrike verbindings, insluitend farmaseutiese middels. As gevolg van die wye reeks toepassings, trek plantweefselkultuur die aandag van molekulêre bioloë, planttelers en nyweraars.

Basiese struktuur en groei van 'n plant:

'n Volwasse plant bestaan ​​basies uit 'n stam en 'n wortel, elk met baie takke (Fig. 42.1). Beide die stam en wortel word gekenmerk deur die teenwoordigheid van apikale groeistreke wat uit meristematiese selle saamgestel is. Hierdie selle is die primêre bron vir al die seltipes van 'n plant.

Plantgroei en -ontwikkeling vind op twee verskillende maniere plaas:

Dit word gekenmerk deur ophou groei aangesien die plantdele sekere grootte en vorm verkry, bv. blare, blomme, vrugte.

2. Onbepaalde groei:

Dit verwys na die voortdurende groei van wortels en stamme onder geskikte toestande. Dit is moontlik as gevolg van die teenwoordigheid van meristeme (in stingels en wortels) wat voortdurend kan vermeerder. Soos die saad ontkiem en saailing te voorskyn kom, vermeerder die meristematiese selle van die wortelpunt. Bokant die worteltop groei die selle in lengte sonder vermenigvuldiging.

Sommige van die langwerpige selle van die buitenste laag ontwikkel in wortelhare om water en voedingstowwe uit die grond te absorbeer. Soos die plant groei, differensieer wortelselle in floëem en xileem. Floëem is verantwoordelik vir die opname van voedingstowwe terwyl xileem water absorbeer.

Die meristematiese selle van die loot se top verdeel wat lei tot die groei van stam. Sommige van die stamselle differensieer en ontwikkel in blaar primordia, en dan blare. Okselknoppe wat tussen die blaar primordia en langwerpige stam voorkom, het ook meristeme wat kan vermeerder en aanleiding gee tot takke en blomme.

'n Diagrammatiese aansig van 'n plant en 'n blom word onderskeidelik in Fig. 42.1 en Fig. 42.2 uitgebeeld.

Konvensionele plantteling en plantweefselkultuur:

Sedert die onheuglike tye is die mens nou betrokke by die verbetering van plante om in sy basiese behoeftes te voorsien. Die konvensionele metodes wat vir oesverbetering gebruik word, is baie vervelige en langdurige prosesse (soms dekades). Verder, in die konvensionele teelmetodes, is dit nie moontlik om gewenste gene in te voer om nuwe karakters of produkte te genereer nie.

Met die ontwikkelings in plantweefselkultuur is dit nou moontlik om die tyd te verminder vir die skepping van nuwe plante met gewenste eienskappe, oordrag van nuwe gene in plantselle en grootskaalse produksie van kommersieel belangrike produkte.

Terme wat in Weefselkultuur gebruik word:

'n Geselekteerde lys van die mees algemene terme in weefselkultuur word kortliks verduidelik

'n Uitgesnyde stuk gedifferensieerde weefsel of orgaan word as 'n eksplantaat beskou. Die eksplantaat kan van enige deel van die plantliggaam geneem word, bv. blaar, stam, wortel.

Die ongeorganiseerde en ongedifferensieerde massa van plantselle word na verwys as callus. Oor die algemeen, wanneer plantselle in 'n geskikte medium gekweek word, verdeel hulle om callus te vorm, d.w.s. 'n massa parenchimatiese selle.

Die verskynsel van volwasse selle wat na meristematiese toestand terugkeer om callus te produseer, is dedifferensiasie. Dedifferensiasie is moontlik aangesien die nie-delende rustige selle van die eksplantaat, wanneer dit in 'n geskikte kultuurmedium gekweek word, terugkeer na meristematiese toestand.

Die vermoë van die eeltselle om tot 'n plantorgaan of 'n hele plant te differensieer, word as herdifferensiasie beskou.

Die vermoë van 'n individuele sel om tot 'n hele plant te ontwikkel, word sellulêre totipotensie genoem. Die inherente kenmerkende kenmerke van plantselle naamlik dedifferensiasie en herdifferensiasie is verantwoordelik vir die verskynsel van totipotensie. Die ander terme wat in plantweefselkultuur gebruik word, word op toepaslike plekke verduidelik.

Kort geskiedenis van plantweefselkultuur:

Ongeveer 250 jaar gelede (1756) het Henri-Louis Duhamel du Monceau eeltvorming op die versierde streke van elmplante gedemonstreer. Baie plantkundiges beskou hierdie werk as die voorspeler vir die ontdekking van plantweefselkultuur. In 1853 het Trecul foto's van callusvorming in plante gepubliseer.

Die Duitse plantkundige Gottlieb Haberlandt (1902), wat as die vader van plantweefselkultuur beskou word, het eers die konsep van in vitro-selkultuur ontwikkel. Hy was die eerste wat geïsoleerde en ten volle gedifferensieerde plantselle in 'n voedingsmedium gekweek het. Gedurende 1934-1940 het drie wetenskaplikes naamlik Gautheret, White en Nobecourt grootliks bygedra tot die ontwikkelings wat in plantweefselkultuur gemaak is.

Goeie vordering en vinnige ontwikkelings het ná 1940 in plantweefselkultuurtegnieke plaasgevind. Steward en Reinert (1959) het die eerste keer somatiese embrioproduksie in vitro ontdek. Maheswari en Guha (1964) van Indië was die eerstes wat helmknopkultuur en pollerkultuur ontwikkel het vir die produksie van haploïede plante.

Tipes Kultuur:

Daar is verskillende tipes plantweefselkultuurtegnieke, hoofsaaklik gebaseer op die eksplantaat wat gebruik word (Fig. 42.3).

Dit behels die kultuur van gedifferensieerde weefsel vanaf eksplantaat wat in vitro dedifferensieer om callus te vorm.

Kultuur van geïsoleerde plantorgane word orgaankultuur genoem. Die orgaan wat gebruik word kan embrio, saad, wortel, endosperm, helmknop, ovarium, ovule, meristeem (lootpunt) of nucellus wees. Die orrelkultuur kan georganiseer of ongeorganiseerd wees.

Georganiseerde orrelkultuur:

Wanneer 'n goed georganiseerde struktuur van 'n plant (saad, embrio) in kultuur gebruik word, word dit na verwys as georganiseerde kultuur. In hierdie tipe kultuur word die kenmerkende individuele orgaanstruktuur gehandhaaf en is die nageslag wat gevorm word soortgelyk in struktuur as dié van die oorspronklike orgaan.

Ongeorganiseerde orgaankultuur:

Dit behels die isolasie van selle of weefsels van 'n deel van die orgaan, en hul kultuur in vitro. Ongeorganiseerde kultuur lei tot die vorming van callus. Die callus kan in aggregate van selle en/of enkelselle versprei word om 'n suspensiekultuur te gee.

Die kultuur van geïsoleerde individuele selle, verkry uit 'n uitplantweefsel of callus, word as selkultuur beskou. Hierdie kulture word in dispensiemedium uitgevoer en word na verwys as selsuspensiekulture.

Protoplast kultuur:

Plantprotoplaste (d.w.s. selle sonder selwande) word ook in die laboratorium vir kweek gebruik.

Basiese tegniek van plantweefselkultuur:

Die algemene prosedure wat gebruik word vir isolasie en kweek van plantweefsel word in Fig. 42.4 uitgebeeld

Die nodige uitplantings (knoppies, stam, sade) word afgesny en dan in 'n skoonmaakmiddel aan sterilisasie onderwerp. Nadat dit in steriele gedistilleerde water gewas is, word die eksplantate in 'n geskikte kultuurmedium (vloeibare of halfvaste vorm) geplaas en geïnkubeer. Dit lei tot die vestiging van kultuur. Die moederkulture kan so gereeld as wat nodig is onderverdeel word om dogterkulture te gee.

Die belangrikste aspek van in vitro-kultuurtegniek is om al die operasies onder aseptiese toestande uit te voer. Bakterieë en swamme is die mees algemene kontaminante in plantweefselkultuur. Hulle groei baie vinniger in kultuur en maak dikwels die plantweefsel dood.

Verder produseer die kontaminante ook sekere verbindings wat giftig is vir die plantweefsel. Daarom is dit absoluut noodsaaklik dat aseptiese toestande regdeur die weefselkultuuroperasies gehandhaaf word. Sommige van die kultuurtegnieke word hier beskryf terwyl 'n paar ander op toepaslike plekke bespreek word.

Toepassings van plantweefselkulture:

Plantweefselkulture word geassosieer met 'n wye reeks toepassings—die belangrikste is die vervaardiging van farmaseutiese, medisinale en ander industrieel belangrike verbindings.

Daarbenewens is weefselkulture nuttig vir verskeie ander doeleindes wat hieronder gelys word:

1. Om die respirasie en metabolisme van plante te bestudeer.

2. Vir die evaluering van orgaanfunksies in plante.

3. Om die verskillende plantsiektes te bestudeer en metodes uit te werk vir die uitskakeling daarvan.

4. Enkelselklone is nuttig vir genetiese, morfologiese en patologiese studies.

5. Embrionale sel suspensies kan gebruik word vir grootskaalse klonale voortplanting.

6. Somatiese embrio's van selsuspensies kan vir lang termyn in kiemplasmabanke gestoor word.

7. In die produksie van variante klone met nuwe eienskappe, word 'n verskynsel na verwys as soma klonale variasies.

8. Produksie van haploïede (met 'n enkele stel chromosome) vir die verbetering van gewasse.

9. Mutante selle kan uit kulture geselekteer word en vir gewasverbetering gebruik word.

10. Onvolwasse embrio's kan in vitro gekweek word om basters te produseer, 'n proses waarna verwys word as embrio-redding.

Eeltkultuur:

Callus is die ongedifferensieerde en ongeorganiseerde massa plantselle. Dit is basies 'n tumorweefsel wat gewoonlik op wonde van gedifferensieerde weefsels of organe vorm. Callusselle is parenchimaties van aard, hoewel nie werklik homogeen nie. By noukeurige ondersoek word gevind dat callus 'n hoeveelheid gedifferensieerde weefsel bevat, behalwe die grootste deel van nie-gedifferensieerde weefsel.

Callusvorming in vivo word gereeld waargeneem as gevolg van wonde aan die snyrande van stamme of wortels. Indringing van mikroörganismes of skade deur insekvoeding vind gewoonlik deur eelt plaas. 'n Skets van tegniek wat gebruik word vir calluskultuur, en aanvang van suspensiekultuur word in Fig. 42.5 uitgebeeld.

Uitplantings vir calluskultuur:

Die beginmateriaal (explate) vir callus-kultuur kan die gedifferensieerde weefsel van enige deel van die plant (wortel, stam, blaar, helmknop, blom, ens.) wees. Die geselekteerde uitplantweefsels kan in verskillende stadiums van seldeling, selproliferasie en organisasie in verskillende afsonderlike gespesialiseerde strukture wees. As die eksplantaat wat gebruik word meristematiese selle besit, sal die seldeling en vermenigvuldiging vinnig wees.

Faktore wat eeltkultuur beïnvloed:

Baie faktore is bekend om kallusvorming in vitro-kultuur te beïnvloed. Dit sluit in die bron van die eksplantaat en sy genotipe, samestelling van die medium (MS-medium wat die meeste gebruik word), fisiese faktore (temperatuur, lig ens.) en groeifaktore. Ander belangrike faktore wat eeltkultuur beïnvloed is - ouderdom van die plant, ligging van uitplanting, fisiologie en groeitoestande van die plant.

’n Temperatuur in die reeks van 22-28°C is geskik vir voldoende eeltvorming. Wat die effek van lig op eelt betref, is dit grootliks afhanklik van die plantspesie - lig kan noodsaaklik wees vir sommige plante terwyl duisternis deur ander vereis word.

Die groeireguleerders na die medium beïnvloed callusvorming sterk. Based on the nature of the explant and its genotype, and the endogenous content of the hormone, the requirements of growth regulators may be categorized into 3 groups

3. Both auxin and cytokinin.

Suspension culture from callus:

Suspension cultures can be initiated by transferring friable callus to liquid nutrient medium (Fig. 42.5). As the medium is liquid in nature, the pieces of callus remain submerged. This creates anaerobic condition and ultimately the cells may die. For this reason, suspension cultures have to be agitated by a rotary shaker. Due to agitation, the cells gets dispersed, besides their exposure to aeration.

Applications of Callus Cultures:

Callus cultures are slow-growth plant culture systems in static medium. This enables to conduct several studies related to many aspects of plants (growth, differentiation and metabolism) as listed below.

i. Nutritional requirements of plants.

ii. Cell and organ differentiation.

iii. Development of suspension and protoplast cultures.

v. Genetic transformations.

vi. Production of secondary metabolites and their regulation.

Cell Culture:

The first attempt to culture single cells (obtained from leaves of flowering plants) was made in as early as 1902 by Haberlandt. Although he was unsuccessful to achieve cell division in vitro, his work gave a stimulus to several researchers. In later years, good success was achieved not only for cell division but also to raise complete plants from single cell cultures.

Applications of Cell Cultures:

Cultured cells have a wide range of applications in biology.

1. Elucidation of the pathways of cellular metabolism.

2. Serve as good targets for mutation and selection of desirable mutants.

3. Production of secondary metabolites of commercial interest.

4. Good potential for crop improvement.

Cell Culture Technique:

The in vitro cell culture technique broadly involves the following aspects:

1. Isolation of single cells.

2. Suspension cultures growth and sub-culturing.

3. Types of suspension cultures.

4. Synchronization of suspension cultures.

5. Measurement of growth of cultures.

6. Measurement of viability of cultured cells.

The salient features of the above steps are briefly described.

1. Isolation of Single Cells:

The cells employed for in vitro culture may be obtained from plant organs, and from cultured tissues.

Plant leaves with homogenous population of cells are the ideal sources for cell culture. Single cells can be isolated from leaves by mechanical or enzymatic methods.

Surface sterilized leaves are cut into small pieces (< 1 cm 2 ), suspended in a medium and subjected to grinding in a glass homogenizer tube. The homogenate is filtered through filters and then centrifuged at a low speed to remove the cellular debris. The supernatant is removed and diluted to achieve the required cell density.

The enzyme macerozyme (under suitable osmotic pressure) can release the individual cells from the leaf tissues. Macerozyme degrades middle lamella and cell walls of parenchymatous tissues.

From cultured tissues:

Single cells can be isolated from callus cultures (grown from cut pieces of surface sterilized plant parts). Repeated sub-culturing of callus on agar medium improves the friability of callus so that fine cell suspensions are obtained.

2. Suspension Cultures — Growth and Subculture:

The isolated cells are grown in suspension cultures. Cell suspensions are maintained by routine sub-culturing in a fresh medium. For this purpose, the cells are picked up in the early stationary phase and transferred. As the cells are incubated in suspension cultures, the cells divide and enlarge.

The incubation period is dependent on:

Among these, cell density is very crucial. The initial cell density used in the subcultures is very critical, and largely depends on the type of suspension culture being maintained. With low initial cell densities, the lag phase and log phases of growth get prolonged.

Whenever a new suspension culture is started, it is necessary to determine the optical cell density in relation the volume of culture medium, so that maximum cell growth can be achieved. With low cell densities, the culture will not grow well, and requires additional supplementation of metabolites to the medium. The normal incubation time for the suspension cultures is in the range of 21-28 days.

3. Types of Suspension Cultures:

There are mainly two types of suspension cultures — batch cultures and continuous cultures.

A batch culture is a cell suspension culture grown in a fixed volume of nutrient culture medium. In batch culture, cell division and cell growth coupled with increase in biomass occur until one of the factors in the culture environment (nutrient, O2 supply) becomes limiting. The cells exhibit the following five phases of growth when the cell number in suspension cultures is plotted against the time of incubation (Fig. 42.6).

1. Lag phase characterized by preparation of cells to divide.

2. Log phase (exponential phase) where the rate of cell multiplication is highest.

3. Linear phase represented by slowness in cell division and increase in cell size expansion.

4. Deceleration phase characterized by decrease in cell division and cell expansion.

5. Stationary phase represented by a constant number of cells and their size.

The batch cultures can be maintained continuously by transferring small amounts of the suspension medium (with inoculum) to fresh medium at regular intervals (2-3 days). Batch cultures are characterized by a constant change in the pattern of cell growth and metabolism. For this reason, these cultures are not ideally suited for the studies related to cellular behaviour.

Continuous cultures:

In continuous cultures, there is a regular addition of fresh nutrient medium and draining out the used medium so that the culture volume is normally constant. These cultures are carried out in specially designed culture vessels (bioreactors).

Continuous cultures are carried out under defined and controlled conditions—cell density, nutrients, O2, pH etc. The cells in these cultures are mostly at an exponential phase (log phase) of growth.

Continuous cultures are of two types—open and closed.

Open continuous cultures:

In these cultures, the inflow of fresh medium is balanced with the outflow of the volume of spent medium along with the cells. The addition of fresh medium and culture harvest are so adjusted that the cultures are maintained indefinitely at a constant growth rate. At a steady state, the rate of cells removed from the cultures equals to the rate of formation of new cells.

Open continuous culture system is regarded as chemostat if the cellular growth rate and density are kept constant by limiting a nutrient in the medium (glucose, nitrogen, phosphorus). In chemostat cultures, except the limiting nutrient, all other nutrients are kept at higher concentrations. As a result, any increase or decrease in the limiting nutrient will correspondingly increase or decrease the growth rate of cells.

In turbidostat open continuous cultures, addition of fresh medium is done whenever there is an increase in turbidity so that the suspension culture system is maintained at a fixed optical density. Thus, in these culture systems, turbidity is preselected on the basis of biomass density in cultures, and they are maintained by intermittent addition of medium and washout of cells.

Closed continuous cultures:

In these cultures, the cells are retained while the inflow of fresh medium is balanced with the outflow of corresponding spent medium. The cells present in the outflowing medium are separated (mechanically) and added back to the culture system. As a result, there is a continuous increase in the biomass in closed continuous cultures. These cultures are useful for studies related to cytodifferentiation, and for the production of certain secondary metabolites e.g., polysaccharides, coumarins.

4. Synchronization of Suspension Cultures:

In the normal circumstances, the cultured plant cells vary greatly in size, shape, cell cycle etc., and are said to be asynchronous. Due to variations in the cells, they are not suitable for genetic, biochemical and physiological studies. For these reasons, synchronization of cells assumes significance.

Synchronization of cultured cells broadly refers to the organized existence of majority of cells in the same cell cycle phase simultaneously.

A synchronous culture may be regarded as a culture in which the cell cycles or specific phase of cycles for majority of cultured cells occurs simultaneously.

Several methods are in use to bring out synchronization of suspension cultures. They may be broadly divided into physical and chemical methods.

Physical methods:

The environmental culture growth influencing physical parameters (light, temperature) and the physical properties of the cell (size) can be carefully monitored to achieve reasonably good degree of synchronization. A couple of them are described

When the suspension cultures are subjected to low temperature (around 4°C) shock synchronization occurs. Cold treatment in combination with nutrient starvation gives better results.

The cells in suspension culture can be selected based on the size of the aggregates, and by this approach, cell synchro­nization can be achieved.

Chemical methods:

The chemical methods for synchronization of suspension cultures include the use of chemical inhibitors, and deprivation of an essential growth factor (nutrient starvation). By this approach, the cell cycle can be arrested at a particular stage, and then allowed to occur simultaneously so that synchronization is achieved.

Inhibitors of DNA synthesis (5-amino uracil, hydroxyurea, 5-fluorodeoxypurine), when added to the cultures results in the accumulation of cells at G1 fase. And on removal of the inhibitor, synchronization of cell division occurs.

Colchicine is a strong inhibitor to arrest the growth of cells at metaphase. It inhibits spindle formation during the metaphase stage of cell division. Exposure to colchicine must be done for a short period (during the exponential growth phase), as long duration exposure may lead to mitoses.

When an essential nutrient or growth promoting compound is deprived in suspension cultures, this results in stationary growth phase. On supplementation of the missing nutrient compound, cell growth resumption occurs synchronously. Some workers have reported that deprivation and subsequent addition of growth hormone also induces synchronization of cell cultures.

5. Measurement of Growth of Cultures:

It is necessary to assess the growth of cells in cultures. The parameters selected for the measuring growth of suspension cultures include cell counting, packed cell volume and weight increase.

Although cell counting to assess culture growth is reasonably accurate, it is tedious and time consuming. This is because cells in suspension culture mostly exist as colonies in varying sizes. These cells have to be first disrupted (by treating with pectinase or chromic acid), separated, and then counted using a haemocytometer.

Packed cell volume:

Packed cell volume (PCV) is expressed as ml of pellet per ml of culture. To determine PCV, a measured volume of suspension culture is centrifuged (usually at 2000 x g for 5 minutes) and the volume of the pellet or packed cell volume is recorded. After centrifugation the supernatant can be discarded, the pellet washed, dried overnight and weighed. This gives cell dry weight.

Cell fresh weight:

The wet cells are collected on a pre-weighed nylon fabric filter (supported in funnel). They are washed to remove the medium, drained under vacuum and weighed. This gives the fresh weight of cells. However, large samples have to be used for accurate weights.

6. Measurement of Viability of Cultured Cells:

The viability of cells is the most important factor for the growth of cells. Viability of cultured cells can be measured by microscopic examination of cells directly or after staining them.

Phase contrast microscopy:

The viable cells can be detected by the presence of healthy nuclei. Phase contrast microscope is used for this purpose.

Evan’s blue staining:

A dilute solution of Evan’s blue (0.025% w/v) dye stains the dead or damaged cells while the living (viable) cells remain unstained.

Fluorescein diacetate method:

When the cell suspension is incubated with fluorescein diacetate (FDA) at a final concentration of 0.01%, it is cleaved by esterase enzyme of living cells. As a result, the polar portion of fluorescein which emits green fluorescence under ultraviolet (UV) light is released. The viable cells can be detected by their fluorescence, since fluorescein accumulates in the living cells only.

Culture of Isolated Single Cells (Single Cell Clones):

A clone is a mass of cells, all of them derived through mitosis from a single cell. The cells of the clone are expected to be identical with regard to genotype and karyotype. However, changes in these cells may occur after cloning. Single cells separated from plant tissues under suitable conditions can form clones.

Single cells can be cultured by the following methods:

1. Filter paper raft-nurse tissue technique

4. Bergman’s plating technique.

Filter paper raft-nurse tissue technique:

Small pieces of sterile filter papers are placed on established callus cultures several days before the start of single cell culture. Single cell is now placed on the filter paper (Fig. 42.7A). This filter paper, wetted by the exudates from callus tissue (by diffusion) supplies the nutrients to the single cell. The cell divides and forms clones on the filter paper. These colonies can be isolated and cultured.

Micro-chamber technique:

A microscopic slide or a coverslip can be used to create a micro-chamber. Sometimes, a cavity slide can be directly used. A drop of the medium containing a single cell is placed in the micro-chamber. A drop of mineral oil is placed on either side of the culture drop which is covered with a coverslip (Fig. 42.7B). On incubation, single cell colonies are formed.

Micro-drop method:

For the culture of single cells by micro-drop method, a specially designed dish (cuprak dish) is used. It has a small outer chamber (to be filled with sterile distilled water) and a large inner chamber with a number of micro-wells (Fig. 42.7C). The cell density of the medium is adjusted in such a way that it contains one cell per droplet.

Bergmann’s plating technique:

Bergmann (1960) developed a technique for cloning of single cells. Now a days, Bergmann’s plating technique is the most widely used method for culture of isolated single cells. This method is depicted in Fig. 42.8 and briefly described hereunder.

The cell suspension is filtered through a sieve to obtain single cells in the filtrate. The free cells are suspended in a liquid medium, at a density twice than the required density for cell plating. Now, equal volumes of melted agar (30-35°C) and medium containing cells are mixed.

The agar medium with single cells is poured and spread out in a petridish so that the cells are evenly distributed on a thin layer (of agar after it solidifies). The petridishes (culture dishes) are sealed with a parafilm and incubated at 25°C in dark or diffused light. The single cells divide and develop into clones. The viability of cells in single clones can be measured by the same techniques that have been described for suspension cultures.


Kingdom Alveolata: Dinoflagellates

Dinoflagellates typically possess distinct shapes due to "frames" of cellulose within their cell walls. Their cell surface is generally ridged with perpendicular grooves that house a pair of flagella (shown left). These flagella, the defining characteristic of this group, beat within their grooves and cause dinoflagellates to rotate as they move forward. The word dinoflagellate is derived from the Greek word dinos, which means "rotation" or "whirling," and the Latin flagellum, which means "whip." Many dinoflagellates are photosynthetic accordingly, they comprise a significant proportion of the phytoplankton that floats near the surface of the ocean, making them a critical component of the food web. Phytoplankton are an essential food resource for many other organisms, ranging from heterotrophic protists to baleen whales and many other organisms in between (most of whom serve as food themselves for creatures at higher trophic levels).


Figure 16. A dinoflagellate. (Click to enlarge) Ceratium tripos.

Not all dinoflagellates are photosynthetic many are heterotrophic. Some of these heterotrophs exploit chloroplasts from photosynthetic protists, becoming autotrophic themselves for a time. Some dinoflagellates live in symbiosis with different species, as parasites in some cases and as mutualists in others.

Some dinoflagellates, such as those in the genus Noctiluca, have the ability to bioluminesce (make their own light). This is accomplished with the compound luciferin, which is the same chemical that makes fireflies glow. Noctiluca floats just under the surface of the ocean, and when individuals number in the millions they can produce spectacular glowing tides (pictured below). The red border at the advancing wave front (tide line) as it washes onto the beach is a real visible glow that is triggered by the tumbling dinoflagellates as they hit the sand. If you walk along the tide line of such a beach, your footprints actually glow with each step when your foot disturbs these bioluminescent protists. How bioluminescence evolved is not completely understood. The Burglar Alarm theory posits that the bioluminescent glow attracts predators of dinoflagellate predators and this allows the glowing protist to escape predation.


Figure 17. A dinoflagellate. (Click to enlarge) Noctiluca scintillans is one dinoflagellate responsible for red tides.


Figure 18. A bioluminescent algal bloom. (Click to enlarge)

This image shows a bloom of bioluminescent Noctiluca scintillans.


ELI5: What are "eye-floaters" and how do they manifest/disappear?

Floaters are deposits . within the eye’s vitreous humour, which is normally transparent. At a young age, the vitreous is transparent, but as one ages, imperfections gradually develop. The common type of floater, which is present in most people’s eyes, is due to degenerative changes of the vitreous humour.

Eye floaters are suspended in the vitreous humour, the thick fluid or gel that fills the eye. . Thus, floaters follow the rapid motions of the eye, while drifting slowly within the fluid. When they are first noticed, the natural reaction is to attempt to look directly at them. . Floaters are, in fact, visible only because they do not remain perfectly fixed within the eye. Although the blood vessels of the eye also obstruct light, they are invisible under normal circumstances because they are fixed in location relative to the retina, and the brain "tunes out" stabilized images due to neural adaptation.

Basically: they are tiny pieces of tissue floating in our eyeballs. They are normal, especially as we get older.

Our brain tunes floaters out when they're still, which is why they ɽisappear'. And, they're easier to see against light backgrounds like the sky.

Like /u/shriekingapples said it is caused by debris in the eye. The retina is the layer of the eye that has photo receptors (rods and cone), which captures light and causes a chemical and electrical reaction to the nerve. Light that "excites" the rods causes us to see monochromatic color or how black and white something is, while "excited" cones gives us high-resolution color. As we age the jelly of the eye, the vitreous gel, can shrink and pull away from the retina. This results in debris from the eye to go into the vitreous gel and appear as floaters in our vision. So it is normal that we may see floaters as we age. However, be careful of sudden appearances of floaters. Retinal tears and retinal holes can also cause floaters and/or flashers to appear as well. If not treated the retinal tears and holes can cause a retinal detachment, which may cause even more floaters to appear. If a retinal tear or hole is found early, a small office procedures like laser retinopexy or retinal cryopexy can be performed. Left untreated your vision and the flasher/floaters can become worse. Ultimately leading to surgery as the only option to fixing a retinal detachment.

Source: I work at an ophthalmologists office who specializes in vitrealretinal surgery.


What causes tissues manifest the various forms that they do? - Biologie

Connective tissue is a term used to describe the tissue of mesodermal origin that that forms a matrix beneath the epithelial layer and is a connecting or supporting framework for most of the organs of the body. This lab will focus on the so-called connective tissue proper and cartilage the next lab will focus on bone.

Overview of Connective Tissue

In contrast to epithelia, connective tissue is sparsely populated by cells and contains an extensive extracellular matrix consisting of protein fibers, glycoproteins, and proteoglycans. The function of this type of tissue is to provide structural and mechanical support for other tissues, and to mediate the exchange of nutrients and waste between the circulation and other tissues. These tissues have two principal components, an extracellular matrix and a variety of support cells. These two components will be the focus of this lab.

Most frequently, the different types of connective tissues are specified by their content of three distinguishing types of extracellular fibers: collagenous fibers, elastic fibers, and reticular fibers.

Ground Substance

The ground substance is an aqueous gel of glycoproteins and proteoglycans that occupies the space between cellular and fibrillar elements of the connective tissue. It is characterized by a gel-like viscous consistency and is polyanionic. The characteristics of the ground substance determine the permeability of the connective tissue layer to solutes and proteins.

Collagenous Fibers

Collagenous fibers consist of types I, II, or III collagen and are present in all types of connective tissue. Collagenous connective tissue is divided into two types, based upon the ratio of collagen fibers to ground substance:

  • Loose (areolar connective tissue) is the most abundant form of collagenous connective tissue. It occurs in small, elongated bundles separated by regions that contain ground substance.
  • Dense connective tissue is enriched in collagen fibers with little ground substance. If the closely packed bundles of fibers are located in one direction, it is called regular if oriented in multiple directions, it is referred to as irregular. An example of regular dense connective tissue is that of tendons an example of irregular dense connective tissue is that of the dermis.

Reticular Fibers

Reticular fibers are composed of type III collagen. Unlike the thick and coarse collagenous fibers, reticular fibers form a thin reticular network. Such networks are widespread among different tissues and form supporting frameworks in the liver, lymphoid organs, capillary endothelia, and muscle fibers.

Elastic Fibers

Elastic fibers contain the protein elastin, which co-polymerizes with the protein fibrillin. These fibers are often organized into lamellar sheets, as in the walls of arteries. Dense, regular, elastic tissue characterizes ligaments. Elastic fibers are stretchable because they are normally disorganized – stretching these fibers makes them take on an organized structure.

Cells of the Connective Tissue Proper

Although the connective tissue has a lower density of cells than the other tissues you will study this year, the cells of these tissues are extremely important.

Fibroblasts are by far the most common native cell type of connective tissue. The fibroblast synthesizes the collagen and ground substance of the extracellular matrix. These cells make a large amount of protein that they secrete to build the connective tissue layer. Some fibroblasts have a contractile function these are called myofibroblasts.

Chondrocytes and osteocytes form the extracellular matrix of cartilage and bone. More details and chondrocytes can be found later in this laboratory osteocytes will be covered in the Laboratory on Bone.

The macrophage is the connective tissue representative of the reticuloendothelial, or mononuclear phagocyte, system. This system consists of a number of tissue-specific, mobile, phagocytic cells that descend from monocytes - these include the Kupffer cells of the liver, the alveolar macrophages of the lung, the microglia of the central nervous system, and the reticular cells of the spleen. You will encounter each of these later in the course for now, make sure you recognize that they all descend from monocytes, and that the macrophage is the connective tissue version. Macrophages are indistinguishable from fibroblasts, but can be recognized when they internalize large amounts of visible tracer substances like dyes or carbon particles. Macrophages phagocytose foreign material in the connective tissue layer and also play an important role as antigen presenting cells, a function that you will learn more about in Immunobiology.

Mast cells are granulated cells typically found in connective tissue. These cells mediate immune responses to foreign particles. In particular, they release large amounts of histamine and enzymes in response to antigen recognition. This degranulation process is protective when foreign organisms invade the body, but is also the cause of many allergic reactions.

White fat cells are specialized for the storage of triglyceride, and occur singly or in small groups scattered throughout the loose connective tissue. They are especially common along smaller blood vessels. When fat cells have accumulated in such abundance that they crowd out or replace cellular and fibrous elements, the accumulation is termed adipose tissue. These cells can grow up to 100 microns and usually contain once centrally located vacuole of lipid - the cytoplasm forms a circular ring around this vacuole, and the nucleus is compressed and displaced to the side. The function of white fat is to serve as an energy source and thermal insulator.

Brown fat cells are highly specialized for temperature regulation. These cells are abundant in newborns and hibernating mammals, but are rare in adults. They have numerous, smaller lipid droplets and a large number of mitochondria, whose cytochromes impart the brown color of the tissue. The electron transport chain of these mitochondria is disrupted by an uncoupling protein, which causes the dissipation of the mitochondrial hydrogen ion gradient without ATP production. This generates heat.

Cartilage

Cartilage is a specialized form of connective tissue produced by differentiated fibroblast-like cells called chondrocytes. It is characterized by a prominent extracellular matrix consisting of various proportions of connective tissue fibers embedded in a gel-like matrix. Chondrocytes are located within lacunae in the matrix that they have built around themselves. Individual lacunae may contain multiple cells deriving from a common progenitor. Lacunae are separated from one another as a result of the secretory activity of the chondrocytes.

A highly fibrous, organized, dense connective tissue capsule known as the perichondrium surrounds cartilage. The fibroblast-like cells of this layer have chondrogenic potentiality, and are responsible for the enlargement of cartilage plates by appositional growth. Appositional growth involves cell division, differentiation, and secretion of new extracellular matrix, thereby contributing mass and new cells at the cartilage surface. It is in contrast to interstitial growth, in which new matrix is deposited within mature cartilage.

Three kinds of cartilage are classified according to the abundance of certain fibers and the characteristics of their matrix: