Lichaamsholte

Matth

Wanneer is een lichaamsholte nu eigenlijk primair en wanneer secundair? Bijvoorbeeld, ik heb al gevonden dat de coeloom een secundaire lichaamsholte is en het hart bij de mollusca is een primaire lichaamsholte.

Alvast bedankt voor jullie hulp

cheerio

Dido

Het is al veel te lang geleden om me nog te herinneren wat dit precies inhield, maar misschien kan het volgende helpen:

Primary and secondary body cavities, acoelomates, pseudocoelomates, and coelomates

Some animals lack any cavity; their cells are in close contact with each other, separated only by the extracellular matrix. Such organisms are known as acoelomates and have what can be called a "compact organization." However, many organisms have some type of cavity: Small interstitial spaces between cells, tube-like systems, large spaces, repeating units, and so forth (Schmidt-Rhaesa 2007).

Generally, two structural types of body cavities are recognized. One type of body cavity may be termed a primary body cavity and the other termed a secondary body cavity. More common terminology is to call one type of body cavity a pseudocoelom, and animals with this body plan pseudocoelomates, and the other type of body cavity a coelom, and animals with this body plan coelomates.

Since a cavity itself lacks features, body cavities can only be characterized on the basis of the surrounding structures or those structures internal to the cavity (Jenner 2004). A coelom is a fluid-filled body cavity that separates the digestive tract and the outer body wall and is completely lined with mesoderm (Simmons 2004). The surfaces of the coelom are covered with a peritoneum, which is a slick epithelial layer (Yeh 2002). Schmidt-Rhaesa (2007), among others, equates coelom with secondary body cavity; "the secondary body cavity is commonly named the coelom." The pseudocoelom is a fluid-filled body cavity that separates the digestive tract and the outer body wall and is not completely lined with mesoderm (Simmons 2004). This pseudocolom, which develops between the mesoderm and the endoderm, is a persistent blastocoel, or fluid-filled cavity, of the blastula stage of the embryo (Yeh 2002). Schmidt-Rhaesa (2007), among others, equates the term primary body cavity with the pseudocoelom: "The primary body cavity is sometimes called a pseudocoel." Schmidt-Rhaesa (2007), in the book The Evolution of Organs, actually differentiates the two types of cavities as the primary body cavity has an extracellular matrix that borders the entire cavity, whereas in the secondary body cavity, there is a cellular layer (epithelium) that itself rests on the extracellular matrix.

However, although coelom is unambiguously defined (Schmidt-Rhaesa 2007), the terminology of primary and secondary cavities, and aceoelomate and pseudocoelomate, although long appearing in the literature, are not rigorously defined and in some cases there has been a misleading use of the terms (Jenner 2004). For example, Jenner (2004) references the use of acoelomate also for some animals with a primary body cavity. And Yeh (2002) refers to the primary body cavity as including the digestive system (gut tube or visceral tube) and the secondary body cavity as including both organisms with a pseudocoelom or with a true coelom (for example, "animal species with a secondary body cavity, either a pseudocoelom or a true coelom"). That is, according to Yeh, acoelomates, such as sponges and flatworms, have a single body cavity, and pseudocoelomates, such as roundworms and rotifers, have a secondary body cavity. Simmons (2004) similarly notes that "primitive animals developed only one major body cavity, the digestive tract" and "all triploblastic animals pass the Playthelminthes have some form of secondary body cavity."

Note that the term human body cavities normally refers to the ventral body cavity, because it is by far the largest one in area.

uit: http://www.newworldencyclopedia.org/entry/Body_cavity

Blijkbaar zijn de termen niet zo duidelijk gedefinieerd en zorgen ze wel eens voor verwarring...

Of anders eventueel nog: http://www.tutorvista.com/ks/secondary-body-cavity

Dido

biologiestudent

Af je schaft je het boek BIOLOGY van solomon, martin en Berg aan

Kalkoen

Ik ben ook nog eens in mijn dierkundeboek gaan snuisteren (Hickman, roberts en larson), en daar spreken ze niet eens van secundaire en primaire holtes. Enkel de acoelomaat, pseudocoelomaat en eucoelomaat worden hier gebruikt. Meestal wordt primair en secundair gebruikt in de betekenis van respectievelijk de oer- of begintoestand en de later gevormde toestand. In die zin ben ik geneigd om te zeggen dat de lichaamsholte van een acoelomaat, den darm dus, de primaire holte is, en later gevormde holtes die voorkomen bij pseudocoelomaten en eucoelomaten (de buikholte als het ware) de secundaire holte is. Het kind moet een naam hebben. Essentieel is dat ge weet hoe de drie verschillende bouwplannen in elkaar zitten.

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