Latebra and nucleus of Pander were described more than 200 years ago, but I could find no data about their role in embryo development. Does anybody have any information about the study of these structures, their functional role?
Salam alaikum
Let me explain to you .The yolk occupies the center of the egg. There are two types of yolk, white yolk and yellow yolk. Yellow yolk is produced during the day by the hen and contains more fat. White yolk is produced at night and contains more protein. In the center of the yolk there is a spherical mass of white yolk called the latebra. A column of white yolk connects the latebra to the Nucleus of Pander, which is also made of white yolk. The Nucleus of Pander provides the place where the embryo develops. The blastoderm is an early stage of the embryo, present when the egg is laid. The blastoderm is attached to the Nucleus of Pander. The blastoderm grows during the incubation period to ultimately become the chick..
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Thank you Saleh. I knew these things very well, I've been working with the early birds' embryos for the long time. But I'm wondering about the physiological function of these structures. Does anyone studied them? How the embryo use these structures?
Hi Makhsud; The centre of yolk was originally a 'small white follicle'. These are the less mature version of ovarian follicles. The darker yellow yolk is deposited on top of this as the follicle matures. However, the embryo disk is there in some form right from the start. If the yolk is growing in layers (like a pearl), the site of fertilization would be deep in the yolk. So, as the ovarian follicle increases in size, the site of fertilization must remain on the surface. The evidence of this movement is the latebra (the flask-shapes column of white yolk connecting the blastodisc to the centre of the yolk). The sperm can get through the perivitelline layers over the blastodisc, but cannot deal with yolk.
Robert -- you state that "the embryo disk" exists in the oocyte "from the start". Are you saying that yolk is laid down in the ovarian follicle progressively after fertilization?
Daniel; I was referring to the germinal disk and what happens during yolk formation. Yolk deposition ends at ovulation (no longer in contact with cells that are involved with yolk deposition), around the time the perivitelline yolk membranes are secreted. I was not using the right terminology in the previous comment.
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