Embroyology

1. Describe the degree of flexion and torsion observed in the 48-hour chick embryo.

Answer: Flexion and torsion:  Bending and twisting of the embryo.

Cranial flexure: A sharp ventral bending of the head of the embryo through almost 180 degree. The anterior end of the embryo thus becomes an inverted U.

Cervical flexure: A gentle curvature of the embryo in the future neck or cervical region. Cranial and cervical flexures are segments of a general ventral bending of the embryo. Later more caudal segments will be involved and the entire embryo will be curved to form a large C.

Torsion: a rotation of the body about its along axis, beginning at the anterior end, so that the embryo comes to lie on its left side.

1. Describe the changes that have occurred in the optic vesicles since 33 hours.

Answer: The optic vesicles in 33-hour-chick embryo are hollow and lateral outgrowths from the prosencephalon .Within a few hours (37 hours) each optic vesicle constricts at its base where it grows out from the ventro-lateral side of the prosencephalon and forms the optic stalk. The vesicles proper continue to push out further in a lateral direction toward the outer ectoderm, and where they approach it closes it thickens to form the primordial crystalline lenses. Each optic vesicle bigens now to invaginate , pushing inward at the lower portion where it is attached to the optic stalk and proceeding upward until the entire optic vesicle id transformed into the optic cup.

1. Describe the changes that have occurred in the primary brain vesicles since its formation.

Answer:

[pic 1]

In comparison with 24hour

1. What changes have occurred in thw neural groove since the 24-hour stage?

Answer: In 24-hour chicks the anterior part of the neural plate is already folded to form the neural groove. Although the neural folds are at that stage beginning to converge mid-dorsally the groove nevertheless remains open throughout its length .By 27 hours the neural folds in the cephaUc region meet in the mid-dorsal line and their edges become fused.                              

1. Name the primary brain vesicles

Answer:

1. About how many somites should there be in a33 hour chick embryo?

Answer: At about 33 hours after fertilization, the embryo is about 4 mm long and the first flexion of the originally straight embryo starts in the head region and the cranial flexure will be visible a few hours later. At this stage 12 to 13 somites are formed. 

1. Name the 3 parts of the heart of a 33-hour chick embryo.

Answer: The circulatory system has advanced so that there is now a heart in the form of a relatively straight tube with four chambers. It will not start beating until 48 hours of development. At this point, it looks very much like a fish heart (if you have ever mucked through shark oil to study the shark heart, this should sound familiar). Posteriorly, the heart has a sinus venosus. This leads forward into an undivided atrium, which opens into an undivided ventricle, swung slightly to the right, which in turn leads into the conus arteriosus (or bulbus cordis). From the conus arteriosus sprout a pair of arteries, the ventral aortae.

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