Embryology notes

What is embryology?

The study of an animal’s development from the fertilized egg to the constitution of the organism.

What does ontogeny refer to?

The complete life history of an individual, including embryological and post-embryological stages.

What is the first phase of development after fertilization called?

Embryogenesis.

Define descriptive embryology.

It focuses on the structural features of embryos at various developmental stages.

What is the purpose of comparative embryology?

To study similarities and differences in developmental patterns among various species.

What is the significance of experimental embryology?

It investigates the factors that control and regulate developmental processes.

What does molecular embryology focus on?

It studies embryonic differentiation and cellular processes such as growth and division.

What are congenital anomalies studied in pathological embryology?

Malformations due to disturbances in normal development.

What are the four major stages of embryonic development?

1. Premorphogenesis (fertilization and segmentation) 2. Primary morphogenesis (gastrulation) 3. Secondary morphogenesis (neurulation) 4. Definitive morphogenesis (organogenesis).

What is the role of cleavage in early embryonic development?

The division of the fertilized egg (zygote) into multiple smaller cells (blastomeres) without increasing the overall size.

What are the three modes of embryonic development?

1. Oviparity (egg-laying) 2. Ovoviviparity (eggs hatch inside mother) 3. Viviparity (live birth).

What distinguishes oviparous organisms?

They lay eggs that develop and hatch outside the mother's body.

What is gastrulation?

The stage of embryonic development during which the embryo reorganizes into three germ layers (ectoderm, mesoderm, endoderm).

Define neurulation.

The process during embryonic development that leads to the formation of the neural tube, which gives rise to the central nervous system.

What is organogenesis?

The process by which different organs and systems are formed during embryonic development.

What are the three primary germ layers formed in triploblastic organisms?

1. Ectoderm 2. Mesoderm 3. Endoderm.

What structure in amphibians will eventually give rise to the central nervous system?

The neural tube formed during neurulation.

What are the cellular movements involved during gastrulation?

1. Invagination 2. Ingression 3. Involution 4. Delamination 5. Epiboly.

What is the significance of the yolk sac in mammals?

It acts as the first source of blood cells before the fetal liver takes over this function.

How does placentation occur in mammals?

The trophoblast differentiates into cell layers that invade the uterine wall to form the placenta.

What is a blastocyst?

A stage of early embryonic development that consists of an outer layer (trophoblast) and an inner cell mass (embryoblast).

What role do Henson's node and the primitive streak play in avian embryos?

They define the axes of the embryo and facilitate the formation of the three germ layers during gastrulation.

What is the fate of the extra-embryonic membranes during mammalian development?

They ensure the embryo receives nutrients and assists in gas exchange, ultimately forming the placenta.

What characterizes the cleavage type in mammals?

Mammals exhibit holoblastic cleavage, which is complete but slow due to the smaller size of their yolk reserves.

During which week of human gestation does implantation occur?

Implantation occurs during the second week of development.

What is the result of compaction during cleavage in mammals?

The formation of a morula, which is a tightly packed ball of cells.