Implantation, Cleavage, 2nd Week of Development

Flashcards about implantation, cleavage and the second week of development.

What are the key steps outlined in the process of cleavage and blastula formation?

Mitotic division results in the blastomeres. Morula reaches uterus by 3rd day. Morula becomes blastocyst by the 5th day.

Describe the process of implantation.

Starts on the 5th day and finishes on the 10th day. Syncytiotrophoblasts erode the endometrium, and the blastocyst burrows into the compact layer of endometrium.

What changes occur during bilaminar germ disc formation?

Differentiation of hypoblasts and epiblasts occurs. Development of the amniotic cavity & primary yolk sac takes place.

When does the morula typically reach the uterus?

By the 3rd day.

On what day does the morula transition into a blastocyst?

5th day.

Up to what cell stage are cells considered totipotent?

8-cell stage

What two main components does a morula consist of?

Outer trophoblasts and inner cell mass

What is the normal site of implantation?

Posterior wall of the body of the uterus close to the fundus in the compact layer of endometrium

What is secreted by Syncytiotrophoblasts and what are their functions?

Proteolytic enzymes, which erode the endometrium to implant, and HCG, which sustains the corpus luteum

When does implantation start and finish?

Starts on the 5th day and finishes on the 10th day

What are the two layers formed by the division of trophoblasts?

Syncytiotrophoblasts and Cytotrophoblasts

What two cell types are formed from the differentiation of the inner cell mass?

Hypoblasts and epiblasts

What is the exocoelomic membrane also known as?

Hueser’s membrane

What cavity appears within the epiblast?

Amniotic cavity

What is the function of the syncytial layer?

Shows villous projections and lacunar spaces and secretes proteolytic enzymes and HCG

From what does the bilaminar embryonic disc form?

The circular area of contact of amniotic cavity & the primary yolk sac

What two layers compose the bilaminar embryonic disc?

Epiblast and Hypoblast

What is the primary or extra-embryonic mesoderm?

Fills the space between the cytotrophoblast & amnion and primary yolk sac

Where does the primary mesoderm originate?

Yolk sac endoderm

What results from clefts appearing in the extra-embryonic (primary) mesoderm?

Formation of extraembryonic coelom

What layers result from the chorionic cavity splitting the extraembryonic (primary) mesoderm?

Somatic and splanchnic layers

What does the extraembryonic coelom split the extraembryonic (primary) mesoderm into?

Somatic & Splanchnic layers

What eventually forms from the fusion of clefts in the extraembryonic (primary) mesoderm?

Extraembryonic coelom or chorionic cavity

Name the three components of the chorion.

Syncytiotrophoblast, Cytotrophoblast, Somatopleuric layer of EEM

When do primary villi appear?

End of the 2nd week

When do secondary & tertiary villi appear?

3rd week

Name the two layers of the Primary Chorionic Villus

Central core of cytotrophoblast & Outer syncytio-trophoblast

What does EEM stand for?

Extraembryonic mesoderm

What is the chorion frondosum?

Covered with multiple villi and related to the decidua basalis

What is the smooth chorion?

Area of the chorion wall where villi degenerate

What do the chorion frondosum and decidua basalis fuse to form?

The placenta

Where does the extraembryonic mesoderm fill?

The space between the cytotrophoblast, amnion, and primary yolk sac.

What are primary chorionic villi composed of?

A central core of cytotrophoblast covered by an outer syncytiotrophoblast layer.

What occurs within the extraembryonic (primary) mesoderm that leads to the formation of the extraembryonic coelom?

Clefts appear which then fuse together.

What is the role of proteolytic enzymes secreted by syncytiotrophoblasts?

Erode the endometrium to facilitate implantation.

What is the function of HCG secreted by syncytiotrophoblasts?

Sustains the corpus luteum.

What membrane lines the inner surface of the cytotrophoblast and what type of cells form this membrane?

Exocoelomic (Heuser) membrane; flattened cells originating from the hypoblast.

How does the extraembryonic coelom contribute to the development of the chorion?

Splits the extraembryonic mesoderm into somatic and splanchnic layers, which are part of the chorion's formation.

Describe the structure of tertiary chorionic villi.

Consist of connective tissue, EEM(Extraembryonic mesoderm), capillaries, and are surrounded by a cytotrophoblastic shell within the intervillous space filled with maternal blood.

Define decidua basalis.

The decidua directly beneath the implantation site that contributes to the maternal part of the placenta.

What is the Amniochorionic membrane?

The fusion of the amnion and chorion layers.

What is the closing plug?

The area where the blastocyst burrows into the endometrial epithelium.