1ST SECTION

From what does the placenta develop?

Trophoblast of embryonic pole + decidua basalis (maternal endometrium).

Where does blood and vessel formation first occur?

Extraembryonic mesoderm (yolk sac and chorionic villi).

At the end of the 2nd week, how does the embryo obtain nutrition?

By diffusion through the extraembryonic coelom and umbilical vesicle.

What are hematopoietic cells?

Pluripotent stem cells that can form all blood cell types.

When and where does hematopoiesis first begin?

In the 3rd week, in the extraembryonic mesoderm.

Which organ produces blood cells after the 4th week?

The liver.

When do stem cells appear in spleen and bone marrow?

Around the 12th week.

Blood cells and blood vessels arise from which germ layer?

Mesoderm.

Two mechanisms of blood vessel formation?

Vasculogenesis (blood islands) and Angiogenesis (sprouting).

What are angioblasts?

Endothelial precursors from mesenchyme, forming primordial endothelium.

What are blood islands?

Aggregates of angioblasts that fuse into endothelial channels.

When does angiogenesis begin relative to vasculogenesis?

About 2 days later.

From what do blood cells develop?

Hematopoietic stem cells and hemangiogenic endothelium.

When does intraembryonic hematopoiesis begin?

At the 5th week.

Which organs later contribute to blood cell formation?

Spleen, bone marrow, lymph nodes.

What forms muscular and connective tissue of vessels?

Mesenchymal cells.

How does the heart form?

Cardiogenic mesenchyme → paired endocardial tubes → fuse into primordial heart tube.

What connects the heart to embryonic & extraembryonic circulation?

Vessels of embryo, chorion, connecting stalk, yolk sac.