BIOL 1410 Early human development

LECTURE 5

What forms the morula?

Zygote undergoes 4-5 mitotic divisions (cleavage divisions)

What is the structure of the morula?

Solid ball of 16-32 cells, same size as zygote

What forms the blastocyst?

As cells continue to divide, they begin to specialize into different cell types with specific forms and functions

Features of the blastocyst

1. Blastocoel/blastocyst cavity

2. Embryoblast (inner cell mass)

3. Trophoblast (made of trophoblast cells)

The embryoblast forms what structure?

The embryo

The trophoblast forms what structure?

The chorion

Function of the chorion

Provides nutrients to the developing embryo

Where does the blastocyst come from and go to for implantation?

Moves from the uterine tube, attaches to endometrium (of uterine wall)

After implantation, what does the embryoblast differentiate into? What are the two subdivisions of it?

A bilayered embryonic disc; Epiblast, hypoblast

The epiblast will undergo mitosis to form what 2 structures?

1. Amnion (fluid filled amniotic cavity)

2. 3 germ layers of the embryo

The hypoblast will undergo mitosis to form what structure?

The yolk sac

After implantation, __________ membranes start to form

“Extraembryonic”

What time period does the embryonic period span?

3rd week to the end of the 8th week

At the beginning of the embryonic period, 3 germ layers are now present forming the embryo. How was each layer formed?

Each layer was formed from mitosis and differentiation of epiblast cells

What are the 3 components of the trilaminar embryonic disc?

Ectoderm, mesoderm, endoderm (trick: remember Ecmeen)

What will the ectoderm form?

The nervous system and epidermis

What will the mesoderm form?

Muscles, cardiovascular system, dermis, most bones

What will the endoderm form?

Epithelial linings of digestive, respiratory, urinary and reproductive system (and their associated glands [e.g. liver, associated with digestive system])

What is the difference between epidermis and dermis?

Epidermis is the thin, outermost layer of skin (protective barrier), while dermis is the thicker middle layer (e.g. structural support)

What are epithelial linings?

Thin, protective tissue (e.g. epidermis)

What are the (4) major events of the embryonic period?

1. Major organ systems almost completely formed

2. Heart begins to beat

3. Limb buds differenciate

4. Extraembryonic membranes continue forming structures

What are chorionic villi contain blood vessels to form what structure?

Fetal part of placenta

The chorionic villi is where what exchange occurs?

Exchange of nutrients, wastes, and gases occurs between fetal and maternal blood (which never mix)

What are the 2 functions of amniotic fluid in the amniotic cavity surrounding the fetus?

Shock absorption and temperature regulation

The yolk sac forms what?

Part of the digestive tract

The yolk sac is a source of what 2 cell types?

Reproductive germ cells and embryonic blood cells

What structure forms the umbilical cord and the urinary bladder?

The allantois, a projection off of the yolk sac

The fetal period spans across what time period?

9th week to end of 40th week

What are the 4 extraembryonic membranes?

Chorion, amnion, yolk sac, allantois