Topic 5: early human development

Question 1

how long is the pre-embryonic period?

Answer 1

-2 weeks

Question 2

what starts off the pre-embryonic period?

Answer 2

-zygote
-1 cell that is diploid
-sperm has one set and
ovum has one set

Question 3

what does a zygote undergo?

Answer 3

-rapid mitotic divisions
-called cleavage
divisions
-short lived interphase

Question 4

what does a zygote change into?

Answer 4

-morula

Question 5

what is a morula

Answer 5

-solid ball of 16-32 cells
-these cells are called blastomeres
-same size as an ovum/zygote

Question 6

what does a morula change into?

Answer 6

-blastocyst

Question 7

what are the features of a blastocyst?

Answer 7

-fluid filled cavity that develops
-blastocoel/blastocyst
cavity
-embryoblast - the inner cell mass
-trophoblast - made of throphoblast cells

Question 8

what forms the embro?

Answer 8

-the division and differentiation of cells within the embryoblast

Question 9

what is the chorion?

Answer 9

-provides nutrients to the developing embryo
-surrounds all embryonic membranes
-contains chorionic villi

Question 10

what forms the chorion?

Answer 10

-the division and differentiation of trophoblast cells

Question 11

where does the blastocyst move and attach to? when does this occur?

Answer 11

-moves from the uterine tube
-attaches to the endometrium (uterine wall)
-5-7 days after fertilization

Question 12

what happens after implantation?

Answer 12

-embryoblast forms a bilayer
-called the embryonic disc

Question 13

what is the embryonic disc composed of?

Answer 13

-epiblast
-hypoblast

Question 14

what does the epiblast form?

Answer 14

-undergoes mitosis
-forms the amnion
-fluid filled cavity
(amniotic cavity)
-3 germ layers of the embryo

Question 15

what does the hypoblast form?

Answer 15

-undergoes mitosis
-forms a sac that sits under the embryo and the epiblast

Question 16

what are germ layers

Answer 16

-groups of cells that form layers
-contributes to the formation of an embryos organs and tissues

Question 17

what is the embryonic period?

Answer 17

-3rd week to the 8th week
-germ layers are present and can now help form the embryo

Question 18

what are the 3 germ layers called?

Answer 18

-ecotoderm (outside)
-mesoderm (middle)
-endoderm (inside)

Question 19

what does the ectoderm control?

Answer 19

-formation of the nervous system
-the epidermis of the skin

Question 20

what does the mesoderm control?

Answer 20

-formation of muscles, cardiovascular system, dermis, and most bones

Question 21

what does the endoderm control?

Answer 21

-formation of epithelial linings of the digestive, reproductive, respiratory, and urinary systems plus their associated glands

Question 22

what occurs during the embryonic phase

Answer 22

-major organ systems are almost fully formed
-heart begins to beat
-limb buds differentiate
-embryonic membranes form

Question 23

what are the embryonic membranes that develop

Answer 23

-chorion
-amnion
-yolk sac (hypoblast)
-allantois

Question 24

what are chorionic villi?

Answer 24

-projections of the chorion that contain blood vessels
-these vessels will form the fetal part of the placenta

Question 25

what is the amnion?

Answer 25

-derived from epiblast
-surrounds the embryo/fetus with amniotic fluid

Question 26

what is the purpose of amniotic fluid?

Answer 26

-shock absorption
-temperature regulation

Question 27

what is the yolk sac (hypoblast) for

Answer 27

-forms part of the gut
-gastrointestinal tract
-produces the earliest blood cells and vessels
-source of primordial germ cells (reproductive cells = primary oocytes + primary spermatocytes)

Question 28

what is the allantois?

Answer 28

-outer pocket of the yolk sac
-forms the umbilical cord and urinary bladder

Question 29

what is the fetal period?

Answer 29

-9th to 40th week
-growth and maturation of organs occurs