Block 4: Anatomy 10/25 - Fertilization, Implantation, Fetal Membranes

Front 1

Describe the stages of cleavage once an oocyte has been fertilized.

Where does cleavage occur?

What becomes of the zona pellucida?

Back 1

Zygote
2-cell
4-cell
8-cell
Morula
Blastula (hatches from zona pellucida)

Occurs in uterine tube

Front 2

Difference between morula and blastula?

Back 2

Morula = solid ball of cells

Blastula = Hollow ball of cells

Front 3

Back 3

Front 4

Back 4

Front 5

What becomes of the embryoblast cells in the blastula?

Back 5

Become embryo

Front 6

What eventually becomes of the trophoblasts in the blastula?

Back 6

Will become extraembryonic membranes (placenta); provides nutrition

Front 7

Which side of the blastula adheres and embeds into the uterus?

Back 7

Bare Zone; side nearest embryoblast

Front 8

What is the outer layer of the oocyte called? What becomes of it?

Back 8

Zona pellucida

It is shed by blastula before it adheres and embeds into uterus

Front 9

How is the oocyte able to enter the uterus from the body cavity? Describe its path.

Back 9

Carried into ovary and uterine tube by peritoneal fluid; beating cilia of uterine tube pass it along into the uterus.

Front 10

What is the normal site of blastula implantation?

Back 10

Endometrium

Front 11

Back 11

Front 12

What cells do trophoblasts differentiate into? What is the purpose of these cells?

Back 12

Trophoblast becomes syncytiotrophoblast and cytotrophoblasts

Syncytiotrophoblast forms syncytium (multinucleate cells without cell borders) which erode endometrial glands and blood vessel walls

Cytrotrophoblast maintain single cell layer around blastula, namely around bare zone

Front 13

What part of the uterus sheds during menstruation?

Back 13

Endometrium

Front 14

What event in blastula implantation marks completion of implantaion?

Back 14

Uterine epithelium encloses embryo within uterine wall

Front 15

What is an ectopic pregnancy?

Where can ectopic pregnancies occur? Which is most common?

Back 15

Ectopic pregnancy: blastula implants in incorrect site

Can be in:
1) Ovary
2) Body Cavity (mesentary)
3) Uterine Tube (MOST COMMON; AKA TUBAL PREGNANCY)
4) Cervix

Front 16

What becomes of embryoblast cells once implantation is complete?

Back 16

Embryoblast cells spread apart to separate blastula cavity into two distinct cavities: Amniotic Cavity, and Yolk Sac

Front 17

Back 17

Front 18

What cell layer is the amniotic cavity derived from?

Back 18

Epiblast

Front 19

What cell layer is the yolk sac derived from?

Back 19

Hypoblast

Front 20

What do the cells of the primitive streak become?

Back 20

Leave embryo to becomes extraembryonic mesoderm (contribute to placenta!)

Front 21

Back 21

Front 22

Back 22

Front 23

How does the chorionic cavity arise?

Back 23

Gaps in extraembryonic mesoderm open to form chorionic cavity

Front 24

What structure forms the umbilical cord?

Back 24

Connecting Stalk

Front 25

What structures comprise the chorion?

Back 25

Syncytiotrophoblast
Cytotrophoblast
Extraembryonic Mesoderm

Front 26

Explain the dual origin of the placenta.

Back 26

Fetal contribution: Chorion

Maternal contribution: Decidua

Front 27

What is the decidua?

Back 27

Decidua = maternal portion of placenta; consists of endometrium, endometrial glands

Front 28

How does the embryo receive nutrition prior to formation of umbilical vessels?

Back 28

Via diffusion

Front 29

How does the allantois form? What does it become?

Back 29

Forms as an extension of urogenital sinus, later becomes urachus, which becomes median umbilical ligament

Front 30

How does weeping bellybutton arise?

Back 30

Patent Urachus:

Failure of urachus to fill in lumen to form median umbilical ligament leaves open canal between bellybutton and urachus. Known as weeping bellybutton (leakage of urine out through umbilicus).

Front 31

What blood vessels allow for early diffusion in embryonic development? What do these vessels become?

Back 31

Allantoic BV's (become umbilical vein and artery)

Vitelline BV's (become SMA and IMA)

Front 32

Where do umbilical blood vessels arise from? Where do t hey go?

Back 32

Umbilical vessels grow out along allantois and into chorionic villi

Front 33

Back 33

Front 34

What is the purpose of chorionic villi? Fetal or maternal contribution?

Back 34

Chorionic villi proliferate under decidual basalis to interact with maternal blood for exchange.

Fetal contribution

Front 35

Back 35

Front 36

What becomes of the uterine cavity?

Back 36

Decidual capsularis expands to meet decidual parietalis and in process obliterates uterine cavity.

Front 37

What becomes of the chorionic cavity?

Back 37

Amnion expands to cover umbilical cord and obliterates chorionic cavity in its expansion

Front 38

Back 38

Front 39

What is the fetus suspended in?

Back 39

Amniotic fluid

Front 40

Does fetal blood ever mix with maternal blood? How does exchange occur between the two?

Back 40

No, fetal blood remains in capillaries in chorionic villi. Intervillous space is filled with maternal blood; bathes chorionic villi.

Front 41

Back 41

Front 42

What is the relative oxygen content of maternal blood in the intervillous space? How does this fetal uptake of oxygen?

Back 42

Blood in intervillous space is partially oxygenated. Fetal hemoglobin has higher affinity for oxygen than maternal hemoglobin and is unaffected by partial oxygenation of blood.