L4,5

Question 1

What is cleavage in embryology?

Answer 1

Cleavage is the repeated mitosis of the zygote, resulting in an increase in cell number without an increase in total size, due to the persistence of the zona pellucida.

Question 2

What happens during the Morula stage?

Answer 2

The zygote divides by mitosis to give 2 blastomeres after 36 hours. Repeated mitosis results in 4, then 8 blastomeres, and so on, until a Morula of 12-16 cells is formed after 72 hours (3 days). The Morula enters the uterus on the 4th day.

Question 3

What is the structure of the blastocyst after cleavage?

Answer 3

• Fluid absorbed from the uterus divides the blastomeres into two parts:
• Inner cell mass (embryoblast): located at the embryonic pole.
• Outer cell mass (trophoblast): forms the wall of the blastocyst.
• The cavity within the blastocyst is called the blastocele.

Question 4

What are embryonic stem cells (ES cells)?

Answer 4

Embryonic stem cells are derived from the inner cell mass of the embryo. These cells are pluripotent, meaning they can form virtually any cell or tissue type, and have the potential to cure diseases like diabetes, Alzheimer’s, Parkinson’s, anemias, and spinal cord injuries. They can be obtained from embryos after IVF (reproductive cloning).

Question 5

What are the three layers of the endometrium during implantation?

Answer 5

The three layers of the endometrium are:
1. Superficial compact layer
2. Intermediate spongy layer
3. Thin basal layer

Question 6

Where does the human blastocyst typically implant in the uterus?

Answer 6

The human blastocyst usually implants in the superficial layer along the anterior or posterior wall of the uterus near the fundus.

Question 7

What is the state of the uterus at the time of implantation?

Answer 7

At the time of implantation, the mucosa of the uterus is in the secretory phase. During this phase, uterine glands and arteries become coiled, and the tissue becomes succulent.

Question 8

What is implantation?

Answer 8

Implantation is the penetration of the blastocyst into the compact layer of the endometrium, where it becomes completely buried after the disappearance of the zona pellucida.

Question 9

When does implantation occur?

What happens to the blastocyst on the 5th day?

Answer 9

Implantation occurs on the 5th day after fertilization.

The zona pellucida disappears, and the blastocyst increases rapidly in size.

Question 10

What happens to the trophoblast on the 5th day?

Into how many layers does the trophoblast differentiate, and what are they?

Answer 10

The trophoblast covering the embryonic pole adheres to the endometrium and proliferates.

The trophoblast differentiates into two layers:
1. Inner cytotrophoblast
2. Outer syncytiotrophoblast

Question 11

What is the role of the syncytiotrophoblast?

Answer 11

The syncytiotrophoblast extends finger-like processes that secrete proteolytic enzymes, which erode the endometrium and create an endometrial hole through which the blastocyst is buried.

Question 12

What happens after the endometrial hole is created?

Answer 12

By the 9th -10th day
The hole in the endometrium is closed by a fibrin plug.

Question 13

When does the endometrium regenerate?

Answer 13

The endometrium regenerates by the 12th day.

Question 14

What happens on the 13th day?

Answer 14

By the 13th day, the surface defect is healed.

Question 15

Where is the normal site of implantation?

Answer 15

The normal site of implantation is the posterior wall of the uterus, in the midline, near the fundus.

Question 16

What is placenta previa?

What are the types of placenta previa?

Answer 16

Placenta previa is the implantation of the placenta in the lower uterine segment, causing ante-partum hemorrhage.

1. Placenta previa lateralis or low-lying placenta.
   
   2. Placenta previa marginalis.
   3. Placenta previa incomplete centralis.
   4. Placenta previa complete centralis.

Question 17

What is an ectopic pregnancy?

What is the most common site for ectopic pregnancy?

Answer 17

An ectopic pregnancy is an abnormal implantation of the fertilized ovum outside the uterus.

The most common site is the fallopian tube, accounting for 95% of cases.

Question 18

What causes tubal pregnancy?

Why is tubal pregnancy commonly confused with appendicitis?

Answer 18

1. Early disappearance of the zona pellucida.
   
   2. Delayed migration of the fertilized ovum due to tubal adhesions.

It is commonly confused with appendicitis when the pregnancy is on the right side.

Question 19

What is ovarian pregnancy?

What is abdominal pregnancy?

Answer 19

Ovarian pregnancy is the implantation of the fertilized ovum in the ovary.

Abdominal pregnancy is the implantation of the fertilized ovum in the peritoneal cavity, such as the peritoneal covering of the Douglas pouch, mesentery, or omentum.

Question 20

What is the outcome of most ectopic pregnancies?

Answer 20

Most ectopic pregnancies result in the death of the embryo around the second month of gestation, causing severe internal hemorrhage.

Question 21

What is the decidua?

What causes the formation of the decidua?

Answer 21

The syncytiotrophoblast secretes HCG, which prolongs the life of the corpus luteum in the ovary. The corpus luteum produces progesterone, which maintains the decidua.

Question 22

What are the parts of the decidua?

What happens to the uterine cavity in the third month of pregnancy?

Answer 22

• Decidua basalis: Located between the embryonic pole of the blastocyst and the myometrium. It forms the maternal part of the placenta.
• Decidua capsularis: Surrounds the rest of the blastocyst.
• Decidua parietalis: Lines the uterine cavity.
——
The uterine cavity becomes occluded in the third month due to the fusion of the decidua parietalis and the decidua capsularis.

Question 23

What does the epiblast (ectoderm) form?

How is the amniotic cavity formed?

What forms the floor of the amniotic cavity?

What lines the roof of the amniotic cavity?

Answer 23

The epiblast forms the dorsal layer of the inner cell mass and is located on the trophoblastic side of the embryoblast.
—-
Vacuoles appear between the epiblast cells and coalesce to form the amniotic cavity.
—-
The floor of the amniotic cavity is formed by the embryonic ectoderm/epiblast.
——
Flat cells called amniotic ectoderm (amnioblasts) line the roof of the amniotic cavity.

Question 24

Where is the hypoblast located?

What happens to the blastocoele after being lined with Heuser’s membrane?

How is the secondary yolk sac formed?

What is the exocoelomic cavity later called?

Answer 24

The hypoblast is located ventrally, facing the blastocoele.
——
The blastocoele becomes the exocoelomic cavity.
—-
The exocoelomic cavity is later called the primary yolk sac.
—-
Endodermal cells migrate from the hypoblast to replace degenerated mesothelial cells, forming a smaller cavity called the secondary yolk sac.

Question 25

What forms the bilaminar germ disc? What is the significance of the bilaminar germ disc? What is the shape of the embryonic disc during development?

Answer 25

The area of contact between the embryonic ectoderm and endoderm forms the bilaminar germ disc. —- The bilaminar germ disc will give rise to the embryo proper. —- The embryonic disc starts as oval-shaped and becomes pear-shaped, with the larger end at the cranial side and the smaller end at the caudal side.

Question 26

Where do the extra-embryonic mesoderm cells originate? What is the function of the extra-embryonic mesoderm? What are the two layers of the extra-embryonic mesoderm?

Answer 26

They are derived from hypoblasts, with a possible contribution from trophoblasts. —- It proliferates and forms spaces that later develop into the extra-embryonic coelom (chorionic cavity). — • Splanchnic layer: Surrounds the yolk sac. • Somatic layer: Lines the trophoblast and covers the amnion.

Question 27

What is the connecting stalk?

Answer 27

It is the connection between the amniotic cavity and the cytotrophoblast, which will later form the umbilical cord.

Question 28

What is the definition of the chorion?

Answer 28

The chorion is the trophoblast with the underlying extra-embryonic mesoderm.

Question 29

How are lacunae formed in the syncytiotrophoblast?

Answer 29

Vacuoles appear in the syncytiotrophoblast, which join with each other to form lacunae that become confluent and form intervillous spaces.

Question 30

What happens to the syncytiotrophoblast during the formation of the chorion?

Answer 30

The syncytiotrophoblast is divided into finger-like chorionic villi that invade the decidua.

Question 31

How are the intervillous spaces filled with maternal blood?

Answer 31

The chorionic villi erode the decidual blood vessels, filling the intervillous spaces (lacunae) with maternal blood that nourishes the embryo by diffusion.

Question 32

What is the structure of a primary villus? How does a secondary villus form? What is the structure of a tertiary villus? During which week do secondary and tertiary villi develop?

Answer 32

A primary villus consists of a core of cytotrophoblast surrounded by syncytiotrophoblast. — A secondary villus forms when a primary villus is invaded by a core of extra-embryonic mesoderm. - A tertiary villus consists of a secondary villus invaded by fetal blood capillaries. — Secondary and tertiary villi develop during the 3rd week.

Question 33

What is the initial state of the outer surface of the chorion? What happens to the villi opposite the decidua capsularis? What happens to the villi opposite the decidua basalis?

Answer 33

At first, the whole outer surface of the chorion possesses villi, so it is called the chorionic vesicle.—- The villi opposite the decidua capsularis gradually degenerate, and the chorion is called chorion laeve. —— The villi opposite the decidua basalis proliferate, and the chorion is called chorion frondosum, which will form the fetal part of the placenta.

Question 34

What are the two types of tertiary villi?

Answer 34

1. Stem (anchoring) villi: Fix the embryonic vesicle to the decidua basalis. 2. Free (absorbing) villi: Increase the surface area for exchange between fetal and maternal blood.

Question 35

What happens to the cytotrophoblast at the end of the anchoring villus? What does the cytotrophoblast do after penetrating the syncytiotrophoblast? What is the function of the cytotrophoblastic shell?

Answer 35

It penetrates the syncytiotrophoblast. —— It extends laterally to fuse with similar cytotrophoblast from other villi, forming a continuous shell. —— It surrounds the embryonic vesicle to prevent further penetration of the decidua by the syncytiotrophoblast (preventing placenta accreta).

Question 36

What are the functions of the villi?

Answer 36

1. Fixation: Fix the embryo. 2. Nutrition: Exchange of nutrient materials. 3. Excretion: Exchange of waste products. 4. Respiration: Exchange of gases.

Question 37

What key events occur on the 8th day of development?

Answer 37

On the 8th day, the trophoblast differentiates into cytotrophoblast and syncytiotrophoblast, the inner cell mass differentiates into a bilaminar germ disc, and the amniotic cavity forms.

Question 38

What happens on the 9th day of development?

Answer 38

On the 9th day, lacunae form in the syncytium, Heuser’s membrane is created, and the primitive yolk sac forms from the hypoblast.

Question 39

What occurs during the 11th to 12th days of development?

Answer 39

1. Blastocyst is completely embedded in the endometrial stroma 2. Maternal blood enters the lacunar system establishing uteroplacental circulation. 3. Formation of the extraembryonic mesoderm. 4. Differentiation of the extraembryonic mesoderm into somatopleuric and splanchnopleuric mesoderm. 5. Formation of the extraembryonic coelom (chorionic cavity). 6. Decidua reaction: cells of endometrium become poyhydral and loaded with glycogen & lipids; intercellular spaces are filled with extravasate and the tissue is oedematous.

Question 40

What key events happen on the 13th day of development?

Answer 40

On the 13th day, the surface defect in the endometrium heals, primary villi form, and the definitive yolk sac is established.