Hy Embryology 02

Front 1

Where does fertilization occur?

Back 1

The ampulla of the uterine tube

Front 2

Describe the events of fertilization

Back 2

1. The sperm binds to the zona pellucida of the secondary occyte arrested in metaphase of meiosis II and triggers the acrosome reaction, causing the release of acrosomal enzymes (eg, acrosin)

2. Aided by the acrosomal enzymes, the sperm penetrates the zona pellucida. Penetration of the zona pellucida elicits the cortical reaction, rendering the secondary oocyte impermeable to other sperm

3. The sperm and secondary oocyte cell membranes fuse, and the contents of the sperm enter the cytoplasm of the oocyte. The male genetic material forms the male pronucleus. The tail and the mitochondria of the sperm degenerate. Therefore, all mitochondria withing the zygotes are of maternal origin (ie, all mitochondrial DNA is of maternal origin)

4. The secondary oocyte completes meiosis II, forming a mature ovum. the nucleus of the ovum is the female pronucleus

5. The male and female pronuclei fuse to form a zygote

Front 3

What is the zygote formed from?

Back 3

The male and female pronuclei

Front 4

What is the female pronucleus?

Back 4

-The nucleus of the ovum
-The mature ovum is from the secondary occyte completing meiosis II

Front 5

Describe zygote mitochondria

Back 5

All are of maternal origins

Front 6

What is the male pronucleus?

Back 6

The male genetic material from the sperm

Front 7

Describe the cortical reaction

Back 7

-Occurs after a sperm penetrates the zona pellicuda
-Renders the secondary oocyte impermeable to other sperm

Front 8

What is the purpose of acrosomal enzymes?

Back 8

Allows the sperm to penetrate the zona pellicida

Front 9

What is cleavage?

Back 9

A series of mitotic divisions of the zygote

Front 10

Describe cleavage

Back 10

1. The zygote cytoplasm is successively cleaved to form a blastula consisting of increasingly smaller blastomeres (eg, the first blastomere stage consists of two cells; the next of 4, then 8, etc)

2. At the 16- to 32-cell stage, the blastomeres form a morula consisting of an inner cell mass and outer cell mass

Front 11

Describe the composition of the morula

Back 11

Consists of an inner cell mass and an outer cell mass

Front 12

Until when are blastomeres considered totipotent?

Back 12

Up to the eight-cell stage

Front 13

Describe blastocyst formation

Back 13

1. Occurs when fluid secreted within the morula forms the blastocyst cavity

2. The inner cell mass, which becomes the embryo , is now called the embryoblast

3. The outer cell mass, which becomes the placenta, is now called the trophoblast

Front 14

What portion of the blastocyst becomes the embryo?

Back 14

The inner cell mass

Front 15

What portion of the blastocyst becomes the placenta?

Back 15

The outer cell mass

Front 16

Describe implantation

Back 16

1. The zona pellucida must degenerate for implantation to occur

2. The blastocyst implants within the posterior superior wall of the uterus

3. The blastocyst implants within the functional layer of the endometrium during the secretory phase of the menstrual cycle

4. The trophoblast differentiates into the cytotrophoblast and syncytiotrophoblast

Front 17

Where does the blastocyst implant?

Back 17

Within the posterior superior wall of the uterus

Front 18

Where/when does the blastocyst implant?

Back 18

Within the functional layer of the endometrium during the secretory phase of the menstrual cycle

Front 19

What does the trophoblast differentiate into?

Back 19

Cytotrophoblast and syncytiotrophoblast

Front 20

Describe ectopic tubal pregnancies

Back 20

-An ETP occurs when the blastocyst implants within the uterine tube due to delayed transport.

-The ampulla of the uterine tube is the most common site of an ETP.

-The rectouterin pouch (pouch of Douglas) is a common site for an ectopic abdominal pregnancy

Front 21

What is the most common site for ectopic tubal pregnancy?

Back 21

Ampulla of the uterine tube

Front 22

What is a common site for an ectopic abdominal prenancy?

Back 22

Rectouterine pouch (pouch of Douglas)

Front 23

What are ectopic tubal pregnancies frequently predisposed to?

Back 23

1. Chronic salpingitis
2. Endometriosis
3. Post-operative adhesions

Front 24

In whom are ectopic tubal pregnancies most often seen in?

Back 24

Women with endometriosis or pelvic inflammatory disease

Front 25

Describe the outcome of ectopic tubal pregnancies

Back 25

Uterine rupture and hemorrhage occur if surgical intervention (ie salpingectomy) is not performed

Front 26

Describe the clinical signs of an ectopic tubal pregnancy

Back 26

1. Abnormal uterine bleeding

2. Unilateral pelvic pain

3. Increased levels of human chorionic gonadotropin (hCG) (but lower than originally expected with uterine implantation pregnancy)

4. Massive first trimester bleed

Front 27

What must a ectopic tubal pregnancy be distinguished from in differential diagnosis?

Back 27

1. Appendicitis

2. Aborting intrauterine pregnancy

3. Bleeding corpus luteum of a normal intrauterine pregnancy

Front 28

Describe dizygotic twins

Back 28

1. Result from the fertilization of two different secondary oocytes by two different sperm; the resulting two zygotes form two blastocyst, which implant separately into the endometrium of the uterus

2. Hence, the twins are no more genetically alike than are siblings born at different types (fraternal)

3. Dizygotic twins and 35% of monozygotic twins have two placentas, two amniotic sacs, and two chorions (ie, a diaminiotic-dichorionic membrane)

Front 29

Describe monozygotic twins

Back 29

1. Results from the fertilization of one secondary oocyte by one sperm. The resulting zygote forms a blastocyst in which the inner cell mass (embryoblast) splits into two

2. Hence, the twins are genetically identical

3. In 65% of cases, monozygotic twins have one placenta, two amniotic sacs, and one chorion (ie, a diamnionic-monochorionic membrane)

Front 30

Describe conjoined (siamese) twins

Back 30

1. Form exactly like monozygotic twins, except that the inner cell mass (embryoblast) does not completely split

2. Hence, two embryos form, but they are joined by tissue bridges at various regions of the body (eg, head, thorax, pelvis)