Fertilization And Gastrulation

Question 1

What are the two different calendars for human development and what is the difference?

Answer 1

1. Obstetrical/gestational calendar: starts of the first day of the last menstrual period
2. Ovulatory Calendar: starts at fertilization

There is typically a 2 week difference between the calendars.

Question 2

What is the corona radiata?

Answer 2

Follicular cells that surround the oocyte.

Question 3

What is the zone pellucida?

Answer 3

It is the layer after the corona radiata, composed of a glycoprotein network.

Question 4

What is the perivitelline space?

Answer 4

Between the zona pellucida and the egg, releases granules with enzymes including esterase, acrosin, neuraminidase

Question 5

What specialized organelle in the sperm is crucial for fertilization?

Answer 5

The acrosome at the head.

Full of enzymes: hyaluronidase

Question 6

Why do sperm have so many mitochondria?

Answer 6

Because they need lots of ATP to swim

Question 7

What events happen during week 1 of human development?

Answer 7

1. Fertilization
2. Cleavage
3. Formation of the blastocyst
4. Formation of the inner cell mass
5. Implantation

Question 8

Where does fertilization occur?

Answer 8

In the ampulla: the distal third of the tube

Question 9

What is capacitation?
Where does it take place?
How long does it take?

Answer 9

1. The removal of the glycoprotein coat and the seminal plasma protein.
2. Happens in uterus
3. Takes 7 hours

*Sperm cannot fertilize without going through capacitation.

Question 10

What is the zona reaction

Answer 10

It is a block to polyspermy.

Conformational change in the zona, becomes more rigid, traps and blocks sperm

Question 11

What happens after the block to polyspermy?

Answer 11

The membrane of the winning sperm and of the oocyte fuse

Question 12

After the fusion of sperm and egg…..

Answer 12

There is the completion of second meiotic division, formation of the male pronucleus, and the fusion of male and female pronuclei

Question 13

What is the gist of cleavage?

When does it start?

Answer 13

Zygote divides, making a bunch of tiny cells, but there is no time to grow them.

Starts 30 hours after fertilization

Question 14

How many cells is a morula?

What day does it form?

Answer 14

12-32 cells

Question 15

When does the blastocyst enter the uterus, and what happens there?

Answer 15

Enters day 3-4.

Fluid diffuses in and creates the blasocytic cavity on day 5

Question 16

What part of the blastocyst gives rise to the embryo?

Answer 16

The inner cell mass

Question 17

When does hatching occur?

What is it?

Answer 17

Starts day 5, done by day 7.

Degeneration of the zona pellucida

Question 18

What are 3 assisted reproductive technologies?

Answer 18

1. In vitro fertilization and embryo transfer
2. Cryopreserevation of embryos
3. Intracytoplasmic sperm injection

Question 19

Describe the trophoblast.

1. What does it secrete
2. What does it give rise to.
3. What do those things do?

Answer 19

1. Secretes early pregnancy factor: an immunosuppressant that protects the embryo from destruction. Produced during first 10 days.
2. Trophoblast becomes cytotrophoblast (mitotically active stem cell layer) and the Syncytiotrophoblast (secrete proteolytic enzymes, hCG, responsible for implantation and initial sign of pregnancy.

Question 20

Two kinds of hyadtidiform mole, describe them

Answer 20

1. Complete: empty oocyte fertilized by one sperm that duplicates its DNA, or by two separate sperms
2. Partial: normal oocyte fertilized by two sperm.
   - clinical features include vag bleed, pelvic pain, enlarged uterus, hyperemesis gravidarium

Question 21

What is choriocarcinoma?

Answer 21

Malignant tumor which develops from hydatidiform mole

Mets include liver, lungs, vagina, intestine, bone, and brain

Question 22

What happens during week 2 of development

Answer 22

Formation of bilaminar disk and further implantation

Question 23

The inner cell mass becomes 2 things during week 2, describe them.

Answer 23

Epiblast: will give rise to ectoderm, amnion, and amniotic cavity

Hypoblast: is temporary and will only be present in week 2

Question 24

What does the hypoblast give rise to?

Answer 24

It actually holds the place for the endoderm which will become the following:

1. The prechordal plate
2. Primary and secondary yolk sac
3. Extraembryonic mesoderm

Question 25

What is the function of the prechordal plate

Answer 25

Fuses to the epiblast and is the future location of the mouth and organizational center for the head

Question 26

What is the difference between the primary and secondary yolk sac?

Answer 26

Time. | The primary yolk sac becomes the secondary yolk after pinching off and becoming smaller.

Question 27

Where does extraembryonic mesoderm come from

Answer 27

Arise from parietal endoderm

Question 28

Describe the extraembryonic somatic mesoderm:

Answer 28

Lining covering the trophoblast and covering the amnion (next to the ectoderm)

Question 29

Describe extraembryonic splanchnic mesoderm:

Answer 29

Lining the yolk sac/umbilical vesicle (next to the endoderm)

Question 30

Describe the connecting stalk

Answer 30

- this becomes the umbilical chord - this point is not fixed, moves - extraembryonic somatic mesoderm

Question 31

Where does primitive blood develop?

Answer 31

In the extraembryonic splanchnic mesoderm | In the walls of the yolk sac

Question 32

What is the chorion?

Answer 32

- Becomes a layer of the placenta. | - Arise from the somatic mesoderm

Question 33

Where does implantation occur?

Answer 33

At the posterior wall of the uterus.

Question 34

implantation outside of the uterus is referred to as what?

Answer 34

Ectopic pregnancy. Some can be viable, but become dangerous to the mother

Question 35

Describe placenta previa

Answer 35

Occurs when implantation occurs over the internal cervical os. Can be marginal, partial, or total. Placenta can sometimes move superiorly and correct the mistake.

Question 36

What must you do before examination if you suspect placenta previa?

Answer 36

ULTRA SOUND. | A digital exam could rupture the placenta and mom could bleed to death

Question 37

What is Gastrulation and when does it occur?

Answer 37

Gastrulation is the formation of all 3 germ layers (which give rise to all tissue types) Happens in week 3

Question 38

What happens in week 3

Answer 38

Gastrulation, Neurulation, and heart formation

Question 39

What are the three layers of Gastrulation, and what do they become?

Answer 39

Ectoderm: skin, hair, nails, brain, spinal cord Mesoderm: muscle, bone, blood, heart, spleen (connective tissues) Endoderm: lungs, GI, bladder, glands (tonsils, parathyroid, thyroid)

Question 40

Describe the primitive streak

Answer 40

There is a proliferation and migration of cells. - the number of cells causes an envagination. - the cells that envaginate first become true endoderm. - cell that envaginate further come true mesoderm *as the cells envaginate, they receive molecular signals that determine their fate (endo or mesoderm) **all of these cells replace the hypoblast

Question 41

Describe the notochord

Answer 41

- midline mesodermal structure - extend from primitive node to prechordal plate - longitudinal axis for embryo - provide template for vertebral column - induce formation of neural plate

Question 42

In what direction does the notochord migrate

Answer 42

From primative pit towards the head

Question 43

Describe notochord formation

Answer 43

- between ectoderm and endoderm - form tube called notochordal process - notochordal process fuses with the endoderm>>notochordal plate - notochordal plate allows amniotic cavity and primary yolk sac to communicate - notochordal cells round back up and form the proper notochord

Question 44

Describe chordomas

Answer 44

- rare and slow growing neoplasm of bone - arise from remnants of notochord - occur in axial skeleton

Question 45

What is the allantois?

Answer 45

- at posterior midline - pouch from wall of yolk sac - endodermic structure - template for umbilical arteries and veins - becomes urachus (important when forming the bladder)

Question 46

Three bits of mesoderm, what are they and what do they become?

Answer 46

1. Paraxial>>Somites - muscle (myotome) - vertebral skeleton (scleratome) - dermis (Dermatome) 2. Intermediate>>Urogenital - kidneys - gonads 3. Lateral plate (somatic layer is dorsal, near ectoderm. Splanchnic layer is ventral, near endoderm.)>>Connective tissues - blood - lymph - Mesenteries - cardiovascular