Embryology

Question 1

What happens to the zone Pellucida once a sperm penetrates the oocyte (corona radiate, zone pellucid, oocyte membrane)?

Answer 1

Zone pellucid becomes impenetrable to other sperms.

Question 2

What is arrested in prOphase of Meiosis I until Ovulation?

Answer 2

1ry (primary) Oocytes –> 2N

Question 3

A 2ry oocyte (1N) is arrested in which phase of Meiosis II until fertilization?

Answer 3

Metaphase II until it is fertilized by sperm

Question 4

Cleavage of the blastomeres occurs where in the female body?

Answer 4

Uterine tube

Question 5

What is the term for 16-32 cells that have gone through mitotic divisions in the uterine tube?

Answer 5

Morula –> then enters the UTERUS at this size

Question 6

What is a Blastocyst?

Answer 6

A fluid filled space which appears after the morula enters the uterus

Question 7

What are the two layers of the Blastocyst?

Answer 7

1. Inner cell mass - EMBRYOBLAST 2. Outer cell mass - TROPHOBLAST

Question 8

When and where does implantation occur?

Answer 8

End of week 1 and occurs in the posterior wall of the superior part of the uterine body (zone pellucid disappears) - ends at week 2

Question 9

Once the Blastocyst adheres to endometrial epithelial, what begins to differentiate into cytotrophoblast and Syncytiotrophoblast?

Answer 9

TROPHOBLAST - SYNCYtiotrophoblast erods the endometrial blood vessels –> uteroplacental circulation formed

Question 10

What is an ectopic pregnancy and what are the symptoms?

Answer 10

1. Ectopic Pregnancy is implantation OUTSIDE the uterus (common = tubal pregnancy) 2. Symptoms - abdominal pain and missed period

Question 11

What is the term for an abnormal pregnancy that occurs in the INFERIOR SEGMENT of the UTERUS?

Answer 11

Placenta Previa Symptoms = vaginal bleeding

Question 12

What occurs during the SECOND week of development? Third? Fourth?

Answer 12

2nd = Bilaminar Disc forms 3rd = Trilaminar Disc 4th week = four limbs appear

Question 13

During week, what are the 4 “period of 2’s” events?: 1. What does the inner cell mall differentiate to? 2. Outer cell Mass? 3. What two cavities form? 4. The extra embryonic mesoderm splits into what layers?

Answer 13

1. Epiblast and hypoblast (bilaminar disc) 2. Cytotrophoblast and suncytiotrophoblast 3. Amniotic Cavity and Yolk Sac cavity 4. Mesoderm –> Somatic and Splanchic Layers

Question 14

What occurs during the third week of development? (Period of 3’s)

Answer 14

1. Primitive streak appears 2. Epiblast (ECTOderm) cells migrate inward to form new cell layers –> ENDOderm and mesoderm 3. Gastrulation –> three germ layers appear (ecto, endo, mesoderm)

Question 15

What are the two components of the placenta? (which is maternal and which is fetal?)

Answer 15

1. Villous Chorion = Fetal 2. Decidua Basalis = Maternal (think: BASE is mom)

Question 16

What are the three types of Chorionic Villi and what are the components of each?

Answer 16

1. 1ry - Cyto and Syncytiotrophoblast 2. 2ry - 1ry and + mesenchyme core 3. 3ry - 2ry +vessels

Question 17

What are the three types of Decidua and describe each

Answer 17

1. Decidua BASALIS = between embryonic pole of blastocyst and myometrium 2. Decidua CAPSULARIS = covers the rest of the embryo 3. Decidua PARIETALIS = lines uterine cavity

Question 18

List the four types of fetal membranes (Fetal is FOUR)

Answer 18

1. Amnion 2. Yolk Sac 3. Allantois 4. Umbilical Chord

Question 19

What is the function of the amniotic fluid?

Answer 19

Three main: - protective buffer for fetus -room for fetal movement -assist in regulation of fetal body temp

Question 20

MZ and DZ twins are how many chorions, amnions, and placenta?

Answer 20

a) MZ (one oocyte and one zygote) = one chorion, two amnions, one placenta b) DZ (*think TWOS - 2 oocytes and 2 zygotes) = two chorions, two amnions, and two placenta

Question 21

What structures arise from the Ectoderm once it forms from the epiblast?

Answer 21

• epidermis, hair, nails, glands of skin - NEURAL CREST and derivatives ( cranial, spinal, sympathetic ganglia and assoc. nerves, PIGMENT cells of the skin)

Question 22

What structures arise from the Endoderm once it forms from the epiblast?

Answer 22

• epithelial lining and glands of digestive and respiratory tracts

Question 23

What structures arise from the MESODERM once it forms from the epiblast? *MESO is MASSIVE*

Answer 23

1. Notochord

2. Somite a) sclerotome- vertebrae b)dermatome - dermis of DORSAL body region c) myotome - trunk and limb muscles

3. Intermediate Mesoderm (kidney +gonads)

4. Lateral Plate Mesoderm

a) Somatic

i. Parietal Serosa
ii. Derma of VENTRAL body
iii. Connective tissue of limbs (bones, joints, ligaments)

b) Splanchic Mesoderm

i. Wall of digestive and resp. tracts
ii. visceral serosa
iii. heart iv. blood vessels

Question 24

What must be degenerated in order for blastocyst implantation to occur?

Answer 24

Zona Pellucida

Question 25

During the later stages of pregancy maternal blood is separated from fetal blood by what?

Answer 25

Syncytiotrophoblast and Fetal Endothelium

Question 26

Prechordal Plate marks the site of future what?

Answer 26

Mouth (oropharyngeal membrane)

Question 27

What is the first indication of gastrulation in the embryo? (Trilaminar Disc)

Answer 27

Formation of the Primitive Streak

Question 28

Limb buds develop during what time period of development?

Answer 28

Weeks 4 - 8

Question 29

What promotes growth and development of the limbs?

Answer 29

AER - Apical Ectodermal Ridge --\> inductive influence on the limb MESENCHYM

Question 30

What arises from the Paraxial Mesoderm?

Answer 30

\*Somites - Dermatome (dermis) - Myotome (limb muscles)

Question 31

Bones and Blood vessels form from which limb element?

Answer 31

Lateral Plate Mesoderm (intermediate = kidney and gonads \*\* DON'T MIX UP)

Question 32

What forms from the neural crest cells?

Answer 32

Schwann cells + Melanocytes

Question 33

What are the steps of limb patterning?

Answer 33

1. **Limb buds** 2. **Paddle like buds** develop from ventrolateral body wall 3. **Circular Groove** appears - separated hand plate from upper limb and foot plate from lower one 4. **Digital Rays** - mesoderm condensations in the hand and foot 5. **Notches **- thin membrane separates the rays and digits become separated 6. 2nd corcular constriction appears dividing UPPER LIMB (these buds developed 2 days b4) and LOWER LIMB

Question 34

What are the three axes that limb buds grow in?

Answer 34

* proximal -distal * anterior - posterior * dorsal-ventral

Question 35

Pre-axial (cephalic) will be future \_\_\_\_\_. Post axial (caudal) will be future \_\_\_\_\_\_\_.

Answer 35

1. Flexor 2. Extensor

Question 36

Proximal to distal growth of the limb buds (from the humerus/femur to the ulna/tibia) is dependant on what type of signaling from the AER?

Answer 36

FGF signaling from the Apical Ectodermal Ridge (AER)

Question 37

The **upper** limb rotates in what direction? The **lower** limb?

Answer 37

upper = 90 degrees LATERALLY (think elbows point out to sides = lateral) lower = 90 degrees MEDIALLY

Question 38

What is a dermatome?

Answer 38

Area of the skin supplied by a single spinal nerve and its spinal ganglion

Question 39

# Define: 1. Amelia 2. Meromelia 3. Phocomeila

Answer 39

1. Amelia = absence of an entire limb 2. Meromelia = absence of **part** of a limb 3. Phocomeila = short, *poorly* formed limb

Question 40

# Define: 4. Polydactyly 5. Syndactyly 6. Lobster Claw Deformity

Answer 40

4. Polydactyly - **extra** digit 5. Syndactyly - **fusion** of digits 6. Lobster claw deformity - **middle finger is absent**