Early embryology

Question 1

Zona pellucida:

Answer 1

thick basement membrane-like structure immediately surrounding ovum after its release

Question 2

Results of fertilization

Answer 2

o	2nd meiotic division completed
o	Restores diploid number
o	Variation of species
o	Sex determination
o	Initiation of cleavage

Question 3

Cleavage

Answer 3

1st stage of rapid cell division after fertilization

- Results in compaction since cells divide and do not grow, but become progressively smaller

Question 4

Trophoblast

Answer 4

involved in implantation, it is the ring around the blastocyst; becomes the fetal part of the placenta

Question 5

Embryoblast

Answer 5

-part of blastocyst that will become the amnion, embryo and yolk sack

Question 6

Hypoblast-

Answer 6

endodermal layer of the embryoblast

Question 7

Epiblast-

Answer 7

ectodermal layer of embryoblast

Question 8

Cytotrophoblast-

Answer 8

outermost ring of that differentiates from the trophoblast of the embryoblast after initial implantation

Question 9

Syncytiotrophoblast

Answer 9

• differentiates from the trophoblast and invades endometrium and uterus

Question 10

Implantation-

Answer 10

occurs approximately 6-8 days after ovulation; superior, posterior wall of uterus is ideal location

Question 11

Placenta/plakuos

Answer 11

• Multifunctional, temporary organ
• Nutrient, gas exchange
• Protection
• Hormones (endocrine)
• Umbilical cord attaches embryo/fetus to placenta
• Complete separation of fetal and maternal blood
• Highly vascular structure with maternal blood bathing the fetal villi
• Development progesses until approx. the 7th month
• Full term – consists of chorionic villi from embryo and decidua basalis from mother

Question 12

Decidua

Answer 12

– the uterine lining during pregnancy formed due to progesterone

• decidual change in the endometrium
• forms highly characteristic cells
• Becomes the maternal part of the placenta
• This plus the trophoblast becomes the placenta
• Has 3 parts: basalis, capsularis, and parietalis

Question 13

Decidua basalis

Answer 13

• majority of placenta

- At base of placenta/trophoblast

Question 14

Decidua Capsularis

Answer 14

• capsule around embryo: will eventually disappear

Question 15

Decidua Parietalis

Answer 15

-forms the rest of the uterus

Question 16

Bilaminar disc-

Answer 16

14 day embryo before gastrulation; consists of endoderm and ectoderm and has the primitive streak that starts with the primitive node

Question 17

Trilaminar disc

Answer 17

-after gastrulation, the embryo has 3 layers, the ecto, meso and endoderm
- 3 areas do not form trilaminar membrane:
o Oropharyngeal or buccopharyngeal membrane
o Cloacal membrane
o Notochordal process

Question 18

Primitive streak, node

Answer 18

• node is first indication of primitive streak-invagination of the bilaminar disc; these are cells that congregate on the central dorsal aspect of the embryo ectoderm; ectodermal cells migrate into the primitive streak through the bilaminr disc to form the mesoderm

Question 19

Neural plate-

Answer 19

• Formation (neurulation) induced by notochord that forms during gastrulation
• formed from neuroectoderm
  o thickening of ectoderm over notochord=neural plate
• folds over to form neural tube that becomes sealed neural tube
  o begins closing during 3rd week
  o complete closing of cranial neuropore on day 26 and caudal neuropore on day 28
• forms brain and spinal cord and PNS (formed from ECTODERM)

Question 20

Neural crest-

Answer 20

• group of cells that separate from the neural plate
• form much of head and neck musculature and bones by migrating to the arches
• also forms peripheral neural ganglia, melanocytes in skin and part of the adrenal gland
• smooth muscle cells, osteoblasts/clasts, adipocytes, chondrocytes, schwann cells and neurons

Question 21

Notochord

Answer 21

• Forms during gastrulation
• Adds rigidity to embryo
• Induces formation of the nueral tube
• Disappears except for remnants in the nucleus pulposus of intervertebral discs

Question 22

Folding (lateral and cranio-caudal)

Answer 22

• Lateral
  o Folding of nueral plate to form neural tube
  o Amniotic cavity folds around embryo and yolk sack forming gut
• Cranio-caudal
  o Cranial and caudal portions of embryo fold inward forming a C shaped embryo

Question 23

Anterior neuropore-

Answer 23

at the caudal region of the neural tube- closes on day 26

Question 24

Posterior neuropore

Answer 24

• posterior of the neural tube- closes on day 28

Question 25

Holoprosencephaly-

Answer 25

caused by halted formation of anterior neuropore

Question 26

Stomodeum-

Answer 26

future oral cavity/primitive mouth- location of buccopharyngeal membrane

Question 27

Buccopharyngeal membrane-

Answer 27

at the stomodeum- only 2 layers, no mesoderm-ruptures to form oral cavity

Question 28

Cloacal membrane-

Answer 28

membrane at the caudal portion of gut- only 2 layers, no mesoderm- ruptures to form anus

Question 29

Dichorionic/diamniotic

Answer 29

Cleavage of morula at days 1-2

Question 30

Monochorionic/diamniotic

Answer 30

Cleavage of blastocyst at days 4-8

Question 31

Monochorionic/monoamniotic

Answer 31

Cleavage of implanted blastocysts at days 8-12 | -Creates mirror image twins

Question 32

Conjoined twins

Answer 32

Cleaved after formation of embryonic disc from days 12-15 | -Names after area attached (pagos-fixed)

Question 33

Down syndrome-trisomy 21

Answer 33

- Slanted palpebral fissures, epicanthal folds, flat nasal bridge - Protruding tongue - Mental deficiency - CHD - Simian crease - macroglossia - slanted palpebral fissures, - epicanthal folds, - flat nasal bridge, - Protruding tongue , - Most common chromosomal abnormality in children - 1-2/1000 live births - 80% of cases due to maternal non-disjunction and Robertsonian Translocation - Risk of non-disjunction increases with maternal age

Question 34

Edward syndrome-trisomy 18

Answer 34

- Micrognathia - Clenched fists - Rocker bottom feet - Short sternum - Narrow pelvis - VSD - Mental deficiency - Growth retardation - 1/7000 live births - Death by 2 weeks of age - Robertsonian Translocation

Question 35

-Patau syndrome – trisomy 13

Answer 35

- Mental deficiency - Growth retardation - Bilateral cleft lip/palate - Malformed ears - CNS malformations - Omphalocele – intestines coming out of abdomen -1/29,000 live births -Death typically before 1 yr of age -Robertsonian Translocation and nondisjunction -Bilateral cleft lip/palate - Malformed ears - CNS malformations - Omphalocele

Question 36

Ectoderm

Answer 36

``` - Gives rise to: o Epidermis and its derived structures: hair, nails & sweat glands o Nervous tissue – brain and SC o Lining of mouth o Tooth structures ```

Question 37

Endoderm

Answer 37

- Gives rise to: o Lining of pharynx o Respiratory tract o GI tract

Question 38

Mesoderm

Answer 38

``` - Gives rise to: o Most of muscles o Bones o Connective tissues o Blood vessels o Heart o blood ```

Question 39

Teratogen- factors

Answer 39

- Heredity – abnormal genes (e.g. trisomies) - Chemicals and drugs (e.g. thalidomide) - Alcohol - Abnormally high hormone levels - Vitamins (A) - Irradiation (e.g. X-Rays, fallout etc.)

Question 40

Thalidomide

Answer 40

- claimed to cure “anxiety, insomnia, gastritis, and tension".[3] Afterwards it was used against nausea and to alleviate morning sickness in pregnant women. - Caused limb deformities