embryogenesis week 2 and 3

Question 1

major events of week 2

Answer 1

completion of implantation, amnion and umbilical cesicle formation, extraembryonic mesoderm formation

Question 2

implantation

Answer 2

a multistep process, occurs between day 5-12, relies on cooperation between uterus and embryo (development of uterus and embryo need to be synchronized). Initiated of implantation influenced by influenced by estrogen and progesterone

Question 3

Implantation Phase one: Attachment of of the blastocyst to endometrium

Answer 3

Attaches at the embryonic pole, receptor mediated, decidual Rx triggered. Results in formation of compact layer (Mass of cells for implantation of embryo)

Question 4

Implantation Phase two: penetration and embedment into the compact layer

Answer 4

formation of the syncytiotrophoblast: formation of synccytiotrophoblast initiatiated with contact with endometrium, no cell boundaries, mediates envasion of endometrium, microvilli on the surface, as more embryo imbeds itself more syncytioblast is formed

Formed of the lacunae: spaces in syncytioblast forma lacunar network, maternal vessela and glands empty into them

The embryo gets fully embedded by day 10-12

Question 5

Sites of Implantation

Answer 5

Intrauterine: if implantation occurs too close to cervix, placenta previa might occur

Extrauterine/ ectopic: most common in outer 1/2 of oviduct, acute pain

Question 6

Development of Embryonic disc, formation of the amnion

Answer 6

an extraembryonic membrane formed from the epiblast, surrounds the embryo by week 8

the epiblast separated a layer and creates an amnion making a amniotic cavity

Amnion/amniotic cavity fluid function: creates the initial source of amniotic fluid (protects embryo and allows for symmetrical growth, allows for proper growth of lung, involved influid homeostasis, allows for embryo development, helps control development

Question 7

Formation of the Umbilical vesicle/ yolk sac

Answer 7

bound by extraembryonic membrane, the exocoelomic membrane, formed by hypoblast

eventually by the end of week 2 the primary UV becomea a primary and secondary UV, with the secondary UV closer to the embryo, the bilaminar embryonic disc and amniotic sac. All connected to the Connecting stalk.

Function of the unbilical vesicle- metabolism and transfer of nutrients from trophoblast to embryo, sit of initial blood and vascular formation. Primordial germ cells appear in the wall as does hematopoisis, portions become primitive gut, positions site of gastrulation, controls epiblast cell migration

Question 8

Extraembryonic mesoderm

Answer 8

a mesenchyme that surrounds the embryo

Non polar, free cell derivative of embryonic epithelium, cells often motile, a second embryonic tissue type

Question 9

Embryo at the end of week 2

Answer 9

Extraembryonic mesoderm (EEM) coats the inside of the trophoblast and the outside of the amnion and umbilical vesicle.

Splits in the EEM form extraembryonic coelem or chorionic cavity

EEM + trophoblast= chorion

Primary chorionic villi form

EEM mesoderm formsa brige between embryo and chorion- the connecting stalk

Question 10

week 3 events

Answer 10

Trilaminar disc formation (gastrulation), establishment of primary germ layers, appearance of symmetry and asymmetry, basic body plan, organogenisis,

Question 11

Primitive streak

Answer 11

happens at day 13
Transient thickening of epiblast with a midline groove. This is the site of E->M. Elongation of primitive streak leads to the embryo shape change

Question 12

Primitive node

Answer 12

Day 16, expansion of cranial end of Primitive streak that contains a pit, also site of E->M transformation. An important inducer signaling center for future structures

Question 13

Definitive endoderm

Answer 13

the first cells to pass throught the primitive node and E>M become the definitive endoderm and replace the hypoblast

Question 14

Formation of the intraembryonic mesoderm

Answer 14

after the endoderm froms, other cells that pass through the primitiv node move to opposite ends of the disc to form the prechordal plate

Cells begin to pass through the streak to form the intraembryonic mesoderm, becomes a layer betweeen the epiblast and definitive endoderm, migrates in many directions

Question 15

Formation of the notochord

Answer 15

central axis of the embryo, solid cord from primitive node, cells invaginate through primitive node, migrate cranially to opposite end of disc

Question 16

there are 2 places where no mesoderm migrates between fused ectoderm and definitive endo derm

Answer 16

oropharyngeal membrane at cranial end of the trilaminar disc, separates mouth from foregut, ruptures at 4th week

cloacal membrane, separates anus and hind gut, forms day 16 and ruptures 7th week

allantois is a diverticulum of the Umbilivcal vesicle (will make the placenta)

Question 17

REgression of primitive streak (day 17-26)

Answer 17

eventually becomes restricted to tail bud (caudal eminence) as notocord grows cranially, streak regresses caudally and the embryo lengthens

Question 18

teratoma

Answer 18

neoplasm of multiple cell types usually sarcooccgeal, most common tumor of newborns