1.3 (Lecture 1) - Embryology - Differentiation + Implantation

Question 1

Zygote

Answer 1

cell that results from the union of the oocyte (female) and sperm (male) during fertilization

the first stage in human development

Question 2

Embryonic stage of development

Answer 2

from fertilization until 8th week of development (D56)

by the end of this period all major structures are present

Question 3

Fetal Stage of development

Answer 3

begins D57 extends until the fetus is completely outside of the mother

= a period of growth and differentiation of tissues and organs formed in the embryonic period

Question 4

fertilization

Answer 4

complex sequence of events - begins with sperm and oocyte contact - results in intermingling of maternal + paternal chromosomes

Question 5

cleavage divisions

Answer 5

• series of mitotic cell divisions of the zygote
• result information of the early embryonic cells (blastomeres)
• size of zygote remains unchanged with these divisions (blastomeres become smaller at each division)

Question 6

blastocyst

Answer 6

stage of development that begins after the developing embryo (morula) enters the uterus a fluid filled cavity develops inside it - developing embryo is now called a blastocyst

Question 7

Inner cell mass - what it is and its other name

Answer 7

• also called embryoblast
• group of centrally located blastomeres
• that will give rise to the embryo

Question 8

Outer cell mass - what it is and its other name

Answer 8

• also called the trophoblast
• thing outer cell layer
• gives rise to the embryonic portion of the placenta

(remember: trophe = nutrition)

Question 9

Endometrium

Answer 9

• internal layer of the uterus

- formed by simple columnar epithelium, with connective tissue stroma

Question 10

Cytotrophoblast

Answer 10

• cytotrophoblast is a thin, mitotically active layer

- comes from the proliferation of the trophoblast following its attachment to the endometrium

Question 11

Syncytiotrophoblast

Answer 11

• the outer mass of the trophoblast

- consists of a multinucleated mass, in which no cell boundaries are observed

Question 12

chorion

Answer 12

• structure formed by the a) extraembryonic mesoderm, b) cytotrophoblast and c) syncytiotrophoblast
• contributes to the fetal portion of the placenta

Question 13

ectopic pregnancy

Answer 13

implantation of the blastocyst outside of the uterus, most commonly int he ampulla of the oviduct

Question 14

bilaminar disc

Answer 14

• flat bilaminar plate of cells
• originates from the changes occurring in the cells of the embryoblast (inner cell mass) during the 2nd week of development

Question 15

epiblast (what is it and what type of cells)

Answer 15

• thick, dorsal aspect of the bilaminar disc
• top layer formed from the epiblast (inner cell mass)
• consists of high columnar cells
• related to the amniotic cavity

Question 16

hypoblast (what is it and what type of cells)

Answer 16

• ventral layer of the bilaminar disc located below epiblast
• also called primitive endoderm
• small cuboidal cells
• related to the yolk sac formation and extraembryonic mesoderm
• do not contribute to tissues of the embryo

Question 17

yolk sac

Answer 17

• ventral structure lined by hypoblast cells (below the hypoblast layer)
• important functions include:
  a) origin of primordial germ cells
  b) early blood cell development
  c) regulation of nutrients to the embryo

Question 18

amnion and amnionic cavity

Answer 18

• formed by cells that separate from the epiblast
• amnion encloses the amniotic cavity
• amniotic cavity surrounds the embryo and fetus + contains amniotic fluid - the amount of the fluid is critical to health of developing embryo

Question 19

primitive streak

Answer 19

= thickened band of epiblast cells appearing at the beg. of week 3 in the caudal, dorsal aspect of the bilaminar disc

• epiblast cells will migrate through this streak to form endoderm and mesoderm during gastrulation

Question 20

gastrulation

Answer 20

=period of epiblast proliferation, migration, and differentiation
- process by which the 3 germ layers develop

Question 21

germ layers

Answer 21

= the three basic cell layers of ectoderm, mesoderm, endoderm
- gives rise to all of the cells, tissues, structures of the embryo

Question 22

blastomeres

Answer 22

= daughter cells formed by the first mitotic (cleavage) divisions of the zygote

Question 23

zona pelucida

Answer 23

= the protective layer surrounding the oocyte and the developing zygote/blastomeres/morula
- disappears after implantation

Question 24

morula

Answer 24

= round, solid mass of cells produced by the cleavage divisions

• the 12-32 blastomere stage
• will enter the uterus ~ 3 days after implantation

Question 25

amnioblast

Answer 25

= the rudiment of the amnion formed from the cells of the epiblast
- encloses a fluid-filled space (amniotic cavity) that developes b/w the epiblast and the adjoining cytotrophoblast

Question 26

primitive groove/pit

Answer 26

= the epliblast covering the primitive streak becomes indented = primitive groove

• cranial end of the groove forms the primitive pit
• the primitive pit communicates with the yolk sac

Question 27

prechordal plate

Answer 27

• arises from the cranial end of the primitive streak + inserts into the endoderm and forms a thickening
• contributes to the oropharyngeal membrane
• forms and important signaling center involved in formation of the forebrain of the CNS
• might contribute to connective tissue in the head region

Question 28

important functions of yolk sac during the first four weeks of development

Answer 28

• major site of blood cell formation (hematopoiesis)

- primordial germ cells are first recognized on the wall of the yolk sac prior to the migration to the developing gonads

Question 29

What cells during gastrulation will later form the endoderm?

Answer 29

• the early migrating cells

- they displace the hypoblast cells (primitive endoderm) to form a new sheet-like epithelial layer (definitive endoderm)

Question 30

what cells during gastrulation will later form the mesoderm?

Answer 30

• the later migrating cells

- spread between the epiblast and the endoderm to form the embryonic mesoderm

Question 31

what cells during gastrulation will later form the ectoderm?

Answer 31

• cells that remain in the epiblast

- sheet-like epithelial layer

Question 32

oropharyngeal membrane

Answer 32

• one of the fates of the hypoblast

- cranial end membrane which will regress/breakdown during development to form the beginning of the GI tract

Question 33

cloacal membrane

Answer 33

• one of the fates of the hypoblast

- caudal end membrane which will regress/breakdown during development to form the end of the GI tract

Question 34

notochord

Answer 34

• forms during gastrulation in the area of the primitive pit
• extends cranially to the prechordal plate
• considered to be mesodermal derivative
• has important inductive roles in development

Question 35

induction (inductive development)

Answer 35

= one tissue acts on another tissues to change its fate

- requires an inducing tissues + responding tissue

Question 36

decidua

Answer 36

the functional layer of the endometrium (layer that is shed during menstruation and parturition)

Question 37

decidua reactions

Answer 37

• seen early in pregnancy whenthe blastocyst contacts the endometrial decidua
• characterized by increased secretory functions of the endometrium at site of implantation and the surrounding stroma
  (Decidua = functional layer of the endometrium during pregnancy)