Chapter 5

Question 1

What genes are expressed by cells in the AVE during the bilaminar disc stage?

Answer 1

Genes expressed by AVE cells include OTX2, LIM1, and HESX1

Question 2

Which secreted factors are expressed by AVE cells to establish head formation?

Answer 2

AVE cells secrete Cerberus and Lefty, members of the TGF-B family.

Question 3

What is the role of Cerberus and Lefty during early embryonic development?

Answer 3

Cerberus and Lefty inhibit nodal activity, establishing the cranial end of the embryo.

Question 4

How do Cerberus and Lefty influence nodal expression?

Answer 4

Cerberus and Lefty inhibit nodal expression at the caudal end, allowing nodal activity to continue and establishing the primitive streak.

Question 5

What is the function of the primitive streak?

Answer 5

The primitive streak is established and maintained by nodal expression. It is responsible for forming the central axis of the embryo.

Question 6

What happens once the primitive streak is formed?

Answer 6

NODAL upregulates genes responsible for dorsal and ventral mesoderm formation, as well as the formation of head and tail structures.

Question 7

How does nodal expression influence mesoderm formation?

Answer 7

NODAL upregulates genes involved in dorsal and ventral mesoderm formation

Question 8

Which member of the TGF-B family is involved in the establishment of the cranial end of the embryo?

Answer 8

Nodal, a member of the TGF-B family, is inhibited by Cerberus and Lefty to establish the cranial end.

Question 9

What are the consequences of Cerberus and Lefty absence at the caudal end?

Answer 9

The absence of Cerberus and Lefty allows nodal expression to continue, leading to the establishment and maintenance of the primitive streak

Question 10

What role does NODAL play in embryonic development?

Answer 10

NODAL activates genes responsible for dorsal and ventral mesoderm formation, as well as head and tail structure formation after the primitive streak is established

Question 11

Derived from inner mass of embryo
Can be obtained from embryo after IVF (reproductive
cloning

Answer 11

Embryonic stem cells

Question 12

can form any cell or tissue;
■ has potential to cure disease

Answer 12

Pluripotent

Question 13

introduction of nuclei to enucleated oocyte

Answer 13

Therapeutic cloning or Somatic Nuclear Transfer:

Question 14

restricted in ability to form different cell or
tissue type

Answer 14

Adult stem cells: Multipotent

Question 15

Lost within 2-3 weeks of fertilization
○ 50% of pregnancies end in spontaneous abortion
○ PCR can detect genetic defects

Answer 15

Abnormal zygotes`

Question 16

Due to the constant erosion of the sinusoids by
the Trophoblast.
Maternal blood begins to flow through the
trophoblastic system

Answer 16

Uteroplacental
Circulation

Question 16

Maternal capillaries which are congested and
dilated, maternal blood enters the lacunar system

Answer 16

Sinusoids (Maternal
sinusoids)

Question 17

Fine, loose connective tissue that appears
between the Cytotrophoblast and Exocoelomic
cavity.

Answer 17

Extraembryonic
Mesoderm

Question 18

The large space or cavity formed by the
extraembryonic mesoderm

Answer 18

Extraembryonic Cavity
aka Chorionic Cavity

Question 19

Additional cells that are produced by the
Hypoblast.

Answer 19

Secondary Yolk Sac or
Definitive yolk sac

Question 20

The pinch portion of the Secondary yolk sac,
which are found in Extraembryonic coelom or
Chorionic cavity.

Answer 20

Exocoelomic Cysts

Question 21

Expansion that forms a large cavity from the
extraembryonic coelom

Answer 21

Chorionic cavity

Question 22

Formed from the connecting stalk (the place
where extraembryonic mesoderm transverses
the chorionic cavity)

Answer 22

Umbilical Cord

Question 23

where the formation begins
○ A narrow groove with slightly bulging regions on the either
side.
■ cells of the epiblast migrate toward this area
○ Clearly evident at 15-16th day embryo

Answer 23

Primitive Streak

Question 24

cephalic end of primitive streak ○ Slightly elevated area surrounding the primitive pit

Answer 24

Primitive Node

Question 25

an inward movement of the epiblast towards the primitive streak then detaches and slips beneath it

Answer 25

INVAGINATION

Question 26

It controls the cell migration and specifications ○ Synthesized by the primitive streak

Answer 26

FIBROBLAST GROWTH FACTOR 8 (FGF8)

Question 27

controls and down regulating by FGF8 ● A protein that binds the epiblast cells together

Answer 27

E-CADHERIN

Question 28

source of all 3 germ layers

Answer 28

Epiblast

Question 29

solid cord of cells formed by endoderm cells; underlies neural tube and basis for axial skeleton

Answer 29

DEFINITIVE NOTOCHORD

Question 30

indentation of epiblast; temporarily connects amniotic fluid and yolk sac cavities

Answer 30

Neurenteric canal

Question 31

formed at caudal end of embryonic disc ○ Consist of endoderm and ectoderm cells; no intervening mesoderm ○ Similar characteristic with oropharyngeal membrane

Answer 31

Cloacal membrane

Question 32

Diverticulum that appear on 16th day

Answer 32

alloenteric diverticulum or allantois

Question 33

Occurs BEFORE and AFTER period of gastrulation

Answer 33

ESTABLISHMENT OF THE BODY OF AXES

Question 34

Express genes essential for head formation ○ Establishes cranial end of embryo prior to gastrulation

Answer 34

Anterior visceral endoderm (AVE)

Question 35

Initiates and maintains primitive streak ○ Upregulates genes responsible for formation of dorsal and ventral mesoderm; tail and head structures

Answer 35

Nodal (member of TGF-beta)

Question 36

Centralizes mesoderm to contribute to kidneys

Answer 36

Bone morphogenetic protein 4 (BMP4)

Question 37

"The Organizer"

Answer 37

Node

Question 38

Dorsalized into notochord, somite, and somitomeres

Answer 38

Cranial mesoderm

Question 39

Maintains node ○ Induces regional specificity in forebrain and midbrain ○ Without this = embryo fail to gastrulate properly; lack forebrain and midbrain

Answer 39

HNF-3B (beta)

Question 40

HNF-3B (beta)

Answer 40

Laterality

Question 41

Induces nodal expression

Answer 41

FGF 8

Question 42

Homeobox-containing transcription factor ○ Responsible for left sidedness ○ Repeated expression on left side of heart, stomach, gut ○ Organs assume normal asymmetrical body positions

Answer 42

PITX2

Question 43

Acts barrier to prevent left-sided signals from crossing over

Answer 43

Lefty

Question 44

Repressor for left sided gene expression on the right ○ Inhibitory

Answer 44

Sonic hedgehog (SHH)

Question 45

Establishes laterality ○ Concentrated on left side ○ Broken down by monoamine oxidase (MAO) on right side ○ Leads to situs inversus and dextrocardia when altered

Answer 45

Serotonin (5HT)

Question 46

a transcription factor ○ Restricted to right lateral plate of the mesoderm ○ Regulates genes for establishing right side

Answer 46

SNAIL

Question 47

becomes paraxial mesoderm

Answer 47

LATERAL EDGES OF THE NODE

Question 47

intermediate mesoderm

Answer 47

Midstreak region

Question 48

extraembryonic mesoderm

Answer 48

CAUDAL MOST PART OF STREAK

Question 48

lateral plate mesoderm

Answer 48

Caudal Part

Question 48

shows regressive changes until it disappears towards the end of the 4th week.

Answer 48

Primitive streak

Question 49

Deficiency of the midline in craniofacial structures ○ May be caused by high doses of alcohol (kills cells in the anterior midline of the germ disc) ○ small forebrain, 2 lateral ventricles are often merge into one, eyes are close together (hypotelorism) and closed

Answer 49

Holoprosencephaly

Question 49

insufficient mesoderm is formed in the caudal-most region of the embryo

Answer 49

Caudal Dysgenesis (sirenomelia)

Question 50

is caused by mutations in zinc finger transcription factor ZIC3

Answer 50

X-linked Heterotaxy

Question 50

stage of trophoblast wherein it consists of cytotrophoblastic core covered by a syncytial layer at the beginning of 3rd week ○ Mesodermal cells penetrate the core of primary villi and grow towards the decidua

Answer 50

Primary Villi

Question 51

formed when the mesodermal cells penetrate the core of primary villains grow towards decidua

Answer 51

Secondary Villi

Question 52

formed at the end of 3rd week when mesodermal cells in the core of the villus begin to differentiate into blood cells and small blood vessels. ○ Capillaries in this villi make contact with capillaries developing in the mesoderm of the chorionic plate in the connecting stalk.

Answer 52

Tertiary Villi (Definitive Placental Villi)

Question 53

villi extension from chorionic plate to decidua basalis

Answer 53

Stem/ Anchoring Villi

Question 54

branch from the sides of stem villi. This is the site for exchange of nutrients and other factors.

Answer 54

Free (Terminal) Villi

Question 55

attaches the embryo to its trophoblastic shell and later on develops into umbilical cord.

Answer 55

Connecting Stalk