The Embryonic Period

Question 1

What is the extraembryonic mesoderm?

Answer 1

A new layer of cells derived from the epiblast and yolk sac that is found between (and SURROUNDING) the two. It separates the embryo from uterine tissue, is important in forming the placenta and gives mechanical and trophic support. It attaches to the CYTOTROPHOBLAST through holes in it.

Question 2

What are the trophoblastic lacunae?

Answer 2

holes in the uterine tissue that allow blood flow and oxygen diffusion to the blastocyst.

Question 3

What is the choreon?

Answer 3

Consists of the syncytiotrophoblast, cytotrophoblast and XE somatic mesoderm. It is the fetal contribution to the placenta.

Question 4

When are the yolk sac and amniotic cavity formed?

Answer 4

After implantation. The yolk sac, hypoblast and epilast form the blimainar geminal disc; the amniotic cavity is also formed.

Question 5

What is the bilaminar disc?

Answer 5

A series of epiblast and hypoblast cells that form a border between the yolk sac cavity and the amniotic sac cavity.

Question 6

When does the XE mesorderm form?

Answer 6

After the amniotic sac and yolk sac form. The maternal vessels also start to enter the trophoblastic lacunae.

Question 7

When does the xe coelom form?

Answer 7

After the XE mesoderm. As it forms, uteroplacental circulation begins.

Question 8

What is a complete mole?

Answer 8

A dipoloid zygote that has only paternal chromosomes; the gg lost its chromosomes by 2 sperm or 1 sperm replicated itself. No fetal tissue present.

Question 9

What is apartial mole?

Answer 9

Fertilization of the haploid ovum and duplication of the paternal haploid chromosomes. Fetal tissue (w/maternal chromosomes) is present.

Question 10

What period of embryogenesis is immune to teratogens?

Answer 10

Pre-embryonic period

Question 11

What occurs during the embryonic period?

Answer 11

major body systems develop, embryo folds, CNS develops, laternal folding of amnion/body wall.

Question 12

Gastrulation

Answer 12

begining of morphogenesis. An embryonic disk is formed and the germ cells are differentiated into the endoderm, mesoderm and ectoderm. The PRIMITIVE STREAK is also formed.

Question 13

What is the primitive streak?

Answer 13

A narrow line of cells that forms on the surface of the embryonic disk. It is the future axis of the embryo, and marks the beginning of GASTRULATION. The region will also be the back end of the fetus.

Question 14

Primitive groove

Answer 14

posterior end of the primitve streak where epiblast cells migrate to, fall through and then spread out. This elongates the embryonic disc and forms the MESODERM and ENDODERM.

Question 15

What layer does the endoderm replace?

Answer 15

hypoblast

Question 16

What layers are derived from the epiblast?

Answer 16

ectoderm, mesoderm and endoderm

Question 17

What replaces the primitive streak?

Answer 17

Notochord

Question 18

primitive pit

Answer 18

anterior end of the primitive streak in the center of the embryonic disk.

Question 19

sacrococcyeal teratoma

Answer 19

disorder that occurs when the primitive streak does not recede. A tumor with derivatives of all 3 germ layers is present in the embryo/infant.

Question 20

caudal dysplasia

Answer 20

A germ layer disorder (mesoderm) in which the lower vertebrae and sacrum do not develop correctly.

Question 21

How is the notochord formed?

Answer 21

Migrating cells form a median column of cells in the mseoderm; looks like a rod and serves as the axis for the embryo.

Question 22

What does the notochord do?

Answer 22

Acts as an axis which things develop around, is a foundation upon which the vertebral column forms and brings about induction of the NEURAL TUBE.

Question 23

Chordoma

Answer 23

Bone cancer in adults that derives from remnants of the embryonic notochord.

Question 24

What does the notochord induce?

Answer 24

The ectoderm to produce epithelial ectoderm (outermost skin) and the neural plate (nervous system) and eventually the neural tube.

Question 25

What is neurulation?

Answer 25

Formation of the nervous system caused by signaling molecules produced by the notochord.

Question 26

What are neural crest cells?

Answer 26

Neural cells that break away from the ectoderm; they form the PNS and reaches the adrenal glands and skin.

Question 27

What is the neural tube?

Answer 27

A tube that breaks away from the ectoderm and forms the spinal cord and brain (CNS).

Question 28

Ectodermal dysplasia syndomes

Answer 28

heritable disorders that affect the ectoderm; may include abnormalities in the skin, teeth, eyes etc.

Question 29

Neurocristopathies

Answer 29

Problems arising from the neural crest. May be nerve rleated or disorders including the eye, teeth and skin (such as pigmentary disorders).

Question 30

What are spinal dysraphism (NTDs)?

Answer 30

Neural tube defects (e.g. failure of neural tubes to close).

Question 31

anencephaly

Answer 31

failure of the full development of the brain due to neuropores failing to close.

Question 32

iniencephaly

Answer 32

extreme retroflexion of the neck and anterior/posterior connections. due to NTD

Question 33

encephalocele

Answer 33

a cranial defect with a tumor-like projection on the anterior or posterior side of the head.

Question 34

arnold-chiari malformation

Answer 34

herniation of cerebellar vermis or tonsils through the formamen magnum blocking flow of CSF.

Question 35

spinal bifida

Answer 35

failure of neural arches to form; is a tumor-projection near the sacral region of the spinal cord.

Question 36

What does folic acid prevent?

Answer 36

NTDs; it may not prevent increased homocysteine levels that can prevent closure of the neural tube.

Question 37

What is the triple marker screen test?

Answer 37

A test that measures AFP (neural defect), bHCG (trisomy) and uE3 levels (trisomy) in maternal blood.

Question 38

Which sac eventually becomes the embryonic disc?

Answer 38

The amniotic sac

Question 39

What layer of cells from the bilaminar disc (hypoblast or epiblast) are the 3 germ layers derived from?

Answer 39

epiblast