Early Embryonic Development (Exam II)

Question 1

Define Teratogen and give some examples.

Answer 1

Any agent or factor that can cause congenital abnormalities in an embryo or fetus.

Genetic factors, radiation, hormones, chemical agents, infectious agents (viruses, parasites)

Question 2

Define Totipotent, Multipotent, Pluripotent, Unipotent

Answer 2

Totipotent - can differentiate into ANY type of cell
Multipotent/Pluripotent - can differentiate into a certain cells
Unipotent - Can differentiate into 1 type of cell

Question 3

What happen when a teratogen acts during….

1. Predifferentiation
2. During Organogenesis
3. During fetal growth stage

Answer 3

1. Embryo dies.
2. Structural defects.
3. Affects functional maturation.

Question 4

Describe the basic process of development from Ootid to gastrulation…

Answer 4

Ootid (female and male pronuclei) –> (Zygote (single cell) –> Morula (compact mass of cells) –> Blastula (fluid filled cyst with cells at periphery) –> Blastocyst (addition of inner cell mass (embryoblast)) –> Hatching Blastocyst (where zona pellucida breaks open) –> Early gastrula (Bilaminar disk) –> Late Gastrula (Trilaminar disk to tube shape)

Question 5

Describe Cleavage

Answer 5

The zygote undergoes divisions in the uterine tube without any change in size. The resulting cells are Blastomeres.

Question 6

What is a Morula

Answer 6

16 cells (blastomeres), zona pellucida is still intact.

Question 7

What is a Blastocyst?

Answer 7

Stage where the cavity has formed (forms in blastula) and there is now an inner cell mass (embryoblast) and an outer cell mass (trophoblast). Still the same size as the zygote (results from cleavage) & compaction).

Question 8

What is a gastrula?

Answer 8

Stage where there is the formation of the 3 germ layers (ectoderm, mesoderm, endoderm) and primitive axial organs (neural tube, notochord, somites, primitive gut)

Question 9

What is the trophoblast? What does the trophoblast become?

Answer 9

Outer cell mass of blastula/blastocyst. Will form parts of the placental/fetal membrane (chorion, amnion)

Question 10

What is the embryoblast? What does it become?

Answer 10

Inner cell mass of blastula/blastocyst. Will become the entire embryo. Forms the bilaminar disk of epiblast (dorsal) and hypoblast (ventral).

Question 11

What does the primitive streak do?

Answer 11

Establishes the cranial/caudal (head/tail) axis.

Question 12

What does the ectoderm form?

Answer 12

Epidermal structures, lining of oral and nasal cavity, anus, nervous system

Question 13

What does the mesoderm form?

Answer 13

Connective tissue (of neural crest origin in head), muscle tissue, cardiovascular system, urogenital tract, endothelium and mesothelium (the linings of body cavities and vessels)

Question 14

What does the endoderm form?

Answer 14

Epithelial structures, lining and glands of the digestive and respiratory systems

Question 15

What is a Teratoma?

Answer 15

A neoplasm with more than one type of germ layer.

Question 16

Describe the steps of Gastrulation

Answer 16

Primitive streak forms in epiblast –> epiblast cells migrate towards primitive streak –> hypoblast cells are replaced by epiblast cells to form primary endoderm, mesoderm formed by epiblast cells that descend through the primitive streak but do not replace the hypoblast cells, ectoderm formed by epiblast cells that do not descend through primitive streak

Question 17

What lines the yolk sac?

Answer 17

Primary endoderm

Question 18

What forms the notochord? What is the notochord?

Answer 18

Notochord is formed from mesoderm. It is a cluster of cells that determines the axis of embryo and is required to signal neural tube formation from the neural ectoderm. It is a transient embryonic midline structure that induces the lateral body folds, neural tube and primitive gut formation.

Question 19

Describe the Mesoderm Inductive Effects..

Answer 19

Mesoderm forms notochord –> notochord induces the ectoderm to form neural tissue –> neural tube and neural crest cells are formed –> somites form

Lateral, cranial, caudal body fold create the head, tail, primitive anus and mouth. Nervous system is defined.

Question 20

Describe the steps in Neural Tube Formation

Answer 20

Neural ectoderm thickens –> Neural folds dip down producing the neural groove –> Neural folds contact. Neural ectoderm cells rearrange –> Forms neural tube.

Question 21

What are the 4 types of mesoderm (named for their location on transverse section of body)? What do they form?

Answer 21

1. Axial - Notochord
2. Paraxial - Somites
3. Intermediate - Urogenital systems
4. Lateral Plate - Somatic and Splanchnic mesoderm - becomes all other cartilage and bones of the body and limbs

Question 22

What are the 3 regions that somites form? What do they give rise to?

Answer 22

1. Dermatome - skin (dermis)
2. Myotome - muscle (skeletal muscle)
3. Sclerotome - cartilage, tendons, endothelium (forms axial skeleton)

Question 23

What does the neural tube become?

Answer 23

The cranial part becomes the brain

The caudal part becomes the spinal cord

Question 24

What does the notochord become?

Answer 24

The nucleus purposes of intervertebral discs.

Question 25

What are neural crest cells?

Answer 25

Transient, multipotent, migratory cell population unique to vertebrates that gives rise to a diverse cell lineage including melanocytes, craniofacial cartilage and bone

Question 26

What does somatic mesoderm (division of lateral plate mesoderm) form?

Answer 26

forms most connective tissue and smooth muscle

Question 27

What does sphlanchnic mesoderm (division of lateral plate mesoderm) form?

Answer 27

Forms most connective tissue and smooth muscles of endoderm lined organs and epithelial linings of body coelom. Forms all tissues of the cardiovascular system.