Embryology

Question 1

Embryology vs Development

Answer 1

• Embryology; the study of embryogenesis-development from fertilization through the next 2 months
• Development occurs throughout life. Refer to our “human” life cycle

Question 2

Fertilization sets the initial plan

Answer 2

The process beginning with penetration of the “secondary oocyte” by the “spermatozoon” and completed by fusion of the male and female “pronuclei”

Question 3

Fertilization involves many sperm, but only 1 allowed entry

Answer 3

• Involves attachment and digestion of protective layers surrounding oocyte
• Sets off massive chemical changes in oocyte
• Blocking entry of > 1 sperm
• Maturing oocyte
• Polarizing oocyte

Question 4

Embryonic period of prenatal development

Answer 4

• up to 8 weeks
– Includes the “egg” period or preimplantation
– Gastrulation (promoted by implantation)
• Primitive streak
– Formation of organ “rudiments”

Question 5

Stem Cells

Answer 5

• The body’s own repair kits

* It appears that every tissue type has some form of stem cells for repair and/or regeneration

Question 6

As cells divide

Answer 6

• 1 daughter cell maintains the cell pool

- 1 daughter cell differentiates

Question 7

As stem cells mature…

Answer 7

They become more differentiated and less versatile

Question 8

Totipotent

Answer 8

The fertilized egg up to morula-capable of becoming any specialized cell

Question 9

Pluripotent

Answer 9

Capable of becoming most specialized cells (embryonic or fetal cells)

Question 10

Multipotent

Answer 10

Capable of becoming multiple cell types (like bone marrow cells)

Question 11

Unipotent

Answer 11

Capable of becoming 1 specialized cell type (precursor sperm)

Question 12

Differentiation

Answer 12

• First observed in the “blastocyst”.
• Blastocyst composed of 2 cell types
- 1. trophoblasts (form extra-embryonic membranes)- now multipotent
- 2. cells forming the inner cell mass (where the embryo proper arises)- now
pluripotent

Question 13

Establishment of Body Organization

Answer 13

Occurs during the embryonic period and involves:

1. Tissue growth and differentiation
2. Establishment of Body Axes
3. Many other patterns to be discussed later in the course

Question 14

Portions of the inner cell mass

Answer 14

Epiblast: in contact with the amniotic cavity
Hypoblast: will form yolk sac and gut lining
- These layers will differentiate into the “primary germ layers” during gastrulation
- An embryonic stage sparked by implantation of the blastocyst

Question 15

The Primitive Streak and Gastrulation

Answer 15

• Forms after the epiblast and hypoblast form
• Site of epiblast cell migration
• Insertion site where epiblast cells become endodermal, ectodermal or mesodermal cells

Question 16

Gastrulation establishes body axes

Answer 16

• Ventral (anterior)/dorsal (posterior)
• Medial/lateral
• Cranial (superior)/caudal (inferior)
• L/R

Question 17

Primary Germ Layers

Answer 17

• ectoderm: the “surface layer”
• (definitive) endoderm: the “inner” layer”
• mesoderm: the “middle layer”
• Each primary germ layer contributes to development of the embryo proper and extraembryonic membranes (chorion, amnion, yolk sac, allantois)

Question 18

Further differentiation in the inner cell mass

Answer 18

3 primary germ layers “give rise” to all mature body tissues (4 categories):
• Epithelium (develops from all 3 germ layers)
• Connective tissue
• Muscle tissue
• Nervous tissue

Question 19

Connective Tissue

Answer 19

• Remains a diverse class with tissues having a common origin
• Mesoderm → mesenchyme → connective tissue
• 3 subgroups:
– CT Proper
– Supportive CT
– Fluid CT

Question 20

Categories of CT derived from mesenchyme

Answer 20

CT Proper: 
- dense
- loose
Supportive CT:
- bone
- cartilage
Fluid CT:
- blood
- lymph

Question 21

Neuroderm

Answer 21

• A “secondary germ layer” where the nervous system mostly develops from
• Derived from ectoderm (dorsal embryo)
• Forms the neural plate and tube
• Many nervous system structures require mesoderm, epithelium, or other tissues to develop

Question 22

Neurulation

Answer 22

Ectoderm -> neuroderm -> nervous system