Embryology (Ch 3)

Question 1

What are the three stages of development?

Answer 1

1. Pre-Embryonic Development (weeks 1-2)
2. Embryonic Development (weeks 3-8)
3. Fetal Development (weeks 9-birth)

Question 2

Pre-Embryonic Development

Answer 2

• -> first two weeks after fertilization
  1. fertilization (zygote)
  2. cleavage: zygote (one cell) -> morula (16 cells)
  3. morula takes up fluid –> blastocyst (hollow ball w/two cell types)
  4. blastocyst implants into uterine wall
  5. blastocyst differentiates into two laters (bilaminar disc)

Question 3

cleavage

Answer 3

series of mitotic divisions that causes zygote to break into 16 cells called the morula

Question 4

blastocyst

Answer 4

hollow ball of two cell types

1. Inner Cell Mass: develops into embryo
2. Outer Ring of cells (trophoblast): develops into placenta

Question 5

bilaminar disc

Answer 5

two layers of the blastocyst

Question 6

Embryonic Development

Answer 6

• ->weeks 3-8
• gastrulation (bilaminar disc–>trilaminar disc)
• blastocyst cells form the 3 germ layers
• primitive streak (raised groove) appears onto of embryo
• epiblast cells begin to migrate inward at primitive streak –> become endoderm

Question 7

What is gastrulation?

Answer 7

–> process by which the cells of the epiblast migrate and form the three primary germ layers
(bilaminar –> trilaminar)
1. formation of primitive streak
2. cells travel up streak forming three layers

Question 8

What are the three germ layers?

Answer 8

1. Ectoderm (outer)
2. Mesoderm (middle)
3. Endoderm (inner)

Question 9

What are parts of the ectoderm?

Answer 9

epidermis, nervous tissue, pituitary gland, tooth enamel

Question 10

What are parts of the mesoderm?

Answer 10

notochord, heart, kidney, skeleton, muscles, dermis

Question 11

What are parts of the endoderm?

Answer 11

linings of digestive/respiratory tract, liver, pancreas, thyroid

Question 12

What are the subdivisions of the mesoderm?

Answer 12

1. Notochord: central axis of embryo in adult
2. Lateral Plate Mesoderm
3. Intermediate Mesoderm
4. Paraxial Mesoderm

Question 13

Somites and their subdivisions

Answer 13

block-like early body segments formed from paraxial mesoderm (become axial skeleton, muscle, cartilage, dermis, and connective tissue)

1. Sclerotome: become vertebrae and ribs
2. Myotome: becomes limb/trunk muscles
3. Dermatome: becomes dermis layer of skin

Question 14

What is the notochord?

Answer 14

cylindrical mass of mesoderm becomes central axis in adults –> signals ectoderm to form neural tube (brain/spinal cord) (aka NEURULATION)

Question 15

Fetal Development

Answer 15

• -> week 9 to birth

- period of rapid growth/maturation of organs

Question 16

zygote

Answer 16

fertilized egg

Question 17

embryo

Answer 17

when the three germ layers have been formed

Question 18

fetus

Answer 18

all organs present in some rudimentary form

Question 19

Neurulation

Answer 19

formation of the neural tube (brain/spinal cord)

-notochord signals ectoderm to form neural tissue (induction) –> neural tube