Embryology

Question 1

How long is the germinal period?

Answer 1

0-2 weeks

Question 2

Embryonic period lasts?

Answer 2

2-8 weeks

Question 3

Fetal period lasts?

Answer 3

8-40 weeks

Question 4

define gastrulation

Answer 4

Early embryo reorganizes into 3 tissue layers. All cells have the same DNA; however, different cells now begin to “turn on”
(express) different genes to become different
organs.

Question 5

what are the 3 layers of gastrulation

Answer 5

endoderm, mesoderm, ectoderm

Question 6

endoderm

Answer 6

digestive, respiratory systems

Question 7

mesoderm

Answer 7

muscles, skeleton, circulatory system, reproductive system, dermis

Question 8

ectoderm

Answer 8

CNS, PNS, eyes, ears, outer skin

Question 9

neurulation

Answer 9

process where the neural plate forms the neural tube

Question 10

closure of cranial neuropore happens when?

and what happens if it doesnt close?

Answer 10

day 25; no formation of brain, not a viable fetus

Question 11

closure of caudal neurpore happens when?

what can occur if it doesnt close?

Answer 11

day 28; spina bifida

Question 12

brain development begins when?

Answer 12

day 28

Question 13

3 main divisions of the brain

Answer 13

prosencephalon (forebrain)
mesenencephalon (midbrain)
rhomboencephalon (hindbrain)

Question 14

Cells formed in segmental pairs along the neural tube from mesoderm layer.
Give rise to vertebrae, muscles of back and body wall, and dermis ofskin.

Answer 14

somites

Question 15

Cells in
dorsolateral regions form
muscle cells; migrate
beneath dorsal epithelium (dermatome).

Answer 15

myotome

Question 16

cells in
ventromedial wall lose
epithelial arrangement; become mesenchymal.

Answer 16

sclerotome

Question 17

embryo week 4

Answer 17

Neural folds fuse: folding of embryo into human-like shape
 Arm and leg buds appear
 Heart pumps blood
 Pharyngeal arches visible
 Length 4-5 mm
 4-12 pairs of somites

Question 18

embryo week 5

Answer 18

Lens placodes appear
 Primitive mouth
 Digital rays on hands
 Forebrain, midbrain and hindbrain form

Question 19

embryo week 6

Answer 19

Primitive nose
 Primary palate
 Auricular Hillocks form – precursor to visible auricle of ear Reflex Response to Touch
 Digital Rays begin to Develop
 Length 9-14 mm

Question 20

embryo week 7

Answer 20

Eyelids begin to form
 Motor behavior first appears as slow neck extensions
 Limbs undergo considerable change in week 7
 Notches appear between digitalrays

Question 21

embryo week 8

Answer 21

Length 3.5 cm; Weight 2 g (.004 lb)
 Ovaries and testes distinguishable
 Eyes, ears, nose, mouth, digits formed
 Muscle contraction appear - lateral flexion movements
 Can see startle, hiccup, isolated arm/leg movement

Question 22

week 9

Answer 22

increased activity and rapid growth
 Length, 5 cm
 Sensory organs developing
 Bone ossification Begins
 Head retroflexion
 Head rotation

Question 23

week 12

Answer 23

Sex is Externally Recognizable
Head large for body
Brain configuration nearly 
complete
Blood Forming in Marrow
Sucking/Swallowing
Yawn

Question 24

weeks 13-16

Answer 24

Breathing and swallowing motion appears
 Tactile stimulation elicits movements
 Growth very rapid
 Limb movements increasingly coordinated

Question 25

week 16

Answer 25

Motor activity begins
 Scalp hair present
 Trunk size increasing relative to head size
 Heart muscle developed
 Sense organs formed

Question 26

week 17

Answer 26

grasp reflex appears

Question 27

week 20

Answer 27

Lower extremities have grown appreciably
 Myelination of spinal cord begins
 Fetus turns and moves easily

Question 28

week 24

Answer 28

Lungs become viable organs

Question 29

week 25

Answer 29

third trimester begins

Question 30

week 26

Answer 30

eye opening

Question 31

week 28

Answer 31

Increasing fat tissue development
 Retina layered and light-receptive
 fetus turns head down

Question 32

week 32

Answer 32

Weight increasing more than length

Taste sense operative

Question 33

week 36

Answer 33

Body More Rounded

 Ossification begins distal femur

Question 34

week 40

Answer 34

myelination of brain begins

Question 35

intramembranous ossification

Answer 35

replacement of connective tissue membranes with bony tissue

Question 36

endochondral ossification

Answer 36

replacement of hyaline cartilage with bony tissue

Question 37

limb buds appear at?

upper limbs begin development?

Answer 37

week 4; 1-2 days before lower limbs

Question 38

most muscle develops from?

Answer 38

mesoderm

Question 39

teratogens

Answer 39

cause human birth defects:

• congenital infection
• alcohol
• smoking
• drugs
• poor nutrition