Embryology

Question 1

What is Embryology?

Answer 1

The study of prenatal development. Defines normal development and identifies the time at which an anomaly/defect may occur

Question 2

Week one of prenatal development

Answer 2

Preimplantation: zygote to blastocyst

Question 3

Weeks two through eight of prenatal development

Answer 3

Embryonic stage: germ disk to embryo

Question 4

What is induction?

Answer 4

Development pathway by cell action

Question 5

What is proliferation?

Answer 5

Controls cellular growth and byproduct production

Question 6

What is differentiation? What are the two types?

Answer 6

Cellular change into distinctly different structures with different functions

Cytodifferentiation: different cells
Histodifferentiation: different tissues

Question 7

What is Morphodifferentiation?

Answer 7

Development of specific tissue structure or shape due to induction and proliferation

Question 8

What is maturation?

Answer 8

Attainment of function in size due to proliferation, differentiation and morphogenesis

Question 9

What is embryogenesis? When does it occur?

Answer 9

Fertilization/fusion of oocyte and spermatozoon forming a zygote

Starts at time of fertilization in the fallopian tubes

Question 10

What is a morula?

Answer 10

Ball of cells formed when a zygote divides

Question 11

How is a blastocyst formed?

Answer 11

The morula forms a central cavity via fluid secretion.

This hollow ball of cells forms a blastocyst

Question 12

What are the two parts of the blastocyst?

Answer 12

Trophoblast: peripheral cells that form the placenta

Embryoblast: Cells trapped inside the morula forms the embryo

Question 13

When does implantation occur?

Answer 13

Days 6 to 11 the blaster cyst will attach to the uterus via trophoblast cells

Question 14

What is the bilaminar germ disk formed from and when does it occur?

Answer 14

Embryoblast cells form two germ layers at days 7 to 8

Question 15

What are the two germ layers of the billaminar germ disc called?

Answer 15

Epiblast (top layer) and hypoblast (bottom layer)

Question 16

What is the amniotic cavity?

Answer 16

Space that forms between the epi-blast and amniotic sac

Question 17

At which end of the bilaminar germ disc is the prechordal plate?

Answer 17

Cephalic end

Forms membrane which will separate future primitive mouth from the primitive gut

Question 18

At which end of the bilaminar germ disk is the cloacal plate?

Answer 18

Caudal end

Forms membrane which establishes external openings for alimentary and genitourinary tract

Question 19

What is the primitive groove and what does it do?

Answer 19

Longitudinal furrow/opening in the epi-blast at the caudal end.

Establishes bilateral symmetry

Question 20

What is the primitive streak? What does it do

Answer 20

Elevation of the Epiblast on the posterior border of the privative groove.

Guides proliferating epiblast in forming the trilaminar germ disc

Question 21

What is the primitive pit?

Answer 21

Depression/opening at the anterior end of the primitive groove/ streak

Question 22

What is the primitive node/Hensens node

Answer 22

Elevation of Epiblast cells on the primitive pit guides more proliferating epiblast responsible for forming the future notochord

Question 23

What are the three layers of the trilaminar germ disc?

Answer 23

Ectoderm
Mesoderm
Endoderm

Question 24

When is the trilaminar germ disc formed and how?

Answer 24

Day 21
Epiblast undergo proliferation/mitosis, migrate to the primitive streak, enter the primitive groove and passing between the Epiblast and hypoblast to form an intermediate layer called the mesoderm 

Question 25

What is the endoderm layer formed from?

Answer 25

Forms from the mesoderm when the HyperBlast is pushed laterally into the yolk sac

Question 26

How is the ectoderm layer created?

Answer 26

Epiblast becomes the ectoderm

Question 27

What is the notochord?

Answer 27

Pencil shaped column of cells that forms the axial skeleton (spine, ribs, sternum) Cells induce the formation of the neural plate and synchronized development of the neural tube

Question 28

 What is the neural plate formed from?

Answer 28

Neuroectoderm (fourth germ layer)

Question 29

What is neurulation?  Which cells are involved?

Answer 29

Process by which the neural plate becomes the neural tube Neural crest cells form the neural tube

Question 30

 Structures formed by the neural tube

Answer 30

Brain, spinal cord, retinas, optic nerves, pineal body and posterior pituitary gland

Question 31

What are the neural crest cells of the head?

Answer 31

Cranial ganglia Autonomic ganglia Adrenal medulla Connective tissue of the lower face and neck

Question 32

What is the ectomesenchyme?

Answer 32

Cells that have not yet been told what they are going to be; give rise to future Dentin, cementum, alveolar bone, pulp etc.

Question 33

What are the neural crest cells of the trunk/body

Answer 33

Melanocytes (large amount, pigment cells) Nerve cells Spinal ganglia (dorsal root ganglion)

Question 34

What is needed for the third germ layer/mesoderm to form?

Answer 34

Need the epiblast to migrate to the primitive streak and enter the primitive groove. Well then passed between the epiblast and the hyper blast to form the intermediate layer

Question 35

What is embryonic folding and when does it occur?

Answer 35

Cephalic and lateral surfaces fold into a tube on day 28 Rearranges the forming tissues with the ectoderm now on the outside, endoderm on the inside and the mesoderm between the ectoderm and the endoderm

Question 36

What does the inner tube form during embryonic folding?

Answer 36

Forms the primitive gut

Question 37

Which structures are developing during week four?

Answer 37

``` Frontonasal process Stomodium (primitive mouth) Oropharyngeal membrane Rathke’s pouch Primitive pharynx and foregut First brachial arch/pharyngeal arch/mandibular arch Second and third brachial arches Primitive heart Somites ```

Question 38

What does the ectoderm give rise to?

Answer 38

Skin, nails, hair, enamel Sensory epithelium and Neuroectoderm Salivary, mammary, cutaneous glands

Question 39

What does the mesoderm give rise to?

Answer 39

``` Dermis/connective tissue Muscles Skeletal system Lymphatics, blood cells and bone marrow Reproductive and excretory organs ```

Question 40

What does the endoderm give rise to?

Answer 40

Digestive tract lining: pharynx, esophagus, stomach, intestines Respiratory tract lining: larynx, trachea, bronchi, lungs Lining of circulatory system Liver and pancreatic cells

Question 41

What does the Neuroectoderm give rise to?

Answer 41

Neural crest cells of the head: pigment cells, connective tissue proper, cartilage, bone, dental connective tissue (dentin, pulp, cementum, PDL and alveolar bone)

Question 42

What does the first brachial groove form?

Answer 42

External auditory canal

Question 43

What do the remaining brachial grooves form? What happens if this fails?

Answer 43

Fuse to form the neck Failure to fuse will form remnants/cervical sinus and may form a cervical cyst

Question 44

What are the derivatives of the first brachial pouch?

Answer 44

Eustachian tube/internal auditory canal Tympanic cavity/eardrum Lining of the eardrum

Question 45

Derivatives of the second brachial pouch

Answer 45

Palatine tonsils

Question 46

Derivatives of the third brachial pouch

Answer 46

Thymus gland and inferior parathyroid gland

Question 47

Derivatives of the fourth brachial pouch

Answer 47

Superior parathyroid gland

Question 48

Derivatives of the 5th brachial pouch/ultimobrachial body

Answer 48

Fuses with thyroid gland and disseminates within it, gives rise to parafollicular cells