Embryology

Question 1

Pregenesis definition and Steps

Answer 1

Developmental pre-conditions (in parents) enabling reproduction
Formation and migration of parental primordial germ cells
Cortico-medullary differentiation of gonads
Increase number of cells by mitosis
Gametogenesis (meiosis) maturation of gametes, fertilization

Question 2

Migration of Primordial germ cells

Answer 2

In 3rd week wander from primary ectoderm into the yolk sac wall
Wander back in the 4-6 week, crossing the dorsal mesentery and colonize the gonadal ridge

Question 3

Meiosis

Answer 3

From diploid forms 4 haploid cells after doubling of DNA and 2 meiotic divisions

Question 4

Meiotic Non-Disjunction

Answer 4

Irregular distribution of homologous chromosomes to cell poles, resulting in aneuploidy
Due to failure of paired chromosomes to seperate or unpaired homologues distribution to the same pole

Question 5

Results of meiotic non-disjunction during
Anaphase I
Anaphase II

Answer 5

Anaphase I: 2 empty, 2 diploid

Anaphase II: 1 empty, 1 diploid, 2 haploid

Question 6

What barriers must a sperm penetrate

Answer 6

Corona Radiata: Granulosa cells embedded in hyaluronic acid
Zona pellucida: glycoproteins
Egg plasma membrane

Question 7

Capacitation

Answer 7

Triggered by bicarbonate
Alters lipid and glycoprotein content of sperm membrane
Increases sperm metabolism and motility

Question 8

Acrosomal Reaction

Answer 8

Receptor on zona pellucida binds with sperm

Influx of Ca causes acrosome cap to release enzymes and break down zona pellucida

Question 9

Cortical Reaction

Answer 9

First sperm to penetrate plasma membrane causes an intracellular influx of Calcium in ovum
Cortical granules (from under plasma membrane) release enzymes to degrade zona pellucida and prevent polyspermy

Question 10

Cleavage

Answer 10

Specialized mitotic divisions
Cells increase in number but not in size
Each cell is termed a blastomere

Question 11

Compaction

Answer 11

Tight junctions between adjacent outer cells
Gap junctions link inner cells
Results in morula, solid ball of cells

Question 12

Blastocyst Formation

Answer 12

Compaction from inside leads to fluid accumulation inside blastocoel
Results into:
Inner Cell Mass
Trophoblast
Blastocoel

Question 13

Hatching

Answer 13

Hatching from zona pellucida involves trophoblast and uterine enzymes to degrade zona pellucida
Growth continues

Question 14

Trophoblast forms…

Answer 14

Cytotrophoblast- outer

Syncytiotrophoblast- inner layer (placenta)

Question 15

Inner cell mass forms…

Answer 15

Epiblast –> Amnion cavity

Hypoblast –> Yolk Sac

Question 16

Amnion

Answer 16

Exercise and cushion room for fetus

Epiblastic tissue

Question 17

Chorion

Answer 17

Exchange between fetal and maternal circulation

Question 18

Yolk Sac

Answer 18

Blood cell precursors and primordial germ cells

Hypoblastic tissue

Question 19

Week 3 Events

Answer 19

Trilaminar embryo formation
Beginning of gastrulation: Primitive node/ pit, neural groove and neural plate, notochord
Formation of paraxial, intermediate, and lateral plate of mesoderm of somitomeres and somites

Question 20

Gastrulation begins with

Answer 20

Begins with depression on epiblast called primitive streak

Question 21

Mesoderm formation

Answer 21

Epiblast cells detach and migrate (invaginate) between epiblast and hypoblast layers to become mesoderm

Question 22

Endoderm formation

Answer 22

Epiblast cells migrate further than mesoderm layer and displace the hypoblast to form endoderm

Question 23

Ectoderm formation

Answer 23

Cells remaining in epiblast become ectoderm

Question 24

Ectoderm Forms

Answer 24

Epidermis
Hair, nails, lens of eye, enamel
Sweat glands, salivary glands, mammary glands, pituitary gland, adrenal medulla
Epithelium of mouth and anus
Nervous tissue

Question 25

Mesoderm Forms

Answer 25

Muscle
Dermis
Connective tissue, bone, cartilage, blood, 
Epithelium of: kidneys, gonads, vessels, 
Heart, 
adrenal cortex, 
mesothelium, 
internal reproductive organs

Question 26

Endoderm Forms

Answer 26

Epithelium of: respiratory tract, GI, bladder/urethra

Liver, gallbladder, pancreas, thymus, thyroid, parathyroid

Question 27

Neural groove formation

Answer 27

Epiblast cells which remain at the primitive streak will gather to form neural groove and develop into the neural tube

Question 28

Paraxial Measoderm

Answer 28

Form somites that flank the neural tube and form
Body and limb muscles
Cartilage, bone, connective tissue, ribs, cranial bones
Dermis

Question 29

Intermediate Mesoderm

Answer 29

Urogenital system and part of genital system

Question 30

Lateral Mesoderm

Answer 30

Forms trunk, muscle of body wall, digestive tract, proximal part of limbs
Associated with Splanchnic (endoderm) and Somatic (ectoderm)

Question 31

Lateral Tranverse Folding

Answer 31

L & R sides curve toward midline
Creates cylindrical trunk w/ endoderm and ectoderm
Splanchnic Mesoderm- Messentery & wall of digestive tract
Somatic Mesoderm- Lateral and ventral body wall & mesenchyme of limb buds

Question 32

Neural tube closure and sequence

Answer 32

Neural plate closure begins midway along neural plate
Anterior (cranial) neuropore closes first
Anterior (caudal) neuropore closes second

Question 33

Placodes

Answer 33

Ectodermal thickenings, signaled by NS

Lens, otic, olfactory, ant pituitary, sensory ganglion of cranial nerves

Question 34

Extraembryonic Mesoderm

Answer 34

Cardiogenic Mesoderm

• Migration of heart forming cells through primitive streak
• Mostly Splanchnic mesoderm
• Blood and blood vessels

Question 35

Endoderm derivatives

Answer 35

Involve mesoderm and endoderm interaction to form major glands of
-Digestive tract (pancreas, salivary), endocrine (thyroid), respiratory tract, liver