Embryology

Question 1

when is a mature ovum release?

Answer 1

ovulation

Question 2

what is fertilization?

Answer 2

process of sperm joining egg

Question 3

describe the process of fertilization

Answer 3

1. sperm makes contact w egg
2. acrosome reacts w zona pellucida & creates a space
3. plasma membranes of sperm & egg fuse
4. sperm nucleus enters egg
5. cortical granules fuse w egg plasma membrane, renders plasma membrane impenetrable to other sperm

Question 4

what is a zygote?

Answer 4

single celled fertilized egg (day 1)

Question 5

what is cleavage?

Answer 5

cell division: zygote to blastocyst

Question 6

what are daughter cells?

Answer 6

products of cell division called blastomeres

Question 7

what is a morula?

Answer 7

32 cell (blastomeres) embryo

Question 8

describe the blastocyst stage (day 4-5)

Answer 8

• trophoblast pumps fluid into cell to form fluid-filled vesicle (blastocoele)
• fluid pushes inner cell mass to one end of tropoectoderm (embryonic pole)
• hypoblast cells line & feed blastocoele

Question 9

what is the epiblast?

Answer 9

inner cell mass of blastocyst

Question 10

what is the trophoblast?

Answer 10

external cell layer of blastocyst

Question 11

what is the blastocoele?

Answer 11

yolk sac that will feed embryo for several weeks

Question 12

what are hypoblasts?

Answer 12

cells that line & feed blastocoele

Question 13

what occurs on day 5-9 of implantation?

Answer 13

blastocyst interacts with uterine wall:
- giant cells from trophoblast implant in uterine wall
- rest of trophoblast gives rise to placenta & membranes
- blastocoele feeds embryo for several weeks

Question 14

what is an embryonic bilaminar disc?

Answer 14

2 distinct layers of embryo at beginning of week 3:
epiblast (outer region of blastocyst)
hypoblast (borders blastocoele)

Question 15

what is gastrulation?

Answer 15

formation of 3 embryonic germ layers from cells of epiblast

Question 16

describe the process of gastrulation

Answer 16

• cells migrate through rift in epiblast called primitive streak
• form endoderm, then mesoderm, remaining epiblast cells become ectoderm

Question 17

what tissues are formed by the ectoderm?

Answer 17

CNS
PNS
ANS
outer layer of skin

Question 18

what tissues are formed by the mesoderm?

Answer 18

connective tissue (bone, cartilage, muscle, adipose)

Question 19

what tissues are formed by the endoderm?

Answer 19

GI tract
lungs
liver

Question 20

what is neurulation and when does it occur?

Answer 20

formation of notochord & neural tube (week 3)

Question 21

describe the process of neurulation

Answer 21

• cells migrate through Henson’s node forming notochord
• notochord signals to overlying ectoderm to thicken to form neural plate
• neural plate begins to fold at midline (neural groove), closing to form neural tube

Question 22

how does the notochord form?

Answer 22

via mesoderm cells that migrate through Henson’s Node

Question 23

what is Henson’s node?

Answer 23

collection of cell bodies at anterior end of primitive streak

Question 24

what is the neural tube?

Answer 24

• cavity for formation of CNS
• vertebral column & skull form around tube

Question 25

what are neural tube defects?

Answer 25

failure of neural tube to close due to folic acid deficiency

Question 26

what are 2 types of spina bifida?

Answer 26

- occulta (no protrusion of CNS/meninges) - cystica (protrusion of CNS/meninges)

Question 27

name 2 types of spina bifida cystica lesions

Answer 27

meningocoele myelomeningocoele

Question 28

meningocoele lesion

Answer 28

protrusion of meninges through defect in spine

Question 29

myelomeningocoele lesion

Answer 29

protrusion of spinal cord & meninges through defect in spine

Question 30

what is anencephaly?

Answer 30

failure of skull to form in which missing skull cap & cerebral cortex (incompatible with life)

Question 31

what is encephalocoele?

Answer 31

failure of skull to form in which part of brain/meninges forms in a sac outside of skull

Question 32

skeleton & articulations derive from ____

Answer 32

mesoderm

Question 33

what is paraxial mesoderm?

Answer 33

mesoderm lateral to neural tube & notochord

Question 34

what happens to paraxial mesoderm by 20 days in utero?

Answer 34

organizes into 42-44 segments

Question 35

lateral plate mesoderm gives rise to ____

Answer 35

body wall/limbs

Question 36

what are somites?

Answer 36

- compact aggregates of paraxial mesoderm - appear as bead-like elevations along dorsal surface - form cranial to caudal

Question 37

how are somites divided?

Answer 37

- sclerotome: skeletal system - myotome: muscular system - dermatome: deeper layers of skin, adipose tissue

Question 38

how many primary ossification centers in typical vertebrae?

Answer 38

3

Question 39

how many secondary ossification centers in typical vertebrae?

Answer 39

5

Question 40

describe primary ossification centers

Answer 40

- body (centrum) - neural arch = 2 centers that meet at dorsal midline to form SP, fuse w body anteriorly

Question 41

describe secondary ossification centers

Answer 41

- tips of each TP - one at tip of SP - 2 ring shaped annular epiphyses at top & bottom of vertebrae

Question 42

where are growth plates located in vertebrae?

Answer 42

between primary & secondary ossification centers

Question 43

describe vertebrae at birth

Answer 43

- 3 primary ossification centers are distinct - joined by cartilage

Question 44

vertebrae by age 1

Answer 44

neural arches fused

Question 45

vertebrae by age 6

Answer 45

- arches fused to bodies - accommodates growing spinal cord

Question 46

when do secondary ossification centers appear?

Answer 46

puberty

Question 47

when do primary ossification centers begin to fuse?

Answer 47

by age 21 - annular epiphyses - presacral complete by age 25 - sacrum complete by 23

Question 48

ossification of atlas (C1)

Answer 48

- 2 primary ossification centers (left & right): bulk of posterior arch & lateral mass - halves of posterior arch fuse by age 4 - anterior arch appears at year 1 & joins lateral masses between 5-9 years

Question 49

ossification of axis (C2)

Answer 49

- same ossification centers as typical, plus 2 for dens (appear in 4-5th month in utero) - at birth: centrum, dens, neural arches - primary centers fused by age 6

Question 50

ossification centers of sacrum

Answer 50

- body: from primary center of centrum & 2 epiphyseal plates - vertebral arches: from 2 primary ossification centers - other centers: laterally for upper 3-4 segments for costal segments - secondary centers on each lateral surface (1 auricular surface, 1 lateral edge)

Question 51

timing of ossification of sacrum

Answer 51

- age 2-5: neural arches join w bodies, lower segments 1st - age 16: annular epiphyses for bodies, 18-20 lateral epiphyses (IVD separate bodies) - age 18: synostosis of discs begins, proceeds cranially

Question 52

ossification of coccyx

Answer 52

each segment has its own ossification center: - 1 - soon after birth - 2 - age 5-10 - 3 - age 10-15 - 4 - age 14-20

Question 53

name the 5 stages of lung development

Answer 53

- embryonic - pseudoglandular - canalicular - saccular - postnatal

Question 54

lungs are derived from ____

Answer 54

endoderm

Question 55

# lung development embryonic stage

Answer 55

- week 3: lung bud develops from foregut, divide into lobar buds - week 8: lobar buds divide & form bronchiopulmonary segments - buds lined by endodermally derived endothelium that differentiates into epithelium that lines airways & alveoli

Question 56

# lung development pseudoglandular stage

Answer 56

weeks 7-18 - conductive airways formed by progressive branching - 13 weeks: cilia appear in proximal airways

Question 57

# lung development canalicular stage

Answer 57

16-25 weeks: gas exchanging portion of lung is formed & vascularized

Question 58

# lung development saccular stage

Answer 58

25 weeks to birth: development of primitive saccules that become alveoli after birth

Question 59

# lung development postnatal stage

Answer 59

birth & after: maturation of alveoli

Question 60

# development of heart truncus arteriosus

Answer 60

divides & gives rise to aorta & pulmonary trunk

Question 61

# development of heart bulbus cordis

Answer 61

right ventricle

Question 62

# development of heart primitive ventricle

Answer 62

left ventricle

Question 63

# development of heart primitive atrium

Answer 63

anterior portions of L & R atria & both auricles

Question 64

# development of heart sinus venosus

Answer 64

- posterior walls of atria - SA node - coronary sinus