3.3 lecture - embryology - development of body plan - MacNeil

Question 1

which conceptus layer is always adjacent to maternal blood supply?

Answer 1

syncytiotrophoblast

Question 2

where is the chorionic cavity in relation to the yolk sac and the amnionic cavity?

Answer 2

chorionic is outside surrounding both yolk sac and amnionic cavity. the chorion is connected to the embryo via the connecting stalk (becomes umbilical cord)

Question 3

what layers are present in each primary villus extending from the chorion into the decidua? secondary villus?
tertiary villus?

Answer 3

• primary - syncytiotrophoblast and cytotrophoblast
• secondary - syncitiotrophoblast, cytotrophoblast, mesoderm core
• tertiary - synciciotrophoblast, cytotrophoblast, mesoderm core, villous capillaries within mesoderm core

Question 4

why is week 3 of embryo development the “week of threes” ?

Answer 4

3 cavities - chroionic, definitive yolk sac, amnionic
3 placental layers - syncytiotrophoblast, cytotrophoblast, extraembryonic mesoderm
3 germ layers - ecto, meso, endoderm
3 body axes - craniocaudal, dorsoventral, R/L

Question 5

function of the:

• amnion
• yolk sac

Answer 5

amnion - line fluid filled amnionic cavity

yolk sac - transfer agent for nutrients, site of primordial germ cells, source of blood cells and blood vessels

Question 6

epiblast cells that migrate through the primitive groove and migrate cranially in the mesoderm along the cranial caudal axis will form the __

Answer 6

notochord

Question 7

what cells is the notochord derived from?

Answer 7

epiblast cells that migrate through the primitive groove and migrate cranially in the mesoderm along the cranial caudal axis

Question 8

what germ layer is the notochord derived from?

Answer 8

mesothelium

Question 9

another name for the notochord is the…

Answer 9

axial mesoderm

Question 10

the notochord is important for 3 reasons:

Answer 10

• signals induction of neural tube, somites, and surrounding structures
• vertebral column and base of skull develop around it
• degenerates to leave behind nucleus pulposus of the intervertebral disc

Question 11

this structure signals the induction of the neural tube, somites, and surrounding structures

Answer 11

notochord

Question 12

the vertebral column and base of the skull develop around this structure

Answer 12

notochord

Question 13

this structure ultimately degenerates to leave behind nucleus pulposus of the intervertebral discs in adults

Answer 13

notochord

Question 14

the location and function of the nucleus pulposus

Answer 14

• located in center of intervertebral discs in adults

- jelly-like structure that functions to distribute compressive loads through hydraulic pressure

Question 15

T/F during gastrulation, the cells in the ectoderm that will ultimately form the heart migrate to just below the oropharyngeal membrane

Answer 15

false - the heart will be derived from cells of the Mesoderm that migrate Above the oropharyngeal membrane during gastrulation (this cranial end will ultimately fold over so these heart deriving cells are located caudally to oropharyngeal membrane)

Question 16

what 2 germ layers are fused at the oropharyngeal and cloacal membranes?

Answer 16

ectoderm and endoderm are fused (no mesoderm)

Question 17

~ what day do the oropharyngeal and cloacal membranes break down?

Answer 17

~ day 26

Question 18

a solid cord of cells that underlies the developing neural tube forming a midline axis and serves as a basis for the axial skeleton. induces the neural plate and sclerotome portion of the somite

Answer 18

notochord

Question 19

describe 7 key structures in the sequence in which they arise in the process of neurulation

Answer 19

• neural plate
• axial neural groove / neural folds
• neural crests
• neural tube
• neural crest cells
• primitive brain
• primitive spinal cord

Question 20

neurulation is…

Answer 20

the process by which the neural tube forms

Question 21

neurulation begins on day __

Answer 21

day 18

Question 22

when the notochord thickens and expands mitotically it forms the…

Answer 22

neural plate

Question 23

folding of the neural plate gives rise to these 2 structures

Answer 23

• axial neural groove

- neural crests

Question 24

this is where the neuroectoderm merges with the somatic ectoderm during neurulation

Answer 24

neural crests

Question 25

fusion of neural folds in neurulation results in the formation of...

Answer 25

the neural tube

Question 26

neural crest cells arise when...

Answer 26

around the time of neural fold fusion to form the neural tube during neurulation, the neural crests detach from the neural tube and migrate into the mesoderm layer

Question 27

the neural crests detach from the neural tube and migrate into the mesoderm to become...

Answer 27

neural crest cells

Question 28

describe the fusion that gives rise to the neural tube

Answer 28

- neural folds approach each other - somatic ectoderm fuses at surface (beginning somewhere mid-axial and zipping up cranially and down caudally) - neural crest cells detach, migrate into paraxial mesoderm - neural tube sinks into mesoderm layer - neural tube folds ventrally to close tube

Question 29

neural crest cell detachment and migration into mesoderm during gastrulation is an example of what kind of transition?

Answer 29

epithelial to mesenchymal transition

Question 30

mesenchyme is..

Answer 30

embryonic connective tissue in the mesoderm

Question 31

T/F fusion of neural folds is due to genetic factors (genes such as sonic hedgehog) and environmental factors (cholesterol and folic acid)

Answer 31

true

Question 32

what day does closure of the neural tube at each neuropore occur?

Answer 32

Anterior/cranial neuropore: ~day 25 | Posterior/caudal neuropore: ~day 28

Question 33

name the four subdivisions of neural crest derivatives

Answer 33

- cranial - cardiac - vagal - trunk

Question 34

examples of neural crest derivatives include:

Answer 34

- connective tissue of bones, neck, face skull - cranial nerve ganglia - heart septum (cavity wall enclosing heart) - dentin of tooth - dermis of head and neck - dorsal root ganglia - enteric nervous system - sympatheitic chain - adrenal medulla - Schwann cells (myelin forming cells in PNS) - glial cells - malanocytes of skin - smooth muscle of head region blood vessels

Question 35

the following are examples of derivatives of what 3rd week structure? - connective tissue of bones, neck, face skull - cranial nerve ganglia - heart septum (cavity wall enclosing heart) - dentin of tooth - dermis of head and neck - dorsal root ganglia - enteric nervous system - sympatheitic chain - adrenal medulla - Schwann cells (myelin forming cells in PNS) - glial cells - malanocytes of skin - smooth muscle of head region blood vessels

Answer 35

derivatives of neural crest cells

Question 36

what are the 2 types of ectoderm in week 3 of development

Answer 36

- neuroectoderm | - surface ectoderm

Question 37

name some derivatives of the surface ectoderm

Answer 37

* epidermis * nails * hair * subcutaneous glands * mammary glands * anterior pituitary * enamel * lens of the eye

Question 38

name some derivatives of the neuroectoderm

Answer 38

* central nervous system * retina * posterior pituitary gland * pineal body

Question 39

``` the following are all derivatives of what 3rd week structure? • epidermis • nails • hair • subcutaneous glands • mammary glands • anterior pituitary • enamel • lens of the eye ```

Answer 39

surface ectoderm

Question 40

``` the following are all derivatives of what 3rd week structure? • central nervous system • retina • posterior pituitary gland • pineal body ```

Answer 40

neuroectoderm

Question 41

what are 2 key regions of the axial mesoderm and why are they important

Answer 41

- cardiogenic mesoderm - at cranial end of embryo, forms heart tubes - axial rod of mesoderm - forms notochord, which strongly influences formation of nervous system and vertebral column

Question 42

what is the importance of the cardiogenic mesoderm?

Answer 42

it is the part of the axial mesoderm that forms the heart tubes at cranial and of embryo

Question 43

what is the importance of the axial rod of the mesoderm?

Answer 43

forms notochord, which strongly influences formation of nervous system and vertebral column

Question 44

from medial to lateral, what are 4 key longitudinal regions of the mesoderm and what do they give rise to?

Answer 44

- axial mesoderm (heart tubes, notochord) - paraxial mesoderm (somites) - intermediate mesoderm (urogenital system) - lateral plate mesoderm (coelum, viscera)

Question 45

what does the paraxial mesoderm give rise to?

Answer 45

somites

Question 46

what does the intermediate mesoderm give rise to?

Answer 46

urogenital system

Question 47

what does the lateral plate mesoderm give rise to?

Answer 47

- coelum (body cavity) - connective tissue and muscle of the viscera - serous membranes

Question 48

what does the coelum refer to?

Answer 48

the body cavity

Question 49

what does the viscera refer to?

Answer 49

the internal organs in the main cavities of the body, esp. those in the abdomen, e.g., the intestines

Question 50

what cells undergo ectodermal to mesenchymal differentiation during neurulation?

Answer 50

neural plate cells

Question 51

which longitudinal region of the mesoderm is continuous with the extraembryonic mesoderm covering the yolk sac and amnion?

Answer 51

lateral mesoderm

Question 52

where do first somites arise from the paraxial mesoderm?

Answer 52

in the occipital region

Question 53

in what kind of sequence to new somites develop from the paraxial mesoderm? until how many somites?

Answer 53

- from cranial to caudal | - until 42 pairs of somites

Question 54

how is the paraxial mesoderm correlated to age of the embryo during week 3 of development?

Answer 54

age is correlated to the number of somite pairs present

Question 55

from inner to outer, what 3 structures does each somite form?

Answer 55

- sclerotome -> bone (axial skeleton) - myotome -> muscle (skeletal muscle) - dermatome -> connective tissue (dermis of skin)

Question 56

what is a scleratome derived from and what does it give rise to?

Answer 56

- from somite (from paraxial mesoderm) | - creates axial skeleton (vertebrae, ribs, occipital bone of skull)

Question 57

what is a myotome derived from and what does it give rise to?

Answer 57

- from somite (from paraxial mesoderm) | - creates skeletal muscle of body, head/neck, and limbs

Question 58

what is a dermatome derived from and what does it give rise to?

Answer 58

- from somite (from paraxial mesoderm) | - contributes to dermis of skin (connective tissue layer of skin)

Question 59

what is a key component that migrates with each sclerotome, myotome, and dermatome derived from a somite?

Answer 59

each has its own segmental nerve component migrating with the developing cells

Question 60

somites and their developing sclerotomes, myotomes, and dermatomes can be classed into what 4 groups?

Answer 60

- occipital - cervical - thoracic - lumbar

Question 61

what is a dermatomal pattern

Answer 61

area of skin supplied by a single spinal nerve

Question 62

what happens to the lateral mesoderm in the trunk ~day 17 of development

Answer 62

develops clefts that eventually split it into two layers associated with the endoderm and ectoderm, and the space between the two layers - splanchnic mesoderm - mesothelial coverings (gut wall) - somatic mesoderm - (body wall) - intraembryonic coelum - primitive body cavity

Question 63

splanchnic mesoderm

Answer 63

formed from the splitting of the lateral mesoderm in the trunk ~day 17, associated with endoderm,, gives rise to mesothelial coverings

Question 64

intraembryonic coelum

Answer 64

primitive body cavity formed from the splitting of the lateral mesoderm in the trunk into splanchnic mesoderm and somatic mesoderm

Question 65

what organ system develops from the intermediate mesoderm

Answer 65

urinary & reproductive systems

Question 66

what is the intermediate mesoderm

Answer 66

in 2-3 week embryo, intermediate mesoderm is mesodermal layer between lateral mesoderm (which is splitting into somatic and splanchnic mesoderms) and the somites / neural tube -develops into the urinary & reproductive systems

Question 67

as folding of the intraembryonic coleum forms a horseshoe pointing up, where is the... - pericardial cavity - pleural cavity - peritoneal cavity

Answer 67

- pericardial cavity - bottom of horseshoe ring - pleural cavity - lateral extensions - peritoneal cavity - lateral extensions

Question 68

summarize week 3 development formations

Answer 68

-gastrulation -major body axes -notochord -primordial nervous system (neural tube) -somites -cardiogenic area -primordial body cavity (still flat trilaminar disk)

Question 69

summarize completion of embryonic period (weeks 4-8)

Answer 69

morphogenesis organogenesis body folding

Question 70

in what week of development does body folding initiate?

Answer 70

week 4

Question 71

in embryonic body folding, the oropharyngeal membrane, cardiogenic area, pericardial cavity, and septum transversum (contributes to diaphragm) are relocated to their appropriate positions by what folding process

Answer 71

head folding

Question 72

in embryonic folding, the cloacal membrane, connecting stalk, and hindgut are relocated to their appropriate positions by what folding process

Answer 72

tail folding

Question 73

what causes head folding?

Answer 73

differential growth at the neural plate

Question 74

what causes tail folding?

Answer 74

growth of spinal cord

Question 75

what causes lateral folding?

Answer 75

growth of somites

Question 76

as abdominal wall form through lateral folding, part of the endoderm of the yolk sac is incorporated into the embryo as the __

Answer 76

midgut

Question 77

what is the yolk stalk

Answer 77

connects midgut (part of yolk sac incorporated into body cavity as lateral folding occurs) to yolk sac (hangs outside folding until abdominal wall closes and disconnects yolk sac

Question 78

3 body cavities in adults

Answer 78

pleural pericardial peritoneal

Question 79

T/F the connecting stalk, which becomes the umbilical cord, is an extension of the yolk sac

Answer 79

false | it is an extension of the chorion

Question 80

at the end of body folding in the embryonic period, the entire embryo is surrounded by the __, which is itself surrounded by the __

Answer 80

amnionic fluid and amnion | chorionic fluid and chorion