CFD 4 - arches 1

Question 1

What are the 4 fundamental aspects of developmental biology?

Answer 1

• proliferation/growth - size
• pattern formation - right place, right time
• morphogenesis - shape
• differentiation - type

Question 2

What is pattern formation?

Answer 2

the process by which cells in a developing embryo acquire identities that lead to a well ordered spatial pattern of cell activities

Question 3

What is organ rudiment usually triggered by?

Answer 3

an epithelial signal, an induction - allows morphogenesis and proliferation to take place over a specific amount of time

Question 4

What is a signalling centre?

Answer 4

the organiser - will organise specific growth factors to ensure that there are the right types of cells growing for the tissue/structure being formed

Question 5

What are signalling gradients?

Answer 5

within a specific area, you’ll get a switch on of genes which will make that specific tissue
- there’s a gradient of the signal, and only at the right points will it actually form the correct tissue

Question 6

What is cell migration?

Answer 6

cells migrate into the area, do what they need to do and undergo differentiation once they get to where they need to be - e.g. by undergoing EMT or MET

Question 7

What are the primary germ layers?

Answer 7

• ectoderm - skin, neural tube etc
• mesoderm - just about everything else
• endoderm - gut
• (neural crest/ecto-mesenchyme - structures of the head and neck)

Question 8

When does formation of branchial arches usually start?

Answer 8

between days 24/25

Question 9

What developing structure affects how the branchial arches differentiate into the different tissues?

Answer 9

the developing spinal column

Question 10

What cartilage forms in arch 1?

Answer 10

Meckel’s cartilage, a very transient structure

Question 11

What cartilage forms in arch 2?

Answer 11

Reichert’s cartilage, a very transient structure

Question 12

After what point have the transient Meckel’s and Reichert’s cartilages basically disappeared?

Answer 12

after 20 weeks
- there are the odd remnants of Meckel’s cartilage

Question 13

What does Meckel’s cartilage differentiate to form?

Answer 13

certain bone structures within the ear and upper face

Question 14

What does Reichert’s cartilage disappear to form?

Answer 14

the styloid ligament

Question 15

What is the stromatodeum?

Answer 15

developing oral cavity, formed from the disintegration of a layer of cells, allowing growth factors to seep into this area

Question 16

When do the pharyngeal arches appear?

Answer 16

in 4th and 5th week of development

Question 17

What are the pharyngeal arches separated by?

Answer 17

• clefts/grooves - externally
• pouches - internally

Question 18

What causes the development of the pharyngeal arches?

Answer 18

the neural crest cells migrating into the head and neck region

Question 19

What does the first pair of pharyngeal arches form?

Answer 19

the primordium of the jaws (lower and upper jaws)

Question 20

What do the first pair of pharyngeal arches appear as?

Answer 20

• surface elevations lateral to the developing pharynx
• soon the other arches appear and are obliquely disposed around ridges on each side of the future head and neck regions

Question 21

What do the pharyngeal arches exclusively contribute to?

Answer 21

the formation of the face, nasal cavities, mouth, larynx, pharynx and neck

Question 22

What happens to the arches during the 5th week?

Answer 22

the second pharyngeal arch enlarged and over grows the 3rd and 4th arches, forming the ectodermal depression called the cervical sinus

Question 23

What has happened to the arches by the end of week 7 of development?

Answer 23

the 2nd and 4th pharyngeal grooves and cervical sinus disappear, giving a smooth contour

Question 24

What does a typical pharyngeal arch contain?

Answer 24

• an aortic arch - artery that arises from trunk of primordial heart
• a cartilaginous rod that forms the skeleton of the arch
• muscular components that differentiate into the muscles of the head and neck
• a nerve that supplies the mucosa and muscles derived from the arch