Embryology Flashcards
What does the neck develop from?
Branchial/pharyngeal arches
What does the face develop from?
5 mesenchymal process/prominences
What does the skull develop from?
Mesenchyme in the head region of developing embryo
Mesenchyme
Mesenchyme is embryonic connective tissue
What does mesenchyme have the same properties as?
Connective tissue
What does mesenchyme develop into?
- Bone
- Cartilage
- Blood vessels
- ETC.
What 2 areas of the embryo lac mesoderm?
Future site of the mouth and anus
What does notochord formation lead to?
Axis formation in the embryo (embryo now has a right and a left side)
What does the trilaminar disc have on either side?
- Amniotic cavity dorsally (side of ectoderm)
- Yolk sac ventrally (side of endoderm)
How is the neural tube formed?
Some of the ectoderm in the midline folds down to form neural tube
What is the neural tube?
Brain and spinal cord
How are the neural crest cells formed?
Some cells a the crest of the neural fold separate to form the neural crest cells
What happens to the neural crest cells once they are formed?
They migrate and give rise to a wide variety of structures
What happens to the neural crest cells in the head and neck region?
They mix with the mesoderm
What are somites derived from?
The paraxial mesoderm
What do the somites form?
Structures like the axial skeleton and muscles
How many somites develop in total in human embryos?
Around 33
What do somites located in the future head region help in?
Cranial skeleton development
What needs to form in the head and neck region?
- Face to house the special sense organs
- Skull cap and base of skull to protect growing brain
- Palate to separate mouth from nose
- Muscles, skeletal elements to support the neck region
Branchial arches
Series of arches which develop around the future mouth (stomatodeum) and pharynx
How did the branchial arches get their name?
Called branchial because in lower animals (fish) it forms the gills (branchium)
What do the branchial arches support?
Primitive pharynx
What develops from the branchial arches?
Face and neck
How many branchial arches are there?
- In humans 5 branchial arches develop.
- 6 arches start to develop but arch number 5 disappears so we are left with arches 1,2,3,4 and 6
Where is the ectoderm found in the branchial arches?
- Lines the outside
- Also forms clefts in between arches
Where is the mesoderm found in the branchial arches?
- In the middle with the neural crest cells
- Forms the cartilage and muscles
Where is the endoderm found in the branchial arches?
- On the inside
- Also forms pouches in between the arches
Which nerve is associated with the 1st branchial arch?
Mandibular branch of the trigeminal
What nerve is associated with the 2nd branchial arch?
Facial nerve
What nerve is associated with the 3rd branchial arch?
Glossopharyngeal nerve
What nerve is associated with the 4th branchial arch?
Superior laryngeal branch of the vagus
What nerve is associated with the 6th branchial arch?
Recurrent laryngeal branch of the vagus
Which branchial arch are the muscles of the face derived from?
2nd branchial arch
What is the anterior belly of the digastric muscle innervated by?
Mandibular division of the trigeminal nerve
What is the posterior belly of the digastric muscle innervated by?
Facial nerve
What forms form the branchial arches around the future pharynx?
Skeletal elements
What skeletal structure is derived from the 1st branchial arch?
Mandible
What skeletal structure is derived from the 2nd branchial arch?
Hyoid body and lesser horn
What skeletal structure is derived from the 3rd branchial arch?
Hyoid body and greater horn
What cartilaginous structure is derived from the 4th branchial arch?
Thyroid cartilage
What cartilaginous structure is derived from the 6th branchial arch?
Cricoid cartilage
Other than bone, cartilage and facial muscles, what other important structures develop from the branchial arches?
- Tongue
- Thyroid gland
- Parathyroid glands
- Part of the pituitary gland
What are the 5 processes/prominences that the face develops from?
-1 frontonasal process
-2 maxillary processes
2 mandibular processes
What does the frontonasal process of the face develop from?
From mesenchyme superior to future mouth
What do the 2 maxillary processes of the face develop from?
From the maxillary part of the 1st branch arch mesoderm
What do the 2 mandibular processes of the face develop from?
1st arch mesoderm
Why is it important to understand the origins of the face?
To understand how congenital facial defects such as clefts develop
Where do the 2 mandibular processes of the face fuse?
Midline
How is the nostril formed?
Ectodermal thickening occurs (nasal placode) which pushes inwards or invanginates to form the nasal pit leading to nostrils
How is the philtrum formed?
The medial nasal process further gowns downwards and laterally to form the philtrum
What is the 1st stage in the development of the palate?
- Medial nasal process grows downwards and forms philtrum.
- This forms the primary palate
What is the 2nd stage in the development of the palate?
From the maxillary processes, two palatine shelves grow inwards
What is the 3rd stage in the development of the palate?
The palatine shelves meet in the midline to form the secondary palate
How are the oral cavity and nasal cavity separated?
Formation of the palate
What is the cranial vault?
Flat bones of the skull
What is the base of the skull?
Irregular bones of the skull
What is the viscerocranium?
Skeleton of the face
How is the cranial vault formed?
Formed from membranous bones by membranous ossification calvaria
How is the base of the skull formed?
Bones formed by endochondral ossification
How is the viscerocranium formed?
Partly form the branchial arches and partly from sensory (special sense) capsules
When does the anterior fontanelle close?
At 1.5 years
What is the cranial vault formed from?
Mesenchyme derived from mesoderm that lies above the surface of developing brain ossify directly (membranous ossification)
Why is the cranial vault not fully formed at birth?
Sutures between bones are soft to allow for deformation during passage through birth canal and brain development
Craniosynostosis
Premature fusion od the suture joints leading to abnormal development of the skull and brain
How is the base of the skull formed?
- Mesenchyme around notochord is derived predominantly from neural crest cells
- Preform in cartilage first
- Later they ossify
What are sensory capsules derived from?
Mesoderm of the somites in head and neck region
What do the sensory capsules preform?
They preform in cartilage and ossify to form bones around the sense organs
What do the sensory capsules form?
- Partly base of the skull
- Partly viscerocranium
What forms the brain?
Neural tube
What forms the skull cap?
Membranous bones over growing the brain
What is the name of the 1st pharyngeal arch abnormality?
Treacher Collins Syndrome
