Lecture 14 - Differentiation of the Ectoderm + Organ Development Flashcards
What part of the ectoderm makes up the neural ectoderm and what does the neural ectoderm give rise to? (2)
The part of the ectoderm that is closer to the midline becomes the neural ectoderm
Neural system
Neural crest cells
What part of the ectoderm becomes the non-neural ectoderm and what does the non-neural ectoderm give rise to? (4)
The part of the ectoderm that is further away from the midline
Epidermis of skin
Associated structures:
- hair
- nails
- tooth enamel
Describe the formation of the neural plate
Cells on the ectoderm placed along/near the midline change shape to become tall + columnar (3rd week of development)
This raised/elevated appearance is the neural plate
Describe the appearance of the neural plate in regards to width along the embryo and what each end will eventually give rise to
Wider at the rostral end - brain
Narrower towards more caudal levels - spinal cord
Describe the process of primary neurulation
The central area of the neural plate shifts downwards (neural groove)
Outer edges of the neural plate rise + curl upwards and inwards (neural folds)
Neural folds eventually meet at midline and fuse
When neural plates fuse, a neural tube is formed
Describe the process of the closure of the neural tube
Begins at neck level and proceeds causally and rostrally (like a zipper)
The neural tube does not initially close fully
- rostral neuropore
- caudal neuropore
What condition occurs when the rostral neuropore fails to close?
Anencephaly - lethal - majority of brain does not form
What condition occurs when the caudal neuropore fails to close?
Spina bifida - treatable depending on severity - sac filled with spinal fluid and sometimes part of the spinal cord formed on external lower back
How many births does failure of neuropore closing affect?
1 in 1000 live births
How does the neural crest arise?
As neural folds arose, a small group of cells differentiate at the place that will become the tip of the neural folds - neural crest cells
What do neural crest cells do?
Neural crest cells become mesenchymal and migrate out of the lateral edges to invade different parts of the embryo and contribute to the production of a variety of tissues
What contribution does neural crest cells give at the level of the spinal cord (trunk neural crest)?
- gives rise to the PNS by producing neurons that carry sensory information from the body to the CNS and the neurons that will carry motor information to the gut
- hormone secreting cells of the adrenal gland
- melanocytes
What contribution does cranial neural crest cells give to the body?
Gives rise to cartilage, bone and muscles of the face + neck
What is the brain and spinal cord derived from?
The neural plate
What does the rostral region of the neural tube exhibit by the 4th week of development?
3 fluid filled brain vesicles/enlargements + a narrow tube behind these that will give rise to the spinal cord
Name the 3 brain vesicles and what they correspond to
Telencephalic vesicle - forebrain
Mesencephalic vesicle - midbrain
Rhombencephalic vesicle - hindbrain
What cells is the formation of the head primarily the result of?
Cranial neural crest cells
_____ neural crest cells give rise to a larger variety of tissue types than _____ crest cells
Cranial neural crest cells give rise to a larger variety of tissue types than trunk crest cells
What structures do cranial neural crest cells give rise to? (6)
Neurons
Glia
Melanocytes
Muscle, bone and cartilage of lower face
Where and when do the paryngeal arches form?
Develop on either side of the embryo at the level of the future head and neck during embryonic folding
What is the inside, middle and outside of the arches composed of?
Inside - endoderm
Middle - mesoderm
Outside - ectoderm
What 3 structures can be found inside each pharyngeal arch?
Cartilage, blood vessel, nerve
What separates the pharyngeal arches on the inside of the embryo?
Pharyngeal pouches
What separates pharyngeal arches on the outside of the embryo?
Pharyngeal clefts
What do the pharyngeal arches give rise to? (3)
Muscles of facial expression
Bones + muscles in theist
Cartilage in pharynx
What contribution does cranial neural crest cells give to the pharyngeal arches? (3)
Formation of the skeleton
Connective tissue
Some of the sensory ganglia of the PNS
What does the endoderm layer of the pharyngeal arch contribute to? (2)
Some glands
Epithelium of pharynx
What does the mesoderm layer of the pharyngeal arch contribute to? (2)
Head and neck muscles
Blood vessels
What does the ectoderm layer of the pharyngeal arch contribute to? (2)
Epithelium of the mouth and face
Some sensory ganglia of the PNS
Derivatives of the first pharyngeal arch: bones (6)
Maxilla (upper jaw)
Mandible (lower jaw)
Maleus and incus of the middle ear
Alisphenoid bone
Squamous part of temporal
Zygomatic
Derivatives of the first pharyngeal arch: muscles of mastication
Masseter
Temporalis
Derivatives of the first pharyngeal arch: nerves (2)
Mandibular nerve
Maxillary nerve
(Both are branches of the trigeminal nerve)
How many swellings are formed by the end of the 4th week?
Five
What are the five initial swellings formed by?
Neural crest + some mesenchyme originating from the cranial somitomeres corresponding primarily to the first branchial/pharyngeal arch
Name the 5 facial prominences and what they eventually give rise to
Fronto-nasal prominence - forehead
Medial nasal prominence - medial pit fuses to form the central pit of the upper lip (philtrum); middle (bridge) of nose
Lateral nasal prominence - sides of the nose and nostrils
Maxillary prominence - increases in size and pushes medial nasal prominences towards midline, forms upper lip with 2 medial prominences + 2 maxillary prominences
Mandibular prominence - lower lip and jaw formed by 2 mandibular prominences growing towards midline and eventually fusing
What is cleft lip the result of?
Failure of the medial nasal process + maxillary nasal process to fuse, affects 1/1000 live births
What are abnormalities in the outer and middle ear the result of?
Defects in development of the 1st pharyngeal arch
What is the first functional organ to develop in the embryo?
The heart
Describe the formation of the primitive heart
Cells that will give rise to the heart found as two patches (heart fields) near the rostral end (anterior third) of the primitive streak
Primitive heart cells organise into two tubes, move towards midline and fuse
At 3 weeks - fusion of two heart primordial tubes = one tube, able to contract
At 4-5 weeks - heart has two chambers - primitive atrium + primitive ventricle
A series of morphogenetic events (heart looping) transforms primitive heart into four-chambered heart
Describe the process of heart looping
Initially, blood flows in at the caudal end via sinus venosis, pumped out at cranial end via bulbus cordis
Rostral end
BC
PV
PA
SV
Caudal end
Tube folds:
PV moves caudally
PA moves rostrally
PA + SV both moved dorsally too
Two ventricles formed by the formation of the internal interventricular septum
PA - LA + RA
What is the purpose of the embryonic circulatory system?
Access to gases and nutrients in the absence of functional lungs + intestines
Name the 3 embryonic circuits and their functions
Intraembryonic circuit - serves tissue of the embryo
Vitelline circuit - gathers nutrients from the yolk sac
Umbilical circuit/Allantois - gets rid of nitrogenous wastes into the allantois, brings in nutrient and oxygen rich blood from the placenta
What happens to the aortic arches one the pharyngeal arch they’re associated with disappears?
The aortic arches give rise to the artery that supplies blood to the derivatives of their respective pharyngeal arches
