BIOMED 2 Flashcards
What is pre-natal development?
Gradual modification + growth of anatomical structures during the period from fertilisation to birth
What does pre-natal development involve?
ntiation of cells
Changes that produce + modify anatomical structures
How long is full-term pre-natal development?
37-40 weeks (approx 9 months)
What are the 3 defined periods of pre-natal development in humans from fertilisation to birth?
Pre-embryonic period
Embryonic period
Foetal period
When does the pre-embryonic period take place and what happens in this period?
0-2w
Early cell division and implantation
Formation of a bilaminar (2-layer) structure
When does the embryonic period take place and what happens in this period?
3-8w
Trilaminar structure forms]Rudiments (basic form) of most organs + tissues develop
When does the foetal period take place and what happens in this period?
9w-birth
Rudiments grow and mature
When do the lip and palate develop?
Between weeks 4-10 of embryogenesis
note: disruptions during this period can leas to cleft lip/palate
Which weeks of development are a critical period for development of the head and neck?
6-9
What are stem cells?
Cells that have the potential to differentiate into more specialised cells
What are the 3 types of stem cells?
Totipotent
Pluripotent
Multipotent
What are totipotent stem cells?
Earliest cells after fertilisation- most potential
What are pluripotent stem cells?
Embryonic stem cells that can develop into different lineages
What are multipotent stem cells?
Can only develop into specific cells within a lineage
eg: haematopoietic stem cells can only differentiate into cells found in blood, not others eg: muscle
What are the 3 germ layers/lineages that pluripotent stem cells in the blastocyst differentiate into?
Ectoderm
Mesoderm
Endoderm
What is the ectoderm germ layer?
Nervous system + skin
What is the mesoderm germ layer?
Heart + blood vessels + muscles + cartilage + bone
What is the endoderm germ layer?
GI tract + associated internal organs
What is the name for a fertilised ovum?
Zygote
What happens in the first week, in the pre-embryonic stage?
Zygote undergoes cell divisions (cleavage)
Produces a morula (ball of 16 identical totipotent cells)
Morula cells differentiate and it develops into a blastocyst, which implants into the wall of the uterus (now pluripotent)
What is the last stage where there are ONLY totipotent cells present?
Morula
Until how many days are scientists allowed to do experiments in pre-natal development?
Up to 14 days
What happens in the second week of the pre-embryonic stage?
Cells in the inner part of the blastocyst differentiate to form a new cell layer
- original layer = epiblast
- new layer = hypoblast
Forms two-layered structure: bilaminar disk
What 2 processes occur during week 3 of development (week 1 of embryonic stage)?
Gastrulation
Neurulation
What is the definition of gastrulation?
The process by which 3 germ layers are established (trilaminar structure)
What is the process of gastrulation?
Epiblast cells (blue) form a primitive streak, and move down into the hypoblast layer, displacing it to form endoderm layer (yellow)
More epiblast cells move between the epiblast and new endoderm layer to form mesoderm (pink)
Epiblast layer becomes known as ectoderm (blue)
What type of stem cells are the 3 germ layers?
Multipotent stem cells
Now called an embryo
What happens to the 3 embryonic (germ) layers?
Organs form by organogenesis
What is the fate of the ectoderm cell layer?
Outer layers of skin
Nervous system
Cornea, lens, pupillary muscle of eye
What is the fate of the mesoderm layer?
Skeleton, skeletal muscle
Smooth muscle
Circulatory system
What is the fate of the endoderm layer?
Epithelial lining of: digestive/respiratory tract + urethra + bladder + reproductive system
Liver + pancreas
What is the definition of neurulation?
Forming the neural tube (brain + spinal cord)
What is the process of neurulation at day 18?
Central tube of mesoderm cells forms notochord (later becomes vertebral discs)
Notochord stimulates ectoderm to thicken, forming a neural plate made of neuroectoderm cells
What is the process of neurulation at day 20?
Neural plate forms 2 ridges which fuse to form neural tube (future brain + spinal cord)
What are the cells on the neural crest called?
Neural crest cells: ectomesenchyme
What is the process of neurulation at day 22-24?
Ectoderm layer forms over neural tube: outer skin of developing embryo
- thus gives rise to neural tube (nervous system) + skin
By when does the neural tube close?
By day 25 (3.5 weeks approx)
Closes at cranial end (brain) & caudal end (spinal cord)
What occurs if the caudal neuropore doesn’t close?
Spina bifida: can be closed or open (open = more serious but rarer)
What occurs if the cranial neuropore doesn’t close?
Anencephaly: incomplete closure of skull, scalp + brain doesn’t develop properly, portions of brain + skull missing, brain tissue usually exposed as not enough skin + bone to cover
What happens at the end of neurulation?
Neural crest cells in anterior region become known as cranial neural crest cells (CNCC)
CNCC migrate to pharyngeal region from neural crest, will start to form outgrowths
What happens in week 4 of development?
New outgrowths + structures start to form
- lens placode (eye)
- optic pit (inner ear)
- heart
- pharyngeal arches (will form mouth, face, head, neck)
Why is the development of the pharyngeal area critical for SLT?
Explains how mouth + lips _ face + jaw + ears + other tissues/nerves involved in speech and swallowing are formed
- can give understanding of how defects in stages can cause changes to normal development of speech
What is the pharyngeal apparatus (3 structures)?
Arches
Clefts
Pouches
How many pharyngeal arches are there?
5 (I II III IV VI, V breaks down/disappears)
Raised part on outside- ectoderm layer
How many pharyngeal clefts are there?
4
On outside- ectoderm layer
How many pharyngeal pouches are there?
4
On inside- endoderm layer
What does each pharyngeal arch have its own source of cells for?
Blood
A specific nerve
Skeletal components
Musculature (mesoderm)
What do the pharyngeal arches form (with some contribution from the pouches + clefts)?
Craniofacial region
What cranial nerve does pharyngeal arch 1 give rise to?
Trigeminal (CN V)
What cranial nerve does pharyngeal arch 2 give rise to?
Facial nerve (CN VII)
What cranial nerve does pharyngeal arch 3 give rise to?
Glossopharyngeal nerve (CN IX)
What cranial nerve does pharyngeal arch 4+6 give rise to?
vagus nerve (CN X)
What are the muscle derivatives from pharyngeal arch 1?
Muscles of mastication (temporalis, masseter)
Myelohyoid: for swallowing/speaking
Anterior belly of digastric: stabilises hyoid bone whilst swallowing
Tensor veil palatini: tenses the soft palate
Tensor tympani: inner ear
What are the muscle derivatives from pharyngeal arch 2?
Muscles of facial expression
Buccinator: blow, chew, suck
Stylohyoid: elevates hyoid bone during swallowing
Posterior belly of digastric: stabilises hyoid bone
Stapedius: smallest muscle in body, moves stapes bone
Platysma: superficial neck muscle
What is the muscle derivative from pharyngeal arch 3?
Sylopharyngeus: elevates pharynx during swallowing
What are the muscle derivatives from pharyngeal arch 4?
Cricothyroid muscle (larynx)
Pharyngeal constrictors: used in swallowing
Soft palate muscles
What are the muscle derivatives from pharyngeal arch 6?
Intrinsic muscles (except cricothyroid) of larynx: moves vocal cords to produce speech
What are the skeletal derivatives from pharyngeal arch 1?
Maxillary prominence: becomes maxilla + zygomatic bone + part of temporal bone + Palestine bone + vomer (part of septum)
Mandibular prominence (made of Meckel’s cartilage): becomes mandible + malleus + incus
What are the skeletal derivatives from pharyngeal arch 2?
Stapes
Styloid process
Part of hyoid bone
What is the skeletal derivative from pharyngeal arch 3?
Hyoid bone
What are the skeletal derivatives from pharyngeal arch 4?
Laryngeal cartilages
Epiglottis
What is the skeletal derivative from pharyngeal arch 6?
Laryngeal cartilages
What is another name for the pharyngeal arches?
Branchial arches
What do the 1st pharyngeal cleft and corresponding pouch develop to form?
Cleft: external ear
Pouch: middle ear cavity + auditory tube
Do the other pharyngeal clefts develop into anything?
No- they grow over and fuse together
What does the 2nd pharyngeal pouch form?
Palatine tonsil
What does the 3rd pharyngeal pouch form?
Inferior parathyroid gland
Thymus
What does the 4th pharyngeal pouch form?
Superior parathyroid gland
Which structure does majority of developmental defects to the pharyngeal apparatus affect?
1st pharyngeal arch, mainly skeletal derivatives
What are 3 skeletal derivatives that may be affected by defects to the 1st pharyngeal arch?
Underdeveloped mandible (severe Class II malocclusion)
Absent/reduced malleus + incus bones (conductive hearing loss)
Malformed external ears
What are 3 rare conditions linked to pharyngeal apparatus defect?
Pierre Robin Sequence- 1:5000
Treacher Collins Syndrome- 1:50,000
Cleft lip and/or palate- 1:700
What is Pierre Robin Sequence?
Underdevelopment of lower jaw
- tongue takes up most of space
- articulation difficulties
- swallowing/feeding difficulties
- resonance disorders
What is Treacher Collins Syndrome?
Underdevelopment of jaw/palate
Hearing loss
