Lectures 1 and 2 Flashcards
What is gestation?
It is the period between conception (fertilization) and birth
Typically 9 months for humans
What is a fetus?
Latin word for offspring
What is pre-natal?
Before birth
What is mesenchyme?
General term for embryonic connective tissue
Will develop into a lot of parts of the body
What is oogenesis?
Formation of a mature oocyte/egg from a small germ cell precursor initiated during the embryonic period
What is a polar body?
One of two small cells produced in the ovum during meiosis and then degenerates
It cannot be fertilized
It is necessary for fertilization and then goes away
What is a ploidy?
Number
What is a diploid?
Double number
Double the number of chromosomes found in a mature germ cell (sperm or egg)
Human cells are diploid
46 chromosomes
What is a haploid?
Germ cells (sperm or egg)
Only 23 chromosomes
What are germ cells?
Egg and sperm
When does development of humans begin?
Fertilization
What does fertilization result in?
A zygote
What is a zygote?
A single celled organism that will continue to divide and develop
What does a zygote turn into 3-4 days after fertilization?
Morula
Where is the morula typically located in the body?
Entering the uterine cavity
What does a morula turn into?
Blastocyst
What is a blastocyst?
It is when cells arrange themselves into an inner and outer cell mass
Where are blastocysts located?
Implants into the uterus
Can there be pregnancy without implantation?
No
What are the carnegie stages of development?
A system used to describe the apparent maturity of embryos
Based on physical features
Not dependent on chronological age or size of embryo
What is postovulatory age?
Used by clinicians to describe the maturity of an embryo
Refers to the length of time since the last ovulation before pregnancy
What can postovulatory age predict?
Due date of baby
Why is it important to know the postovulatory age?
Important to know to meet all pregnancy milestones
What are the three stages of development?
Pre-embryonic period
Embryonic period
Fetal period
What is the pre-embryonic period?
After fertilization to about the end of the 2nd week of gestation
Germ cells (three germ layers) develop
What is the embryonic period?
About the 3rd to the 8th week of gestation
Major period of organ development
What is the fetal period?
About the 3rd month (9 weeks) post-fertilization to birth
Rapid growth and maturation
What develops during the pre-embryonic period?
The three germ cells
What are the germ cells?
They are comprised of three layers
Give rise to all fetal tissues and organs
Besides the germ cells, what else develops during the pre-embryonic stage?
Nervous and cardiovascular system
Start 3rd week of development
Why do the nervous system and cardiovascular system develops so early?
They are very important for sustaining life
What two layers does the inner cell mass divide into during the beginning of the second week?
Epiblast and hypoblast
When does gastrulation start?
The third week of development
What happens during gastrulation?
The rapid process by which the blastocyst becomes a gastrula
The three germ layers are acquired
What is the source of all three germ layers?
The epiblast
T/F: the hypoblast sort of becomes part of the endoderm
True
What marks the start of gastrulation around day 15 of development?
The primitive streak
What is the primitive streak?
An elongated groove originating from the anterior epiblast
What is the primitive node?
A node situated at the cranial tip of the primitive streak
Acts as an embryonic organizer
What is the primitive node consisted of?
Mesoderm cells that give rise to the notochord (primitive backbone)
What is the function of the primitive node?
It organizes cells during development
It tells cells where they need to be
What is the depression of the primitive node called?
Primitive pit
Gastrulation
What does ectoderm give rise to?
CNS
PNS
Schwann cells and meninges
Sensory epithelium of the ear, nose, and eye
Lens of the eye
Subcutaneous glands and pituitary gland
Bones and connective tissue of craniofacial structures
Epidermis (outermost skin layer)
Hair and nails
Enamel of teeth
What does mesoderm give rise to?
Supporting tissue (cartilage and bone)
Dermis
Straited and smooth muscle
Blood and lymph cells
Walls of the heart, blood, and lymph vessels
Kidneys, gonads, and corresponding ducts
Spleen
What does the endoderm give rise to?
The gastrointestinal system (main one)
The epithelial lining of respiratory tract
Epithelial lining of the lymphatic cavity and eustachian tube
The parenchymal cells of the thyroid and parathyroids, liver, and pancreas
What develops during the embryonic period?
All major organ systems begin and/or undergo major development
Why is the embryonic period of development critical?
Exposure to teratogens (drugs, infections, or toxins) can result in either death of the embryo or major congenital anomalies affecting multi-organ systems
Which organs are affected the most by teratogens?
It depends on when the exposure occurred and which system was at the most crucial stage of development at the time
Is radiation typically a big problem at the embryonic stage of development?
Yes
Do some teratogens only effect certain organs and structures?
Yes
Such as thalidomide only effecting limbs
What is organogenesis?
When the ectoderm, mesoderm, and endoderm develop into the internal organs
Cells of each layer proliferate, migrate, reaggregate, and differentiate into various tissues that form organs
When does organogenesis happen?
During the embryonic period
When does development of the brain and spinal cord begin?
Week 3
What does the CNS develop from?
The neural tube
What does the PNS develop from?
Neural crest cells
Where are neural crest cells located?
Along the sides of the spinal cord
What are the divisions of the primitive brain?
Prosencephalon (forebrain), Mesencephalon (midbrain), and Rhombencephalon (hindbrain)
How is the neural tube formed?
By the closure of ectodermal tissue
Where are neural crest cells located?
Dorsolateral to the developing spinal cord
Do neural crest cells separate into clusters?
Yes, these clusters develop into a variety of tissues
Incomplete development of the neural tube results in what?
Spina bifida
What is spina bifida?
Some vertebrae overlaying the spinal cord are not fully formed and remain unfused and open
If the opening is large enough, a portion of the spinal cord will protrude through the opening in the bones
There may or may not be a fluid filled sac surrounding the spinal cord
Is spina bifida common?
It is one of the most common birth defects (1 in every 1000 births)
Can spina bifida be surgically closed/corrected?
Yes, but it does not restore normal function to the affected part of the spinal cord
Could result in paralysis
What is believed to be the cause of spina bifida?
Combination of environmental and genetic factors
After having one child with the condition, risk for a second increases by 4%
Incidence can decrease up to 70% when the mother starts taking folic acid supplements early in pregnancy
What is the most common location for spina bifida?
Lower back
Can you carry a gene, but never get the disease due to environmental factors?
Yes
What results when other parts of the brain remain unfused?
Encephalocele
What is the most common location for encephalocele?
Lower back and sacral areas
What is the most common encephalocele?
Myelomeningocele, leads to disability in most effected individuals
Are the terms spina bifida and myelomeningocele used interchangeably?
Yes, but they are actually different
What is a chiari malformation?
Skull is smaller than normal or misshapen
Forces the cerebellum to be pushed down into the foramen magnum and upper spinal cord
What could a chiari malformation lead to?
Causes pressure on the cerebellum and brainstem that may affect function controlled by these areas and block the flow of CSF (hydrocephalus)
What is the most common chiari malformation?
Type 2
What is chiari malformation II?
It is the most common one
It can co-exist with encephalocele or spina bifida
Cerebellum and brainstem extend further into the foramen magnum than normal and also into the upper spinal cord
Normal flow of fluid out the brain can be obstructed, causing hydrocephalus
What is a dermatoid cyst?
A benign tumor
Can occur in combination with spina bifida in the medial sacral region
If a fistula stays connection with an existing dermoid cyst, it indicates the location of the non-closure of the primitive neural tube
The cyst represents the last place of separation between the superficial ectoderm and the neuroectoderm
What is anencephaly?
A condition in which the portion of the neural tube that will become the cerebellum does not close
The baby will be born without a forebrain and a cerebellum
The remaining parts of the brain are often not covered by bone or skin
Is anencephaly deadly?
Yes, most babies with this are either stillborn or die shortly after birth
Can zika cause anencephaly?
Yes, it also effects the auditory system
When does the cardiovascular system begin to develop?
Week 3 of gestation
What happens to the cardiovascular system by week 4?
The primitive heart divides into two ventricles
What happens to the cardiovascular system by week 7?
The septum communication between the two chambers is closed off
Is the heart very large in a fetus?
Yes, it decreases in size after the atriums are formed and before birth
When does the respiratory system begin to develop?
Begins at week 3
When does the laryngotracheal tube form?
Week 4
What is the laryngotracheal tube?
The precursor to the trachea and larynx
T/F: the primitive pharynx is also present by week 4
True
T/F: doctors of a pre-me baby will give the mother medication to help the lungs mature, so the baby can breathe on its own when born
True
When does the primitive gut form?
Week 4
Are there divisions of the primitive gut?
Yes, foregut, midgut, and hindgut
When does the urinary system start to develop?
Kidneys - week 4
Producing urine - week 11
Is the gender of the fetus determined at fertilization?
Yes
Which parent chooses the gender?
The father
When do gonads (testes and ovaries) begin to develop?
About week 7 of gestation
When can gender of the baby be determined?
Between weeks 18-22
This is because external genitalia are formed at this time
How large is an embryo at the end of the embryonic period?
About the size of a jellybean
How large is the head of an embryo in comparison to its body at the end of the embryonic period?
It makes up about 50% of its length
What physical features can be seen at the end of the embryonic period?
Facial features and ears are distinguishable
Ears are low-set
Future eyes are visible
Formation of upper and lower limbs are visible
What is the fetal period characterized by?
Maturation of tissues and organs and rapid growth of the body
Do teratogens cause any physical malformations in the fetal period?
No, it is not likely
Major organ systems have been established by this time
Can teratogens play any role in development when exposed during the fetal period?
Yes, they still may interfere with growth and normal function
But they will appear physically normal
Can teratogen exposure during the fetal period cause cell death in the CNS, and therefore postnatal behavior abnormalities?
Yes
What are some developmental disorders that are believed to occur during the fetal period?
Central auditory processing disorders
Learning disabilities and language issues
What are some characteristics of the fetal period?
Relative head size decreases
Completion of the development of the organ systems
Hair appears on the head and body
Fetus gains weight from the development of subcutaneous fat
Fetus is getting ready for extrauterine life
During which weeks do the major features of the ears, face, and palate emerge during the embryonic period?
Weeks 4 through 8
Does each ear section have a unique embryologic origin?
Yes, because they all have a different function
What day post conception do the branchial arches form?
Day 22
Initially, how many arches are there?
6
But arch 5 disappears and 4-6 fuse together
Which arches are critical for the development of the face, outer, and middle ear?
1st and 2nd
T/F: Mesoderm arches develop into the facial and auditory muscles?
True
What are the arches separated by externally?
Clefts
What are the arches separated by internally?
Pouches
T/F: Each arch, cleft, and pouch gives rise to different structures
True
Does each arch have it’s own artery, nerve, and cartilage?
Yes
What is the EAM formed from?
The 1st and 2nd pharyngeal clefts
What is the process of the EAM being formed?
Initially, it is lined with a meatal plug
EAM formation begins around week 6 with the invagination of the 1st pharyngeal cleft
EAM formation ends week 26 with recanalization (opening) of the meatal plug
How long does it take the EAM to fully develop?
6 or 7 years
What do the clefts or grooves from the 2nd, 3rd, and 4th arches form?
Cervical sinuses
They later disappear
If they don’t, they form the lateral or branchial cysts or fistulas
Are lateral or branchial cysts or fistulas dangerous?
Not unless they get larger or infected
What is the outer layer of the TM formed by?
The ectodermal meatal plug of the EAM
What is the middle layer of the TM formed by?
The middle layer is mesoderm derived from neural crest cells
What is the inner layer of the TM formed by?
The inner layer is endoderm and the epithelial lining of the tympanic cavity
When does the formation of the middle ear start and end?
Starts week 8 of gestation and ends about week 21
What is the middle ear formed by?
The tubotympanic recess (extension of the first pharyngeal pouch)
What is the tubotympanic recess derived from?
Endoderm
What two sections does the first pharyngeal pouch (tubotympanic recess) break into?
Proximal extension (future eustachian tube)
Distal extension (future tympanic cavity)
What is in the ME and clears out mucous and pathogens out through the eustachian tube?
Motile cilia
What develops these cilia in the ME cavity?
Neural crest cells
What happens if these cilia break down?
ME infections
Do the ossicles develop independently of the tubotympanic recess with neural cell contribution?
Yes
What are the ossicles derives from?
The first and second pharyngeal arches
Are all of the ossicles derived from the same arch?
No, they all have unique origins
What are the ossicles made up of and surrounded by during development?
Cartilage
Mesenchyme
Do all bones start from cartilage?
Yes
What happens to the ossicles during the 8th month of gestation?
The tympanic cavity envelops them
What middle ear muscles and bones are derived from the first pharyngeal arch?
Tensor tympani
Malleus and incus (derived from the cartilage of the first arch)
What middle ear muscles and bones are derived from the second pharyngeal arch?
Stapedius muscle
Stapes (derived from the cartilage of the second arch)
What nerves are associated with the first and second arches?
First - trigeminal
Second - facial
What does the pinna develop from?
6 mesenchymal projections (auricular hillocks)
Produced by the migration of the neural crest cells
Where are the hillocks located?
Between the first and second pharyngeal arches
Three on each side of the ear canal
When do the hillocks arrive on the branchial clefts?
Week 5
When do the hillocks enlarge and fuse to form the pinna?
Week 7
When is pinna formation complete?
Week 30
Where are the branchial clefts in comparison to the arches?
Outside
Develops external structures like the pinna
Is the pinna fully developed when born?
No, continues to grow with time
Is formation of the pinna a complex process that can lead to abnormalities?
Yes
Might indicate problems with the EAM, ME, or inner ear
Because all develop from the brachial arches
If one thing is off, they might all be off
What three pinna structures come out of the 1st pharyngeal cleft?
Tragus, helix, and cymba
What three pinna structures come out of the 2nd pharyngeal cleft?
Antitragus, antihelix, and concha
What are the major features of the syndromes that result from the malformation of the 1st and 2nd arches, pouches, and clefts?
Cleft lip with or without cleft palate
Micrognathia (small lower jaw)
EAM abnormalities with or without pinna abnormalities
Will all three major features be present for the syndromes that result from the malformation of the 1st and 2nd arches, pouches, and clefts?
No, but at least one will be present
What are some 1st and 2nd arch syndromes that affect the auditory system resulting in hearing loss and other auditory abnormalities?
Treacher Collins syndrome
Pierre Robins syndrome
Stickler syndrome
What are some characteristics of Treacher Collins syndrome?
Small lower jaw
Poor development of the mouth (large)
Mandible underdeveloped
Peanut ear
What are some characteristics of Pierre Robin syndrome?
Smaller lower jaw
Tongue placed further back in mouth and large
Cleft palate
Can result in difficulty breathing and eating
Otitis media and conductive hearing loss
What type of hearing loss is most common with 2nd arch syndromes?
Conductive
2nd arch develops the outer ear and ossicles
What are some characteristics of Stickler syndrome?
Distinctive facial features
Underdeveloped middle of the face
Small lower jaw
Myopia and retinal detachment
Conductive or mixed hearing loss
Joint problems in early age (arthritis)
What does the hindbrain (rhombencephalon) subdivide into?
Pons and medulla oblongata
Both play a part in the development of the inner ear and sensory organs
When does the first indication occur that the inner ear is forming?
Day 22
What develops into the inner ear?
Otic placode (ectoderm)
What does the otic placode form once it invaginates?
The otic pit
Located dorsal to the 2nd pharyngeal cleft
When does complete invagination of the otic placode happen?
Day 26
What is the period from the thickening to the invagination of the placode called?
Otic induction
Why can so many genes cause hearing loss?
Because a number of genes are implicated in the process of otic induction, the disruption of which can cause inner ear abnormalities and hearing loss
What do the neural crest cells that the otic placode is parallel to form?
TM
Ossicles
Otic capsule and sensory neurons
What are the ventral and dorsal portions of the otic vesicle (week 4)
Ventral - saccule and cochlear duct (future scala media)
Dorsal - utricle and semicircular canals, endolymphatic duct
When are the 2 3/4 turns of the cochlea complete?
Week 8
How is the cochlea connected to the saccule?
Ductus reuniens
How do the utricle and saccule communicate?
Utricolosaccular duct
Where does the endolymphatic duct lead to?
The dura mater
When does the mesenchyme around the inner ear labyrinth turn into a cartilaginous otic capsule?
Week 9
Why is the otic capsule necessary?
Proper development of the inner ear and for housing perilymph
Will eventually become the petrous portion of the temporal bone (bony labyrinth
What is the auditory nerve formed from?
Neural crest cells
When does the cartilage around the cochlear duct for the scala vestibuli and scala tympani?
Week 10
When does the cochlea exit the cell cycle?
Week 7 to 8
What does it mean to exit the cell cycle?
You are done will cell development
For hair cells, because they exit the cell cycle so early, those hair cells can never be grown back
What are the two ridges that are formed from the epithelial cells in the cochlear duct?
Inner ridge - will form the future spiral limbus, forms the tectorial membrane
Outer ridge - will give rise to the 3 rows of outer hair cells and the 1 row of inner hair cells
When is the cochlea developed and functional?
At the end of the 5th month of gestation
What do the semicircular canals appear as at the 6th week of gestation?
Flattened out-pockets of the utricular portion of the otic vesicle
The central portions of the out pockets eventually disappear and the canals are formed
The end of each canal dilates to form the crus ampullare
T/F: The semicircular canals, utricle, and the saccule are all filled with endolymph
True
T/F: The fluid between the outer bony covering and the semicircular canals is perilymph
True
What kind of motion are the three semicircular canals sensitive to?
Angular motion
What kind of motion are the utricle and the saccule (macculae) sensitive to?
Linear motion
Where are otoliths?
In the utricle and saccule
