Embryology Flashcards
what is mitosis
cell division of all somatic cells in the human body
what is the funciton of mitosis and what does it produce
- Functions to produce cells for growth, repair and cell replacement
- Occurs in 5 phases
- Produces 2 daughter (identical) cells from 1 parent cells
what is meiosis
process of 2 successive cell divisions of gametes (sex cells)
what does meiosis produce
- Occurs in 2 cycles
* Produces 4 daughter cells with a haploid number (half the number of chromosomes, 1 set)
what is gametogenesis
the process of cell division that coverts an embryonic cell into a mature gamete (sperm or ova)
what is spermatogenesis/oogenesis
- Spermatogenesis= formation of sperm
* Oogenesis= formation of egg
what is fertilization
the combination of a sperm and an egg
- only one sperm will penetrate an ova
what is a zygote
- Fertilisation of the egg by a sperm
- It is a single cell (approx. 100 microns) thinner than hair
- Contains all the genetic information necessary to for a new person (23 chromosomes)
What is a zygote surrounded by
Surrounded by a thick, transparent membrane called a Zona Pellucida, till implantation
How does a zygote become an embryo
- Once a zygote travels through the fallopian tube and into the uterus it then implants into the wall of the uterus–> endometrial lining
- Once the zygote undergoes implantation, it becomes an embryo (approx. week 2)
- It remains an embryo from week 2 to week 8
What is a fetus
- From the end of the embryonic stage to birth (from week 8 onwards)
- All major organs and tissues are visible by this point however they have not yet developed
What is cleavage
- cell division without growth
- cell size gets smaller as cell division continues but the zona pellucida stays smae size
- results in a single cell to multi-cell organism
what is a morula
- a solid ball of cells resulting from division of an ovum
- Usually forms when cell division reaches 16-32 cells
how does the blastocoele cavity form and what day does it occur
- day 5
- The morula begins to absorb fluid and a cavity (blastocoele) forms
how do cells in the morula re-organise and what do they form on day 5
•Inner cell mass (ICM)–> what will eventually become the embryo and fetus
•Trophoblast–>a single thin layer epithelium which will develop into a large part of the placenta (provides nutrients to the embryo)
-Trophoblast and inner cell mass consist of different cell types
what is a blastocyst
an embryo which has developed to the point of having 2 different cell components and a fluid cavity
-hence when ICM and trophoblast form
What occurs at day 6 post fertilisation
- The blastocyst begins to hatch from its shell
- This is because the cells are still confined within the zona pellucida and hence cannot get any bigger–> in order to grow it must hatch out of its zona pellucida ‘shell’
- This allows the blastocyst to grow to its full size
where and when does fertilisation occur
occurs 7 days after fertilisation in the uterus
what is fertilisation
the fastening of the embryo to the wall of uterus
how does the embryo embed into the endometrial lining
- Trophoblast releases villi that attach to the endometrium and anchors itself to the endometrium
- It will then dig itself into the endometrium, until the egg is completely covered in the endometrium
what is an atopic pregnancy
when the blastocyst is not imbedded in the endometrium but in some other place such as fallopian tube etc; these type of pregnancies
what are the main events of week 1 of embryological development
Fertilisation Zygote Cleavage Morula Blastocyst Implantation
What are the main events of week 2 of embryological developmen
Cell Division
Differentiation of blastocyst
Bilaminar germ disc formation
Start of the uteroplacental circulation
There is a slight infolding of cells at the caudate end
how is the bilaminar embryonic disc produced
The inner cell mass differentiates into 2 layers of cells, producing a bilaminar embryonic disc
what is the bilaminar disc composed of
- Epiblast (future embryonic ectoderm and mesoderm)–>layer of high columnar cells, not in contact with the blastocyst cavity
- Hypoblast–>layer of small, cuboidal cells still in contact with the blastocyst cavity
- Primitive yolk Sac–>provides nourishment to the embryo
- Amnion space above between a single layer of epiblast cells
what is the purpose of the bilaminar germ disc
- The bilaminar germ disc is the beginnings of embryo and involves cell differentiation
- This is a process of induction
What are the main events of week 3 of embryological development
- granulation
- trilaminar germ disc
- notochord formation
- somite formation
what is granulation
- formation of trilaminar disc layer from bilaminar
- from the bilaminar layer, cells migrate towards primitive streak–> line at which cells fold in epiblast layer
- epiblast starts to form 2 layers (mesoderm and endoderm) and itself becomes the ectoderm
what is the notochord
- Derived from mesoderm primarily
- Defines the midline
- Forms a tube and then solid cylinder–>enables embryo to form around it
- Eventually becomes vertebral bodies
what are somites
-From mesoderm
-Form the vertebral bodies, ribs and differentiate and become voluntary muscle
-Axial skeleton, voluntary muscle
-Skin dermis
-Organises vertebral alignment and peripheral NS
37 somite pairs:
•1-4 - occiput, bones of face and inner ear
•5-12-cervical spine
•13-24-thoracic spine
•25-29-lumbar spine
•30-34-sacral vertebrae
•35-37-coccyx
What is the ectoderm layer in the trilaminar germ disc for
outermost layer; central and peripheral nervous systems (all neural tissue, brain, spinal cord), lining of respiratory and digestive systems
What is the ectoderm layer in the mesoderm germ disc for
intermediate layer; skeletal and muscular systems, cardiovascular system
What is the ectoderm layer in the endoderm germ disc for
respiratory and digestive tracts–>innermost layer, hence affects inside structures
what is the placenta for
- Develops from the trophoblast
- Highly specialised organ that supports growth and development of embryo and fetus
what are the functions of placenta
Gas exchange Nutrient uptake Thermos-regulation Waste elimination Fights internal; infection-->Won’t fight major infectors, only minor once, hence mother needs to be immunised Produces hormones to sustain pregnancy
what are the main events of week 4 of embryological development
Beginning of organogenesis–> when all the basic organs start to develop
- Differentiation of the somites and the NS
- Segmental development and integration
- Limb buds
- Rudimentary heart and lungs (as well as beginning of other body systems)
what is neuralation
- formation of neural tube
- Conversion of neural plate into a neural tube by a process of folding
- CSF flows through here
- Fold starts at somite 5
- Proceeds in both cephalad and caudal directions
what is the limb development for the embryo
Limb buds appear on day 24 (mid-week 4)
Growth occurs from weeks 4-8 (including rotation of the limbs)
UL is slightly earlier than LL
Hand plates appear by day 33
Digital rays appear by week 6 (UL) and week 7 (LL)
how does lung/respiratory development occur
Lung buds start forming during the 4th week
Initially appear as the respiratory diverticulum, which is a ventral outgrowth of foregut endoderm
Lungs are immature at birth
Post-natal increase in bronchioles, growth and maturation of alveoli and lungs
Lungs are fluid filled at birth the first breath expels fluid
Surfactant on surface of alveoli
How does the heart develop
Heart begins to beat 22-23 days
Blood flow during 4th week
Septation= separate chambers ~ 6th week
Prenatal and postnatal circulation different
At birth foramen ovale (between atria) is open and closes early in neonatal life
how does the trachea and oesophagus develop
Splitting of foregut into oesophagus and trachea
If the 2 don’t separate clearly, then when the child is born and they have their first feed, they will cough cause it’ll will go into lungs
Sometimes they have a fistula that is very small which they only detect if that mother reports the child coughing every time they feed
How do the abdominal and thoracic cavities get separated
Development of the septum transversum and diaphragm
Extension of the septum transversum partially divides abdominal and thoracic cavities
Diaphragm is important as it separates abdominal and thoracic cavity and prevents herniation of abdominal into thoracic space, and vice versa
what are numerical chromosomal defects
- Missing a chromosome from a pair (monosomy)
* Missing more than 2 chromosomes (trisomy)
what are structural chromosomal defects
- Deletions
- Duplications
- Translocations
- Inversions
- Substitutions
what is a genetic disorder
❖ Caused by a change in the DNA sequence
❖ Inheritance of a mutated disease-causing gene that is passed on
what is an example of a monogenetic disorder
CF
what is Duchenne Muscular dystrophy
DMD–> mother is the carrier
- only affects boys
- when skeletal muscle fibres are replaced by soft tissue, hnce lose muscle tissue and become weaker
- eventually need ventilation support, lungs and heart start to fail
what are environmentally derived abnormalities
Maternal lifestyle: ❖ Poor nutrition ❖ Alcohol no save dosage ❖ Illicit drugs amphetamines, cannabis etc. ❖ Smoking ❖ Domestic violence Maternal infections: ❖ Rubella
what is the chromosomal defect causing downs syndrome
trisomy 21
what is the pathogenesis of downs syndrome
❖ Non-disjunction –> failure during meiosis
➢ The older the mum (over 35/40yo) the higher the chance of child having down syndrome–> older= ova differentiating becomes more abnormal
❖ Translocation –> fusing of chromosomes 21 to 13, 14 and 15 during gametogenesis
❖ Mosaic –>mutation during mitosis after formation of zygote
what are the central defects in downs syndrome
➢ Cerebellar dysfunction smaller and lighter cerebellum
➢ Cerebrum cortex smaller and smoother, fewer shallow sulci
what are the peripheral defects of downs syndrome
muscle abnormality
what are the cerebellum defects in downs syndrome
➢ Though to be damaged to cortex and deep nuclei
➢ Results in decreased input to lateral vestibular nucleus, motor cortex and brain stem motor nuclei
➢ Therefore decreased resting muscle state of muscle= hypotonic
what are the upper motor neuron defects in downs syndrome
➢ Decreased segmental motor neuron pool excitability
➢ Stretch reflex pathology conflicting evidence
• Normal or reduced short latency myotatic reflexes (0-50ms) DTR respond at normal time but can’t generate enough power quick enough hence seems slower
• Delayed postural response
what is the muscle abnormality in downs syndrome
➢ Hyper-extensibility
➢ Decreased muscle stiffness
➢ Decreased muscle damping:
• Decreased internal frictional force of the muscle
• Decreased control about an end position
list some impairments in downs syndrome
❖ Intellectual disability ❖ Hypotonic ❖ Muscle hyper-extensibility ❖ Ligamentous laxity ❖ Atlanto-axial instability (4%) ❖ Risk of arthritis especially RA ❖ Heart defects (45%) ❖ Respiratory vulnerability ❖ Visual defects (myopia, nystagmus) (60%) ❖ Low frequency hearing loss (60-80%) ❖ Leukaemia (2%)acute lymphoblastic leukaemia ❖ Premature aging Alzheimer’s
what is spina bifida
❖ Birth defect where there is incomplete closing of the tissue/membranes surrounding the developing spinal cord of foetus
❖ Abnormal neurulation folding process in vertebrae of embryos
❖ Abnormal canalisationformation of CNS of new pathways by repeated passage of nerve impulses
➢ S2 onwards
➢ Canalisation lesions less likely to have associated CNS malformations
what are causes of spina bifida
➢ Genetics
➢ Nutritional deficiencies
➢ Drug and alcohol associations
➢ Folate is protective hence important to take folate during pregnancy to prevent this should have folate before thinking of becoming pregnant
what is myelomeningocele
❖ Commonly referred to as spina bifida
❖ Open spinal cord defect
❖ Not skin covered might be a thin layer of meninges
❖ Spinal nerve damage motor and sensory loss in LL depending on site
❖ CSF leak have nervous tissue in this space (nerve roots etc)
what is meningocele
❖ Spina bifida apearta but less severe
❖ Skin covered
❖ Spinal nerve damage may be less extensive
❖ Contains membranes or non-functional nerves
❖ ‘Not a clean cut’ kind of lesion
what is lipoma
❖ Spina bifida occulta
❖ Subcutaneous fat mass cephalad to gluteal cleft
❖ Associated with:
➢ Abnormal pigmentation
➢ Hirsuitism
➢ Dimples
❖ Lipomatous or fibromatous tract runs from lipoma into subdural space adjacent to SC
❖ Classified according to location of the tract
❖ Has enough cover to not be exposed
❖ Severity of the condition will depend on where on the SC it is, and how much it is covered
what is congenital scoliosis
❖ Hemivertebrae lack of formation of one half of vertebral body
❖ Rotation/twisting of spine compromises heart and lung function as it disrupts the space
is congenital talipes equinovarus a structural or positional defect
structural–> because occurs in the utero
what is the presentation of congenital talipes equinovarus
➢ Antenatal ultrasound or at birth ➢ Ankle and subtalar joints PF (equinus) ➢ Hindfootvarus (turned in) ➢ Forefoot inversion and adduction ➢ 1st ray drops to create cavus
what are the structural changes to skeletal system in congenital talipes equinovarus
❖ Talus smaller, deformed, uncovered laterally, equinus position
❖ Navicular orientated downwards
❖ Calcaneum hypoplastic
what are the structural changes to muscular system in congenital talipes equinovarus
❖ Ligaments thickened
❖ Muscles hypoplastic
❖ Cellular changes
is talipes equinovarus structural or positional
positional–> because the foot is still mobile
what is the presentation of talipes equinovarus
❖ Hindfoot PF’ed (equinus) and inverted (varus)
❖ Forefoot adducted and supinated
❖ +/- deep medial crease
❖ No structural abnormality to skeletal or muscular systems
❖ Can correct foot passively
❖ ‘Normal’ 4-6 weeks post natally
what are the degrees of severity in developmental hip dysplasia
❖ Ligamentous laxity transient in the newborn due to maternal hormones
❖ Acetabular dysplasia shallow, flattened socket
❖ Subluxation incompletely covered femoral head – deficient cartilaginous roof of acetabulum
what is a diaphragmatic hernia
❖ Birth defect with abnormal opening in diaphragm, allowing parts of organs from abdominal cavity to move into thoracic cavity and vice versa
what is a non-cyanotic congenital heart defect
Non-cyanotic= not present at birth
-Congestive heart failure and respiratory distress
what is patent ductus arteriosus (PA)
- congenital non-cyanotic heart defect
➢ Patent= persistent
➢ Failure of ductus to close in early weeks of life
➢ Allows blood to flow between aorta and pulmonary artery= increase in flow in lung circulation
➢ Circulation of oxygenated blood in lungs
➢ Mixing of oxygenated and deoxygenated blood
what is ventricular septal defect (VSD)
- congenital non-cyanotic heart defect\
➢ Hole in the heart
➢ Hole occurs in the wall (septum) that separates the left and right ventricles
➢ Allows blood to pass from the left to right side of heart
what is atrial spetal defect (ASD)
- congenital non-cyanotic heart defect
➢ Hole in the wall between the 2 upper chambers of heart- atria
➢ Allows blood to flow between atria
what is tetralogy of fallot (TOF)
-cyanotic congenital heart defect
➢ Combination of 4 congenital abnormalities VSD, pulmonary valve stenosis, misplaced aorta ad thicken right ventricular wall (right ventricular hypertrophy)
➢ Blueish skin tone
➢ Limits blood flow to lungs
what is Transposition of the great arteries (TGA)
➢ Aorta connected to right ventricle
➢ Pulmonary artery connected to left ventricle
➢ Arteries transposed from their normal position
what is defined as a preterm birth
-born <37 weeks gestational age
