Embryology Flashcards
Stages of first trimester
Embryogenic(14-16 days)
Embryonic(16-50 days)
Embryogenic stage function
Determine pluripotent embryonic cells and extraembryonic cells
Embryonic stage function
Determine germ layers and differentiate tissue layers
What is foetal stage
50-270 days
Migration of organs to final position
Extensive growth and foetal viability
What does the ovulated oocyte become
Zygote
Embryo
Morula
Blastocyst
Maternal to zygotic genome transition
Before 4 cell stage: embryo is dependent on maternal mRNA and proteins
4-8 cell stage: zygotic genome activation
What is pluripotent embryonic cells and extraembryonic cells made of
Pluripotent embryonic cells->inner cell mass
Extraembryonic cells->trophoectoderm
Blastocoel is fluid filled cavity from trophoblasts pumping Na into cavity
How and when does implantation occur
Day 7-9
Trophoblasts fuse->syncitiotrophoblast
Invades and destroys maternal cells in endometrium
What does inner cell mass separate into
Epiblast->foetal tissue
Hypoblast->yolk sac
When and how does bilaminar embryonic disc formation occur
Day 12+
Epiblasts separate->form amniotic cavity
Amnion cells contribute to extraembryonic membrane
2 layered disc of epiblast and hypoblast between cavities
What is gastrulation
Occurs after bilaminar disc formation
Formation of primitive streak: head/tail and left/right axes
Invagination of cells into primitive streak: endoderm, mesoderm, ectoderm
What is notochord and when does it form
Day 13+
Rod-like structure along embryo midline
Organising centre for neurulation and mesoderm development
Process of neurulation
Notochord signals->neural plate invagination->neural groove
2 neural folds form along craniocaudal axis
Neural crest cells reside in neural folds
Neural folds move over neural groove, fusing and forming a hollow tube
Neural tube overlaid with epidermis
Crest cells migrate from neural folds
When does neural tube close
Head: day 23
Tail: day 27
Failure to close neural tube
Anencephaly(head fail) Spina bifida(tail fail)
What is somitogenesis
Formation of somites(paired blocks of paraxial mesoderm)
Blocks of somites condense and bud off
What are some somite derived tissue
Sclerotome->vertebrae and rib cartilage
Dermomyotome->muscles and skin
When and how does gut tube form
Day 16+
Lateral and ventral folding
Pinches off part of yolk sac
When and how does heart form
Day 19
From mesoderm
Starts pumping at day 22
Foetal heartbeat at week 6
When and how do lungs form
From endoderm in week 4
Lung splits and progressively branches
How do gonads form
From mesoderm
XX: gonadal cells become granulosa cells
XY: gonadal cells become sertoli cells
Causes of early pregnancy loss
Embryo-foetal development errors
Implantation failure
Inability to sustain development
Miscarriage classification
Early: <12 weeks
Late: >23 weeks
Aneploidy mechanism and causes
Maternal age
Cohesin that holds homologous chromosomes together is not replaced ->chromatids separate and drift
Cause of recurrent pregnancy loss/miscarriage
Lif deficiency->implantation failure
Types of gestational trophoblastic disease(GTD)
Benign: hydatidiform moles-> complete(empty egg) or partial(normal egg)
Malignant: gestational trophoblastic neoplasia
Gene mutation causing recurrent hydatidiform moles
NLRP7
Main location for ectopic pregnancy
Fallopian tube
Ectopic pregnancy treatment
Expectant management
Chemotherapy
Surgery->remove trophoblast and/or tube
How does smoking affect ectopic pregnancy
Cotinine:increase PROKR1 expression-> fallopian tube smooth muscle contractility dysregulated
Cotinine: induce proapoptosis protein
Tobacco smoke inhibits ciliary function
How does cannabis affect ectopic pregnancy
CB1 receptor expression reduced
Endocannabinoid levels higher
THC hinders embryo transit
Difference between first and second trimester nutrition
1st: histiotrophic->uterine gland secretions and breakdown of endometrium
2nd: haemotrophic->maternal blood contacts foetal membranes
Origins of placenta
Ammion
Chorion(outer membrane)
Connecting stalk(embryo to chorion)
Trophoblastic lacunae
What is trophoblastic lacunae
Large spaces filled with maternal blood from breakdown of maternal capillaries
Becomes intervillous spaces
What is amnion
Inner foetal membrane
Forms a closed avascular sac
Secretes amniotic fluid->protect foetus
What is chorion
Outer foetal membrane
Highly vascular
Gives rise to chorionic villi
What is allantois
Outgrowth of yolk sac
Grows along connecting stalk
Coated in mesoderm and vessels to become umbilical cord
Formation of chorionic villi
Outgrowths of cytotrophoblast into syncitiotrophoblast layer
Undergo branching
Convolution and dilation->slows blood flow to enable exchange
Spiral artery remodelling
Undergo conversion
Extravillus trophoblast(EVT) invade maternal spiral arteries
Endothelium and smooth muscle broken down
EVT coats inside of vessels
Important points of nutrient exchange
Calcium: actively transported
Amino acids: reduced maternal urea excretion, active transport to foetus
Stages of labour
1: contractions start, cervix dilates
2: delivery of foetus, maximal myometrial contractions
3: placenta delivery, post partum repair
How does cervix retain foetus in uterus
High connective tissue content provides rigidty and is stretch resistant
What happens during ripening of cervix
Monocyte infiltration
IL-6, IL-8
Hyaluronan deposition
What happens during cervix dilation
Raised hyaluronidase
Raised MMPs
Initiation of labour
Foetal CRH rises
High ACTH->high cortisol->placental CRH production->positive feedback
Switch from activating to repressing progesterone receptor
Uterus blind to progesterone, sensitise to oestrogen
Stretch receptors->Ferguson reflex-> oxytocin
Oxytocin function in labour
Raise connectivity of myocyte in myometrium
Destabilise membrane potential->lower threshold for contraction
Liberates Ca stores
Prostaglandin functions in labour
Leukocyte recruited, IL release->cervix remodelling
Myocyte connectivity->myometrial contractions
Lower uterine relaxation
How does placental expulsion occur
Foetal membranes fold and peel off endometrium
Haematoma forms between decidua and placenta
Uterus remains contracted->uterine vessel thrombosis
Pre-eclampsia diagnosis
New onset hypertension
>20 weeks gestation
Reduced foetal movement/amniotic fluid volume by 30%
Pre-eclampsia subtypes
Early onset(10%): <34 weeks, foetal and maternal symptoms, placental changes
Late onset(90%): >34 weeks, maternal symptoms, little placental changes
Pre-eclampsia risk factors
Previous pregnancy with PE BMI>30 Age>40 Hypertension Comirbidities: diabetes, PCOS, renal, autoimmune
Pre-eclampsia prognosis
Mother:
Systemic damage(liver/kidneys/brain)
Eclampsia(seizures, unconsciousness)
Placental abruption
Foetus:
Reduced growth
Premature birth
Pregnancy loss
Pre-eclampsia pathophysiology
EVT invasion limited to decidual layer
Spiral arteries not extensively remodelled
Placental perfusion limited
Pre-eclampsia investigations
PLGF: proangiogenic so low->risk if premature delivery
Flt-1/PLGF ratio: Flt-1 is antiangiogenic so >38 -> risk of PE
Pre-eclampsia management
<34 weeks: maintain pregnancy
>37 weeks: deliver
Antihypertensive
Corticosteroids for <34 for foetal lung development
Pre-eclampsia prevention
Weight loss
Exercise throughout pregnancy
Aspirin for high risk individuaks
Primitive reflexes(infant)
Moro reflex: neck extension->arm moves
Standing reflex
Grasp reflex
Parachute reflex
4 Domains of infant development
Gross motor skills
Fine motor skills
Speech/language skills
Social skills
Gross motor skills red flags
Head control 4m
Unsupported sit 9m
Independent stand 12m
Independent walk 18m
Fine motor and vision red flags
Follows object 3m
Reaches for objects 6m
Transfers 9m
Pincer grip 12m
Speech and language red flags
Polysyllabic babble 7m
Consonant babble 10m
6 words with meaning 18m
3 word sentences 2.5 years
Social red flags
Smiles 8w Fear of strangers 10m Feeds self 18m Symbolic play 2.5y Interactive play 3.5y
Healthy child programme
Screening: newborn bloodspot, hearing and physical, vision(4-5y)
General examination/immunisation: 6-8w, 1y, 2y reviews
Health education/promotion
Causes of global developmental delay
Down syndrome Fragile X Hypothyroid Infection, drug, toxin, folate deficiency Environmental social Chronic illness
Causes of motor development delay
Cerebral palsy Duchenne’s muscular dystrophy Spina bifida Hydrocephalus Congenital hip dislocation
Causes of language development delay
Hearing loss Developmental dysphasia Stammer, dysarthria Learning disability Autism
Developing brain dorsal view
Prosencephalon(fore)
Mesencephalon(mid)
Rhombencephalon(hind)
Developing brain flexures
Cephalic
Pontine
Cervical
Which germ layer are neural crest cells derived from
Ectoderm
Neural crest cells and final structure
Cranial: face and cranial neurons
Cardiac: aortic arch, large arteries
Trunk: sympathetic ganglia, melanocytes, adrenal medulla
Vagal & sacral: parasympathetic and enteric ganglia
