S5- Embryology Flashcards
2 causes of human birth defects:
Genetic= monogenic mutations/ chromosomal mutations (numeral/ aneuploidy or structural)
Environmental= teratogens
5 types of teratogens:
- Infectious (TORCH)= 5 examples
- Chemical= thalidomide and alcohol
- Physical= radiation
- Maternal disease= diabetes
- Deficiency= folic acid
Highest Risk of birth defects in embryonic period is around…
5 weeks
(3-8 weeks)
Infectious teratogens can…
Cross the placenta and cause birth defects
Folic acid deficiency (vitamin B) causes malformations in…
OTC supplements…risk by…
2 congenital malformations are:
Central nervous formations
Reduce, 60%
- Spina bifida (gaps in spinal cord/ doesn’t develop fully)
- Anencephaly (born without parts of brain or skull)
Diabetes can cause…
4 congenital malformations:
Cellular structural defects and changes in cellular physiology
- Macrosomia (larger than average0
- Ventricular septal defect
- Spina bifida
- Renal agenesis
Trophoblasts are the….cells of zygote and they differentiate into…
outside
Cytotrophoblasts and syncytiotrophoblasts (membranes break down/ have no defined membranes)
Embryoblasts are…and they differentiate into…
Cells in the middle
Hypoblast and epiblast
the terminology used to describe an embryo
Cranial= head region
caudal= tail region
ventral= front
dorsal= back
the planes used to describe an embryo
transverse= cutting across waste
sagittal= cutting through midline
coronal= divide into ventral and dorsal
the 2 techniques used to date a pregnancy
- menstrual age (clinicians)= from last mentrual cycle (1st day of bleeding) + 3 equal trimesters
- Fertilisation age (embryologists)= more specific + 3 unequal trimesters
the 3 trimesters of fertalisation age
- early development (includes cell division + pre-embryonic) 0-3 weeks
- Embryonic + organ development (organogenesis) 3-8 weeks
- foetal period 8-38 weeks
radiation can cause…and make the CNS more…
it is most sensitive in…trimester
3 congenital malformations are:
cell death or chromosomal changes
Sensitive
First
1. Microcephaly
2. mental and congnitive disabilities
3. haemopoietic malignancies (cancers in blood-forming tissues such as bone marrow) and leukemia (cancers of the blood)
two chemical teratogens
- thalidomide= prescribed for morning sickness and causes shortened or absent limbs (now used to treat leprosy and HIV)
- foetal alcohol syndrome= prenantal and postnatal growth retardation (doesnt grow at normal rate), intellectual disability, impaired motor ability and coordination
TORCH infectious teratogens and zika virus
1.toxoplasmosis= parasite in cat faeces and undercooked/ raw meat= asymptomatic
2. Other (hipatitis B, syphilis)
3. rubella (german measles)= rubella virus, use MMR vaccine= rash
4. cytomegalovirus (CMV)= via bodily fluids= asymptomatic
5. Herpes simplex virus (HSV)= varicella zoster virus- chickenpox
6. zika virus= mosquito, bodily fluids, fever/rash/ red eyes/ joint pain
outline the steps in the hormone cycle
- hypothalamus= GnRH (gonadotropin releasing hormone)
- stimulates gonadotropes in pituitary gland to release FSH and LH
- FSH and LH stimulate follicular phase and production of oestrogen
names of cells and follicles as they develop in hormone cycle
- oogonia (diploid 2n cell)
- primordial follicle (2n)= frozen in prophase 1
- primary follicle (2n)
- early secondary follicle (2n)
- late secondary follicle (2n)
- graafian follicle (n)- frozen in metaphase 2- contains antrum
once oestrogen reaches a critical level as oocytes mature in ovary, oestrogen exerts….feedback on…
follicle notices rise in oestrogen= produce…to inhibit pituitary from producing FSH
this results in…
Positive
hypothalamus= more GnRH= more FSH and LH
inhibin B
LH surge
the rule of LH in ovulation
ovulation occurs around day…
- increase blood flow and permeability into second half of follicle (blood vessels local to antrum)= more follicular fluid in antrum
- activate proteases enzymes that cleave tissue around graafian follicle= oocyte erupts from graafian follicle (ovulation)
- stimulate the remaider of graafian follicle into hormone factory= corpus luteum (produce progesterone)
14-15
if no fertalisation occurs, the corpus luteum….approx…days after…and oestrogen and progesterone…
if fertalisation occurs then cells called…secrete…to stimulate secretion of hormones until….takes over
degrades
10 days
Ovulation
Decrease
syncytiotrophoblasts
hCG
an implanted placenta
the outline/ steps of fertalisation/ week one after ovulation:
- capacitation of sperm (cleaning up head of sperm= removal of proteins and increase motility) -> pass through corona radiate
- acrosome reaction= releases enzymes to penetrate zona pellucida
- cortical reaction= impermeable zona pellucida
- cleavage= proliferation
- formation of morula= 16-32 cells (inner mass and outer mass)
- blastulation= morula-> blastocyte (fluid-filled cavity and emryoblasts and trophoblasts)
after sperm joins egg, a….forms and after fusion of….a…forms
zygote
pronuclei
embryo
The…sweep the oocyte into the uterine tube/ fallopian tube and fertalisation takes place at the….
fimbriae
ampulla
significance of the bilaminar disc
establish dorsal/ ventral axis of embryo
epiblast= dorsal/ back
hypoblast= ventral/ front
the small fluid filled ceviity forms in the epiblast layer to form the bilaminar disc is called…
amniotic cavity
to establish uteroplacental circulation, syncytiotrophoblasts….
erode walls of maternal capillaries
outline of week 2 (implantation)
- Amniotic cavity forms in epiblast layer (day 8)
- migration of hypoblast to encase blastocyte cavity (important fo yolk sac to form) (day 9)
- uteroplacental circulation + primary yolk sac (day 10-11)
- new layer of connective tissue forms from yolk sac and cytotrophoblast = extraembryonic mesoderm (10-12)
- chorionic cavity forms in extraembryonic mesoderm (12-13)
- Hypoblasts migrate again= form secondary yolk sac
- end of week 2= amniotic cavity+ secondary yolk sac suspended in chorionic cavity by CONNECTING STALK
the cells….secrete hormone….that is used in pregnancy testing
it makes corpus luteum continue to secrete…
syncytiotrophoblasts
hCG= human chorionic gonadotrophin (and may play a role in maternal immunotolerance)
progesterone (to maintain endometrium)
abnormal implantations (ectopic pregnancy) occurs in..% of prgnancy and causes…% of mother deaths
2
9
3 types of abnormal implantations
- placenta previa = placenta blocks cervix/ exit= cause severe bleeding in late pregnancy
- tubal implantation= mejority of ectopic pregnancies occur in uterine tube (80% in ampulla)= cramping/ bleeding/ medical emergency diagnosed in weeks6-8
- abdominal implantation= egg enter abdomen through gap between ovary and uterine tube
lithopaedion occurs in….when it remains…and the foetus dies
the foetus is too…to be…so instead it…
it is thought to protect the mother formt he necrotic tissue of the foetus
litho (stone)- paedion (child)
Abdominal pregnancy
undiagnosed
Large
reabsorbed
calcifies
hydatidiform mole is
a results of abnormal fertilization of the oocyte (egg).
leads to an abnormal fetus.
The placenta grows normally with little or no growth of the fetal tissue.
The placental tissue forms a mass in the uterus
2 types of hydatidiform mole
- complete= egg with no nucleus fertalised by 2 haploid sperms (enucleated oocyte)
paternal imprinting= trophoblasts develops without embryo
syncytiotrophoblasts produces hCG= positive pregnancy - Partial= normal oocyte fertalised by 2 sperms (69XXY or 69XXX)= triploid zygote
development of trophoblasts without embryonic tissue (or malformed embryo)= not compatible with life
risks and solutions of hydatidiform moles
- complete= high hCG results in choriocarcinoma (cancer of placenta)
require surgical/ medical management (Dand C) - partial= moderately high hCG= moderate risl of choriocarcinoma
spontaneously aborts (miscarry)
in week 3, the…streak is formed
and the…of the embryo are firmly established
primitive streak
Cranial/ caudal and right/ left axis
the process that transforms bilaminar disc to trilaminar disc is called…
gastrulation
outline the steps of gastrulation
- formation of primitive streak (thick layer of epiblast that has cavity in middle/ pit)
- epiblasts move through pit and replace hypoblast cells= now called definitive endoderm (day 14-15)
- more epiblasts continue to move down (successive migration)= form middle layer= mesoderm (day 16)
- remaining top epiblast layer is now= ectoderm (day 16)
3 parts of primitive streak
- primitive groove
- primitive node
- primitive pit
the…plate is thicked portion of…that is in contact with…
prochordal
Endoderm
ectoderm
derivatives of ectoderm layer
epidermis of skin (+ hair/ nails/ glands)
nervous tissue and sense organs
pituitary gland
adrenal medulla
enamel of teeth
lens of eye
derivatives of mesoderm (lots of epithelia)
dermis of skin
epithelial lining of vessels/ lymph/ cavities
connective tissue (bone, cartilage etc)
adrenal cortex
Heart
kidneys and ureters
internal reproductive organs
spleen
derivatives of endoderm (lots of glands)
epithelial lining of respiratory tract/ GI tract/ urinary bladder/ urethra
Gallbladder
Pancreas
thyroid gland
parathyroid gland
2 conditions due to abnormal gastrulation
- sirenomelia= mermaid syndrome (due to lack of mesoderm tissues in caudal regions of embryo)= abnormalities of urogenital system and lower limbs
- Sacrococcygeal teratoma (most commone tumour in newborns)= when remainders of primitive streak give rise to tumour (most are benign and 80% in females)= resection to remove it
abnormal gastrulation can also lead to….
2 types of inversus in patients
right to left asymmetry of body is reveresed= situs inversus
1. complete= harmless but 20% suffer from kartagener syndrome
2. partial= is much rarer and associated with other malformations ie: dextrocardia (isolated right sided heart)
…is the first event in the development of the…
it is initiated by…from…to cause ectoderm to thicken and form the…from (neuroectoderm)
neurulation
CNS
signals
notochord
neural plate (induction)
the steps of neurulation
- ectoderm proliferation (layer thickens)
- form neural plate
- neural fold (lateral edges of neural plate elevate), crest, groove form
- fusion to lateral sides to form nueral tube
when the neural folds…, the neural tube is formed (day 22)
the…starts in…and continues…
the tube…from the surface ectoderm
fuse together
fusion, cervical (neck) region, cranially and caudally (both directions)
seperates
the anterior (front/top) neuropore fuses on day…
the posterior neuropore fuses on day…
the cranial end of neural tube will form…
the caudal end will form…
25
28
brain
spinal cord
failure of anterior neuropore to fuse causes…
failure of posterior neuropore to fuse causes…
anencephaly (brain does not form but a brainstem is present- heart/ lungs and some reflexes are present)
spinal cord does not form properly- paralysis
open neural tube prevent formation of vertebrae (spina bifida)
plate of neural tissue expoased at birth- infection
as neural folds elevate and fuse, the neural crest cells…from the neural tube
they…laterally and ventrally and…into a variety of structure
sometimes refered to as…
Separate
migrate
differentiate
4th germ layer
during 4th week, the embryo goes through…
the 2 directions are..
this is due to…
folding in 2 directions
1. craniocaudal folding
2. lateral folding
the differntial growth of amniotic sac and yolk sac (amniotic sac grows rapidly while yolk sac stays the same size)
the….mesoderm starts dividning into blocks called…on day…
this beings in…and progresses towards…at rate of 3 or 4 pairs a day until 42-44 pairs form
it is a…process which helps with estimating…
Paraxial
somites
20
Cranial region
caudal region
predictable
age of embryo
When the primitive streak closes up, the…forms
it then…with endoderm to form…
the plate then…and…to form a notochord (initiates neurulation)
notochordal process (hollow tube)
fuses, flattened notochordal plate
seperates from endoderm and fuses together
2 roles of notochord:
- initiates neurulation (induction)
- initiates and organises formation of vertebrae from somites= induces differentiation of somites into 3 parts:
- sclerotome (bone and cartilage)
- myotome (skeletal muscle)
- dermatome (dermis)
notochord also organises the sclerotome cells as they form…
the notochord then….as the vertebrae form and its remains persist as…
the vertebral body and surround the neural tube to form certebral arch
Degenerate
nucleus pulposus of intervertebral discs
abnormal induction of sclerotomes leads to…
spinal defects such as:
spina bifida (gap in spine)
Meningocele (cerebrospinal fluid fills the gap)
myolomeningocele (spinal cord and spinal nerves in the meningeal sac- with the fluid)
…acid reduces neural tube defects (NTDs) such as…by…%
folic
Anecephaly, rachischisis, spina bifida
50-70%
defects in neural crest cell development is:
neurofibromatosis- genetic disorder
mutation in neurofibromas 1 (NF1) gene which is a tumour suppressor (now switched off)= increased cell division
cause: benign tumours of nervous system, skin and cranial bones
the connecting stalk is the future…
umbilical cord
allantois is a…
sac connected to fetal bladder
vitelline duct
Duct/ tube providing connection between yolk sac and midgut
2 Ventral/ front body defects
ectopia cordis = lateral fold fails to fuse in thoracic region (chest) leaving the heart outside the body
Gastroschisis = lateral fold fails to fuse in abdominal region (intestine outside the body wall)
