Stages of Prenatal Development Flashcards
human development begins with
fertilization
fertilization results in
new organism (single celled zygote)
what is a zygote
diploid cell with 22 autosome and 1 sex chromosome from EACH parent
total of 46 chromosomes
When does the zygote multiply its cells?
around 3 to 4 days post fertilization
what enters the uterine cavity
morula
these cells arrange as an inner and outer cell mass
blastocyst
what implants into the uterus
blastocyst
Can you have a pregnancy with no implantation?
no you have to have uterine implantation in order to have a pregnancy even though fertilization occurred
what must happen in order to have pregnancy?
the morula must enter the uterine cavity and implant
What sex chromosomes can mom and dad provide to zygote?
mom only an x because she is XX
dad either an x or a y because he is XY
what is a polar body
small haploid cell that is formed concomitantly as an egg during oogenesis but does not generally have the ability to be fertilized and degenerates
it cannot be fertilized
disappears around 12 hours after fertilization
1 of 2 small cells produced with the ovum (oogenesis) during meiosis and then degenerates
Morula =
Many cells
what is the blastulation process
where we are going from the morula to the blastocyst
inner and outer cell mass
blastocyst
outer cell mass becomes
trophoblast
trophoblast becomes
placenta
inner cell mass becomes
embryoblast
embryoblast becomes
gives rise to other body parts
what hours do we see 2 cell stage with polar body and blastomere
12-15 hours
at 12-15 hours after fertilization, what do we see
2 cell stage with polar body and blastomere
what hours do we see 4 cell stage
24-30 hours
what is the carnegie stages of development
system used by embryologists to describe the apparent maturity of embryosh
how is the carnegie stages determined
embryo assigned a stage from 1-23 based on external features
why is carnegie stages of development based on external features
the development of a fetus is very regular and we know what occurs when and what should look like during development and due to this we can find problems if there is one
in carnegie stages, when do the limb buds show?
16 (37 days)
when does the external ears show in carnegie?
21 (52 days)
what are the largest organs in early development?
ead and heart but as they develop it decreases in size
how do you determine when the due date is?
postovulatory age
what is the menstrual cycle?
day 1 is the first day of the menstrual cycle and last is the day before the next period begins
when does ovulation occur?
about 2 weeks before the next expected period
if an average cycle is 28 days, ovulation occurs around day 14
postovulatory age is used by clinicians to describe
maturity of an embryo
what is postovulatory age
refers to the length of time since the last ovulation before pregnancy
postovulatory age is good indication of embryonic age because
approx time of ovulation can be determined
fertilization must occur close to time of ovulation (around 12-24 hours)
why is the due date important
to make sure the fetus is meeting all of the milestones
if too early or too late, the fetus could be in danger
if they need to induce, want to make sure it is not too early or too late to take the fetus out
what are the stages of development?
pre-embryonic (fertilization to end of 2nd week)
embryonic (3-8th week of gestation)
fetal (3rd month, 9 weeks to birth)
what is the time frame for pre embryonic stage
after fertilization to end of the 2nd week of gestation
what occurs in pre-embryonic period
germ cells (3 germ layers) develop - gastrulation
nervous and cardiovascular system start to develop
what is gastrulation
process of cellular rearrangement which involves migration, invagination and differentiation of the epiblast
process by which the 3 germ layers are acquired
gastrulation
rapid process which a blastula becomes a gastrula
gastrulation
through the process of gastrulation, what is the course of all 3 germ layers in the embryo?
epiblast
what forms the bilaminar germ disc?
epiblast and hypoblast
2nd week there are how many layers
2
3rd week there are how many layers
3
Two sheet-like discs
bilaminar disk
upper layer of bilaminar disk
epiblastl
lower layer of bilaminar disk
hypoblast
what layers are in the trilaminar disk
ecto meso and endo
what is the primitive streak
transient structure who forms on day 15 of human development and marks the start of gastrulation
process that the inner cell mass converts into the trilaminar disc made up of the 3 layers
gastrulation
what marks the beginning of organogenesis
neural tube and notochord
where does the primitive streak originate from
anterior epiblast
appears as an elongated groove (primitive groove) on the caudal midline of the bilaminar disc
primitive streak
local thickening of epiblast at the cephalic end of the p.s. of the embryo
hensen’s node
the embryonic organizer
hensen’s node
primitive backbone is eventually replaced by the vertebral column in mammals
primitive node
contains the depression called a primitive pit
primitive node
what organizes the cells where they need to go and keeps them where they need to be?
primitive node
primitive backbone that turns into the vertebral column?
notocord
What gives rise to all fetal tissues and organs?
germ cells
3 places with no mesoderm
Where notochord is
Where procordal plate is (rostral)
Cloacal plate (caudal)
epiblast is derived from
inner cell mass
epiblast lies
above the hypoblast
epiblast gives rise to
3 primary germ layers
ecto meso endo
what are progenitor cells
descendants of stem cells that can differentiate to form 1 or more kinds of cells
they cannot divide and reproduce indefinitely
what day do we see epiblast cells appear
day 8 of development
epiblast cells make up
columnar epithelium with dense microvilli
what do microvilli do
move things where they need to go
what becomes the loose mesenchym of the p streak
epiblast cells when they undergo epithelial to mesenchymal transition during gastrulation
what does ectoderm give rise to
organs and tissues that maintain contact with the OUTSIDE world
all external features come from this
what develops from the ectoderm
CNS
PNS
Schwann cells
sensory epithelial of the ear nose and eye
what develops from the mesoderm
heart, vascular system, male and female reproductive organs, spleen
what develops from the endoderm
Gastrointestinal system is the main one
epithelial lining of eustachian tube, respiratory tract and lymphatic cavity
what happens in the embryonic period
cells become differentiated into the organ structures
all major organ systems begin and/or undergo major development
3rd to 8th week of gestation
major period of organ development
what is the significance of thalidomide
BP medication that used in 50’s for adults and found in Europe that it could be used for morning sickness
wasn’t approved for pregnant women
when babies are born the upper and lower limbs were not formed (hand where elbow should be) - skeletal limb abnormalities
called thalidomide babies
didn’t see in US because it was developed in europe
only affected the limbs
what is organogenesis
development of organs/systems
process which the ecto meso and endo develop into internal organs of the organism
exposure to teratogens (drugs, infections, toxins) during this period can result in either death or major congenital anomalies affecting multi organ systems
embryonic
development of brain and spinal cord begins at
week 3
what develops from the neural tube
CNS
what develops from the neural crest cells
PNS
forebrain
prosencephalon
midbrain
mesencephalon
hindbrain
rhombencephalon
formed by closure of ectodermal tissue in the early vertebrate embryo
neural tube
band of neuroectodermal cells that lie dorsolateral to developing spinal cord
neural crest cells
develop into a variety of tissues
including spinal and autonomic ganglia and connective tissue around the brain and spinal cord
neural crest cells
seen when neural tube has incomplete development
neural tube defects
what is spina bifida
vertebrae overlying the spinal cord are not fully formed and remain unfused and open
if opening is large enough a portion of the spinal cord will protrude through the opening of the bones
may or may not have fluid filled sac surrounding the spinal cord (encased in a cyst)
most common birth defect - 1/1000 births
spina bifida
split spine
spina bifida
will surgery after birth fully restore normal function of affected part of spinal cord in spina bifida?
no, can be closed but not a guarantee 100% fix
after having one child with SB, risk for a second increases by _%
4, environment plays more of a role than genes
incidence of sb can be decreased by 70% when the mom takes
daily folic acid supplements early in pregnancy
S.B. believed to be caused by
combination of genetic and environmental factors
what is encephalocele
sac containing meninges/brain/CSF forms outside skull due to bone defects
results when other parts of brain remain unfused
most common location is lumbar and sacral areas
used interchangeably with spina bifida
myelomeningocele
most significant and common encephalocele and leads to disability in most affected individuals
myelomeningocele
what is myelomeningocele
fluid filled sac containing neural tissue protruding from the back
form of spina bifida
what is chiari malformation
most common form
when lower part of the cerebellum pushes into the opening
evelops when part of the skill is smaller than normal or misshapen, forcing the cerebellum to be pushed down into the foramen magnum and upper spinal canal
causes pressure on cerebellum and brainstem that can affect functions controlled by these areas and block flow of CSF
usually noticed in adolescence or adulthood
chiari malformation
which type of CM is the most severe
Type IV
What is arnold-chiari II malformation
can co-exist with encephalocele or spinal bifida
involves the cerebellum and brainstem tissue pushing into the foramen magnum
causes hydrocephalus - collection of fluid on the brain
arnold chiari II
usually results in partial or complete paralysis below the spinal opening with myelomeningocele
arnold chiari II
what is a dermoid cyst
can occur in combo with spina bifida
benign tumor, remnant of p streak and contains all 3 germ layers
represents the last place of separation between the superficial ectoderm and neuroectoderm
dermoid cyst
what is anencephaly
portion of the neural tube that becomes the cerebrum doesn’t close
will be born without front part of the brain (forebrain) and thinking and coordinating part of the brain (cerebrum?)
remaining parts are not covered by bone or skin
Is anencephaly compatible with life
no, usually are stillborn or die after birth
what is the most common cause of anencephaly
maternal zika virus
does the maternal zika virus affect the auditory system?
yes
deficiency of brain tissue and cranium and not compatible with life
anencephaly
microcephaly
small brain
is microcephaly compatible with life
yes
What are the most common locations of sb?
can happen anywhere due to the groove but we don’t know for certain why it is mostly the lower back
what happens if the neural tube doesn’t develop the way it is supposed to?
spinal bifida
describe the development of the cardiovascular system
development begins at week 3 of gestation
primitive heart divides into two ventricles at week 4
by week 7 septum communication between the two chambers closed off
describe the development of the respiratory system
begins at week 3
at week 4 laryngotracheal tube present
by 8 weeks, developed but needs to mature to be able to breath once it is born
what is the laryngotracheal tube present at week 4
precursor to trachea and larynx
what happens with the respiratory system in premature babies
lungs are not mature enough to sustain life so they give medication to cause lung maturation so they are not on o2 as long
high levels of 02 causes damage to eyes and ears
when does the primitive gut
develops around week 4
foregut, midgut and hindgut
describe the development of the urinary system
begins early in embryonic development
kidneys around week 4
produce urine around week 11
describe when we determine fetus gender
determined at fertilization
gonads begin developing at week 7
external genitalia not distinct until fetal period; ultrasound determination is b/w 18-22 wks
what are the external visible features at the end of the embryonic period (8 weeks)
head makes up 50% of the embryo’s length
facial features and ears are clearly distinguishable
ears are low set
future eyes visible
formation of upper and lower limbs visible
describe the fetal period
everything is laid down and the organs just need to mature
3rd month (9 weeks post fertilization to birth)
rapid growth and maturation of organs and tissues occurs
characterized by maturation of tissues and organs and rapid growth of the body
mom starts to show and gain weight
what are characteristics of the fetal period
fetus looks more human
Relative head size decreases
Completion of the development of the organ systems
Hair appears on the head and body
Fetus gains weight gain from the development of subcutaneous fat
Fetus is getting ready for extrauterine life
few physical malformations arise during this time because
major organ systems have been established
what are developmental disorders believed to occur during the fetal period
autism
learning disabilities
dyslexia
adhd
CAPD
language issues (delay, dyslexia etc)
why do they smack the baby right after birth?
to cry so the lungs can expand and they start breathing
when does pregnancy start
first day of the last menstrual period
this is the getstational age of the fetus
when must fertilization occur after ovulation
12-24 hours
what joins to create a zygote
egg and sperm
by day 10-12, zygot becomes
embryo
development of the head and neck formation by branchial and pharyngeal arches and can be seen
hillocks arise on branchial clefts
week 5
Arm and leg buds develop
EAC formation begins
begins with invagination of 1st pharyngeal cleft
week 6
External ears begin to show
Septum communication between the two chambers of the heart closed off
Hillocks enlarge and fuse to form pinna
week 7
Lungs are developed but need to mature to be able to breath once it is born
middle ear formation begins
week 8
arms, hands, fingers, feet, and toes fully formed
fingernails and toenails develop
external ears form
week 10
Fetus opens and closes fists and mouth
bones hardening
facial features more prominent
Produce urine
week 11
B/w ____weeks, can determine sex by ultrasound
18-22
middle ear formation ends
formed by tubotympanic recess - extension of the 1st pharyngeal pouch
week 21
EAC formation ends
ends with recanalization (opening/passage) of the meatal plug
week 26
pinna formation complete
week 30
