Development in Utero Flashcards
Describe the developmental stages in utero
1-zygote-fusion of gametes to 16 cells
2-morula-day 3 clump of cells undergoing mitosis
4-blastocyst-day 4/5-20 inner cell mass to bilaminar disc
5-embryo-day 21-56 from somites through organogenesis
6-fetus week 9 to birth
Name the different structures of the ovum from outer to inner
-corona radiate-outer cell layer
-zona pellicuda
-membrane
-cortical granule
-mitochondria, nucleus, chromosomes
Describe the events that occur during fertilization
1-conception
2-sperm pentrates the corona radiate and zona pellicuda
3-acrosome secretes enzymes that digest the zona pellucida of the ovum
4-sperm binds to plasma membrane of the ovum and enters the cell
5-depolarisation of cell membrane of the fertilised ovum and release of calcium ions to prevent polyspermy
6-genetic info of the sperm fuses with the ovum nucleus to complete fertilization
-zygote formed
Describe the structure of the zygote
-46 chromosomes total
-number of chromosomal changes occur and bring together male and female chromosomes to form a diploid cell within the first 2-3 hours following fertilisation
-first mitotic division occurs- proccess is called cleavage
What happens during cleavage?
-2-3 hrs after=2 cells
-1 day after=4 cells
2 days after= 8 cells
3 days after=16 (Morula)
-morula remains within the zona pellucida, prevents implantation in the fallopian tubes due to its smooth surface
Describe the development of the blastocyst
-blastocyst shape changes so there is an outer layer of cells- trophoblast and inner cell mass and a blastocyctic cavity
-embryoblast ( inner mass) differentiates into two layers ( epiblast and hyperblast) together these form the bilaminar embryonic disc
-bilaminar embryonic disc differentiates into the endoderm, mesoderm and ectoderm ( primary germ layers)
What is implantation?
Blastocyst has travelled into the uterus and is ready to be embedded into the upper posterior wall of the uterus
What happens during implantation?
-7-10 days after fertilisation
-before implantation endometrium becomes ready- decidualisation
-endometrial glands accumulate glycogen, growth factor proteins which supply the blastocyst with essential nutrients until 9 weeks
-endometrium only receptive for implantation for a short time period
-trophoblast cells make inital contact with endometrium
-cytotrophoblast and syncitiophoblast then formed
-blastocyst is quickly enveloped by folds of the endometrium and trophoblasts rapidly proliferate
Describe the structure and function of trophoblasts
-from 16-23 cells the outer surface changes to the trophoblast
-trophoblast layer becomes the fetal part of the placenta
-the inner cell mass of blastocyst becomes the fetus
-decidua basalis
-upon implantation hCG hormone produced trophoblast cells to maintain corpus luteum
What is the decidua basalis?
the maternal part of the placenta is formed from the endometrium where the implantation occurred
What happens in gastrulation? ( week 3)
-cells in the embryo begin to invaginate
-the amnion ( fetal side membrane) begins to develop
-the 3 primary germ layers start to develop from bilaminar embryonic disc
-3 layers eventually form all of the tissues and organs
-gastrulation is complete when all three layers are present
What is invagination?
embryos fold back on themselves to create a cavity
What are the 3 primary germ layers?
-ectoderm
-endoderm
-mesoderm
What does the ectoderm become?
-CNS
-sensory epithelia of eye, ear, nose
-dermis, hair, nails
-mammary glands
-pituitary glands
-subcutaneous glands
-enamel of teeth
What does the mesoderm become?
-skeleton,
-muscles,
-kidneys,
-heart,blood,lymph
-cartilage and bone
-connective tissue
-striated and smooth muscle
-gonads
-spleen
-adrenal gland cortex
What does the endoderm become?
-GI tract
-lungs/respiratory system
-liver
-biliary system
What other things form during gastrulation?
-yolk sac and amniotic cavity
-primordial mouth and anus form
-notochord form - gives rise to primitive axis of the body
-neurulation= neural tube and neural crest form from primitive streak
2nd and tertiary chorionic villi begin to form
Describe structures of the extra embryonic membrane
-chorion-part of placenta and facilitates gas exchange, nutrients and waste
-blood cells in yolk sac
-blood vessels of allantois are part of the umbilical cord
-amnion contains fluid that cushions and protects the embryo
What is the allantois?
temporary respiratory organ and store for fetal excretions
What happens to embryo- day 21 onwards?
-organogenesis
-heart= first organ to function
-neural tube closes
-somite development formed from mesoderm
-limb buds day 28
-primordial eye and ear day 28
-ongoing proliferation and differentiation
How is fetal circulation established?
-day 15 mesoderm of yolk sac
-isolated blood islands
-angioblasts- 1st cells, primitive endothelium
-haemoblasts-primitive cells
-vessels very hyperplastic
-day 18 blood in embryo
-day 25 basic circulation
How does the heart form?
-In the mesoderm- intraembryonic coelom ) is formed. It then separates into 2 layers
(tubes)
-Day 20- endocardial tubes (1 each side)
-Blood islands develop in each tube
-Two tubes meet, grow, merge, twist
-Proliferation, differentiation, specialisation
-Sensitive to environmental conditions
-Congenital abnormalities
How do the lungs develop?
-Day 28 – tracheo-
oesphageal fold
-Budding to develop
bronchi
-Week 5-17 -
pseudoglandular
-Week 16-25 –
canalicular stage –
growth of capillary
network
-Week 24 - birth –
terminal sac
-Birth to age 8 - alveolar
How is the gut formed?
-Day 28 tube from mouth to anus and bulges
start to form – stomach
-Involves yolk sac which has to be enclosed
into abdominal cavity
-From day 40 undergoes proliferation and
series of rotations
-Liver and gall bladder develops from buds
(same as lungs)
Describe fetal development weeks 9-12
-Eyelids meet and fuse, fingernails form
-Gut within abdomen develops
-The fetus CRL(crown rump length is approx. 55-60 mm)
-The uterus is still a pelvic organ
What screening test are offered to detect abnormalities?
-Up to 12 weeks: infectious diseases (blood test)
–Up to 10 weeks: sickle cell and thalassaemia (blood test)
– 10-14 weeks: (US scan and blood test) for genetic conditions e.g. Trisomy 21 (Down’s syndrome), trisomy 13 (Patau’s
syndrome), trisomy 18 (Edwards syndrome)
Describe fetal development week 13-16
-Ossification, lanugo, brown fat, moving sucks
thumb
-The uterus is now an abdominal organ
-Fetal movements can start to be felt from 16
weeks onwards
Describe fetal development week 17-20
-Sebaceous glands active – vernix present
-Myelination of spinal cord where a layer of myelin
forms around the axons which allows the nerve
impulses to travel
-Eyelids remain closed
-Screening offered (between 18-21 weeks): US
Scan for 11 physical conditions e.g. congenital
heart defect
Describe fetal development week 21-25
-Viability week 24
-A baby born after 24 weeks gestation will be
treated in NICU. As the lungs are not fully
developed the baby will need assistance with
breathing
Describe fetal development week 26-29
Eyes open, scalp hair, testes in scrotum
Skin thickens
Describe fetal development week 30 onwards
-Brain myelination
-Lungs now fully developed
-Brown fat stores laid down
-Full term (when the fetus is fully
developed) is said to be 37-42 weeks
gestation
Function of the placenta in pregnancy?
-Zygote embedded in
endometrium
-Nourished by uterine secretions
until placenta established
-Placenta secretes progesterone:
prevents uterine contractions
-After 40 weeks oestrogen &
oxytocin promote uterine
contractions
What is the structure of the placenta?
-Made up of embryonic tissue & uterine wall
-Chorionic villi of the chorion project into the uterine
wall to facilitate exchange between fetus and mother
-Umbilical cord carrier fetal blood to & from the
placenta
-Fetal and maternal blood do not mix, but antibodies,
viruses & a variety of chemicals (hormones & drugs)
can cross the placenta into the fetus
Main roles of the placenta?
-Allow diffusion of oxygen, nutrients & wastes
-Remove waste products and CO2
-Provide a protective barrier against micro-
organisms
-Provide a protective barrier between mother and
fetus who are genetically and immunologically
different
-Produces hormones (human chorionic
gonadotrophin, oestrogen and progesterone
Source and stimulus of FSH
source-anterior pituitary
-stimulus GnRH
Source and stimulus of LH
source-anterior pituitary
-stimulus GnRH
Source and stimulus of oestrogen
source-Developing follicles &
corpus luteum
After 6 wks of pregnancy:
placenta
Stimulus-FSH (and LH)
Source and stimulus of progesterone
source-Corpus luteum
After 6 wks of pregnancy:
placenta
stimulus- LH
Primary and secondary effects of FSH
P-Stimulate
maturation of
ovarian follicle
s-Stimulates
production of
oestrogen
Primary and secondary effects of LH
P-Stimulate
maturation of
ovarian follicles, ovulation
s-Stimulates
production of
oestrogen and progesterone
Primary and secondary effects of oestrogen
p-Growth & maturation of
reproductive organs &
breasts; promote
proliferative phase of the
uterine cycle; facilitate
oogenesis; stimulate
capacitation of sperm;
stimulate growth of uterus
and mammary glands in
pregnancy
s-Promote long bone growth
& feminisation of the
skeleton; inhibit bone
resorption; promote female
pattern of fat deposit;
female libido, etc.
Primary and secondary effects of progesterone
P-Facilitates growth of breasts;
promotes secretory phase;
during pregnancy quiets the
myometrium and enhances the
ability of mammary glands to
produce milk; increases body
temperature
What is the function of hCG during pregnancy?
Acts like LH to maintain corpus luteum
(and preventing menstruation), normally corpus luteum
atrophies
What is the function of oestrogen during pregnancy?
-myometrial hypertrophy
-external genitalia enlargement
-softening of pelvic ligaments
What is the function of progesterone during pregnancy?
-Proliferation of endometrium
-inhibition of uterine
contractions
-development of alveoli in mammary glands
What is the function of prolactin during pregnancy?
Milk production when oestrogen falls after parturition.
Inhibits FSH release and ovulation after parturition
What is the function of relaxin during pregnancy?
-produced for the flexibility of tissue
What is the function of oxytocin during pregnancy?
for uterine contractions during labour
Define the first stage of labour
onset, regular painful contractions until the cervix reaches full dilation
Describe the second stage of labour
from full dilation of the cervix until expulsion of the fetus
Describe the third stage of labour
from expulsion of the fetus until the placenta and membranes delivered are complete
