Conception & Fetal Development Flashcards
After ovulation, the ruptured follicle collapses and forms what?
The corpus luteum
What does the corpus luteum do?
Secretes progesterone and oestrogen
What happens to the corpus luteum if pregnancy does not occur?
Degenerates in 10 days, leaving a scar called corpus albicans
What happens to the corpus luteum if pregnancy does occur?
It produces hormones until the placenta takes over the role at about week 10 of pregnancy
Explain the process pre-conception
- ovulation, an oocyte is in the fallopian tube
- spern ejaculated into vagina and some cross the cervical os and entered fallopian tubes
- before fertilisation sperm undergoes two maturational changes
What are the two maturational changes sperm undergoes before fertilisation?
Capacitation and acrosome reaction
Explain sperm maturation - Capacitation
- degeneration of the membrane over the acrosome (sperm head)
- stimulated by chemical within female genital tract
- increases mobility of sperms tail
Explain sperm maturation - acrosome reaction
- binding a sperm to the zona pellicuda triggers the acrosome reaction
- release of enzymes prior to the binding disperse to corona radiate
- following binding enzymes, sperm digests and penetrates a path to egg cell
What is the zona pellicuda?
outer layer of the ovum, jelly-like layer
What is the corona radiate?
The outermost layer of the ovum
What occurs upon entry of sperm during fertilisation?
the ovum nucleus swells, creating the female pronucleus. The sperm nucleus is released in the cytoplasm of the oocyte and the two nuclei approach each other
What makes the female and male nuclei both ‘haploid’?
They contain 23 chromosomes
What are the fused nuclei named as the conceptus (product of fertilisation)?
Zygote
The zygote is ‘diploid’ because..
It holds 46 chromosomes
Within 24 hours what happens to the zygote?
undergoes mitosis and splits into 2 smaller cells
What is the process of the zygote splitting called?
cleavage
What is the name of the smaller cells of zygote called when split?
blastomeres
The zygote continues cleaving, dividing into:
- 2 cells within 24 hours
- 4 cells within 48 hours
- 8 cells within 60 hours
- 16 cells within 72 hours
What is the zygote known as at the point of 16 cell division?
Morula
The zygote structure has not increased in size despite cleavage. How?
The cells become more compact
During the development of the blastocyst (morula) what is the process of cavitation?
occurs where the outer cells secrete fluid into the moral creating a fluid filled cavity
What is the name of the fluid filled cavity made through cavitation?
blastocyst
When does the formation of the blastocyst occur?
When there is at least 32 cells - cleavage
What is the blastocyst composed of?
- a single layer of trophoblasts (flattened outer cells)
- an inner cell mass, embryoblast
What do the trophoblasts form?
the placenta and chorion
What do the embryo blasts form?
the embryonic disc including umbilical cord and amnion
Define chorion?
Outermost layer of membranes surrounding the embryo
Define amnion?
The amnion is membrane that covers the embryo when first formed. Fills with amniotic fluid which causes the amnion to expand and become the amniotic sac
When does implantation occur?
Between day 6 and 14 after ovulation
What allows implantation to occur?
when the trophoblasts adhere to/stick to the prepared endometrium
Implantation can result in…
a small amount of vaginal bleeding that can be mistaken as menstruation - known as implantation bleed
Day 14 when implantation is complete, what begins to develop?
The placenta (trophoblast cells)
Define ‘embryo’
this term refers to the conceptus form implantation until 8 weeks after conception
By week 2 the embryo blast cells differentiate into 2 types of cells:
epiblasts and hypoblasts
What do the epiblast and hypoblast cells form?
Bilaminar embryonic disc
What does the hypoblast cells form?
The umbilical vesicle (sac) and umbilical cord
What does the epiblast cells form?
the amnion
What does the umbilical vesicle do that is formed by hypoblast cells?
- provides nourishment
- forms part of digestive system
- produces earliest blood cells and vessels
What does the amnion do formed by the epiblast cells?
grows more rapidly than the embryo and surrounds it
Define ‘organogenesis’
Development of the embryo
What happens to the bilaminar embryonic disc around day 15
further differentiation enables the inner cell mass to become the trilaminar embryonic disc
What are the 3 primary germ layers of the trilaminar embryonic disc?
- ectoderm
- mesoderm
- endoderm
What does the ectoderm layer do within the trilaminar embryonic disc?
forms structures of nervous system, skin epidermis, hair and nails
What does the mesoderm layer do within the trilaminar embryonic disc?
forms the skeleton, muscles, connective tissues, kidneys, heart, lymph, dermis of skin, blood and blood vessels
What does the endoderm layer do within the trilaminar embryonic disc?
forms the epithelial layer of digestive, respiratory and urogenital systems and glandular cells of liver and pancreas
Define ‘embryonic folding’
the disc results in a tube from a change of shape and relationship of the organs - after 4 weeks
Fetal Development: Weeks 8-12
Eyelids develop Kidneys begin to function Passing urine from week 10 Fetal circulation functioning Sucking and swallowing begins Lanugo appears (thin hair) Moves freely Gaining weight Fetal heart rate heard
Fetal Development: Weeks 12-16
Skeletal development
Meconium present in gut (first stool)
Nasal septum and palate fuse
Sex distinguishable
Fetal Development: Weeks 16-20
‘Quickening’ - mother feels movement Fetal heart easily heard on auscultation Vernix appears Fingernails can be seen Skin cells begin to be renewed
Fetal Development: Weeks 20-24
Periods of sleep and activity
Respond to sound
Skin red and wrinkled
Fetal Development: Weeks 24-28
Survival can be expected if born
Eyelids open
Respiratory movements
Fetal Development: Weeks 28-32
Begins to store fat and iron
Testes descend into the scrotum
Lanugo disappears from face
Fetal Development: Weeks 32-36
Increased fat make the baby more rounded
Lanugo disappears from the body
Nails reach tips of fingers
Head hard lengthens
Producing surfactant to help lung inflate at birth
Weight gain 25g per day
Plantar creases visible - i.e. creases in hands and feat
Fetal Development: 36-40 weeks
Contours rounded
Skull fully formed by soft and pliable - so the plates can override making the head as small as possible for birth
At ‘term’ - birth is due
