fertilisation and embryology Flashcards
what can influence fertility
exercise , smoking , PCOS ,endo
how long do eggs live for after ovulation
12 - 24
how many sperms are released at each ejaculation
300 million
Explain the process of ovulation and the journey of the oocyte, including how sperm interacts with the secondary oocyte during fertilization.
Primary oocyte undergoes meiosis 1 to form a secondary oocyte.
Ovulation typically occurs on day 14 of the menstrual cycle, releasing the oocyte.
After ovulation, the oocyte enters the fallopian tube, where it is carried along by the cilia and the peristaltic muscular contractions of the tube (the oocyte itself has no locomotion).
The cervix produces alkaline mucus, which attracts sperm, aiding their journey towards the oocyte.
The unfertilized oocyte can only survive for a short time, roughly 12-72 hours.
Upon sperm penetration, the secondary oocyte undergoes meiosis 2, leading to fertilization.
Describe the journey of sperm during ejaculation and explain the factors that affect their ability to reach the fallopian tube and fertilize the oocyte.
Each ejaculation releases about 300
million sperm (2-6ml)
o Only about 15% are thought to reach
the oocyte, the other 85% will die on
the journey
o The sperm which reach the cervical
mucus survive and propel themselves
towards the fallopian tubes, but the
others are destroyed by the acid
medium of the vagina
o Only normal, healthy and vigorous
sperm will reach the fallopian tube
what is fertilisation
fertilisation is known as conception fusion of sperm with oocyte to form a zygote
what is capacitation in fertilisation
changes in plasma membrane
when the acorsomal layer of the sperm becomes more reactive what happens
releases an enzyme known as hyaluronidase
what happens in the acromosone reaction
acromosone reaction disperses the corona radiata allowing sperm to access the zone pellucida first sperm that reaches the zone pellucida penetrates it
what is the fertlization general acrosomal reaction
sperm makes contact with the egg
acrosome react with zone pellucida
acrosome reacts with privitelline space
plasma membrane of sperm and egg fuse
sperm and nucleus enters the egg
what happens when penetration of sperm and egg happen
cortical reaction
what happens at the development of the zygote week 0-2
pre embryonic period - includes implantation of the zygote into the endometrium
what happens at the development of the zygote at week 2 - 8
embryonic period
what happens at the development of the zygote at week 8
birth fetal period
what happen in the pre embryonic period
The first week – the zygote travels along the
fallopian tube towards the uterus
o The zygote receives nourishment (mainly
glycogen) from the goblet cells of the fallopian
tubes and the secretory cells of the uterus
o During this travel the zygote goes through
cleavage (mitotic cellular replication and
division). This results in the formation of smaller
cells known as blastomeres.
o Day 1 – zygote splits into 2 cells
o Day 2 – zygote has into 4 cells
o Day 2.5 – zygote has split into 8 cells
o Day 3 – zygote has split into 16 cells
Now known as the morula!
what is the blastocyst
58 cells
what is the inner cell mass of the blastocyst and outer cell mass
inner cell mass is known as embryo blast and an outer cell mass is known as trophoblast
what does the trophoblast become
the placenta and chorion
what does the embryo blast become
embryoblast becomes the embryo , amnion and umbilical cord
what happens in implantation
on 6th day implantation happens this happens in. the upper posterior wall where trophoblastic cell make contact with the endometrium they undergo rapid DNA synthesis this mass of tissue is called syncitrophoblast.
what does the villi do
helps enable gas exchange
what is the function of the corpus luteum
HCG is secreted maternal circulation and maintains the corpus luteum this ensures continued production of oestrogen and progesterone
what happens in embryonic development
as implantation occurs embryo develops from the embryo blast cell of embryo blast differentiate into two different types of cells
embryonic epiblast
hypoblast
what is the embryonic epiblast
closest to the trophoblast becomes the embryo and amniotic cavity
what is the hypoblast
closest to blastocyst cavity and becomes the yolk sac
what are the three layers of the epiblast cells
here are three layers of epiblast cells, which
form particular parts of the embryo. These three
germ layers are developed through gastrulation.
1. Ectoderm – the start of the tissue which covers
most of the surfaces of the body: the epidermis
layer of the skin, hair and nails. It also forms the
nervous system
2. Mesoderm – forms the muscle, skeleton, dermis
of skin, connective tissue, urogenital glands,
blood vessels and blood and lymph cells
3. Endoderm – forms the epithelia lining of the
digestive, respiratory and urinary systems, and
glandular cells
what is organogenesis
from 3 weeks the embryo enters a vulnerable stage of organogenesis completed by 8 weeks
what happens at week 4- 7 embryonic development
Visible on ultrasound from 5-6 weeks
Nervous system starts developing at 5 weeks
Heart forming in a tube link structure (5 weeks)
Arms and legs become visible as small swellings (6 weeks)
See through skin present (6 weeks)
Head and facial features develop
ALL major organs present in primitive form
Inner ear starts to develop (7 weeks)
External genitalia present
Fetal movement seen on ultrasound
what happens at week 8 - 11
Still getting nourishment from yolk sac (8 weeks)
Eyelids fuse, eyes develop colour pigment
Fully functioning fetal circulation
Sucking and swalling begin
Kidneys begin to function and the fetus can pass dilute urine
Some primitive reflex present
Outer ear begins to develop (10 weeks)
Heart is fully formed (10 weeks)
Fetal head makes up 1/3 of the total body length
what week is fetes fully formed
12 weeks
