fertilisation and embryology

Question 1

what can influence fertility

Answer 1

exercise , smoking , PCOS ,endo

Question 2

how long do eggs live for after ovulation

Answer 2

12 - 24

Question 3

how many sperms are released at each ejaculation

Answer 3

300 million

Question 4

Explain the process of ovulation and the journey of the oocyte, including how sperm interacts with the secondary oocyte during fertilization.

Answer 4

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.

Question 5

Describe the journey of sperm during ejaculation and explain the factors that affect their ability to reach the fallopian tube and fertilize the oocyte.

Answer 5

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

Question 6

what is fertilisation

Answer 6

fertilisation is known as conception fusion of sperm with oocyte to form a zygote

Question 7

what is capacitation in fertilisation

Answer 7

changes in plasma membrane

Question 8

when the acorsomal layer of the sperm becomes more reactive what happens

Answer 8

releases an enzyme known as hyaluronidase

Question 9

what happens in the acromosone reaction

Answer 9

acromosone reaction disperses the corona radiata allowing sperm to access the zone pellucida first sperm that reaches the zone pellucida penetrates it

Question 10

what is the fertlization general acrosomal reaction

Answer 10

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

Question 11

what happens when penetration of sperm and egg happen

Answer 11

cortical reaction

Question 12

what happens at the development of the zygote week 0-2

Answer 12

pre embryonic period - includes implantation of the zygote into the endometrium

Question 13

what happens at the development of the zygote at week 2 - 8

Answer 13

embryonic period

Question 14

what happens at the development of the zygote at week 8

Answer 14

birth fetal period

Question 15

what happen in the pre embryonic period

Answer 15

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!

Question 16

what is the blastocyst

Answer 16

58 cells

Question 17

what is the inner cell mass of the blastocyst and outer cell mass

Answer 17

inner cell mass is known as embryo blast and an outer cell mass is known as trophoblast

Question 18

what does the trophoblast become

Answer 18

the placenta and chorion

Question 19

what does the embryo blast become

Answer 19

embryoblast becomes the embryo , amnion and umbilical cord

Question 20

what happens in implantation

Answer 20

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.

Question 21

what does the villi do

Answer 21

helps enable gas exchange

Question 22

what is the function of the corpus luteum

Answer 22

HCG is secreted maternal circulation and maintains the corpus luteum this ensures continued production of oestrogen and progesterone

Question 23

what happens in embryonic development

Answer 23

as implantation occurs embryo develops from the embryo blast cell of embryo blast differentiate into two different types of cells

embryonic epiblast
hypoblast

Question 24

what is the embryonic epiblast

Answer 24

closest to the trophoblast becomes the embryo and amniotic cavity

Question 25

what is the hypoblast

Answer 25

closest to blastocyst cavity and becomes the yolk sac

Question 26

what are the three layers of the epiblast cells

Answer 26

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

Question 27

what is organogenesis

Answer 27

from 3 weeks the embryo enters a vulnerable stage of organogenesis completed by 8 weeks

Question 28

what happens at week 4- 7 embryonic development

Answer 28

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

Question 29

what happens at week 8 - 11

Answer 29

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

Question 30

what week is fetes fully formed

Answer 30

12 weeks