General Anatomy (ovulation To Implantation)

Question 1

What are the stages for the ovarian cycle?

Answer 1

Hypothalamus—releases GnRH—anterior pituitary—Gonadotrophins

1. Follicle stimulating hormone (FSH) - important to stimulate primary follicles to mature
2. Leutinizing hormone (LH) - Important for the secondary follicles to further go into Graafian and for Graafian to break and release the secondary oocytes in the surrounding corona radiata into the uterine tube.

Question 2

How much does the secondary follicle grow in the days preceding up to ovulation?

Answer 2

25mm

Question 3

What happens when there is an LH surge in the mid cycle?

Answer 3

• causes oocytes to complete meiosis 1 and initiate meiosis 2, but it is arrested in metaphase 2, 3 hours before ovulation.
• stimulates production of progesterone by follicular stromal cells
• causes follicular rupture and ovulation

Question 4

What is the process of ovulation?

Answer 4

• During ovulation, the ovary begins to bulge and the apex of the bulge has an avascular spot the stigma
• LH increases the collagenase activity which digest the collagen fibers around the follicle
• prostaglandins produce local muscular contractions in the ovarian wall to extrude the oocyte
• ovulations occurs as a process of extrusion of the oocyte with its surrounding granulosa cells
• some of the cumulus oophorus cells rearrange around the zona pellucida to form the corona radiata

Question 5

What is the process of post-ovulation?

Answer 5

• After ovulation the corona radiata cells remain with the oocyte.
• Under influence of LH the remaining granulosa cells acquire a yellow pigment and change into lutean cells which form the corpus luteum.
• The corpus luteum secretes estrogen and progesterone (main).
• The hormones cause the uterus to enter the secretory stage.
• All the other follicles which developed with the mature Graffian follicle degenerate.
• When a follicle become atretic the surrounding cells degenerate and replaced by connective tissue, corpus atreticum.

Question 6

How is the oocyte transported?

Answer 6

• The fimbriae of the uterine tube sweep over the surface of the ovary.
• The oocyte with the surrounding cells are taken into the tube.
• The oocyte is propelled by peristaltic muscle contractions of the tube and cilia together with the regulation from the hormones.
• The fertilized oocyte reaches the uterine lumen in 3-4 days.

Question 7

What happens if the oocyte is not fertilized?

Answer 7

If the oocyte is not fertilized the corpus luteum reaches its maximum development 9 days after ovulation and degenerates called as corpus albicans

Question 8

What happens if the oocyte is fertilized?

Answer 8

• If fertilized the degeneration is prevented by Human chorionic gonadotropin (hCG) from the trophoblast.
• The corpus luteum secretes progesterone till 4th month of pregnancy before the placenta takes over.

Question 9

What happens if progesterone is removed before 4 months?

Answer 9

It can cause abortion

Question 10

What is fertilization?

Answer 10

It is a process by which male and female gametes fuse and it occurs in the ampulla of the uterine tube

Question 11

What is the process of the sperm to reach the ampulla of the uterine tube?

Answer 11

• Only 1% of the sperms entering the vagina enter the cervix, where they survive for many hours.
• The trip from cervix to uterine tube takes 2-7 hours.
• Up on ovulation the cumulus cells produces chemo- attractants and the sperms swim towards the ampulla.

Question 12

What are the two processes that the sperm undergoes to acquire the ability to fertilize?

Answer 12

• Capacitation
• Acrosomal reaction

Question 13

What happens in capacitation?

Answer 13

• Conditioning in the female genital tract especially in the uterine tube.
• Lasts for approximately 7 hours
• Glycoprotein coat and seminal plasma proteins are removed from the plasma membrane overly

Question 14

What happens in Acrosomal reaction?

Answer 14

• Occurs after the sperm binds to zona proteins.
• The zona pellucida induces acrosomal reaction.
Changes in the sperm
• Acrosin and trypsin like enzymes are secreted to penetrate the zona

Question 15

What are the three stages of fertilization?

Answer 15

Phase I: penetration of corona radiata
Phase II: penetration of zona pellucida
Phase III: fusion of the oocyte and sperm cell membranes

Question 16

What happens in Phase 1: penetration of corona radiata?

Answer 16

• Of the 200-300 million sperms that deposit, only 300-500 reach the site fertilization.
• Only one of these fertilizes the egg.

Question 17

What happens in phase 2: penetration of zona pellucida?

Answer 17

• The zona is a glycoprotein shell surrounding the egg that facilitates sperm binding and induces acrosome reaction.
• Release of acrosin allows the sperm to penetrate the zona.
• When the head of one sperm comes into contact with the oocyte, the cortical granules in the cytoplasm release lysozymes which alter the properties of the zona pellucida.
• This makes the environment hostile for the penetration of the zona by other sperms.

Question 18

What happens in phase 3: fusion of the oocyte and sperm cell membrane

Answer 18

• Both the head and tail of the spermatozoon enter the cytoplasm of the oocyte.
• The plasma membrane is left on the surface of the oocyte.

Question 19

What happens when the sperm enters the oocyte?

Answer 19

1. Cortical and zona reactions- massive exocytosis of cortical granules that induce zona reaction.
   - Induced by proteases from cortical granules the zona pellucida hardens and sperm receptors in the zona pellucida are destroyed.
2. Resumption of second meiotic division
   • The one which gets the major portion of the cytoplasm is the definitive oocyte and the other is the 2nd polar body.
   • The definitive oocyte with haploid number of chromosomes (22 X) is called the female pronucleus.
3. Metabolic activation of the egg
   • The activation factor is carried by the sperm
   • Activation encompasses the initial cellular and molecular events associated with embryogenesis.

Question 20

What happens during fertilization?

Answer 20

• The nucleus of the sperm becomes swollen and
becomes the male pronucleus.
• The male and female pronuclei are indistinguishable and lose their nuclear envelopes and fuse.
• Haploid gametes fuse to restore the diploid number of chromosomes.

Question 21

What is the result of fertilization?

Answer 21

1. Restoration of the diploid number of chromosomes.
   Half from the father and half from the mother.
2. Determination of the sex of the fetus.
   X carrying sperm produces XX embryo and Y carrying sperm produces XY embryo.
3. Initiation of cleavage.
   The fertilized zygote starts dividing.
   Without fertilization the ovum degenerates in 24 hours.

Question 22

What happens after the two cell stage?

Answer 22

• Afterthetwo-cell stage, the zygote undergoes series of mitosis.
•The number of the cells increase but the size decreases.
They are called blastomeres

Question 23

What happens after the 8 cell stage?

Answer 23

• Afterthe8-cellstagethe blastomeres undergo
compaction forming a compact ball of cells.
• 3 days after fertilization, the cells divide to form the 16-cell morula.

Question 24

What happens when the Morula enters the uterine cavity?

Answer 24

• When the morula enters the uterine cavity, fluid penetrates through the zona into the intercellular spaces of the inner cell mass.
• A single cavity is formed after the confluence of the spaces.
• Now the embryo is called as the blastocyst.
• Cells of the inner cell mass are called embryoblast.
• Cells of the outer cell mass called trophoblast flatten and form the epithelial wall of the blastocyst.

Question 25

What is the uterine cycle?

Answer 25

In every menstrual cycle, the innermost lining of the uterus undergoes 3 phases
1. Follicular (proliferative) phase
2. Secretory phase
3. Menstrual phase
- zygote implants in the endometrium of the uterus during secretory phase
- the uterine glands and arteries are coiled, and tissue is succulent

Question 26

What is the process for implantation?

Answer 26

• The zona pellucida disappears allowing implantation.
Implantation
• In humans the trophoblastic cells penetrate between the cells of the uterine mucosa at about the 6th day.

• The human blastocyst implants in the
  endometrium of the anterior or posterior wall of the uterus.
• Approx.7 days after fertilization.
• It becomes embedded between the openings of the glands.

Question 27

What is the ovulation pain (Mittelschmerz)?

Answer 27

• Pain in lower abdomen in the middle of the cycle. Due to prostaglandin induced ovarian contractions.
• Associated with rise of basal body temperature.
• Fern like pattern of cervical mucus.
• Useful in recognizing ovulation when the woman is treated for ovulation failure.

Question 28

What is implantation bleeding?

Answer 28

• Bleeding is common during implantation and often mistaken for menstrual period.
• It is only for few days.
• Lighter bleeding.
• No abdominal pain.
• Ultrasound examination is normal.

Question 29

What is ectopic pregnancy?

Answer 29

• Abnormal implantation outside the normal area of implantation (within or outside the uterine cavity)
• Most commonly occurs in the ampulla of the Fallopian tube.
• Can cause rupture of tube and bleeding in the peritoneal cavity.
• Produces symptoms of P/V bleeding and abdominal pain.
Ectopic pregnancy
• Can be life threatening.