Coitus and Fertilisation

Question 1

What are the 4 stages of the sex response?

Answer 1

• excitement
• plateau
• orgasm
• resolution

Question 2

Describe the excitement stage of the male sex response

Answer 2

• psychological and physical stimulation of reogenous zones
• tumescence and erection of penis
  ( due to stimulation of PSNS)
• relaxation of smooth muscle of corpora cavernosa, corpus spongiosum allows inflow of blood resulting in increase in volume and rigidity

Question 3

Describe the plateau stage of the male sex response

Answer 3

• movement of ejaculate into prostatic or proximal part of urethra (under SNS control)
• spinal reflex: forceful expulsion of semen from urethra
• triggered by entry of semen from prostatic urethra into bulbous urethra

Question 4

Describe the orgasm and resolution stage of the male sex response

Answer 4

Orgasm:

• release of tension
• generalised, rhythmic contraction of pelvic floor, ischiocavernoosus and bulbospongiosus muscles
• spasmodic contractions of muscles of hips and anal sphincter

Resolution:

• return to pre-excitement state, personal satisfaction and well being
• refractory period

Question 5

Describe the excitement stage of female sex response

Answer 5

• psycological and physical stimulation of erogenous zones

- tumescence and erection of clitoris, engorgement of female tract (due to stimulation of PSNS)

Question 6

Describe the plateau stage of female sex response

Answer 6

• marked vasocongestion
• sex flush on breasts, chest and epigastrium
• engorgement of labia, lower third of vagina with narrowing of diameter, dilation of upper 2 thirds of vagina
• clitoral swelling and erection

Question 7

Describe the orgasm and resolution stage of female sex response

Answer 7

Orgasm:

• release of tension
• generalised, rhythmic myotonic contractions of perivaginal muscles, anal sphincter and uterus

Resolution:

• return to pre-excitement state, personal satisfaction and well being
• new excitement cycles may be initiated

Question 8

When must sexual activity occur for successful fertilisation?

Answer 8

no more than 3 days before ovulation and no more than 1 day after ovulation

Question 9

Describe the transport of the ovum to the fallopian tube

Answer 9

• at ovulation egg is extruded onto the surface of the ovary
• fimbriae sweep over ovary surface and pick up ovum
• sticky cumulus cells cling to ciliated surface of fimbriae
• movement of cilia and smooth muscle of fallopian tube propel ovum towards uterus
• ovum released from ovary and wafted by fimbriae into fallopian tube
• fertilised in ampulla

Question 10

Describe the transport of the conceptus to the uterus

Answer 10

• conceptus held in fallopian tube as oestrogen maintains contraction of smooth msucle near where fallopian tube enters wall of uterus
• conceptus undergoes mitotic cell divisions (cleavage and morula is formed)
• plasma progesteron levels rise 3-4 days after fertilisation, smooth muscle relaxes and conceptus moves into uterus
• cavities then develop between cells (blastocyst)
• blastocyst then lies free in uterine cavity supported by secretions

Question 11

Describe the transport of sperm

Answer 11

• ejaculation deposits millions of sperm into the vagina
• sperm mortality from vagina to fallopian tube is large
• passage into cervical mucus dependent on oestrogen- induced changes in mucus consistency
• movement through uterus and fallopian tube is by sperms own propulsions and vaginal, cervical, uterine contractions and ciliary beat movement in fallopian tubes

Question 12

What barriers are there to sperm making it to the fallopian tubes?

Answer 12

• acidic vaginal environment
• uterotubal junction anatomical barrier
• phagocytosis by leucocytes in uterine lumen
• length and energy requirements of the trip

Question 13

What is capacitation?

Answer 13

a process involving:

• increase in Ca2+ permeability causing a rise in intracellular Ca2+
• removal of membrane proteins
• change in surface charge
• depletion of cholesterol

to allow sperm to fuse with egg

Question 14

What are the results of capacitation?

Answer 14

• instead of wave-like beats of sperm, whip-like action to propel sperm forward
• sperm’s plasma membrane is altered so it can fuse with surface membrane of egg (acrosome reaction)

Question 15

Describe how the sperm cell enters the egg

Answer 15

• sperm cell binds to zona pellucida
• rise in intracellular Ca2+ in sperm cell triggers exocytosis of acrosome, which contains hydrolytic enzymes that are released
• enzymes locally dissolve zona pellucida and whip-like tail pushes sperm head toward oocyte membrane
• microvilli on occyte surround sperm head and 2 membranes fuse
• contents of sperm cell enter oocyte

Question 16

Describe the events that take place after the sperm has entered the egg

Answer 16

• a rise in intracellular Ca2+ inside oocyte triggers a cortical reaction
• exocytosis of granules that before lay beneath plasma membrane
• leads to changes in zona pellucida causing it to harden preventing entry of other sperm cells
• second meiotic division completes forming a secon polar body
• head of sperm enlarges to become male pronucleus with fuses with female pronucleus

Question 17

How does the blastocyst avoid maternal rejection?

Answer 17

• releases immunosuppressive agents

- secretes hCG