S5.1 Getting Pregnant

Question 1

Where is semen made and in what amounts?

Answer 1

Testis - 10%
Seminal vesicles - 60%
Prostate - 25%
Bulbourethral glands - 5%

Question 2

Describe the composition of seminal vesicle semen

Answer 2

Alkaline fluid which neutralises acid, contains fructose and prostaglandins

Question 3

Describe the composition of prostate semen

Answer 3

Milky acidic fluid which contains proteolytic enzymes to break down clotting factors

Question 4

Describe the composition of bulbourethral semen

Answer 4

Alkaline mucus

Question 5

What is the normal volume of the ejaculate?

Answer 5

2-6ml

Question 6

Describe the stages of the human sexual response

Answer 6

Excitement phase – Psychogenic or somatogenic stimuli
Plateau phase – stimulus maintained
Orgasm phase – if stimulus reaches threshold, orgasm occurs
Resolution phase – Return to haemodynamic norm

Question 7

Describe the physiological processes involved in erection of the penis

Answer 7

Activation of parasympathetic NS and inhibition sympathetic
ACh acts on M3 receptors raising Ca2+, this activates eNOS, more NO produced so vasodilation of arterioles in corpus cavernosa

Question 8

What are some causes of erectile dysfunction?

Answer 8

Physiological
Tears
Vascular damage
Drugs

Question 9

How does viagra make you hard?

Answer 9

Inhibits cGMP breakdown , increasing NO so increasing vasodilation, allowing increased penile blood flow to cause erection.

Question 10

Describe how the composition of cervical mucus changes over the course of the menstrual cycle

Answer 10

In early cycle, lots of oestrogen present, so mucus is thin and stretchy (spinnbarkeit mucus) so can facilitate the entry of male gamete into female tract.
After ovulation Oestrogen and progesterone are present, so mucus is thick and sticky; so limits access of sperm or bacteria into the female tract.

Question 11

What is sperm capacitation?

Answer 11

Sperm glycoprotein coat is removed to allow binding to the corona radiata so sperm can penetrate zona pellucida.
Acrosomal enzymes exposed so can initiate acrosome reaction.

Question 12

What is the acrosome reaction?

Answer 12

Sperm contact the corona radiata then bind to ZP3 proteins of zona pellucida triggering acrosome reaction.
Acrosomal enzymes digest the path through ZP, one sperm penetrates and fuses with the oocyte forming a zygote.

Question 13

Describe the first stages of fertilisation

Answer 13

One sperm penetrates oocyte forming a zygote.
Cortical reaction (wave of Ca2+ spikes change oocyte membrane) prevents polyspermy.
Pronuclei of male and female move together and form a diploid zygote.
Each cell at this stage is totipotent

Question 14

Describe the morula stage of fertilisation

Answer 14

16 cell stage, 3-4 days following fertilisation, embryo moves into uterus

Question 15

Describe the blastocyst stage of fertilisation

Answer 15

Morula develops the fluid-filled blastocoele, loss of totipotency
Embryoblast/inner cell mass–>embryo
Trophoblast/outer cell mass–>placenta (produces hCG)

Question 16

Describe the hatching stage of fertilisation

Answer 16

Trophoblast digests Zona pellucida
Blastocyst hatches from ZP
Blastocyst can now interact with uterine surface to implant

Question 17

Describe the implantation stage of fertilisation

Answer 17

Trophoblast interacts with endometrium controlling degree of invasion.
Progesterone primes endometrium