Sex And Fertilisation

Question 1

Outline maturation of sperm in the epididymis

Answer 1

• spermatozoa not capable of movement on entry
• at tail of epididymis they are capable of movement
• addition of secretory products to surface of sperm
• maturation

Question 2

What is semen made of?

Answer 2

Spermatozoa
Seminal plasma

Question 3

Function of seminal plasma

Answer 3

• transport medium
• nutrition
• buffering capacity

Question 4

Where is seminal plasma released from?

Answer 4

Seminal vesicles
Prostate gland
Bulbourethral glands

Question 5

Describe the seminal plasma from the seminal vesicles

Answer 5

• 65%
• Alkaline fluid to neutralise acid
• Prostaglandins, fructose, clotting factor

Question 6

Describe the seminal plasma from the prostate gland

Answer 6

• 25%
• milky slightly acidic fluid
• Proteolytic enzyme - breaks down clotting protein to reliquefy semen
• citric acid, acid phosphatase

Question 7

Function of the seminal vesicle seminal plasma

Answer 7

Neutralises acidic environment of vagina

Question 8

Function of prostate gland seminal plasma

Answer 8

Breaks down clotting proteins + reliquefies semen due to proteolytic enzymes

Question 9

Describe the seminal plasma from bulbourethral glands

Answer 9

• ~1%
• alkaline fluid
• mucous that lubricates end of penis + urethral lining
  (Pre ejaculate)

Question 10

Normal range of semen volume

Answer 10

1.4-1.7ml

Question 11

Normal range of total sperm count

Answer 11

33 - 46 x10^6

Question 12

Where does fertilisation normally occur?

Answer 12

Ampulla of uterine tube

Question 13

What are the phases of the human sexual response?

Answer 13

• excitement phase
• plateau phase
• orgasm phase
• resolution phase (includes refractory period in men)

Question 14

What nervous system controls erections?

Answer 14

Parasympathetic
- parasympathetic efferents via pelvic nerve
- somatic efferents via pudendal nerve

Question 15

What is the refractory period in the resolution phase in men?

Answer 15

When a man is unable to ejaculate again

Question 16

Nerve roots of the pudendal nerve

Answer 16

S2-S4

Question 17

Anatomy of the penis in an erection

Answer 17

• smooth muscle in helicine arteries relax + straighten
• blood flows into corpus cavernosum (arterial dilatation)
• bulbospongiosus + ischiocavernosus muscles compress venous plexus (venous dilatation > retains blood in penis)
• corpus spongiosum is not completely compressed

Question 18

Outline the neurophysiology of an erection

Answer 18

• inhibition of sympathetic arterial vasoconstrictor nerves
• activation of PNS
• release of nitric oxide

Question 19

Role of nitric oxide in an erection

Answer 19

• released in response to increased [Ca2+] via M3 receptors
• causes vascular smooth muscle relaxation > increased blood flow to penis
• a key mediator in this process in cGMP

Question 20

Causes of erectile dysfunction

Answer 20

• psychological
• vascular e.g. diabetes, hypertension, vascular disease
• anatomical
• neurological
• hormonal
• drugs

Question 21

What nervous system controls ejaculation?

Answer 21

Sympathetic

Question 22

What are the two parts of ejaculation?

Answer 22

• emission: deposition of seminal fluid into prostatic urethra
• expulsion: expulsion of semen through the urethra + out the urethral meatus (ejaculation)

Question 23

What prevents retrograde ejaculation?

Answer 23

Internal sphincter contracts

Question 24

Outline the changes in the cervical mucus throughout the menstrual cycle

Answer 24

• ovulation: oestrogen: thin + stretchy
• around ovulation: oestrogen + progesterone: thick, sticky - forms a plug

Question 25

Outline the female sexual response

Answer 25

- **excitement**: vaginal lubricaiton appears, labia + clitoris enlarge - **plateau**: uterus elevates, vagina expands + orgasmic platform appears - **orgasm**: contractions in orgasmic platform + uterus - **resolution**: orgasmic platform disappears + vagina + uterus returns to normal

Question 26

What is capacitation?

Answer 26

- further maturation of stem in female reproductive tract - sperm cell membrane changes to allow fusion with oocyte - tail movement changes from beat to whip action

Question 27

When does capacitation occur?

Answer 27

After 6-8 hours

Question 28

Fertile window of sperm

Answer 28

48-72 hours

Question 29

Fertile window of oocyte

Answer 29

6-24 hours

Question 30

What is the acrosome?

Answer 30

- Derived from Golgi region of developing spermatic - Contains enzymes to breakdwon oocyte membrane

Question 31

Outline the events of fertilisation

Answer 31

- in the ampulla of uterine tube - acrosome reaction - penetration of ovum membrane - fusion of ova + sperm

Question 32

What is the acrosome reaction?

Answer 32

- sperm push through corona radiata (outer layer of oocyte) - binding of sperm surface receptor to Zona pellucida - triggers acrosome reaction - digestion of Zona pellucida

Question 33

What is the cortical reaction?

Answer 33

- Occurs after first sperm penetrates Zona pellucida - induces the Ca2+ dependent exocytosis of protease containing cortical granules - prevents other sperm from penetrating

Question 34

Outline implantation

Answer 34

- trophoblast interacts with endometrium - implants within the stroma where secretory glands + increased vasculature has formed during metal cycle

Question 35

What is the fertile window?

Answer 35

Sperm can be deposited three days before ovulation as sperm can survive for up to 72 hours

Question 36

Difference in the human sexual response in men and women

Answer 36

Men have a refractory period where as women don’t

Question 37

Outline the excitement phase in men

Answer 37

- occurs due to psychogenic stimulation - parasympathetic efferents via pelvic nerve - somatic efferents via pudendal nerve - causes an erection

Question 38

How do erectile dysfunction drugs improve erectile function?

Answer 38

- Inhibition of cGMP breakdown - Leading to increased NO production + vasodilation