Lecture 11: Sex and fertilisation

Question 1

What does coitus mean?

Answer 1

Sex

Question 2

How many oocytes are produced per cycle?

Answer 2

1 (of good quality)

Question 3

How do the sperm mature in the epididymis?

Answer 3

-on entry, spermatozoa are not capable of movement
-once at tail end of the epididymis they are capable of movement and have potential to fertilise
-addition of secretory products to surface of sperm
(dependent on androgens)

Question 4

What is semen made of?

Answer 4

• spermatozoa

- seminal plasma (derived from accessory glands in the male reproductive tract)

Question 5

What is the function of semen?

Answer 5

• transport medium
• nutrition
• buffering capacity (differences in pH in areas)
• prostaglandins stimulate muscular activity in female tract?

Question 6

What is the seminal plasma made from?

Answer 6

Seminal vesicles:

• 60% of volume
• alkaline fluid (neutralises the acid in male urethra and female reproductive tract)
• fructose, prostaglandins, clotting factors to ensure the sperm stays in the female reproductive tract (semenogelin)

Prostate gland:

• 25% of volume
• milky, slightly acidic (buffer alkali from vesicles slightly)
• proteolytic enzymes to breakdown the clotting proteins, after the sperm has been deposited
• citric acid, acid phosphotase (nutrition)

Bulbourethral glands:

• very small volume
• alkaline fluid (buffering)
• mucous that lubricates the end of the penis and urethral lining

Question 7

What are the normal values for semen analysis?

Answer 7

Volume of ejaculate: 2-6ml
Viscosity: liquefaction in 1 hr 
pH: 7-8
Count: >/= 20 million/mL
Motility: >/= 50%
Morphology: 60% normal

(check all of these for subfertility issues)

Question 8

Where does fertilisation usually occur?

Answer 8

Ampulla of the uterine tube

male gamete needs to travel 100000 times its own length

Question 9

What are the different phases in the human sexual response?

Answer 9

Excitement phase (psychogenic/somatogenic stimuli)
Plateau phase
Orgasm phase
Resolution phase (return to haemodynamic norm, followed by a refractory period in males)

Question 10

What is the first male sexual response and why does it happen?

Answer 10

Erection
Stimulants:
-psychogenic
-tactile (sensory afferents of penis and perineum)
SPINAL REFLEX (afferents)
-somatic and autonomic efferents stimulated (pelvic nerve and the pudendal nerve-somatic)
-this causes haemodynamic changes

Question 11

What haemodynamic changes happens during an erection?

Answer 11

-sinusoidal relaxation
-dilation of arterioles
-venous compression
=more blood coming in, less leaving
(tunica albuginea allows for a strong cover around the erection)

-controlled by parasympathetics

Question 12

What is the function of nitric oxide?

Answer 12

Large amounts of NO released: driver of erection
-post-ganglionic fibres released ACh
-ACh binds to M3 receptors on endothelial cells
-causing a rise in intracellular Ca2+, activating nitric oxide synthase and formation of NO
-NO diffuses into vascular smooth muscle and causes relaxation (dilation)
(NO can also be released directly from nerves)

Question 13

What are some causes of erectile dysfunction?

Answer 13

• psychological
• tears in fibrous tissue of corpora cavernosa
• vascular control
• drugs

Question 14

How does viagra work?

Answer 14

Slows the rate at which cGMP degrades, which is involved in the production of NO

Question 15

What is the second part of the male sexual reponse (after erection)?

Answer 15

Emission and ejaculation (under sympathetic control)
Emission:
-movement of semen into the prostatic urethra
-caused by contraction of smooth muscle in prostate, vas def and seminal vesicles
Ejaculation
-expulsion of semen into female reproductive tract
-contraction of glands and ducts (smooth muscle)
-bladder internal sphincter contracts to prevent retrograde ejaculation
-rhythmic striatal muscle contractions (pelvic floor, perineal muscles, bulbospongiosus)

Question 16

How does the cerival mucus change in the menstrual cycle?

Answer 16

Oestrogen: thin and stretchy (good for male gametes: lubrication)
Oestrogen and progesterone: thick, sticky, forms a plug (prevents further access of other sperm, or infection)

Question 17

When does capacitation occur?

Answer 17

• further maturation of sperm occurs in female reproductive tract (6-8hrs)
• sperm cell membrane changes to allow fusion with oocyte cell surface
• tail like movement change from beat to whip like action
• now capable of undergoing the acrosome reaction

Question 18

What is the fertile window?

Answer 18

Spermatozoa: 48-72 hrs
Oocyte: 6-24 hrs max
Sperm deposition up to 3 days prior to ovulation or day of ovulation

Question 19

How do the gametes move?

Answer 19

Oocyte: beating cilia and peristalsis of uterine tube
Sperm: own propulsion

Question 20

What is the acrosome?

Answer 20

• derived from golgi region of developing spermatid
• contains enzymes (to get through zona pellucida)
• necessary for fertilisation

Question 21

What is the acrosome reaction?

Answer 21

• sperm pushes through the corona radiata (supporting cells)
• binding of sperm surface receptor to ZP3 glycoprotein of zona pellucida
• triggers acrosome reaction and therefore the digestion of the zona pellucida
• one sperm penetrates and this leads to fusion of plasma membrane as we only want one sperm to penetrate

Question 22

What is the cortical reaction?

Answer 22

Fusion between zona pellucida and head of sperm, causes a wave of calcium signalling, which makes the membrane impregnatable
-blocks polyspermy

Question 23

When does completion of meiosis 2 occur?

Answer 23

• series of calcium waves are activated following fusion of oocyte and sperm membranes
• resumption of meiosis 2
• pronuclei move together
• mitotic spindle forms leading to cleavage

-further divisions take place and we get a morula (each cell is totipotent)

Question 24

How does assisted reproductive technology work?

Answer 24

• oocytes are fertilised in vitro and allows to divide to the 4 or 8 cell stage
• morula is then transferred into the uterus

Question 25

What is pre-implantation genetic diagnosis? (PGD)

Answer 25

A cell can be safetly removed from the morula and tested for serious heritable conditions prior to transfer of embryo into mother

Question 26

When can the embryo interact with the uterine surface?

Answer 26

Formation of the blastocyst (first differentiation forming inner and outer cell masses)
-blastocyst hatches from zona pellucida and is free to enlarge an interact with the uterine surface to implant

Question 27

What happens in implantation?

Answer 27

• outer cell mass (trophoblast) interacts with the endometrium
• endometrium controls the degree of invasion

(Ectopic implantation: at sites other than endometrium lined uterine cavity, implantation in lower uterine segment can cause placenta praevia)