Lecture 11– Getting pregnant: sex and fertilisation

Question 1

Maturation of sperm in the epididymis – the sperms journey (continues!)

• *

Answer 1

• On entry, spermatozoa not capable of movement
• Once at the tail of the epididymis they are capable of movement and have the potential to fertilise
• Addition of secretory products to surface of sperm
• Maturation
  
  • Dependent on support of the epididymis by androgens

Question 2

constituents of semen

Answer 2

• Spermatozoa
• Seminal plasma
• Seminal plasma derived from accessory glands of the male reproductive tract

Question 3

function of semen

Answer 3

• Transport medium
• Nutrition
• Buffering capacity
• Role for prostaglandins in stimulating muscular activity in the female tract

Question 4

seminal palsma contirbutions from

Answer 4

• seminal vesicles
• prostate gland
• bulbourethral glands (Cowpers glands)

Question 5

• Seminal vesicles
  *

Answer 5

• 60% of volume
• Alkaline fluid (neutralises the acid: male urethra and female repro tract)
• Fructose, prostaglandins, clotting factors (semenogelin)

Question 6

• Prostate gland

Answer 6

• 25% volume
• Milky, slightly acidic fluid
• Proteolytic enzymes (breakdown clotting proteins, re-liquefying semen in 10-20 minutes)
• Citric acid, acid phosphatase

Question 7

• Bulbourethral glands (COwpers glands)

Answer 7

• Very small volume
• Alkaline fluid
• A mucous that lubricates the end of the penis and urethral lining

Question 8

normal values of semen

Answer 8

Question 9

next step after sperm and egg mature

Answer 9

Next step….

• Male and female gametes need to meet in the female reproductive tract
• Male gamete needs to travel 100,000 times its own length
• Fertilisation site is normally ampulla of uterine tube

Question 10

Fertilisation site is normally

Answer 10

ampulla of uterine tube

Question 11

The human sexual response….

*

Answer 11

• Excitement phase
  
  • Psychogenic and/ or somatogenic stimuli
• Plateau phase
• Orgasm phase
• Resolution phases
• Return to haemodynamic normal followed by a refractory period in males
  
  • Before the male is ready to initiate excitement phase
  • In the female no refractory phase

Question 12

male sexual stimulations

Answer 12

• psychogenic
• tactile (sensory afferents of penis and perineum)

Question 13

male sexual response after stimulation

Answer 13

spinal reflex

somatic and autonomic efferents

• pelvic nerve (PNS)
• pudendal nerve (somatic)

cause haemodynamic changes- namely vasodilayion

Question 14

tunica albiginea qualities

Answer 14

verg rigid - not much venous return

Question 15

• Erection requires

Answer 15

• Sinusoidal relaxation
• Arterial dilation- blood rushes into corpus cavernosum and spongiosum= erection
• Venous compression

Question 16

summarise erection

Answer 16

• Sympathetic- inhibition (reduction of tone at arterioles)
• Parasympathetic- activates

Question 17

which fibres are involved with parasympathetic innervation

Answer 17

• Lumbar and sacral spinal levels
• Pelvic nerve and pelvic plexus
• Cavernous nerve to corpora and vasculature

Question 18

Neurophysiology of erection

Answer 18

• Inhibition of sympathetic arterial vasoconstrictor nerves
• Activated PNS- vasodilation
• Activation of non-adrenergic, non-cholinergic, autonomic nerves to arteries, releasing Nitric oxide (NO)

Question 19

role of NO in erection

Answer 19

• Post-ganglionic fibres release ACh
• Ach binds to M3 receptor on endothelial cells
• A rise in [Ca2+]i , activation of NOS and formation of NO
• NO diffuses into vascular smooth muscle and causes relaxation (vasodilation)
• NO also released directly from nerves

Question 20

Erectile dysfunction causes

Answer 20

• Psychological (descending inhibition of spinal reflexes)
• Tears in fibrous tissue of corpora cavernosa
• Vascular (arterial and venous)
• Drugs

Question 21

emission is the

Answer 21

• Movement of semen into prostatic urethra
• Caused by contraction of SM in prostate, vas deferens and seminal vesicles

Question 22

ejaculation

Answer 22

expulsion of semen- sympathetic response

Question 23

outline ejaculation

Answer 23

• Contract of the glands and ducts (smooth muscle)
• Bladder internal sphincter contracts
  
  • Preventing retrograde ejaculation
• Rhythmic striatal muscle contraction (pelvic floor, and perineal muscles ischiocavernosus, bulbospongiosus)

Question 24

Menstrual cycle changes in female tract

*

Answer 24

• The character of cervical mucus changes over the course of the menstrual cycle
• Oestrogen
  
  • Thin, stretchy
• Oestrogen and progesterone
  
  • Thick, sticky; forms a plug

Question 25

ways to test fertility

Answer 25

fern test

spinnbarkeit mucus

Question 26

sperm deposition

Answer 26

Question 27

capacitation

Answer 27

• Further maturation of sperm in female reproductive tract (6-8h)
• Sperm cell membrane changes to allow fusion with oocyte cell surface
• Tail movement changes from beat to whip=like action (b)
• Now capable of undergoing the acrosome reaction (C)

Question 28

uterus anteversiona dn anteflexion changes during the sexual response

Answer 28

Question 29

Fertile window- window of opportunity for fertility

Answer 29

Spermatozoa will survive for 3 days in the vagina

• Spermatozoa 48 -72hr
• Oocytes 6 –24 hr (max)
• Fertile period: sperm deposition up to 3 days prior to ovulation or day of ovulation
• Gamete transport
  
  • Oocyte: beating cilia & peristalsis of uterine tube
  • Sperm: own propulsion

Question 30

Overview of events in fertilisation

Answer 30

• Occurs normally in the ampulla of the uterine tubes
• Requires loss of sperm outer shell (acrosome)
• Penetration of ovum membrane, fusion of ova and sperm membrane
• Eventual formation and fusion of pronuclei

Question 31

the acrosome is derived from the

Answer 31

• golgi region of developing spermatids
• contains enzyme necessary for fertilisation

Question 32

Acrosome reaction- allows the sperm to

Answer 32

• Sperm pushes through corona radiate
• Binding of sperm surface receptor ZP3 glycoprotein of zona pellucida
• Triggers acrosome reaction  digestion of zona pellucida

Question 33

Fertilisation

*

Answer 33

• One sperm penetrates leading to fusion of plasma membranes
• Cortical reaction
  
  • Blocks polyspermy

Question 34

completion of meiosis II

Answer 34

• series of calcium waves are activated following fusion of oocyte and sperm membrane
• resumption of meiosis II occurs
• pronuclei move together
• mitotic spidlle froms leading to cleavage

Question 35

assisted reproductive technology

Answer 35

• oocytes fertilised in vitro and allowd to divide to the 4 or 8 cell stage
• morula transferred into the uterus
• pre-implanation genetic diagnosis (PGD)
  
  • a cell can be safely removed from the morula and tested for serious heritable conditions priot to transfer of the embyro into the mother

Question 36

the blastocyst and hatching

Answer 36

• first differnetiation
  
  • inner and outer cell masses
• formation of the balstocyst
• blastocyst hatches from zona pellucida
• it is no longer constrained - free to enlarge
• can now interact with uterine surface to implant

Question 37

implantation

Answer 37

• outer cell mass (trophoblast) interacts sigh endometrium
• endometrium controls degree of invasion
• ectopic implantation
  
  • at sites other than endometrium lined uterine cavity
  • invasion not controlled
• implantation in lower uterine segment can cause placenta praevia