S5) Sexual Function and Fertilisation Flashcards
Describe the composition of semen
- Spermatozoa +
- Seminal plasma
Identify 3 functions of the semen
- Transport medium
- Nutrition
- Buffering capacity
Where is seminal plasma derived from?
Accessory glands of the male reproductive tract:
- Prostate gland
- Seminal vesicles
- Bulbourethral gland
What is the usual site for fertilisation?
Ampulla of uterine tube
Identify the 4 phases in the sexual response
- Excitement phase
- Plateau phase
- Orgasm phase
- Resolution phase
What sort of stimuli trigger the excitement phase?
Psychogenic and / or somatogenic stimuli
What happens after the resolution phase in the sexual response?
Return to haemodynamic norm followed by a refractory period (males), build up of blood in the penis goes back to normal
Identify the 2 stimulants of the male sexual response – erection
- Psychogenic
- Tactile (sensory afferents of penis and perineum)
Identify the 2 efferent nerves in the male sexual response – erection
in the first part of the sexual response its the parasympathetic part that causes change (erection)
Somatic and autonomic efferents:
- Pelvic nerve dominates the → PNS
- Pudendal nerve → Somatic
Which three processes are required for an erection to occur?
- Sinusoidal relaxation
- Arterial dilation
- Venous compression → muscles expand and compress the veins within the tunica alburgenia to stop blood flowing back
Identify the nerves involved in the parasympathetic innervation of the penis
- Pelvic nerve and pelvic plexus
- Cavernous nerve
Describe 3 neurophysiological events which produce an erection
- Inhibition of sympathetic arterial vasoconstrictor nerves
- Activation of non-adrenergic, non-cholinergic, autonomic nerves to arteries
- Release of Nitric Oxide (NO)
In five steps, describe the events leading to the release of NO in an erection
⇒ Post-ganglionic fibres release ACh
⇒ ACh bonds to M3 receptor on endothelial cells
⇒ Rise in [Ca2+]i activates NO synthase and formation of NO
⇒ NO diffuses into vascular smooth muscle and causes vasodilation
⇒ NO is also directly released from nerves
- nerves involved are pelvic and cavernous nerves
Identify 4 causes of erectile dysfunction
- Psychological (nervous)
- Tears in fibrous tissue of corpus cavernosa
- Vascular
- Drugs (anti-depressants)
Describe the psychological cause for erectile dysfunction
Psychological – descending inhibition of spinal reflexes
What sort of neural control governs emission and ejaculation?
Sympathetic Nervous System
Which 2 events occur in the male sexual response – emission?
- Movement of semen into prostatic urethra
- Contraction of smooth muscle in prostate, vas deferens and seminal vesicles
What occurs in the male sexual response – ejaculation?
Expulsion of semen:
- Contraction of smooth muscle in glands and ducts
- Bladder internal sphincter contracts preventing retrograde ejaculation into the bladder
- Rhythmic striatal muscle contractions
Why does the bladder internal sphincter contract in ejaculation?
To prevent retrograde ejaculation
Which structures are involved when the striatal muscles contract in ejaculation?
- Pelvic floor
- Perineal muscles
- Ischiocavernosus muscle
- Bulbospongiosus muscle
Describe the hormonal influence over the changes of the character of cervical mucus in the menstrual cycle
- (follicular phase) Oestrogen: thin, stretchy cervical mucus
- (luteal phase) Oestrogen & progesterone: thick, sticky cervical mucus (forms a plug)
What is the site of sperm deposition?
Cervix
Describe the process which occur as part of capacitation in the female reproductive tract?
- Further maturation of sperm (6-8 hours)
- Sperm cell membrane changes to fuse with oocyte
- Sperm tail movement changes to a whip-like action
- Acrosome reaction can now occur
State the fertility windows for the sperm and oocyte respectively
- Spermatozoa: 48 - 72hr
- Oocytes: 6 - 24 hr
- so if trying to get pregnant want to have sex the same day or maybe ⅔ days before ovulation as sperm should be alive till then
What is the fertile period?
Fertile period: sperm deposition up to 3 days prior to ovulation or day of ovulation
Distinguish between the transport of the gametes
- Oocyte: beating cilia & peristalsis of uterine tube
- Sperm: own propulsion
Describe the origin, structure and function of the acrosome
- Origin: derived from golgi region of developing spermatid
- Structure: contains enzymes
- Function: necessary for fertilisation
Which 2 events trigger the acrosome reaction?
- Sperm pushes through corona radiata
- Binding of sperm surface receptor to ZP3 glycoprotein of zona pellucida and zone pellucid gets digested
What is the result of the acrosome reaction?
- sperm loses its outer membrane so the single head can penetrate and fuse with membrane
Which 2 processes lead to fertilisation?
- One sperm penetrates leading to fusion of plasma membranes
- Cortical reaction occurs (blocks polyspermy)
Explain how fertilisation leads to the completion of meiosis II in the oocyte
- cortical reaction occurs and this means oocyte will not accept any more sperm
- Series of calcium waves are activated
- Resumption of meiosis II occurs:
I. Pronuclei move together
II. Mitotic spindle forms leading to cleavage
What is unique about the cells of the morula?
Each cell at this stage of development is totipotent
Define the term totipotent
A totipotent cell has the potential to give rise to any type of cell
Explain the process of assisted reproductive technology
- Oocytes are fertilised in vitro and allowed to divide to the 4- or 8- cell stage
- The morula is then transferred into the uterus
What is the benefit of Pre-implantation Genetic Diagnosis in assisted reproductive technology?
A cell can be safely removed from the morula and tested for serious heritable conditions before transferring the embryo into the mother
Describe the structure of a blastocyst
- It has an inner cell mass which eventually forms the embryo
- It has an outer cell layer called the trophoblast
What is the significance of the blastocyst hatching from the zona pellucida?
- Blastocyst can enlarge freely
- Blastocyts interact with uterine surface & implants
How does implantation occur?
- Outer cell mass (trophoblast) interacts with endometrium
- Endometrium controls degree of invasion
What is ectopic implantation and how does it occur?
- Blastocyst implants at sites other than endometrium
- Invasion is not controlled
How is placenta praevia caused?
Implantation of blastocyst in lower uterine segment can cause placenta praevia
what is the female sexual response
- vasodilation in vessels
- most structures swell
- labia swell and change colour
- vagina expand and tents so easier passage of sperm
- vaginal lubrication occurs and this is what comes out in an orgasm
what is ART
- oocytes are fertilised in vitro
- morula is transferred into the uterus
