Sex And Fertilisation Flashcards
Outline maturation of sperm in the epididymis
- 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
What is semen made of?
Spermatozoa
Seminal plasma
Function of seminal plasma
- transport medium
- nutrition
- buffering capacity
Where is seminal plasma released from?
Seminal vesicles
Prostate gland
Bulbourethral glands
Describe the seminal plasma from the seminal vesicles
- 65%
- Alkaline fluid to neutralise acid
- Prostaglandins, fructose, clotting factor
Describe the seminal plasma from the prostate gland
- 25%
- milky slightly acidic fluid
- Proteolytic enzyme - breaks down clotting protein to reliquefy semen
- citric acid, acid phosphatase
Function of the seminal vesicle seminal plasma
Neutralises acidic environment of vagina
Function of prostate gland seminal plasma
Breaks down clotting proteins + reliquefies semen due to proteolytic enzymes
Describe the seminal plasma from bulbourethral glands
- ~1%
- alkaline fluid
- mucous that lubricates end of penis + urethral lining
(Pre ejaculate)
Normal range of semen volume
1.4-1.7ml
Normal range of total sperm count
33 - 46 x10^6
Where does fertilisation normally occur?
Ampulla of uterine tube
What are the phases of the human sexual response?
- excitement phase
- plateau phase
- orgasm phase
- resolution phase (includes refractory period in men)
What nervous system controls erections?
Parasympathetic
- parasympathetic efferents via pelvic nerve
- somatic efferents via pudendal nerve
What is the refractory period in the resolution phase in men?
When a man is unable to ejaculate again
Nerve roots of the pudendal nerve
S2-S4
Anatomy of the penis in an erection
- 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
Outline the neurophysiology of an erection
- inhibition of sympathetic arterial vasoconstrictor nerves
- activation of PNS
- release of nitric oxide
Role of nitric oxide in an erection
- 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
Causes of erectile dysfunction
- psychological
- vascular e.g. diabetes, hypertension, vascular disease
- anatomical
- neurological
- hormonal
- drugs
What nervous system controls ejaculation?
Sympathetic
What are the two parts of ejaculation?
- emission: deposition of seminal fluid into prostatic urethra
- expulsion: expulsion of semen through the urethra + out the urethral meatus (ejaculation)
What prevents retrograde ejaculation?
Internal sphincter contracts
Outline the changes in the cervical mucus throughout the menstrual cycle
- ovulation: oestrogen: thin + stretchy
- around ovulation: oestrogen + progesterone: thick, sticky - forms a plug
Outline the female sexual response
- 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
What is capacitation?
- 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
When does capacitation occur?
After 6-8 hours
Fertile window of sperm
48-72 hours
Fertile window of oocyte
6-24 hours
What is the acrosome?
- Derived from Golgi region of developing spermatic
- Contains enzymes to breakdwon oocyte membrane
Outline the events of fertilisation
- in the ampulla of uterine tube
- acrosome reaction
- penetration of ovum membrane
- fusion of ova + sperm
What is the acrosome reaction?
- sperm push through corona radiata (outer layer of oocyte)
- binding of sperm surface receptor to Zona pellucida
- triggers acrosome reaction
- digestion of Zona pellucida
What is the cortical reaction?
- Occurs after first sperm penetrates Zona pellucida
- induces the Ca2+ dependent exocytosis of protease containing cortical granules
- prevents other sperm from penetrating
Outline implantation
- trophoblast interacts with endometrium
- implants within the stroma where secretory glands + increased vasculature has formed during metal cycle
What is the fertile window?
Sperm can be deposited three days before ovulation as sperm can survive for up to 72 hours
Difference in the human sexual response in men and women
Men have a refractory period where as women don’t
Outline the excitement phase in men
- occurs due to psychogenic stimulation
- parasympathetic efferents via pelvic nerve
- somatic efferents via pudendal nerve
- causes an erection
How do erectile dysfunction drugs improve erectile function?
- Inhibition of cGMP breakdown
- Leading to increased NO production + vasodilation
