Sex and fertilisation Flashcards
Briefly outline spermatogenesis
- Occurs in seminiferous epithelium found in testis
- Controlled by HPG axis
- 100 million sperm produced per day
What is the sperm’s journey through the epididymis?
- On entry, spermatozoa not capable of movement
- Once at tail of epididymis, they are capable of movement and have potential to fertilise
- Addition of secretory products to surface of sperm
- Maturation dependent on support of epididymis by androgens
What makes up the semen?
- Spermatozoa and seminal plasma
Where is seminal plasma derived from?
- Accessory glands of male reproductive tract
What are the functions of seminal plasma?
- Transport medium
- Nutrition
- Buffering capacity
- Prostaglandins may stimulate muscular activity in female tract
Which glands contribute to making seminal plasma?
- Seminal vesicles
- Prostate gland
- Bulbourethral glands (Cowper’s glands)
What do seminal vesicles contribute to seminal plasma?
- 60% of volume
- Alkaline fluid - neutralises acid in male urethra and female
- Fructose, prostaglandins, clotting factors (semenogelin)
What do bulbourethral (Cowper’s) glands contribute to seminal plasma?
- Very small volume
- Alkaline
- A mucous that lubricates end of penis and urethral lining
- (pre ejaculate)
What does the prostate gland contribute to seminal plasma?
- 25% volume
- Milky, slightly acidic
- Proteolytic enzymes (keep semen fluid)
- Citric acid, acid phosphatase
What should the normal sperm count be?
- 33-46 million
- Normally around 40 million
How far does the sperm have to travel to meet the female gamete?
- 100 000 times its own length
What is the normal site of fertilisation?
- Ampulla of uterine tube
What are the phases of the human sexual response?
- Excitement phase - due to psychogenic and/or somatogenic stimuli
- Plateau phase
- Orgasm phase
- Resolution - return to haemodynamic norm followed by a refractory period in males
Which nervous system causes erection in males?
- Parasympathetic
What are the stimulants for erection?
- Psychogenic
- Tactile (sensory afferents of penis and perineum)
What are the efferents for erection?
- Somatic and autonomic
- Pelvic nerve (PNS)
- Pudendal nerve (somatic)
- Causes haemodynamic changes
What does erection involve?
- Straightening of coiled helicine arteries
- Allows blood to fill the corpus cavernosum
Describe blood flow in the flaccid penis?
- Arterio-venous anastomoses allows blood to bypass corpus cavernosum
Describe blood flow to the penis during erection
- Smooth muscle in helicine arteries relaxes and straightens
- Blood flows into corpus cavernosum
- Bulbospongiosus and ischiocavernosus muscles compress venous plexus
- This retains blood in the penis
Which nerves provide parasympathetic innervation to the penis?
- Fibres from lumbar and sacral spinal levels
- Pelvic nerve and pelvic plexus
- Cavernous nerve to corpora and vasculature
Outline the neurophysiology of erection
- Inhibition of sympathetic arterial vasoconstrictor nerves
- Activation of PNS
- Activation of non-adrenergic, non-cholinergic, autonomic nerves to arteries
- NO released
What are the effects of NO on erection
- Post-ganglionic fibres release ACh
- ACh binds to M3 receptor on endothelial cells
- Causes a rise in Ca2+ concentration, activation of NOS and formation of NO
- NO diffuses into vascular smooth muscle and causes vasodilation
- This leads to erection
(NO is also released directly from nerves)
What causes erectile dysfunction?
- Psychological (descending inhibition of spinal reflexes)
- Vascular - CVD, DM, HTN
- Anatomical
- Neurogenic - peripheral (polyneuropathy/DM) or central (spinal cord lesion/MS)
- Hormonal
- Drugs
Which nervous system causes emission and ejaculation?
- Sympathetic
What happens in emission of semen?
- Movement of semen into prostatic urethra
- Contraction of smooth muscle in prostate, vas deferens and seminal vesicles
What happens in ejaculation?
- Expulsion of semen
What happens to facilitate ejaculation?
- Contraction of glands and ducts
- Bladder internal sphincter contracts
- Prevents retrograde ejaculation
- Rhythmic striatal muscle contractions of pelvic floor and perineal muscles (ischiocavernosus and bulbospongiosus)
How does the character of cervical mucus change over the course of the menstrual cycle?
- Oestrogen alone causes thin and stretchy mucus
- Oestrogen and progesterone forms thick and sticky mucus (forms a plug)
Outline capacitation of sperm?
- Further maturation of sperm in female productive tract (6-8 hours)
- Sperm cell membrane changes to allow fusion with oocyte cell surface
- Tail movement changes from beat to whip-like action
- Now capable of undergoing acrosome reaction
How long can sperm survive once they’ve left the body?
- 48-72 hours
How long do oocytes survive after ovulation?
- 6-24 hours
How long is the fertile period?
- Sperm deposition up to 3 days prior to ovulation or day of ovulation
How do oocytes move after ovulation?
- Beating cilia and peristalsis of uterine tube
What is the acrosome?
- Derived from golgi region of developing spermatid
- Contains enzymes
- Necessary for fertilisation
What is the acrosome reaction?
- Sperm pushes through corona radiata
- Binding of sperm surface receptor to ZP3 glycoprotein of zona pellucida
- Triggers acrosome reaction
- Digestion of zona pellucida
What is the cortical reaction?
- One sperm penetrates zona pellucida
- Plasma membranes fuse
- Blocks polyspermy
What does fertilisation trigger?
- Series of calcium waves activated
- Meiosis II continues
- Pronuclei move together
- Mitotic spindle forms leading to cleavage
Describe the cells of the morula
- Each cell is totipotent
Outline what happens in IVF
- Oocytes fertilised in vitro
- Divide to the 4 or 8 cell stage
- Morula is then transferred into uterus
What is Pre-implantation genetic diagnosis?
- Cell safely removed from morula
- Tested for serious heritable conditions
- Prior to transfer of embryo
What is the process of hatching?
- Occurs after formation of blastocyst
- Blastocyst hatches from zona pellucida
- Now can enlarger without constraint
- Can interact with uterine surface to implant
Outline the process of implantation
- Outer cell mass (trophoblast) interacts with endometrium
- Endometrium controls degree of invasion
What happens in ectopic implantation?
- Implantation occurs at sites other than endometrium lined uterine cavity
- Invasion not controlled
What causes placenta praevia?
- Implantation in lower uterine segment
