Lecture 38: Coitus, Fertilisation and Contraception Flashcards
what is coitus?
- sexual intercourse/copulation
what happens in coitus?
- erect penis introduced into vagina (intromission)
- semen released into upper part of vagina (insemination) so that sperm can travel to appropriate site for fertilisation (ampulla of uterine tube)
what are the stages of the male sexual act?
- erection of the penis (parasympathetic)
- mucus secretion into urethra
- ejaculation (2 phases: emission and expulsion - sympathetic)
- resolution
what are fascia?
the erectile tissues are surrounded by different layers of fascia
how do the clitoris and penis compare?
- structure of the clitoris and penis share developmental origins
- tissues of clitoris are erectile as in the penis
what are the branches of the abdominal aorta involved in supplying the penis?
- abdominal aorta
- common iliac artery
- internal iliac artery
- internal pudendal artery
what does the internal pudendal artery do?
internal pudendal artery feed perineum and external genitalia, including penis
the branches to the penis:
- artery to bulb
- urethral artery
- dorsal artery
- deep (cavernosal) artery
how is the blood supply to the penis during an erection?
what regulates the genital sexual reflexes?
- coordination of sympathetic, parasympathetic and somatic divisions of the nervous system
what is the nerve supply of the penis?
- penis is richly innervated by sensory and motor nerves
- includes sensory fibres responsive to touch, pressure and temperature
- pudendal nerve supplies sensory and somatic motor innervation to perineum and external genitalia, including penis (dorsal nerve)
- autonomic innervation to penis derives to pelvic plexus (parasympathetic and sympathetic)
what is the parasympathetic nervous system involved in? how?
erection
- stimulates production of nitric oxide by deep arteries of penis
- deep arteries dilate and fill lacunae in corpora cavernosa
what is the sympathetic nervous system involved in? how?
- stimulates contraction of smooth muscle
- reproductive ducts
- accessory glands
what is the somatic motor division involved in? how?
- stimulates contraction of skeletal muscles around bulb of penis
what happens in the erection phase of the male sexual act?
- parasympathetic response to stimuli
- deep artery in the penis dilate
- trabecular muscle of erectile tissue relaxes
- erectile tissues become engorged with blood
- bulbourethral gland secrete bulbourethral fluid
- erect penis can be inserted into vagina
what happens in the emission phase of the male sexual act?
- sympathetic response
- smooth muscle of ductus deferens contracts to move sperm into the ampulla (peristalsis)
- smooth muscle of ampulla, seminal vesicles and prostate gland contract and move sperm and seminal fluid into urethra
what happens in the expulsion phase of the male sexual act?
- semen in the urethra activates somatic and sympathetic reflexes
accessory glands:
- additional secretion from prostate gland and seminal fluid
- internal urethral sphincter contracts (urine remains in bladder)
bulbospongiosus muscle:
- contracts and rhythmically compresses root/bulb of penis, which compresses urethra
- semen ejected
what happens in the resolution phase of the male sexual act?
- the internal pudendal artery constricts and reduces blood flow to penis
- trabecular muscle contract and squeeze blood from erectile tissues
- penis becomes flaccid
what are the stages of the female sexual response?
- similar sequence of reflex responses as the male
- engorgement of clitoris, labia and vagina is response to autonomic stimulation
- lubricating fluid secreted through vaginal wall; secretion of mucus into vestibule (greater vestibular glands)
- increased width and length of vagina. uterus elevates upwards
- rhythmic contraction of vaginal, uterine and perineal muscles
what happens to sperm after ejaculation?
- semen released into the upper part of the vagina (insemination)
- sperm travels to uterine tube for fertilisation (ampulla)
- sperm fuses with secondary oocyte
- oocyte complete meiosis 2
- fertilised oocyte/ovum known as zygote
- zygote initiates cleavage (takes about 7 days) and travels towards the uterus for implantation
what is contraception? what types?
any method used to prevent pregnancy and regulate when and how many pregnancies
- natural methods
- artificial methods: barrier, hormonal contraception, intrauterine devices, sterilisation
what are the natural methods of contraception?
- rely on timing of coitus or behaviour during coitus
- high failure rate
- rhythm method (periodic abstinence)
- withdrawal method (coitus interruptus)
- lactational infertility
what are the types of barrier methods?
- caps, diaphragms
- condoms
what are caps/diaphragms?
- imperfect barrier so should be used with foams/jellies/creams/sponges
- needs to remain at least 6 hours after intercourse
- not commonly used anymore as there are more convenient and effective methods now
what are condoms?
- cheap
- readily available
- easy to use
- reduce risk of STIs
what are the types of steroidal contraceptive for females?
- combined oral contraceptive pills
- progestin-only contraception
- subdermal implant/injectable progestins
what is the combined oral contraceptive pill?
- contains estrogen and progestin
- suppresses ovulation by affecting the feedback loops to hypothalamus and pituitary
- affects mucus produced by cervix to prevent sperm penetration
what is the progestin-only contraception?
- progesterone only pill
- low doses of progestin
- effect on servical mucus
what is subdermal implant/injectable progestins?
- long acting (over years)
- act primarily by disrupting follicular growth and ovulation
what are the types of intrauterine devices (IUD)?
- copper IUD
- hormonal IUD
what is the copper IUD?
- causes low grade inflammation
- reduces sperm transport
- toxic for oocyte and zygote
- impairs implantation
what is the hormonal IUD?
- contains progestins
- affects cervical mucus, reducing sperm transport
- local effects on endometrium
- may prevent ovulation
what sterilisation can be done on females?
tubal ligation
- cut uterine tubes
what sterilisation can be done on males?
vasectomy
- cut ductus deferens
