Lecture 38: Coitus and fertilisation/contraceptives Flashcards
What is Coitus?
- From the Latin ‘a meeting together; sexual union’
- Sexual intercourse / copulation
What is intromission?
- Erect penis introduced into Vagina (intromission)
What is insemenation?
- Semen released into upper part of vagina (insemination) so that sperm can travel to appropriate site for fertilization
(ampulla of uterine tube).
What is the muscle at the base of the penis?
Bulbospongiosus, Also known as the bulbocavernosus muscle
What are the three layers of fascia that can be found in the penis (from innermost to out)?
The Tunica albuginea (1 for the corpus carvernosum’s and 1 for the corpus spongiosum)
The Deep (Buck’s) fascia (whole ring layer around)
The Superficial fascia (another ring layer around)
Why is the gonadal artery branched so high in the aorta near the abdominal cavity?
Gonadal artery high because the gonads develop in the abdominal cavity and descend down bringing the vasculature with them
What is the pathway for blood to the penis starting at the abdominal aorta?
Abdominal Aorta
Common Iliac artery
Internal iliac artery
Internal pudendal artery
- Internal pudendal artery feeds perineum and external genitalia, including penis.
What are the arteries inside the penis?
Branches to the penis include:
* Artery to bulb
* Urethral artery
* Dorsal artery
* Deep (cavernosal) artery
What are the veins of the penis? Also what is the main nerves showed in the lectures?
The veins include:
- Superficial dorsal vein
- Deep dorsal vein
- Subtunical veins (form venous plexus surrounding erectile tissue)
Dorsal nerves - The small yellow circles on the dorsal aspect of the penis
In terms of blood supply and pressure, how do males maintain an erection?
As the Lucunae fill with blood and the trabecular muscle of the erectile tissue relaxes the penis becomes full of blood
This exerts pressure on the fascia and subtunical veins that form the venous plexus (which drains blood from the erectile tissue)
This pressure slows blood drainage and helps males maintain an erection
What response is responsible for generating an erection?
The parasympathetic response
What is the role of nitric oxide (NO) in erection?
Nitric Oxide is a vasodilator, stimulated by the PARASYMPATHETIC response that dilates deep arteries in the penis, facilitating erection by filling the corpora cavernosa with blood.
What does sympathetic stimulation do during ejaculation?
It stimulates contraction of smooth muscles in reproductive ducts and accessory glands.
How does somatic motor stimulation contribute to ejaculation?
It stimulates contraction of skeletal muscles around the bulb of the penis.
What type of nerve supply does the penis have?
The penis is richly innervated by sensory and motor nerves.
What sensory stimuli are the sensory fibers of the penis responsive to?
Touch, pressure, and temperature.
Which nerve supplies sensory and somatic motor innervation to the perineum and external genitalia, including the penis?
The pudendal nerve (dorsal nerve is a branch of this nerve).
Where does the autonomic innervation to the penis come from?
The autonomic innervation is derived from the pelvic plexus, which includes parasympathetic and sympathetic fibers.
What is the overall process of erection and what are the stimulus for this?
- Parasympathetic response to stimuli
- seeing, thinking or feeling, etc.
- Arteries in erectile tissue dilate
- Erectile tissue becomes engorged with blood
- Erect penis can be inserted into vagina (intromission)
Bulbourethral gland secretes bulbourethral fluid lubricating and neutralising the urethra
What is the overall process of Emission?
- Sympathetic response
- Smooth muscle of ductus deferens contracts to move sperm into ampulla (peristaltic contractions)
- Smooth muscle of ampulla, seminal vesicles and prosate gland contract moving sperm and seminal fluid into urethra
What is the overall process of Expulsion?
- Semen in urethra activates somatic and sympathetic reflexes
- Contractions of urethral smooth muscles
- Pelvic floor muscles contract
- Semen ejected
What are the efferent sympathetic and somatic signals and respective actions during ejaculation?
Efferent sympathetic signals:
Accessory glands:
- additional secretion from prostate glands and seminal vesicles
- internal urethral sphincter contracts (urine remains in bladder)
Efferent somatic signals:
Bulbospongiosus muscle:
- contracts and rhythmically compresses bulb/root of the penis, which compresses the urethra helping semen be expelled
What is the overall process of resolution?
- Blood flow to penis is reduced via constricting pudendal artery
- trabecular muscles contract squeezing blood out of the erectile tissue
- Penis becomes flaccid
What are the stages of the female sexual response?
- Similar sequence of reflex responses as in the male
- Engorgement of clitoris, labia and vagina in 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 (pelvic floor) muscles.
What is the process of fertilisation (very simple) and what does the zygote then initiate?
- Sperm fuses with secondary oocyte
- Oocyte completes meiosis II.
- Fertilized oocyte/ovum known as a zygote.
- Zygote initiates cleavage (takes about 7 days) and travels towards the uterus for
implantation.
What are the natural methods of contraception?
- Rely on timing of coitus or behavior during coitus
- High failure rate
- Rhythm method (periodic abstinence)
- Withdrawal method (coitus interruptus)
- Lactational infertility - period after childbirth, stimulated by breastfeeding that prevents the mother from ovulating immediately
What are the barrier methods of contraception?
Caps, diaphragms
* Imperfect barrier so should be used in conjunction with spermicidal foams / jellies / creams / sponges.
* Needs to remain at least 6 hours
after intercourse.
Condoms
* Cheap
* Readily available
* Easy to use
* Reduce risk of sexually transmitted infections (STIs)
What is an example of a Non-hormonal Intrauterine device (IUD)?
Copper IUD
* Causes low grade inflammation
* Reduces sperm transport
* Toxic - oocyte and zygote
* Impairs implantation
What are the mechanisms of action for steroidal contraceptives?
- Variable depending on type, concentration and mode of delivery of hormones
- Deliver a progestin with/without an estrogen
- Suppress ovulation (affect feedback loops to hypothalamus and pituitary)
- Affect mucus produced by cervix (prevent sperm penetration)
What are some examples of steroidal contraceptives:
Combined oral contraceptive pills
* Contain estrogen and progestin
* Suppress ovulation (affect feedback loops to hypothalamus and pituitary)
* Affect mucus produced by cervix (prevent sperm penetration)
Progestin-only contraception
* Progesterone-only pill
* Low doses of progestin
* Effects on cervical mucus
Subdermal implant / Injectable progestins
* Long acting (over years)
* Act primarily by disrupting follicular growth and ovulation
Hormonal IUD (e.g. Mirena)
* Contains progestins
* Affects cervical mucus, reducing sperm
transport
* Local affects on endometrium
* May prevent ovulation
What are the methods of sterilisation for females and males?
- Tubal ligation or salpingectomy –
cut/cauterise or remove uterine tubes - Vasectomy – cut ductus (vas) deferens
Where does the sympathetic innervation of the penis specifically come from?
The thoracic region of the spinal cord (travels through hypogastric nerves to the pelvic plexus and finally to the penis)
Where does the parasympathetic innervation of the penis specifically come from?
The sacral region (travels through pelvic plexus)
