Lecture 38: Coitus, Fertilisation and Contraception Flashcards
What two events occur during coitus?
intromission and insemination
Define intromission
when the erect penis is introduced into the vagina
Define insemination
the semen is released into the upper pat of the vagina so that the sperm can travel to the appropriate site for fertilisation
What is the purpose of coitus?
to ensure the male gamete can be transported to the female reproductive tract
What determines whether the spermatozoa can go into the external os, internal os into the uterus and up into the ampulla?
the stage of the menstrual cycle and the consistency of the mucus
What must happen in order to allow for intromission?
an erection
What is an erection associated with in terms of secretion? Where is this coming from and what is its purpose?
mucous secretion for the bulbourethral glands to provide lubrication for the urethra and clearing out any residual urine that might be present
What follows erection?
ejactulation
What are the two phases of ejaculation?
emission
expulsion
What occurs in ejaculation?
transporting sperm into the urethra and getting the accessory glands to secrete the seminal fluids which can be ejaculated by urethra
What occurs after ejaculation?
resolution
What are the lacunae and where are they?
The spaces where blood can fill in the corpus cavernosum to engorge the tissues
What is the bulbospongiosis muscle?
encases the root and is important in ejaculation
The erectile tissues are surrounded by different layer of
fascia
What are fascia?
layers of connective tissue
What are lacunae of the corpus cavernosa surrounded by?
trabeculae
What are trabeculae?
connective tissue containing smooth muscle which are important for constraining and allowing the blood to cause the engorgement of the tissues
Venules form a venous plexus around the
outside of the erectile tissues
What are the columns of erectile tissue surrounded and supported by?
various layers of fascia
What fascia surrounds the corpora cavernosa?
tunica alberginia
Apart from being around the corpora cavernosa, where is the other tunica alberginia?
around the corpus spongiosum
What fascia surrounds the two tunica alberginia?
the deep/Buck’s fascia
What fascia surrounds the the deep/Buck’s fascia?
the superficial facia
What is the purpose of the fascia?
restraining the erection so that when the erectile tissues fill with blood, they put pressure back against the fascia to support the erection
Why is the tunica alberginia around the corpus spongiosum not as dense as the one around the corpora cavernosa?
because we don’t want the urethra to be blocked during ejaculation so it prevents the engorgement being sufficient to block the urethra
What are deep to the labia manora?
the bulbs of vestibule
The glans, the body and the crus of the clitoris are homologous to what in the penis?
copora cavernosa
The bulbs of the vestibule are homologous to what of the penis?
the corpus spongiosum
Are tissues of the clitoris erectile?
yes
What are the gonadal arteries in males and females?
- ovarian in females
- testicular in males
Where did the testes originate?
in the abdominal cavity and then they migrate down into the scrotum
What are the arteries that supply the penis and the external genitalia? (4)
- abdominal aorta
- common iliac artery
- internal iliac artery
- internal pudendal artery
What does the internal pudendal artery supply?
feeds the perineum and external genitalia including the penis
Internal pudendal artery supplies what different regions of the penis? (4)
the artery to the bulb
the urethral artery
the dorsal artery
the deep (cavernosal) artery
What is the venous return from the penis? (3)
the superficial dorsal vein, the deep dorsal vein and the subtunical veins
What happens during an erection?
the lacunae fill with blood, the trabeculae relax and the engorgement puts pressure against the venous plexus and the fascia which allows the erection to take place and reduces the venous return back to the body
What divisions of the nervous system innovate the genital sexual reflexes for both males and females?
- the somatic nervous system
- the autonomic nervous system (both the sympathetic and the parasympathetic nervous systems)
What is the somatic (efferent) nervous system?
voluntary motor control due to impulses conducted from the CNS to the skeletal muscles
What is the autonomic (efferent) nervous system?
involuntary motor control due to impulses from the CNS to the cardiac muscle, smooth muscle, and glands
What are the sensory fibres of the glans responsive to?
touch, pressure, temperature
Describe the pathway of the afferent signals from the penis to the CNS
The afferent signals from the sensory nerve fibres from the glans of the penis are sent via the dorsal nerve of the penis via the pudendal nerve up to the sacral region of the spinal cord
What region of the spinal cord provides the efferent/motor signal to the penis?
the sacral region
Describe the autonomic nervous supply to the penis including both sympathetic and parasympathetic:
sympathetic:
- derives from up within the thoracic lumber region via the hypogastric nerves converging on the pelvic plexus
parasympathetic:
- comes from the sacral region converging via the pelvic plexus
What does the parasympathetic nervous supply to the penis innervate?
providing innervation within the arteries of the ______ and the outer regions of the ____ _____ and to the ______ _____ and _____, particularly the ______ ________
providing innervation within the arteries of the penis and the outer regions of the external genetalia and to the accessory glands and ducts, particularly the ductus deferens.
When is the parasympathetic nervous system required?
during erection
Describe the role of the parasympathetic nervous system during an erection
It stimulates the production of NO by the deep arteries of the penis. This acts as a vasodilator which causes the deep arteries to dilate to allow blood to fill the lacunae in the corpora cavernosa
When is the sympathetic nervous system required?
during both phases of ejaculation
When is the somatic/motor nervous system required?
during ejaculation
Describe the role of the sympathetic nervous system during ejaculation
it has a role of contracting the smooth muscle in the ductus deferens and around the accessory glands to allow movement of the sperm and seminal fluid so they can combine to form semen in the urethra
Describe the role of the somatic/motor nervous system during ejaculation
stimulates the contraction of the skeletal muscles around the bulb of the penis
What nervous response is an erection?
parasympathetic
Describe how an erection occurs:
- parasympathetic response in response to stimuli (such as tactile, thoughts, memories)
- this causes efferent parasympathetic signals to the penis and bulbourethral gland
- this causes the deep arteries of the penis to dilate in response to NO
- the smooth trabecular muscle around the lacunae relaxes which allows the lacunae to fill with blood which causes engorgement of the erectile tissues
- there is pressure against the venous plexus which is being restrained by the fascia which allows for erection
- there is also contraction of the bulbourethral glands which allows for secretion of the lubrication of the urethra and for cleaning during from the urethra
Describe how emission occurs
- this is a sympathetic response
- efferent sympathetic signals causes peristalsis of the ductus deferens which moves the spermatozoa up the ductus and into the ampulla
- the smooth muscle of the ampulla contracts as well as the smooth muscle around the seminal vesicles and prostate glands which then allows for the sperm and seminal fluid to be moved into the prostatic urethra
Describe how expulsion occurs
- the presence of the semen stimulates the reflex response (efferent sympathetic signals) which causes contractions of the urethral smooth muscle and secretion from the prostate glands and from seminal vesicles
- it also causes contraction of the internal urethral sphincter to stop sperm from entering the bladder
- there is also efferent somatic signals which causes contraction of the bulbospongiosus muscle which surrounds the root of the penis which compresses the root of the penis which compresses the urethra and expels the semen
Describe how resolution occurs
this is a sympathetic response
- after ejaculation, the internal pudendal artery will contract which will reduce blood flow into the penis
- the trabecular smooth muscle around the lacunae will contract which will squeeze the blood out of the erectile tissues and the penis becomes flaccid
Describe the stages of the female sexual response
- stimuli (physical, thoughts or tactile) increases the blood flow to the female external genitalia (including the clitoris, labia and vagina)
- there is secretion of fluids for lubricating the vaginal wall and secretions into the vestibule by the greater vestibular glands
- the vagina lengthens and widens especially the upper regions of the vagina and the uterus moves from the leaving over position to be in a more upright position
- there are rhythmic contractions of the vaginal, uterine and pelvic floor muscle
What is needed for fertilisation to occur?
- semen to be released into the upper part of the vagina (insemination)
- depending on the stage of the menstrual cycle, the sperm needs to get through the cervix (needs to be watery not thick mucous) and into the uterus then uterine tube to fuse with the secondary oocyte
What happens when fertilisation occurs?
the oocyte completes meiosis II
Where does the zygote go?
it initiates cleavage (division of the cells) and travels towards the uterus
Define contraception including what it regulates
any method used to prevent pregnancy and it can regulate when and how many pregnancies you can have
What are the two methods contraception? give examples
- natural methods
- artificial methods
including - barrier
- hormonal
- intrauterine device
- sterilisation
What are three natural methods of contraception?
- rhythm method
- coitus interruptus
- lactational infertility
What do natural methods rely on?
the timing of coitus or behaviour during coitus
What is involved in the rhythm method of contraception?
monitoring the cycle and having sex at the correct point in the cycle (eg. not ovulating)
What is involved in the coitus interruptus method of contraception?
When the penis is removed before ejaculation occurs
What are examples of barrier methods and how do these work?
caps, diaphragms
- an imperfect barrier so should be used in conjunction with spermicide
- block and kill sperm from trying to enter the uterus
condoms (male and female)
- cheap and readily available and can reduce STIs
What are examples of steroidal contraceptives and how do these work?
the combines oral contraceptive pills
- contain an oestrogen and a progestin to suppress ovulation by preventing the feedback loops to hypothalamus and pituitary and affecting the mucus produced by the cervix
Progestin only contraception such as pills (which affects the cervical mucus) or implants (disrupting follicular growth and ovulation)
How do the IUDs work?
- cooper IUD:
causes low grade inflammation of the endometrium and reduces sperm transport and impairs implantation - hormonal IUD which contains progestins and it affects cervical mucus reducing transport and may prevent ovulation
What are examples of sterilisation and how do these work?
- tubal ligation: cut the uterine tube
- vasectomy: cut the vas deferens
