Erection and Ejaculation Flashcards
A castrated bull is a ……………
Steer
A castrated ram is a …………….
wether
A castrated boar is a ……………..
barrow
A castrated rooster is a ………….
capon
What is the function of the ischiocavernosus muscle?
Originates at the ischal arch and inserts on the root of the penis to force blood into the corpus cavernosum and spongiosum, intermittent contractions causes pump like action at the base of the penis.
What is the function and origin of the retractor penis muscle?
Paired retractor penis muscle which originates at the caudal vertebrae and inserts on the sigmoid flexure (ruminants/pig) or distal penis and allows retraction and protrusion of the penis
What is pre-copulatory behaviour?
Search for sexual behaviour Courtship Sexual arousal Erection Penile protrusion
What lines the erectile tissue?
Erectile tissue is surrounded by a heavy capsule of varying thickness called the tunica albuginea, connective tissue trabeculae penetrate the erectile tissue and break up the space into sinusoids ad are lined by endothelium.
What prevents venous return?
Blood pressure increases markedly in the cavernous tissue as engorgement of corpus cavernous tissue causes a blockage of the oblique veins.
How does nervous stimulation bring on an errection?
Adrenergic nerves secrete norepinephrine and this causes vasoconstriction of the helicine arteries.
Erection is stimulated by the parasympathetic nervous system which inhibits (relaxes) the longitudinal muscle fibres in the helicine arteries, this allows blood to flow into the central sinusoids causing swelling and compression of the oblique veins (which further increases swelling)
In the dog, where does the corpus cavernosum stop and what is it replaced by?
The corpus cavernosum in the dog stops at around the Os penis, bulbis glandis and pars glandis (in the glans penis) are extensions of the corpus spongiosum.
What is the erection mechanism in the dog?
Contraction of the ischiourethral muscles causes limited outflow from the penis and this is stimulated by contraction of the constrictor vestibulae muscle of the female, so erection doesn’t occur until after intromission.
What is the principle neurotransmitter that drives the erection process?
Nitric oxide
How does parasympathetic nerve stimulation cause an erection?
Parasympathetic nerve innervates helcine arteries and their nerve terminals release nitric oxide. NO stimulates Guanylate cyclase to convert Guanylate triphosphate (GTP) to cyclic guanosine monophosphate (cGMP)
cGMP then causes smooth muscle of helicine arteries to relax so that sinuses engorge and Intracorporal pressure increases.
What happens to the cGMP when the erection needs to become flaccid?
cGMP is then broken down to GTP by phosphodiesterase 5 (PDE5) and this is how Viagra (sildenafil) works by blocking the action of PDE5
How does the erection in the ram, bull and boar differ?
They have fibroelastic penis’
Contain much fibrous tissue so do not permit much expansion in diameter during erection
Length increased by straightening of sigmoid flexure as a result of relaxation of retractor penis m.
Blood pressure greatly increased to c. 600mm.Hg
What causes ejaculation?
Stimulation of the glans penis (pressure and temperature) via the internal pudendal nerve to the lumbosacral region of the spinal cord
Causes reflex innervation of the Urethralis muscle (bulbospongious) and Ischiocavernosus
Describe stallion ejaculation
Stallion produces a series of jets
Sperm rich fraction ejaculated in 3 to 4 squirts
Last 5 to 8 squirts are at lower pressure + less sperm
Describe boar ejaculation
Boar (series of seminal fractions)
First fraction: accessory fluids + few sperm
2nd fraction: rich in spermatozoa
Final fraction: thick coagulum
Describe dog ejactulation
Dog (3 fractions)
Pre-sperm fraction from prostate
Sperm rich fraction
Then a prostate derived fraction delivered with greater force
What causes the loss of erection?
Sympathetic tone takes over and the helicine arteries close, blood flows out of sinusoids and erection subsides slowly.
Which species ejaculate into the uterus and which ejaculate into the vagina?
Bull, Ram, dog and cat are vagina
Stallion and boar are uterus
What are the sites of AI sperm deposition in the species?
Bull, boar and stallion: Uterus
Ram (fresh): Cervix Ram (frozen): uterus
Dog and cat (fresh): vagina (frozen: Uterus
Where does the sympathetic innervation to the penis come from?
Sympathetic supply comes from hypogastric so injury in the pelvic region
