Midterm 2 - Lecture 16 Flashcards
Two important roles of the scrotum and spermatic cord
- support and maintain the male gonads
- regulate testicular temp
At what temperature must spermatogenesis occur at?
- lower than normal body temp
- internal testicular temperature is generally 4-6 degrees below rectal temperature
What 5 key tissues are involved in thermoregulation?
- testicular artery
- pampiniform plexus
- external cremaster muscle
- scrotum skin
- tunica dartos muscle
What is the pampiniform plexus?
specialized vascular network found within the spermatic cord
- consists of testicular veins that elaborately intertwine around the testicular artery
What is the function of the pampiniform plexus?
- provides a countercurrent heat exchange mechanism that cools the arterial blood before it enters the testicle
What is the cremaster muscle?
- striated muscle that surrounds the spermatic cord and attaches to the testicular connective tissue
- contraction to draw the testes close to the body during cold periods (NOT CONSTANT)
- muscle relaxes during periods of high temp so testes move away from the body = cooler AND lengthens the PP for greater SA for countercurrent heat exchange to fxn
4 major layers of the scrotum
- Scrotal skin
- rich in sweat glands and sensory tissue - Tunica dartos
- smooth muscle that responds to temperature - Scrotal fascia
- connective tissue - Parietal vaginal tunic
- connective tissue
What does sweating of the scrotal skin allow for?
- the scrotum & testes to be cooled by evaporation
- scrotum heavily populated with sweat glands and thermosensitive nerves
- scrotal glands are innervated by sympathetic nerves
What controls the degree of scrotal sweating and or respiratory rate via a reflex pathway?
- scrotal sensory nerves
What do scrotal sensory nerves do?
Control the degree of scrotal sweating and/or respiratory rate via a reflex pathway
What does scrotal warming induce?
- panting at 40 degrees
How is respiration linked to scrotal temperature?
- respiration rate increases if scrotal skin temp reaches 36 degrees
- at 40 degrees the ram will pant
- warming an equivalent region of the body surface does not elicit the same response
What is the tunica dartos?
- mesh like smooth muscle that lies beneath the scrotal skin
- degree of contraction constantly adjusting in response to scrotal temp - as detected by sensory nerves in the scrotal skin
What does the Tunica Dartos do in cold periods vs hot periods?
- Cold periods - smooth muscle can maintain sustained contraction to hold the testes close to the body
- Hot periods - muscle relaxes and testes move away from the body = cooler AND greater SA to be cooled by evaporation of perspiration
What are the 2 mechanisms of testicular cooling?
- Heat dissipation
- pampiniform plexus = countercurrent heat exchange
- scrotal skin (sweat glands) = perspiration - Testes position
- cremaster muscle
- tunica dartos (relaxes)
What are the effects of short-term heat exposure? (ex. fever, summer heat)
- compromises sperm viability
- reduced sperm motility
- poor embryo survival following fertilization
What are the effects of long-term heat exposure?
- cessation of spermatogenesis
- spermatogenic DNA polymerase b and recombinase activity is reduced
What are varicoceles?
- abnormal collection of dilated veins in the spermatic cord (varicose veins)
- impedes the ability of the Pampiniform Plexus to cool arterial blood before it reaches the testes
- caused infertility or reduced fertility
- not common in livestock but highly heritable
What is thermal “castration” aka short “scrotumed” bulls?
- testes are forced close to the body by placing a rubber band around the lower portion of the scrotum
- creates an artificial cryptorchid
- bull is sterile, but experiences better growth efficiency and leaner carcasses due to continued T4 production by testes
Why is thermal castration not a common practice?
- elevated T4 causes aggressive behaviour amongst bulls = difficult to manage!
What is a noninvasive means to evaluate testicular cooling capacity?
- infrared thermography
- males with inefficient testicular cooling can be identified and eliminated as breeding males
What is unique about mammals who do not have scrotal sacs and instead the testes remain within the abdomen?
- have a relatively low body temp
- many have evolved unique cooling systems to regulate body and testicular temp
