REVISION: Equine reproductive anatomy and physiology (male and female) Flashcards
What accessory glands does the stallion have?
ampulla (each deferent duct) 2 seminal vesicles 1 prostate gland 2 bulbourethral glands
How is the stallion repro tract supported within the pelvic cavity?
by the genital fold
What are the 4 layers of the scrotum?
skin - sweat glands tunica dartos - SMCs for vertical mobility fascia - vertical and lateral movement vaginal tunic - watery fluid facilitates testes movement
When do testes descend?
enter the inguinal canal before closure of internal inguinal ring during first 2 weeks after birth and descend into scrotum
What is the size of a mature equine testis? Weight?
Length: 80-100mm Width: 50-80mm Weight: 225g
What does testicular parenchyma consist of?
seminiferous tubules and interstitial tissue
When does equine male pre-pubertal stage start?
approx 6 months old, few colts produce sufficient sperm for ejaculation before 14 months of age.
How long does it take for a spermatozoa to form?
57 day cycle (70,000 sperm/second)
What is the function of the external cremaster muscle?
temperature control
What end of the testis is the corpus epididymis found?
cylindrical, loosely attached to dorsal testis, sperm storage (also ampullae)
How wide is the epididymal duct versus the ampulla?
Epididymal duct = 5mm Ampulla = 18mm (paired ampullae contain crypts and glands)
What is the pelvic portion of the urethra covered in?
striated urethralis mm - contracts during ejaculation
What are seminal vesicles like?
elongated hollow pouches, 15-20mm diameter, seminal plasma
Describe the prostate gland
single firm solid gland with two narrow lobes connected via the transverse isthmus, seminal plasma
Where are the bulbourethral glands?
either side of the ischial arch, function unclear in stallions, also called Cowper’s glands
Is the corpus spongiosum erectile?
Yes (like corpus cavernosum) but is not contained within the tunica albuginea, small and surrounds the urethra
What is the size of a stallion’s penis: Relaxed? Erect?
RELAXED: 50cm long, 2.5-5cm diameter, 15-20cm in prepuce ERECT: 50% increase in length and diameter, 300-400% increase in diameter of glans penis
Outline oxytocin in stallions.
Leydig cells release oxytocin into interstitial fluid. This facilitates rhythmic contraction of the seminiferous tubules to help evacuate sperm.
How is spermatogenesis regulated
Sertoli cells release inhibin and activin regulate this. Episodic bursts of LH control testosterone production. Testes also produce high levels of oestrogens but precise function unknown (also activin/inhibin)
What controls erection, emission and ejaculation?
Erection - initiated by cerebral responses, penile arterioles dilated by PS override of nromal S control Emission - sympathetic impulses Ejaculation - PS impulses, series of strong pulsatile contractions of urethralis and bulbospongiosus mm results in 5-7 jets of semen, first few pulses contain more sperm than later
What causes variation in semen
age month testicular size extent and duration of sexual arousal
How much sperm do stallions have enough for ejaculate-wise?
optimum = 1/day (for ideal sperm reserves) May have sufficient reserves for 2-3 ejaculates per day in season Libido, testicular size and morphologically-normal live sperm numbers are limiting factors for mare numbers
How are daylight length and melatonin related?
As daylight length increases, melatonin production by pineal gland decreases and inhibition of the HPO axis is downregulated. This leads to production of hypothalamic GnRH. When in large enough quantities, FSH and LH release is stimulated and cyclicity returns. Other factors such as nutrition, age and breed also play a role in the transition form anoestrous to normal cycling.
What do oestrogens produced by the ovary regulate? 3
behaviour, tract changes, LH
