CHAPTER 15: THE REPRODUCTIVE SYSTEM
Sexual reproduction is the process by which organisms produce offspring by making germ cells called gametes. After the male gamete (sperm) unites with the female gamete (oocyte), fertilization occurs. This results in a cell that contains 1 set of 32 chromosomes from each parent. The male and female reproductive organs are grouped by functions. The gonads produce the gametes and secrete the sex hormones.
Stallion Anatomy
Scrotum: supporting structure for the testes consisting of loose skin and underlying subcutaneous tissue. It is located in the inguinal region placed between the thighs of stallions. It is often asymmetrical and divided externally by the medium raphe which extends cranially onto the prepuce and caudally onto the perineum. The scrotum is partially responsible for thermoregulation via papiniform plexus.
Layers of the scrotum are as follows:
1. Skin - scrotal skin is thin, elastic, supple, shiny and oily to the touch due to the secretions of numerous sweat and sebaceous glands. A few fine hairs are present, and the skin is usually deeply pigmented. 2. Tunica Dartos – this smooth muscle forms a complete median septum separating the 2 testicles. Upon contraction, the tunica dartos wrinkles the skin of the scrotum and reduces the size of the scrotum. This occurs when the testes are raised toward the superficial inguinal ring by the cremaster muscle. The dartos muscle raises the scrotum in cold weather and lowers it during hot weather.
3. Scrotal fascia 4. Vaginal Tunic
a. Parietal vaginal tunic – fibroserous sac which is continuous with parietal peritoneum of abdominal cavity (also covers testes, epididymis & spermatic cord) b. Visceral vaginal tunic – adheres to the teste
Testes: paired oval gonads in the scrotum. They vary in size and weight depending on the stallion, but generally they are 8-14 cm in length, 5-8 cm in width and weigh about 250-300 grams. The testes are divided into a series of internal compartments called lobules (100’s). Each lobule contains 1-3 tightly coiled tubules called seminiferous tubules where sperm is produced. The seminiferous tubules contain 2 types of cells: spermatogenic cells and sertoli cells. The spermatic cells produce the sperm. The large sertoli cells are joined by tight junctions to form the blood- Testis Barrier. Substances must first pass through the sertoli cells before reaching the developing
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