lab 16: reproductive system

• The reproductive system includes the gonads (the primary sex organs) and the accessory reproductive structures
• the accessory reproductive structures include ducts, glands and external genitalia.
• The gonads are the reproductive organs that produce the gametes and the sex hormones
• The reproductive role of the male is to produce the male gametes, known as sperm cells or spermatozoa, and to deliver these gametes to the female reproductive tract
• The testes (singular: testis) are the gonads of the male.
• the testes hang within the scrotum, which is essentially a pair of abdominal pouches forming a common cutaneous sac
• Each testis is an oval-shaped organ that lies in a separate compartment within the scrotum.
• Normal sperm production requires a temperature about 3°C lower than core body temperature.
• Muscles associated with the scrotum can move the testes closer to or further from the body to maintain this lower temperature.
• Partly surrounding each testis, is an accessory duct known as the epididymis.
• In this highly coiled duct, the sperm mature and are stored.

  epididymis
• Emerging from the epididymis is another accessory duct, the ductus deferens (vas deferens)
• The ductus deferens and the associated blood vessels, nerves and connective tissue form the spermatic cord by which each testis is suspended within the scrotum
• the spermatic cord, the ductus deferens runs upward, passes through the inguinal canal and enters the abdominal cavity
• the vas deferens then leaves the spermatic cord, loops over the ureter and descends along the posterior surface of the urinary bladder
• The end of each ductus deferens enlarges to form an ampulla, which then joins with the duct from one of the seminal vesicles (a pair of accessory glands) to form a short ejaculatory duct.
• The ejaculatory ducts pass into the prostate gland (a single accessory gland), where they empty into the urethra.
• The urethra extends from the urinary bladder to the tip of the penis
• the urethra is divided into 3 regions: the prostatic urethra, the membranous urethra and the penile (spongy) urethra
• The urethra of males serves both the reproductive and urinary systems
• The accessory glands of the male reproductive system are the paired seminal vesicles, prostate gland and the paired bulbourethral glands
• The secretions of the male accessory glands form the semen (seminal fluid) which carries the sperm during ejaculation, activates and produces certain nutrients for the sperm, and contains substances that neutralize the somewhat acidic environment in the vagina.
• The penis is the organ that conducts urine to the exterior and delivers sperm into the female reproductive tract
• Internally, the penis consists of three cylindrical columns of erectile tissue (elastic connective tissue, smooth muscle and vascular channels) each surrounded by fibrous tissue called the tunica albuginea
• The two dorsal columns are called the corpora cavernosa (singular: corpus cavernosum) and the column surrounding the urethra is the corpus spongiosum.
• Each testis is covered by a dense connective tissue capsule and is composed of many coiled seminiferous tubules
• The germinal epithelium lining each seminiferous tubule is made up of cells in various stages of development.
• Spermatogenesis, the process of sperm production occurs in the seminiferous tubules
• The most immature cells are the spermatogonia which are located near the basement membrane
• These cells develop from primordial germ cells in the embryonictestis


  spermatogonia
• The spermatogonia remain dormant during childhood and begin actively producing sperm at puberty, around age 10 to 12 in males.
• Under the influence of reproductive hormones, spermatogonia begin to divide by mitosis to increase their numbers and some form primary spermatocytes
• A primary spermatocyte gives rise to four sperm cells
• Each primary spermatocyte undergoes meiosis I to produce two haploid secondary spermatocytes which then undergo meiosis II to produce four haploid spermatids
• The spermatids are then transformed into sperm cells (spermatozoa) by growing a flagellum and shedding most of its cytoplasm.
• The sperm cells are recognizable by their tails which project into the lumen of the seminiferous tubule.
• Sperm are produced throughout the male lifetime although the sperm count and sex drive do diminish
• Located between the seminiferous tubules are the interstitial cells, or Leydig cells.
• These cells secrete the hormone, testosterone which is necessary for spermatogenesis and for the development of the secondary sexual characteristics in the male.

  Leydig cells
• The reproductive role of the female is to produce the female gametes, known as ova or eggs.