Reproduction Asexual reproduction Involves splitting, budding or fragmentation of the parent Beneficial when population density is low and are not mates readily available Parthenogenesis is the development of an unfertilized egg into an adult Common amongst mollusks, crustaceans, insects and some reptiles This usual alternates with sexual reproduction Fastest way to achieve reproduction Sexual reproduction Male ? sperm; female ? ovum; each provides unique genetic information Sperm are small and motile; eggs are large and nonmotile Internal fertilization is more reliable; female body provides watery medium for sperm movement and houses the developing embryo Hermaphroditism is a form of sexual reproduction in which a single organism has both eggs and sperm Some hermaphrodites are both male and female at the same time; others are functionally one sex and then the other It maintains diversity in a species; by mixing genetic components and recombining them, the offspring is much more complex and able to adapt to a changing environment and may be able to better survive than either parent Sexual selection removes harmful mutations Male reproductive system Testes are in the scrotum Sperm go thru the epididymis to the vas deferens around the sides and front of the scrotum; the vas deferens passes over the pubic bone and bladder to the seminal vesicle, which is under the bladder; the vas deferens then passes thru the prostate where it is renamed the ejaculatory duct and then it joins with the urinary duct ? urethra; it then receives input from the bulbourethral gland before entering the base of the penis and the corpora cavernosa Testis Paired testes produce gametes and hormones The testes hang below the body housed in the scrotum, which maintains a lowered body temperature (2oC cooler) If the testes do not drop the male is sterile Sperm are produced by spermatogenesis in the seminiferous tubules Sperm are collected in the epididymis that lead to the vas deferens Spermatogenesis Occurs in the seminiferous tubules Spermatongonia divide by mitosis to form more spermatogonia Primary spermatocytes produce secondary spermatocytes, which produce spermatids Four haploid spermatids are produced by one diploid primary spermatocyte The Sertoli Cells, which supply nutrients to the sperm, phagocytize mich of the cytoplasm of the spermatid Sertoli cells are held together with tight junctions that separate spermatogenesis from the blood supply The inguinal canals connect the scrotum to the pelvic cavity and contain the vessels, nerves, muscles, and ducts Cannot happen unless Sertoli cells are present Sperm Leave seminiferous tubules and move into tubules of the epididymis Sperm mature in the epididymis and may be stored there Sperm are ejaculated from the epididymis into the vas deferens which leads to the ejaculatory ducts which passes thru the prostate gland and empties into the urethra, which can carry urine or semen, and passes out thru the penis Accessory glands and the sexual response Accessory glands produce the fluid portion of semen A single ejaculation consists of about 3.5mL of semen and contains about 400 million sperm cells Paired seminal vesicles secrete fluid that is rich in fructose and prostaglandins Paired bulbourethral glands produce a mucous secretion which lubricates the penis Semen is the sperm suspended in the fluid productions of the seminar vesicles Priatism ? erect for too long because of clogged veins Limp penis ? dorsal veins (dilated), dorsal artery (constricted) Erect penis ? dorsal veins (constricted), dorsal artery (dilated) Testosterone Testosterone is secreted by interstitial cells in the testes These cells are located outside the seminiferous tubules Testosterone is also necessary for the development and function of the male reproductive tract It promotes the development and maintenance of sexual behavior It stimulates the development of secondary sexual characteristics such as beard growth, deepening of the voice, etc. and has growth-promoting effects Hormonal regulation of male reproduction Hypothalamus, pituitary, and testes interact to regulate male reproduction At the age of 10, hypothalamus secretes GnRH GnRH stimulates the anterior pituitary to secrete the gonadotrophic hormones, FSH (follicle stimulating hormone) and LH (lutenizing hormone) FSH stimulates Sertoli cells to secrete ABP ABP results in development of the seminiferous tubules and stimulates spermatogenesis LH stimulates the interstitial cells to secrete testosterone
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