Meiosis and the male reproductive system
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Used to (re)ntroduce high school anatomy and physiology students to the process of meiosis / gametogenesis. More specifically, this presentation focuses on spermatogenesis and the male reproductive system anatomy.
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Meiosis and the male reproductive system
- 2. Male and female reproductive systems Function together to produce offspring Female reproductive system nurtures developing offspring Gonads (Ovaries / Testes) Function as endocrine glands; produce hormones Function as exocrine glands; produce gametes
- 3. Gametogenesis Meiotic division of cells; spermatogenesis and oogenesis One replication of DNA, two sets of PMAT divisions Results in Haploid cells (one of each type of chromosome) Fusion of haploid cells (fertilization) results in diploid zygote
- 11. Structures of Male Reproductive System 11
- 12. Male Reproductive System Testes Primary organs Develop in the abdominal pelvic cavity of fetus Descend into scrotal sac shortly before or after birth Produce the male sex cells (sperm) Produce the male hormone testosterone Scrotum – sac that holds the testes Seminiferous tubules Within testes, site of spermatogenesis initiation Filled with spermatogenic cells that produce sperm cells Interstitial endocrinocyte cells produce testosterone
- 13. Structures of Male Reproductive System
- 15. Structures of Male Reproductive System 15
- 16. Male Reproductive System: Internal Accessory Ducts Epididymis - duct Sits on top of each testis Receives spermatids from seminiferous tubules Spermatids become sperm cells Vas deferens - duct Tube connected to epididymis Carries sperm cells to urethra Ejaculatory ducts Within prostate Formed by union of seminal vesicle and vas deferens Urethra Shared terminal duct of reproductive and urinary systems
- 17. Male Reproductive System: Internal Accessory Glands Prostate gland Surrounds urethra Produces and secretes a milky, alkaline fluid into urethra just before ejaculation Fluid protects sperm in the acidic environment of the vagina 40% of semen Seminal vesicle Secretes Fluid rich in sugar used for energy Prostaglandins – stimulate muscular contractions in female to propel sperm forward Bulbourethral (Cowper’s) glands Produce a alkaline mucus-like fluid Secreted just before ejaculation Neutralizes urine acidity Lubricates end of penis Semen Alkaline mixture Nutrients Prostaglandins 1.5 to 5.0 ml per ejaculate Sperm count of 40 to 250 million / ml
- 18. Male Reproductive System: External Accessory Organs Scrotum Holds testes away from body 3 C below body temperature Lined with serous membrane that secrets fluid Testes move freely Testes separated from one another by septum Penis Shaft Erectile tissues surround urethra Glans penis Cone-shaped structure on end of penis Prepuce Skin covering glans penis in uncircumcised males Functions Deliver sperm Urination
- 19. Spermatogenesis Spermatogonia (46 chromosomes) 31-19 Mitosis – produces primary spermatocytes Undergo meiosis two secondary spermatocytes Divides – two spermatids = 4 spermatids Develop flagella to become mature sperm cells with 23 chromosomes
- 24. Sperm cells Head Nucleus with 23 chromosomes Acrosome – enzyme-filled sac Helps sperm penetrate ovum Midpiece Mitochrondria that generate cell’s energy Tail Flagellum that propels sperm forward
- 26. Hormonal signaling in male reproduction
Editor's Notes
- Cross over (exchange of chromosomal material between non-sister chromatids) occurs during prophase 1. This recombines genes and increases the genetic variation of chromosomes. This, in part, explains changes in phenotypes of organisms over time (evolution). Increased variation is also inherently beneficial for species, as a greater variation increases the chance that some portion of a population survives changing environmental conditions
- As chromosomes line up in tetrads during metaphase 1, they can line up in multiple ways. The total number of chromosome combinations that can end up in haploid gametes is 2 to the nth power. (If n = 12, total number of combinations would equal 4096) This is why you don’t look like your siblings (unless you have an identical twin)
- Micrographic cross section of seminiferous tubule showing maturing spermatocytes