Meiosis and the male reproductive system

Reproductive SystemOverviewMeiosis

SpermatogenesisHormone signaling in Males

Male and female reproductive systems

Function together to produce offspring Female reproductive system nurtures developing offspring Gonads (Ovaries / Testes)

Function as endocrine glands; produce hormonesFunction as exocrine glands; produce gametes

GametogenesisMeiotic division of cells; spermatogenesis and oogenesisOne replication of DNA, two sets of PMAT divisionsResults in Haploid cells (one of each type of chromosome)Fusion of haploid cells (fertilization) results in diploid zygote

Possible number of chromosome combinations

= 2n

Structures of Male Reproductive System

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Male Reproductive System

TestesPrimary organs

Develop in the abdominal pelvic cavity of fetusDescend 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 tubulesWithin testes, site of spermatogenesis initiation

Filled with spermatogenic cells that produce sperm cells

Interstitial endocrinocyte cells produce testosterone

Structures of Male Reproductive System

Structures of Male Reproductive System

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Male Reproductive System: Internal Accessory Ducts

Epididymis - ductSits on top of each testisReceives spermatids from seminiferous tubulesSpermatids become sperm cells

Vas deferens - ductTube connected to epididymisCarries sperm cells to urethra

Ejaculatory ductsWithin prostate

Formed by union of seminal vesicle and vas deferens

UrethraShared terminal duct of reproductive and urinary systems

Male Reproductive System: Internal Accessory Glands

Prostate gland Surrounds urethraProduces and secretes a milky, alkaline fluid into urethra just before ejaculationFluid protects sperm in the acidic environment of the vagina40% of semen

Seminal vesicleSecretes

Fluid rich in sugar used for energyProstaglandins – stimulate muscular contractions in female to propel sperm forward

Bulbourethral (Cowper’s) glandsProduce a alkaline mucus-like fluid

Secreted just before ejaculationNeutralizes urine acidityLubricates end of penis

SemenAlkaline mixture

NutrientsProstaglandins

1.5 to 5.0 ml per ejaculateSperm count of 40 to 250 million / ml

Male Reproductive System:External Accessory Organs

ScrotumHolds 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

PenisShaft

Erectile tissues surround urethraGlans penis

Cone-shaped structure on end of penis

Prepuce Skin covering glans penis in uncircumcised males

FunctionsDeliver spermUrination

SpermatogenesisSpermatogonia (46 chromosomes)

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Mitosis – produces primary spermatocytes

Undergo meiosis two secondary spermatocytes

Divides – two spermatids = 4 spermatids

Develop flagella to become mature sperm cells with 23 chromosomes

Sperm cells

HeadNucleus with 23 chromosomesAcrosome – enzyme-filled sac

Helps sperm penetrate ovum

MidpieceMitochrondria that generate cell’s energy

TailFlagellum that propels sperm forward

Hormonal signaling in male reproduction