14.1 Male Reproductive System

Organisms that carry out sexual reproduction produce gametes, haploid sex cells that are united during fertilization.• In the male reproductive system, the sperm are gametes that are produced in paired

testes (male gonads)o Seminal fluid: a nutrient-rich fluid in which sperm leave the penis during

ejaculationo Semen: combination of sperm and seminal fluid

Genital Tract• Testes: paired structures that produce sperm and sex hormones• Epididymides: ducts outside the testes where sperm mature and are stored• Vas deferens: stores sperm; empties into an ejaculatory duct• Urethra: connected to the ejaculatory duct• Seminal vesicles: contribute nutrients and fluids to semen• Prostate gland: contributes basic solution to semen (sperm are more viable in a basic

solution)• Cowper’s glands: secrete a mucus-rich fluid that helps lubricate the penis• Penis: male organ of sexual

intercourse• Circumcision: surgical

removal of the foreskin

Erection and Orgasm in Males

Erection• Erectile tissue extends throughout the

shaft of the penis• Sexual excitement causes the arteries in

the penis to relax and widen• Increased blood flow causes the penis to

enlarge and become erect

Ejaculation and Orgasm• When sexual stimulation intensifies, sperm enter the urethra from the vasa deferentia

and the accessory glands contribute secretions to the semen• Rhythmic muscle contractions cause semen to be ejaculated

from the peniso These contractions are part of male orgasm (climax of

sexual stimulation)• A refractory period occurs after ejaculation, where sexual

stimulation does not cause an erection• More than 400 million sperm are expelled in 2 to 6 mL of

semen during ejaculation

Male Gonads, the TestesTestes• Lie within the scrotum• The scrotum helps regulate testicular temperature by holding

the testes closer or farther away from the body• Increases in temperature may decrease sperm production

Seminiferous Tubules• A testis is composed of lobules, each of which contains tightly coiled seminiferous

tubules• Intersitial cells that lie between the tubules secrete male sex hormones (androgens)• Seminiferous tubules contain cells undergoing spermatogenesis (production of sperm)

Spermatogenesis• Occurs in the walls of the seminiferous tubules• Spermatogonia become primary spermatocytes that undergo meiosis I to produce

secondary spermatocytes• Secondary spermatocytes undergo meiosis II to produce four haploid spermatids• Spermatids differentiate into sperm• Sertoli cells support, nourish, and regulate the spermatogenic cells

Sperm• Mature sperm (spermatozoa) have a head, middle piece, and a tail• Mitochondria in the middle piece is the site of ATP production for

the movement of the tail• The acrosome is a cap that stores enzymes needed to penetrate the

egg• The nucleus of the sperm has the male’s DNA as 23 chromosomes• Sperm usually do not live more than 48 hours in the female genital

tract

Hormonal Regulation in MalesHypothalamus controls secretions of the pituitary gland by secreting gonadotropin-releasing hormone (GnRH). • GnRH: stimulates the pituitary gland to release follicle-

stimulating hormone (FSH) and luteinizing hormone (LH)o FSH: promotes sperm production in the

seminiferous tubules (which secrete inhibin, a hormone which inhibits FSH synthesis)

o LH: also called interstitial-cell-stimulating hormone (ICSH) because it promotes the production of testosterone by interstitial cells

Testosterone• The main sex hormone in males• Essential for normal development and functioning of

male reproductive structures• Maintains male secondary sex characteristics that develop at puberty (body hair, deeper

voices, greater muscular development)