Male Reproductive System: Gametes and Sperm

• Sexual reproduction involves the formation of a diploid zygote from two haploid gametes through fertilization.
• A male's roles in sexual reproduction include producing sperm cells and delivering them to the female reproductive system to fertilize an egg cell.

Male Reproductive System

• The male reproductive system contains two egg-shaped testes.
• Testes are the gamete-producing organs.
• Each testis is about 4 cm (1.5 in.) long and 2.5 cm (1 in.) in diameter.
• Each testis has about 250 compartments containing tightly coiled seminiferous tubules.
• Each seminiferous tubule is approximately 80cm (32 in.) long.
• Total length of seminiferous tubules in both testes is about 500m (1,640 ft).
• Sperm form through meiosis in the lining of these tubules.
• Testes develop within the abdominal cavity and descend into the scrotum before birth.
• The scrotum maintains a temperature about 2°C to 3°C cooler than the abdomen.
• This lower temperature is essential for normal sperm development.
• Sperm production begins during puberty.
• Luteinizing hormone (LH) stimulates testosterone secretion.
• Testosterone, the main androgen, is produced by cells between the seminiferous tubules.
• Follicle-stimulating hormone (FSH), along with testosterone, stimulates sperm production.
• Males continue to produce sperm as long as testosterone levels are high enough.
• Meiosis reduces the chromosome number from diploid (2n) to haploid (1n).
• During meiosis in sperm cells, the chromosome number drops from 46 to 23.
• Each cell undergoing meiosis results in four sperm cells.

Sperm Structure

• Mature sperm consists of a head, midpiece, and tail (flagellum).
• The head contains enzymes to penetrate the egg's protective layers during fertilization.
• It also contains 23 chromosomes.
• The midpiece is packed with mitochondria, providing energy for sperm to reach the egg.
• The tail is a flagellum that propels the sperm.

Path of Sperm Through the Male Body

• Mature sperm move through several reproductive structures.
• Sperm move from the seminiferous tubules to the epididymis.
• The epididymis is a long, coiled tubule attached to each testis where sperm mature and gain the ability to swim.
• Sperm are stored in the epididymis.
• Some sperm leave the epididymis and pass through the vas deferens.
• The vas deferens is a duct extending from the epididymis.
• Smooth muscles in the vas deferens contract to move sperm.
• Each vas deferens enters the abdominal cavity, loops around the bladder, and merges with the urethra.
• The urethra is the duct for urine excretion.
• In males, both urine and sperm exit through the urethra, but not simultaneously.
• In the urethra, sperm mix with fluids from the seminal vesicles, prostate gland, and bulbourethral glands.
• These glands secrete fluids that nourish and protect sperm.
• Seminal vesicles produce a sugar-rich fluid for energy.
• The prostate gland secretes an alkaline fluid to neutralize acids in the female reproductive system.
• Bulbourethral glands secrete an alkaline fluid to neutralize acidic urine traces in the urethra.
• Sperm and secretions form semen.
• Semen contains prostaglandins that stimulate contractions in the female reproductive tract.

Delivery of Sperm

• The urethra passes through the penis.
• The penis deposits sperm into the female reproductive system.
• During sexual arousal, spongy tissue in the penis fills with blood, causing an erection.
• Ejaculation is the forceful expulsion of semen from the penis.
• Each ejaculation expels 3 to 4 mL of semen.
• Sperm make up only 10 percent of the semen volume.
• A single ejaculation can expel 300 million to 400 million sperm.
• Few sperm reach the fertilization site due to the acidic environment of the female reproductive tract.

Explore the male reproductive system, focusing on the testes and sperm production. Learn about the structure of the testes, the role of seminiferous tubules, and the importance of temperature regulation for sperm development.