Science Sponge What is the name of the tubes that the egg travels down to become fertilized? How long does it take for the zygote to implant? What is the temperature needed for semen to form properly?

Male Reproductive System

External organs Penis scrotum Internal Organs Testes Various ducts Seminal vesicles Prostate gland Bulbourethral gland

Testes Paired walnut shaped organs that are located in the scrotum Consists of highly coiled tubes called seminiferous tubules, where sperm are formed Leydig cells are scattered between the seminiferous tubules and produce testosterone and other androgens.

Why place the testes outside the body? Normal sperm development must occur at a lower temperature (2°C lower in scrotum) Scrotum is a fold of tissue that develops from the abdominal wall cavity Testes develop high in the abdominal cavity and then descend into the scrotum just prior to birth

In some mammals, such as rodents, the testes are drawn back into the abdominal cavity between breeding seasons. Some mammals that have low body temperatures (monotremes, whales and elephants) retain their testes within the abdominal cavity permanently

Ducts From seminiferous tubules, the sperm pass into coiled tubes called the epididymis It takes about 20 days for sperm to pass through the 6 meter long tubes As they progress through the epididymis, the sperm become motile (move) and gain the ability to fertilize an egg

During ejaculation, sperm are propelled from the epididymis through the muscular tubes of the vas deferens ducts The vas deferens run from the scrotum around and behind the urinary bladder, where each joins a duct from the seminal vesicle forming an ejaculatory duct that opens into the urethra The urethra runs through the penis to the outside environment (remember that both urine and semen pass through the urethra)

Accessory Glands Three sets of glands that contribute secretions to form semen (sperm and secretions)

Seminal vesicles- contribute most of the volume of semen. Secretes mucus and fructose, a sugar which provides nutrients to sperm Prostate gland- secretes anticoagulant enzymes and nutrients Bulbourethral glands- secretes a mucus that neutralizes any acidic urine left in the urethra

Penis Composed of 3 cylinders of spongy erectile tissue derived from modified veins and capillaries. During sexual arousal, the erectile tissue fill with blood from arteries. As tissue fills, increasing pressure seals off the veins that drain the penis causing it to engorge with blood and stiffen.

Semen Approximately 2-5 mL of semen is released with each ejaculation and carries million sperm. Once in the female reproductive tract, prostaglandins in the semen cause thinning of the mucus and stimulate uterine contractions to move the sperm toward the waiting egg

Growth and Development The fertilized egg (zygote) becomes an embryo once the first cell division occurs days after fertilization, implantation occurs. This means the baby has implanted itself on the uterine wall of the mother.

Growth and Development The placenta is a special two-way exchange organ that provides the baby with nutrients, and oxygen.

Growth and Development A normal pregnancy lasts for 280 days At the end of week 4 implantation is complete and the woman is pregnant. The embryo’s blood begins to form.

Growth and Development Weeks 5 to 8 a tiny amniotic sac of fluid surrounds the baby to protect from bumps and injury. The umbilical cord develops along with heart, brain, other organs, and blood vessels. Limbs are also in development.

Growth and Development At week 9-16 the baby is officially called a fetus. The muscles of the baby grow stronger and the baby grows rapidly during this stage.

Growth and Development At about 25 or 26 weeks the fetus has developed lungs although the fetus still gets oxygen from its mother. By 32 weeks the fetus can open and close its eyes. By 36 weeks the fetus is ready to be born.

Pregnancy is full of Surprises