Chapter 23 Reproduction and Development Gametes Sex cells

Chapter 23: Reproduction and Development

Gametes: • Sex cells

Sperm: • Male gamete. Head and long tail. • The first part of the tail contains many mitochondria, which provide the energy to swim. • The head contains the nucleus and enzymes to help the sperm enter the egg.

Ova: (singular: ovum) • Female gamete. • Large cell full of nutrients and other materials to help the new life grow.

Gametes are haploid: • Haploid: Containing only one set of chromosomes. • When a haploid sperm and a haploid ovum join, they make a diploid cell (contains two sets of chromosomes), which is the number of chromosomes that all other body cells have.

Fertilization: • Sperm cell joins with the ovum to form a new cell called a zygote. • Zygote combines the chromosomes from the sperm and ovum in its nucleus, making the new diploid cell.

Male reproductive system: • Testes: Male organs that make sperm (and testosterone).

Adult males constantly make new sperm cells. • Epididymis: Collects new sperm cells and stores them until they mature and develop the ability to swim. – Testes and epididymis are suspended in scrotum (pouch of skin that keeps the testes outside the body cavity because sperm need lower temperatures to mature.

• Vas deferens: Tube that carries sperm from epididymis to urethra. Glands add fluids that help move sperm toward the ovum. – Semen: Sperm plus fluids. • Semen leaves the body through the urethra. The penis places semen inside the female reproductive tract.

vas

Female reproductive system: • Ovaries: Make ova. – Newborn girl’s ovaries contain ALL of the cells that will become ova throughout her life. • An oviduct (fallopian tube) is wrapped around each ovary. – Cilia in oviduct sweep released egg toward uterus. – Fertilization usually occurs in the oviduct.

• Uterus: Muscular, pear-shaped organ with a thick lining, in which the fertilized egg implants and develops. – Walls are stretchable as the embryo grows and can produce strong contractions to push the baby out at birth. • Cervix: Opening to uterus. • Vagina (birth canal): Stretchy, muscular tube that opens to the outside of the body.

Menstrual cycle: Female reproductive cycle • Menstruation: Process of shedding the uterine lining.

First week after the start of menstruation: • Pituitary gland releases a hormone that makes an egg develop in an ovary. – Follicle: Case in which ovum develops. • Follicle secretes estrogen, which makes the uterus grow a new lining.

Day 14: • Pituitary hormones make follicle release egg into oviduct. – Ovulation: Release of ovum. • Empty follicle keeps releasing estrogen and starts releases progesterone, which makes the uterine lining grow thicker to support fertilized egg.

• If the egg is not fertilized, it dies and disintegrates. – Uterine lining is shed at the beginning of the next menstrual cycle.

23. 2 Development before birth • Fertilization: Only one sperm can enter the egg. – 2 haploid nuclei become 1 diploid nucleus. – Occurs in the oviduct.

• Zygote divides as cilia push it toward the uterus. – 1 cell 2 cells 4 cells 8 cells…. . – Blastocyst: Hollow ball of cells formed after many divisions

Blastocyst

Pregnant: • The blastocyst has embedded in the uterine lining.

• Some blastocyst cells continue to develop into the new individual, while others form the placenta. – Placenta: Grows into the uterine lining and contacts the mother’s circulatory system to exchange nutrients, oxygen, and wastes between the mother and the offspring. – Umbilical cord: Stalk of tissue that connects embryo to placenta.

Pregnancy • Embryo: Term for the developing individual from the time the blastocyst embeds in the uterine wall to 8 weeks. – 1 week: distinct head and start of digestive tract – 2 weeks: simple, tube-shaped heart – 1 month: 4 buds that will become arms and legs • Now surrounded by amnionic sac: cushions the embryo.

Fetus: • Term for the developing individual from 8 weeks until birth. • At 8 weeks, all organs systems have developed, and the fetus is 4 centimeters long.

During the last 7 months of pregnancy, the fetus: • • • Grows Brain and other organs mature Makes its own blood cells Fat tissue develops under the skin Hair and nails develop Moves felt after 4 th month) • In the ninth month, the fetus is upside down with its head against the cervix, ready to be born.

Birth: • When the fetus’s lungs have matured, they release a protein that crosses the placenta into the mother. • This protein triggers the hormone oxytocin to be released, which causes labor.

• After the baby is born, the placenta is released and expelled. • The umbilical cord is cut and the remaining piece eventually dries and falls off. – The scar becomes the naval (belly button).

Twins: • Fraternal twins: Two eggs are released at the same time and both get fertilized and implant. • Identical twins: Single zygote splits in two. Both individuals have the exact same genes.

23. 3 Human life stages:

Infancy: • From birth to 18 months. • Period of greatest physical and mental changes. • Rapid growth. • Coordination of nervous system and muscles. – Roll over, sit up, grab toys, crawl. Walk by 18 months. • Ability to think and reason grows. • First words said by end of infancy.

Childhood: • From 18 months until puberty (approximately 12 -13 years). • Steady growth and development occurs during this time.

Adolescence: • Puberty through the teens. • The child’s body becomes an adult body. • Hormones cause reproductive organs to mature, making the person fertile (capable of having children).

• Secondary sexual characteristics: Adult physical characteristics.

In boys: • • • Testes release testosterone. Penis and testes grow. Testes start to make sperm. Larynx grows, causes a deeper voice. Body and facial hair develops. Muscles in chest and shoulders get bigger.

In girls: • Ovaries release estrogen. • Hips grow wider. • Breasts develop.

In both boys and girls: • Underarm and pubic hair develops. • Growth spurt: – Girls – ends at 16. – Boys – ends at 18.

Adulthood: • From the end of adolescence to age 60. • No height changes. • After age 45: – Metabolism shows. – Physical strength declines. – Bones become more brittle. – Skin loses elasticity (causes wrinkles). – Hair loses pigment (becomes gray). – Women: Ovaries stop producing estrogen • Menstrual cycle stops (menopause).

Older adulthood: • • • After age 60. Cell division and tissue repair slows. Wrinkles deepen. Eyesight and hearing diminish. Reflexes slow. Response time slows.