Human Biology 4.3

The reproductive system allowsthe production of offspring.

The reproductive system producesspecialized cells.

• The reproductive system allows adults to produce offspring.

• Males and females have different reproductive systems which make specialized cells. – Female specialized cells are called egg cells. – Male specialized cells are called sperm cells.

• Each specialized cell provides genetic material, needed information for the organism to form, develop, and grow.

• Both male and female reproductive systems rely on hormones to signal the process of sexual development.– Growth of reproductive organs– Development of sexual characteristics.

• Once mature, reproductive organs produce hormones to maintain secondary sexual characteristics.

The reproductive system producesspecialized cells.

Main Idea Detail Notes

The reproductive system produces specialized cells.

A. Males and females have different reproductive systems.

E. Each cell contains all the genetic material needed for growth and

development.

D. In the male, the specialized cells are called sperm cells.

C. In the female, the specialized cells are called egg cells.

B. Both males and females make specialized reproductive cells.

The Female Reproductive System• The female reproductive

system has two functions. – produce egg cells– protect and nourish the

offspring until birth. • Two reproductive organs

called ovaries.– Each contains hundreds of

egg cells.– Pituitary gland releases a

hormone that stimulates some of the eggs to develop and grow every 28 days.

Menstruation• After an egg cell develops another hormone signals the

ovary to release the egg.• Egg moves from the ovary into a fallopian tube.• If within ten to twelve hours the egg cell is fertilized by a

sperm cell, it will move to the uterus. • After implanting inside the thick lining of the uterus, the

fertilized egg cell rapidly grows and divides.• If fertilization does not occur within 24 ,the egg and the

lining of the uterus begin to break down.• Muscles in the uterus contract in a process called

menstruation.• During menstruation there is a flow of blood and tissue

from the body through a canal called the vagina over a period of about five days.

The Female Reproductive System and Menstruation

The Male Reproductive System• The organs that produce sperm are called the testes.• Produced inside tiny, coiled tubes hundreds of feet long inside the

testes. • The testes release a hormone that controls the development of

sperm. • This hormone is also responsible for physical characteristics such as

facial hair and a deep voice.• Sperm cells are the specialized cells of the male reproductive system.• Sperm starts being produced sometime during adolescence.

The Male Reproductive System•The sperm is a single cell with a head and a tail. •The head is filled with chromosomes.•The tail functions as a whip to make the sperm mobile.

•Sperm travel from the testes, through several different structures of the reproductive system.•While they travel, the sperm mix with fluids called semen which contains nutrients for the sperm cells. •One drop of semen contains up to several million sperm cells.

Chromosomes are contained in the

nucleus.

The reproduction of offspring includesfertilization, pregnancy, and birth.

• Each sex cell has half of the genetic material needed for a human being to grow and develop.

• During sexual intercourse, millions of sperm cells leave the testes and exit the body through the urethra.

• Sperm is ejaculated into the female’s vagina.• Sperm travel into the uterus and continue to

the fallopian tube.

Reproduction includes fertilization, pregnancy, and birth.

Fertilization• Occurs when one sperm cell joins the egg cell. • Once fertilized in the fallopian tube, chemical

changes to the egg’s surface prevent any more sperm from entering.

• Once inside the egg, the genetic material from the sperm combines with the genetic material of the egg cell.

• The fertilized egg cell moves down the fallopian tube toward the uterus.

• It divides into two cells, then each of those cells divides again.

• Cell division continues, and within a few days, the embryo implants itself to the lining of the uterus

The egg cell moves down the fallopian tube following fertilization. Its final destination is the uterus.

Pregnancy• Three periods of specific stages of development.• Week 1 the embryo grows rapidly and the placenta forms.– Blood vessels lead from the mother’s circulatory system to the

embryo through the umbilical cord. – Oxygen and nutrients move through the placenta and umbilical

cord to the growing embryo.• Week 8 the developing embryo is called a fetus.– Begins to have facial features– Major organ systems– Beginnings of a skeleton– Becomes male or female

• Week 12 fetus continues to grow and bones develop further.• In the last twelve weeks the fetus and all its organ systems

develop fully.

Labor and Delivery• At the end of pregnancy, the fetus is fully developed. • Birth of a fetus is divided into three stages.– Labor

• Begins with muscular contractions of the uterus. • Contractions start at 10 to 30 minutes and last about 40 seconds.• They progress until they are occurring about every 2 minutes.

– Delivery• Cervix dilates until it becomes wide enough for the mother’s muscles

to push the fetus out.• The fetus is pushed out of the uterus, through the vagina, and out of

the body. • The fetus is still connected to the mother by the umbilical cord.

– Birth of the placenta• The umbilical cord is cut shortly after the fetus is delivered.• The placenta separates from the uterine wall and the mother pushes

it out with more muscular contractions.

Third

Second

First

Name of the Stage

labor

Delivery of the fetus

birth The placenta is pushed out

The baby is pushed out of the uterus

The uterus contracts

What Happens in This Stage

Pregnancy, Labor and Delivery, and Multiple Births

Multiple Births• The birth of more than one offspring is called a multiple

birth.– Uncommon in humans

• Identical twins are produced when a single fertilized egg divides in half, forming two complete organisms.– Always of the same sex– Look alike– Have identical blood types– Form early in pregnancy– Approximately 1 in 29 births is a set of identical twins

• Fraternal twins are produced when two eggs are released at the same time and are fertilized by two different sperm. – May be very different from each other– Can be the same sex or different sexes

Identical twins, which begin as a single fertilized egg, are

always the same sex and blood type, and are very hard to tell

apart.

Fraternal twins may or may not be the same sex or blood type, and they often do not look

any more alike than other siblings.