human body systems · reproduction and hormones in the last lesson, you learned how the endocrine...

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Reproduction and HormonesIn the last lesson, you learned how the endocrine system

works with other organ systems to help the body grow and maintain homeostasis. The endocrine system also has another important function. It ensures that humans can reproduce.

Some of the organs of the endocrine system produce hormones that help humans reproduce. Reproduction is the process by which new organisms are produced. Life on Earth could not continue without reproduction.

A male and a female each have special organs for reproduction. Organs in the male reproductive system are different from the organs in the female reproductive system.

Human reproductive cells, called gametes (GA meets), are made by the male and female reproductive systems. Male gametes are called sperm. Female gametes are called ova (OH vah; singular, ovum), or eggs.

A sperm joins with an egg in a reproductive process called fertilization.The cell that forms when a sperm cell fertilizes an egg cell is called a zygote (ZI goht). A zygote is the first cell of a new human. It contains genetic information from the sperm and the ovum. The zygote will grow and develop in the female’s reproductive system.

What do you think? Read the two statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind.

Before Statement After

5. The testes produce sperm.

6. Puberty occurs during infancy.

Key Concepts • What do the male and

female reproductive systems do?

• How do humans grow and change?

Reading Check1. Summarize How do gametes enable humans to reproduce?

Make an Outline As you read, highlight the main idea under each heading. Then use a different color to highlight a detail or an example that might help you understand the main idea. Use your highlighted text to make an outline with which to study the lesson.

Human Body Systems

Reproduction and Development

120 Human Body Systems Reading Essentials

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The Male Reproductive SystemThe male reproductive system is shown at left in the

figure below. It produces sperm and delivers it to the female reproductive system. Sperm are produced in the testes (TES teez; singular, testis). Sperm develop inside each testis and then are stored in tubes called sperm ducts. Sperm mature in the sperm ducts.

The testes also produce a hormone called testosterone. Testosterone helps sperm change from round cells to long, slender cells that can swim. When sperm are fully developed, they can travel to the penis. The penis is a tubelike structure that delivers sperm to the female reproductive system. Sperm are transported in a fluid called semen (SEE mun). Semen contains millions of sperm and nutrients. The nutrients provide the sperm with energy.

The Female Reproductive SystemThe female reproductive system is shown at right in the

figure below. It contains two ovaries, where eggs grow and mature. Two hormones are made by the ovaries—estrogen (ES truh jun) and progesterone (proh JES tuh rohn). These hormones help eggs mature. When eggs are mature, they are released from the ovaries and enter the fallopian tubes. The fallopian tubes connect the ovaries to the uterus.

Key Concept Check2. Explain What does the male reproductive system do?

Visual Check3. Locate Circle the names of the organs that produce male and female gametes.

Make a horizontal two-tab book, label it as shown, and use it to organize information about the male and female reproductive systems.

MaleReproductive

System

FemaleReproductive

System

Male and Female Reproductive Systems

Uterus

Vagina

OvaryOvary

Fallopian tubes

Female Reproductive System

The female reproductive system produces eggs and provides a place for a new human to grow and develop before birth.

Sperm duct

Penis

Testis

The organs of the male reproductive system produce sperm and deliver it to the female reproductive system.

Male Reproductive System

Reading Essentials Human Body Systems 121


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Fertilization If sperm are also present in the fallopian tube, fertilization can occur as the egg enters the fallopian tube. Sperm enter the female reproductive system through the vagina. The vagina is a tube-shaped organ that leads to the uterus. A fertilized egg, or zygote, can move through the fallopian tube and attach inside the uterus. If there are no sperm in the fallopian tube, the egg will not be fertilized. But the egg will still travel through the fallopian tube and uterus. Then it will break down.

The Menstrual Cycle The endocrine system controls egg maturation and release and thickening of the lining of the uterus in a process called the menstrual (MEN stroo ul) cycle. The menstrual cycle takes about 28 days and has three parts:

1. Eggs grow and mature. The thickened lining of the uterus leaves the body.

2. Mature eggs are released from the ovaries. The lining of the uterus thickens.

3. Unfertilized eggs and the thickened lining break down. The lining leaves the body in the first part of the next cycle.

Human DevelopmentHumans develop in many stages, as shown in the table

below. When a sperm fertilizes an egg, a zygote forms. The zygote develops into an embryo (EM bree oh). An embryo is a ball-shaped structure that attaches inside the uterus and continues to grow.

Pregnancy The embryo develops into a fetus, the last stage before birth. It takes about 38 weeks for a fertilized egg to fully develop. This developmental period is called pregnancy. During pregnancy, the organ systems of the fetus will develop. The fetus will get larger.

Early Stages of Human Development5 weeks The embryo is about 7 mm long. The heart and other organs have started to develop. Arms and

legs are beginning to bud.

8 weeks The embryo is about 2.5 cm long. The heart is fully formed and beating. Bones are beginning to harden. Nearly all muscles have appeared.

14 weeks Growth and development continue. The fetus is about 6 cm long.

16 weeks The fetus is about 15 cm long and is about 140 g. The fetus can make a fist and has a range of facial expressions.

22 weeks The fetus is about 27 cm long and is about 430 g. Footprints and fingerprints are forming.

Reading Check4. Identify In what part of the female reproductive system does fertilization take place?

Key Concept Check5. State What does the female reproductive system do?

Interpreting Tables 6. Recognize Circle the stage when the heart is fully formed in the embryo.



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Birth Pregnancy ends with birth. During birth, the endocrine system releases hormones that help the uterus push the fetus through the vagina and out of the body.

From Birth Through ChildhoodThe first life stage after birth is infancy, the first 2 years of

life. The figure below shows several stages of development in infancy. During infancy, the muscular and nervous systems develop. An infant begins walking. Growth and development continue in childhood, which is from about 2 years to about 12 years of age. Bones in the skeletal system grow longer and stronger. The lymphatic system matures.

Visual Check7. State When does an infant usually crawl?

Key Concept Check8. Explain How do humans change during adulthood?

Adolescence Through AdulthoodAdolescence follows childhood. During adolescence, growth

of the skeletal and muscular systems continues. Organs get larger. As the endocrine system develops, the male and female reproductive systems mature. The time during which the reproductive system matures is called puberty.

After adolescence is adulthood. During adulthood, humans continue to change. In later adulthood, hair turns gray, wrinkles might form in the skin, and bones become weaker. This process is called aging. Aging is a slow process that can last for decades.

Milestones in Infancy

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Age (months)0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Walks without support

Stands without support

Crawls

Sits without support

Lifts head

Reading Essentials Human Body Systems 123


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Mini Glossary

Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind?

What do you think

END OF LESSON

Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson’s resources.

ConnectED

fertilization: a reproductive process in which a sperm joins

with an egg

gamete (GA meet): a human reproductive cell

ovum (OH vum): a female gamete

reproduction: the process by which new organisms are

produced

sperm: a male gamete

zygote (ZI goht): the cell that forms when a sperm cell

fertilizes an egg cell

1. Review the terms and their definitions in the Mini Glossary. Write a sentence explaining the relationship between gametes and zygotes.

2. Use the graphic organizer below to identify at least one change that occurs in each stage of life.

3. Use information from the lesson to write a definition of the word pregnancy.

Infancy Childhood Adolescence Adulthood



human body systems · reproduction and hormones in the last lesson, you learned how the endocrine...

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