Reproduction and Development

The Reproductive System
Video    Project   Puberty

Strands of Hair?

David M. Phillips/Photo Researchers

The things that look like strands of hair are sperm, the male reproductive cells. The red structure is an egg, the female reproductive cell. Why are there so many sperm but only one egg?

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Reproduction and Hormones

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We have read how the endocrine system works with other organ systems and helps the body grow and maintain homeostasis. The endocrine system has another very important function—to ensure 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. Reproduction is essential to the continuation of life on Earth.

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

 

As shown in the photo at the beginning of the lesson, 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 both the sperm and the ovum. The zygote will grow and develop in the female’s reproductive system.

 

1. Reading Check How do gametes enable humans to reproduce?

 

 

The Male Reproductive System

The male reproductive system, shown in Figure 1, 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 matures 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. Once sperm have 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 that provide the sperm with energy.
 

2. Key Concept Check What does the male reproductive system do?
 

Figure 1 Males and females have specialized organs for reproduction.

The Female Reproductive System

The female reproductive system contains two ovaries, as shown in Figure 1. Eggs grow and mature in the ovaries. Two hormones made by the ovaries, estrogen (ES truh jun) and progesterone (proh JES tuh rohn), help eggs mature. Once mature, eggs are released from the ovaries and enter the fallopian tubes. As shown in Figure 1, the fallopian tubes connect the ovaries to the uterus.

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, 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. However, it will still travel through the fallopian tube and uterus and then 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.

During the first part of the cycle, eggs grow and mature in the ovaries, while the broken down lining of the uterus leaves the body. In the second part of the cycle, mature eggs are released from the ovaries and the lining of the uterus thickens. In the third part of the cycle, unfertilized eggs and the thickened lining break down. The lining leaves the body in the first part of the next cycle.

 

3. Key Concept Check What does the female reproductive system do?

 

WORD ORIGIN

zygote
from Greek zygoun, means “to join”

4

Human Development

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As shown in Figure 2, humans develop in many stages. You have read that 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.

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 this period, the organ systems of the fetus will develop and the fetus will get larger. 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.

(clockwise from bottom left) Biophoto Associates/Photo Researchers, Dr. G. Moscoso/Photo Researchers, Anatomical Travelogue/Photo Researchers, Anatomical Travelogue/Photo Researchers, Neil Bromhall/Photolibrary

Figure 2 During pregnancy, a unicellular zygote develops into a fetus.

 

Visual Check When is the heart fully formed?

Notice anything about the beginning stages of each of these different organisms?

 

 

From Birth Through Childhood

The first life stage after birth is infancy, the first 2 years of life. During infancy, the muscular and nervous systems develop and an infant begins walking, as shown in Figure 3. 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, and the lymphatic system matures.

Figure 3 During infancy, a human learns to crawl and walk.

Visual Check When does an infant usually crawl?

Adolescence Through Adulthood

Adolescence follows childhood. During adolescence, growth of the skeletal and muscular systems continues. Organs such as the lungs and kidneys get larger. As the endocrine system develops, the male and female reproductive systems mature. The period of time during which the reproductive system matures is called puberty

Interactive Information on Puberty

 

After adolescence is adulthood, as shown in Figure 4. During adulthood, humans continue to change. In later adulthood, hair turns gray, wrinkles might form in the skin, and bones become weaker in a process called aging. Aging is a slow process that can last for decades.

 

1. Key Concept Check How do humans change during adulthood?

Digital Vision

Figure 4 Humans continue to change during adolescence and adulthood.

Lesson Review - Visual Summary

Sperm are produced and develop in the testes.

Eggs grow and mature in the ovaries.

During pregnancy, a zygote develops into an embryo and then into a fetus.

Biophoto Associates/Photo Researchers

What do you think NOW?

You first read the statements below at the beginning of the lesson.

1. The testes produce sperm.

2. Puberty occurs during infancy.

Did you change your mind about whether you agree or disagree with the statements? Rewrite any false statements to make them true.

Lesson Assessment

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Use Vocabulary

     1. Sperm and ova are types of __________.

     2. Distinguish between an ovum and a zygote.

     3. Define fertilization in your own words.

Understand Key Concepts

     4. The period between birth and 2 years is called

         A.adolescence.

         B.adulthood.

         C.childhood.

         D.infancy.

     5. Compare the functions of the ovaries and the testes.

     6. Distinguish between a zygote and a fetus.

     7. Which hormone helps the cells produced in the system below mature?

         A.estrogen

         B.insulin

         C.progesterone

         D.testosterone

     8. Which connects the ovaries to the uterus?

           A.bladder

           B.cervix

           C.fallopian tubes

           D.seminiferous tubules

     9. Which system works with the reproductive system?

           A.endocrine

           B.excretory

           C.respiratory

           D.skeletal

 

Interpret Graphics

 

     10. Summarize Copy and fill in the graphic organizer below to show the stages of life.

 

     11. Evaluate the changes in aging using the photo below.

PhotoLink/Getty Images

Critical Thinking

12. Hypothesize why development before birth takes a long time, about 38 weeks.

13. Summarize the role of puberty in the transition from adolescence to adulthood.

14. Compare the functions of the male and female reproductive systems.

15. Describe how the endocrine system and the reproductive system are related.
16. Why so many sperm and only one egg? To ensure that the one sperm is able to reach an egg, in
       order to fertilise it.

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The nervous system, shown in Figure 3, and the endocrine system, which you will read about later, receive and process information about your internal and external environments. These two systems control many functions, including movement, communication, and growth, by working with other systems in the body and help maintain homeostasis.

 

1. Key Concept Check How does the body respond to changes in its environment?

Doug Pensinger/Getty Images

 

Figure 3 The brain and the spinal cord form the central nervous system. All other nerves are part of the peripheral nervous system that extends throughout the entire body. 

The Nervous System

The nervous system is a group of organs and specialized cells that detect, process, and respond to information. The nervous system constantly receives information from your external environment and from inside your body. It can receive information, process it, and produce a response in less than 1 second.

 

Nerve cells, or neurons, are the basic units of the nervous system. Neurons can be many different lengths. In adults, some neurons are more than 1 m long. This is about as long as the distance between a toe and the spinal cord.

 

The nervous system includes the brain, the spinal cord, and nerves. The brain and the spinal cord form the central nervous system. Nerves outside the brain and the spinal cord make up the peripheral nervous system.

 

Processing Information The central nervous system is protected by the skeletal system. Muscles and other organs surround the peripheral nervous system. Information enters the nervous system through neurons in the peripheral nervous system. Most of the information then is sent to the central nervous system for processing. After the central nervous system processes information, it signals the peripheral nervous system to respond.

 

Voluntary and Involuntary Control The body carries out many functions that depend on the nervous system. Some of these functions such as breathing and digestion are automatic, or involuntary. They do not require you to think about them to make them happen. The nervous system automatically controls these functions and maintains homeostasis.

 

Most of the other functions of the nervous system are not automatic. They require you to think about them to make them happen. Tasks such as reading, talking, and walking are voluntary. These tasks require input, processing, and a response.

 

Reflexes Have you ever touched a hot pan with your hand? Touching a hot object sends a rapid signal that your hand is in pain. The signal is so fast that you do not think about moving your hand; it just happens automatically. Automatic movements in response to a signal are called reflexes. The spinal cord receives and processes reflex signals, as shown in Figure 4. Processing the information in the spinal cord instead of the brain helps the body respond more quickly.

 

Figure 4 Reflexes happen automatically.

Visual Check What detects heat when you touch a hot pan?

 

The Senses Humans detect their external environment with five senses—vision, hearing, smell, touch, and taste—as shown in Figure 5. Each of the five senses has specific neurons that receive signals from the environment. Information detected by the senses is sent to the spinal cord and then to the brain for processing and a response. Responses depend on the specific signal detected. Some responses cause muscles to contract and move such as when you touch a hot surface. The aroma of baking cookies might cause your mouth to produce saliva.

 

Figure 5 Each sense receives a different type of signal.

 

The Endocrine System

How tall were you in first grade? How tall are you now? From the time you were born until now, your body has changed. These changes are controlled by the endocrine system, shown in Figure 6. Like the nervous system, the endocrine system sends signals to the body. Chemical signals released by the organs of the endocrine system are called hormones. Hormones cause organ systems to carry out specific functions.

Why does your body need two organ systems to process information? The signals sent by the nervous system travel quickly through neurons. Hormones travel in blood through blood vessels in the circulatory system. These messages travel more slowly than nerve messages. A signal sent by the nervous system can travel from your head to your toes in less than 1 s, but a hormone will take about 20 s to make the trip. Although hormones take longer to reach their target organ system, their effects usually last longer.
 

Many of the hormones made by the endocrine system work with other organ systems and maintain homeostasis. For example, parathyroid hormone works with the skeletal system and controls calcium storage. Insulin is a hormone that is released from the pancreas that signals the digestive system to control nutrient homeostasis. Other hormones, such as growth hormone, work with many organ systems to help you grow.

2. Reading Check How do hormones help the body maintain homeostasis?
 

Mark Andersen/Getty Images

 

Figure 6 The endocrine system uses hormones to communicate with other organ systems.

 

Lesson Assessment

 

Use Vocabulary

1. Distinguish between compact bone and spongy bone.

2. A chemical signal that is released by the endocrine system is a(n) __________.

3. Use the term neuron in a sentence.

 

Understand Key Concepts

4. An automatic movement in response to a signal is called a

      A.hormone.

      B.muscle.

      C.neuron.

      D.reflex.

5. Compare the role of tendons in helping the skeletal system and the muscular system work together
     to a bridge between two cities.

6. Infer How does the skeletal system protect other organ systems in the body?

7. Which part of the nervous system is shown below?

     A.brain

     B.neuron

     C.peripheral nerve

     D.spinal cord

8. Which is NOT a type of muscle tissue?

     A.cardiac

     B.lymphatic

     C.skeletal

     D.smooth

9. Which is a part of the skeletal system?

     A.ligament

     B.spleen

     C.thymus

     D.trachea

Interpret Graphics

10. Summarize Copy and fill in the graphic organizer below to show the three types of muscle tissue.

11. Predict the effect of having less compact bone than normal on the strength of the skeletal system by examining the figure below.

Critical Thinking

12. Hypothesize What would be the effect of losing one’s sight on the ability to digest food? Explain your answer.

13. Hypothesize how an injury to the spinal cord might affect the ability of the nervous system to sense and respond to a change in the environment.

14. Assess how the nervous system helps the muscular system control heart rate, digestion, and respiration.

15. Assess the role of the skeletal system in the storage of nutrients.

16. Name two hormones produced by the endocrine system and describe how they work with other organ systems and maintain homeostasis.

17. Identify the main functions of the skeletal, muscular, nervous, and endocrine systems.

Can you say the color name not read the word?

 That's all for now....

Mrs. Sandoval

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