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HUMAN BODY SYSTEMS. CHAPTER 1 The Reproductive System.

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The Reproductive System

This chapter is about the reproductive system of human beings. This system consists of organs that make it possible for people to produce more human beings and thus ensure that our kind will continue to live on Earth. In this chapter, you will study the parts, functions and care of the reproductive system.

Module 1: Changes during Puberty


Are you between 11 and 13 years old? This is the beginning of the period in life called puberty. If you are of this age, do you notice any change happening to your body lately?

Most boys and girls experience body changes when they reach puberty. It is also during puberty that their sex organs mature. During puberty, boys and girls gradually develop into young adolescents – no longer children but not yet adults.







What changes take place during puberty?

Changes in Behavior & Attitude

Physical Changes

What causes these changes?


Physical Changes

Whether you are a boy or a girl, your body changes in many ways during puberty. The changes do not all happen at the same time; they happen gradually. Changes begin between the ages of 11 and 15 girls and between the ages of 12 and 16 in boys.

During puberty, boys and girls increase in height and weight more rapidly than they did before. Body proportions also change. The once small hands and feet become bigger. The short arms become longer.

Physical Changes

Aside from changes in body size and proportion, the primary sex characteristics also change. At the start of puberty, the outer sex organs, called the genitals, begin to enlarge. Boys start to produce sperm. Girls start to experience menstrual flow

Secondary sex characteristics that distinguish boys from girls also develop during puberty. Boys develop deeper voice. Their shoulders become broader and their muscles grow bigger and stronger. Girls develop broader hips and larger breasts. In both boys and girls, hair grows around the genitals and under the arms. They also experience change in skin texture. They may have acne or pimples at this time.

Changes in Behavior and Attitude

Boys and girls undergoing physical changes during puberty also undergo changes in behavior and attitude. A boy may feel awkward when he suddenly grows tall or when his voice becomes deeper. This is more so when other boys in his group do not appear to have changed yet. He feels that he is different’. A girl whose breasts have become noticeable may feel self-conscious and will try to keep away from others. The appearance of acne or pimples may be a cause of embarrassment to a boy or a girl.

As boys and girls change physically, their interests also change. Before, they may be interested in toys; now they are interested in other things such as their appearance. Boys and girls may also feel restless and irritable as they go through puberty because they are no longer children but not yet adults.

Cause of Changes

In both boys and girls, changes during puberty are brought about by the pituitary gland produces a growth hormone and another hormone that stimulates the sex glands to greater activity

During puberty, more growth hormone is produced, so there is a rapid increase in height and weight. The testes produce testosterone. This is the hormone that is responsible for the development of a boy’s secondary sex characteristics. In girls, the changes are brought about by estrogen, the hormone produced by the ovaries.

Changes that take place during puberty are natural. They are signs of growing up.

  • The male reproductive system consists of several organs.
  • The male reproductive organs are the testes, ducts, accessory glands, and penis.
  • There are two testes located inside the scrotum, a pouch of skin that hangs outside the body. When a boy is not yet born, his testes develop inside his abdominal cavity. A few weeks before birth, the testes go down into the scrotum.
  • Each testis (singular for testes) is attached to the epididymiswhich, together with the vas deferens, forms a tube connected to the urethra.
  • The glands that produce secretions are the prostate gland and the seminal vesicle. The prostate gland is found under the bladder while the seminal vesicle is on the side along the rectum.
  • The penis consists of spongy tissue that is full of tiny blood vessels. The tip of the penis is the glans. The skin over the glans forms a loose fold called the foreskin. The foreskin may be removed when the baby is born or during adolescence. The removal of the foreskin is called the circumcision. Circumcision is done primarily for hygienic reasons. When the foreskin is removed, fluids secreted by the body will not accumulate on the glans.

Each organ in the male reproductive system performs a different function. The testes produce sperm, the male sex cells. Each sperm cell measures about 0.05 millimeter in length.

The testes also produce testosterone a hormone that determines the secondary characteristics of males such as a change in voice and growth of pubic hair.

The scrotum, which is outside the body, provides a cool place where the testes can produce healthy sperm. Sperm pass from the testes to the epididymis where they are stored.

The seminal vesicle and the prostate gland produce fluids. These fluids nourish the sperm and lubricate the epididymis and vas deferens.

The fluids, together with the sperm, form semen. Semen is expelled from the body through the urethra. The process by which semen is expelled from the body is called ejaculation.

A boy may discharge semen while he is asleep. Discharging semen during sleep is known as wet dreams. Having wet dreams is normal for boys.

The male reproductive system has two important functions, namely : (1) to produce and deliver sperm; and (2) to produce hormones that are responsible for the development of secondary sex characteristics.

Module 3: Female Reproductive System

Parts and Functions

The female reproductive system is different from the male reproductive system not only in structure but also in function.


The female reproductive system consists of the ovaries, the fallopian tubes, the uterus, the cervix and vagina, or birth canal.

  • Each part of the female reproductive system has its own function.
  • The ovaries hold and release egg cells. They also produce the hormones estrogen and progesterone. Estrogen causes the formation of secondary sex characteristics while progesterone maintains the lining of the uterus.
  • The fallopian tube provides a way through which an egg released from the ovary can travel.
  • When a mature egg leaves an ovary, the fingerlike projections called fimbriaeat one end of the fallopian tube sweep it up. The sperm cell meets the egg cell in the fallopian tube. Secretions from the lining of the tube nourish the fertilized egg until it reaches the uterus or womb.
  • The inner wall of the uterus is lined by a soft mucous membrane called endometrium. The uterus provides a place for a fertilized egg to develop. It has a muscular wall that can expand. It houses the unborn baby for nine months. The cervix connects the uterus to the vagina.
  • The vagina is the passageway for sperm, for blood during menstruation, and for the baby during birth.
  • All the parts of the female reproductive system work together to perform the following functions :
  • to produce eggs
  • to receive sperm
  • to nourish a fertilized egg
  • to give birth
Module 4: The Menstrual Cycle

Most girls between the ages of 10 and 16 already experience menstruation.

Menstruation is part of the menstrual cycle – a process which is a preparation for pregnancy. Why does menstruation happen

The Female Reproductive Cycle

When a girl is born, her ovaries already contain thousands of egg cells, When she reaches puberty, an egg matures and develops each month. The mature egg is released from the ovary to the fallopian tube. This is called ovarian cycle. Before the release of the egg, however, the uterus already prepares for pregnancy. The lining of its walls becomes thick and rich in blood vessels. If the egg that enters the uterus is fertilized, it will be embedded in the lining of the uterus and pregnancy starts. If the egg is not fertilized, it dies and the lining of the uterus disintegrates or breaks down. Blood, together with the unfertilized egg and the disintegrated lining flows out of the body through the vagina. This flow of blood, which may last from three to five days, is called menstruation or menstrual flow or monthly period. In a healthy female, menstruation occurs regularly once every 28 days.

All these changes constitute the female reproductive cycle, also known as menstrual cycle.

The Menstrual Cycle

The diagram beside shows the menstrual cycle. The duration of the whole cycle from the beginning of one period to the start of another is not the same for all females. However, the average time is one month. The menstrual cycle is controlled by the hormones estrogen and progesterone.

The Menstrual Cycle

The first menstruation is called menarche. A female experiences menstruation until she is about 45 to 55 years old. The period between puberty and the time before menstruation stops is a female’s fertile years. This means that she can be pregnant within this period. The period when menstruation naturally stops is called menopause. At this period, a female can no longer be pregnant.

When menopause occurs, the ovaries will slow down in its production of estrogen. After sometime, there will be no more estrogen produced.

Module 5: Fertilization and Development
  • In this module, you will
  • explain the process of fertilization in humans;
  • describe the development of a fertilized egg.
  • Would you believe that a newborn baby starts life as a fertilized egg that is no bigger than a pinhead?
  • How is an egg fertilized? How does it develop into a new human being?
How Fertilization Takes Place

Fertilization is the union of a sperm and an egg cell.

Sperm are the smallest cells in the body. A sperm cell looks like a tadpole. It has a head and a long thrashing tail. Egg cells are larger than a sperm cells.

When a mature egg cell leaves the ovary, it is swept up the fallopian tube. Millions of sperm cells may enter the female reproductive system but only one of these will fertilize the egg. As the egg travels in the fallopian tube, it sends out a chemical that signals the sperm where to find it. The sperm swim toward the egg. When a sperm cell enters the egg, fertilization takes place. The egg then secretes a covering. This covering prevents other sperm from entering the egg.

The life of a new human being begins when fertilization happens. The fertilized egg called zygote carries the characteristics that come from both parents.

How A Zygote Develops

After fertilization, the zygote begins to divide, first into two cells, then four, eight, sixteen, and so on. As this happens, the zygote continues to travel down the fallopian tube. By the time it reaches the uterus, it is a tiny ball of about a hundred cells. This ball of cells settles in the lining of the uterus. It is called an embryo until it is eight weeks old.

The embryo is protected by a sac of fluid that surrounds it. It gets its food and oxygen from the mother’s blood through the placenta. Waste products from the embryo pass through the placenta into the mother’s blood for excretion. The embryo is attached to the placenta by the umbilical cord.

How A Zygote Develops

The embryo develops fast. At five weeks, it has a head and a tail. At five weeks, it has a head a tail. By the eight week, the tail disappears and the limbs develop. Its hand, feet and facial parts take shape and its body systems start to develop. On its ninth week, the embryo is already called a fetus.

The fetus grows fast. At 14 weeks, it is about 12.5 centimeters long. Its internal organs are already working. At 16 weeks, it has well developed finger and toes. It has fingernails and fingerprints. Most of its organs are already working. The mother can feel the fetus kicking.

As the fetus grows larger, there is less space for it to move about. By the 32nd week of pregnancy, the fetus has already assumed a head-down position. A fetus is usually born around the 38th week of pregnancy.

A newborn baby may look like his/her mother or father or both of them.

Module 6: Caring for the Reproductive Organs
  • identify health habits to keep the reproductive organs healthy; and
  • practice precautionary measures to keep the reproductive organs healthy
  • The reproductive organs are important. A person without them is not capable of reproduction. They need to be taken care of so that they will stay healthy.
  • What practices should boys and girls do to keep their reproductive organs healthy?
Proper Practices for Boys
  • Boys can take care of their reproductive organs by doing the following:
  • Wash the genitals daily with soap and water. If not yet circumcised, be sure to pull back the foreskin to remove semen that may have accumulated under it.
  • Change underwear daily. Be sure the underwear you will use is clean.
  • If you feel any pain in your genitals, ask your parents to help you consult a doctor.
  • Do not let anybody touch your genitals
Proper Practices for Girls
  • Some girls experience painful menstruation with cramps in the lower abdomen. To ease the pain, the following can be done.
  • Have adequate rest
  • Apply a warm compress on the lower abdomen.
  • Eat fibrous foods to avoid constipation.
  • Do moderate exercise.
  • If the pain is unbearable, a doctor should be consulted. The doctor can prescribe a drug that will lessen the pain.
Proper Practices for Girls
  •  Girls should also take care of their reproductive organs even if they are not having menstruation. In addition to washing the genitals, here are some other practices that are helpful.
  • Wash underwear properly. Iron them to kill germs that may cause infection.
  • Avoid using somebody else’s underwear.
  • Change underwear as often as needed