Ch.6.reproduction in humans

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Puberty: Body changes & differences

© Changing Faces 2009 Registered Charity No. 1011222 Charity registered in Scotland SC039725


What happens during puberty?

Humans are born with a complete set of sex organs. However, they do not usually become active until between the ages of 10 and 18.

In males, the testes start to make sperm, and in females, the ovaries start to release eggs.

This stage of development is called puberty, and is caused by hormones.

During this important time, many changes take place in the bodies of young men and women.


Hormones

Hormones are chemicals that are produced in one part of the body, circulates all round the body in the blood but only has an effect on a specific part of the body.

At the age of 10 – 13 in girls and 12 – 14 in boys, the pituitary glands (beneath the brain) secrete growth hormones and gonadotropin.

Gonadotropin stimulates the production of sex hormones.


In females the sex hormones produced are oestrogen and progesterone (produced in the ovaries).

In males the sex hormones produced is testosterone (produced in the testicles).

The sex hormones cause the sex organs to develop fully.

They work with the growth hormones and cause the body to develop (secondary sexual characteristics)


• What is puberty?

• What changes can we expect?

• A look at the differences between girls and boys and amongst each other

What this lesson will cover…What this lesson will cover…


What is puberty?• PubertyPuberty is the time in life when you begin to become

an adult. This means a lot of changing and growing – both inside and out.

• Some of the changes that happen in puberty are also known as adolescenceadolescence..

• Puberty starts because of sex hormonessex hormones (chemicals in our bodies that send messages about our development).

• In adolescence a person also develops adult emotions and social skills.


Changes in boys

• Growth of PenisPenis & testestestes (size)• Body & facial hair• Pubic hairPubic hair (the hair around sex organs)

• Shoulders grow wider• Voice change (or voice breaking)

• Body odourBody odour (smell) & acneacne (spots)


Changes in girls

• Breast development• Body hair (e.g. on legs, arms,

underarms) & pubic hairpubic hair (the hair around our sex organs)

• MenstruationMenstruation (a monthly bleed or period)

• Hips grow wider• Body odourBody odour (smell) & acneacne (spots)


What is reproduction?

Reproduction is one of the seven life processes.

Humans use sexual reproduction to produce their young.

In order to do this, the two parents (male and female) have different reproductive systems and organs that produce different sex cells.

All living things reproduce.


Sex cells

Sperm cell (Male) Egg cell (Female)

The main function of a sperm cell is to FERTILISE the egg cell and pass on the genetic information (DNA) needed to make a baby

The main function of an egg cell is to join with a SPERM CELL (fertilisation) and pass on the genetic information (DNA) needed to make a baby


Sex cells – sperm

Sperm are produced in sex organs called testes.

In males, the sex cells are called sperm.

headtail middle piece

cell membrane nucleus containing DNA


Sex cells – egg

Eggs are produced in sex organs called ovaries.

In females, the sex cells are called eggs.

nucleus containing DNA

membrane jelly coat

cytoplasm


Penis and testicles Penisis a cylindrical shaped organ filled with ‘spongy tissue’.

TesticlesMales are born with a pair of testicles. Sperm cells are made inside them. On its own, sperm is actually like jelly. Each testicle is connected to a gland. These add a pale white fluid to the sperm called semen.


GlandsThe sperm must be mixed with a fluid called semen so that it can flow freely. This semen is made inside the glands.

The semen also helps to nourish the sperm so it can stay alive during its journey to the egg.

FactMen who have had their testicles severely damaged or removed still ejaculate.

Q. Will they still be able to fertilise an egg cell?

Glands


ScrotumScientific DescriptionThe scrotum is a sack of skin that protects the testicles. When a man is cold, the scrotum tightens up pulling the testicles closer to the body.

When a man is hot, the scrotum relaxes to allow the testicles to hang further away from the body.

Q. How does this protect the sperm?


Sperm DuctsThe sperm is carried away from the testicles through the sperm ducts. These tubes take the sperm to the glands where they are mixed with semen.


Prostate

The prostate is a gland that acts like a pump. During ejaculation the prostate mixes the semen and sperm together, then pumps it out the end of the penis.


UrethraScientific DescriptionThe urethra is a tube that runs down the centre of the penis. The semen and sperm mixture flows out the end of the urethra when a man ejaculates.

The urethra is not only used for sexual intercourse. It also carries urine from the bladder when a man urinates.


The male reproductive system


Female reproductive system

The two ovaries contain hundreds of undeveloped female sex cells called egg cells or ova. Women have these cells in their bodies from birth - whereas men produce new sperm continually.


Oviduct or Fallopian tube.

Oviduct or Fallopian tube is lined with cilia, which are tiny hairs on cells. Every month, an egg develops and becomes mature, and is released from an ovary. The cilia waft the egg along inside the egg tube and into the uterus.


Uterus

The uterus is also called the womb. It is a muscular bag with a soft lining. The uterus is where a baby develops until its birth.


Cervix

The cervix is a ring of muscle at the lower end of the uterus. It keeps the baby in place while the woman is pregnant.


Vagina

The vagina is a muscular tube that leads from the cervix to the outside of the woman's body.


The female reproductive system


Male or female?


Roles of the reproductive system


Sperm or egg?



Menstruation

An important part of puberty for girls is the beginning of their monthly cycle. This is known as the menstrual cycle.

The menstrual cycle involves the preparation of the uterus lining so that it can receive a fertilized egg. If an egg is fertilized, it can implant itself in the prepared uterus lining.

If the egg is not fertilized, the lining of the uterus breaks down and is lost from the body. This is called menstruation, or a period.


Periods


What is fertilization?

Fertilization is the fusing of an egg and a sperm cell. In this process the sperm’s nucleus will join with the egg’s nucleus.

For a woman to become pregnant fertilization must occur.

Females produce an egg approximately every 28 days. This is called ovulation.

Males continually produce sperm in the testes.

How do these cells come into close contact with each other?


Sexual intercourse

During sexual intercourse the man inserts his penis into the woman’s vagina.

Millions of sperm cells are ejaculated into the top of the vagina.

They enter the uterus through the cervix, where the sperm cells may meet an egg.

Now fertilization can occur.


Fertilization and implantation


Reproduction terms



The placenta

How does an embryo receive food and oxygen and how does it get rid of waste?

An embryo forms a structure called the placenta, which attaches to the uterus wall.

The umbilical cord joins the fetus to the placenta.

In the placenta, food and oxygen diffuse from the mother’s blood into the blood of the fetus.

Carbon dioxide and waste products diffuse from the blood of the fetus into the mother’s blood.

umbilicalcord


How does the placenta work?


From embryo to fetus

In the earliest stages of development, a human baby is called an embryo.

After the first eight weeks of pregnancy, a human embryo is then called a fetus.

At this stage, the fetus has all the main human features.

The fetus continues to develop and grow inside its mother’s uterus for a total of 40 weeks.


What are the stages of development?


The stages of pregnancy


Birth

After 40 weeks of gestation, the baby is ready to be born. At this point, the head usually lies just above the cervix.

Eventually the contractions cause the amnion to break and the fluid escapes.

1st - Birth begins with small contractions (30 min. apart) of the uterus wall (12 – 14 hrs), which gradually become stronger and more frequent (2 – 3 min. apart).


After a few minutes, the placenta comes away from the uterus wall. This is pushed out as the afterbirth.

The cervix then widens and dilates as the baby is pushed through the vagina.

2nd – Mother contracts her abdominal muscles with the uterus contractions to push the foetus down.




What are contraceptives?

Contraceptives are devices designed to prevent pregnancy.

Sexually transmitted infections are diseases that can be passed on by sexual contact.

How do the different types of contraceptives work?

Contraceptives are not 100% reliable and some can cause other side effects.

Some types of contraception can also stop the spread of sexually transmitted infections.


Different types of contraceptives Condoms – a latex barrier worn

over an erect penis. This barrier prevents sperm entering the vagina and causing pregnancy. It can also help to stop the spread of sexually transmitted infections.

Contraceptive pill – a pill containing a mixture of hormones taken every day. These hormones stop the release of eggs, preventing pregnancy. However the pill cannot protect against disease.

Diaphragm and cap – these are barriers inserted into the vagina to prevent sperm reaching the egg.


Alternatives to contraception

Some people in long term relationships choose to use natural family planning instead of contraceptives.

This involves working out when the woman is fertile and avoiding sexual intercourse at these times.

This method does not have any effect on the body, but it can be an unreliable form of birth control and does not protect against sexually transmitted infections.


Emergency contraception

Emergency contraception is available to women that have had unprotected sex, to prevent pregnancy.

This is in the form of a pill, often called the ‘morning after pill’. It should be taken within 3 days of unprotected sex, in order to be effective.

However, it does not protect against sexually transmitted diseases and it can have side effects.


Which contraceptive?



Sexually transmitted infections


HIV and AIDS



Glossary


Anagrams


Multiple-choice quiz

Education

Ch.6.reproduction in humans