NATURAL SCIENCE SUMMARY: UNIT 3+ EXCRETORY SYSTEM

 

NATURAL SCIENCE SUMMARY

1.     THE EXCRETORY SYSTEM

It eliminates waste products.

It includes the urinary system and the sweat glands.

 

1.1  The urinary system

It removes waste products from the blood and then eliminates them from the body.

ORGAN	FUNCTION
Renal arteries	They carry blood to the kidneys.
Kidneys	They remove waste products from the blood. Then, they mix with water and form urine ( 1.4 litres everyday)
Ureters	They carry the urine from the kidneys to the bladder
Bladder	Urine is stored there. When the bladder is full, it sends signals to the brain that tell us to urinate.
urethra	It eliminates the urine from the body.

 

 

-Dialysis machines: they filter the blood acting like “artificial kidneys”.  These people have health problems because their own kidneys don´t work properly (can´t remove enough waste from the blood)

 

-Transplants: if the kidneys don´t work at all, they may need a kidney transplant. They will receive a new kidney/s from a donor.

 

 

 

1.2  Sweat glands

Our body can also eliminate waste products through the sweat glands in our skin.

We excrete sweat. It is a mixture of water, salt and other minerals. It has two functions:

-It eliminates waste products

-It regulates the temperature by cooling us down when we do exercise or when we are hot.

The sweat glands are located in the dermis. The sweat is produced there. Then it leaves the body through tiny holes in the epidermis called pores. We have between 2-4 million pores.

When the sweat reaches the epidermis:

-the water evaporates

-the salt and minerals stay on the skin

It is important to keep our body hydrated when we sweat, especially while doing exercise or during hot weather.

 

2.     THE REPRODUCTIVE SYSTEM

2.1  The female reproductive system

The sexual characteristics are the physical differences between men and women. There are two types:

-Primary sexual characteristics: They are the differences between male and female reproductive organs.

 

-Secondary sexual characteristics: They are other physical characteristics between men and women that appear during puberty.

 

-The female reproductive organs are:

ORGAN	FUNCTION
Ovaries	They produce female reproductive cells called ovum or ova. *Remember that when girls are born, their ovaries already contain all the ova they will have in their life, but they are immature. However, when girls reach puberty, their ovaries start releasing mature ova.
Fallopian tubes	They carry mature ova from the ovaries to the uterus.
Uterus	-It is where a fertilised ovum develops into a baby.   -During birth, its muscular walls start to contract to push the baby out.
Cervix	The baby leaves the uterus through the cervix.
Vagina	-The penis is inserted into the vagina during sexual intercourse (the sperm enters the body through that part)   -The baby is pushed out of the body through the vagina.
Vulva	It is the external part of the female reproductive organ.

 

-Puberty in girls: it begins at between 10-16 years old.

 They go through physical changes:

-they grow taller and fuller

-their breasts start to develop

-hair grown in the armpits and pubic area

-glands in the skin produce more oil causing acne

They go through emotional changes:

-Changing mood, emotions and thoughts.

 

-The menstrual cycle

It starts at around 10-15 years old, during puberty.

The brain produces hormones that cause ovaries to release a mature ovum into the fallopian tubes (ovulation).

Before ovulation, the ovaries release two hormones: progesterone and oestrogen------ > they make the walls of the uterus become thicker with extra tissue (to prepare for a fertilised ovum).

Two things can happen then:

-If fertilisation occurs, the fertilised ovum will develop into a baby attached to the walls of the uterus.

-If fertilisation does not occur, the uterus released the ovum along with the extra blood and tissue. That is what we call menstruation or period.

Remember, women have the period or menstruation every 28 days and it usually lasts 3-5 days.

Menopause: when women get older (around 50), their menstrual cycle stops.

 

2.2  The male reproductive system

The sperm cell is the male reproductive cell. They have a head with oval shape and a tail which help them move along the fallopian tubes and fertilise the ovum.

The male reproductive organs are:

ORGAN	FUNCTION
Testicles	They produce millions of sperm cells a day.
Scrotum	It contracts and relaxes, regulating the temperature of the testicles
Vasa deferentia/ vas deferens	They carry the sperm from the testicles to the seminal vesicles and prostate.
Seminal vesicles	They produce liquids that when mixed up with the sperm produce the semen
Prostate	They produce liquids that when mixed up with the sperm produce the semen
Penis	It is very important for sexual intercourse.
Urethra	It releases semen (ejaculation) and urine.

 

-Puberty in boys: it starts around 11 and 16 years old, later than in girls. The testicles produce testosterone which causes the following changes:

*Physical changes:

-they become taller and heavier

-their reproductive organs grow

-their voice becomes deeper

-facial and body hair starts to grow

-their skin produces more oil causing acne

 

*Emotional changes:

-They go through changing moods, emotions and thoughts.

 

2.3  Pregnancy and birth

The human sexual reproduction requires two reproductive cells:

-an ovum from the mother

-a sperm cell from the father

These cells contain the genes, which are the genetic information that the parents pass onto the baby (DNA). It determines the baby’s physical characteristics.

The steps of a pregnancy are:

1.     Fertilisation

It occurs when a sperm cell joins with an ovum. This happens in the fallopian tubes.

During sexual intercourse, the man’s penis is inserted into the woman’s vagina and the sperm cells are released (ejaculation).

The sperm cells move up through the uterus and into the fallopian tubes. Only one sperm cell will fertilise the ovum.

Then the fertilised ovum start to divide and grown in size and form a zygote.

 

2.     From zygote to embryo

After fertilisation, the zygote will travel to the uterus and attaches to its wall.

 

It continues to grow and divide.

 

After two weeks, they zygote becomes an embryo

 

3.     From embryo to foetus

At 9 weeks (around 2 months), the embryo becomes a foetus (all of its organs have formed already)

 

ORGAN-SUBSTANCE	FUNCTION
Amniotic fluid *The amniotic sac contains the amniotic fluid.	It protects the foetus from accidents and impacts
Umbilical cord	It connects the foetus with the mother.
Placenta	-It provides the foetus with oxygen and nutrients.   - It also eliminates carbon dioxide and other waste products that come from the foetus.

 

4.     Labour and birth

Pregnancy lasts around 9 months/ 40 weeks.

When the baby is ready to be born, or the mother is reading to give birth, she goes into labour.

 

1.     Contractions start: the muscles of the uterus start to contract. They push the baby against the cervix which starts to open.

2.     The amniotic sac breaks (“water break”): The amniotic fluid is released. The baby is pushed through the cervix and into the vagina and then out of the body. Babies should be born in “head-first” position because otherwise, they can die from chocking (lack of oxygen).

3.     The umbilical cord comes out at the same time. Doctors or nurses cut the umbilical cord and tie it. This is where the belly button will form.

4.     Finally, the placenta comes out as well. If not, the mother can have dangerous infections.

 

*Remember

1.  There are two ways of giving birth:

-natural labour: the baby is pushed out of the mother’s body naturally.

-caesarean section (cesárea): the doctor extracts the baby from the mother’s womb using a scalpel (bisturí).

 

2. Pregnant women have to follow a special diet and life style to avoid infections from viruses, bacteria or parasites:

-they shouldn´t eat raw fish or meat such as sushi or Spanish ham.

-They shouldn´t eat unpasteurized dairy products such as milk and cheese.

-They shouldn´t eat raw eggs.

-They should wash carefully fruits and vegetables.

-They should avoid harmful substances such as alcohol and tobacco.

 

 

3. Sometimes, the mother looses the baby due to natural causes especially during the first three months of pregnancy. This is called having a spontaneous abortion or miscarriage.