UNIT 2. NUTRITION (NATURAL SCIENCE)

UNIT 2. NUTRITION

THE DIGESTIVE SYSTEM

Nutrients are the substances that iliving things need to live and grow. Tthe digestive system is the group of organs that extract nutrients and expel waste.

Digestion

1.       The nose and the mouth: because of our smell sense, our mouth produces saliva and it helps teeth to chew food.

2.       The oesophagus: the tongue moves the food and forms a ball called bolus. We swallow the bolus and passes through the oesophagus, which is a big tube that connects the the throat with the stomach. The epiglottis, at the back of the tongue, prevents food from going to the windpipe and lungs.

3.       The stomach: it breaks down food using muscular walls and gastric juices, which mix with the bolus and kill dangerous bacteria.

4.       The small intestine: when the food is disolved into a liquid, it passes into the small intestine. It mixes with mile (produced by liver) and pancreatic juices (produced by pancreas).  The food mixture is broken down into proteins, carbohydrates, vitamins, minerals and fats. Nutrients pass through the walss of the small intestine and are absorbed into the blood.

5.       The large intestine: the waste passes to the large intestine. Water from this waste is absorbed into the blood and the solid waste leaves our body through the anus.

THE CIRCULATORY SYSTEM

The circulatory system delivers blood through blood vessels. The main organ is the heart.

-          Blood is made up of:

o   Plasma: is a yellowish liquid which is 90% water and it carries the nutrients and waste products.

o   Red blood cells:  give blood its colour and carry oxygen and carbon dioxide.

o   White blood cells: fight ifection and abrsorb germs which enter the body.

o   Platelets join together and avoid bleeding.

Blood is transported through three types of blood vessels:

o   Arteries carry blood, which contains oxygen,  from the heart to the rest of the body.

o   Veins carry the blood, which contains carbón dioxide,  back to the heart.

o   Capillaries are tiny blood vessels that connect the arteries and the veins and gases and nutrients can pass through them to the cells.

-          The heart is a muscle that pumps blood through the body. It is made up of four chambers. The two chambers at the top are called right and left atria (they receive blood coming into the heart). The two chambers at the bottom are right an dleft ventricles. They are separated by valves which prevent blood from coming backwards.

·         Circulation

Blood flows around the body in a double circuit:

-          During pulmonary circulation , blood flows from the heart to the lungs and back to the heart again.

-          During systematic circulation, the blood flows from the heart to the rest of the body.

1.       The deoxygenated blood passes from the right atrium to the right ventricle. From there it leaves the heart through the pulmonary artery and travels to the lungs.

2.       In the lungs, blood expels carbón dioxide and collects oxygen. Blood returns to the heart through the pulmonary veins.

3.       The oxygenated blood goes to the left atrium and then to the left ventricle. From there the blood is pumped through the aorta (the biggest artery) to the rest of the body.

4.       The aorta carries the blood into small arteries and then to the capillaries.  In the capillaries, the blood releases oxygen and nutrients into the cells and collects carbon dioxide and other waste substances.

5.       The deoxygenated blood passes from the capillaries to the small veins and then to the largest veins in the body called the superior vena cava and the inferior vena cava. Theses veins carry the blood to the heart and the pocress begins again.

THE RESPIRATORY AND THE EXCRETORY system

·         The respiratory system

Our cells need oxygen to combine with nutrients and produce energy.  Duirng this process, cells produce carbon dioxide that has to be expeled from the body. We use the respiratory system to obtain energy and expel carbon dioxide.

When we breathe, air enters through the nose and the mouth and passes through the phraynx and trachea or windpipe. The trachea divides into two tubes called bronchi and they into small bronchi called bronchioles. A the end of each bronchiole, there is a sack called alveoli which are covered by capillaries. The gas Exchange takes place in the alveoli. Oxygen passes from the alveoli to the capillaries and into the blood. At the same tima carbón dioxide leaves the blood and enters the alveoli. The air with carbón dioxide goes through the bronchioles to the bronchi and the trachea and finally out of the mouth and nose.

-          Inhalation: when we take air our diaphragm contrat and the lungs ínflate. The ribs expand.

-          Exhalation: when we expel air the ribs and the diaphragm relax and move up. Carbon dioxide leaves the lungs, the trachea and the mouth and nose.

THE EXCRETORY SYSTEM

The excretory system eliminates waste products from our body. The excretory system consists of the urinary system and the sweat glands.

·         The urinary system

1.       The renal arteries carry blood to the kidneys.

2.       The kidneys eliminate water and urine (mixture of water and harmful substances) from blood.

3.       Urine leaves the kidneys and passes down through the ureters to the bladder.

4.       When the bladder is hlaf full, it sends signals to the brain to be emptied.

5.       The bladder is emptied through the urethra.

·         The sweating

Our body also eliminates waste products through the skin. When we get hot, sweat glands activate to cool down our body. Sweat glands, through the pores,  excrete sweat, which is a mixture of water and minerals.