Lesson 2 Human Nutrition (II)
Breathing and the respiratory system
The respiratory system gives our cells the oxygen they need to perform the vital functions. We take oxygen and eliminate carbondioxide as a waste material.
The respiratory system has got two parts:
a) Respiratory tract: Connects the lungs to the exterior. It consists on the nassal cavity, pharynx, larynx, trachea and the bronchi. The bronchi are divided into bronchioles and at the end of them there are small sacs covered by capillaries called alveoli.
b) The lungs: Two spongy organs found in the thorax separated from the stomach by an organ called diaphragm.
Breathing step by step
a) The diaphragm contracts and the lungs expand
b) Air enters the mouth and the nasal cavity and the air is warmed.
c) The air travels to the alveoli where the exchange of gases happens. The oxygen goes to our blood.
d) The carbon dioxide is transferred from the blood to the alveoli.
e) The diaphragm relaxes, the lungs contract
f) The air (that contains carbon dioxide) is expelled out of our body
Blood and the circulatory system
Everything in our body travels from one place to another through our circulatory system:
It´s made up of:
a) The heart: It´s a muscular organ divided into two halves. Each part has two chambers, the upper part (called atrium) and the lower part (called ventricle). Inside them there is a valve. It opens and closes to let the blood go through our heart.
b) Blood vessels are a network of tubes that circulate blood. There are:
- Arteries: Carry blood from the heart to the organs.
- Veins: Carry blood from the organs to the heart.
- Capillaries: exchange the substances between the cells and the blood.
c) Blood: Is a red liquid formed by plasma that is a translucent liquid made up of water, salt, minerals… and blood cells. There are red blood cells (where haemoglobin gives the blood its red colour and transport oxygen and carbon dioxide), white blood cells (that protect us from infections) and placelets (that seal up cuts).
Blood Circulation
The heartbeat
This movement has two different parts:
a) Systole: The heart contracts and the blood that is in the two ventricles leaves the heart
b) Diastole: The heart expands and the blood leaves the pulmonary veins, The blood passes from the two atria to the two ventricles.
The circulatory system
There are two different circuits:
a) The pulmonary circuit: The blood goes to the heart, then it goes to the lungs where it takes oxygen and later it comes back to the heart
b) The systemic circuit: The blood full of oxygen goes to the systems and leaves oxygen, then the blood goes to the heart again.
Excretion
It contains:
a) The Kidneys: Two oval shaped organs that filter the blood and remove waste from the blood.
b b) The urinary tract: ureters (two tubes connected to the bladder), The bladder and the urethra.
How the excretory system works:
- The blood reaches the kidneys.
- They extract waste from the blood that is converted into urine.
- The urine is stored in the bladder (through our ureters)
- The urine is released from our body.
Excretion through the skin:
- The skin has got sweat glands and the capillaries take waste to them.
- The mixture of waste and water forms sweat.
