Human Organs

The lungs are in the thorax:

• The air that you breathe in goes through the trachea. This splits into two tubes called bronchi (each one is a bronchus), one going to each lung.
• The bronchi split into progressively smaller tubes called bronchioles.
• The bronchioles finally end at small bags called alveoli where the gas exchange takes place.

Alveoli carry out gas exchange in the body:

• Alveoli (little air sacs) are surrounded by a network of blood capillaries-- this is where gas exchange takes place.
• The blood passing next to the alveoli contains a lot of carbon dioxide and very little oxygen, as it has just returned to the lungs.
• Oxygen diffuses out of the alveolus into the blood (high to low concentration).
• Carbon dioxide diffuses out of the blood into the alveolus (high to low concentration) to be breathed out.
• When blood reaches body cells, oxygen is released from the red blood cells and diffuses into the body cells and vice versa for carbon dioxide. 

The circulatory system:

• 1)The right ventricle pumps deoxygenated blood to the lungs to take in oxygen. The blood then returns to the heart.
• 2) The left ventricle pumps oxygenated blood around all the other organs of the body. The blood gives up its oxgen at the body cells and the deoxygenated blood returns to the heart to be pumped out to the lungs again.

The heart uses its four chambers to pump blood around:

• 1) Blood flows into the two atria from the vena cava and the pumonary vein.
• 2) The atria contract, pushing the blood into the ventricles.
• 3) The ventricles contract, forcing the blood into the pulmonary artery and the aorta, and out of the heart.
• 4) The blood then flows to the organs through arteries, and returns through veins.
• 5) The atria fill again and the whole cycle starts over.#

The heart has valves that prevents the blood from flowing backwards

The three different types of blood vessel:

• ARTERIES- these carry the blood away from the heart
• CAPILLARIES- these are involved in the exchange of materials at the tissues
• VEINS- these carry blood to the heart

Arteries carry blood under pressure:

• 1) The heart pumps the blood out at high pressure so the artery walls are strong and elastic.
• 2) The walls are thick compared to the size of the hole down the middle (the "lumen")
• 3) They contain thick layers of muscle to make them strong, and elastic fibres to allow them to stretch and spring back.

The rate of blood flow = the volume of blood / number of minutes

Veins take blood back to the heart:

• 1) Capillaries eventually join up to form veins.
• 2) The blood is at lower pressure in the veins so the walls don't need to be as thick as artery walls.
• 3) They have a bigger lumen than arteries to help the blood flow despite the lower pressure.
• 4) They also ave valves to help keep the blood flowing in the right direction.

Capillaries are really small:

• 1) Arteries branch into capillaries and are really tiny- too small to see.
• 2) They carry blood really close to every cell in the body to exchange substances with them.
• 3) They have permeable walls, so substances can diffuse in and out.
• 4) They supply food and oxygen, and take away wastes like CO2.
• 5) Their walls are usually one cell thick. This increases the rate of diffusion by decreasing the distance over which it occurs.

Red blood cells carry oxygen:

• 1) Red blood cells carry oxygen from the lungs to the cells in the body.
• 2) Their shape is like a donut which gives a large surface area for absorbing oxygen.
• 3) They don't have a nucleus- this allows more room to carry oxygen.
• 4) In the lungs, haemoglobin (a red pigment) binds to oxygen to become oxyhaemoglobin. In body tissues, the reverse happens (oxyhaemoglobin splits up into haemoglobin and oxygen, to release oxygen to the cells)

White blood cells defend against infection:

• 1) Some can change shape to engulf microorganisms.
• 2) Others produce antibodies to fight microorganisms, as well as antitoxins to neutralise any toxins produced by the microorganisms.
• 3) They do have a nucleus.

Platelets help blood clot:

• 1) These are small fragments of cells. They have no nucleus.
• 2) They help the blood to clot at a wound- to stop all your blood pouring out and to stop microorganisms getting in.
• 3) Lack of platets can cause excessive bleeding and bruising.

Plasma is the liquid that carries everything in blood:

• It is a pale straw-colured liquid that carries almost everything like:
  • Red and white blood cells and platelets
  • Nutrients like glucose and amino acids
  • Carbon dioxide
  • Urea
  • Hormones
  • Proteins
  • Antibodies and antitoxins