BLOOD

Flowing all around your body , blood delivers food , oxygen , and other essentials to trillions of cells and remove their wastes . blood also distributes heat around your body and defends it against infection. blood is made up of a yellow liquid plasma in which blood cells float. red blood cells pick up oxygen in the lungs and deliver it to your body's cells. white blood cell can defend the body against disease causing germs. blood also contain platelets, which enable it to clot to seal damaged blood vessels. the heart pumps blood around the body along three types of blood vessels. arteries carry blood away from the heart, while veins return blood to the heart. microscopic capillaries link arteries and veins and supply blood to cells.

Circulating around the average body are 5 litres (8.8 pints) of blood.
Oxygen rich blood in arteries is bright red in colour oxygen poor blood in veins is dark purple red.
Blood is 55 % plasma and 45% blood cells.

One drop of blood contains 250 millions of red blood cells.375,000 white blood cells ,and 16 million platelets.
Oxygen carrying red blood cell make up 99% of all blood cells.
Every second,two million new red blood cells are made by jelly like red marrow inside bones.

During a lifespan of 120 days, A red blood cells travel around the body 170,000 times - once each minute. It is ten dismantled and recycled by the spleen and liver.
Packed into every red blood cells are 250 million red - coloured haemoglobin molecules.Each one carries four oxygen molecules, so a single red blood cell can transport one billion oxygen molecules.
Plasma is 90% water and contains more than 100 different dissolved substances including food,waste,hormones,and salts.

White blood cells called neutrophils and macrophages eat germs. Lymphocyte white blood cells disable germs by releasing chemicals called antibodies.
Unravelled and stretched out, one adult's blood vessels would encircle earth twice. Capillaries would make up 98% of the total length.
Each as broad as  a thumb , the largest artery and vein (the aorta and vena cava) are 2,500 times wider than a capillary, which is just one - tenth the width of a hair.
The heart is made largely of cardiac muscle, which does not tire.

Over a lifetime of 70 years, the heart beats 2.5 billion times without taking a rest.
 The heart beats, on average, 70 times a minute. Heart rate can double or triple during exercise to get extra oxygen to your muscles.
Each person belongs to one of four blood groups-A,B,AB,or O . Blood groups are determined by tiny "markers" carried by red blood cells.