Blood Cells (photo: Wellcome Images).Blood is a fluid in your body that contains red and white blood cells, platelets and plasma. The most important job of blood is to carry oxygen to your body’s tissues. This fluid also removes waste products from the tissues. In addition to oxygen, it also carries antibodies and nutrients to the tissues.

Photo: Platelets (gray) and red and white blood cells (Creative Commons: Wellcome Images).

Composition of Blood

Blood is primarily plasma which is a liquid. Plasma is mostly water but contains small amounts of proteins, sugars, minerals, and hormones. Carbon dioxide dissolves in the plasma and is transported away from the body’s tissues. Plasma makes up about 55% of the blood.

Within the plasma, there are red blood cells (erythrocites), white blood cells (leucocytes) and platelets. Red blood cells obtain their color from the chemical hemoglobin which is a protein. Hemoglobin binds and unbinds itself to oxygen and is the primary means of transporting oxygen to the body’s tissues. These cells are produced in the bone marrow. When they grow older (after 3-4 months) they are broken down in the spleen, liver and lymph nodes.

White blood cells helps protect the body from infectious diseases and foreign invaders. They make up about 1% of the blood. There are five main types of these defensive cells. These cells attack bacteria, fungi, parasites, and virus or tumor infected cells. They may also help regulate inflammatory responses by releasing histamines.

Where there is an injury, platelets help control bleeding by clumping and clogging blood vessels.

Improving Your Reading and Thinking Skills

Think for a few moments. Try to recall the major ideas in this article. When you are done, click the box below for a list of main ideas.


How did you do? With practice, you should be able to identify many of the major ideas. You may even discover some important ideas that aren’t listed.


Heart Health Center, WebMD.


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11 comments on "Blood: Good Blood In and Bad Blood Out"

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Ronand Abella

Cells have basic part nucleus nucleus membrane and more.
The cells are the most important part because it gets something in our body.Some cell are difficult because they have a part that can’t really see.Like some bacteria have cells and others don’t have.

Ronand Abella

Ang cells ay isang maliit na hilalang. sabi nila na ito ay walang kamatayan.Sa mga ito ay mga siyentipiko.

Ronand Abella

Cells is when you put then together they become tissue. and when you put tissue together it becomes organs. when you put all organs together it becomes systems.when you put all systems it becomes organisms
The most important job of the cells is to get oxygen to our body tissue.
The size of the cells is nanometers


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Webster Gabiana

A blood carry oxygen and the inportan is a blood becaes it carry oxygen so we will be alave
and can bried if no oxygen we will die and tere are a wigth blood. I learn that are blood is carry oxygen and hart and brin is a inpotant takecare of your body