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Blood and blood vessels carry cells, nutrients and oxygen around the body.

Blood and blood vessels carry cells, nutrients and oxygen around the body.
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Blood and blood vessels

Blood, the heart and the vessels that carry blood around the body together make up the cardiovascular system. They are vital for carrying nutrients, oxygen and waste around the body.

Blood is made of cells and plasma. There are three main types of blood cells – red cells, white cells and platelets. All are made in the marrow found in many bones.

Red blood cells deliver oxygen from the lungs to the rest of the body, and carry waste products to be released by the lungs or the kidneys. Red blood cells contain haemoglobin, which is the protein that binds and releases oxygen.

White blood cells are part of the immune system. They detect and fight infections or foreign molecules that enter the body.

Platelets are small cells that help the blood clot.

Plasma is the clearish fluid that carries the cells. It also carries the nutrients from our diet such as sugars, fats, proteins, vitamins and minerals.

As well as carrying cells, nutrients, oxygen and waste, blood also helps to regulate body temperature.

What are blood vessels?

Blood vessels carry blood around the body. The three main types of blood vessels are:

  • arteries that carry blood pumped from the heart – these are the largest and strongest
  • veins that return blood to the heart
  • capillaries, which are tiny vessels that connect arteries and veins, and allow blood to come into close contact with tissues for the oxygen, carbon dioxide, food and waste.

Blood leaves the heart in large arteries, then moves through progressively smaller ones to the capillaries in tissues. The blood then leaves the tissues in veins that get larger as they get closer to the heart.

The arteries can expand and contract to lower or increase blood pressure, according to your needs.

Diseases of blood and blood vessels

The blood can be affected by trauma or diseases in other parts of the body leading to anaemia, a lack of red blood cells that reduces supply of oxygen to tissues, or polycythaemia, in which there are too many red blood cells. Also, there are cancers of blood cells like leukaemia .

Problems with blood vessels can also lead to high blood pressure, heart attack and stroke.

Last reviewed: August 2017

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Blood and blood vessels

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A bleeding disorder is an acquired or inherited tendency to bleed excessively. Normally, blood remains in the circulatory system inside the blood vessels. However, if veins or arteries are injured, they will begin to leak blood, either externally or into body tissues. The body stops the blood loss through a complex clotting process called haemostasis. During haemostasis, the injured blood vessel constricts to reduce blood flow, platelets adhere to the injury site and clump together to form a loose platelet plug, and a process of clot formation called the coagulation cascade is initiated.

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