Healthdirect Free Australian health advice you can count on.

Medical problem? Call 1800 022 222. If you need urgent medical help, call triple zero immediately

healthdirect Australia is a free service where you can talk to a nurse or doctor who can help you know what to do.

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

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

Blood and blood vessels

5-minute read

Blood, the heart and the vessels through which blood is pumped around the body, together make up the cardiovascular system. They are vital for carrying nutrients, oxygen and waste around the body.

Blood is made up of cells and plasma. An average adult has about 5 litres of blood in their body. As well as carrying cells, nutrients, oxygen and waste, blood also helps to regulate body temperature.

Blood cells

Most blood cells are made in the bone marrow. There are 3 main types of blood cells:

  • red blood cells
  • white blood cells
  • platelets.

Red blood cells

Red blood cells transport oxygen from the lungs to the rest of the body, and carry waste products to the lungs or kidneys for release. Red blood cells contain haemoglobin, which is the protein that enables them to carry oxygen.

White blood cells

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

There are 5 main types of white blood cell — neutrophils, lymphocytes, monocytes, eosinophils and basophils.

Platelets

Platelets are small cell fragments that help the blood clot. They circulate in the blood until there is an injury to a blood vessel. Then they clump together and help a clot form at the injury site.

Plasma

Plasma is the straw-coloured fluid that carries the blood cells. It makes up around half of your blood. It also carries the nutrients from our diet such as sugars, fats, proteins, vitamins and minerals.

Blood tests

Your blood can give useful information on how well your body is working and help doctors test for some diseases and conditions. Some common blood tests are:

  • full blood count — this measures the number of the different types of cells in your blood
  • Blood glucose test — this measures the amount of glucose (sugar) in your blood and can be used to diagnose or monitor diabetes
  • Kidney function test — this measures substances in your blood to see how well your kidneys are working
  • Liver function tests — these measure substances in the blood that show whether the liver cells are damaged

Blood types

Everyone has a particular blood type (blood group), which is determined by the genes inherited from their parents. The main blood types are A, B, AB, and O. Doctors check a person’s blood type before a blood transfusion or organ transplant, to ensure compatibility with the donor’s blood type. Blood type is also important in pregnant women to work out which Rhesus type they are and whether the mother’s blood and baby’s blood are compatible.

What are blood vessels?

Blood vessels are the network of tubes through which blood is pumped around the body. Along with the heart and the blood, the blood vessels form the cardiovascular system. The 3 main types of blood vessels are:

  • arteries — these carry blood pumped away from the heart; they are the largest and strongest blood vessels
  • veins — these return blood to the heart
  • capillaries — these are tiny vessels that connect arteries and veins. Their thin walls allow blood to come into close contact with tissues to exchange oxygen, carbon dioxide, nutrients and waste products

Blood leaves the heart in large arteries, then moves through progressively smaller ones to reach the capillaries in the tissues. Oxygen and nutrients pass through the thin capillary walls into the tissues, and waste products from the tissues pass into the capillary blood. The blood then leaves the capillaries and moves into veins that progressively get larger as they get closer to the heart.

Once at the heart, this de-oxygenated blood (blood that needs oxygen) enters the right-hand side of the heart. From there it is sent to the lungs where the carbon dioxide is removed and replaced with oxygen.

Some of the waste products that were picked up by the capillaries from the tissues are filtered out from the blood as it flows through the kidneys.

The walls of arteries are strong and elastic and can expand and contract to lower or increase blood pressure, according to your needs. Blood pressure is the pressure of your blood on the walls of the arteries as your heart pumps blood around the body. Veins have thinner walls, and some veins (for example in the legs) have valves to prevent the backflow of blood due to gravity.

Diseases of blood and blood vessels

The blood and blood vessels can be affected by physical injury (trauma) or disease, such as cancer.

Problems that can happen with the blood include:

  • anaemia — a lack of red blood cells or of haemoglobin (the protein that carries oxygen in the blood) that reduces supply of oxygen to tissues
  • polycythaemia — a condition in which there are too many red blood cells
  • other blood disorders — where the number of certain types of blood cells is either too high or too low, such as neutropenia where there are too few neutrophils, a type of white blood cell
  • clotting disorders — where the blood doesn’t clot adequately, leading to haemorrhage, or where the blood clots too much, leading to thrombosis
  • cancers affecting blood cells for example leukaemia
  • haemochromatosis — where an inherited disorder leads to too much iron in the blood

Problems that may happen to blood vessels include:

  • Atherosclerosis — where build-up of cholesterol in blood vessel walls leads to narrowing. When this happens in the blood vessels that supply the heart, it’s called coronary artery disease. Atherosclerosis can lead to heart attack and stroke.
  • peripheral vascular disease — this involves problems with the arteries outside of the heart and brain — usually in the legs and feet — affecting circulation. One of the causes is atherosclerosis
  • high blood pressure — over time having high blood pressure can damage your arteries and kidneys
  • Raynaud phenomenon — a temporary constriction of the blood flow to the fingers and toes, causing them to become cold and appear blue or white.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: September 2021


Back To Top

Need more information?

These trusted information partners have more on this topic.

Top results

How your heart works | The Heart Foundation

Your heart is a muscle that pumps blood to all parts of your body. The blood gives your body the oxygen and nourishment it needs to work properly.

Read more on Heart Foundation website

Blood Tests - St Vincent's Heart Health

Information about common cardiac blood tests.

Read more on St Vincent's Hospital Heart Health website

Blood pressure and your heart | Heart Foundation

High blood pressure is a major risk factor for heart disease. Luckily, a healthy lifestyle and getting regular blood pressure checks can help manage it.

Read more on Heart Foundation website

Heart conditions - endocarditis - Better Health Channel

Endocarditis is an infection of the heart valves or the inner lining of the heart.

Read more on Better Health Channel website

Heart conditions - angina - Better Health Channel

Angina attacks can be prompted by exertion or physical exercise, when the hard-working heart muscle requires greater amounts of oxygen.

Read more on Better Health Channel website

Heart conditions - atrial fibrillation - Better Health Channel

Atrial fibrillation (AF) is a type of arrhythmia, which means that the heart beats fast and abnormally.

Read more on Better Health Channel website

When The Heart Gets Heavy: Emotional Wellbeing and Heart Conditions | The Heart Foundation

When The Heart Gets Heavy: Emotional Wellbeing and Heart Conditions

Read more on Heart Foundation website

Coronary heart disease

The underlying cause of coronary heart disease is a slow build up of fatty deposits on the inner wall of the blood vessels that supply the heart muscle with blood (the coronary arteries).

Read more on WA Health website

Heart Health | myVMC

If the amounts of cholesterol in the blood are excessive, cholesterol can build up in arteries, which can lead to coronary heart disease and many other serious conditions.

Read more on myVMC – Virtual Medical Centre website

Heart disease and stroke risk – what can be done?  - NPS MedicineWise

Diseases that affect the heart and blood vessels include angina, coronary heart disease, and stroke. Find out the causes and what can be done to prevent these conditions.

Read more on NPS MedicineWise website

Healthdirect 24hr 7 days a week hotline

24 hour health advice you can count on

1800 022 222

Government Accredited with over 140 information partners

We are a government-funded service, providing quality, approved health information and advice

Australian Government, health department logo ACT Government logo New South Wales government, health department logo Northen Territory Government logo Government of South Australia, health department logo Tasmanian government logo Victorian government logo Government of Western Australia, health department logo

Healthdirect Australia acknowledges the Traditional Owners of Country throughout Australia and their continuing connection to land, sea and community. We pay our respects to the Traditional Owners and to Elders both past and present.