Blood (Anatomy): Function, Components, Types... | biology dictionary (2023)


Blood is the body fluid in humans and other animals that supplies the body's cells with the substances necessary for life. It is sometimes called liquid "tissue" because, like solid tissue, it contains many types of cells that perform complex functions for the human body.

Blood components are produced mainly in the bone marrow, where special cells produce red blood cells, white blood cells and platelets. So-called "blood cancers" such as leukemia are actually cancers of the bone marrow. As cancerous tissue replaces healthy bone marrow tissue, healthy red blood cells, white blood cells and platelets cannot be produced.

Although blood looks like a simple red liquid, it is as complex as any tissue in the body. Here we will discuss its functions, its components and some clinically important properties of blood.

blood function

Important functions of blood are:

Bring vital substances into the cell

Complex multicellular organisms need complex circulatory systems; This is because we have a lot of cells and these cells have a high metabolism.

Complex, active life forms like us couldn't exist without highly efficient means of delivering essential substances like oxygen, water, and nutrients.

The vital substances that blood supplies our cells include:

  • Oxygen - Nearly constant supply needed for cellular respiration.
  • Water – The right balance is needed for enzyme activity to run smoothly.
  • Nutrients – Fuel for cellular respiration and materials needed for cellular maintenance.
  • Biological building blocks - molecules that can be used to make spare parts and daughter cells.
  • Chemical messages from other cells – allows the body's cells to appropriately alter their activity in response to environmental changes.

Blood also performs other important functions for our body, including…

Remove hazardous waste

Most living beings produce residues that, above a certain concentration, become toxic to their own cells. Highly metabolizing multicellular organisms like us had to find a way to deal with all these waste products so that many cells could live together in a single organism.

We have our liver and kidneys, which break down toxic substances into harmless substances and excrete them from the body in the form of urine. Our blood transports toxins from all our tissues to these organs, where they are processed and removed.

Our blood also releases unwanted gases into the lungs, where they are exchanged for fresh oxygen.

Blood protects our cells by transporting all these waste products from our tissues to the proper processing and excretory organs. Some waste products that our blood helps us get rid of are:

  • Carbon Dioxide Gas – By-product of cellular respiration, stops cellular respiration and causes blood acidification if not removed.
  • Excess water, salt and other substances - Too much of a good thing can be bad.
  • Debris from dead cells – Cells die regularly, especially red blood cells that are not designed to live more than two weeks. Dead cells release toxic substances as they decompose.
  • Toxic Metabolic Waste – Some forms of routine cellular metabolism produce highly toxic substances that can be safely eliminated from the blood to the liver and kidneys.
  • Toxins we ingest from our food and water – Our liver and kidneys are not infallible, but they can handle some toxins we may encounter in the environment.

In addition to transporting substances to and from cells in other organs, blood also contains its own cells and performs its own functions. These include:

Contains and transports immune factors

Our blood contains antibodies and white blood cells that fight viruses, bacteria and other invaders. Without these vital cells, we would quickly succumb to infection and die.

Our white blood cells even fight cancer that arises in our own bodies. It is believed that most people will develop cancer cells at some point in their lives – but in most healthy people, the immune system destroys them before they are noticed. Because of this, people with immune disorders have a higher risk of developing certain cancers than people with healthy immune systems.

The lymphatic system is also important for the movement, storage and formation of immune factors.

Contains and transports clotting factors

One of the most serious risks of injury to our body is the risk of blood loss. As all of our organs, including the brain, depend on a constant flow of blood to stay alive, losing large amounts of blood can be devastating. This is the leading cause of death from trauma.

Fortunately, our blood has a system for responding when we are injured. A combination of cell fragments called platelets, chemicals called clotting factors, and other blood components work together to turn the blood into clots and scabs to stop bleeding.

Our blood clotting system cannot protect us from serious injuries like B. those that lead to tears in our arteries. But its power can be seen in cases of people who do not have a properly functioning blood clotting system.

People with certain cancers, vitamin deficiencies, and other illnesses have blood that doesn't clot normally. These people can bruise and bleed for no apparent reason, and sometimes die from minor injuries or apparently spontaneous bleeding.

This happens because your clotting systems are not working properly. We can be grateful that most of our clotting systems do!

blood components

There are several major components of the seemingly uniform fluid that is our blood. During centrifugation, components of different densities separate and look like this:

Here we will discuss the main components of blood, including serum, white blood cells or "leukocytes", red blood cells and platelets.


Plasma is the liquid that contains red blood cells, white blood cells, platelets, and other substances found in the blood. More than half of our blood volume consists of this fluid.

Our blood plasma is mostly water, but it also contains salts, proteins and other substances that can make it appear thick and syrupy even after the red and white blood cells have been filtered.

An important protein, albumin, exists in part to keep blood thick and syrupy. This ensures that blood does not leak from our vessels into the tissues and slows down bleeding when we are injured.

Other substances that can be found in plasma are:

  • Antibodies, which are proteins that attack invading pathogens
  • clotting factors that stop bleeding
  • Hormones, which are chemical messages sent between different tissues in the body
  • electrolytes like salt
  • Nutrients like sugar, vitamins and minerals
  • lipids including cholesterol

So even this seemingly simple liquid is a real stew of ingredients for life! But he couldn't do his job without...

red blood cells

Red blood cells can be considered the body's cargo ships. They are small, numerous cells, specially designed to transport oxygen from the lungs to the cells and transport carbon dioxide back to the lungs to be expelled in exhalation.

Red blood cells contain hemoglobin - a protein perfectly adapted to aggressively bind oxygen in the lungs, then release it and absorb carbon dioxide at a slow, steady pace as it travels through the body.

Hemoglobin is a pigment that changes color slightly depending on whether or not it is bound to an oxygen molecule. Because of this, blood taken from the veins that carry deoxygenated blood back to the lungs is a dark red that can appear almost brown. Blood taken from the arteries that carry oxygen-rich blood from the lungs to the tissues is bright red.

White blood cells

White blood cells perform immune and cleansing functions for the body. Like red blood cells, they are produced by stem cells in the bone marrow.

There are many types of white blood cells that play different roles in the immune response to infection and injury. Some types of white blood cells include:

  • Neutrophils - target of bacteria and fungi.
  • Eosinophils - target larger parasites such as B. those that cause malaria. They also play a role in allergic inflammatory reactions.
  • Basophils – release chemicals that increase inflammatory responses.
  • B lymphocytes – release antibodies and help activate T cell lymphocytes.
  • T Lymphocytes – Different subtypes help the immune system learn to “recognize” new infections so it can fight them off; help the immune system activate in response to the infection and return to normal after the infection is over; target virus-infected and tumor cells.
  • Natural Killer Lymphocytes - Targeting virus-infected cells and tumor cells for destruction.
  • Monocytes - invade tissues and mature into macrophages, literally "big eaters" that engulf and destroy harmful cells and cellular debris; some mature into Kupffer cells, which live in the liver and break down and recycle dying red blood cells.


Platelets are cell fragments - membrane-bound pieces of cytoplasm - that stop bleeding by clumps together and closes wounds. Like red and white blood cells, they are produced in the bone marrow. Bone marrow cancer can prevent the production of platelets that work properly.

Platelets have two states: active platelets, which are primed to form blood clots, and inactive platelets, which do not clot. Under normal circumstances, the endothelial lining of healthy blood vessels produces chemical messages that tell platelets to remain in their inactive form so they don't form clots in healthy blood vessels.

Under normal circumstances, platelets are activated when a nearby injury triggers a chemical cascade that stimulates the activation of platelets and other nearby clotting factors. These factors then release their own pro-coagulation messages, encouraging more clotting factors to join the growing clot.

Platelets can sometimes be incorrectly activated when the endothelial layer is damaged and does not produce the usual inhibitory messages for platelets. This can happen in people with some metabolic disorders and some forms of cardiovascular disease.

blood groups

In early medical history, it was believed that blood transfusions from one person to another could be impossible. This was because most test subjects died when this was attempted.

Over time, however, scientists discovered the existence of "blood types" - certain basic proteins that coat the surface of our blood cells and help the immune system distinguish between our own blood cells and foreign invaders.

Attempting to transfuse a person with blood of an incompatible type can cause a clotting reaction, which can be fatal. Fortunately, physicians now have rapid tests to determine a patient's blood type and store blood bags for transfusion sorted by type so that patients can be assured of a compatible treatment.

The three common blood group protein markers recognized by science are called the A, B, and Rh proteins.

Protein group A/B can result in blood group A, B, AB or O. There is no such thing as an "O" blood group protein - instead, "O" is the blood type used to describe people who do not have A or B marker proteins.

Each of these blood types can also be Rh protein positive or negative, resulting in blood types such as "AB+" or "AB-".

The "O negative" blood group is known as the universal donor. Because it does not contain A or B proteins and is Rh protein negative, people of any blood type can obtain O-negative blood without having an adverse immune response to foreign proteins.

Unfortunately, people with the "O negative" blood group also have the most restricted selection of possible donors. Negative people cannot receive blood containing A, B or Rh proteins; You can only get blood from other O negative people.

When platelets are deficient or absent, the results can be seen in an increased likelihood of catastrophic bleeding events, including spontaneous bleeding and bleeding from minor injuries.


1. Which of the following functions is NOT a function of blood?
AN.To transport oxygen to our cells
B.To carry water to and from our cells when needed
C.To break down toxins into harmless substances fight infections

Answer to question #1

Cthat's right. Blood cannot remove toxins; However, it can deliver toxic substances from our cells to the liver and kidneys, which can do this job.

2. Which of the following substances is NOT likely to be found in a blood sample? blood cells
C.White blood cells
D.bone marrow cells

Answer to question #2

Dthat's right. Although bone marrow cells are the sites of production of red blood cells, white blood cells, and platelets, bone marrow cells themselves are normally not found in the blood.

3. Which of the following substances is probably NOT found in blood plasma?
B.digestive enzymes

Answer to question #3

Bthat's right. Digestive enzymes are not normally found in blood plasma. However, the other items are all standard Plasma parts!


  • Laki, K. (1972). Our ancient heritage in blood clotting and some of its consequences.Annals of the New York Academy of Sciences, 202(1), 297-307. doi:10.1111/j.1749-6632.1972.tb16342.x
  • Haubrich, WS (2004). Kupffer the celulas de Kupffer.Gastroenterology, 127(1), 16. doi:10.1053/j.gastro.2004.05.041
  • Wilson, JH e Hunt, T. (2002).Molecular Biology of the Cell, 4th ed.Nova York: Garland.
  • American Society of Hematology. (2014, March 29). Retrieved July 11, 2017 from
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