Blood (Anatomy): Function, Components, Types... | Biology Dictionary (2023)

Blood Definition

Blood is the body fluid in humans and other animals that delivers the essential materials for life to the body’s cells. It has sometimes been called a fluid “tissue,” because like solid tissues it contains several types of cells which perform complex functions for the human body.

The components of blood are produced mainly in the bone marrow, where special cells produce red cells, white 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 made.

Despite looking like a simple red fluid, blood is as complex as any tissue in the body. Here we will discuss its functions, its components, and some clinically important characteristics of blood.

Function of Blood

Important functions of the blood include:

Bringing Vital Substances to Cells

Complex multicellular organisms need complex circulatory systems; that’s because we have many cells, and these cells have high metabolisms.

Without highly efficient means of delivering vital substances like oxygen, water, and nutrients, complex and active life forms like ourselves could not exist.

Some of the vital substances which blood delivers to our cells include:

  • Oxygen – Near-constant supply needed for cellular respiration.
  • Water – Correct balance needed for enzymatic activity to proceed smoothly.
  • Nutrients – Fuel for cellular respiration, and necessary materials for cellular maintenance.
  • Biological building blocks – Molecules out of which replacement parts and daughter cells can be made.
  • Chemical messages from other cells – Allows body cells to alter their activity appropriately in response to environmental changes.

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

Removing Dangerous Wastes

Most living things produce waste products that, at a certain concentration, become toxic to their own cells. Multicellular organisms with high metabolisms like us have had to find a way to deal with all those waste products in order to allow many cells to live together in a single organism.

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

(Video) The Composition and Function of Blood

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

The blood keeps our cells safe by carrying all of these waste products out of our tissues and to the correct processing and elimination organs. Some waste products our blood helps us get rid of include:

  • Carbon dioxide gas – Byproduct of cellular respiration, stops cellular respiration and causes acidification of blood if not removed.
  • Excess water, salt, and other substances – Too much of a good thing can be a bad thing.
  • Debris from dead cells – Cells die regularly, especially red blood cells which are not made to live longer than two weeks. Dead cells release toxic substances as they break down.
  • Toxic waste products of metabolism – Some forms of routine cellular metabolism produce highly toxic substances that can be safely swept away by the blood to the liver and kidneys.
  • Toxins we ingest in our food and water – Our liver and kidneys aren’t fool-proof, but they can handle some toxins we might encounter in the environment.

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

Contains and Transports Immune Factors

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

Our white blood cells even fight cancers that originate within our own bodies. It’s thought that most people develop cancerous cells at some point in their lives – but in most healthy people, the immune system destroys them before they are noticed. That’s why people with immune disorders have a higher chance of developing certain cancers than those with healthy immune systems.

The lymphatic system is also important for the movement, storage, and creation 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. Because all of our organs, including our brains, rely on constant blood flow to stay alive, loss of large amounts of blood can be devastating. This is the most common cause of death from trauma.

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

Our blood clotting system cannot save us from large injuries, such as those that result in ruptures to our arteries. But their power can be seen in cases of people who do not have properly working blood clotting system.

People with certain cancers, vitamin deficiencies, and other diseases have blood that does not clot normally. These people can bruise and bleed with no apparent cause, and sometimes die from minor injuries or apparently spontaneous bleeding.

This happens because their clotting systems are not functioning properly. We can be thankful that most of our clotting systems do!

(Video) Learn All about Blood - Anatomy, Physiology, Composition, Function & Disorders

Components of Blood

There are several major components of the seemingly uniform liquid that is our blood. When centrifuged, the components of different densities separate to look something like this:

Here we will discuss the most vital components of blood, including serum, white blood cells or “leukocytes,” red blood cells, and platelets.


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

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

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

Other substances that can be found in the plasma include:

  • Antibodies, which are proteins that attack invading pathogens
  • Clotting factors, which prevent bleeding
  • Hormones, which are chemical messages sent between different tissues in the body
  • Electrolytes such as salt
  • Nutrients such as sugar, vitamins, and minerals
  • Lipids including cholesterol

So even this seemingly simple fluid is a veritable stew of the ingredients for life! But it could not do its job without…

Red Blood Cells

Red blood cells can be thought of as the cargo ships of the body. They are small, numerous cells which are specifically designed to carry oxygen from the lungs to cells, and carry carbon dioxide back to the lungs to be expelled when we exhale.

Red blood cells contain hemoglobin – a protein which is beautifully tailored to bind aggressively to oxygen in the lungs, and then release it and pick up carbon dioxide at a slow, steady rate as it passes through the body.

Hemoglobin is a pigment which changes color slightly, depending on whether it is bound to a molecule of oxygen or not. That’s why blood drawn from veins, which carry oxygen-depleted blood back toward the lungs, is a dark red that can appear almost brown. Blood drawn from arteries, which carry oxygen-rich blood from the lungs to the tissues, is a bright red.

White Blood Cells

White blood cells perform both immune and clean-up functions for the body. Like red blood cells, they are made by stem cells in the bone marrow.

(Video) Blood, Part 1 - True Blood: Crash Course Anatomy & Physiology #29

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

  • Neutrophils – Target bacteria and fungi.
  • Eosinophils – Target larger parasites such as those which cause malaria. Also play a role in allergic inflammatory responses.
  • Basophils – Release chemicals that enhance inflammatory responses.
  • B Lymphocytes – Release antibodies and assist in activating T cell lymphocytes.
  • T Lymphocytes – Different subtypes help the immune system learn to “recognize” new infection so it can target it; help immune system to activate in response to infection, then return to normal after infection has passed; target virus-infected and tumor cells.
  • Natural Killer Lymphocytes – Target virus-infected and tumor cells for destruction.
  • Monocyte – Migrate into tissues and mature into macrophages, literally “big eaters,” which engulf harmful cells and cellular debris and destroy them; some mature into Kupffer cells, which live in the liver and break down and recycle dying red blood cells.


Platelets are cell fragments – bits of membrane-bound cytoplasm – which stop bleeding by clumping together to form clots and scabs seal wounds. Like red and white blood cells, they are made in the bone marrow. Cancer of the bone marrow may prevent production of properly functioning platelets.

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

Under normal circumstances, platelets are activated when a nearby injury starts a chemical cascade that urges platelets and other nearby clotting factors to activate. These factors then release clot-promoting messages of their own, encouraging more clotting factors to join their growing clot.

Platelets can sometimes be incorrectly activated when endothelial lining 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 Types

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

In time, however, scientists discovered the existence of “blood types” – a few basic proteins that coat the surface of our blood cells, helping the immune system to differentiate between our own blood cells and foreign invaders.

Attempting to transfuse blood of an incompatible type into a person can cause a clotting reaction, which may be fatal. Fortunately, today doctors have rapid tests to determine a patient’s blood type, and store blood bags for transfusion sorted by type so that patients are assured of getting a compatible treatment.

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

The A/B protein group can give rise to blood types A, B, AB, or O. There is no “O” blood type protein – instead “O” is the blood type used to describe people who have neither A nor B marker proteins.

Each of these blood types can also be positive or negative for the Rh protein, leading to blood types such as “AB+” or “AB-.”

The blood type “O negative” is known as the universal donor. Because it does not have A or B proteins and is negative for the Rh protein, people of any blood type can receive O negative blood without having an adverse immune response to foreign proteins.

(Video) The Components of Blood and Their Importance

Unfortunately, people with “O negative” blood type also have the narrowest selection of possible donors for themselves. O negative people cannot receive any blood that has A, B, or Rh proteins; they can only receive blood from other O negative people.

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


1. Which of the following is NOT a function of blood?
A. To transport oxygen to our cells
B. To transport water to and away from our cells, as needed
C. To break down toxins into harmless substances
D. To fight infections

Answer to Question #1

C is correct. Blood cannot break down 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 is NOT likely to be found in a blood sample?
A. Red blood cells
B. Plasma
C. White blood cells
D. Bone marrow cells

Answer to Question #2

D is correct. Although bone marrow cells are the sites of production for red blood cells, white blood cells, and platelets, bone marrow cells themselves are not normally found in the blood.

3. Which of the following is NOT likely to be found in blood plasma?
A. Salt
B. Digestive enzymes
C. Hormones
D. Albumin

Answer to Question #3

(Video) GCSE Biology - What Is Blood Made of? / What Does Blood Do? #25

B is correct. Digestive enzymes are not normally found in blood plasma. The other items, however, are all common components of plasma!


  • 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, W. S. (2004). Kupffer of Kupffer cells. Gastroenterology, 127(1), 16. doi:10.1053/j.gastro.2004.05.041
  • Wilson, J. H., & Hunt, T. (2002). Molecular biology of the cell, 4th ed. New York: Garland.
  • American Society of Hematology. (2014, March 29). Retrieved July 11, 2017, from


What are the 7 blood components? ›

An average-sized man has about 12 pints of blood in his body, and an average-sized woman has about nine pints.
  • The Components of Blood and Their Importance. ...
  • Plasma. ...
  • Red Blood Cells (also called erythrocytes or RBCs) ...
  • White Blood Cells (also called leukocytes) ...
  • Platelets (also called thrombocytes) ...
  • Complete Blood Count (CBC)

What are the 4 components of blood and each of their functions? ›

Plasma is the main component of blood and consists mostly of water, with proteins, ions, nutrients, and wastes mixed in. Red blood cells are responsible for carrying oxygen and carbon dioxide. Platelets are responsible for blood clotting. White blood cells are part of the immune system and function in immune response.

What are the 7 functions of blood? ›

Functions of the Blood: 8 Facts about Blood
  • Blood Is Fluid Connective Tissue. ...
  • Blood Provides the Body's Cells with Oxygen and Removes Carbon Dioxide. ...
  • Blood Transports Nutrients and Hormones. ...
  • Blood Regulates Body Temperature. ...
  • Platelets Clot Blood at Sites of Injury. ...
  • Blood Brings Waste Products to the Kidneys and Liver.

What are the 3 types of blood cells and their functions? ›

There are 3 types of blood cells – red blood cells, white blood cells and platelets.
  • Red blood cells (erythrocytes) carry oxygen to all cells in the body. ...
  • White blood cells (leukocytes) are an important part of the.
  • Platelets (thrombocytes) make the blood clot and help stop bleeding.

What are the 7 types of blood cells? ›

Blood contains many types of cells: white blood cells (monocytes, lymphocytes, neutrophils, eosinophils, basophils, and macrophages), red blood cells (erythrocytes), and platelets.

How many blood functions are there? ›

Blood has three main functions: transport, protection and regulation. Blood transports the following substances: Gases, namely oxygen (O2) and carbon dioxide (CO2), between the lungs and rest of the body. Nutrients from the digestive tract and storage sites to the rest of the body.

What are the components of blood 12? ›

Complete answer: Blood is fluid in the body. It has four components-plasma, red blood cells, white blood cells and platelets.

What are 4 main components of blood? ›

  • Whole Blood. Whole blood contains red cells, white cells, and platelets (~45% of volume) suspended in blood plasma (~55% of volume). ...
  • Red Cells. Red blood cells (RBCs), or erythrocytes, give blood its distinctive color. ...
  • Platelets. ...
  • Plasma. ...
  • Cryo. ...
  • White Cells & Granulocytes.

What are the 4 main parts of blood? ›

This important substance has many different elements that make it the main carrier of oxygen, carbon dioxide, and essential nutrients throughout the body. There are four parts of blood: platelets, plasma, and red and white blood cells.

What are the 4 main functions blood does for your body quizlet? ›

  • Transport nutrients.
  • Help regulate body temperature.
  • Protect the body.
  • Helps stabilize pH and electrolyte levels.

What are all the components of blood? ›

Components of Blood
  • Plasma.
  • Red Blood Cells.
  • White Blood Cells.
  • Platelets.

What are the 5 function of blood? ›

Functions of blood.

Transports O2, CO2, nutrients, hormones, heat and wastes. Regulates pH, temperature, water content of cells. Protects against blood loss through clotting. Protects against disease through phagocytic white blood cells and antibodies.

What are the 5 functions of blood quizlet? ›

  • Define Blood. ...
  • 5 functions of Blood? ...
  • Transporting Dissolved Gases, Nutrients, Hormones, and Metabolic wastes. ...
  • Blood Clot or Clotting. ...
  • Defending against Toxins and Pathogens. ...
  • Stabilizing Body Temperature. ...
  • What is Normal Blood Temperature? ...
  • What is the Average pH level of Blood?

What are the 3 components of blood? ›

The three classes of formed elements are the erythrocytes (red blood cells), leukocytes (white blood cells), and the thrombocytes (platelets).

What are the three 3 solid components of blood? ›

The solid part of your blood contains red blood cells, white blood cells, and platelets.

What are the 3 main cells in blood? ›

There are three main types of cells in your blood – red blood cells, white blood cells and platelets.

What are the 8 human blood types? ›

In addition to the A and B antigens, there is a protein called the Rh factor, which can be either present (+) or absent (–), creating the 8 most common blood types (A+, A-, B+, B-, O+, O-, AB+, AB-).

What type of tissue is blood? ›

Blood is one of the connective tissues. As a connective tissue, it consists of cells and cell fragments (formed elements) suspended in an intercellular matrix (plasma). Blood is the only liquid tissue in the body that measures about 5 liters in the adult human and accounts for 8 percent of the body weight.

What are the 6 possible blood types? ›

Since there are three different alleles, there are a total of six different genotypes at the human ABO genetic locus. The different possible genotypes are AA, AO, BB, BO, AB, and OO.

How many cells are in blood? ›

Men: 4.7 to 6.1 million red blood cells per microliter of blood. Women: 4.2 to 5.4 million red blood cells per microliter of blood. Children: 4.0 to 5.5 million red blood cells per microliter of blood.

Which is not a function of blood? ›

Answer and Explanation: Among the given options, the one which is not a function of blood is: A) Gather sensory information. Gathering sensory information is the function of nerve cells or neurons.

What is blood PDF? ›

Blood-Blood is a viscous fluid formed of cellular element suspended in plasma.-The cellular element composed of: Erythrocytes (red blood cells), Leucocytes (white blood cells), and Platelets.-Plasma is a viscous, translucent, yellowish fluid composed of water (90%), proteins (7%), organic salts (1%), and organic ...

What is class 10 blood composed? ›

Blood is a fluid connective tissue composed of 55% plasma and 45% formed elements including WBCs, RBCs, and platelets.

What is blood class 7? ›

Blood is a fluid connective tissue containing plasma, red blood cells (RBC), white blood cells (WBC), and platelets. It is the primary circulating fluid that aids in the movement of oxygen, carbon dioxide, nutrients, hormones, and wastes.

What are the 8 components of blood plasma? ›

Plasma contains about 90 percent water, with 10 percent being made up of ions, proteins, dissolved gases, nutrient molecules, and wastes. The proteins in plasma include the antibody proteins, coagulation factors, and the proteins albumin and fibrinogen which maintain serum osmotic pressure.

What are the 5 components of blood plasma? ›

Important elements in plasma include albumin, coagulation factors, fibrinolytic proteins, immunoglobulin and other proteins. Plasma usually is frozen within hours of donation in order to preserve the clotting factors.

What are the 5 types of plasma? ›

Plasma classification (types of plasma)
  • 1 Pseudo-plasmas vs real plasmas.
  • 2 Cold, warm and hot plasmas. 2.1 Hot plasma (thermal plasma) ...
  • 3 Plasma ionization. 3.1 Degree required to exhibit plasma behaviour. ...
  • 4 Collisional plasmas. 4.1 Collisional plasma. ...
  • 5 Neutral plasmas. ...
  • 6 Plasmas densities. ...
  • 7 Magnetic plasmas. ...
  • 8 Complex plasmas.

What is the function of blood? ›

Blood brings oxygen and nutrients to all the parts of the body so they can keep working. Blood carries carbon dioxide and other waste materials to the lungs, kidneys, and digestive system to be removed from the body. Blood also fights infections, and carries hormones around the body.

What are the components of blood quizlet? ›

List the major components of blood. It has four main components: plasma, red blood cells, white blood cells, and platelets.

What are 3 physical properties of blood? ›

Important physiological characteristics of blood to remember are its alkaline pH (7.35-7.45), high temperature (38°C), high viscosity (five times more viscous than water), and volume in the human body (approximately 8%).

What are the 4 components of blood and their percentages? ›

Red blood cells make up about 45% of the blood volume. White blood cells make up about one percent and platelets less than one percent. Plasma makes up the rest of the blood. Mature red blood cells do not have nuclei or other organelles.

What are the heart's main two roles in blood circulation 4? ›

  • The right side of your heart receives oxygen-poor blood from your veins and pumps it to your lungs, where it picks up oxygen and gets rid of carbon dioxide.
  • The left side of your heart receives oxygen-rich blood from your lungs and pumps it through your arteries to the rest of your body.

What are the components of the blood and their functions quizlet? ›

List and describe the 4 components of blood.
  • RBCS: Contain hemoglobin, transport oxygen to an remove co2 from body tissues.
  • WBCS: Fight infection.
  • Platelets: Help blood clot.
  • Plasma: contains salts and various kinds of proteins.

What is the main function of blood quizlet? ›

What are the 3 functions of blood? (1) Transport - oxygen, nutrients, hormones and removes wastes. (2) Regulation - pH, temperature, volume of fluid in circulation. (3) Protection - prevent blood loss (clots), prevent infection (antibodies, immune proteins & WBCs).

What are the 5 steps of blood flow? ›

Blood comes into the right atrium from the body, moves into the right ventricle and is pushed into the pulmonary arteries in the lungs. After picking up oxygen, the blood travels back to the heart through the pulmonary veins into the left atrium, to the left ventricle and out to the body's tissues through the aorta.

What is blood 7 give the composition of plasma? ›

Whole blood minus erythrocytes (RBCs), leukocytes (WBCs), and thrombocytes (platelets) make up the plasma. Serum, sometimes mistakenly considered synonymous with plasma, consists of plasma without fibrinogen. Plasma contains 91% to 92% of water and 8% to 9% of solids.

What are the 7 formed elements of blood quizlet? ›

  • Erythrocytes. (red blood cells, RBCs) ...
  • Leukocytes. (white blood cells, WBCs) ...
  • Neutrophil. Description: Nucleus multilobed; pale red and blue cytoplasmic granules; diameter 10-12 um. ...
  • Eosinophil. Description: Nucleus bilobed; red cytoplasmic granules; diameter 10-14 um. ...
  • Basophil. ...
  • Lymphocyte. ...
  • Monocyte. ...
  • Platelets.

What are the 4 key components of blood? ›

Whole blood contains red cells, white cells, and platelets (~45% of volume) suspended in blood plasma (~55% of volume).

What are the six different blood products? ›

Different Types of Blood Products
  • Packed Red Blood Cells.
  • Fresh Frozen Plasma.
  • Platelets.
  • Albumin.
  • Cryoprecipitate.
Aug 5, 2017

What organ makes blood? ›

Blood cells are made in the bone marrow. The bone marrow is the soft, spongy material in the center of the bones. It produces about 95% of the body's blood cells. Most of the adult body's bone marrow is in the pelvic bones, breast bone, and the bones of the spine.

What are the 8 components of blood? ›

The main components of blood are: plasma.
  • glucose.
  • hormones.
  • proteins.
  • mineral salts.
  • fats.
  • vitamins.

What is responsible for blood clotting? ›

Platelets (a type of blood cell) and proteins in your plasma (the liquid part of blood) work together to stop the bleeding by forming a clot over the injury.

What is blood made of PDF? ›

Blood-Blood is a viscous fluid formed of cellular element suspended in plasma.-The cellular element composed of: Erythrocytes (red blood cells), Leucocytes (white blood cells), and Platelets.-Plasma is a viscous, translucent, yellowish fluid composed of water (90%), proteins (7%), organic salts (1%), and organic ...

What are the 5 formed elements of blood? ›

Blood is composed of formed elements—erythrocytes, leukocytes, and cell fragments called platelets—and a fluid extracellular matrix called plasma. More than 90 percent of plasma is water.

Why is blood needed by all the parts of a body Class 7 science? ›

Blood is a significant part of transport system in our body, and we need blood for the following reasons: It transports substances like digested food from the small intestine to the other parts of the body. It carries oxygen from the lungs to the cells of the body. It also helps in removal of wastes from the body.

What are the five function of blood? ›

Functions of blood.

Transports O2, CO2, nutrients, hormones, heat and wastes. Regulates pH, temperature, water content of cells. Protects against blood loss through clotting. Protects against disease through phagocytic white blood cells and antibodies.


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