Functions of the Blood: Everything You Need to Know About the Composition, Structure and Function of the Blood in Our Body

Invertebrates it is composed of blood cells suspended in the blood plasma.

The plasma, which constitutes 55% of the blood fluid, is mainly water (92% by volume) and contains dissipated proteins, glucose, mineral ions, hormones, and carbon dioxide (plasma is the primary means of transporting the excretory product) and blood cells.

Blood cells are mainly red blood cells (also called red blood cells or erythrocytes ), white blood cells (also called white blood cells or leukocytes ), and platelets (also called thrombocytes).

The most abundant cells in the blood of vertebrates are red blood cells. These contain hemoglobin, an iron-containing protein, which facilitates oxygen transport by reversibly binding to this respiratory gas and significantly increasing its solubility in the blood.

In contrast, carbon dioxide is transported mainly extracellularly as bicarbonate ions transported in plasma.

The blood of vertebrates is bright red when their hemoglobin is oxygenated and dark red when deoxygenated.

Some animals, such as crustaceans and mollusks, use hemocyanin to transport oxygen instead of hemoglobin. Insects and some mollusks use a hemolymph fluid instead of blood, with the difference that hemolymph is not contained in a closed circulatory system.


In most insects, this “blood” does not contain oxygen-carrying molecules such as hemoglobin because their bodies are small enough that their tracheal system is sufficient to supply oxygen.

Vertebrates with jaws have an adaptive immune system based mainly on white blood cells. White blood cells help resist infections and parasites. Arthropods, which use hemolymph, have hemocytes as part of their immune system.

Medical terms related to blood often start with hemo- or hemato- (also hemo- and hemato- spelled) from the Greek word αἷμα (haima) for “blood.” In terms of anatomy and histology, blood is considered a specialized form of connective tissue, given its origin in the bones and the presence of possible molecular fibers in the form of fibrinogen.

Blood performs many vital functions within the body, including:

  • Supply oxygen to tissues (linked to hemoglobin, transport in red blood cells).
  • Supply of nutrients such as glucose, amino acids, and fatty acids (dissolved in the blood or attached to plasma proteins (for example, lipids in the blood).
  • Waste disposal such as carbon dioxide, urea, and lactic acid.
  • Immunological functions include circulating white blood cells and detecting foreign material by antibodies.
  • Coagulation is a broken blood vessel response, converting blood from a liquid to a semi-solid gel to stop bleeding.
  • Messaging functions, including hormone transport and signaling for tissue damage
  • Regulation of the central body temperature.
  • Hydraulic functions.

Functions of the Blood

The functions of the blood can be enumerated in various ways and described in different levels of detail. Introductory biology courses often include at least basic information about the structure and functions of blood.

One way to remember the main functions of blood is to divide them into three categories:

  • Homeostatic functions of blood

(How does blood help the body maintain homeostasis?)

  • Blood transport functions

(What moves the blood through the body? How, where, why, and what are these benefits?)

  • Immune functions of the blood

(How does blood help defend the body against infections, especially disease-causing organisms?)

  1. Homeostatic functions of blood

Homeostasis is the maintenance (through the body’s physiological mechanisms) of relatively stable conditions within the body’s internal environment despite changes occurring both inside and outside the body, for example, due to feeding, exercise, pregnancy, and variations in external conditions, etc.

The composition of blood plasma provides the body’s cells with a good and stable chemical environment.

Coagulation factors in the blood plasma and the platelets in the blood ensure that any tiny tear or hole is covered immediately.

The blood has specific blood pressure so that no defect can be tolerated, which could cause significant bleeding.

Interestingly, the clotting/platelet factors coagulation and fibrinolysis are constantly balanced automatically.

  1. Blood transport functions

These functions usually co-occur; some constantly occur, for example, breathing, while others occur at intervals depending on what is happening in the body.

For example, the distribution of digestion products may increase sometime after eating a meal. Hormones are transported throughout the body after being released, which may be in response to various causes.

More than anything, blood transports oxygen from the lungs to all tissues through the hemoglobin embedded in red blood cells.

It transports oxygen from the lungs to the tissues around the body. It transports carbon dioxide from the tissues around the body to the lungs (to remove it from the body). On the way back to the heart and lungs, it carries CO2, exhaling the lungs.

It transports the products of digestion (i.e., nutrients) from the intestine to the tissues around the body.

Nutrients are absorbed in the capillaries of the intestine and transported through the portal vein to the liver. Here many metabolic pathways are followed, and nutrients are transported through the blood to all body cells.

The soluble products of digestion include glucose, salts, some vitamins, and some proteins. They are transported in solution by the blood plasma. Transports nitrogenous waste from the liver to the kidneys.

It transports the hormones of the hormone-producing glands to the target organs of specific hormones.

It transports heat released by chemical processes in the body, that is, functions of metabolism, to colder regions of the body or the skin, for example, in the extremities and the head, to be released from the body if all areas of the body already have enough thermal energy.

Blood does not move from a specific place (part of the body) or organ to another, for example, “from the liver to the kidneys.” Blood flows through the body’s blood circulation system, as shown in the systemic circulation diagram.

Therefore, a specific molecule can move throughout the body several times before it is removed by a relevant gland or organ, for example, in the case of a hormone for which a specific “target organ” exists or before it is removed. Absorb into the tissue that uses it, for example, to release oxygen or a product of digestion.

  1. Immune functions of the blood

Of the major components of blood (blood plasma, red blood cells, white blood cells, and blood platelets), white blood cells called leukocytes perform critical immune functions and are described as an essential part of the immune system.

However, other parts of the blood also help protect the body against invasion and disease caused by pathogens, such as red blood cells forming blood clots to seal damaged blood vessels.

Blood coagulation helps prevent harmful microorganisms, for example, bacteria that enter the body through open wounds.

The response of blood and blood vessels to blood vessel damage (including blood clotting) prevents not only further loss of blood from the site of an injury but also prevents foreign bodies, such as harmful bacteria, from entering the bloodstream through the injury site. (The wounds from which blood is released are called open wounds).


Monocytes (also known as phagocytes) can swallow and digest small particles such as bacteria, protozoa, cells, and cell debris, some of which could cause damage to the body. This process is called phagocytosis.

Phagocytes can protect the body at the site of the wounds, inside the blood vessels or lymph nodes, and even inside the tissues outside the blood vessels because the phagocytes are small enough to pass through the capillaries to attack the bacteria present in the surrounding tissue.

Production of antibodies

Lymphocytes produce proteins called antibodies that attack antigens (chemical markers) on the surfaces of potentially harmful cells, for example, bacteria and other unrecognized cells as part of the person’s own body.

This is a very effective system to fight infections. Occasionally, antibiotics are needed when our immune system is overwhelmed.

The antibodies can function in different ways, for example, by binding to the surface of the alien cells, for example, bacteria, which facilitates the body’s phagocytes to ingest those foreign cells, for example, bacteria.

‘Grouping’ of alien cells and bacteria neutralizes toxins (toxic proteins) released by foreign cells, for example, bacteria.

The infection is contained by white blood cells (lymphocytes for viruses, neutrophils for bacteria) on the one hand and plasma cell antibodies on the other.

What are the other functions of the blood?

Blood has many functions; hormones and other signaling molecules (e.g., nitric oxide) integrate the role of various organs. While all the hormones are present and balanced, we have energy, and all our organs work perfectly.

But when hormones are lacking, we feel terrible. As we get older, some hormones are not produced enough. After reviewing the literature, bioidentical hormone replacement will allow our system to rebalance.

The distribution of heat and the redistribution of blood are other aspects of the perfusion of our extremities with blood, our abdominal organs, the head, and the skin.

After a meal, the blood runs to the intestine and liver when we begin to digest our food. We can get tired because part of the blood in the brain goes to the stomach, the small intestine, and the liver.

On a hot day, our skin veins are wide open, and we sweat and lose part of the heat of our body through our skin. It is the body’s way of keeping us fresh inside.

There is one aspect that seems to be beyond our control. When we get excited, or a person is timid, the head, neck, and ears turn red. This is out of our control.

Some people have this more than others, and some do not have it. It comes from dilated blood vessels. When they enlarge, the blood rushes into that region, giving your skin reddened.