Blood Anatomy and Physiology- What You Need to Know

How much do you know about your blood? You use it every day to deliver nutrients and oxygen to your cells, so it’s probably important to know a little bit about it. We’ve put together this short overview of the anatomy and physiology of blood in case you want to learn more! (Or, you can use this information as study notes before your next exam.)


The Body’s Transportation System We rely on our bodies’ transportation system every single day. Whether it’s traveling to work, going grocery shopping, or meeting a friend for lunch, we use our blood vessels daily without even thinking about it.

Learn all about how our bodies transport oxygenated blood from our hearts through arteries and veins back to our lungs in today’s lesson on the anatomy and physiology of blood.

Blood Anatomy and Physiology
Blood Anatomy and Physiology

But first, let’s start with some basic definitions. When people talk about blood, they usually mean one of two things: plasma or whole blood. Plasma is essentially a liquid medium that allows cells to move around in our bodies, as well as providing nutrients and oxygen delivery via red blood cells (RBCs). Whole blood is a mixture of cellular elements suspended in plasma, which makes up about 55% of our total blood volume.

The components of blood

erythrocytes, leukocytes, plasma, formed elements, and hemopoiesis. Each component of blood plays a different role in our bodies. The following is a list of their characteristics.

Red blood cells (erythrocytes) carry oxygen from your lungs to all of your body’s tissues. White blood cells (leukocytes) are responsible for fighting infection and disease, while platelets (thrombocytes) help with clotting, so wounds don’t keep bleeding. The remaining plasma is what actually makes up most of your blood’s volume, carrying around red blood cells, white blood cells, hormones, nutrients, and antibodies that help fight disease.

While blood cells last about a month in your body, plasma lasts for about a week. And while red blood cells make up only around 5% of your total blood volume, they make up 40% of your total hematocrit (the percentage of all blood that is made up of red blood cells).

Additionally, women have smaller bodies than men. As such, their hematocrits are on average 10–15% lower.

Also Read : What is Omicron, and What Are the Symptoms?

Functions of the Blood

Our blood is responsible for many essential functions in our body. Since blood is integral to our survival, it is vital that we understand how it works. Here are some of its key roles

The blood is made up of plasma, formed elements, erythrocytes, leukocytes, hemoglobin (which transports oxygen), platelets (which clots blood), and other factors. It is present in all body tissues apart from the bone marrow, where it flows freely.

The average adult has around 5 liters of blood. The structure of red blood cells varies according to their age; they are usually larger when they are newly formed than as a cell matures.

The red blood cells, white blood cells, and platelets

these are just a few of our more than five hundred different types of cells. But what do these seemingly microscopic components actually do? How do they function in our bodies? And how do they impact our everyday lives?

Here’s your quick rundown: Blood is made up of plasma, formed elements, erythrocytes (red blood cells), leukocytes (white blood cells), hemoglobin, and platelets. The plasma makes up 55% of total blood volume; water makes up 92% of plasma.

Red blood cells carry oxygen from our lungs throughout our body; erythrocytes make up just 2% of total blood volume. There are about twenty billion red blood cells in each microliter of blood.

White blood cells are another important part of our immune system; there are approximately forty million white blood cells per microliter of blood. Platelets help to clot; platelets make up 1% of total blood volume.


The fluid portion of blood, which is mainly water, contains dissolved gasses such as oxygen, carbon dioxide, nutrients, antibodies, and hormones. It makes up 55%-60% of blood volume. Formation of red blood cells: These red blood cells take their color from hemoglobin which carries oxygen around in our bodies.


The process by which cells that form blood are produced. There are three basic types of hematopoietic stem cells: progenitor stem cells, pluripotent stem cells, and multipotent stem cells.
The process of hematopoiesis is a self-renewing cycle involving multiple cell lineages, with each lineage developing into various types of blood cells.

The red blood cells (erythrocytes), white blood cells (leukocytes), and platelets are all derived from different forms of stem cells.


Red blood cells (erythrocytes) are biconcave discs that are responsible for carrying oxygen throughout your body. Their surface is covered with membrane receptors called CD36 (cluster of differentiation 36), which allows them to effectively bind with hemoglobin molecules.

Red blood cells survive in your bloodstream an average of 120 days before they become too brittle, lose their membranes, and die by phagocytosis.


There are many types of leukocytes, but for our purposes, we will just cover four: neutrophils, eosinophils, basophils, and lymphocytes. Neutrophils are part of your innate immune system; they form an important first line of defense against invaders such as bacteria or fungi.

As part of your adaptive immune system, T lymphocytes (which we’ll discuss later) play a crucial role in destroying foreign invaders that have already entered your body.

In human blood, there are four major types of cells: erythrocytes, leukocytes, thrombocytes (platelets), and lymphocytes. The hematopoietic cells can be found in red bone marrow as well as in blood. Bone marrow is a spongy tissue inside bones where most blood cells are made.

This diagram shows that these four types of cells circulate through your body in your bloodstream.
You need at least two of these types of cells in your blood: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

Components, formation, physical characteristics, volume

There are four main components of blood: plasma, formed elements, erythrocytes, leukocytes. The human blood volume is 5–6 liters (about 12 pints) in males 4–5 liters (about 10 pints) in females.

Formation of Red Blood Cells

  1. Proerythroblast
  2. Basophilic erythroblast
  3. Polychromatophilic erythroblast
  4. Orthochromatic erythroblast
  5. Reticulocyte
  6. Hemoglobin Mature RBC

The blood cell that carries oxygen from our lungs to our tissues is called a red blood cell or erythrocyte. It’s unique in its ability to transport large amounts of oxygen throughout our body while holding onto it until it is needed.

This process of picking up oxygen molecules in alveoli (tiny air sacs) and then delivering them through a network of hemoglobin molecules is known as oxyhemoglobin dissociation.


The body is constantly working to maintain a delicate balance between protecting itself from injury in case of external wounds or internal damage and being able to quickly heal from those wounds. When you cut yourself shaving, for example, your blood vessels constrict as soon as they are damaged.

This prevents further blood loss until it’s time for clotting factors (platelets) to stick together and form a clot that stops the bleeding. The underlying reason behind these processes is hemostasis.

Factors affecting blood clotting, blood flow, and blood pressure

High blood pressure is a state of high blood pressure in which blood flows through your veins and arteries with extra force. This state can lead to damage to your body’s organs, particularly ones closest to where it enters your heart.

High blood pressure tends to run in families, so you may have a greater chance of experiencing it than other people who have family members who did not experience these issues. Factors affecting blood clotting: When you are injured or cut yourself, it is natural for some amount of bleeding to occur.

However, sometimes bleeding can become too severe because of a medical condition called von Willebrand disease. This is a bleeding disorder caused by inadequate levels of clotting factors in your blood that reduce or prevent excessive bleeding.

People with von Willebrand disease may experience frequent nosebleeds, bleeding gums, bruises, or heavier than normal periods. Factors affecting blood clotting: When you have von Willebrand disease, your body does not produce an adequate amount of two key types of proteins: factor VIII and factor IX.

Blood Typing

Type A, Type B, Type AB, Type O. In human blood typing, an individual’s blood is classified based on antibodies (specific types of proteins) that are produced by their body as part of their immune system. In addition to providing protection against infection from foreign invaders such as bacteria or viruses, these antibodies also determine compatibility between donors and recipients in transfusions.
Antibodies are produced by B lymphocytes. In addition to antibodies, other components of blood such as red blood cells, white blood cells, platelets, and plasma also play important roles in protecting your body from disease.

Lymphocytes, macrophages, and neutrophils are all types of white blood cells that fight against infection.

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