Human Blood

Human Heart

Table of Contents

Introduction of Human Blood

What is blood? Blood is a special fluid that travels throughout your body. Imagine it as a living river carrying essential cargo.

Why is it important? Blood is vital! It’s like a delivery truck, constantly on the move:

  • Bringing oxygen and nutrients: It picks up oxygen from your lungs and delivers it to all your cells, keeping them alive and functioning.
  • Removing waste: Blood also acts as a garbage truck, carrying away waste products from your cells to be eliminated.
  • Fighting infection: Special cells in your blood called white blood cells help fight off germs and keep you healthy.

The components of blood

A unique tissue: Interestingly, blood is considered a fluid connective tissue. Connective tissues normally provide support and structure, but blood does this in a different way.

  • Liquid highway: Blood doesn’t have a solid structure like bones or muscles. Instead, it has a liquid part called plasma that acts like a highway.
  • Cellular passengers: Within this “highway” travel various “passengers” – tiny cells like red blood cells (carrying oxygen), white blood cells (fighting infection), and platelets (helping with clotting).

Where does it come from? Most of your blood cells are produced in your bone marrow, a soft tissue found inside some bones.

Composition of Blood


Plasma is the straw-colored liquid that makes up about 55% of your blood volume. Think of it as the body’s internal transportation system, carrying essential components throughout your body. Here’s a breakdown:

Plasma or Serum: Their Differences and Uses in medical research. |  Helvetica Health Care


  • Water (90-92%): The base for transporting everything else.
  • Proteins (7-8%): Play crucial roles:
    • Albumin: Maintains fluid balance in the body, preventing leaks.
    • Globulins: Act like warriors, fighting infections and carrying various molecules.
    • Clotting factors: Help seal wounds by forming clots when needed.

Other solutes (1-2%):

  • Electrolytes (salts): Maintain proper nerve and muscle function, regulate blood pressure.
  • Waste products: Carried to organs like kidneys and liver for removal.
  • Nutrients (glucose, vitamins): Delivered to cells for energy and growth.

Protein Powerhouse

Plasma proteins are vital for various functions:

Plasma Proteins – A Comprehensive Review - My Endo Consult

  • Albumin: Keeps fluid within blood vessels, preventing swelling.
  • Globulins:
    • Antibodies (Immunoglobulins): Fight off infections by recognizing and destroying harmful substances.
    • Transport proteins: Carry various molecules like hormones, vitamins, and fats.
  • Clotting factors: Work together to form a clot at the site of injury, stopping blood loss.

Blood Cells

Our blood is a vital river carrying tiny heroes called blood cells. These cells, though small, have critical roles in keeping us healthy. Let’s dive into the three main types:

Red Blood Cells (RBCs)

Imagine them as oxygen taxis.

Lesson Explainer: Components of the Blood | Nagwa

  • Structure: RBCs are unique. They are disc-shaped and lack a nucleus, allowing them to squeeze through tiny blood vessels. They are packed with a special protein called hemoglobin, which gives blood its red color.
  • Function: Hemoglobin acts like a magnet, attracting oxygen in the lungs and delivering it throughout the body. RBCs also carry carbon dioxide waste back to the lungs for exhalation.

White Blood Cells (WBCs)

Think of them as the body’s army.

WBCs come in two main groups:

  • Granulocytes: These guys contain visible granules like packets in their cytoplasm. They are the first line of defense, like soldiers:
    • Neutrophils: Phagocytes (eating cells) that gobble up bacteria and dead cells. 
    • Eosinophils: Attack parasites and allergic reactions.
    • Basophils: Release chemicals to trigger inflammation and allergic reactions.

Blood cells and its types with functions

  • Agranulocytes: These lack prominent granules:
    • Lymphocytes: They are the strategists, coordinating the immune response. Some directly attack infected cells, while others produce antibodies (memory cells) to fight future infections.
    • Monocytes: They mature into macrophages, powerful phagocytes that go after bacteria, fungi, and cellular debris.


Tiny sticky patches that help with clotting.

Understanding Blood Platelets and Their Role in Hemostasis

  • Structure: Platelets are small cell fragments.
  • Function: When there’s an injury, platelets rush to the site and clump together to form a clot, sealing the wound and preventing excessive bleeding.

Blood Clotting

Imagine your body as a complex network of pipes (blood vessels) carrying a vital fluid (blood). Blood clotting acts like a built-in plug system to prevent excessive bleeding when a pipe gets damaged (injured blood vessel).

Thrombus - Wikipedia

Here’s a breakdown:

  • Importance: Blood clotting is crucial to preventing blood loss after an injury.
  • Platelets: These are tiny cell fragments in your blood that clump together at the site of injury, forming an initial plug.
  • Clotting Cascade: This is a series of steps involving special proteins in your blood called clotting factors.
    • Platelet activation triggers these factors to work together like a chain reaction.
    • Each activated factor stimulates the next, forming a mesh of protein strands (fibrin) that traps blood cells, solidifying the clot and sealing the leak.

Blood Coagulation (Blood Clotting) - CBSE Class Notes Online - Classnotes123

Think of it like this:

  1. Injury: The pipe (blood vessel) gets a hole.
  2. Platelets: Like tiny repair crew members, they rush to the leak and clump together to form a temporary patch.
  3. Clotting Cascade: Imagine a bucket brigade where one protein bucket fills another, passing on the message.
  4. Fibrin Mesh: This protein mesh acts like a strong net, trapping blood cells and forming a clot that plugs the hole.

Abnormal Clotting (Thrombosis)

While clotting is essential, problems arise when:

  • Clots form too easily: This can block healthy blood vessels even without an injury.
  • Clots don’t dissolve naturally: Clots that persist can restrict blood flow to vital organs.

Deep Vein Thrombosis (DVT) | Warnings Signs & Treatment

These abnormal clots, called thrombosis, can be dangerous and lead to serious complications like:

  • Deep vein thrombosis (DVT): A blood clot in a deep leg vein.
  • Pulmonary embolism (PE): A blood clot that breaks off and travels to the lungs, blocking blood flow.
  • Stroke: A blood clot that blocks blood flow to the brain.

Blood Groups

ABO Blood Group System

Imagine tiny markers on your red blood cells: These markers, called antigens, can be of type A or B.

Blood Groups" Images – Browse 2,751 Stock Photos, Vectors, and Video | Adobe Stock

Your body also has special defenders: These are proteins called antibodies that can attack foreign antigens. Think of them as lookouts ready to react if something unrecognized enters.

  • Blood Type A: Red blood cells have A antigens and plasma (liquid part of blood) has anti-B antibodies.
  • Blood Type B: Red blood cells have B antigens and plasma has anti-A antibodies.
  • Blood Type AB: Red blood cells have both A and B antigens, but the plasma has no antibodies (universal recipient).
  • Blood Type O: Red blood cells have no antigens (A or B), but the plasma has both anti-A and anti-B antibodies (universal donor).

Transfusion Compatibility Matters

  • Incorrect matches can cause clumping of red blood cells, blocking blood vessels and leading to serious complications.
  • Doctors carefully check blood type to ensure transfused blood is compatible with the recipient’s immune system.

Rh Blood Group System

The Rh Factor: Another protein marker, the Rh factor, can be present (Rh positive ) or absent (Rh negative ) on red blood cells.

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Rh Incompatibility in Pregnancy:

  • If a mother is Rh negative and her baby is Rh positive (inherited from the father), the mother’s body can develop antibodies against the baby’s Rh factor.
  • Subsequent pregnancies can lead to complications like anemia or jaundice in the baby due to the mother’s immune system attacking the baby’s blood cells.

Key Points

  • Blood type is determined by inherited antigens (A, B) and antibodies (anti-A, anti-B).
  • ABO compatibility is crucial for safe blood transfusions.
  • Rh factor needs matching to prevent complications during pregnancy.

Circulatory System

Imagine a complex network of highways delivering vital supplies throughout your body. That’s exactly what your circulatory system does! Here’s a simplified explanation of its key parts and functions:

Circulatory system

Your Heart

Chambers: Think of your heart as a muscular pump with four chambers:

How many chambers are in our hearts, and what is the working system of each  chamber? - Quora

  • Upper chambers (atria): Two thin-walled chambers (left and right) that receive incoming blood.
  • Lower chambers (ventricles): Two thicker-walled chambers (left and right) that pump blood out with more force.


These one-way doors ensure blood flows in the right direction:

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  • Atrioventricular valves (tricuspid and mitral): Control flow between atria and ventricles.
  • Semilunar valves (aortic and pulmonary): Control flow out of the ventricles to arteries.

Blood Circulation

Two Loops: Your circulatory system has two main loops:

Circulatory System - Types of Blood Circulation Diagram | Quizlet


  • Pulmonary circulation: A short loop that takes blood low in oxygen (deoxygenated) from the heart to the lungs, picks up fresh oxygen, and returns the oxygenated blood back to the heart.
  • Systemic circulation: The main loop that carries oxygenated blood from the heart to all organs and tissues throughout the body, delivering oxygen and nutrients, and picking up waste products (carbon dioxide).

Blood Vessels

Biology of the Blood Vessels - Heart and Blood Vessel Disorders - MSD  Manual Consumer Version

  • Arteries: Strong, elastic vessels that carry oxygenated blood away from the heart to the body. Imagine them as highways delivering fresh supplies.
  • Veins: Wider vessels that carry deoxygenated blood back to the heart. Think of them as roads collecting waste products.
  • Capillaries: Microscopic vessels that connect arteries and veins, forming a dense network throughout your body. They allow oxygen, nutrients, and waste to be exchanged between the blood and tissues. Imagine these as narrow alleys where the deliveries and pickups happen.

Blood Donation and Safety

Why Donate Blood?

Saves Lives: Every donation can help up to 3 people in need during surgeries, accidents, or medical conditions. Blood cannot be manufactured, so voluntary donations are essential.

Blood Donation Vector Art, Icons, and Graphics for Free Download

Donating Blood

Eligibility Check:

  • Age (usually 17-65 years old).
  • Weight (minimum requirement varies).
  • General health (free from certain illnesses).
  • Prior travel or medical history may be reviewed.

Donation Process:

  • Registration: Answer questions about your health and lifestyle.
  • Blood Draw: Takes about 10-15 minutes.
  • Refreshments: Provided after donation to help with recovery.

Remember: Trained staff are present throughout the process to ensure your comfort and safety.

Safety First: Preventing Disease Transmission

  • Strict Screening: Donors are screened for diseases like HIV, Hepatitis B & C, and syphilis.
  • New & Sterile Equipment: Fresh needles and equipment are used for every donation.
  • Thorough Testing: Donated blood undergoes rigorous testing to ensure it’s free of viruses and bacteria.

Overall, blood donation is a safe and controlled procedure with minimal risks.


Human blood is the lifeblood of our existence, a remarkable fluid playing a multifaceted role in maintaining our health and well-being.

  • Composition: Blood is a complex mixture of plasma, a liquid component transporting vital substances, and cellular elements like red blood cells (oxygen carriers), white blood cells (immune defenders), and platelets (involved in clotting).
  • Function: Blood acts as a vital transport system, delivering oxygen and nutrients to cells, removing waste products, and aiding in the body’s defense mechanisms.
  • Blood Clotting: This crucial process prevents excessive blood loss after injury.
  • Blood Groups: The ABO and Rh systems determine blood group compatibility, essential for safe blood transfusions.
  • Circulatory System: Blood flows through a network of vessels, powered by the pumping action of the heart, ensuring continuous delivery to all parts of the body.


An adult human body typically holds around 5 liters (or about 1.3 gallons) of blood. This volume can vary slightly depending on factors like body size and gender.

Blood is a liquid tissue with two main components:

  • Plasma: A straw-colored liquid (about 55%) that carries water, proteins, nutrients, hormones, and waste products.
  • Blood cells: These specialized cells make up the remaining 45% and are further categorized into:
    • Red blood cells (erythrocytes): Carry oxygen throughout the body (around 40%).
    • White blood cells (leukocytes): Fight infection and disease (around 1%).
    • Platelets: Assist with blood clotting (less than 1%).

There are actually eight main blood types determined by the combination of proteins (antigens) present on red blood cells. These are:

  • A positive (A+)
  • A negative (A-)
  • B positive (B+)
  • B negative (B-)
  • AB positive (AB+)
  • AB negative (AB-)
  • O positive (O+)
  • O negative (O-)

A normal blood cell percentage refers to the relative proportion of different cell types in your blood.

  • Red blood cells: Typically range between 38% and 50% of total blood volume.
  • White blood cells: Normally make up less than 1% of your blood volume.
  • Platelets: Usually account for a very small percentage, less than 1%.

One unit of donated blood typically amounts to around 450 milliliters (almost 1 pint). This is because a whole blood donation collects not just red blood cells, but also plasma and other blood components.


  1. What is the primary function of human blood?

    • A) Transporting oxygen and nutrients
    • B) Regulating body temperature
    • C) Producing hormones
    • D) Fighting infections
  2. Which component of blood is responsible for carrying oxygen to the body tissues?

    • A) Platelets
    • B) Red blood cells
    • C) White blood cells
    • D) Plasma
  3. What is the liquid part of blood called?

    • A) Hemoglobin
    • B) Serum
    • C) Plasma
    • D) Erythropoietin
  4. Which blood type is known as the universal donor?

    • A) A
    • B) AB
    • C) O
    • D) B
  5. Which blood type is known as the universal recipient?

    • A) AB
    • B) O
    • C) A
    • D) B
  6. Which blood cells are responsible for clotting to stop bleeding?

    • A) Red blood cells
    • B) Platelets
    • C) White blood cells
    • D) Plasma
  7. Which organ is primarily responsible for producing blood cells in adults?

    • A) Liver
    • B) Kidneys
    • C) Bone marrow
    • D) Spleen
  8. What is the average lifespan of a red blood cell in the human body?

    • A) 1 day
    • B) 1 week
    • C) 120 days
    • D) 1 year
  9. Which component of blood plays a crucial role in the immune system and fights against infections?

    • A) Red blood cells
    • B) Platelets
    • C) White blood cells
    • D) Plasma
  10. What is the protein in red blood cells that carries oxygen called?

    • A) Hemoglobin
    • B) Globulin
    • C) Albumin
    • D) Fibrinogen
  11. Which of the following is NOT a type of white blood cell?

    • A) Neutrophils
    • B) Lymphocytes
    • C) Monocytes
    • D) Hemoglobin
  12. What is the process of blood cell formation called?

    • A) Hemostasis
    • B) Hemolysis
    • C) Hematopoiesis
    • D) Hemagglutination
  13. Which blood component is responsible for maintaining blood pressure and volume?

    • A) Red blood cells
    • B) White blood cells
    • C) Plasma
    • D) Platelets
  14. What is the scientific term for a low red blood cell count?

    • A) Anemia
    • B) Erythropenia
    • C) Thrombocytosis
    • D) Leukopenia
  15. What is the most abundant type of white blood cell in the human body?

    • A) Basophils
    • B) Neutrophils
    • C) Eosinophils
    • D) Lymphocytes
  16. Which blood cell is known as the “master regulator” of the immune system?

    • A) Basophils
    • B) Neutrophils
    • C) Lymphocytes
    • D) Monocytes
  17. Which vitamin is essential for the production of healthy red blood cells?

    • A) Vitamin C
    • B) Vitamin D
    • C) Vitamin B12
    • D) Vitamin A
  18. Which of the following is a symptom of high blood pressure?

    • A) Dizziness
    • B) Headache
    • C) Low heart rate
    • D) Blurred vision
  19. What is the term for the process of blood cell destruction?

    • A) Hemostasis
    • B) Hemolysis
    • C) Hematopoiesis
    • D) Hemagglutination
  20. Which blood component is responsible for carrying hormones and nutrients throughout the body?

    • A) Red blood cells
    • B) Platelets
    • C) White blood cells
    • D) Plasma

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