Blood as a Tissue - Grade 11 Life Sciences

BLOOD AS A TISSUE

Definition of Blood

  • Blood is described as a vital fluid necessary for transporting nutrients to all organs and tissues in the body and for carrying away waste materials.

  • The total blood volume in an adult human body is approximately 5-6 liters.

Composition of Blood

  • Blood is composed of two main components:

    • Plasma

    • Blood cells

Proportions in a Drop of Blood

  • Blood Cells: comprise 45% of blood volume.

    • Red blood cells (RBCs): Approximately 250 million per drop.

    • White blood cells (WBCs): Approximately 375,000 per drop.

    • Platelets: Approximately 16 million per drop.

  • Plasma: comprises 55% of blood volume.

    • Contains 91% water, 7% proteins, and 2% other solutes (ions, hormones, and gases).

BLOOD PLASMA

Characteristics of Blood Plasma

  • Plasma is defined as the liquid component of blood in which cells are suspended.

  • Mostly made up of water but contains essential proteins necessary for life.

  • Appears as a watery, straw-colored liquid.

  • Contains dissolved substances including:

    • Nutrients

    • Waste materials

    • Ions

    • Hormones

    • Gases

Important Proteins Found in Plasma

  • Fibrinogen: Essential for blood clotting.

  • Albumen: Helps maintain osmotic pressure in the blood.

  • Antibodies (immunoglobulins): Proteins necessary to combat pathogens.

FUNCTIONS OF BLOOD PLASMA

  • Blood plasma serves various transport functions, including:

    1. Carrying blood cells.

    2. Transporting carbon dioxide to the lungs as bicarbonate ions.

    3. Delivering nutrients throughout the body.

    4. Conveying urea from the liver to the kidneys for excretion.

    5. Distributing hormones from endocrine glands to various tissues.

    6. Transmitting heat from muscles and the liver to regulate body temperature.

    7. Transporting blood clotting factors (e.g., calcium ions, fibrinogen, and prothrombin).

    8. Carrying antibodies, which are critical for the immune response against pathogens.

TYPES OF BLOOD CELLS

  • Blood is primarily composed of:

    • Red Blood Cells (Erythrocytes)

    • White Blood Cells (Leukocytes)

    • Platelets

Red Blood Cells (Erythrocytes)

Characteristics

  • Comprise approximately 95% of blood cells.

  • Produced in red (spongy) bone marrow.

  • Lifespan is about 120 days before being broken down in the liver and spleen.

  • The structure is described as:

    • Biconcave discs, increasing surface area for gas exchange.

    • Contains hemoglobin, which is responsible for the red color and oxygen transport.

    • Lacks a nucleus and has few organelles, enhancing flexibility.

Functions of Red Blood Cells

  • Primarily tasked with transporting oxygen from the lungs to the body.

  • Oxygen binds to iron in hemoglobin to form oxyhemoglobin, giving blood its bright red color.

  • Secondary function includes transporting a small amount of carbon dioxide back to the lungs, where it binds to hemoglobin to form carbaminohemoglobin.

White Blood Cells (Leukocytes)

Characteristics

  • There are significantly fewer WBCs compared to RBCs, with a ratio of 700 RBCs for every 1 WBC.

  • WBCs are generally larger than RBCs.

  • Produced in the red bone marrow, spleen, and lymph nodes.

  • Lifespan varies greatly, typically only a few days to a few hours.

Structure of White Blood Cells

  • Display irregular shapes.

  • Composed of:

    • Large nucleus

    • Colourless cytoplasm

  • Types:

    1. Granulocytes: Characterized by a large lobed nucleus and numerous granules (e.g., neutrophils).

    2. Agranulocytes: Smaller and have an unlobed nucleus (e.g., lymphocytes, monocytes).

Functions of White Blood Cells

  • Play a vital role in defending the body against diseases and infections:

    • Phagocytes (e.g., neutrophils and monocytes) engulf and digest bacteria, foreign particles, and cellular debris via phagocytosis.

    • Monocytes transform into macrophages in connective tissues to enhance their phagocytic ability.

    • Lymphocytes generate antibodies and antitoxins that neutralize pathogens.

Platelets

Characteristics

  • Smallest cellular component of blood.

  • Enclosed by a membrane, but lack a nucleus.

  • Contain granules that hold substances crucial for blood clotting.

Functions of Platelets

  • Initiate the clotting process (thrombus formation).

  • In case of a blood vessel injury:

    • Platelets adhere to the edges of the wound and to one another, forming a plug to halt bleeding.

    • Release chemicals that activate fibrinogen and other clotting proteins, leading to the development of a blood clot.

    • Facilitate the healing of the blood vessel.

CONCLUSION

  • Understanding blood as a tissue is crucial for recognizing its vital functions in human physiology such as transport, immune response, and healing processes.

LEARNING ACTIVITY

  • Students are encouraged to complete Learning Activity 12 on pages 98-99 as a reinforcement of the material covered.