Functions and Composition of Blood

Jessica's Symptoms and Test Results

Jessica presents with a low red blood cell (RBC) count characterized by microcytic RBCs, low hemoglobin, and low hematocrit levels. Additionally, there is evidence of hemoglobin in her feces. These symptoms suggest potential issues with hemoglobin production or a possible gastrointestinal bleed, which may warrant further investigation.

FUNCTIONS OF BLOOD

Learning Outcomes

Upon completion of this section, students should be able to:

  • State the functions of blood.

Overview of Blood's Significance

Blood has intrigued humans throughout history, with various civilizations viewing it as the "essence of life." The uncontrolled loss of blood can lead to death, conveying its critical role in survival. Cultural beliefs often attribute mystical qualities to blood, linking it to character and emotion, such as the concept of "blue blood" for nobility and "bad blood" for criminals. The scientific investigation of blood reveals both fascinating characteristics and essential functions necessary for life.

Essential Functions of Blood

  1. Transport of Gases, Nutrients, and Waste Products
    Blood serves as a primary medium for transporting various substances throughout the body. Oxygen is absorbed in the lungs and then delivered to cells for metabolism. Conversely, carbon dioxide, a byproduct of cellular respiration, is transported back to the lungs for exhalation. Additionally, blood carries nutrients, ions, and water from the digestive system to cells, while also transporting metabolic wastes to the kidneys for excretion.

  2. Transport of Processed Molecules
    Blood facilitates the movement of substances processed at various sites within the body. An example of this is the precursor to vitamin D, produced in the skin. It goes through the liver and kidneys before becoming active vitamin D, which is crucial for calcium absorption in the intestine. Another instance includes lactate from muscles during anaerobic respiration being transported to the liver for conversion into glucose.

  3. Transport of Regulatory Molecules
    Blood carries hormones and enzymes that play crucial roles in regulating bodily functions. These molecules are essential for communication between different parts of the body.

  4. Regulation of pH and Osmosis
    Blood contains buffers that maintain its pH in the range of 7.35 to 7.45, which is critical for proper cellular function. The osmotic composition of blood is vital for fluid and ion balance in the body.

  5. Maintenance of Body Temperature
    As blood flows through metabolically active areas, it absorbs heat from cellular activities. This heat is then dispersed to the body's surface, contributing to temperature regulation.

  6. Protection Against Foreign Substances
    Blood contains cells and chemicals that are integral components of the immune system, providing defense against pathogens and toxic substances.

  7. Clot Formation
    Blood clotting mechanisms prevent excessive blood loss when vessels are damaged, also playing a vital role in tissue repair and recovery following injuries.

COMPOSITION OF BLOOD

Learning Outcomes

After reviewing this section, students will be able to:

  • List the components of blood.

Overview of Blood Composition

Blood is categorized as a type of connective tissue composed of a liquid matrix known as plasma and formed elements, which include various cell types and fragments. Generally, plasma constitutes slightly over 55% of total blood volume, while formed elements comprise slightly less than 45%. The average blood volume in adult females is approximately 4 to 5 liters (L) and 5 to 6 L in adult males, representing about 8% of total body weight.

Components of Blood

  • Liquid Matrix (Plasma): Accounts for over 55% of blood volume.

  • Formed Elements: Constitute less than 45% of blood volume, primarily red blood cells (RBCs), white blood cells (WBCs), and platelets.

PLASMA

Learning Outcomes

This section should enable you to:

  • Name the components of plasma and describe their functions.

Description of Plasma

Plasma is a pale yellow fluid composed mostly of water (91%) and other components including proteins (7%) and miscellaneous substances (2%) such as ions, nutrients, gases, waste products, and regulatory substances.

Components of Plasma

  • Proteins:

    1. Albumin (58% of plasma proteins): Contributes significantly to osmotic pressure and plays a role in water balance between blood and tissues through osmosis.

    2. Globulins (38% of plasma proteins): Includes antibodies and complement proteins which are part of the immune response, as well as transport molecules carrying hormones.

    3. Fibrinogen (4% of plasma proteins): A crucial clotting factor that, when activated, transforms into fibrin to form blood clots.

  • Ions: Vital for osmotic pressure and membrane potentials, contributing to acid-base balance.

  • Nutrients: Provide energy and serve as building blocks for complex molecules.

  • Gases: Essential for aerobic respiration, including oxygen and carbon dioxide.

  • Waste Products: Include urea and ammonia salts, which are byproducts of protein metabolism.

  • Regulatory Substances: Such as enzymes and hormones that catalyze reactions and regulate various bodily functions.

Homeostasis of Plasma Composition

Typically, plasma volume and composition are relatively stable due to the balance between water intake and loss through various body systems. The concentrations of dissolved substances are closely regulated within narrow limits to maintain physiological functions.

FORMED ELEMENTS

Learning Outcomes

After completing this section, students should be able to:
A. Describe the origin and production of formed elements.
B. Describe the structure and function of red blood cells.
C. Describe the life history of a red blood cell.
D. Compare the structures and functions of the five types of white blood cells.
E. Describe the origin and structure of platelets.

Overview of Formed Elements

Formed elements constitute 45% of blood's composition, primarily including:

  1. Red Blood Cells (RBCs) or Erythrocytes (Erythro-, red + kytos, cell): The most abundant formed elements, representing about 95% of this component.

Further Details Needed

The uploaded transcript cuts off before detailing white blood cells and platelets. Continued study will further illuminate these essential aspects of blood's formed elements.