An Overview of Blood

Overview of Blood

Introduction to Anatomy & Physiology II

  • Focus: In-depth exploration of the human body, including components, functions, diseases, and conditions.
  • Prerequisite: Completion of Anatomy & Physiology I recommended; prior knowledge is assumed.
  • Objective: Understanding the organization and function of various organ systems.

Course Content Areas

  • Systems covered:
    • Cardiovascular
    • Endocrine
    • Lymphatic
    • Respiratory
    • Digestive
    • Urinary
    • Reproductive
  • Goal: Ability to explain basic body organization and understand relevant diseases/conditions.

Functions of Blood

  • Blood serves multiple crucial functions:
    1. Transportation: Transfers nutrients, gases (O₂ and CO₂), and waste products between body cells and external environments.
    2. Defense: Protects against pathogens and other external threats through leukocyte action and clotting mechanisms.
    3. Maintenance of Homeostasis: Regulates body temperature, pH, and electrolyte levels.

Detailed Functions

3a. Transportation
  • Nutrient absorption occurs in the digestive tract and is processed by the liver before distribution through the bloodstream.
  • Oxygen enters the blood via the lungs and is transported throughout the body by the heart.
  • Carbon dioxide and other metabolic wastes are carried to excretory organs for removal (lungs for CO₂, kidneys and liver for other wastes).
3b. Defense
  • Various leukocytes function in:
    • Combatting infections by neutralizing bacteria and viruses.
    • Destroying potentially cancerous cells with mutated DNA.
  • Platelets and plasma proteins initiate blood clotting to prevent excessive blood loss from damaged vessels.
3c. Maintenance of Homeostasis
  • Homeostasis refers to maintaining internal equilibrium or balance.
    • Utilizes sensors (neurons and hormonal signals) to detect environmental changes and send responses from the control center (brain/spinal cord) to effectors (muscles, organs).
    • Feedback Mechanisms:
    • Negative Feedback: Mitigates the initial stimulus (e.g., temperature regulation during exercise).
    • Positive Feedback: Enhances the stimulus (e.g., childbirth contractions).

Example Homeostatic Response

  • Temperature Regulation: During exercise, blood redistributes towards cooler body surfaces (skin) to dissipate heat; during cold exposure, blood flow is minimized to preserve core temperature.

Composition of Blood

  • Whole Blood: Comprises both formed elements (cells) and plasma (fluid).
  • Formed Elements:
    • Erythrocytes: Responsible for gas exchange (O₂ and CO₂).
    • Leukocytes: Immune response; fewer in number than RBCs.
    • Thrombocytes: Platelets involved in clotting.

4. Blood Components

  • Hematocrit: Ratio of erythrocytes to total blood volume.
    • Varies: General values 36–50% (around 45% is typical for adults).
    • Female levels: 37–47%; Male levels: 42–52%.
Hematocrit Test
  • Conducted via centrifugation to separate blood components - erythrocytes settle at the bottom, buffy coat (leukocytes & thrombocytes) in the middle, plasma on top.

Characteristics of Blood

  • Color: Red when oxygenated; darker when deoxygenated due to hemoglobin.
  • Viscosity: Approximately five times greater than water, impacting blood pressure and flow (resistance).
  • Temperature: Slightly higher than body temperature (~38°C or 100.4°F).
  • pH: Averages 7.4 (normal range 7.35-7.45), slightly alkaline compared to pure water (pH 7.0).
  • Volume: Approx. 8% of body weight:
    • Males: 5-6 liters
    • Females: 4-5 liters.

Blood Plasma

  • Primarily water (92%); also contains proteins and solutes.

6a. Plasma Proteins

  • Types:
    • Albumin (54%): Most abundant, regulates osmotic pressure, transports lipids.
    • Globulins (35-38%): Includes alpha (transport functions) and gamma globulins (immune function).
    • Fibrinogen (4–7%): Critical for clotting.

6b. Other Plasma Solutes

  • Electrolytes (Na⁺, K⁺, Ca²⁺), dissolved gases (O₂, CO₂, N₂), nutrients (vitamins, lipids), wastes contribute to 1% of plasma volume.

Major Blood Components

  • Plasma: 43-63%

    • Water: 92%
    • Proteins: 7%
    • Albumin: 54-60%
    • Globulins: 35-38%
    • Fibrinogen: 4-7%

  • Formed Elements: 37-54%

    • Erythrocytes: 99%
    • Leukocytes: <1%
    • Thrombocytes: <1%

Career Connection

  • Phlebotomy: Art of drawing blood; uses venipuncture for larger samples or capillary punctures for small ones.
  • Medical Labs: Employ MTs and MLTs for blood testing, essential for diagnosis and treatment monitoring.

Summary of Key Terms

  • Blood: Fluid connective tissue for transportation, defense, and homeostasis.
  • Plasma: Liquid component containing proteins and solutes.
  • Formed Elements: Cellular components including erythrocytes, leukocytes, and thrombocytes.
  • Hematocrit: Red blood cell percentage in blood sample.
  • Buffy Coat: Layer of leukocytes and platelets in centrifuged blood.