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Capillary Types and Functions

• Types of Capillaries

  • There are three types of capillaries based on permeability:

    • Continuous Capillary

      • Least permeable and most common type.

      • Found in skin, muscles, lungs, and the central nervous system.

      • Contains structures called intracellular blebs through which materials can pass.

      • Tight junctions prevent materials from passing, providing protection (e.g., brain).

    • Fenestrated Capillary

      • Contains pores or fenestrations that increase permeability.

      • Found in organs involved in absorption such as the digestive tract.

      • Pores make them appear like Swiss cheese.

    • Sinusoid Capillary

      • Most permeable type with large intercellular clefts and incomplete basement membranes.

      • Found in liver, bone marrow, spleen, and adrenal glands.

• Permeability and Pressure

  • As blood moves through capillaries, pressure decreases, allowing plasma and small proteins to leak out into the interstitial fluid.

  • Some of the leaked plasma can return to the capillary, although some remains in the interstitial fluid, which contributes to lymph formation.

Blood and Lymphatic System

• Blood Vessels vs. Lymphatic Vessels

  • Blood vessels contain blood (which includes red blood cells and large proteins), while lymphatic vessels carry lymph, which contains interstitial fluid devoid of red blood cells and large proteins.

  • Lymph is essentially interstitial fluid that has entered lymphatic vessels, differing only in location.

• Lymphatic System's Role

  • Transports lymph and plays a critical role in the immune response.

  • The lymphatic system and the immune system are closely linked but not the same.

Immune System Overview

• Function of the Immune System

  • Protects against foreign material (pathogens) that can cause damage.

  • Immunocompromised individuals lack effective immune responses, making them susceptible to infections (e.g., cancer patients).

Immunity Types

• Innate Immune Defenses (non-specific)

  • First line of defense includes skin barriers and mucous membranes (found in open body cavities).

    • Skin: forms a physical and chemical barrier (e.g., sweat is slightly acidic).

    • Mucous Membranes: trap particles and are often ciliated to expel trapped materials.

  • Other innate responses include inflammation and phagocytosis.

• Adaptive Immune Defenses (specific)

  • More complex and tailored to specific pathogens. Will explore this further in later discussions.

Phagocytosis

• Definition

  • A type of endocytosis where a cell engulfs pathogens (e.g., bacteria).

• Process of Phagocytosis

  1. Pathogen is engulfed by the plasma membrane of the cell, forming a phagosome.

  2. Lysosome fuses with the phagosome, introducing enzymes to digest the pathogen.

  3. Leftover material may be expelled through exocytosis.

Complement Fixation

• Overview

  • A key nonspecific immune response mainly directed against bacterial infections.

  • About 20 blood proteins (complement proteins) become activated in response to infection.

  • Activation leads to three outcomes:

    1. Enhanced Inflammation: Release of histamines increases blood flow and permeability.

    2. Opsonization: Complement proteins coat pathogens to promote phagocytosis.

    3. Membrane Attack Complex (MAC): Proteins insert into the pathogen's membrane, causing cell lysis.

• The complement system enhances overall immune responses through increased vascular permeability and attracting phagocytes.

Inflammation Process

• Inflammation and Healing

  • Cardinal signs of inflammation include heat, redness, pain, and swelling.

  • Increased blood flow (hyperemia) leads to heat and redness; vascular permeability leads to swelling (exudate).

  • Pain signals that an area needs attention, promoting localized rest and care.

  • Healing occurs as inflammation resolves; acute inflammation is short-term, while chronic inflammation can lead to tissue damage.