2E notes (tissue repair)

Integumentary System Overview

• The integumentary system is made up of three primary layers:

  • Epidermis: Provides protection.

  • Dermis: Offers strength and support, housing various structures.

  • Hypodermis (subcutaneous layer): Functions for insulation and anchoring.

Cell Death Mechanisms

• Two main types of cell death:

  • Necrosis:

  • Definition: Uncontrolled cell death due to injury, leading to inflammation and damage to surrounding tissues.

  • Apoptosis:

  • Definition: Programmed, regulated cell death that removes damaged or unnecessary cells without triggering inflammation.

  • Examples of Apoptosis:

    • Webbing removal between embryonic fingers.

    • Shedding of the uterine lining.

    • Elimination of precancerous cells.

  • Mechanism Involved in Apoptosis:

    • Enzymatic breakdown of cellular components:

    • DNA and cytoskeleton are degraded.

    • Organelles are broken down.

    • Cytoplasm condenses, and the membrane forms apoptotic blebs.

Tissue Adaptation Responses

• Tissues may change in response to various stimuli, resulting in:

• Regulated

  • Hyperplasia:

  • Increased cell number (e.g., breast tissue development during pregnancy).

  • Hypertrophy:

  • Increased cell size (e.g., growth of skeletal muscle).

  • Atrophy:

  • Decrease in size of tissues or organs (e.g., muscles that are immobilized).

  • Metaplasia:

  • Transformation from one mature cell type to another (e.g., changes in the airway of smokers).

• Dysregulated

  • Dysplasia:

  • Abnormal changes in cell growth, shape, or organization (e.g., changes due to HPV infection).

  • Neoplasia:

  • Uncontrolled growth of cells, which can result in either benign or malignant tumors.

Regeneration and Repair

• Normal regeneration entails replacing damaged cells with the same cell type, preserving function.

• Injury repair consists of three main processes:

  • Inflammation to initiate healing.

  • Regeneration when feasible.

  • Fibrosis occurs with extensive damage, leading to scar tissue formation that may reduce function.

Burns

• Burns are a leading cause of accidental death, classified into three categories:

  • Superficial Burns:

  • Damage is confined to the epidermis only.

  • Partial-thickness Burns:

  • Damage extends to the epidermis and part of the dermis.

  • Full-thickness Burns:

  • Damage penetrates through the epidermis, dermis, and into the hypodermis.

• Consequences of burns include fluid loss, increased risk of infection, and disruption of temperature regulation.

• Pain perception is influenced by the severity of the burn:

  • Superficial burns:

  • Vasodilation and increased permeability lead to nutrient delivery to the healing epidermis.

  • Partial-thickness burns:

  • Some sensory nerves may be destroyed, resulting in variable pain sensation.

  • Full-thickness burns:

  • Complete destruction of the dermis and sensory nerves results in reduced pain at first, as nerve endings are damaged.

Physiological Responses to Burns

• In severe burns, extensive vessel damage can lead to hypotension (low blood pressure).

• Feedback loop in response to low blood pressure:

  • Detected by stretch receptors, leading to
    the activation of the medulla oblongata.

  • Results in sympathetic response:

  • Increased heart rate (HR)

  • Vasoconstriction.

• Hypovolemic shock arises from significant fluid loss and is characterized by:

  • Tachycardia (increased heart rate).

  • Weak or absent peripheral pulses.

  • Cool, clammy skin due to vasoconstriction Decreased urine output as kidneys conserve fluid.

  • Altered mental status resulting from reduced cerebral perfusion.

Wound Healing Stages

• Wound healing occurs in a series of stages:

  • Blood vessels at the injury site bleed, and a clot forms a protective barrier.

  • Inflammation: White blood cells (WBCs742695) clean the wound area.

  • Granulation: New connective tissue forms with tiny blood vessels.

  • Reepithelization: The epithelium regenerates over the wound site.

  • Fibrosis: Scar tissue formation occurs through the action of fibroblasts; scar tissue is collagen-rich but often lacks the same full function as the original tissue.

  • Vessel permeability: allows large plasma proteins to enter tissue to, defend against pathogens, draw water into the tissue to maintain fluid balance

Scarring and Healing Considerations

• Scarring is most likely to occur with deep burns, classified as partial-thickness or full-thickness burns.

• Lines of Cleavage: Collagen fibers are oriented in specific, predictable directions.

  • Surgical incisions made parallel to these lines tend to heal faster compared to incisions made perpendicular to the lines, which may result in slower healing and a higher likelihood of scarring.

• Stretch Marks:

  • Result from tearing of the dermis due to stretching collagen fibers beyond their capacity.