AE

Complete Study Guide: Tissues, Integument, and Homeostasis

Complete Study Guide: Tissues, Integument, and Homeostasis

I. Four Major Tissue Types

  • Epithelial Tissue:

    • Definition: Tissue made of tightly packed cells that are avascular (lacking blood vessels) and capable of regenerating quickly.
    • Structural Characteristics:
    • Apical Surface: Faces the lumen (interior space) or the external environment.
    • Basal Surface: Attached to the basement membrane, which anchors the epithelium to connective tissue.
    • Functions:
    • Protection: Acts as a barrier to protect underlying structures.
    • Secretion: Produces substances such as sweat, oil, or digestive enzymes.
    • Absorption: Takes in nutrients or substances from the environment.
    • Filtration: Allows certain substances to pass through while blocking others.

  • Connective Tissue:

    • Definition: The most abundant tissue type in the body, made up of cells that are widely spaced apart.
    • Extracellular Matrix (ECM): Composed of fibers (collagen, elastin, reticular) and ground substance.
    • Types of Cells:
    • Resident Cells: Include fibroblasts, adipocytes, and mesenchymal cells.
    • Wandering Cells: Include macrophages, mast cells, plasma cells, and leukocytes.
    • Functions:
    • Binding: Connects different tissues and organs together.
    • Support: Provides structural support to organs and structures.
    • Transport: Transports substances throughout the body (e.g., blood).
    • Protection: Cushions and protects the organs.

  • Muscle Tissue:

    • Definition: Composed of elongated, contractile fibers with a rich blood supply.
    • Types:
    • Skeletal Muscle:
      • Characteristics: Striated, under voluntary control, and multinucleated.
      • Location: Attached to bones, enabling voluntary movement.
    • Cardiac Muscle:
      • Characteristics: Striated, involuntary control, and features intercalated discs for electrical signaling.
      • Function: Pumps blood throughout the body.
    • Smooth Muscle:
      • Characteristics: Non-striated, involuntary, with a single nucleus.
      • Location: Found in the walls of hollow organs such as the intestines and blood vessels.

  • Nervous Tissue:

    • Components:
    • Neurons: Excitable cells that send and receive impulses.
    • Glial Cells: Support and protect neurons; play roles in nourishing neurons and maintaining homeostasis.
    • Functions:
    • Communication: Transmits signals throughout the body.
    • Integration: Processes information and directs responses.
    • Control: Regulates body functions through signaling.

II. Epithelium Details

  • Apical Surface: Exposed to the lumen or outside environment, crucial for its protective and absorptive functions.
  • Basal Surface: Anchored to the basement membrane, providing stability and structural integrity.
  • Transitional Epithelium:
    • Location: Found in the urinary bladder.
    • Function: Allows for stretching and expansion as the bladder fills with urine.
  • Cilia: Hair-like structures that move substances, such as mucus in the respiratory tract, aiding in clearing pollutants and pathogens.

III. Connective Tissue

  • Extracellular Matrix (ECM): Composed of ground substance and fibers, providing support and structure.
  • Fibers:
    • Collagen: The most abundant fiber, known for its strength and durability.
    • Elastin: Provides elasticity and flexibility to tissues.
    • Reticular: Forms a supportive mesh that helps maintain the structure of organs.
  • Resident Cells:
    • Fibroblasts: Responsible for producing collagen and other fibers.
    • Adipocytes: Fat cells that store energy.
    • Mesenchymal Cells: Stem cells that can differentiate into various connective tissue cells.
  • Wandering Cells:
    • Macrophages: Involved in defense and cleanup, engulfing pathogens and debris.
    • Mast Cells: Release histamine during inflammatory responses.
    • Plasma Cells: Produce antibodies in response to immune challenges.
    • Leukocytes: White blood cells that are part of the immune system.

IV. Muscle Tissue

  • Skeletal Muscle:
    • Characteristics: Striated appearance, voluntary control, composed of long, multinucleated cells.
    • Function: Connects to bones to facilitate movement.
  • Cardiac Muscle:
    • Characteristics: Striated, branched, under involuntary control; contains intercalated discs for synchronization of contractions.
    • Function: Pumps blood autonomously, works continuously without fatigue.
  • Smooth Muscle:
    • Characteristics: Non-striated, involuntary, single nucleus; capable of sustained contractions.
    • Location: Found in the walls of hollow organs, such as the intestines and bladder.

V. Nervous Tissue

  • Neurons:
    • Characteristics: Excitable cells that transmit impulses; consist of a cell body, axon, and dendrites.
  • Glial Cells:
    • Functions include supporting neurons, providing nutrients, and maintaining homeostasis in neural environments.

VI. Body Membranes

  • Mucous Membrane:
    • Function: Lines passageways that open to the outside environment, involved in secretion and absorption.
    • Example: Gastrointestinal (GI) tract lining.
  • Serous Membrane:
    • Structure: Composed of a double layer with serous fluid in between.
    • Locations: Pleura (lung cavity), pericardium (heart cavity), peritoneum (abdominal cavity).
  • Cutaneous Membrane:
    • Definition: Skin, which provides protection against environmental hazards.
  • Synovial Membrane:
    • Function: Lines joints, secreting synovial fluid for lubrication and shock absorption.

VII. Glands

  • Endocrine Glands:
    • Characteristics: Ductless glands that secrete hormones directly into the bloodstream.
  • Exocrine Glands:
    • Definition: Glands that secrete substances into ducts that transport them to epithelial surfaces.
    • Modes of Secretion:
    • Merocrine: Secretes via exocytosis; cells remain intact after secretion.
    • Apocrine: Secretes by pinching off part of the cell, which then regenerates.
    • Holocrine: Ruptures the entire cell, releasing its contents and destroying the cell.
  • Exocrine Structure:
    • Composed of a duct and a secretory portion; can be classified as simple (one duct) or compound (multiple ducts), tubular (tube-shaped) or alveolar (sac-like).

VIII. Response Pathway

  • Components:
    • Receptor: Detects the stimulus and sends signals.
    • Control Center: Processes the information received from receptors.
    • Effector: Carries out a response.
  • Types of Feedback:
    • Negative Feedback: Mechanism that reduces or eliminates changes, maintaining a setpoint (e.g., temperature, blood glucose regulation).
    • Positive Feedback: Mechanism that amplifies or increases a process until a specific endpoint occurs (e.g., childbirth, blood clotting).
  • Response Pathway Flow:
    • Stimulus → Receptor → Control Center → Effector → Response.

IX. Homeostasis

  • Setpoint: The desired target value for a physiological variable (e.g., human body temperature is approximately 37°C).
  • Regulated Variables:
    • Temperature, blood glucose, blood pressure, pH, and electrolytes are maintained within certain limits.
  • Disruptions: Main consequences can lead to disease conditions such as heat stroke, hypothermia, and diabetes.
  • Compensation Mechanisms:
    • Include physiological processes like sweating, shivering, vasodilation (widening of blood vessels), and vasoconstriction (narrowing of blood vessels) to help restore homeostasis.

X. Integumentary System

  • Functions:
    • Protection against environmental agents, temperature regulation, sensation (perception of stimuli), vitamin D synthesis, and excretion.
  • Interactions:
    • Engages with the immune system (defense), nervous system (sensation), circulatory system (nutrient and waste transport), and skeletal system (structural support).
  • Epidermis Layers:
    • Basale Layer: Base layer where mitosis occurs to produce new cells.
    • Spinosum Layer: Contains desmosomes that join cells together.
    • Granulosum Layer: Involves keratinization, where cells begin to die and keratin protein is produced.
    • Lucidum Layer: Present only in thick skin areas (e.g., palms, soles).
    • Corneum Layer: Composed of dead, keratinized cells that form a protective barrier.
  • Cell Types in Epidermis:
    • Keratinocytes: Produce keratin protein for skin structure and protection.
    • Melanocytes: Produce melanin pigment for skin coloration and UV protection.
    • Langerhans cells: Play a role in immune defense.
    • Merkel Cells: Function as touch receptors for sensation.
  • Dermis Layers:
    • Papillary Layer: Composed of areolar connective tissue; includes dermal papillae that create fingerprints.
    • Reticular Layer: Composed of dense irregular connective tissue; contains glands and hair roots.
  • Hypodermis:
    • Definition: Subcutaneous layer below the skin; composed of adipose and areolar connective tissue.
    • Note: Not technically part of the integument but supports skin functions.

XI. Tissue Repair

  • Steps in Tissue Repair:
    • Inflammation: Body's initial response to injury, which includes swelling, redness, warmth, and pain.
    • Regeneration: Replacement of damaged tissue with new tissue.
    • Fibrosis: Formation of scar tissue that replaces normal tissue after injury.
  • Cells Involved in Repair:
    • Fibroblasts: Produce collagen to reform the extracellular matrix.
    • Macrophages: Clean up debris and pathogens.
    • Epithelial Stem Cells: Responsible for regenerating epithelium during repair.
  • Granulation Tissue: A temporary connective tissue that forms during repair, characterized by a rich supply of blood vessels.
  • Outcome: Repaired tissue is often less functional than the original due to the presence of scar tissue.

XII. Tissue Modifications

  • Hyperplasia: Increase in cell number within a tissue, often in response to stimuli.
  • Hypertrophy: Increase in the size of individual cells within a tissue.
  • Atrophy: Decrease in size or number of cells due to disuse or decreased demand.
  • Metaplasia: Replacement of one tissue type with another, often as an adaptive response.
  • Dysplasia: Abnormal growth or development of cells, which can be a precursor to cancer.
  • Neoplasia: Uncontrolled growth leading to the formation of tumors, can be benign or malignant.

XIII. Lines of Cleavage

  • Definition: Orientation of collagen fibers in the dermis, critical for surgical considerations.
  • Implications: Surgical incisions made parallel to the lines of cleavage tend to heal better and result in less scarring compared to perpendicular incisions.

XIV. Burns

  • Consequences of Burns:
    • Hypovolemic Shock: Severe fluid loss due to damage to the skin barrier.
  • Types of Burns:
    • Superficial Burns: Affect the epidermis only; characterized by pain and redness.
    • Deep Burns: Affect the dermis and subcutaneous layers; may result in less pain due to nerve destruction.
  • Management Concerns: Significant burns can disrupt fluid balance, circulation, thermoregulation, and increase the risk of infection.