Tissues and Histology Review

BSC2085L: Tissues

Histology

  • Histology is the study of tissues and cells under a microscope.
  • Histopathology involves the diagnosis and study of diseases of the tissues, examining tissues and/or cells under a microscope.
  • Histopathologists are responsible for making tissue diagnoses and aiding clinicians in patient care management.
  • There are four basic tissue types, categorized by morphology and function:
    • Epithelial tissue
    • Connective tissue
    • Muscle tissue
    • Nervous tissue

Epithelial Tissue

  • Epithelial tissue can be classified into three principal categories based on cell shape:
    1. Squamous epithelium: Cells that are wider than they are tall.
    2. Cuboidal epithelium: Cells whose height and width are approximately equal.
    3. Columnar epithelium: Cells that are taller than they are wide.
  • Key functions of epithelial tissue include:
    • Protection of surfaces
    • Absorption of substances
    • Secretion of fluids and hormones
    • Acting as a barrier to control permeability and selective transfer of materials
    • Facilitating filtration
    • Sensory reception and gland formation

Stratified Squamous Epithelium

  • Stratified squamous epithelium has protective functions, including:
    • Protection against microorganisms
    • Protection against water loss
  • The epidermis, or outer skin layer, consists of stratified squamous epithelial cells.
  • This type of epithelium protects the body from physical and chemical damage by forming a barrier of keratinized cells.
  • Goblet cells aid in maintaining a protective layer of surface tissue through secretions, such as mucus, that form a barrier.

Transitional Epithelium

  • Transitional epithelium, also known as urothelium, consists of multiple layers of cells that flatten when stretched.
  • It is found lining most of the urinary tract and enables bladder expansion.
  • In its relaxed state, cells typically appear cuboidal or columnar; when stretched, they resemble squamous cells.
  • Transitional epithelium is found in the renal calyces, ureters, bladder, and urethra.

Pseudostratified Columnar Epithelium

  • Pseudostratified columnar epithelium serves functions such as:
    • Protection
    • Absorption
    • Secretion
  • It is characterized by trapping and moving foreign particles via mucus and cilia, prominently observed in the respiratory tract.
  • This epithelium can be ciliated or non-ciliated, affecting its specific functions.

Muscle Tissue

  • There are three types of muscle tissues:
    1. Cardiac Muscle:
    • Located in the walls of the heart.
    • Appears striped (striated) and is under involuntary control.
    1. Smooth Muscle:
    • Involuntary, non-striated muscle found in the walls of internal organs (e.g., gastrointestinal tract).
    1. Skeletal Muscle:
    • Voluntary, striated muscle attached to bones, allowing for conscious movement.
  • Four major functions of muscle tissue include:
    • Movement
    • Posture
    • Joint stability
    • Heat production

Skeletal Muscle

  • Skeletal muscle is characterized as voluntary, striated, and attached to bones, providing for conscious movement.
  • This specialized tissue consists of long, multinucleated muscle cells called muscle fibers or myocytes organized into bundles (fascicles).
  • It also incorporates other tissue types, including connective tissue, nervous tissue, and blood vessels.

Cardiac Muscle

  • Cardiac muscle tissue (myocardium) forms the heart.
  • It functions involuntarily, maintaining blood circulation through rhythmic contraction.
  • The major function is to pump blood, delivering oxygen and nutrients.
  • Specialized cardiac cells (cardiomyocytes) contract rhythmically, regulated by the SA node (the heart's pacemaker).
  • Electrical signals spread via Purkinje cells for coordinated ventricular contraction, while intercalated discs with gap junctions synchronize electrical and mechanical activity for consistent blood flow.

Smooth Muscle

  • Smooth muscle is involuntary and non-striated, present in the walls of internal organs such as the GI tract, uterus, and blood vessels.
  • Functions of smooth muscle include:
    • Propelling substances through hollow organs
    • Regulating organ diameter
    • Maintaining muscle tone with reduced energy expenditure
  • It is classified into two categories:
    • Single-unit: Contracts synchronously (due to gap junctions)
    • Multi-unit: Contracts independently with distinct neural input

Nervous Tissue

  • Nervous tissue is located in the brain, spinal cord, and nerves.
  • It is essential for coordinating and controlling body activities, including:
    • Stimulating muscle contraction
    • Creating environmental awareness
    • Influencing emotions, memory, and reasoning

Connective Tissue

  • Connective tissues provide support, binding, and connection for other tissues and organs, serving roles such as:
    • Acting as structural frameworks
    • Providing cushioning
    • Transporting nutrients
    • Storing energy
    • Protecting the body
  • Major types include:
    • Connective Tissue Proper (loose and dense)
    • Cartilage
    • Bone
    • Blood
    • Adipose Tissue

Connective Tissue Proper

  • Composed of cells, fibers, and ground substance; can be divided into two types:
    • Loose connective tissue: Fewer fibers, abundant ground substance.
    • Dense connective tissue: More fibers, less ground substance.
  • Functions include:
    • Providing structural support
    • Binding body parts
    • Storing fat for energy
    • Transporting nutrients
    • Supporting immune defense and tissue repair

Loose Connective Tissue

  • Characterized by a loose arrangement of collagen and elastic fibers suspended in a semi-fluid ground substance.
  • Functions:
    • Binding tissues together
    • Supporting organs
    • Facilitating nutrient and waste diffusion
    • Sites for immune responses
  • Main types include:
    • Areolar tissue: Highly vascularized, with extensive ground substance.
    • Adipose tissue: Stores fat.
    • Reticular tissue: Forms soft organ frameworks.

Adipose Tissue

  • Specialized type of loose connective tissue consisting mainly of adipocytes (fat cells).
  • Functions include:
    • Energy reserve
    • Thermal insulation
    • Organ protection
    • Endocrine functioning (hormone secretion)
  • Types of adipose tissue:
    • White adipose tissue (WAT): Stores lipids.
    • Brown adipose tissue (BAT): Generates heat via thermogenesis.
    • Beige fat: Develops from WAT, exhibiting thermogenic properties.

Reticular Connective Tissue

  • Composed of reticular fibers (type III collagen) and reticular cells, forming a delicate mesh-like framework (stroma).
  • Provides structural support for soft organs and blood cells.
  • Found in lymphoid organs (lymph nodes, spleen, Peyer's patches), liver, red bone marrow, and endocrine glands.

Dense Connective Tissue

  • Provides support and protection, holding structures in place.
  • Includes types such as ligaments, tendons, the inner skin layer, and sclera (the white outer eye layer).

Supporting Connective Tissues

  • Supporting connective tissues include bone, cartilage, and dense connective tissues.
  • Functions:
    • Bone: Forms the skeletal structure for support
    • Cartilage: Offers flexible support in joints, nose, and ribs
    • Tendons and ligaments: Connect muscles to bones and bones to other bones, respectively.

Bone Tissue Locations

  • Bone consists of compact bone, spongy bone, and bone marrow.
  • Compact Bone: Outer layer of bone.
  • Spongy Bone: Located at bone ends and contains red marrow.
  • Bone Marrow: Located centrally in bones, is highly vascularized.

Blood

  • Circulates throughout the circulatory system via blood vessels (arteries, veins, capillaries).
  • Blood cells originate in the red bone marrow, particularly in larger bones.
  • Red Blood Cells (Erythrocytes): Responsible for transporting oxygen and carbon dioxide.
  • White Blood Cells: Part of the immune system, fighting infections and diseases. Types include:
    • Granulocytes (neutrophils, eosinophils, and basophils)
    • Monocytes
    • Lymphocytes (T cells and B cells)

Exercise Activity

  1. List the four primary tissue types of the body.
  2. What is the name of the noncellular layer that connects epithelial tissue to deeper tissues?
  3. Name the three general cell shapes of epithelial tissue.
  4. What is the specific name for multiple layers of flattened epithelial cells?
  5. What epithelial tissue lines the inside of the urinary bladder?
  6. Identify muscle tissues with the following features:
    A) Striated & Voluntary:
    B) Striated & Involuntary:
    C) Nonstriated & Involuntary: _
  7. The heart is primarily composed of what type of muscle?
  8. The muscles of the arms consist mostly of which type?
  9. Name the five types of white blood cells.

Activities

  • Complete the questions from Chapter 4 Exercise on pages 61-64.