Epithelial Tissue

Fundamental Tissue Types of the Human Body

  • In the human body, cells are organized into tissues, and each tissue serves a specific function.
  • There are four main types of fundamental tissues (tejidos humano fundamentales):
    • Epithelial tissue (Tejido Epitelial)
    • Connective tissue (Tejido Conectivo)
    • Muscle tissue (Tejido Muscular)
    • Nerve tissue (Tejido Nervioso)

Epithelial Tissue

  • Overview & Primary Functions:

    • Epithelial tissue (designated as A) covers the body surface and lines internal organs.
    • It executes seven main physiological functions:
    • Protection: Protects the outer and inner surfaces of the body (e.g., skin epidermis).
    • Absorption: Takes up nutrients and fluids (e.g., small intestine and large intestine).
    • Transport of Material: Facilitates surface transport mediated by cilia.
    • Secretion: Performed by specialized cellular structures (e.g., glands).
    • Sensory Stimuli: Detects and transmits sensory inputs.
    • Excretion: Eliminates waste products (e.g., renal tubes / kidney tubules).
    • Gas Exchange: Enables gas diffusion (e.g., pulmonary alveoli).

  • Structural Classification Principles:

    • Epithelial tissues are classified into main groups based on two structural criteria:
    • Number of Cell Layers (Strata / Capas):
      • Simple: Consists of a single layer of cells.
      • Stratified: Consists of two or more layers of cells.
      • Pseudostratified (asemeja/similar): Appears stratified but consists of a single layer (1 layer) resting on the basement membrane without true multi-layered stacking (no head).
    • Shape of Cells in the Outermost Layer:
      • Squamous (Escamoso): Flat cells.
      • Cuboidal (Cúbico): Cube-shaped cells of equal height and width.
      • Columnar (Cilíndrico): Tall, rectangular, or pillar-like cells.

  • Simple Epithelium:

    • Formed by a single cell layer resting on the basement membrane.
    • Subdivided according to the height and width of the cell:
    • Simple Squamous Epithelium (A1): Composed of flat cells that protect the body.
    • Simple Cuboidal Epithelium (A3): Composed of cube-shaped cells that form glands and kidney tubules.
    • Simple Columnar Epithelium (A2): Composed of tall cells that absorb nutrients in the digestive tract.

  • Stratified Epithelium:

    • Formed by two or more cell layers.
    • Subdivided based on the shape of the cell in its outermost or superficial layer.
    • Most frequent and classified into two major categories based on keratinization:
    • Not Keratinized: Superficial cells conserve their nuclei (e.g., lining of the vagina or esophagus).
    • Very Keratinized: No nuclei remain in the outermost cell layer of the epithelium (e.g., skin epidermis).

  • Pseudostratified Epithelium and Special Subtypes:

    • Consists of basal and cylindrical cells that both rest on the basement membrane.
    • Only cylindrical cells reach the luminal surface.
    • Subtypes identified:
    • A) Cylindrical or Columnar Pseudostratified Epithelium.
    • B) Pseudostratified Cylindrical Epithelium with Stereocilia: Specific to the epididymis.
    • C) Transitional Epithelium: The specialized epithelium of the urinary tract, also called Urothelium.

  • Apical Surface Specializations:

    • Cilia:
    • Mobile cellular projections.
    • Act as local defenses of the respiratory system.
    • Responsible for the transport of the fertilized egg to the uterine cavity.
    • Microvilli:
    • Digitiform (finger-like) projections of the apical surface of epithelial cells.
    • Contain an internal cross-linked microfilament axis.
    • The intestinal epithelium is lined by epithelial cells with microvilli that form a brush border, indicating an absorptive function.

Connective Tissue

  • Overview & Structure:

    • Connective tissue (designated as D) supports, binds, and protects the body.
    • Composed of cells embedded within an Extracellular Matrix (ECM):
    • Matrix consists of a viscous solution mixture.
    • Contains fibers (collagen and elastin) providing structural connection and support.

  • Vascularization and Innervation:

    • Unlike epithelial tissue, connective tissue cells receive:
    • Lymphatic vessels
    • Blood vessels
    • Direct nerves

  • Subtypes of Connective Tissue:

    • Loose Connective Tissue (Laxo):
    • Fibroblasts are the primary cell type, recognized by their oval nuclei.
    • Fibers consist of thin elastic fibers and thick collagen beams/bundles.
    • Dense Irregular Connective Tissue:
    • Contains thick collagen fibers that are irregular, entwined, and wavy.
    • Features abundant elastic fibers and collagen bundles.
    • Cartilage (D2):
    • Made of chondroblasts (D1), which help maintain structure.
    • Bone (D4) (Hueso):
    • Made of osteoblasts (D3), which form and strengthen bone.
    • Tendons (D6):
    • Made of tendon-forming cells (D5).
    • Connect muscle to bone.
    • Ligaments (D7):
    • Connect bone to bone.
    • Fat / Adipose Tissue (D9/Da) (Grasa):
    • Made of adipose cells (D8).
    • Store energy and provide insulation.
    • Blood (Sangre):
    • Includes Red Blood Cells (D10) (carry oxygen).
    • Includes White Blood Cells (D11) (defense/immune function).
    • Includes Platelets (D12) (help clotting).

Muscle Tissue

  • Muscle tissue (designated as B) is responsible for movement throughout the body.
  • Composed of muscle cells (B1).
  • Muscle cells are long and contract to move parts of the body, especially in the arms and legs.

Nerve Tissue

  • Nerve tissue (designated as C) transmits signals throughout the body.
  • Made of nerve cells (C1), also called neurons, which carry nerve impulses.

Document Identifiers and Source Metadata

  • Institutional Header / Motto: Todo a Jesús por María… (MARISTAS / DAC)
  • Source Entry Dates and Clave Tracking Identifiers:
    • Date: 09/08/26 | Clave: 335-28 | DAC
    • Date: 09/07/26 | Clave: 335-18
    • Date: 09/07/26 (07/26) | Clave: 335-28 | Reference Code: 2/022945
    • Date: 09/07/26 | Clave: 335-28
    • Date: 09/10/26 | Clave: 335-28