Anatomy & Physiology - Tissue Organization

Tissue Organization

Overview of Tissues

  • Epithelial Tissue
    • Composition: Tightly packed cells with minimal extracellular matrix
    • Functions: Covers body and organ surfaces, lines body cavities and organ cavities, forms glands
    • Subtypes:
    • Simple Epithelium:
      • Types: Simple squamous, simple cuboidal, simple columnar, pseudostratified columnar
    • Stratified Epithelium:
      • Types: Stratified squamous, stratified cuboidal, stratified columnar, transitional
  • Connective Tissue
    • Composition: Contains cells, protein fibers, and ground substance
    • Functions: Binds, supports, and protects other tissues and organs
    • Subtypes:
    • Connective Tissue Proper:
      • Types: Loose (areolar, adipose, reticular), Dense (regular, irregular, elastic)
    • Supporting Connective Tissue:
      • Types: Cartilage (hyaline cartilage, elastic cartilage, fibrocartilage), Bone
    • Fluid Connective Tissue:
      • Types: Blood, lymph
  • Muscle Tissue
    • Composition: Cells that may be cylindrical, branching, or spindle-shaped; contain contractile proteins (myofilaments)
    • Functions: Moves the skeleton, organ walls, or body structures; contractile, conductive, elastic, extensible, and excitable
    • Subtypes:
    • Skeletal
    • Cardiac
    • Smooth
  • Nervous Tissue
    • Composition: Contains neurons and glial cells
    • Functions: Neurons transmit nerve impulses and process information; glial cells support, protect, and nourish neurons

Classification of Epithelia

Structure
  • Apical Surface: The top layer of cells, facing an open space.
  • Lateral Surface: The sides where cells connect to each other.
  • Basement Membrane: A thin layer that anchors the epithelium to the underlying connective tissue.
  • Basal Surface: The bottom of the epithelium that faces the basement membrane.
Types
  • Simple Epithelium: Single layer of cells
  • Stratified Epithelium: Multiple layers of cells
Classification by Shape
  • Squamous Cell: Flat and thin cells
  • Cuboidal Cell: Short, cube-like cells
  • Columnar Cell: Tall, column-like cells

Simple Epithelia

Types and Functions
  • (a) Simple Squamous Epithelium
    • Structure: Single layer of thin, flat cells; nucleus bulges at the center
    • Function: Allows rapid diffusion and filtration; secretion in serous membranes
    • Location:
    • Air sacs in lungs (alveoli)
    • Lining of lumen of blood vessels (endothelium)
    • Serous membranes of body cavities (mesothelium)
  • (b) Simple Cuboidal Epithelium
    • Structure: Single layer of cells as tall as they are wide; spherical and centrally located nucleus
    • Function: Absorption and secretion; forms secretory tissue of most glands and small ducts
    • Location:
    • Lining of kidney tubules
    • Thyroid gland follicles
    • Surface of ovary
  • (c) Nonciliated Simple Columnar Epithelium
    • Structure: Taller than wide with an oval-shaped nucleus, possibly with microvilli and goblet cells
    • Function: Absorption and secretion
    • Location:
    • Lining of most gastrointestinal tract (stomach, small intestine, and large intestine)
  • (d) Ciliated Simple Columnar Epithelium
    • Structure: Ciliated cells taller than wide with possibly goblet cells
    • Function: Secretion of mucin and movement of mucus via cilia
    • Location: Larger bronchioles and uterine tubes
  • (e) Ciliated Pseudostratified Columnar Epithelium
    • Structure: Varying heights but all cells connect to the basement membrane; has goblet cells and cilia
    • Function: Protection and secretion of mucin, and movement of mucus
    • Location: Major airways of the respiratory tract
  • (f) Nonciliated Pseudostratified Columnar Epithelium
    • Structure: Varying heights but lacking goblet cells and cilia
    • Function: Protection
    • Location: Rarely seen; lining of parts of male urethra and epididymis

Stratified Epithelia

Types and Functions
  • (a) Keratinized Stratified Squamous Epithelium
    • Structure: Multiple layers with basal cells being cuboidal; superficial cells are squamous, keratinized, and dead
    • Function: Protection from abrasion
    • Location: Epidermis of skin
  • (b) Nonkeratinized Stratified Squamous Epithelium
    • Structure: Multiple layers of living cells; all have nuclei and organelles
    • Function: Protection from abrasion
    • Location: Oral cavity, part of pharynx, larynx, esophagus, vagina, and anus
  • (c) Stratified Cuboidal Epithelium
    • Structure: Two or more layers of cuboidal cells at the apical surface
    • Function: Protection and secretion
    • Location: Ducts of most exocrine glands and ovarian follicles
  • (d) Stratified Columnar Epithelium
    • Structure: Two or more layers of taller than wide cells at the apical surface
    • Function: Protection and secretion
    • Location: Large ducts of salivary glands, conjunctiva of the eye, lining of male urethra
Transitional Epithelium
  • Structure: Varies from cuboidal (relaxed) to flattened (distended); binucleated cells are present
  • Function: Accommodates changes in urine volume
  • Location: Urinary bladder, ureters, and part of the urethra

Exocrine Gland Secretion Methods

  • (a) Merocrine Gland
    • Method: Normal exocytosis without damage to the secreting cell
  • (b) Apocrine Gland
    • Method: Pinching off of the apical portion of the cell to release its contents
  • (c) Holocrine Gland
    • Method: Rupturing of the entire cell releasing its contents

Connective Tissue Proper: Loose Connective Tissue

  • (a) Areolar Connective Tissue
    • Structure: Scattered fibroblasts in viscous ground substance; abundant blood vessels
    • Function: Protects tissues and binds skin to deeper tissues
    • Location: Dermis, subcutaneous layer, surrounding organs, nerve cells, and muscle cells
  • (b) Adipose Connective Tissue
    • Structure: Closely packed adipocytes, large fat droplet
    • Function: Stores energy; insulates and cushions organs
    • Location: Subcutaneous layer and around some organs
  • (c) Reticular Connective Tissue
    • Structure: Meshwork of reticular fibers, fibroblasts, and leukocytes
    • Function: Provides stroma to lymphatic organs
    • Location: Spleen, lymph nodes, bone marrow
Dense Connective Tissue
  • (a) Dense Regular Connective Tissue
    • Structure: Densely packed collagen fibers with limited blood vessels
    • Function: Attaches bones to bones and muscles to bones
    • Location: Tendons and ligaments
  • (b) Dense Irregular Connective Tissue
    • Structure: Randomly arranged collagen fibers, more ground substance than in regular dense tissue
    • Function: Withstands stresses in all directions
    • Location: Dermis of skin, epimysium over skeletal muscle, perichondrium over cartilage
  • (c) Elastic Connective Tissue
    • Structure: Limited fibroblasts between densely packed elastic fibers
    • Function: Allows for stretching and recoil
    • Location: Walls of elastic arteries, trachea, vocal cords

Supporting Connective Tissue: Cartilage

  • (a) Hyaline Cartilage
    • Structure: Glassy ground substance with irregularly arranged chondrocytes
    • Function: Provides support, forms most of the fetal skeleton
    • Location: Nose, trachea, bronchi, larynx, and costal cartilage
  • (b) Fibrocartilage
    • Structure: Large chondrocytes in lacuna and numerous parallel collagen fibers
    • Function: Resists compression; acts as shock absorber
    • Location: Intervertebral discs, menisci of joints
  • (c) Elastic Cartilage
    • Structure: Abundant elastic fibers with closely packed chondrocytes
    • Function: Maintains shape with flexibility
    • Location: External ear and epiglottis

Bone

  • Structure: Osteocytes within lacuna; organized in osteons with central canals
  • Function: Provides support, protects organs, stores minerals
  • Location: Throughout the body in all bones

Blood

  • Structure: Contains erythrocytes, leukocytes, and platelets in liquid plasma
  • Function: Transports gases, supports immune response, and assists in clotting
  • Location: Blood vessels and heart