Epithelial Tissue

Simple Epithelia (Consist of One Layer of Cells)

Simple epithelia are composed of a single layer of cells and are specialized for absorption, secretion, and filtration. The shape of the cells determines their specific function and location.

• Simple Squamous Epithelium:

  • Components: Single layer of flat cells

  • Function: Allows passage of materials by diffusion and filtration; secretes lubricating substances

  • Location: Air sacs of lungs, lining of heart, blood vessels, and lymphatic vessels

• Simple Cuboidal Epithelium:

  • Components: Single layer of cube-like cells

  • Function: Secretion and absorption

  • Location: Kidney tubules, ducts and secretory portions of small glands, ovary surface

• Simple Columnar Epithelium:

  • Components: Single layer of tall, column-like cells; may have cilia or goblet cells

  • Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus

  • Location: Non-ciliated: digestive tract, gallbladder; ciliated: small bronchi, uterine tubes

• Pseudostratified Columnar Epithelium:

  • Components: Single layer of cells of differing heights, may have cilia

  • Function: Secretion, particularly of mucus; propulsion of mucus by ciliary action

  • Location: Non-ciliated: male's sperm-carrying ducts; ciliated: trachea, upper respiratory tract

Stratified Epithelia (Consist of More Than One Layer of Cells)

Stratified epithelia are composed of two or more layers of cells, providing protection against abrasion and friction. The shape of the surface cells is used to name the tissue.

• Stratified Squamous Epithelium:

  • Components: Several layers; surface cells are flattened

  • Function: Protects underlying tissues in areas subject to abrasion

  • Location: Non-keratinized: moist linings of esophagus, mouth, vagina; keratinized: epidermis of skin

• Stratified Cuboidal Epithelium:

  • Components: Generally two layers of cube-like cells

  • Function: Protection

  • Location: Largest ducts of sweat glands, mammary glands, salivary glands

• Stratified Columnar Epithelium:

  • Components: Several cell layers; basal cells usually cuboidal, superficial cells elongated and columnar

  • Function: Protection and secretion

  • Location: Rare; small amounts in male urethra and in large ducts of some glands

• Transitional Epithelium:

  • Components: Resembles both stratified squamous and stratified cuboidal; surface cells dome-shaped or squamous-like, depending on degree of organ stretch

  • Function: Stretches readily and permits distension of urinary organ by contained urine

  • Location: Lines the ureters, bladder, and part of the urethra

Muscle Tissue

Types of Muscle Tissue

Muscle tissue is specialized for contraction and movement. There are three main types, each with distinct structural and functional characteristics.

• Skeletal Muscle: Responsible for voluntary movements; striated appearance due to organized actin and myosin filaments.

• Cardiac Muscle: Found only in the heart; striated; cells connected by intercalated discs for synchronized contraction.

• Smooth Muscle: Involuntary control; no striations; found in walls of hollow organs.

Example: Skeletal muscle is used to move limbs, cardiac muscle pumps blood, and smooth muscle moves food through the digestive tract.

Connective Tissue

Connective Tissue Proper

Connective tissue proper includes a variety of tissues that support, bind, and protect other tissues and organs. It is divided into loose and dense types, each with specific functions and locations.

• Proper connective tissue includes loose and dense types, as well as elastic, reticular, and adipose tissues.

• Specialized connective tissue includes cartilage, bone, and blood.

• Note: For fibrocartilage and elastic cartilage, collagen or elastic fibers are added to the base model hyaline cartilage.

Nervous Tissue

Structure and Function

Nervous tissue is specialized for communication via electrical and chemical signals. It consists of two main cell types: neurons and glial cells.

• Neurons: Large cells responsible for transmitting electrical impulses. They have a cell body, dendrites (receive signals), and axons (send signals).

• Glial Cells: Smaller supporting cells that protect, nourish, and support neurons.

• Processes: Extensions from the neuron cell body, which may be axons or dendrites.

• Spinal Cord Slide: Neurons are found in the central "H" or "butterfly" shaped zone of the spinal cord.

Example: Neurons in the brain and spinal cord process and transmit information, while glial cells provide structural and metabolic support.