Experiment 4: Microscopic Study of Epithelial and Connective Tissue

• Epithelial tissue
• Connective tissue
• Muscular tissue
• Nervous tissue

Epithelial cells cover or line all body surfaces, cavities, and tubes (covering epithelia). They also form the functional units of secretory glands (glandular epithelia).

General Characteristics

• Closely attached to each other forming a protective barrier
• One free (apical) surface open to outside or internal cavity
• One fixed (basal) surface attached to connective tissue
• Avascular but nourished by underlying connective tissue
• Innervated
• Highly regenerative (e.g., sunburn, skinned knee)

Functions

• Protection from radiation, desiccation, toxins, pathogens, trauma
• Regulation and exchange of chemicals
• Secretion of hormones, sweat, mucus, enzymes
• Sensation
• Absorption (gut lining)
• Filtration (kidney)
• Formation of secretory glands

Classification of Epithelia

• Simple: One cell layer
• Stratified: More than one layer (named by apical cell shape)

• Squamous: Wider than tall
• Cuboidal: As tall as wide
• Columnar: Taller than wide

Types of Epithelial Tissue

1. Simple Squamous Epithelium
   Description: Single layer of flattened cells with disc-shaped nuclei
   Function: Passive transport of gases and fluids
   Location: Alveoli, mesothelium, endothelium
2. Simple Cuboidal Epithelium
   Description: Single layer of cubelike cells with spherical nuclei
   Function: Secretion and absorption
   Location: Kidney tubules, small gland ducts, ovary surface
3. Simple Columnar Epithelium
   Description: Single layer of tall cells with oval nuclei
   Types: Ciliated and non-ciliated
   Function: Absorption; secretion of mucus, enzymes
   Location: Digestive tract, gall bladder
4. Stratified Squamous Epithelium
   Description: Multilayered; surface cells squamous, basal cells cuboidal
   Function: Protection
   Location: Oral cavity, cervix, anal canal
5. Stratified Cuboidal Epithelium
   Description: Two layers of cube-like cells
   Function: Protection
   Location: Sweat, mammary, salivary gland ducts
6. Stratified Columnar Epithelium
   Description: Multilayered; superficial cells columnar
   Function: Protection and secretion
   Location: Male urethra (rare)
7. Pseudostratified Columnar Epithelium
   Description: Single layer; all cells touch basement membrane, nuclei at different levels
   Function: Mucus secretion and propulsion
   Location: Trachea lining
8. Transitional Epithelium
   Description: Dome-shaped cells; shape changes
   Function: Stretching and protection
   Location: Bladder, part of urethra

Connective tissues bind and support various parts of the body.

General Characteristics

• Abundant intercellular material, minimal cellular content
• Major component: Extracellular matrix (ECM)
• Contains cells, fibers, and ground substance

Functions

• Support and binding of tissues
• Fluid retention
• Defense against infection (macrophages, plasma cells, mast cells, WBCs)
• Fat storage

Types of Connective Tissue

1. Areolar Connective Tissue
   Description: Gel-like matrix with all fiber types; includes fibroblasts, macrophages, mast cells, WBCs
   Function: Phagocytosis, inflammation, fluid conveyance
   Location: Under epithelia, around capillaries
2. Adipose Tissue
   Description: Sparse matrix; packed adipocytes with displaced nuclei
   Function: Energy storage, insulation, organ protection
   Location: Under skin, around kidneys/eyeballs, abdomen, breasts
3. Reticular Tissue
   Description: Network of reticular fibers in loose ground substance
   Function: Internal skeleton for immune cells
   Location: Lymph nodes, bone marrow
4. Irregular Connective Tissue
   Description: Irregular collagen fibers, some elastic fibers; fibroblasts
   Function: Elasticity and support
   Location: Dermis, digestive tract submucosa, joints
5. Regular Connective Tissue
   Description: Parallel collagen fibers, few elastic fibers; fibroblasts
   Function: Muscle-to-bone and bone-to-bone attachment
   Location: Tendons, ligaments
6. Hyaline Cartilage
   Description: Firm matrix; chondroblasts in lacunae
   Function: Support, compression resistance
   Location: Embryonic skeleton, long bone ends, nose cartilage
7. Elastic Cartilage
   Description: Similar to hyaline but with more elastic fibers
   Function: Shape maintenance and flexibility
   Location: External ear (pinna)
8. Fibrocartilage
   Description: Predominantly collagen fibers; less firm matrix
   Function: Tensile strength, shock absorption
   Location: Intervertebral discs, knee joints
9. Bone
   Description: Hard, calcified matrix with collagen; vascularized
   Function: Support, protection, movement, mineral storage, blood formation
   Location: Skeleton
10. Blood
    Description: Liquid matrix with red and white blood cells
    Function: Transport of gases, nutrients, wastes
    Location: Blood vessels