Histology Essentials: Epithelial and Connective Tissue Structure

Epithelial Tissue: Simple Layers

• Simple Squamous Epithelium (Protection + Filtration)
  • Locations: Blood vessels, lymph vessels, Bowman's capsule, inner surface of the tympanic membrane, endocardium, pulmonary alveoli.
• Simple Cuboidal Epithelium (Secretion + Absorption)
  • Locations: Ovarian surface, posterior surface of the lens, renal tubules.
• Simple Columnar Epithelium
  • Non-ciliated: Digestive tract (stomach to anus), microvilli, ducts of mucous glands.
  • Ciliated: Upper respiratory tract, Fallopian tubes, ependyma, paranasal sinuses.
  • Function: Performs and receives stimuli, movement (cilia), cough, and sneezing.

Epithelial Tissue: Stratified Layers

• Stratified Squamous Epithelium
  • Keratinized: Skin.
  • Non-keratinized: Mouth, esophagus, epiglottis.
• Stratified Cuboidal Epithelium (Protection)
  • Locations: Sweat glands, male urethra.
• Stratified Columnar Epithelium (Protection + Secretion)
  • Locations: Some glands, anal mucosa, part of the conjunctival mucous membrane.
• Transitional Epithelium (Protection)
  • Locations: Bladder, urethra, and ureters.
• Pseudostratified Columnar Epithelium
  • Ciliated: (Secretion + Movement/Support) Respiratory tract.
  • Non-ciliated: (Secretion + Movement/Support) Epididymis, testes, some glands.

Glandular Secretion Mechanisms

• Holocrine: Produce, store, and secrete; the cell dies upon release.
• Merocrine: Production followed by exocytosis.
• Apocrine: Cytoplasm accumulates in the secretory product, bursts, and releases the contents.

Connective Tissue Classification

Includes loose, dense, cartilage, bone, blood, and lymph tissues.

Loose Connective Tissue

• Areolar Tissue:
  • Locations: Hypodermis, between muscle masses, lamina propria of digestive, respiratory, and urinary tracts, adventitia of vessels, under serous epithelium, stroma of organs.
  • Matrix: Lax fibers, various cells.
  • Function: Binding, packaging organs, defense, wound healing.
• Adipose Tissue (Fat):
  • Structure: Formed by adipocytes. Stores triglycerides (TG).
  • Function: Energy storage and support.
• Reticular Tissue:
  • Structure: Formed by reticular fibers.
  • Locations: Lymphoid and hematopoietic organs.

Dense Connective Tissue

Characterized by many collagen and elastic fibers, few cells, and minimal ground substance.

• Regular: Ligaments and tendons.
• Irregular: Dermis, periosteum, capsules surrounding organs.
• Elastic: Ligamentum flavum, walls of large arteries, lung tissue.

Bone Tissue

• Compact Bone:
  • Structure: Formed by osteons, ground substance, collagen fibers, mineral salts (calcium carbonate, calcium phosphate), lacunae containing osteocytes, canaliculi (for nutrient exchange), Haversian canals (for blood vessels).
• Spongy Bone:
  • Structure: Organized in trabeculae, composed of the same components as compact bone.

Cartilage Tissue

Composition: Collagen + Elastic fibers and chondroitin sulfate. Cells: Chondrocytes.

• Hyaline Cartilage: Articular cartilage, respiratory passages, costal cartilage.
• Fibrocartilage: Intervertebral discs, meniscus.
• Elastic Cartilage: Epiglottis and ear pinna.

Blood Tissue

• Matrix: Plasma.
• Blood Cells: Red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes).

Lymph Tissue

Auxiliary system that carries lymph (rich in proteins and lipids). Drains into the venous system.