Histology Lecture Notes

Overview

• Subject emphasis on differentiation between various epithelial cells, glands, muscles, cartilages, lymphoid tissues, and specific structures like the kidney, pancreas, and cerebral cortex.

Epithelia and Epitheloid Cells

• Epithelium: Covers body walls and cavities from inside and outside.
• Epitheloid Cells: No free surface, may have basement membrane. Examples: Leydig cells, lutein cells, islands of Langerhans, adrenal gland, anterior pituitary, epithelial reticular cells of the thymus, sebaceous glands.

Sebaceous Gland (Holocrine Gland)

• Cells: Rounded with central nuclei, filled with lipid vacuoles, appearing clear when washed with alcohol.
• Located at the base of hair follicle.
• Secretion Type: Holocrine (cell disintegration).

Types of Glands

• Apocrine Glands: Apex secretion via membrane-bound vesicles. Ex: Mammary gland.
• Merocrine Glands: Exocytosis secretion. Ex: Submandibular gland.

Salivary Glands

• Mixed Salivary Gland: Both serous and mucous acini present.
• Submandibular Gland: Predominantly serous.
• Submandibular Gland: Predominantly mucous.
• Serous Demilunes: Histological artifacts showing a mucous acinus capped by serous cells.
• Features: Tall acinar cells, basal nuclei for mucous acini; pyramidal cells, basophilic cytoplasm, zymogen granules for serous acini.

Skeletal Muscle

• Sarcomere: Functional unit from Z-line to Z-line.
• A Band: Represents myosin filament length (constant during contraction).
• I Band: Represents non-overlapped actin length (shortens during contraction).
• H Zone: Central region, decreases during contraction.
• Identification: Striations, peripheral nuclei.

Cardiac Muscle

• Characteristics: Branched fibers, centrally placed oval nuclei, faint striations.
• Intercalated Discs: Composed of fascia adherens, desmosomes, and gap junctions, facilitating ionic movement (functional syncytium).

Cartilage Types

• Hyaline Cartilage: Chondrocytes in clusters (cell nests), pericondrium present, type II collagen.
• Fibrocartilage: Chondrocytes in rows, type I collagen, no pericondrium.
• Elastic Cartilage: Elastic fibers not visible in H&E stain, perichondrium present, individual elastic fibers visible with special stains.

Lymphoid Tissues

• Lymph Node: Contains capsule, trabeculae, subcapsular sinus, lymphatic nodules in cortex, paracortex (T-lymphocytes), medullary cords and sinuses.
• Spleen: Lacks cortex/medulla distinction, contains lymphatic nodules (white pulp), splenic arteries, red pulp indicating open circulation.
• Palatine Tonsil: Stratified squamous epithelium, lymphatic nodules, presence of crypts.
• Thymus: No lymphatic nodules, divided into lobules by septa, presence of Hassall's corpuscles (central hyaline mass surrounded by epithelial cells).

Thyroid Gland

• Active Thyroid Follicle: Cuboidal cells with scalloped borders of colloid.
• Inactive: Squamous cells, smooth borders of colloid.
• Parafollicular Cells: Pale staining, derived from neural crest cells.

Pancreas and Parotid Gland

• Pancreas: Serous acini with centroacinar cells, Islets of Langerhans present (predominantly in tail).
• Parotid Gland: Predominantly serous acini, no centroacinar cells.

Gastrointestinal Tract

• Esophagus: Stratified squamous epithelium, esophageal glands located in submucosa.
• Duodenum: Closely packed villi, Brunner's glands in submucosa.

Kidney

• Glomerulus: Presence of Bowman's space.
• Tubules: Proximal convoluted tubule (hazy lumen), distal convoluted tubule (clear lumen).

Cerebellar Cortex

• Layers: Molecular (stellate and basket cells), Purkinje (Purkinje cells), Granular (Golgi and granule cells).
• Largest collection of inhibitory neurons: Excitatory only granular cells.

Taste Buds and Tongue Papillae

• Filliform Papillae: Conical keratin projections, no taste buds.
• Fungiform Papillae: Vertical indentations with taste buds on surface.
• Foliate Papillae: Taste buds within vertical furrows.
• Circumvallate Papillae: Mushroom-shaped, taste buds within furrows.