BU MAMS COT: Cartilage, Bone, Epithelia, and Connective Tissues

Epithelial Polarity (Apical vs. Basal)

Apical domain faces lumen or exterior, often bearing microvilli or cilia; basal domain anchors to basement membrane via hemidesmosomes.

Simple Squamous Epithelium

Single layer of flat cells specialized for rapid diffusion and filtration; found in lung alveoli, endothelium, and mesothelium.

Simple Cuboidal Epithelium

Single layer of cube-like cells specialized for secretion and absorption; found in kidney tubules and small gland ducts.

Simple Columnar Epithelium

Single layer of tall rectangular cells often featuring microvilli or cilia; found lining the gastrointestinal tract.

Pseudostratified Columnar Epithelium

Appears stratified due to staggered nuclear heights, but all cells attach to the basement membrane; found in the respiratory tract.

Transitional Epithelium (Urothelium)

Stratified epithelium featuring dome-shaped surface cells capable of significant distension; found exclusively in the urinary tract.

Exocrine vs. Endocrine Glands

Exocrine glands secrete products through ducts onto surfaces; endocrine glands are ductless and secrete hormones directly into capillaries.

Merocrine (Eccrine) Secretion

Release of products via exocytosis without cellular damage or loss of cytoplasm; most common exocrine mechanism (e.g., sweat glands).

Holocrine Secretion

Entire cell accumulates secretory product and disintegrates/ruptures to release contents; exemplified by sebaceous glands.

Collagen Type I vs. Type II

Type I provides tensile strength in bone, skin, and tendons; Type II resists compression primarily within cartilage extracellular matrix.

Elastin & Elastic Fibers

Composed of an amorphous elastin core wrapped in fibrillin microfibrils; allows tissues like the aorta and vocal cords to stretch and recoil.

Reticular Fibers (Type III Collagen)

Thin, branching argyrophilic fibers forming a supportive stroma in lymphoid organs, liver, and bone marrow; stained black with silver.

Fibroblasts

Primary resident cells of connective tissue proper; synthesize collagen, elastic, and reticular fibers, and ground substance components.

Macrophages (Histiocytes)

Phagocytic antigen-presenting cells derived from blood monocytes; feature irregular surfaces, abundant lysosomes, and bean-shaped nuclei.

H&E and PAS Staining in Connective Tissue

H&E stains nuclei blue and proteins pink; Periodic acid-Schiff (PAS) stains carbohydrates, mucins, and basement membranes magenta.

Loose (Areolar) Connective Tissue

Flexible, highly cellular tissue with abundant ground substance and loosely arranged fibers; supports epithelia and underlying organs.

Dense Regular Connective Tissue

Packed parallel collagen bundles with flattened fibroblasts squeezed between them; provides strong unidirectional tensile resistance (tendons).

Dense Irregular Connective Tissue

Randomly interwoven collagen bundles providing multi-directional tensile strength; found in organ capsules and the dermis.

Neutrophils

Multilobed (3-5 segments) nucleus with pale granules; primary acute phagocytic responders to bacterial infection (most abundant leukocyte).

Eosinophils

Bilobed nucleus with bright red/orange cytoplasmic granules containing major basic protein; combats parasitic infections and allergic responses.

Basophils

Rare granulocytes with heavily basophilic, dark purple granules obscuring a bilobed nucleus; store histamine and heparin for inflammation.

Lymphocytes & Monocytes

Agranulocytes; lymphocytes feature a spherical nucleus with a thin rim (adaptive immunity); monocytes are large, becoming tissue macrophages.

Hyaline Cartilage ECM & Appearance

Glassy ECM rich in Type II collagen and aggrecan; chondrocytes sit in lacunae singly or in isogenous groups; found in trachea and joints.

Elastic Cartilage

Similar to hyaline cartilage but contains a dense network of branching elastic fibers within the ECM; maintains flexible shape (ear, epiglottis).

Fibrocartilage

Hybrid tissue combining dense connective tissue and hyaline cartilage with thick Type I collagen bundles; lacks a perichondrium (discs).

Perichondrium

Dense irregular connective tissue capsule surrounding hyaline and elastic cartilage; contains fibrous and inner chondrogenic layers.

Interstitial vs. Appositional Cartilage Growth

Interstitial growth occurs via division of existing chondrocytes within lacunae; appositional growth occurs via differentiation of perichondrial cells.

Chondrocytes and Lacunae

Mature cartilage cells trapped within small cavities called lacunae; responsible for maintaining the surrounding extracellular matrix.

Osteoblasts

Cuboidal bone-forming cells on bone surfaces that synthesize osteoid (unmineralized ECM) and direct its subsequent calcification.

Osteocytes

Mature bone cells enclosed in mineralized bone matrix within lacunae; communicate with neighbors via cytoplasmic processes in canaliculi.

Osteoclasts

Large, multinucleated bone-resorbing cells derived from monocyte lineages; feature a ruffled border and reside in Howship lacunae.

Periosteum

Fibrous outer sheath of bone containing an outer fibrous layer and inner cellular osteogenic layer; essential for bone repair and growth.

Osteon (Haversian System)

Structural unit of compact bone consisting of concentric lamellae surrounding a central Haversian canal with blood vessels and nerves.

Volkmann Canals vs. Haversian Canals

Haversian canals run longitudinally down the center of osteons; Volkmann canals run transversely, connecting canals and the periosteum.

Intramembranous Ossification

Direct conversion of mesenchymal connective tissue into bone without a cartilage intermediate; forms flat bones of the skull and clavicle.

Endochondral Ossification

Bone formation via a hyaline cartilage model precursor that is progressively calcified, resorbed, and replaced by bone; forms long bones.

Epiphyseal Growth Plate Zones

Zones of endochondral growth: resting, proliferating, hypertrophic, calcified cartilage, and ossification zones driving bone elongation.

Synovial Joint Structure

Diarthrosis joint featuring articulating bone ends covered by articular cartilage, enclosed by a joint capsule lined with synovial membrane.

Articular Cartilage in Synovial Joints

Specialized hyaline cartilage lacking a perichondrium; provides a smooth, frictionless weight-bearing surface nourished by synovial fluid.

Synovial Membrane (Synovium)

Specialized vascular membrane lining joint cavities; contains type A (macrophage-like) and type B (fibroblast-like) synoviocytes.