2.1 Epithelial Tissue

Epithelial tissue covers and lines all body surfaces, including internal cavities and organ surfaces. The defining structural feature is that all cells rest on a basement membrane and the tissue is avascular. Simple epithelium (single layer) is classified by cell shape: squamous (flat — diffusion in alveoli and capillaries), cuboidal (cube — secretion/absorption in kidney tubules), columnar (tall — secretion/absorption in the gut), ciliated columnar (cilia — particle clearance in trachea, ovum movement in oviducts), and glandular (secretory — goblet cells and salivary glands). Compound epithelium (multiple layers) is protective and found in skin, pharynx, and buccal cavity.

2.2 Connective Tissue

The most abundant tissue type, defined by an extensive extracellular matrix. Loose connective tissue subtypes: areolar (semi-fluid matrix with fibroblasts, mast cells, macrophages — repair and support) and adipose (fat storage, insulation). Dense connective tissue: regular tendons and ligaments (collagen-parallel) and irregular dermis (collagen-random). Specialized: cartilage (chondrocytes in lacunae, chondroitin sulfate matrix; three types: hyaline, elastic, fibrocartilage), bone (osteocytes in concentric lamellae, Haversian system, calcium phosphate matrix), blood (fluid matrix = plasma; RBCs, WBCs, platelets).

2.3 Muscular Tissue

Three types compared across five properties — striation, voluntary control, nuclear count, cell shape, and special features. Skeletal: striated, voluntary, multinucleated, cylindrical, fatigable. Smooth: non-striated, involuntary, uninucleated, spindle-shaped, slow sustained contraction. Cardiac: striated, involuntary, uni/binucleated, branched, intercalated discs, autorhythmic. The most-tested distinction: cardiac is striated + involuntary, which contradicts the common assumption that all striated muscles are voluntary.

2.4 Neural Tissue

Neurons (cyton + dendrites + axon) transmit electrical impulses. Neuroglia support neurons: Schwann cells (PNS myelination), astrocytes (CNS support), oligodendrocytes (CNS myelination), microglia (immune defense). Neural tissue does not regenerate significantly after injury, which is clinically significant.

2.5 Frog Anatomy (Rana tigrina)

Circulatory: 3-chambered heart (2 atria + 1 ventricle) with sinus venosus and truncus arteriosus; hepatic and renal portal systems present. Respiratory: skin (cutaneous), buccal cavity (buccopharyngeal), and lungs (pulmonary) — three simultaneous routes. Excretory: mesonephric kidneys, ureotelic; cloaca as common exit for digestive, excretory, and reproductive products. Nervous: brain with 10 pairs of cranial nerves. Reproductive: external fertilization; male has vocal sacs and nuptial pads.