Essentials of Anatomy & Physiology   3/e   Seeley/Stephens/Tate
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Histology is the study of tissues.

Epithelial Tissue

• Epithelial tissue covers surfaces, usually has a basement membrane, has little extracellular material, and has no blood vessels.

Functions of Epithelia

• General functions of epithelia include protection, acting as barriers, and secretion and absorption of substances.

Classification of Epithelia

• Simple epithelium has one layer of cells, whereas stratified epithelium has more than one.
• Pseudostratified columnar epithelium is simple epithelium that appears to have two or more cell layers.
• Transitional epithelium is stratified epithelium that can be greatly stretched.

Structural and Functional Relationships

• Simple epithelium is involved with diffusion, secretion, or absorption. Stratified epithelium serves a protective role. Squamous cells function in diffusion or filtration. Cuboidal or columnar cells, which contain more organelles, secrete or absorb.
• A smooth, free surface reduces friction. Microvilli increase surface area, and cilia move materials over the cell surface.
• Desmosomes mechanically bind cells together, tight junctions form a permeability barrier, and gap junctions allow intercellular communication.
• Hemidesmosomes mechanically bind cells to the basement membrane.

Glands

• A gland is a single cell or a multicellular structure that secretes.
• Exocrine glands have ducts, and endocrine glands do not.

Connective Tissue

• Connective tissue holds cells and tissues together.
• Connective tissue has an extracellular matrix consisting of protein fibers, ground substance, and fluid.
• Collagen fibers are flexible but resist stretching, reticular fibers form a fiber network, and elastic fibers recoil.
• Blast cells form the matrix, cyte cells maintain it, and clast cells break it down.

Functions of Connective Tissue

• Connective tissues enclose and separate; connect tissues to one another; and support, store, cushion, insulate, transport, and protect.

Classification

• Connective tissue that has protein fibers as the primary feature of the extracellular matrix are dense connective tissue (tendons, ligaments, and dermis of skin), loose connective tissue ("loose packing" material of the body), and adipose tissue.
• Connective tissue that has protein fibers and ground substance as important features of the extracellular matrix are cartilage and bone.
• Connective tissue that has a fluid matrix is blood.

Muscle Tissue

• Muscle tissue is specialized to shorten, or contract.
• The three types of muscle tissue are skeletal, cardiac, and smooth muscle.

Nervous Tissue

• Nervous tissue is specialized to conduct action potentials (electrical signals).
• Neurons conduct action potentials, and neuroglia support the neurons.

Membranes

• Mucous membranes line cavities that open to the outside of the body (digestive, respiratory, excretory, and reproductive tracts). They contain glands and secrete mucus.
• Serous membranes line trunk cavities that do not open to the outside of the body (pleural, pericardial, and peritoneal cavities). They do not contain glands but do secrete serous fluid.
• Other membranes include the cutaneous membrane (skin), synovial membranes (line joint cavities), and periosteum (around bone).

Inflammation

• The function of the inflammatory response is to isolate and destroy harmful agents.
• The inflammatory response produces five symptoms: redness, heat, swelling, pain, and disturbance of function.

Tissue Repair

• Tissue repair is the substitution of viable cells for dead cells. Labile cells divide throughout life and can undergo regeneration. Stable cells do not ordinarily divide but can regenerate if necessary. Permanent cells have little or no ability to divide. If killed, repair is by replacement.
• Tissue repair involves clot formation, inflammation, formation of granulation tissue, and the regeneration or replacement of tissues. In severe wounds, wound contracture can occur

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