Tissues and Histology

Tissue Structure and Function

• Tissue is a group of cells with similar structure and function, along with extracellular substances between the cells.

• Histology is the microscopic study of tissue structure, focusing on the organization and the relationship between structure and function.

• Examination of tissues provides valuable health information; for instance, cancer can be identified and classified based on characteristic tissue changes.

• Biopsy involves removing tissue samples for diagnostic purposes, aiding in determining appropriate therapy.

Epithelial Tissues

• Epithelial tissues cover surfaces, lack blood vessels, and have a basement membrane.

• Functions include protection, acting as barriers, permitting passage of substances, secretion, and absorption.

• Classification based on the number of cell layers and cell shape includes simple, stratified, pseudostratified columnar, and transitional epithelium.

• Structural and functional relationships: Simple epithelium is involved in diffusion, secretion, or absorption, while stratified epithelium plays a protective role.

Glands

• Glands can be single cells or multicellular structures that secrete substances.

• Exocrine glands have ducts, while endocrine glands do not.

Connective Tissues

Connective Tissue Functions

• Connective tissues hold cells and tissues together, with an extracellular matrix comprising protein fibers, ground substance, and fluid.

• Functions include enclosing and separating, connecting tissues, supporting and moving, storing, cushioning and insulating, transporting, and protecting.

• Classification of connective tissues includes loose or areolar, adipose, dense, cartilage, bone, and blood.

Muscle Tissues

• Muscle tissues are specialized for contraction and can be skeletal, cardiac, or smooth.

• Skeletal muscle is striated and multinucleated, cardiac muscle is striated and branched, while smooth muscle is non-striated and found in hollow organs.

Nervous Tissue

• Nervous tissue forms the brain, spinal cord, and nerves, coordinating and controlling bodily activities by conducting action potentials.

• It consists of neurons and support cells.

Membranes and Inflammation

Membranes

• Membranes are thin sheets covering structures or lining cavities, typically composed of epithelium and connective tissue.

• Types include mucous membranes (lining cavities open to the outside), serous membranes (lining trunk cavities), cutaneous (skin), synovial (joint cavities), and periosteum (around bone).

Inflammation

• Inflammation occurs when tissues are damaged, aiming to isolate and destroy harmful agents.

• Mediators of inflammation include histamine, kinins, prostaglandins, and leukotrienes, leading to symptoms like redness, heat, swelling, pain, and disturbance of function.

• Chronic inflammation results from the persistence of the injuring agent or hindrance in the healing process.

Tissue Repair

• Tissue repair involves the substitution of viable cells for dead cells through regeneration or replacement.

• Regeneration restores normal function by producing new cells of the same type, while replacement leads to scar formation and loss of tissue function.

• Cells are classified as labile (divide throughout life), stable (regenerate if necessary), or permanent (little to no ability to divide).