Defining and Classifying Tissues

Defining and Classifying Tissues

• Tissues are groups of similar cells performing a specific function. They are the building blocks of organs and organ systems.
• Four primary tissue types exist in the human body: epithelial, connective, muscle, and nervous.

Epithelial Tissue

• Definition: Sheets of tightly packed cells covering body surfaces, lining body cavities, and forming glands. They act as barriers and are involved in secretion, absorption, and excretion.

• Classification: Epithelial tissues are categorized by cell shape (squamous, cuboidal, columnar) and arrangement (simple, stratified).

• Structure: Cells are closely joined by specialized junctions (tight junctions, adherens junctions, desmosomes, gap junctions). A basement membrane anchors the epithelium to underlying connective tissue. Epithelial cells lack blood vessels (avascular). They rely on diffusion from the underlying connective tissue for nourishment.

• Location:

• Covering surfaces of the body (skin)

• Lining body cavities (lung alveoli)

• Form glands (salivary glands)

• Functions:

• Protection: Forms a barrier against pathogens, dehydration, and physical trauma.

• Secretion: Produce substances like hormones, mucus, enzymes, and sweat.

• Absorption: Take up substances from the external environment (intestines).

• Excretion: Removes wastes from the body.

• Filtration: Allows certain substances to pass through while blocking others (kidneys).

• Diffusion: Allows movement of substances across a surface (lungs).

• Sensory reception: Detect stimuli (taste buds, nasal lining).

Connective Tissue

• Definition: A diverse group of tissues that connect, support, and protect other tissues and organs. They are usually comprised of cells embedded within an extracellular matrix composed of protein fibers (collagen, elastic) and ground substance.

• Classification: Types include loose connective tissue, dense connective tissue, cartilage, bone, and blood.

• Structure: Characterized by cells scattered within a matrix. The matrix varies greatly in composition depending on the type of connective tissue, providing structural support and influencing function.

• Location:

• Tendons and ligaments

• Dermis of skin

• Cartilage (ear, nose)

• Bone

• Blood

• Functions:

• Support and structure: Provides framework for organs and body parts (bone, cartilage).

• Protection: Forms a protective barrier (bone, adipose).

• Binding and connection: Connects different tissues and organs (tendons, ligaments).

• Transport: Blood transports oxygen, nutrients, and wastes.

• Storing energy: Adipose tissue stores energy reserves.

• Insulation: Adipose tissue provides insulation to regulate body temperature.

• Immune response: Cells of connective tissue (like macrophages) play important roles in immunity.

• Repair: Connective tissue plays a vital role in healing wounds.