Biology: Epithelial Tissue

Forms the lining of organs, glands, and body surfaces
Functions:
- Protection and barrier formation
- Absorption and secretion
- Sensation (e.g., sensory receptors in skin)
Characteristics:
- Cells are tightly packed and connected by tight junctions
- Basement membrane (a thin layer of extracellular matrix) separates epithelial tissue from underlying connective tissue
- Lacks blood vessels (avascular)
Types:
- Simple epithelial tissue (single layer of cells)
- Stratified epithelial tissue (multiple layers of cells)
- Pseudostratified epithelial tissue (single layer of cells that appear stratified due to varying cell heights)

Provides support, structure, and connectivity to the body
Functions:
- Connects and supports organs and tissues
- Provides cushioning and shock absorption
- Acts as a medium for exchange of nutrients and waste
- Stores energy in the form of fat
Characteristics:
- Cells are widely spaced and embedded in an extracellular matrix
- Matrix is composed of fibers (collagen, elastin, and reticular) and ground substance
- Richly supplied with blood vessels
Types:
- Loose connective tissue (e.g., areolar tissue, adipose tissue)
- Dense connective tissue (e.g., tendon, ligament)
- Specialized connective tissue (e.g., bone, cartilage, blood)

Responsible for transmitting and processing information
Functions:
- Conducts electrical impulses (action potentials)
- Integrates and interprets sensory information
- Controls voluntary and involuntary actions
Characteristics:
- Consists of neurons (nerve cells) and supporting cells (glial cells)
- Neurons have a cell body, dendrites, and an axon
- Forms the central nervous system (CNS) and peripheral nervous system (PNS)
Types:
- CNS (brain, spinal cord)
- PNS (sensory neurons, motor neurons, and interneurons)

Responsible for movement and contraction
Functions:
- Voluntary movement (skeletal muscle)
- Involuntary movement (smooth muscle)
- Regulates body temperature (shivering)
Characteristics:
- Composed of muscle fibers (cells)
- Muscle fibers contain contractile units (sarcomeres)
- Muscle fibers are innervated by motor neurons
Types:
- Skeletal muscle (voluntary, striated)
- Smooth muscle (involuntary, non-striated)
- Cardiac muscle (involuntary, striated, found in the heart)

Forms a barrier on body surfaces, lining organs and glands
Protects underlying tissues and regulates exchange of substances
Specialized for absorption, secretion, and sensation (e.g., sensory receptors in skin)
Characteristics:
- Tight junctions connect cells
- Basement membrane separates epithelial tissue from underlying connective tissue
- Lacks blood vessels (avascular)
Types:
- Simple epithelial tissue (e.g., lining of blood vessels, respiratory tract)
- Stratified epithelial tissue (e.g., skin, mucous membranes)
- Pseudostratified epithelial tissue (e.g., respiratory tract lining, some glands)

Provides structural support, connectivity, and cushions the body
Facilitates exchange of nutrients and waste between blood vessels and tissues
Stores energy in the form of fat and connects organs and tissues
Characteristics:
- Cells embedded in a matrix with fibers (collagen, elastin, reticular) and ground substance
- Richly supplied with blood vessels
- Supports mechanical stress and absorbs shock
Types:
- Loose connective tissue (e.g., areolar tissue, adipose tissue)
- Dense connective tissue (e.g., tendon, ligament, bone, cartilage)
- Specialized connective tissue (e.g., blood, bone marrow, fat)

Transmits and processes information through electrical impulses (action potentials)
Integrates and interprets sensory information from the environment
Controls voluntary and involuntary actions through the central and peripheral nervous systems
Characteristics:
- Composed of neurons (nerve cells) and supporting glial cells
- Neurons have a cell body, dendrites, and an axon
- Central nervous system (brain, spinal cord) and peripheral nervous system (sensory, motor, and interneurons) components
Functions:
- Controls muscle movement, sensation, and cognitive processes

Enables movement, contraction, and regulation of body temperature
Voluntary movement through skeletal muscle contraction
Involuntary movement through smooth muscle contraction (e.g., in digestion)
Characteristics:
- Composed of muscle fibers (cells) with contractile units (sarcomeres)
- Muscle fibers are innervated by motor neurons
- Regulates body temperature through shivering
Types:
- Skeletal muscle (voluntary, striated, e.g., biceps, quadriceps)
- Smooth muscle (involuntary, non-striated, e.g., in digestive tract)
- Cardiac muscle (involuntary, striated, found in the heart)