Human Body Tissues

• Human body cells are organized into tissues, which are groups of similar cells with a common function.
• The four major types of human body tissues are epithelial, connective, muscle, and nervous tissue.
• Epithelial tissues provide protective coverings and facilitate secretion and absorption.
• Connective tissues support soft body parts and bind structures.
• Muscle tissues are responsible for body movements.
• Nervous tissues conduct impulses for control and coordination.

Epithelial Tissue Characteristics

• Found throughout the body, epithelia cover surfaces/organs, line body cavities/hollow organs, and form glands.
• Epithelium has a free apical surface exposed to the outside or to an internal open space.
• The underside is anchored to connective tissue via a thin, nonliving basement membrane.
• Nutrients diffuse to epithelium from underlying connective tissues because epithelial tissues lack blood vessels.
• Epithelial cells readily divide, enabling rapid injury repair.
• These cells are tightly packed, which forms protective barriers.
• Epithelial functions include secretion, absorption, and excretion.
• Epithelial tissues are classified by cell shape and number of cell layers.

Simple Squamous Epithelium

• Consists of a single layer of thin, flattened cells.
• Functions in gas exchange in the lungs.
• Lines blood and lymph vessels.
• Is part of membranes lining body cavities and covering viscera.

Simple Cuboidal Epithelium

• Composed of a single layer of cube-shaped cells.
• Engaged in secretion and absorption in the kidneys.
• Present in various glands.

Simple Columnar Epithelium

• Made up of elongated cells with nuclei near the basement membrane.
• Lines the uterus and digestive tract.
• Includes many absorbing cells with microvilli.
• Goblet cells may be present for mucus secretion.

Pseudostratified Columnar Epithelium

• Nuclei are located at different levels, giving a stratified appearance.
• Cilia move mucus over the tissue surface.
• Lines respiratory passages.

Stratified Squamous Epithelium

• Has many layers of cells.
• Protects underlying cells.
• Forms the superficial layer of skin.
• Lines the oral cavity, esophagus, vagina, and anal canal.

Stratified Cuboidal Epithelium

• Composed of two or three layers of cube-shaped cells.
• Lines the ducts of mammary, sweat, and salivary glands, and the pancreas.
• Its primary function is protection.

Stratified Columnar Epithelium

• The top layer has columnar-shaped cells and the bottom layers have cube-shaped cells .
• Found in parts of the male urethra, and lining of exocrine gland ducts.
• It protects and secretes.

Connective Tissue General Characteristics

• Binds structures; provides support, protection, and frameworks.
• Fills spaces and stores fat.
• Produces blood cells.
• Protects against infections and helps repair tissue damage.
• Connective cells have good blood supplies for nourishment, although vascularity varies.
• Includes fixed cells like fibroblasts and mast cells and wandering cells like macrophages.

Fibroblasts

• Most common fixed connective tissue cell.
• Produces fibers by secreting proteins into the extracellular matrix.

Mast Cells

• Large, widely distributed cells usually near blood vessels.
• Release heparin (prevents blood clotting) and histamine (related to inflammation/allergies).

Macrophages

• Originate as white blood cells (histiocytes).
• Specialized for phagocytosis.
• Clear foreign particles from tissues.

Connective Tissue Fibers

• Fibroblasts produce collagen, elastic, and reticular fibers.
• Collagen and elastic fibers are the most abundant.

Categories of Connective Tissue

• Connective tissue proper includes loose and dense connective tissue.
• Specialized connective tissue includes cartilage, bone, and blood.

Areolar Tissue

• Contains fibroblasts that produce collagen and elastic fibers.

Adipose Tissue

• Contains cells with large fat droplets.
• Fat droplets push the nuclei close to the cell membranes.

Cartilage

• Chondrocytes are located in lacunae.
• Lacunae are surrounded by extracellular matrix containing collagen fibers.

Elastic Cartilage

• Contains many elastic fibers in its extracellular matrix.

Fibrocartilage

• Has large collagen fibers in its extracellular matrix.

Bone Tissue

• Bone matrix is deposited in concentric layers around central canals.
• Osteocytes are within lacunae (6,000x magnification in a scanning electron micrograph)

Blood Tissue

• Consists of red blood cells, white blood cells, and platelets suspended in plasma.
• Can be seen as an idealized representation or under a microscope at 1,000x magnification.

Muscle Tissue General Characteristics

• Muscle tissues can contract.
• Elongated cells (muscle fibers) shorten and thicken.
• Contraction moves body parts where fibers pull at their attached ends.
• Skeletal muscle is about 40% of body weight.
• Smooth and cardiac muscle is almost another 10%.

Skeletal Muscle Tissue

• Attaches to bones and are controlled voluntarily.
• Threadlike cells have light and dark striations.
• Cells are multinucleate
• A nerve cell stimulates contraction; relaxation occurs when stimulation ceases.
• The muscles move limbs, head and trunk
• Enable facial expressions, writing, talking, singing, chewing, swallowing, and breathing.
• striated muscle fibers contain many nuclei.

Smooth Muscle Tissue

• Non-striated cells.
• Cells are spindle-shaped, shorter than skeletal muscle cells, and have a single, central nucleus.
• It is present in the walls of hollow internal organs like the stomach, intestines, uterus, urinary bladder, and vessels.
• Actions are involuntary.
• Moves food through digestive tract, constricts blood vessels, and empties the urinary bladder.
• Consists of spindle-shaped cells, each with a large nucleus.

Cardiac Muscle Tissue

• Found only in the heart.
• Striated and branched cells are joined, forming networks.
• Each cell has a single nucleus.
• Intercalated discs are specialized intercellular junctions
• Cardiac muscle is involuntary.
• Makes up most of the heart and pumps blood.
• Cells are branched and interconnected, with a single nucleus each.

Nervous Tissue

• Found in the brain, spinal cord, and peripheral nerves.
• Neurons sense changes and conduct electrical impulses to muscles, glands, or other neurons.
• They coordinate, regulate, and integrate body activities.
• Some neuroglia cells bind and support tissue.
• Some cells carry out phagocytosis
• Some cells connect neurons to blood vessels.
• Some cells are involved in cell-to cell communication.
• A neuron has cellular processes that extend into its surroundings.