Tissues and Organ Systems

• Cells form tissues, tissues form organs, organs form organ systems, and organ systems form an organism.
• Cells are the least complex, while the organism is the most complex.

Basic Tissues

• Epithelial tissue covers body surfaces and lines body cavities, providing protection and requiring substances to pass through for entry.
• Connective tissue binds and supports body parts, with four types: loose fibrous, dense fibrous, cartilage and bones, and blood.

Types of Connective Tissue

• Loose fibrous connective tissue connects epithelium to other tissues, forms protective coverings for internal organs, contains fibroblasts, and includes adipose tissue for fat storage.
• Dense fibrous connective tissue contains more collagen fibers, connecting muscles to bones via tendons and bones to bones at joints via ligaments.
• Blood consists of cells in liquid matrix (plasma), transporting nutrients/oxygen, removing wastes, spreading heat; red blood cells carry oxygen, white blood cells fight infection, platelets aid clotting.

Muscular Tissue

• Muscular tissue moves the body, contains actin and myosin, and comes in skeletal, cardiac, and smooth types.
• Skeletal muscle is voluntary, attached to bones via tendons, striated, cylindrical, long, and multinucleated
• Cardiac muscle is involuntary, found only in the heart wall, and has a single nucleus.
• Smooth muscle lacks striations, is involuntary, visceral, and found in viscera walls.
• Nervous tissue receives stimuli and conducts nerve impulses.
• Homeostasis is the maintenance of constant internal conditions, achieved by all body systems.

The Heart

• The human heart is a double pump.
• The right side pumps deoxygenated blood to the lungs.
• The left side pumps oxygenated blood to the body.
• A complete septum prevents blood mixing.
• Each side has two chambers: atria (upper, thin-walled, receiving) and ventricles (lower, thick-walled, pumping).
• The heart has three vessels: arteries, capillaries, and veins.
• Arteries transport blood away; arterioles are small arteries with thicker walls than veins.
• Capillaries, made of epithelial cells, allow nutrient/waste exchange via thin walls.
• Veins have thinner, wider walls than arteries, with valves preventing backflow.
• Fish have a single-loop heart with one atrium and ventricle.
• Amphibians and some reptiles have 3-chamber hearts with two-circuit loops.
• Crocodiles, birds, and mammals have two-circuit/double loop (4-chamber) hearts.

Upper Respiratory Tract

• Nose: external, acting as a screening device with hairs.
• Nasal Cavities: receive tear drainage and connect to sinuses.
• Pharynx: connects the nasal cavity/mouth to the larynx/esophagus; contains tonsils (lymphatic tissue), the epiglottis covers the glottis during swallowing.
• Larynx: receives air from pharynx, held open by cartilage rings, with vocal cords at the glottis's edge.

Lower Respiratory Tract

• Respiratory Tree: consists of the trachea, bronchi, and bronchioles.
• Trachea/Windpipe: allows food to pass down the esophagus.
• Bronchioles: branch/subdivide with thinner walls, less cartilage, and more smooth muscle; each ends in an alveolus.

Lungs

• In the lungs, blood exchanges carbon dioxide for oxygen.
• Breathing involves external gas exchange between air and blood, and internal gas exchange between blood and tissue fluid.
• Air moving through the respiratory tract is filtered, warmed, and humidified.