Levels of Structural Organization

• The human body has six levels of structural organization, increasing in complexity.

Chemical Level

• Atoms bond to create molecules with 3D structures.
• The study of the chemical level requires examining matter's most basic components.
• Subatomic particles, atoms, and molecules are crucial parts of this level.
• Molecules serve as the building blocks for all bodily structures.

Cellular Level

• Molecules combine to form the fluids and organelles of the body's cells.
• Cells represent the smallest independently functioning units in a living organism which even bacteria possess.
• Cytoplasm is a water-based fluid in cells which contains different functioning units called organelles.
• Cells perform all functions of life in all organisms including humans.

Tissue Level

• Similar cells form body tissues.
• Tissues are groups of similar cells working together for a specific function.
• There are four primary tissue types in the human body.
• Epithelial tissue consists of closely packed cells, covering body surfaces like skin, providing protection, secretion, excretion, filtration, and absorption.
• Nervous tissue consists of neurons and glial cells, transmitting signals and information to other cells.
• Muscular tissue consists of elongated, excitable cells specialized for contraction and movement which facilitates various functions like digestion, breathing, and blood circulation.
• Skeletal muscle is voluntary, while cardiac and smooth muscle are involuntary.
• Connective tissue connects, separates, and supports other tissues, with cells loosely arranged in an extracellular matrix.

Organ Level

• Organs are formed when two or more different tissues combine.
• Each organ is an anatomically distinct structure.
• Organs perform one or more specific physiological functions.

Organ System Level

• Multiple organs work together to perform major bodily functions
• The human body contains has 11 organ systems.
• The integumentary system includes skin, hair, and nails, and contains sensory receptors.
• The skeletal system which contains cartilage, bones, and joints supports body movement and structure.
• The muscular system which contains tendons and skeletal muscles enables movement and maintains body temperature.
• The nervous system includes CNS & PNS: brain, spinal cord, and peripheral nerves, detects and processes sensory information.
• The endocrine system includes: pituitary, thyroid, adrenal glands, pancreas, ovaries, and testes, secretes hormones, and regulates body processes.
• The cardiovascular system contains the heart and blood vessels, delivering oxygen and nutrients to tissues.
• The lymphatic system contains the thymus, lymph nodes, spleen, and lymphatic vessels, returning fluid to the blood and defending against pathogens.
• The respiratory system contains the nasal passage, trachea, and lungs, removes CO2 and delivers O2 to the blood.
• The digestive system which contains the stomach, liver, gall bladder, pancreas, large and small intestine, processes food, and removes waste.
• The urinary system includes the kidneys and urinary bladder, controlling water balance and removing waste from blood.
• Male reproductive system produces sperm and the female reproductive system produces sex hormones and eggs.

Organism Level

• Organ systems function harmoniously to sustain the independent organism.
• The organism level represents the highest level of organization.