Nervous System
The brain, spinal cord, and nerves process information and send signals for movement, senses, memory, and automatic body functions.
Major Body Systems
The body is a connected set of systems that trade oxygen, nutrients, signals, motion, heat, waste, and protection every moment.
Cardiovascular System
The heart, blood, and vessels move oxygen, nutrients, hormones, and waste products so organs can keep working.
Respiratory System
The lungs and airways bring oxygen in and remove carbon dioxide, while breathing muscles adjust airflow during activity.
Digestive System
The digestive tract breaks food into nutrients small enough for the body to absorb and use for energy, growth, and repair.
Musculoskeletal System
Bones, joints, and muscles create body shape, posture, protection, and motion.
Immune and Lymphatic Systems
Immune cells, lymph vessels, nodes, and related organs help fight infection and move extra fluid back into the blood.
Endocrine System
Hormone-producing glands help regulate growth, metabolism, sleep rhythms, stress, reproduction, and blood sugar.
Integumentary System
Skin, hair, nails, and glands form a protective surface, sense the outside world, and help manage temperature.
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Organs Working Together
A simple action like running uses many systems at once: the brain sends commands, lungs exchange gases, the heart moves blood, muscles create motion, and digestion supplies fuel.
1. Brain
Coordinates decisions, senses, movement, memory, breathing rhythm, and heart-rate responses.
2. Lungs
Move oxygen into the blood and remove carbon dioxide from the body.
3. Heart
Pumps blood through vessels so oxygen and nutrients reach tissues.
4. Digestive organs
Break food down and absorb nutrients for energy, repair, and growth.
Smallest to Largest
Cells build tissues, tissues build organs, organs form systems, and systems keep the full organism alive.
CellsThe basic living units that perform specialized jobs.
TissuesGroups of similar cells working together.
OrgansStructures like the heart, lungs, brain, stomach, and skin.
SystemsGroups of organs that cooperate for larger functions.
OrganismThe complete body with all systems connected.
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