The circulatory system is switched on. Choose any system with the buttons, click an organ in the 3D body, or press “Systems working together” to play a scenario.
3D anatomy: Z-Anatomy (CC BY-SA 4.0, from BodyParts3D, CC BY-SA 2.1 JP) and the Human Reference Atlas (HuBMAP/NIH, CC BY 4.0). Vessels of the head, arms and legs and the lymph vessels are modeled by SciSim. The derived model files are shared under CC BY-SA 4.0. Lymph nodes are drawn about twice their real size. Arteries are red and veins blue to show oxygen-rich and oxygen-poor blood; real blood is always red.
The main organs from the 3D model, seen from the front. Pick Basic (10 labels) or Advanced (15). Switch between the labeled diagram, a blank one, a label quiz and match the jobs. The kidneys and ureters lie behind the intestines and are drawn see-through. On a phone, swipe the diagram sideways.
Tap a word, then tap the numbered box it belongs to (on the diagram or in the list below). Tap a filled box to take the word back.
Each line describes the job of one part. Tap a part name, then tap the box next to the job it does. Tap a filled box to take the word back.
Tap a card, then tap the system it belongs to. Press Check when all 16 are placed.
A printable worksheet: label the organs, sort the organs into systems, match each system to its job, multiple choice and three “systems working together” explain questions, with an answer key. The label part uses the level (Basic or Advanced) chosen in the diagram above.
The body is built in levels. Cells of the same kind form a tissue (for example muscle tissue). Several tissues form an organ with a job (the stomach has muscle, gland and lining tissue). Organs that work on the same task form an organ system (the digestive system), and all the systems together make the organism: you.
The skeletal and muscular systems support and move the body. The nervous and endocrine systems control it, with fast nerve signals and slower hormones. The respiratory, digestive and circulatory systems bring in oxygen and food and deliver them to every cell. The urinary system removes wastes, the lymphatic and immune system defends, the integumentary system (skin) forms a barrier, and the reproductive system makes new humans possible.
Every cell needs oxygen and glucose and makes carbon dioxide and other wastes. So the lungs (respiratory) and the gut (digestive) have to hand their products to the blood (circulatory), which delivers them; the kidneys (urinary) and lungs clean the blood again. The nervous and endocrine systems adjust all of this. Many organs even belong to two systems: the pancreas (digestive and endocrine), the hypothalamus (nervous and endocrine), the thymus (immune and endocrine) and the red bone marrow (skeletal, circulatory and immune).
The systems also keep conditions inside the body steady: temperature, blood glucose, water and salt, oxygen and carbon dioxide. This is homeostasis. It mostly works by negative feedback: a receptor detects a change, a control center (often the brain or a gland) compares it with the set point, and effectors (muscles or glands) make a response that reverses the change.
Press All systems, then click organs to see which systems they belong to. Turn on Show several systems at once and combine the respiratory and circulatory systems. Then press Systems working together and play Go for a run: watch the heart rate and breathing rate rise, and count how many systems light up on the map.
Each system is listed with its main organs, its main job and the systems it works with most. Follow the links for a detailed 3D model of each one.
| System | Main organs | Main job | Works closely with | Explore in 3D |
|---|---|---|---|---|
| Skeletal | Bones, cartilage, ligaments, joints, red bone marrow | Support, protection, movement (with muscles), makes blood cells, stores calcium | Muscular (movement), circulatory and immune (marrow makes blood cells), endocrine (parathyroid hormone controls calcium) | Skeletal & muscular 3D |
| Muscular | Skeletal muscles, tendons; smooth and cardiac muscle | Movement, posture, heat; moves food (smooth) and blood (cardiac) | Skeletal (levers), nervous (control), circulatory (oxygen supply), integumentary (heat loss) | Muscle contraction |
| Nervous | Brain, spinal cord, nerves, sense organs | Senses changes, fast control and coordination, thinking and memory | Every system; with the endocrine system through the hypothalamus | Nervous system 3D |
| Endocrine | Hypothalamus, pituitary, pineal, thyroid, parathyroids, thymus, adrenals, pancreas, ovaries or testes | Slower, longer-lasting control by hormones in the blood: growth, metabolism, blood glucose, water balance, stress | Circulatory (carries hormones), urinary (ADH), digestive (insulin), reproductive | Endocrine system 3D |
| Circulatory | Heart, arteries, veins, capillaries, blood | Transports oxygen, nutrients, hormones, heat, wastes and white blood cells | Every system; the delivery service of the body | Heart & circulation 3D |
| Respiratory | Nose, pharynx, larynx, trachea, bronchi, lungs, diaphragm | Gas exchange: oxygen into the blood, carbon dioxide out | Circulatory (gas transport), muscular (diaphragm), nervous (breathing rate) | Respiratory system 3D |
| Digestive | Mouth, esophagus, stomach, intestines, rectum; liver, gallbladder, pancreas | Breaks food down into small molecules and absorbs them | Circulatory (carries nutrients), endocrine (insulin), urinary (liver makes urea) | Digestive system 3D |
| Urinary (excretory) | Kidneys, ureters, bladder, urethra | Filters the blood, removes urea, balances water and salt | Circulatory (filters the blood), endocrine (ADH), respiratory (also removes waste CO₂) | Urinary system 3D |
| Lymphatic & immune | Lymph vessels and nodes, spleen, thymus, tonsils, white blood cells | Returns fluid to the blood, absorbs fats, fights germs | Circulatory (returns fluid), skeletal (marrow), integumentary (first barrier) | Immune system 3D |
| Integumentary | Skin, hair, nails, sweat and oil glands | Barrier against germs and water loss, touch and temperature senses, cooling by sweat, makes vitamin D | Nervous (receptors), circulatory (heat loss), immune (barrier) | — |
| Reproductive | Ovaries, uterus (female); testes, sperm ducts (male) | Makes eggs or sperm and sex hormones; reproduction | Endocrine (sex hormones), circulatory | — |
Some books count 12 systems by splitting the lymphatic and the immune system, or join the skeletal and muscular systems into one “musculoskeletal system”. The organs are the same; only the grouping differs.
Every homeostatic control has a stimulus (a change), a receptor that detects it, a control center that compares it with the set point, and effectors that respond. The nervous system gives fast, short responses through nerves; the endocrine system gives slower, longer-lasting responses through hormones carried by the circulatory system.
After a meal, blood glucose rises above about 90–100 mg/dL. Beta cells in the pancreatic islets detect this and release insulin; liver, muscle and fat cells take up glucose and the liver stores it as glycogen. Between meals, falling glucose makes alpha cells release glucagon, and the liver breaks glycogen down again. In type 1 diabetes the beta cells are destroyed by the immune system; in type 2 diabetes cells respond poorly to insulin.
The hypothalamus holds the temperature set point (about 37 °C). Too warm: sweating and vasodilation. Too cold: shivering, vasoconstriction and raised hairs. For water balance, osmoreceptors in the hypothalamus detect concentrated blood and the posterior pituitary releases ADH, which makes the collecting ducts of the kidneys take back more water.
In positive feedback the response makes the change bigger, so it is used only for events that must finish quickly: blood clotting, and the contractions of childbirth driven by the hormone oxytocin. A fever is not positive feedback: the set point is raised, and the body then uses negative feedback around the new value.
The skeletal, muscular, nervous, endocrine, circulatory (cardiovascular), respiratory, digestive, urinary (excretory), lymphatic and immune, integumentary (skin) and reproductive systems. Some books count 12 by separating the lymphatic and immune systems.
Key takeaway: eleven systems, each a group of organs with one main job.They pass materials and signals to each other. The respiratory and digestive systems take in oxygen and food, the circulatory system delivers them to every cell, the urinary and respiratory systems remove wastes, and the nervous and endocrine systems control the rest. During exercise, for example, the nervous, muscular, skeletal, respiratory, circulatory, endocrine and integumentary systems all change what they do at the same time.
Key takeaway: no system works alone; the blood links them all.Cell, tissue, organ, organ system, organism. Similar cells form a tissue, different tissues form an organ, organs that share a task form an organ system, and the systems together form the whole organism.
Key takeaway: cells → tissues → organs → organ systems → organism.The respiratory system brings air to the alveoli in the lungs, where oxygen diffuses into the blood. The circulatory system then pumps that oxygen-rich blood from the heart through the arteries to the capillaries of every tissue, and brings carbon dioxide back to the lungs.
Key takeaway: lungs load the blood, the heart and vessels deliver it.Both control the body. The nervous system uses electrical impulses along nerves: very fast (milliseconds), short-lived and aimed at exact targets. The endocrine system uses hormones carried in the blood: slower (seconds to hours), longer-lasting and able to reach many organs at once. The hypothalamus links the two.
Key takeaway: nerves are fast and precise; hormones are slow and widespread.The pancreas (digestive enzymes and the hormones insulin and glucagon), the hypothalamus (brain and hormones), the thymus (immune and endocrine), the red bone marrow (makes blood and immune cells), the pharynx (air and food), the diaphragm (a muscle used for breathing) and the testes and ovaries (reproductive and endocrine).
Key takeaway: many organs do two jobs for two systems.Nerves make muscles contract and pull on bones. Working muscles need more oxygen and glucose, so the brainstem raises the breathing rate (from about 12–15 to 40 or more per minute) and nerves and adrenaline raise the heart rate (from about 70 to 150 or more beats per minute). The extra heat is lost by sweating and by wider blood vessels in the skin, and the kidneys save water.
Key takeaway: exercise speeds up the delivery and removal systems.Excretion is removing waste made by the body’s own chemical reactions: urea in urine (kidneys), carbon dioxide (lungs) and some salts in sweat. Egestion is getting rid of food that was never digested or absorbed, as feces. Feces are not excretion because the food never became part of the body’s cells.
Key takeaway: kidneys and lungs excrete; the anus egests.Homeostasis is keeping the conditions inside the body steady even when the outside changes. Body temperature is kept near 37 °C: when you get too hot you sweat and the skin vessels widen; when you get too cold you shiver and the vessels narrow. Blood glucose, water and carbon dioxide are kept steady in the same way, mostly by negative feedback.
Key takeaway: homeostasis = a steady inside, kept by negative feedback.Most organs come from real anatomy: the Z-Anatomy model (based on BodyParts3D, built from medical scans) and the Human Reference Atlas of the US National Institutes of Health (HuBMAP). The vessels of the head, arms and legs and the lymph vessels were modeled by SciSim along their real routes. The lymph nodes are drawn about twice their real size, the model is of one adult male body, and real bodies vary.
Key takeaway: real anatomy, with a few parts drawn by SciSim and labeled as such.