# The human body

The body is composed of multiple independent systems that work with each other.

- These systems are highly interconnected, but can be parsed based on the [purpose](purpose.md) they accomplish.

1. Breathing (respiratory)
   - Takes in oxygen, expels carbon dioxide
   - Nose, mouth, paranasal sinuses, pharynx, larynx, trachea, bronchi, lungs, thoracic diaphragm
2. Food (digestive + excretory)
   - Takes in calorie energy as food, excretes solid waste
   - Teeth, tongue, salivary glands, esophagus, stomach, liver, gallbkadder, pancreas, small intestine, large intestine, rectum, anus
3. Blood (cardiovascular/circulatory)
   - Transports things between most of the other systems
     - Nutrients
     - Waste
     - Hormones
     - Oxygen
     - Carbon dioxide
   - Assists in maintaining pH and temperature
   - Blood, heart, arteries, veins, capillaries
4. Peeing (renal/urinary)
   - Dissolves waste products in the blood and expels them as urine
   - Maintains fluid and electrolyte balance
   - Kidneys, ureters, bladder, urethra
5. Exterior (integumentary)
   - Protective barrier between the outside and inside the body that stops foreign objects and regulates heat
   - Skin, hair, fat, nails
6. Structure (skeletal)
   - Structurally supports and protects the body, produces blood cells
   - Bones, cartilage, ligaments, tendons
7. Movement (muscular)
   - Moves the body, produces heat
   - Skeletal muscles, smooth muscles, cardiac muscle
8. Signals (endocrine)
   - Sends hormones from glands that regulate *all* the other systems
   - Hypothalamus, pituitary, pineal, thyroid, parathyroid, adrenal, ovaries/testicles
9. Lubrication (exocrine)
   - Ceruminous, lacrimal, sebaceous, mucus
10. Internal protection (lymphatic/immune)
    - Fights foreign and potentially dangerous things within the body
    - Returns fluid from tissues for recirculation, aids immune responses, makes white blood cells
    - Lymph, lymph nodes and vessels, tonsils, spleen, thymus
11. Information (nervous)
    - Sends and processes information back-and-forth between the brain and the rest of the body, controls body activities
    Brain, spinal cord, nerves, sensory organs
12. Reproduction
    - Helps [make children](parenting-babies.md) through sex organs
    - Broken out by [gender](people-gender.md):
      - Females: ovaries, fallopian tubes, uterus, vagina, vulva
      - Males: penis, testicles, vasa defentia, seminal vesicles, prostate

Almost all of these systems runs through [the central flow of the spine](body.jpg).