Anatomy & Physiology · Systems
Cells, Tissues & Organs
The body's levels of organization: ~37 trillion cells, organelles, the four tissue types, organs and the 11 organ systems, with how cells renew at very different rates.
Step 1 of 5 · Overview25 min read ·
Key idea
Prereqs: none. Next: Hormones & the endocrine system; Heart and circulation. Sources: Bianconi et al., 'An estimation of the number of cells in the human body', *Ann Hum Biol* (2013); Sender & Milo, *Nature Medicine* (2021) on cell turnover; OpenStax *Anatomy & Physiology* (2nd ed.).Next: 1. Levels