the human system

• humans + other multicellular organisms are a collection of specialized cells. they develop from a single zygote

• examples of specialized cells eg. cardiac muscle, skin, liver, neuron, etc.

• cells produced during the first few divisions of the zygote are known as embryonic stem cells

• these stem cells have the potential to become any type of specialized cell in the body

• within a few weeks, a process called determination occurs in which most stem cells

• differentiation: process by which committed cells acquire the structures + functions of highly specialized cells

• eg. different types of muscle cells, sperm cells, nerves, etc.

• programmed cell death (apoptosis) ie. hand/mitten in embryo

levels of organization

1. cells: all have a particular structure and perform specific tasks

2. tissues: groups of similar cells that work together to perform a specialized function; the human body is made of four types of tissues

3. epithelial tissue: lines body cavities + organs eg. skin, membranes that line the respiratory + digestive tracts

4. muscle tissue: capable of contracting to produce movement

   • 3 types: cardiac, skeletal, and smooth

5. nervous tissue: transmits + receives impulses, processes information, and regulates the body's response to its environment