KEY CONCEPT The human body has five levels of organization.

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KEY CONCEPT The human body has five levels of
organization.
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Specialized cells develop from a single zygote.

• Organisms are made up of specialized cells.

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• Zygotes first divide into embryonic stem cells.

• Stem cells develop in two stages.
• determination, or committing to become one cell
  type
• differentiation, or acquiring specialized
  structures and functions

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Specialized cells function together in tissues,
organs, organ systems, and the whole organism.

• Specialized cells perform specific tasks.

• Tissues are groups of similar cells working
  together.

• epithelial tissue
• connective tissue
• muscle tissue
• nervous tissue

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• Organs are different tissues working together.

• Organ systems are two or more organs working
  together.
• Organism is all organ systems working together.

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• There are 11 major organ systems in the human
  body.

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KEY CONCEPT 28.2Homeostasis is the regulation
and maintenance of the internal environment.
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Conditions within the body must remain within a
narrow range.

• Homeostasis involves keeping the internal
  environment within set ranges.

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• Control systems help maintain homeostasis.

• sensors gather data
• control center receives data, sends messages
• communication system delivers messages to target
  organs, tissues
• targets respond to change

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Negative feedback loops are necessary for
homeostasis.

• Feedback compares current conditions to set
  ranges.
• Negative feedback counteracts change.

Negative Feedback Loop
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• Positive feedback increases change.

• Torn vessel stimulates release of clotting factors

• growth hormones stimulate cell division

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KEY CONCEPT 28.3 Systems interact to maintain
homeostasis.
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Each organ system affects other organ systems.

• An organ system must do a specific job.

• Organ systems must also work together to keep the
  organism healthy.

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• Organ systems must also work together to keep the
  organism healthy.

• Organ systems work together to produce Vitamin D.
• Thermoregulation maintains a steady body
  temperature.

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A disruption of homeostasis can be harmful.

• Homeostasis can be disrupted for several reasons.
  
• sensors fail
• targets do not receive messages
• injury
• illness

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• Short-term disruption usually causes little or no
  harm.

• Long-term disruptions can cause more damage.
• Diabetes is a serious long-term disruption of
  homeostasis.