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• Characteristics of life:

  • Movement: change in position; motion
  • Responsiveness: reaction to a change
  • Growth: increase in body size; no change in shape
  • Reproduction: production of new organisms and new cells
  • Respiration: obtaining oxygen; removing carbon dioxide; releasing energy from foods
  • Digestion: breakdown of food substances into simpler forms
  • Absorption: passage of substances through membranes and into body fluids
  • Circulation: movement of substances in body fluids
  • Assimilation: changing of absorbed substances into chemically different forms
• • Excretion: removal of wastes produced by metabolic reactions
• Life depends on five environmental factors:

  • Water
  • Food
  • Oxygen
  • Heat
  • Pressure
• Requirements of organisms: Water:

  • Most abundant substance in the body
  • Required for metabolic processes
  • Required for transport of substances
  • Regulates body temperature
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  • Food:
  • Provides necessary nutrients
  • Supplies energy
  • Supplies raw materials
  • Oxygen (gas):
  • One-fifth of air
  • Used to release energy from nutrients
  • Heat:
  • Form of energy
  • Partly controls rate of metabolic reactions
  • Pressure:
  • Application of force on an object
  • Atmospheric pressure is important for breathing
  • Hydrostatic pressure keeps blood flowing
• Homeostasis:

  • Body fluids are dilute, watery solutions containing dissolved chemicals inside or outside of the cell
  • Maintaining the volume and composition of body fluid is important
  • Intracellular fluid (ICF) is the fluid within cells
  • Extracellular fluid (ECF) is the fluid outside cells (more accessible)
  • Interstitial fluid is ECF between cells and tissues
• Important body fluids:

  • Blood plasma: ECF within the blood vessels
  • Lymph: ECF within lymphatic vessels
  • Cerebrospinal fluid (CSF): ECF in the brain and spinal cord
  • Synovial fluid: ECF in joints
  • Aqueous humor: ECF in eyes
• Control of homeostasis:

  • Cellular function depends on the regulation of the composition of the interstitial fluid
  • Composition of interstitial fluid changes as substances move between plasma and interstitial fluid
  • Control of homeostasis is constantly challenged by physical insults, changes in the internal environment, and physiological stress
• Homeostatic control mechanisms:

  • Monitors aspects of the internal environment and corrects as needed
  • Variations are within limits
  • Three parts: Receptor (provides information about the stimuli), Control Center (tells what a particular value should be, called the set point), Effector (elicits responses that change conditions in the internal environment)