Human Body Organization Levels

Levels of Organization in the Human Body

• The human body is organized into several levels, ranging from the smallest chemical level to the whole organism level.
• The levels of organization are:
  • Chemical level: atoms and molecules
  • Cellular level: single cells
  • Tissue level: groups of similar cells
  • Organ level: contains two or more types of tissues
  • Organ system level: organs that work closely together
  • Organismal level: all organ systems combined to make the whole organism

Necessary Life Functions

• Maintaining boundaries: separation between internal and external environments
• Movement: enabled by the muscular system
• Responsiveness: ability to sense and respond to stimuli
• Digestion: breakdown of ingested foodstuffs, followed by absorption of simple molecules into the blood
• Metabolism: all chemical reactions that occur in body cells
• Excretion: removal of wastes from metabolism and digestion
• Reproduction: at the cellular level, involves division of cells for growth or repair; at the organismal level, involves the production of offspring
• Growth: increase in size of a body part or of the organism

Survival Needs

• Nutrients: chemicals for energy and cell building
• Oxygen: essential for the release of energy from foods
• Water: most abundant chemical in the body; provides the watery environment needed for chemical reactions
• Normal body temperature: if body temperature falls below or goes above 37°C, rates of chemical reactions are affected
• Appropriate atmospheric pressure: specific pressure of air is needed for adequate breathing and gas exchange in the lungs

Anatomical Terminologies

• The Language of Anatomy: uses standard terms to describe the body and its parts
• Anatomical position: standard body position used to avoid confusion; terminology refers to this position regardless of actual body position
• Directional terms:
  • Superior (cranial or cephalic): toward the head or upper part of a structure or the body; above
  • Inferior (caudal): away from the head or toward the lower part of a structure or the body; below
  • Anterior (ventral): toward or at the front of the body; in front of
  • Posterior (dorsal): toward or at the backside of the body; behind

Body Cavities and Membranes

• Body cavities: internal cavities that are closed to the environment
• Dorsal body cavity: protects the fragile nervous system; has two subdivisions:
  • Cranial cavity: encases the brain
  • Vertebral cavity: encases the spinal cord
• Ventral body cavity: houses the internal organs (collectively called viscera); has two subdivisions:
  • Thoracic cavity: contains the heart and lungs
  • Abdominopelvic cavity: contains the digestive organs and other viscera

Blood Typing

• Blood typing is based on the presence or absence of antigens A and B on the surface of red blood cells
• Type A blood: has antigen A and anti-B antibodies in the plasma
• Type B blood: has antigen B and anti-A antibodies in the plasma
• Type AB blood: has both antigens A and B and neither anti-A nor anti-B antibodies in the plasma
• Type O blood: has neither antigen A nor B and both anti-A and anti-B antibodies in the plasma
• Blood compatibility: type A cannot receive type B or AB blood; type B cannot receive type A or AB blood; type O can only receive type O blood; type AB can receive any type of blood