Biological Levels of Organization
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1. Cell – basic unit of structure and function
Organelles – structures in the cell that perform
specific functions
2. Groups of cells form tissues.
3. Groups of different tissues form organs.
4. Groups of different organs working together
form organ systems.
5. Organ systems make up an organism.
Organization of the Human Body:
1. Body cavities
2. Layers of membranes within body cavities
3. Organ systems
1. Body Cavities
1. Axial portion – head, neck, and trunk
2. Appendicular portion – upper and lower
limbs (“append” = to hang)
 Axial portion:
 Dorsal cavity (“dors” = back)
 Ventral cavity
 Dorsal cavity:
 Cranial cavity (“cran” = helmet)
 Vertebral canal
1. Body Cavities (cont.)
Ventral cavity:
Thoracic cavity
Abdominopelvic cavity
Thoracic cavity:
Thoracic and abdominopelvic cavities are
separated by the diaphragm.
Mediastinum
A region that separates the thoracic cavity into 2
compartments containing the right and left lungs
All other thoracic viscera (organs) are in the
mediastinum.
1. Body Cavities (cont.)
Abdominopelvic cavity:
Abdominal cavity – contains stomach, spleen, liver,
gallbladder, kidneys, and most of the small and large
intestines
Pelvic cavity (“pelv” = basin) – contains the terminal
portion of the large intestine, urinary bladder, and
internal reproductive organs.
Smaller cavities in the head:
Oral cavity
Nasal cavity
Orbital cavities
Middle ear cavities
1. Body Cavities Summary
Appendicular portion
Upper limbs
Lower limbs
Axial portion
Dorsal cavity
Vertebral canal
Cranial cavity
Oral cavity
Nasal cavity
Orbital cavities
Middle ear cavities
1. Body Cavities Summary (cont.)
– Ventral cavity
• Thoracic cavity
– Mediastinum
– Right lung
– Left lung
• Abdominopelvic cavity
– Abdominal cavity
– Pelvic cavity
2. Thoracic and Abdominal Pelvic
Membranes
Thoracic membranes:
Walls of right and left compartments are lined
with parietal pleura (“pariet” = wall; “pleur” = rib)
Lungs are covered with visceral pleura (“viscera”
= organs in a body cavity)
Pleural cavity – fluid-filled “space” between the
parietal and visceral pleural membranes
Heart is surrounded by pericardial membranes
(“peri” = around; “cardi” = heart)
Visceral pericardium
Parietal pericardium
Pericardial cavity