Organization of the Human Body

Organization of the Human Body

Body Cavities

• The human body is divided into axial and appendicular portions.

  • Axial: Head, neck, and trunk.

  • Appendicular: Upper and lower limbs.

• Axial portion contains:

  • Cranial cavity: Houses the brain.

  • Vertebral canal (spinal cavity): Contains the spinal cord, surrounded by vertebrae.

  • Thoracic cavity.

  • Abdominopelvic cavity.

• Organs within the thoracic and abdominopelvic cavities are called viscera.

• Smaller cavities within the head:

  1. Oral cavity: Contains teeth and tongue.

  2. Nasal cavity: Connects with air-filled sinuses.

  3. Orbital cavities: Contain eyes, skeletal muscles, and nerves.

  4. Tympanic cavities: Contain middle ear bones.

Thoracic and Abdominopelvic Cavities

• Thoracic cavity:

  • Separated from the abdominopelvic cavity by the diaphragm.

  • The diaphragm curves upward into the thorax when at rest.

  • During inhalation, the diaphragm contracts and presses down upon the abdominal viscera.

  • The wall is composed of skin, skeletal muscles, and bones.

  • Mediastinum: Compartment extending from the sternum to the vertebral column, forming a boundary between the right and left sides of the thoracic cavity.

    • Contains most of the thoracic cavity viscera (heart, esophagus, trachea, thymus), except for the lungs.

    • The right and left lungs are on either side of the mediastinum.

• Abdominopelvic cavity:

  • Includes an upper abdominal portion and a lower pelvic portion.

  • Extends from the diaphragm to the floor of the pelvis.

  • The wall consists of skin, skeletal muscles, and bones.

  • Abdominal cavity viscera: Stomach, liver, spleen, gallbladder, kidneys, small and large intestines.

  • Pelvic cavity: Enclosed by the pelvic bones.

    • Contains the terminal end of the large intestine, urinary bladder, and internal reproductive organs.

Thoracic and Abdominopelvic Membranes

• Thin serous membranes line the walls of the thoracic and abdominopelvic cavities.

• These membranes fold back to cover the organs within these cavities.

• Serous membranes secrete a slippery serous fluid that separates:

  • Parietal layer: Lining the wall of the cavity.

  • Visceral layer: Covering an organ.

• Thoracic compartments:

  • Right and left compartments contain the lungs.

  • Lined with parietal pleura.

  • The parietal pleura folds back to cover the lung, forming the visceral pleura.

  • Pleural cavity: Potential space between the parietal and visceral pleural membranes.

• Heart:

  • Located in the broadest portion of the mediastinum.

  • Surrounded by pericardial membranes.

  • Visceral pericardium (epicardium): Covers the heart's surface.

  • Parietal pericardium: Separated from the visceral pericardium by a small volume of serous fluid.

  • Pericardial cavity: Potential space between these membranes.

  • Fibrous pericardium: A thicker third layer covering the parietal pericardium.

• Abdominopelvic cavity membranes:

  • Called peritoneal membranes.

  • Parietal peritoneum: Lines the wall of the abdominopelvic cavity.

  • Visceral peritoneum: Covers most of the organs in the abdominopelvic cavity.

  • Peritoneal cavity: Potential space between these membranes.