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Body Cavities

A body cavities is any space, compartment, or potential space in an animal body, accommodating organs and structures or containing fluid.

Function

Cavities accommodate organs and other structures, aiding in the protection, separation, and support of these organs.

Largest Human Body Cavities

The two largest human body cavities are the ventral (anterior) cavity and the dorsal (posterior) cavity.

The ventral cavity is located at the front of the trunk and contains organs such as the lungs, heart, stomach, intestines, and reproductive organs. It is subdivided into the thoracic cavity, which holds the lungs and heart, and the abdominopelvic cavity, which contains the digestive organs, kidneys, and reproductive organs.

The dorsal cavity is located at the back of the body and is subdivided into the cranial cavity, which holds the brain, and the spinal cavity, which contains the spinal cord. The brain and spinal cord are protected by the bones of the skull and vertebral column, as well as by cerebrospinal fluid.

The ventral and dorsal cavities are separated by membranes and other structures, which allow the organs within them to change size and shape without disrupting the activities of nearby organs.

The cavities found in human bodies contain fluid and house the internal organs. Excessive fluid buildup in these cavities could potentially cause problems, but the body’s structures are designed to accommodate changes in organ size and shape during normal function.

Types of Cavities

Common types of cavities include:

  • Cranial
  • Thoracic
  • Abdominal
  • Pelvic

Cranial Cavity

The primary cavity of the skull that houses the cranial nerves, blood vessels, and protective membranes surrounding the brain is called the cranial cavity. It is divided into three main sections:

  • The anterior cranial fossa, which houses the olfactory bulbs and frontal lobes of the brain.
  • The middle cranial fossa, which contains the temporal lobes of the brain as well as important structures like the optic chiasma and pituitary gland.
  • The brainstem and cerebellum are located in the posterior cranial fossa.

The cranial cavity is lined by the dura mater, which has two layers – an outer endosteal layer that attaches to the skull bones, and an inner meningeal layer that provides a protective covering for the brain. The dura mater also forms several folds or septa, such as the falx cerebri and tentorium cerebelli, that help divide and support different parts of the brain.

The cranial cavity communicates with the vertebral canal through the foramen magnum, allowing the brain to connect with the spinal cord. Various foramina in the skull also allow the cranial nerves to pass through and innervate structures outside the skull.

Thoracic Cavity

The thoracic cavity, or chest cavity, is the body chamber in vertebrates protected by the rib cage, skin, muscles, and fascia.

The thoracic cavity is the second largest hollow space of the body, enclosed by the ribs, vertebral column, and sternum. It contains several important structures:

  • The thoracic cavity includes the cardiovascular system, such as the heart and great vessels like the thoracic aorta, pulmonary artery, vena cava, and pulmonary veins.
  • It also contains the respiratory system, including the diaphragm, trachea, bronchi, and lungs.
  • Additionally, the thoracic cavity houses parts of the digestive system, such as the esophagus, as well as endocrine glands like the thymus.
  • The thoracic cavity has three potential spaces lined with mesothelium: the paired pleural cavities and the pericardial cavity. The mediastinum is the central compartment between the lungs that contains many of these structures.

Injuries to the thoracic cavity, such as a penetrating wound, can lead to conditions like pneumothorax where air enters the pleural space and causes the lung to collapse, requiring immediate medical attention.

Abdominal Cavity

In humans and many other animals, the abdominal cavity is the largest body cavity. The peritoneum membrane lines it, and it is situated above the pelvic cavity and below the thoracic cavity.

Key points:

  • The abdominal cavity is bounded superiorly by the diaphragm, inferiorly by the pelvic inlet, and laterally and anteriorly by the abdominal muscles.
  • It contains most of the digestive organs, including the stomach, liver, gallbladder, pancreas, small and large intestines, as well as the kidneys, adrenal glands, and spleen.
  • The abdominal cavity is lined by the peritoneum, which has a parietal layer lining the cavity walls and a visceral layer covering the organs. The space between the parietal and visceral peritoneum is the peritoneal cavity, which normally contains a small amount of lubricating fluid.
  • The peritoneum forms various folds and ligaments that support and connect the abdominal organs, such as the mesentery, omentum, and peritoneal ligaments.
  • The abdominal cavity can be divided into the greater sac (supracolic and infracolic compartments) and the smaller lesser sac (omental bursa), connected by the epiploic foramen.
  • Clinically, the abdominal cavity and peritoneal spaces are important for procedures like paracentesis, peritoneal dialysis, and in the spread of infections and cancers.

In summary, the abdominal cavity is the largest body cavity, containing most of the digestive organs and lined by the peritoneum, which forms supporting structures and divides the cavity into compartments.

Pelvic Cavity

The pelvic cavity is a space within the pelvis that contains reproductive organs, urinary bladder, distal ureters, proximal urethra, terminal sigmoid colon, rectum, and anal canal.

Enclosed by the pelvic bones, the pelvic cavity is a funnel-shaped area that houses the reproductive organs, urinary bladder, proximal urethra, distal ureters, terminal sigmoid colon, rectum, and anal canal.
There are two parts to the pelvic cavity:

  • The greater pelvis (false pelvis) – the region above the pelvic brim, which is regarded as a component of the abdominal cavity
  • The lesser pelvis (true pelvis) – the space below the pelvic brim, between the pelvic inlet and the pelvic floor. This is the true pelvic cavity.

The lesser pelvis is bounded anteriorly by the pubic symphysis, posteriorly by the sacrum and coccyx, and laterally by the inner surfaces of the hip bones. It contains the pelvic colon, rectum, bladder, and sex organs.

The pelvic cavity is separated from the perineum inferiorly by the pelvic floor, also known as the pelvic diaphragm. The pelvic floor is made up of muscles that support the pelvic viscera.

In females, the uterus, fallopian tubes, ovaries and upper vagina occupy the space between the other pelvic organs. The bladder is situated anteriorly, behind the pubic symphysis, and the rectum is situated posteriorly, in the curve formed by the sacrum and coccyx.

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