Body Cavities And Membranes

BODY CAVITIES AND MEMBRANES

Cavity is an empty space in the body of multicellular organism,containing the viscera or fluid.

Membrane is a thin sheet of tissue or layers of cells acting as a boundary,lining,or partition in an organism.

DORSAL BODY CAVITY

The dorsal body cavity, which protects the fragile nervous system organs, has two subdivisions.

The cranial cavity, in the skull, encases the brain.

The vertebral, or spinal, cavity, which runs within the bony vertebral column, encloses the delicate spinal cord.

The spinal cord is essentially a continuation of the brain, and the cranial and spinal cavities are continuous with one another

VENTRAL BODY CAVITY

• The more anterior and larger of the closed body cavities is the ventral body cavity .
• Like the dorsal cavity, it has two major subdivisions:
• The thoracic cavity.

2.The abdominopelvic cavity.

The ventral body cavity houses internal organs collectively called the viscera, or visceral organs.

The superior subdivision, is surrounded by the ribs and muscles of the chest.

The thoracic cavity is further subdivided into lateral pleural cavities, each enveloping a lung, and the medial mediastinum.

The mediastinum contains the pericardial cavity, which encloses the heart, and it also surrounds the remaining thoracic organs.

The thoracic cavity is separated from the more inferior abdominopelvic cavity by the diaphragm, a dome-shaped muscle important in breathing

The abdominopelvic cavity, has two parts.

However, these regions are not physically separated by a muscular or membrane wall.

Its superior portion, the abdominal cavity, contains the stomach, intestines, spleen, liver, and other organs.

The inferior part, the pelvic cavity, lies in the bony pelvis and contains the bladder, some reproductive organs, and the rectum.

• The abdominal and pelvic cavities are not aligned with each other.

Instead, the bowl-shaped pelvis tips away from the perpendicular.

When the body is subjected to physical trauma e.g MTA/RTA, the abdominopelvic organs are most vulnerable.

This is because the walls of the abdominal cavity are formed only by trunk muscles and are not reinforced by bone.

The pelvic organs receive a somewhat greater degree of protection from the bony pelvis.

MEMBRANES IN THE VENTRAL BODY CAVITY

The walls of the ventral body cavity and the outer surfaces of the organs it contains are covered by a thin, double-layered membrane, the serosa, or serous membrane.

• The part of the membrane lining the cavity walls is called the parietal serosa.

It folds in on itself to form the visceral serosa, covering the organs in the cavity.

Body Cavities And Membranes

In the body, the serous membranes are separated not by air but by a thin layer of lubricating fluid, called serous fluid, which is secreted by both membranes.

Although there is a potential space between the two membranes, the barely present, slitlike cavity is filled with serous fluid.

Body Cavities And Membranes

The slippery serous fluid allows the organs to slide without friction across the cavity walls and one another as they carry out their routine functions.

The serous membranes are named for the specific cavity and organs with which they are associated.

The parietal pericardium lines the pericardial cavity and reflects back as the visceral pericardium, which covers the heart.

Likewise, the parietal pleura lines the walls of the thoracic cavity, and the visceral pleura covers the lungs.

The parietal peritoneum is associated with the walls of the abdominopelvic cavity, while the visceral peritoneum covers most of the organs within that cavity.

When serous membranes are inflamed, their normally smooth surfaces become roughened.

This leads to excruciating pain as the organs stick together and drag across one another, as anyone who has experienced pleurisy (inflammation of the pleurae) or peritonitis (inflammation of the peritonea)

ABDOMINOPELVIC REGIONS AND QUADRANTS

Because the abdominopelvic cavity is large and contains several organs, it helps to divide it into smaller areas for study.

One division method, used primarily by anatomists, uses two transverse and two parasagittal planes.

These planes, positioned like a tic-tac-toe grid on the abdomen, divide the cavity into nine regions

The umbilical region is the centermost region deep to and surrounding the umbilicus (navel).

• The epigastric region is located superior to the umbilical region.

The hypogastric (pubic) region is located inferior to the umbilical region.

The right and left iliac, or inguinal, regions are located lateral to the hypogastric region.

• The right and left lumbar regions lie lateral to the umbilical region.

The right and left hypochondriac regions flank the epigastric region laterally.

Medical personnel usually use a simpler scheme to localize the abdominopelvic cavity organs .

In this scheme, one transverse and one median sagittal plane pass through the umbilicus at right angles.

The resulting quadrants are named according to their positions from the subject’s point of view:

The right upper quadrant (RUQ), Left upper quadrant (LUQ), Right Lower quadrant (RLQ), and Left lower quadrant (LLQ).

OTHER BODY CAVITIES

• In addition to the large closed body cavities, there are several smaller body cavities.

Most of these are in the head and most open to the body exterior:

• Oral and digestive cavities. The oral cavity, commonly called the mouth, contains the teeth and tongue.

This cavity is part of and continuous with the cavity of the digestive organs, which opens to the exterior at the anus.

• Nasal cavity. Located within and posterior to the nose, the nasal cavity is part of the respiratory system passageways.
• Orbital cavities. The orbital cavities (orbits) in the skull house the eyes and present them in an anterior position

4. Middle ear cavities. The middle ear cavities carved into the skull lie just medial to the eardrums.

These cavities contain tiny bones that transmit sound vibrations to the hearing receptors in the inner ears.

• Synovial cavities.

Synovial cavities are joint cavities.

They are enclosed within fibrous capsules that surround freely movable joints of the body .

Like the serous membranes, membranes lining synovial cavities secrete a lubricating fluid that reduces friction as the bones move across one another.

QUIZ