BODY CAVITIES

 Body Cavities

Vertebrates have fluid-filled spaces called body cavities that contain the organs. 

NB:

i. The dorsal cavity contains the primary organs of the nervous system, including the brain and spinal cord.

ii. The diaphragm is a sheet of muscle that separates the thoracic cavity from the abdominal cavity.

iii. Special membrane tissues surround the body cavities, such as the meninges of the dorsal cavity and the mesothelium of the ventral cavity.

iv.  The mesothelium consists of the pleura of the lungs, the pericardium of the heart, and the peritoneum of the abdominopelvic cavity.

Terminologies 

1. Thoracic Cavity :The ventral body chamber that contains the pericardial cavity (the heart) and the pleural cavity (the lungs).

2. Dorsal cavity : The cavity in the back of the body that contains the cranial and vertebral cavities, which house the brain and spinal cord respectively.

3. Abdominoplevic cavity : The ventral body chamber that contains the abdominal cavity (primarily digestive system) and the pelvic cavity (primarily reproductive system).

      By the broadest definition, a body cavity is any fluid-filled space in a multicellular organism. However, the term usually refers to the space where internal organs develop, located between the skin and the outer lining of the gut cavity. "The human body cavity," normally refers to the ventral body cavity because it is by far the largest one in volume. Blood vessels are not considered cavities but may be held within cavities. Most cavities provide room for the organs to adjust to changes in the organism's position. They usually contains protective membranes and sometimes bones that protect the organs.

Anatomical terminology for body cavities

Humans have multiple body cavities, including the cranial cavity, the vertebral cavity, the thoracic cavity (containing the pericardial cavity and the pleural cavity), the abdominal cavity, and the pelvic cavity. In mammals, the diaphragm separates the thoracic cavity from the abdominal cavity.

Dorsal : The dorsal cavity is a continuous cavity located on the dorsal side of the body. It houses the organs of the upper central nervous system, including the brain and the spinal cord. The meninges is a multi-layered membrane within the dorsal cavity that envelops and protects the brain and spinal cord.

Cranial : The cranial cavity is the anterior portion of the dorsal cavity consisting of the space inside the skull. This cavity contains the brain, the meninges of the brain, and cerebrospinal fluid. 

Vertebral : The vertebral cavity is the posterior portion of the dorsal cavity and contains the structures within the vertebral column. These include the spinal cord, the meninges of the spinal cord, and the fluid-filled spaces between them. This is the most narrow of all body cavities, sometimes described as threadlike.

Ventral : The ventral cavity, the interior space in the front of the body, contains many different organ systems. The organs within the ventral cavity are also called viscera. The ventral cavity has anterior and posterior portions divided by the diaphragm, a sheet of skeletal muscle found beneath the lungs.

Thoracic : The thoracic cavity is the anterior ventral body cavity found within the rib cage in the torso. It houses the primary organs of the cardiovascular and respiratory systems, such as the heart and lungs, but also includes organs from other systems, such as the esophagus and the thymus gland. The thoracic cavity is lined by two types of mesothelium, a type of membrane tissue that lines the ventral cavity: the pleura lining of the lungs, and the pericadium lining of the heart.

Abdominopelvic : The abdominoplevic cavity is the posterior ventral body cavity found beneath the thoracic cavity and diaphragm. It is generally divided into the abdominal and pelvic cavities. The abdominal cavity is not contained within bone and houses many organs of the digestive and renal systems, as well as some organs of the endocrine system, such as the adrenal glands. The pelvic cavity is contained within the pelvis and houses the bladder and reproductive system. The abdominopelvic cavity is lined by a type of mesothelium called the peritoneum.

 Abdominopelvic Regions

The abdomen is subdivided into four quadrants and nine areas.

NB :

The abdominopelvic cavity can be subdivided into four quadrants and nine areas. The quadrants are labeled by location: the right upper, right lower, left upper, and left lower quadrants.

The nine regions are smaller than the four abdominopelvic quadrants and include the right hypochondriac, right lumbar, right illiac, epigastric, umbilical, hypogastric (or pubic), left hypochondriac, left lumbar, and left illiac divisions.

The perineum is sometimes considered to be the tenth division.

The purpose of the abdominal divisions is to describe regional anatomy in the abdomen, and to help clinicians determine which organ and tissues are involved in a disease based on which regions experience pain. 

Terminologies 

Left lower quadrant : The left lower quadrant houses the majority of the small intestine, some of the large intestine, the left female reproductive organs, and the left ureter.

Right upper quadrant : The right upper quadrant contains the right portion of the liver, gallbladder, right kidney, a small portion of the stomach, portions of the ascending and transverse colon, and parts of the small intestine.

Left upper quadrant : The left upper quadrant is the location of the left portion of the liver, the larger portion of the stomach, the pancreas, left kidney, spleen, portions of the transverse and descending colon, and parts of the small intestine.

NINE DIVISIONS

An alternate system for dividing the abdominopelvic cavity into regions.

Right lower quadrant : In the right lower quadrant sits the cecum, appendix, part of the small intestines, the right female reproductive organs, and the right ureter.

Anatomists and medical personnel divide the abdominopelvic cavity into smaller regions to facilitate study and discussion. These divisions are often used to categorize the individual abdominal organs by their location and function and are used by clinicians to help diagnose the source of abdominal pain and determine appropriate treatment. The most common divisions for the abdominopelvic region are the four quadrants and nine regions.

Abdominal nine divisions (a) and quadrant regions (b)

The abdomen is subdivided into four quadrants and nine areas.

This image illustrates the organs included in the four quadrants and nine regions as described above.

Abdominal Four Quadrants

The abdominopelvic region can be divided into four quadrants. These quadrants are defined by the intersection of the saggital plane with the umbilical plane (the transverse plane through the navel). Clinicians use these regions to determine the organs and tissues that may be causing pain or discomfort in that region.

1. Right Upper Quadrant : The right upper quadrant contains the right portion of the liver, the gallbladder, right kidney, a small portion of the stomach, the duodenum, the head of the pancreas, portions of the ascending and transverse colon, and parts of small intestine. Pain in this region is associated with infection and inflammation in the gallbladder and liver or peptic ulcers in the stomach.

2. Left Upper Quadrant : The left upper quadrant is the location of the left portion of the liver, part of the stomach, the pancreas, left kidney, spleen, portions of the transverse and descending colon, and parts of the small intestine. Pain in this region is associated with malrotation of the intestine and colon.

3.Right Lower Quadrant :In the right lower quadrant sits the cecum, appendix, part of the small intestines, the right half of the female reproductive system, and the right ureter. Pain in this region is most commonly associated with appendicitis.

4. Left Lower Quadrant : The left lower quadrant houses the majority of the small intestine, some of the large intestine, the left half of the female reproductive system, and the left ureter. Pain in this region is generally associated with colitis (inflammation of the large intestine) as well as pelvic inflammatory disease and ovarian cysts in females.

Abdominal Nine Divisions

The nine divisions of the abdominopelvic region are smaller than the four quadrants, allowing for a more detailed discussion. These divisions are marked by two parasagittal and two transverse planes centered around the navel. Most organs are part of multiple regions, including the gallbladder, duodenum, stomach, kidneys, spleen, small intestine and colon. The perineum (the area beneath the hypogastric region at the bottom of the pelvic cavity) is sometimes considered to be a tenth division in this system.

i. Right Hypochondriac : The right hypochondriac region contains the right portion of the liver, the gallbladder, the right kidney, and parts of the small intestine.

ii. Left Hypochondriac : The left hypochondriac region contains part of the spleen, the left kidney, part of the stomach, the pancreas, and parts of the colon.

iii. Epigastric : The epigastric (above stomach) region contains the majority of the stomach,  part of the liver, part of the pancreas, part of the duodenum, part of the spleen, and the adrenal glands. This region pushes out when the diaphragm contracts during breathing.

iv.  Right Lumbar : The right lumbar region consists of the gallbladder, the left kidney, part of the liver, and the ascending colon.

v. Left Lumbar : The left lumbar region consists of the descending colon, the left kidney, and part of the spleen. 

vi. Umbilical : The umbilical region contains the umbilicus (navel), and many parts of the small intestine, such as part of the duodenum, the jejunum, and the illeum. It also contains the transverse colon (the section between the ascending and descending colons) and the bottom portions of both the left and right kidney. 

vii. Right Iliac : The right iliac region contains the appendix, cecum, and the right iliac fossa. It is also commonly referred to as the right inguinal region. Pain in this area is generally associated with appendicitis.

viii. Left Iliac : The left illiac region contains part of the descending colon, the sigmoid colon, and the right illiac fossa. It is also commonly called the left inguinal region.

ix.  Hypogastric : The hypogastric region (below the stomach) contains the organs around the pubic bone. These include bladder, part of the sigmoid colon, the anus, and many organs of the reproductive system, such as the uterus and ovaries in females and the prostate in males.