Abdominal cavity

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Front view of the thoracic and abdominal viscera

The abdominal cavity is the cavity in the abdomen, protected by the anterior, and posterior abdominal walls. It is divided into left and right, as well as upper and lower halves, giving four quadrants. These divisions occur along the vertical and horizontal plane, with the umbilicus as the center of either plane. The abdominal cavity is also divided into nine regions, as shown by the image to the right. These regions are:

  • Right and left hypochondriac
  • Epigastric
  • Right and left lumbar
  • Umbilical
  • Right and left inguinal
  • Suprapubic (hypogastrum)

The planes are also shown on the image to the right. They are:

  • Median plane
  • Lateral planes
  • Trans tubercular plane
  • Subcostal plane
  • Transpyloric plane
Vertical disposition of the peritoneum

Peritoneum

Distally, the two layers of the mesentery separate and surround the gut as visceral peritoneum. Something can also be said about parietal peritoneum, but I don't know it.


Omentum

Sacs

Greater sac

  • The bulk of the peritoneal cavity forms the greater sac
  • Extends from the diaphragm to the pelvic floor

Lesser sac

  • A recess of the greater sac, the lesser sac (omental bursa), is located behind the stomach
  • Towards the right, the lesser sac communicates with the greater sac via a narrow opening, the epiploic foramen
  • The lesser sac is a site where inflammatory exudate forms due to disease in its adjoining structures, e.g. stomach or pancreas
  • The exudate may gain access to the greater sac via the epiploic foramen.

Pain

Visceral pain

  • Usually vague, ill-localized and deep-seated
  • Visceral pain fibers are sensitive to stretching and anoxia
  • fiber endings are located in the muscular walls or fibrous capsule of the viscera
  • A diseased gut segment (e.g. acute appendicitis) will initially elicit visceral pain

Somatic pain

  • Specific, localized, and not deep-seated
  • Produced by the stimulation and stretching of parietal peritoneum
  • Inflammation of the anteriolateral wall will produce pain that is sharp and limited to the area of inflammation
  • In the diseased gut, the subsequent spread of inflamation to the parietal peritoneum will involve somatic innervation
  • the pain will therefore become somatic in nature (sharp and well localized to the right iliac fossa in the case of acute appendicitis)

Referred pain

  • Diseased viscera may also elicit referred pain to regions of the body wall that share the same segmental innervation as that of the viscus
  • The dermatomes of the painful cutaneous region are innervated by the same spinal cord segments that innervate the diseased or injured viscus
  • In case of an appendicitis, the pain may be referred to the region of the umbilicus, since afferent fibres (both visceral and somatic) reach the T10 segment of the spinal cord

Objectives

  • name and define the quadrants and regions of the abdomen using anatomical landmarks and planes
  • review the terms parietal and visceral peritoneum, mesentery, dorsal and ventral mesentery, greater and lesser sac
  • list the structures found at the transpyloric plane
  • describe the recesses and gutters of the peritoneal cavity
  • define the terms epiploic foramen and describe its borders
  • list the components of the gastrointestinal tract
  • state the fate of the mesenter(y)ies associated with the components of the GI tract
  • state which components are intraperitoneal, secondary retroperitoneal, retroperitoneal
  • outline the general pattern of efferent and afferent innervation of the gastrointestinal tract and state their functions
  • define the terms "visceral pain", "referred pain" and "somatic pain" in relation to the anatomy of the gastrointestinal tract.

Resources