Nine Regions Of Abdomen ( Anatomy )

INTRODUCTION Abdominal cavity is the largest cavity. It encloses the peritoneal cavity between its parietal and visceral layers. Parietal layer clings to the wall of parieties while visceral layer is intimately adherent to viscera concerned. So their vascular supply and nerve supply are same as the parieties and viscera respectively. There are very lengthy organs in the abdominal cavity. These had to be disciplined with limited movements for proper functioning of the gut in particular and the body in general. Infections involving the parietal peritoneum impart protective "board-like rigidity" to the abdominal wall. Referred pain from the viscera to a dístant area is due to somatic and sympathetic nerves reaching the same spinal segment.

NINE REGIONS OF ABDOMEN

 For the purpose of describing the location of viscera, the abdomen is divided into nine regions by four imaginary planes, two horizontal and two vertical. The horizontal planes are the transpyloric and transtuber- cular planes. The vertical planes are the right lateral and the left lateral planes. The pelvic cavity lies below and posterior to the abdominal cavity. The transpyloric plane of Addison passes midway between the suprasternal notch and the pubic symphysis. It lies roughly a hand's breadth below the xiphisternal joint. Anteriorly, it passes through the tips of the ninth costal cartilage; and posteriorly through the body of vertebra L1 near its lower border.

Organs present on this plane are pylorus of stomach beginning of duodenum, neck of pancreas and hila of the kidneys. The transtubercular plane passes through the tubercles of the iliac crest and the body of vertebra L5 near its upper border. The right and left lateral planes correspond to the midclavicular or mammary lines. Each of these vertical planes passes through the midinguinal point and crosses the tip of the ninth costal cartilage. The nine regions marked out in this way are arranged in three vertical zones, median, right and left. From above downwards, the median regions are epigastric, umbilical and hypogastric. The right and left regions, in the same order, are hypochondriac, lumbar and iliac. Position of many organs is mentioned in Table 18.1. Liver chiefly occupies the right hypochondrium. Stomach and spleen occupy the left hypochondrium. Duodenum lies in relation to posterior abdominal wall. Coils of jejunum and ileum fill up the umbilical, lumbar and iliac regions. Large intestine lies at the periphery of abdominal cavity, caecum, ascending colon on right side, descen- ding colon on left side and transverse colon across the cavity. The pelvic cavity lies posteroinferiorly between pubic symphysis anteriorly and concavity of sacrum including coccyx posteriorly.

PERITONEUM

The peritoneum (Greek stretched over) is a large serous membrane lining the abdominal cavity. Histologically, it is composed of an outer layer of fibrous tissue, which gives strength to the membrane and an inner layer of mesothelial cells which secrete a serous fluid which lubricates the surface, thus allowing free movements of viscera.

The peritoneum is in the form of a closed sac which is invaginated by a number of viscera. As a result, the peritoneum is divided into:

 a. An outer or parietal layer. 

b. An inner or visceral layer; 

c. Folds of peritoneum by which the viscera are suspended. 

  The peritoneum which is a simple cavity, before being invaginated by viscera becomes highly compli- cated. 

Parietal Peritoneum

 1 It lines the inner surface of the abdominal and pelvic walls and the lower surface of the diaphragm. It is loosely attached to the walls by extraperitoneal connective tissue and can, therefore, be easily stripped. 

2 Embryologically, it is derived from the somato- pleuric layer of the lateral plate mesoderm. 

3 Its blood supply and nerve supply are the same as those of the overlying body wall. Because of the somatic innervation, parietal peritoneum is pain sensitive. 

Visceral Peritoneum 

1 It lines the outer surface of the viscera, to which it is firmly adherent and cannot be stripped. In fact it forms a part and parcel of the viscera. 

2 Embryologically, it is derived from the splanchno- pleuric layer of the lateral plate mesoderm. 

3 Its blood supply and nerve supply are the same as those of the underlying viscera. Because of the autonomic innervation, visceral peritoneum evokes pain when viscera is stretched, ischaemic or distended.