Human Anatomy - Kotsan I. Y. 2009

Splanchnology
Major glands of the digestive system
Peritoneum

The Abdominal cavity (cavitas abdominis) is the largest of all human Body Cavities. It is bounded superiorly by the Diaphragm, anteriorly and laterally by the Abdominal Muscles, posteriorly by the lumbar vertebrae and the quadratus lumborum muscles, and inferiorly by the walls of the greater and lesser pelvis. The interior of the abdominal cavity is lined with the endoabdominal fascia, which is closely covered by the parietal peritoneum. Between them lies a layer of adipose tissue that varies in thickness throughout the cavity; for instance, it is absent in the region of the diaphragm, poorly developed on the anterior abdominal wall (except for its lower part, where the peritoneum connects more loosely to the abdominal wall, allowing a full Urinary Bladder to displace the peritoneum so that its anterior surface directly contacts the abdominal wall 5 cm above the Pubic Symphysis). On the posterior abdominal wall, the Adipose tissue is well developed and retroperitoneally encloses the Kidneys, Adrenal Glands, Ureters, Abdominal Aorta, INFERIOR VENA CAVA, and several other structures.

The peritoneum is a serous membrane that lines the walls of the ABDOMINAL CAVITY AND envelops its Internal Organs. It consists of a basement membrane and a single layer of squamous epithelium known as the mesothelium. By transitioning from the cavity walls onto the organs and back again, the peritoneum forms a continuous, closed sac (Fig. 160).

The peritoneum comprises two layers: the parietal layer and the visceral layer. It should be noted, however, that these are not separate entities, but rather continuous Regions of the same serous membrane transitioning seamlessly into one another.

The parietal layer of the peritoneum, or parietal peritoneum (peritoneum parietale), lines the internal walls of the abdominal cavity, including the Inferior surface of the diaphragm, the posterior and lateral abdominal walls, and the floor of the pelvis.

The visceral layer of the peritoneum, or visceral peritoneum (peritoneum viscerale), covers the organs to varying degrees. Some organs are completely surrounded by the peritoneum (intraperitoneal position), others are covered on three sides (mesoperitoneal position), and some on only one side (extraperitoneal position). Certain organs are located entirely outside the peritoneal cavity, i.e., retroperitoneally. Typically, these retroperitoneal organs lie with one of their surfaces against the parietal peritoneum.

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Fig. 160. Course of the peritoneum (semi-schematic).

Sagittal section of the male abdominopelvic cavity

1 — coronary ligament of the Liver; 2 — superior omental recess; 3 — hepatogastric ligament; 4 — probe inserted into the omental bursa through the epiploic foramen; 5 — Pancreas; 6 — retroperitoneal space; 7 — duodenum; 8 — ROOT of the mesentery of the Small Intestine; 9 — loops of the jejunum; 10 — mesocolon of the sigmoid colon; 11 — promontory of the sacrum; 12 — rectum; 13 — rectovesical pouch; 14 — anus; 15 — Ductus deferens (vas deferens); 16 — Epididymis; 17 — Testis; 18 — cavity of the tunica vaginalis testis; 19 — tunica vaginalis testis; 20 — glans Penis; 21 — Urethra; 22 — corpus cavernosum of the penis; 23 — pubic symphysis; 24 — urinary bladder; 25 — retropubic space; 26 — loops of the ileum; 27 — greater omentum (posterior layers); 28 — greater omentum (anterior layers); 29 — parietal peritoneum; 30 — peritoneal cavity; 31 — transverse colon; 32 — inferior omental recess; 33 — transverse mesocolon; 34 — omental bursa; 35 — Stomach; 36 — liver; 37 — xiphoid process; 38 — diaphragm; 39 — body of the Sternum

Organs completely enveloped by the peritoneum (intraperitoneal position) include The Stomach, the duodenal bulb, the jejunum and ileum, the cecum with the vermiform Appendix, the transverse and sigmoid colons, the upper third of the rectum, the Spleen, and the liver (except for its bare area).

Organs covered by the peritoneum on three sides (mesoperitoneal position) include the middle third of the duodenum, the ascending and descending colons, the middle third of the rectum, the Gallbladder, the Uterus, the uterine tubes, and the distended urinary bladder.

Organs covered by the visceral peritoneum on only one side or not covered at all (extraperitoneal position) include the descending and ascending PARTS OF THE duodenum, the lower third of the rectum, the pancreas, and the empty urinary bladder.

Retroperitoneal organs, which lie behind the peritoneal cavity, include the kidneys, adrenal glands, and ureters.

The slit-like space between the parietal and visceral peritoneum is called the peritoneal cavity (cavitas peritonealis). The peritoneal cavity contains approximately 20 ml of serous fluid produced by the outer layer of the peritoneum, the simple squamous epithelium. This fluid lubricates the walls of the cavity, facilitating the continuous gliding Movements of the organs against one another. In males, the peritoneal cavity is completely closed. In females, it communicates with the external environment via the openings of the uterine tubes, the uterus, and the Vagina.

As the peritoneum transitions from the walls of the abdominal cavity onto the organs and from one organ to another, it forms ligaments, mesenteries, and omenta.

A peritoneal ligament is formed where the peritoneum passes from one organ to another (e.g., the gastrosplenic ligament, the hepatorenal ligament) or from the abdominal walls to the organs. Examples include the falciform and coronary ligaments of the liver. Peritoneal ligaments anchor the internal organs to the abdominal walls or to each other.

A mesentery is a double fold (duplication) of the peritoneum formed where the parietal layer transitions into the visceral layer. The mesentery serves to anchor organs in their proper positions within the abdominal cavity. It consists of two peritoneal leaves enclosing Blood Vessels and nerves that supply the organ. The various mesenteries include the mesentery of the small intestine, the transverse mesocolon, the sigmoid mesocolon, the mesorectum (mesentery of the upper third of the rectum), the mesoappendix, the broad ligament of the uterus (mesometrium), and the mesosalpinx and mesovarium.

The mesentery of the small intestine is the largest of these. It suspends the jejunum and ileum. The root of the mesentery of the small intestine runs obliquely across the posterior abdominal wall from the level of the second lumbar vertebra on the left to the right sacroiliac joint. The root of the mesentery is about 15–16 cm long, whereas its peripheral margin matches the length of the small intestine (5–6 m), meaning it fans out and becomes folded toward the intestinal border—hence the term mesentery, derived from ancient Greek words meaning "folded collar."

The transverse mesocolon lies horizontally at the level of the first lumbar vertebra, dividing the peritoneal cavity into two compartments: superior and inferior.

The superior compartment of the peritoneal cavity is bounded superiorly by the diaphragm, laterally by the lateral abdominal walls lined with parietal peritoneum, and inferiorly by the transverse colon and its mesentery. This compartment contains the stomach, liver with the gallbladder, spleen, superior part of the duodenum, and pancreas. The superior compartment is subdivided into three relatively distinct sacs or recesses: the hepatic bursa, located mainly in the right half of the superior compartment; the pregastric bursa, located chiefly in the left half; and the prominent omental bursa, situated behind the stomach.

The hepatic bursa (bursa hepatica) lies to the right of the falciform ligament of the liver, enclosing the right lobe of the liver. Deep within this bursa, beneath the liver, the superior pole of the right Kidney and the right Adrenal gland can be palpated.

The pregastric bursa (bursa pregastrica) is situated in the frontal plane to the left of the falciform ligament. It is bounded superiorly by the diaphragm, to the right by the falciform ligament, to the left by the phrenicocolic ligament, anteriorly by the anterior abdominal wall, and posteriorly by the lesser omentum and the gastrosplenic ligament. The pregastric bursa contains the left lobe of The Liver and the spleen.

The omental bursa (bursa omentalis) is located posterior to the stomach and the lesser omentum. It is bounded superiorly by the caudate lobe of the liver, inferiorly by the transverse colon and its mesentery, anteriorly by the posterior surface of the stomach, the lesser omentum, and the gastrocolic ligament, and posteriorly by the parietal peritoneum covering the aorta, inferior vena cava, upper pole of the left kidney, left adrenal gland, and pancreas on the posterior abdominal wall. The cavity of the omental bursa is a frontally disposed, irregularly trapezoid-shaped cleft with a shortened superior wall, a widened base, and three recesses: the splenic, superior omental, and inferior omental recesses.

The splenic (lienal) recess (recessus splenicus (lienalis)) is located in the left part of the omental bursa. Its walls are formed anteriorly by the gastrosplenic ligament and posteriorly by the phrenicosplenic ligament, which is a peritoneal fold extending from the diaphragm to the posterior end of the spleen.

The superior omental recess (recessus superior omentalis) is situated between the lumbar part of the diaphragm posteriorly and the posterior surface of the caudate lobe of the liver anteriorly.

The inferior omental recess (recessus inferior omentalis) is located between the gastrocolic ligament anteriorly and superiorly, and the posterior lamina of the greater omentum—which is fused with the transverse colon and its mesocolon—inferiorly and posteriorly. The omental bursa communicates with the hepatic bursa via the omental foramen (foramen omentale). The omental foramen, or Winslow's foramen, is relatively small (accommodating 1–2 fingers) and lies posterior to the hepatoduodenal ligament. It is bounded superiorly by the caudate lobe of the liver, inferiorly by the superior part of the duodenum, and posteriorly by the parietal peritoneum covering the inferior vena cava.

The inferior compartment of the peritoneal cavity lies inferior to the transverse colon and its mesocolon, extending downward into the pelvic cavity. This region of the peritoneal cavity contains the small intestine (except for the superior part of the duodenum) and the Large Intestine (except for the lower portion of the sigmoid colon and the rectum). Within the inferior compartment of the peritoneal cavity, the right and left lateral channels (gutters) as well as the right and left mesenteric sinuses are distinguished.

The right lateral channel (canalis lateralis dexter) is bounded by the peritoneum covering the right lateral wall of the abdominal cavity, the ascending colon, and the cecum. This channel communicates broadly with the hepatic bursa superiorly and the pelvic cavity inferiorly.

The left lateral channel (canalis lateralis sinister) is bounded by the peritoneum lining the left lateral wall of the abdominal cavity, the descending colon, and the sigmoid colon. It communicates with the pelvic cavity (broadly) and with the lesser sac / anterior gastric area (partially).

The right mesenteric sinus (sinus mesentericus dexter) is bounded on the right by the ascending colon, superiorly by the transverse colon, and on the left by the root of the mesentery of the small intestine. It contains loops of the lower part of the small intestine. Additionally, retroperitoneal structures project into this area, including the right kidney with its Ureter, the right suprarenal gland, the upper part of the inferior vena cava, the upper part of the abdominal aorta, the right Lumbar plexus, and the lumbar portion of the right Sympathetic trunk.

The left mesenteric sinus (sinus mesentericus sinister) is bounded on the left (laterally) by the descending and sigmoid colons, on the right (medially) by the root of the small intestine mesentery, and opens broadly inferiorly into the pelvic cavity. This sinus mainly contains loops of the jejunum. Retroperitoneal structures located here include the left kidney with its ureter, the lower parts of the inferior vena cava and abdominal aorta, the gonadal Arteries and Veins, the inferior mesenteric vessels, the left lumbar plexus, and the lumbar portion of the left sympathetic trunk.

The parietal peritoneum covering the posterior wall of the abdominal cavity forms folds and recesses at sites where it transitions from one organ to another or between an organ's margin and the abdominal wall. These recesses may serve as sites for retroperitoneal hernias. For instance, small superior and inferior duodenal recesses (recessus duodenalis superior et recessus duodenalis inferior) are present between the duodenojejunal flexure on the right and the superior duodenal ligament on the left. Where the ileum enters the cecum, the peritoneum forms folds that bound the superior and inferior ileocecal recesses (recessus ileocaecalis superior et recessus ileocaecalis inferior), located respectively above and below the terminal part of the ileum. Posterior to the cecum and the lower part of the ascending colon lies the retrocecal recess (recessus retrocaecalis). On the left side of the sigmoid mesocolon, at the attachment of its left leaf to the pelvic wall, There is a small intersigmoidal recess (recessus intersigmoideus).

The inferior compartment (region) of the peritoneal cavity continues into the pelvic cavity. Within the pelvis, the peritoneum covers the upper and partly middle thirds of the rectum, as well as the URINARY AND REPRODUCTIVE organs. The arrangement of the peritoneum in the pelvic cavity varies depending on sex.

In males, the peritoneum covering the anterior surface of the rectum reflects onto the posterior wall and then onto the superior wall of the urinary bladder. From there, it continues into the parietal peritoneum of the anterior abdominal wall. Between the urinary bladder and the rectum, the rectovesical pouch (excavatio rectovesicalis) is formed, bounded laterally by the rectovesical folds (plicae rectovesicales).

In females, the peritoneum passes from the anterior surface of the rectum onto the posterior wall of the upper vagina, ascends to cover the posterior and then anterior aspects of the uterus, and continues onto the urinary bladder. Between the uterus and the rectum, the rectouterine pouch (excavatio rectouterina) is formed, bounded laterally by the rectouterine folds (plicae rectouterinae). Between the uterus and the urinary bladder lies the vesicouterine pouch (excavatio vesicouterina).

Omenta are also peritoneal folds (duplications). They received this name because, unlike other peritoneal duplications, their tissue accumulates larger amounts of adipose tissue. There are only two omenta: the lesser and the greater omentum.

The lesser omentum (omentum minus) consists of two layers of peritoneum. It is situated between the porta hepatis on one side, and the lesser curvature of the stomach and the initial part of the duodenum on the other. The lesser omentum comprises the hepatoduodenal and hepatogastric ligaments (lig. hepatoduodenale et lig. hepatogastricum). The former contains the portal vein, proper hepatic artery, and common Bile duct; the latter contains Blood Vessels running along the lesser curvature of the stomach. In addition, Lymphatic vessels and nerves pass through these ligaments.

The greater omentum (omentum majus) is a double duplication (4 layers) of the peritoneum located behind the anterior abdominal wall. It hangs down apron-like from the stomach and transverse colon, anteriorly covering the intestines (Fig. 161). The anterior double layer of the greater omentum represents a peritoneal duplication descending from the greater curvature of the stomach along the anterior abdominal wall. Inferiorly, this duplication folds backward, turns upward, reaches the transverse colon, and fuses with its mesocolon. Containing adipose tissue, the greater omentum acts as a protective cushion that shields the internal organs from external mechanical impacts originating from the anterior abdominal wall. Beyond its mechanical role, the greater omentum Functions as a fat depot. Furthermore, it contains A large number of macrophages—specialized Cells capable of phagocytizing microorganisms and foreign bodies that invade the peritoneal cavity.

The peritoneal lining plays a remarkably significant and versatile role in the body.

First of all, the serous fluid contained within the peritoneal cavity facilitates the continuous physiological gliding of mobile abdominal organs, preventing adhesions between organs and with the walls of the abdominal cavity.

In addition, the peritoneum possesses considerable bactericidal properties; the greater omentum, long regarded as the "guardian of the abdominal cavity," plays a particularly vital role in this regard. Peritoneal duplications (mesenteries, certain ligaments, and folds) serve as pathways for blood vessels and nerves traveling to the abdominal organs. Moreover, the peritoneum—along with subperitoneal, interperitoneal (adipose tissue of the omenta and mesenteries), and retroperitoneal fatty tissue—plays a major role in anchoring the abdominal organs in place. Rapid and drastic weight loss (partial disappearance of the adipose tissue in the omenta, mesenteries, and retroperitoneal space), combined with other factors (weakening or overstretching of the anterior abdominal wall, heavy lifting, etc.), can lead to significant visceral ptosis (sagging of the stomach, kidneys, large intestine, etc.), resulting in impaired organ function. Under such conditions, inguinal, femoral, umbilical, and other hernias may also develop.

Fig. 161. Abdominal organs (anterior view)

1 — falciform ligament of the liver; 2 — liver (left lobe); 3 — round ligament of the liver; 4 — stomach; 5 — greater omentum (anterior lamina); 6 — sigmoid colon; 7 — small intestine; 8 — parietal peritoneum; 9 — ascending colon; 10 — transverse colon (contour/relief); 11 — Cytology/practical/108.html">Fundus of the gallbladder

The peritoneum of a newborn is considerably thinner than that of an adult; the greater omentum is thin and short, and folds and fossae are poorly developed.

Blood supply and Innervation of the peritoneum. The parietal peritoneum receives its blood supply and innervation from somatic (parietal) vessels and nerves, whereas the visceral peritoneum is supplied by the vessels and nerves branching within the organs it invests.