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Observe abdominal viscera and peritoneum
Find these structures:
Falciform ligament
Greater omentum
Gastrocolic ligament
Omental apron
Stomach
Liver
Spleen
Small intestine
Large intestine
1.) If not complete from a previous session, remove the rectus abdominis mm. and external oblique mm from their subcostal attachments. Reflect the entirety of the anterior and lateral abdominal walls inferiorly.
1.) If not complete from a previous session, remove the rectus abdominis mm. and external oblique mm from their subcostal attachments. Reflect the entirety of the anterior and lateral abdominal walls inferiorly.
Photo 1. Reflected anterior abdominal wall
2.) Examine the anterior aspects of the abdominal cavity and the posterior aspect of the anterior and lateral abdominal walls. Identify the liver and stomach which are covered with visceral peritoneum and considered intraperitoneal.
2.) Examine the anterior aspects of the abdominal cavity and the posterior aspect of the anterior and lateral abdominal walls. Identify the liver and stomach which are covered with visceral peritoneum and considered intraperitoneal.
Note: The peritoneum, serous membrane lining the abdominopelvic cavity, consists of two layers: visceral and parietal peritoneum. Parietal peritoneum lines the walls of the cavity, whereas visceral peritoneum covers viscera suspended within the cavity. Between the parietal and visceral peritoneum is a dynamic potential space, the peritoneal cavity.
Note: Intraperitoneal refers to viscera covered by visceral peritoneum and suspended within, but not inside the peritoneal cavity. Retroperitoneal refers to organs located posterior to the peritoneum. Structures may either be primary or secondary retroperitoneal, depending on their developmental history. A primary retroperitoneal structure (i.e. kidneys, inferior vena cava, aorta, proximal rectum, ureters, and suprarenal glands) develops and remains retroperitoneal, whereas secondary retroperitoneal structures (i.e. the 2nd and 3rd parts of the duodenum, the ascending and descending colon, and most of the pancreas) begin development intraperitoneal, but eventually are drawn retroperitoneal.
Locate and identify the falciform ligament between the right and left lobes of the liver.
Locate and identify the falciform ligament between the right and left lobes of the liver.
Note: The falciform ligament is a peritoneal ligament (reflection) between the anterior abdominal wall and the liver. This ligament surrounds the round ligament of the liver (the remnant of the umbilical vein).
Identify the greater omentum, and locate a specific portion of the greater omentum: omental apron of the gastrocolic ligament.
Note: Omenta are folds of peritoneum which bind viscera to other viscera, or to the abdominal wall. The omenta are derived from the dorsal and ventral mesogastria (mesenteries), which anchored the primitive gut tube to the abdominal wall.
Note: Derived from the dorsal mesogastrium, the greater omentum is largely rooted on the stomach. It consists of several specialized peritoneal connections to viscera, such as the gastrocolic ligament (greater curvature of stomach to transverse colon), gastrosplenic ligament (greater curvature of stomach to hilum of spleen), and gastrophrenic ligament (fundus of stomach to left superior diaphragm). The omental apron is a ‘free-hanging’ double layer of the gastrocolic ligament, which hangs inferiorly from the greater curvature of the stomach anterior to the jejunum and ileum, before looping back to the transverse colon.
Photo 2. Abdominal cavity
Reflect the omental apron superiorly to locate, and identify the small intestine and portions of the large intestine.
Reflect the omental apron superiorly to locate, and identify the small intestine and portions of the large intestine.
Photo 3. Small intestine
3.) Examine the lengths of the jejunum and ileum.
3.) Examine the lengths of the jejunum and ileum.
Locate the:
Locate the:
Duodenojejunal flexure
Jejunum
Ileum
Ileocecal junction
Note: The small intestine consists (proximally to distally) of the duodenum, jejunum, and ileum. The duodenum connects the stomach to the jejunum, and will be studied with the pancreas in a later lab. The midportion of the duodenum is retroperitoneal, thus the duodenum is well anchored to the posterior abdominal wall. The jejunum and ileum are anchored by ‘THE’ mesentery to the posterior abdominal wall.
Photo 4. Jejunum, ileum, & mesentery
Photo 5. Ileocecal junction
Examine the mesentery (of jejunum and ileum) and its attachment to the posterior abdominal wall.
Examine the mesentery (of jejunum and ileum) and its attachment to the posterior abdominal wall.
Note: The mesentery of the jejunum and ileum is a double layer of peritoneum encasing fatty connective tissues and neurovasculature serving the alimentary canal. The root of the mesentery anchors in an oblique line on the posterior abdominal wall, starting adjacent to the duodenojejunal flexure to the right sacroiliac joint.
4.) Run the length of the ileum to its terminus and junction with the large intestine. Examine the length of the large intestine, and identify its features.
4.) Run the length of the ileum to its terminus and junction with the large intestine. Examine the length of the large intestine, and identify its features.
Locate the:
Cecum
Appendix
Ascending colon
Right colic (hepatic) flexure
Transverse colon
Left colic (splenic) flexure
Descending colon
Sigmoid colon
Rectum
Photo 6. Large intestine
Photo 7. Large intestine, continued
Note: The large intestine is comprised of several regions, proximal-to-distal: the cecum & appendix, ascending colon, R. colic (hepatic) flexure, transverse colon, L. colic (splenic) flexure, descending colon, sigmoid colon, and rectum.
Note: The ascending and descending colons are secondarily retroperitoneal. The proximal two-thirds of the rectum is also retroperitoneal.
Note: Fusion fascia are double layers of connective tissue formed by secondarily retroperitoneal structures colliding with the posterior body wall. Fusion fascia consist of what was previously parietal peritoneum and the visceral peritoneum on the posterior aspect of a structure fusing. The visceral peritoneum of the anterior structure then becomes the parietal peritoneum. Fusion fascia are clinically important because they allow for greater facility in either mobilizing or accessing a structure and are devoid of neurovasculature.
Photo 8. Cecum & appendix
5.) Carefully free the ascending and descending colons from the posterior body wall. Closely examine a length of one of these structures (or the transverse colon).
5.) Carefully free the ascending and descending colons from the posterior body wall. Closely examine a length of one of these structures (or the transverse colon).
Locate the:
Locate the:
Haustra of colon
Taeniae coli
Omental appendices
Note: The outer longitudinal layer of the muscularis of the colon condenses into three bands of muscle: the taeniae coli. Deviations of fibers from the free taenia coli form circumferential bands around the large intestine at regular intervals. These bands give the large intestine a sacculated appearance, and these sacs are known as haustra. Appendages of the large intestine are omental appendices, fat-filled outpouchings from the peritoneum.
Note: In your donor, you may notice diverticula, small outpouchings of the intestinal wall. Diverticulosis is common in older adults.
Photo 9. Features of the large intestine
Photo 10. Diverticula
6.) Examine the mesenteries associated with the large intestine.
6.) Examine the mesenteries associated with the large intestine.
Locate the:
Locate the:
Mesentery of the appendix (mesoappendix)
Transverse mesocolon
Sigmoid mesocolon
Note: The mesoappendix is a triangular fold of peritoneum connecting the appendix to the distal ileum. The mesoappendix is clinically important as it contains the appendicular artery.
Photo 11. Mesoappendix
Note: The transverse mesocolon is a double layer of peritoneum connecting the transverse colon to the posterior abdominal wall.
Photo 12. Transverse mesocolon
Locate superior mesenteric artery, vein, and branches
Locate superior mesenteric artery, vein, and branches
7.) With the large intestine in (roughly) anatomical position, left laterally reflect the bulk of the small intestines to expose the posterior parietal peritoneum.
7.) With the large intestine in (roughly) anatomical position, left laterally reflect the bulk of the small intestines to expose the posterior parietal peritoneum.
Photo 13. Procedural: reflected small intestine
Locate the:
Locate the:
Superior mesenteric a.
Jejunal & ileal aa.
Ileocolic a.
Appendicular a.
Right colic a.
Middle colic a.
Marginal a.
Superior mesenteric v.
8.) Starting at the root of the mesentery, and using blunt dissection, strip the visceral peritoneum from the intestines to expose the SMA & intestinal arteries beneath the right side of the mesentery.
8.) Starting at the root of the mesentery, and using blunt dissection, strip the visceral peritoneum from the intestines to expose the SMA & intestinal arteries beneath the right side of the mesentery.
Note: The SMA supplies the derivatives of the midgut (distal duodenum through the proximal two-thirds of the transverse colon).
Note: The SMA has several major branches:
inferior pancreaticoduodenal aa. (distal duodenum & pancreas)
jejunal and ileal (intestinal) aa.
ileocolic a. (distal ileum, cecum, & appendix)
right colic a. (ascending colon)
middle colic a. (transverse colon).
N.B. The branches are listed by the order of the structures of the midgut they supply, not by their branching order off the SMA. Keep in mind that the SMA branches from the abdominal aorta inferior to the celiac trunk. It becomes intraperitoneal as it emerges between the pancreas and the duodenum (posterior to the stomach).
Note: The marginal artery is considered a branch of the superior mesenteric artery, but it is an anastomotic arcade of the terminal branches of the SMA and IMA serving the large intestine. Relatively short straight arteries (arteriae rectae) bridge the distance from the marginal a. to the large intestine.
Note: The distal small intestine is supplied by a series of SMA branches called the jejunal and ileal (intestinal) aa. Intestinal branches exit the SMA linearly, form elaborate anastomotic arcades, and relatively long straight arteries (arteriae rectae) deliver blood to the jejunum and ileum. These intestinal arteries (and their venous counterparts) are sandwiched in the mesentery of the small intestine.
Photo 14. Procedural: removing the mesentery
Photo 15. Intestinal arteries
9.) Continue to remove the peritoneum to uncover the colic branches of the SMA.
9.) Continue to remove the peritoneum to uncover the colic branches of the SMA.
Note: The ‘colic’ arteries typically deliver blood from the SMA to the marginal artery (arcade) in the vicinity of their target regions. Straight arteries then deliver the blood a short distance to the large intestine. The ileocolic a. is considered the terminal branch of the SMA, but often it appears as a branch of the SMA leading to the vicinity of the ileocecal junction, and the SMA will continue to descend inferiorly, giving off intestinal aa. Carefully follow all branches in this area, and often you may find anastomoses among these branches with the marginal a.
Photo 16. Colic arteries of SMA
Note: The hepatic portal system is a series of veins collecting blood from capillary beds of the alimentary canal and delivering the blood to capillary beds of the liver. Nearly all veins of the GI drain into the hepatic portal system. The major architecture of the hepatic portal system is the union of the superior mesenteric v. with the splenic v. to form the hepatic portal v.
Photo 17. Superior mesenteric v.
Locate inferior mesenteric vasculature
Locate inferior mesenteric vasculature
10.) Reflect the small intestine laterally to the right side of the peritoneal cavity, exposing the descending colon, sigmoid colon, and rectum.
10.) Reflect the small intestine laterally to the right side of the peritoneal cavity, exposing the descending colon, sigmoid colon, and rectum.
Photo 18. Distal large intestine
Locate the:
Locate the:
Inferior mesenteric a.
Left colic a.
Sigmoid aa.
Superior rectal a.
Inferior mesenteric v.
11.) Bluntly remove the peritoneum covering the abdominal aorta and inferior mesenteric a.
11.) Bluntly remove the peritoneum covering the abdominal aorta and inferior mesenteric a.
Note: The IMA supplies blood to the derivatives of the hindgut (the distal third of the transverse colon through to the rectum).
Note: The IMA has several major branches:
left colic a. (descending colon)
sigmoid aa. (sigmoid colon)
superior rectal a. (rectum)
Note: Do not trace the superior rectal a. distally. We will revisit blood supply of the rectum when dissecting the pelvis.
Photo 19. Inferior mesenteric a.
Photo 20. Inferior mesenteric v.
Note: The inferior mesenteric v. is a portion of the hepatic portal system. Typically, the IMV drains into the splenic v., but it may also be a tributary of the SMV.
Examine the diaphragm and associated apertures
Examine the diaphragm and associated apertures
Locate the:
Locate the:
Diaphragm
Central tendon
Aortic hiatus
Esophageal hiatus
Caval opening
12.) Turning your attention to the thoracic cavity, view the diaphragm superiorly. Also take note of the diaphragm and associated features in subsequent labs, especially from an inferior approach, but realize that further dissect will necessitate destruction of the diaphragm.
12.) Turning your attention to the thoracic cavity, view the diaphragm superiorly. Also take note of the diaphragm and associated features in subsequent labs, especially from an inferior approach, but realize that further dissect will necessitate destruction of the diaphragm.
Photo 21. Diaphragm
Note: The diaphragm is the muscular division between the thoracic and abdominopelvic cavities. The muscular fibers of the diaphragm originate circumferentially from the thoracic outlet/inferior thoracic aperture (an uneven ring following the inferior margins of the 12th and 11th ribs, the costal cartilages, and the xiphisternal junction), and insert on the central tendon.
Note: There are three major apertures of diaphragm:
caval opening, at T8 (contents: inferior vena cava, right phrenic n., & lymphatics)
esophageal hiatus, at T10 (contents: esophagus, vagal trunks, esophageal br. of left gastric a., & lymphatics)
aortic hiatus, at T12 (contents: descending aorta, thoracic duct, & br. of the azygos v.).
Note: The aortic hiatus may be difficult to see superiorly. Look for it in subsequent labs.
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