Case 12- anatomy 2 Flashcards
Blood supply to the small intestine
The superior mesenteric artery (L1). The SMA then branches off into the jejunal and ileal arteries. The arteries pass through the mesentery then form the arterial arcades and the vasa recta. The terminal end of the ileum receives blood from the Superior ileal branches of the Ileocolic artery. The Ileocolic artery is a branch of the SMA
Venous drainage of the small intestine
The blood drains from the jejenum and the ileum through the jejunoileal and ileocolic vein, into the superior mesenteric vein. The SMV joins with the splenic vein to form the hepatic portal vein and drain through the liver.
Border between jejenum and ileum
There is no clear border between the jejenum and ileum but they have distinct features.
The large intestine
About 1.5m. It absorbs fluids and salts from the gut to form faeces. The large intestine consists of a cecum and vermiform appendix, colon (which can be split into four parts; ascending, descending, transverse and sigmoid colon), rectum and anal canal.
Characteristics of large intestine- Taeniae coli
Three longitudinal bands of smooth muscle. They are mesocolic, omental and free. The Mesocolic is where the transverse and sigmoid mesocolon attach. The Taeniae coli runs the whole length of the large intestine in three bands which merge at the rectosigmoid junction into a continuous layer around the rectum.
Characteristics of the large intestine- Haustra
Sacculation’s in the wall of the LI, they are due to contractions of the teniae coli. Look like bulges.
Characteristics of the large intestine- Omental/epiploic appendices
Fatty projections which attach to the mental Teniae coli
Cecum
The first part of the large intestine, inferior to the ileocecal junction. An intestinal pouch which is continuous with the ascending colon. It is located in the right iliac fossa. Bound to the abdominal wall by caecal folds of peritoneum.
Ileocecal valve
Between the cecum and the ileum, prevents reflux
Veniform appendix
A narrow hollow tube, normally called appendix. Attached to the posteromedial wall of the cecum. Contains lymphoid tissue and the meso-appendix which is a triangular bit of mesentery. Whilst the base of the appendix is constant, the rest of its position can differ between individuals
Variable position of the veniform appendix
- Retrocecal – posterior to the cecum or ascending colon
- Subcecal – below the cecum
- Pelvic – over the pelvic brim
- Preileal – anterior to the terminal ileum
- Postileal – posterior to the terminal ileum
McBurney’s point
Surface projection of the base of the appendix. It is a third of the way along line a line from the right anterior superior iliac spine to the umbilicus. Tends to be where people feel pain in appendicitis.
Colon parts
Made of the ascending colon, transverse colon, descending colon and sigmoid colon
Colon- flexure’s
The junction between the ascending colon and the transverse colon is the right colic flexure (hepatic flexure). The junction between the transverse colon and the descending colon is the left colic flexure (splenic flexure)
Colon structure
The ascending and descending colon are retroperitoneal but the transverse and sigmoid colon are intraperitoneal. It is attached to the diaphragm at the phrenicolic legament at the left colic flexure.
Colon- gutters
Behind the ascending colon is the right paracolic gutter. Behind the descending colon is the left paracolic gutter
The sigmoid colon
The sigmoid colon extends from the pelvic inlet to the level of S3 where it is continuos with the rectum. The sigmoid colon is attached to the abdominal wall using the sigmoid mesocolon.
Which areas of the LI are derived from the midgut
Ascending colon and proximal 2/3 of transverse colon. Branches of the superior mesenteric artery
Which areas of the LI are derived from the hindgut
Distal 1/3 of transverse colon, descending colon and sigmoid colon. Branches of the inferior mesenteric artery
Arterial supply to the cecum and appendix
Provided by the SMA which branches into the Ileocolic artery. The Ileocolic artery branches into the inferior branch, which then divides into the Anterior cecal artery, the Posterior cecal artery and the Appendicular artery.
Venous drainage of the cecum and appendix
The Ileocolic vein which drains in the superior mesenteric vein.
Arterial supply to the ascending colon
Supplied by the SMA which branches into the Ileocolic artery and right colic artery, both supply the ascending colon. The Ileocolic artery branches into the inferior branch which provides the Colic artery, Anterior cecal artery and the Posterior cecal artery.
Anastomoses in the ascending colon
- The descending branch of the right colic artery anastomoses with the ileocolic artery.
- The ascending branch of the right colic artery anastomoses with the middle colic arteries.
Arterial supply to the transverse colon
Supplied by SMA and IMA. The SMA branches into the the right colic artery and the middle colic artery. The IMA branches into the left colic artery.
Anastomoses in the transverse colon
- Ascending branch of the right colic artery anastomoses with the right branch of the middle colic artery.
- The left branch of the middle colic artery anastomoses with the ascending branch of the left colic artery.
Arterial supply to the descending and sigmoid colon
Supplied by the IMA. The IMA branches into the left colic artery which supplies the descending colon. The IMA branches into the sigmoid artery which supplies the sigmoid colon.
Anastomoses to the descending and sigmoid colon
- Ascending branch of the left colic artery anastomoses with branches of the sigmoid artery.
- Branches of the sigmoid artery anastomoses with branches from the superior rectal artery.
Marginal artery of Drummond
The SMA and IMA anastomose together to form a continuous channel around the large intestine. This is a continuous arterial channel. This supplies collateral blood supply to the colon, if there is occlusion of a vessel, another artery can supply the area. There is a break at the left colic flexure, leaving it more open to ischaemia
Venous drainage of the colon- tributaries if the SMV
- Ascending colon: Ileocolic vein, Right colic vein
* Transverse colon: Middle colic vein
Venous drainage of the colon- tributaries of the IMV
- Descending colon: Left colic vein
* Sigmoid colon: Sigmoid veins
The rectum
Continuous with the sigmoid colon proximally and the anal canal distally. It is located in the pelvic canal. The junction between the rectum and the sigmoid colon is the Rectosigmoid junction at the level of S3 or at the end of the sigmoid mesocolon
The rectum- flexures
Contains three lateral flexures (superior, intermediate and inferior) which are formed from the transverse folds (part of internal surface). The flexures are indentations in the rectum and are external features.
The lower part of the rectum
The rectal ampulla
Areas where the peritoneum covers in the rectum
- Superior third- anterior and lateral surfaces
- Middle third- anterior surface
- Inferior third- sub-peritoneal
Sacral flexure
Curve of the sacrum and the coccyx
Anorectal flexure
Passes through the pelvic floor muscles. The puborectalis muscle forms a sling indenting the rectum. Important for maintain continence. During defaecation the puborectalis muscle relaxes, it increases the anorectal angle to increase. The angle is normally 90 degrees when its relaxed it goes to 180 degrees. The rectum ends at the anorectal flexure.
Internal anal sphincter
Involuntary and surround the superior 2/3rds of the rectal canal. It is a thickening of the circular muscle layer. Has sympathetic and parasympathetic innervation. Contraction stimulated by sympathetic fibres which is from the superior rectal and hypogastric plexus’s. Contraction is inhibited by the Parasympathetic fibres which is stimulated by peristalsis and the pelvic-splenic nerve. Also relaxes in response to stretching of the rectal ampulla.
External anal sphincter
Voluntary and found on the inferior 2/3rds of the anal canal. Blends with the pubalis rectalis muscle. Has three parts, subcutaneous, superficial and deep parts. Formed from skeletal muscle.
Pectinate line
Junction of the superior (hindgut) and inferior part (proctodeum) of the anal canal. The anal valves forms a circle around the anal canal forming the Pectinate line.
Anorectal junction
Superior ends of the anal column, where the rectum joins the anal canal. The anal columns are linked by the anal valves, superior to each valve is an anal sinus which produces mucus when compressed.
Anal sinus
Produces mucus when compressed
Anal pecten
Transition zone inferior to pectinate line. Ends at the Anocutaneous line where it becomes skin.
Arterial supply to the proximal part of the rectum
The inferior mesenteric artery gives off the Superior rectal artery
Arterial supply to the middle and inferior part of the rectum
Internal Iliac artery (anterior division) –> Middle rectal artery –> right and left middle rectal artery –> Middle and inferior parts of the rectum
Arterial supply to the Anorectal junction and rectal canal
The Internal pudendal artery gives of the inferior rectal artery
Arterial supply and pectinate line
The superior rectal artery provides the blood supply above the pectinate line and the inferior rectal artery provides the blood supply below the pectinate line.
Anastomoses above the pectinate line
The superior rectal artery (branch of IMA) anastomoses with branches from the middle rectal artery
Anastomoses below the pectinate line
The inferior rectal artery (branch of the internal pudendal artery) anastomoses with branches from the middle rectal artery
Venous drainage of the rectum
• Superior rectal vein (branch of IMV)- drain into the portal venous system
• The middle rectal vein (branch of the internal iliac vein- drains into the systemic circulation
• The inferior rectal veins (branch of the internal pudendal vein)- drains into the systemic circulation.
Forms portocaval anastomoses where the postal veins anastomose with the systemic veins.
Internal rectus plexus
Deep to the mucosa of the anorectal junction. Found within the connective tissue. Drains both directions of the pectinate line. Superior to the pectinate line it drains into the superior rectal vein. Inferior to the pectinate line drains into the inferior rectal vein.
Anal cushions
Within the internal rectus plexus. Where the sacculated veins anastomose with the arterial blood. These arteriovenous anastomoses can form a valve and help with continence as they squeeze on the rectal wall.
External rectus plexus
External to the muscular wall of the rectum, subcutaneous
Anastomoses above the pectinate line
The superior rectal vein (empties into IMV) anastomoses with the portal venous system
Anastomoses below the pectinate line
The inferior rectal veins (empties into the internal pudendal veins) anastomoses with the systemic venous system
Microscopic structural changes between sigmoid colon and rectum
- No taeniae coli as form continuous layer of smooth muscle
* No haustra or omental (epiploic) appendices on the rectum
