Case 12- anatomy 2

Question 1

Blood supply to the small intestine

Answer 1

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

Question 2

Venous drainage of the small intestine

Answer 2

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.

Question 3

Border between jejenum and ileum

Answer 3

There is no clear border between the jejenum and ileum but they have distinct features.

Question 4

The large intestine

Answer 4

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.

Question 5

Characteristics of large intestine- Taeniae coli

Answer 5

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.

Question 6

Characteristics of the large intestine- Haustra

Answer 6

Sacculation’s in the wall of the LI, they are due to contractions of the teniae coli. Look like bulges.

Question 7

Characteristics of the large intestine- Omental/epiploic appendices

Answer 7

Fatty projections which attach to the mental Teniae coli

Question 8

Cecum

Answer 8

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.

Question 9

Ileocecal valve

Answer 9

Between the cecum and the ileum, prevents reflux

Question 10

Veniform appendix

Answer 10

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

Question 11

Variable position of the veniform appendix

Answer 11

• 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

Question 12

McBurney’s point

Answer 12

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.

Question 13

Colon parts

Answer 13

Made of the ascending colon, transverse colon, descending colon and sigmoid colon

Question 14

Colon- flexure’s

Answer 14

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)

Question 15

Colon structure

Answer 15

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.

Question 16

Colon- gutters

Answer 16

Behind the ascending colon is the right paracolic gutter. Behind the descending colon is the left paracolic gutter

Question 17

The sigmoid colon

Answer 17

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.

Question 18

Which areas of the LI are derived from the midgut

Answer 18

Ascending colon and proximal 2/3 of transverse colon. Branches of the superior mesenteric artery

Question 19

Which areas of the LI are derived from the hindgut

Answer 19

Distal 1/3 of transverse colon, descending colon and sigmoid colon. Branches of the inferior mesenteric artery

Question 20

Arterial supply to the cecum and appendix

Answer 20

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.

Question 21

Venous drainage of the cecum and appendix

Answer 21

The Ileocolic vein which drains in the superior mesenteric vein.

Question 22

Arterial supply to the ascending colon

Answer 22

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.

Question 23

Anastomoses in the ascending colon

Answer 23

• 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.

Question 24

Arterial supply to the transverse colon

Answer 24

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.

Question 25

Anastomoses in the transverse colon

Answer 25

• 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.

Question 26

Arterial supply to the descending and sigmoid colon

Answer 26

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.

Question 27

Anastomoses to the descending and sigmoid colon

Answer 27

• 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.

Question 28

Marginal artery of Drummond

Answer 28

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

Question 29

Venous drainage of the colon- tributaries if the SMV

Answer 29

• Ascending colon: Ileocolic vein, Right colic vein

* Transverse colon: Middle colic vein

Question 30

Venous drainage of the colon- tributaries of the IMV

Answer 30

• Descending colon: Left colic vein

* Sigmoid colon: Sigmoid veins

Question 31

The rectum

Answer 31

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

Question 32

The rectum- flexures

Answer 32

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.

Question 33

The lower part of the rectum

Answer 33

The rectal ampulla

Question 34

Areas where the peritoneum covers in the rectum

Answer 34

• Superior third- anterior and lateral surfaces
• Middle third- anterior surface
• Inferior third- sub-peritoneal

Question 35

Sacral flexure

Answer 35

Curve of the sacrum and the coccyx

Question 36

Anorectal flexure

Answer 36

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.

Question 37

Internal anal sphincter

Answer 37

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.

Question 38

External anal sphincter

Answer 38

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.

Question 39

Pectinate line

Answer 39

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.

Question 40

Anorectal junction

Answer 40

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.

Question 41

Anal sinus

Answer 41

Produces mucus when compressed

Question 42

Anal pecten

Answer 42

Transition zone inferior to pectinate line. Ends at the Anocutaneous line where it becomes skin.

Question 43

Arterial supply to the proximal part of the rectum

Answer 43

The inferior mesenteric artery gives off the Superior rectal artery

Question 44

Arterial supply to the middle and inferior part of the rectum

Answer 44

Internal Iliac artery (anterior division) –> Middle rectal artery –> right and left middle rectal artery –> Middle and inferior parts of the rectum

Question 45

Arterial supply to the Anorectal junction and rectal canal

Answer 45

The Internal pudendal artery gives of the inferior rectal artery

Question 46

Arterial supply and pectinate line

Answer 46

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.

Question 47

Anastomoses above the pectinate line

Answer 47

The superior rectal artery (branch of IMA) anastomoses with branches from the middle rectal artery

Question 48

Anastomoses below the pectinate line

Answer 48

The inferior rectal artery (branch of the internal pudendal artery) anastomoses with branches from the middle rectal artery

Question 49

Venous drainage of the rectum

Answer 49

• 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.

Question 50

Internal rectus plexus

Answer 50

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.

Question 51

Anal cushions

Answer 51

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.

Question 52

External rectus plexus

Answer 52

External to the muscular wall of the rectum, subcutaneous

Question 53

Anastomoses above the pectinate line

Answer 53

The superior rectal vein (empties into IMV) anastomoses with the portal venous system

Question 54

Anastomoses below the pectinate line

Answer 54

The inferior rectal veins (empties into the internal pudendal veins) anastomoses with the systemic venous system

Question 55

Microscopic structural changes between sigmoid colon and rectum

Answer 55

• No taeniae coli as form continuous layer of smooth muscle

* No haustra or omental (epiploic) appendices on the rectum