Large Intestine Week 6 FINISHED Flashcards
What are the parts of the large intestine?
Caecum Appendix Colon Rectum Anal canal
What is the first part of the large intestine?
The caecum
What is the caecum continuous with?
The ascending colon
How long/wide is the caecum?
~ 7.5 cm in both length and breadth
Where is the caecum found?
Right lower quadrant
OR
Left iliac region
Caecum:
Inferior to the junction between the terminal ileum and large intestine
Where the ileum enters the caecum find folds superior and inferior forming the ileocecal valve
Ileocecal orifice
Does the caecum have mesentery?
No mesentery, is almost entirely covered by peritoneum
What is the appendix, AKA, how long is it, where is it and does it have mesentery?
An accessory part attached to a main structure
AKA vermiform appendix ( vermis = wormlike)
- 6 -10 cm in length
Arises from the posteriomedial aspect of the caecum
Inferior to the ileocecal junction (Mc Burney’s point 1/3 rd up line between ASIS and umbilicus)
Has a short mesentery = mesoappendix ( between the terminal ileum, and caecum and appendix)
What is the function of the appendix?
Function = contains lymphoid tissue, Stores, produces or processes lymphocytes
What is the arterial supply for the appendix and caecum?
Caecum - ileocolic artery, terminal branch of the SMA
Appendix - appendicular artery (branch of the ileocecal artery)
What is the venous drainage of the appendix and caecum?
Caecum and appendix - ileocolic vein > SMV
What is the nervous suply of the appendix and caecum?
Parasympathetic = vagus, Sympathetic = lower thoracic T12
What are the 4 parts of the colon?
Ascending, transverse, descending and sigmoid
What is the second part of the large intestine?
The ascending colon
Where does the ascending colon run?
Passes superiorly on the right side of the abdominal cavity
Passes from the caecum to the liver, here it turns left at the right colic flexure or the hepatic flexure
Is the ascending colon retroperitoneal? Does it have mesentery?
Yes it is retroperitoneal, covered by peritoneum anteriorly and on its sides
25% of people have a short mesentery
What is the arterial supply for the ascending colon?
Arterial supply to ascending colon and hepatic flexure
- branches from the SMA
- ileocolic and Rt colic arteries
What is the venous drainage of the ascending colon?
Venous drainage
- veins same names as arteries
- drain to SMV
What is the nervous supply of the ascending colon?
Parasympathetic – vagus
Sympathetic - entire colon T10 - L2
How long s the transverse colon?
45 cm long
Which is the largest and most mobile part of the large intestine?
The transverse colon
Where is the transverse colon/where does it run?
Variable in position, usually hanging to the level of the umbilicus
Passes across the abdomen from the Rt colic flexure (hepatic flexure) to the Lt colic flexure (splenic flexure)
What attaches the transverse colon to the diaphragm?
Attaches to the diaphragm by the phrenicocolic ligament
What is the mesentery of the transverse colon called?
Mesentery of the transverse colon = transverse mesocolon
What is the arterial supply of the transverse colon?
Arterial supply
- mainly from the middle colic artery, branch of the SMA
- also supply from the Rt colic artery (SMA) and Lt colic artery (IMA)
What is the venous drainage of the transverse colon?
Venous drainage - SMV
What is the nervous supply of the transverse colon?
Nerve supply:
- sympathetics - entire colon T10 - L2
- parasympathetics - vagus
What parts of the descending colon are covered in peritoneum?
Passes retroperitoneally
Covered with peritoneum anteriorly and laterally
Where does the descending colon pass?
Passes from the Lt colic flexure (splenic flexure) down to the iliac fossa
What is the descending colon continuous with inferiorly?
Continuous with the sigmoid colon
How long is the sigmoid colon?
Variable length ~ 40 cm long
Between what bony landmarks does the sigmoid colon pass?
Extends from the iliac fossa to S3 where joins the rectum
What is the rectosigmoidjunction signified by?
The termination of the teniae coli
Does the sigmoid colon have mesentery?
Has a mesentery and thus considerable freedom of movement
What are the teenier coli?
3 bands of longitudinal muscle
What is the arterial supply of the sigmoid colon and descending colon?
Lt colic (IMA) and superior sigmoid arteries (IMA)
What is the venous drainage of the descending and sigmoid colon?
IMV flows into the splenic vein and into the portal system
What is the nerve supply to the descending and sigmoid colon?
Sympathetics - lumbar part of the sym trunk via the superior hypogastric plexus
Parasympathetics - pelvic splanchnics S2-4
At what level is the junction between the rectum and the sigmoid colon?
S3
Where does the rectum end/become the anal canal?
Ends at the tip of the coccyx where it turns sharply in a posterior inferior direction at the anorectal flexure at the level of the pelvic diaphragm
What muscle forms a sling around the rectum, helping with bowel continence?
Puborectalis
What is the distal end of the rectum called?
Distal end of the rectum is called the rectal ampulla
= a dilated part of the rectum
Where is the rectal ampulla in relation to the pelvic diaphragm?
This lies directly above and is supported by the pelvic floor
What is the function of the rectal ampulla?
It receives and hold the accumulating faecal mass
It relaxes to accommodate accumulating faecal mass
What is the peritoneal covering of the rectum?
Superior 1/3 rd - covered anteriorly and laterally by peritoneum
Middle 1/3 - covered anteriorly
Inferior 1/3 rd - none because it is subperitoneal
What is the pouch in males where the peritoneum reflects from the posterior bladder to the rectum?
Rectovesicle pouch
What is the pouch in females where the peritoneum reflects from the posterior aspect of the vagina and uterus to the rectum?
Rectouterine pouch or Pouch of Douglas
What is the arterial supply of the rectum?
Superior rectal artery - (proximal rectum) from the inferior mesenteric artery
Middle rectal arteries - ( middle and inferior rectum) from the anterior division of the internal iliac
Inferior rectal arteries - (anorectal junction and anal canal) from the internal pudendal arteries (from the anterior division of the internal iliac)
What is the venous drainage of the rectum?
Superior rectal veins > portal venous system
Middle and inferior rectal veins > systemic system
What is the nervous supply of the rectum?
PSNS - pelvic splanchnics (S2-4)
SNS - Lumbar part of the sympathetic trunk
Differences from the large intestine to the small intestine:
Teniae coli ( 3 thickened bands of muscle)
- Comprise most of the longitudinal mm of the large intestine
- none in the appendix or rectum
- extends from the caecum to the beginning of the rectum
Haustrations ( sacculations of the colon between the teniae)
Omental appendices (small fatty projections of the omentum)
Calibre ( the internal diametre is greater)
