Lecture 10 - Large intestines Flashcards
The components of the large intestines
- Vermiform appendix
- Caecum
- Ascending colon
- Right colic flexure (hepatic flexure)
- Transverse colon
- Left colic flexure (splenic flexure)
- Descending colon
- Sigmoid colon
- Rectum
- Anal canal
Large intestines: function
To absorb water and electrolytes from indigestible intestinal contents and compact this undigested material for excretion as faeces
Taenia Coli
Three thickened bands of longitudinal muscle, contracting makes them act like drawstrings, compressing the haustra, squeezing water and electrolytes out of faecal matter
Semilunar folds
Folds in between the haustra - very pronounced, bulges/bags formed between each semilunar folds
Haustra
Sacculations of the wall between Taenia coli
Very pronounced, bulges/bags formed between each semilunar folds
Epiploic appendages
AKA - Omental appendices
Small pouches of fat-filled omentum
Crypts of Lieberkühn: what cell types are presennt?
Absorptive cells - more near the lumen
Mucous-secreting goblet cells - More near bases of crypts, useful in lubricating faecal matter
Caecum: what is it, where is it located, and what are its relations?
Saclike part of the large intestines
1st part of the large intestine - lies in the right lower quadrant (RLQ)
- Ileum opens into its medial aspect
- The appendix opens into its medial aspect inferiorly
Ileocolic lips and ileal orifice
Located at the connection between the ileum and caecum
Vermiform appendix: what is it, what are its relations, and what are some key facts?
A blind-ended diverticulum
Taenia coli converge at this point – easy to find during surgery
- Supported by mesoappendix - mesentery supporting the appendix
- Contains lots of lymphoid tissue
- Appendicitis may occur
- The Appendix is variable in length and position, which affects how easy it is to palpate
McBurneys point
The reason that appendicitis is so painful
McBurney’s point lies 1/3 the way from the ASIS to the umbilicus - at the appendix base
Why do patients complain of pain in the umbilical region?
Think about visceral afferent fibres
T10 is the nerve that is a receptor for the pain, causing poor localisation
Large intestine’s blood supply
Right and left sides of the large intestines are supplied by the SMA and the IMA respectively
Right side - SMA:
* Middle colic - Transverse colon
* Right colic - Ascending colon
* Ileocolic - supplies the caecum and lower parts of the large intestines
* Appendicular - splits from the ileocolic, supplies the appendix
Left side - IMA:
* Marginal artery - supplies the transverse colon
* Left colic - supplies the splenic flexure and the descending colon
* Sigmoidal branches - supply the ((descending colon and)?) sigmoid colon
* Superior rectal - supplies the rectum
Large intestine’s venous drainage
Right and left sides of the large intestines are supplied by the SMV and the IMV respectively - but the IMV flows into the SMV along with the splenic vein
Right side (midgut) - SMA:
* Middle colic - Transverse colon
* Right colic - Ascending colon
* Ileocolic - drains the caecum and lower parts of the large intestines
* Appendicular - splits from the ileocolic, drains the appendix
Left side (hindgut) - IMA:
* Marginal vein - drains the transverse colon
* Left colic - drains the splenic flexure and the descending colon
* Sigmoidal branches - drains the ((descending colon and)?) sigmoid colon
* Superior rectal - drains the rectum
Large intestines lymphatic drainage
ileocolic vein -> superior mesenteric vein -> portal system
Ascending colon: where is it located, how big is it, what is its peritoneum like, is mesentery present, and what are its relations?
From caecum to hepatic flexure, in RLQ
12-20 cm long, narrower diameter than caecum
Retroperitoneal, covered with peritoneum anteriorly, medially, and laterally
Has short mesentery in 25% of people
- Small intestine, abdominal wall and greater omentum anteriorly
- Illiacus, iliac crest, quadratus lumborum and lower pole of right kidney posteriorly
- Hepatic flexure at level of 9th or 10th rib
Transverse colon: where is it located, how big is it, how is it held in place, and what are its relations?
From hepatic to splenic flexures, hangs downward with a variable position (sometimes reaching as far as the pelvis)
40 cm long - the longest part of the colon
Supported by transverse mesocolon
Suspended from the anterior border of the pancreas
- Abdominal wall and greater omentum anteriorly
- Second part of the duodenum, head of the pancreas and jejunum & ileum posteriorly
Descending colon: where is it located, how big is it, what is its peritoneum like, is mesentery present, and what are its relations?
From splenic flexure to pelvic brim, about 15 cm from the anus - faeces stored in the sigmoid colon until just before defaecation
About 25 cm long
Retroperitoneal, covered by the peritoneum anteriorly, and laterally, the peritoneum binds it to the posterior abdominal wall
Short mesentery in 33% of people
- Small intestine, abdominal wall and greater omentum anteriorly
- Left psoas major, illiacus, iliac crest, quadratus lumborum and lateral border of the left kidney posteriorly
Sigmoid colon: where is it located, what is it, how big is it, how is it held in place, what is volvulus, what is Taenia coli, and what are its relations?
From iliac fossa to S3
Named for its S-shape
25 to 38 cm long
Supported by sigmoid mesocolon, therefore mobile
Volvulus is a possibility - occurs when a loop of intestine twists around itself and the mesentery that supplies it, causing a bowel obstruction - this may occur in any part with mesenteries
Taenia coli vanish as longitudinal muscle broadens to form a complete layer in rectum - three longitudinal muscles becomes just one layer
- Males: urinary bladder
- Females: uterus & superior vagina
- Posterior relations - rectum and sacrum
Mesenteries: which parts of the large intestines lie outside of the peritoneal cavity, which parts are retroperitoneal, and which parts are subperitoneal?
The ascending and descending colons, rectum and anal canal lie outside of the peritoneal cavity
The ascending and descending colons are
retroperitoneal - they are not supported by mesenteries
The rectum (inferior 1/3) and anal canal are
subperitoneal
Large intestines innervation
Midgut: sympathetic fibres from superior mesenteric plexus, parasympathetic fibres from vagus nerve
Hindgut: sympathetic fibres from inferior mesenteric plexus, parasympathetic fibres from sacral nerves 1 to 3 via pelvic splanchnic nerves
Visceral afferent fibres: T8 – S4
