Large intestine, rectum, anus Flashcards
Name the structures through this sagittal section of the abdomen
Structure of LI
- What are teniae coli
- where do they begin
- How do they terminate
- What do they form when they contract lengthwise
- 3 distinct bands of SM that run longitudinally
- Begin at the appendix
- Terminate by merging together at the rectosigmoid junction
- Contract lengthwise to form haustra
What are omental appendices
What are they also known as
Small fatty projections that are only found on the colon
epiploic appendages/appendices epiploicae
How do the haustrations and sacculations form
Wall becomes baggy and gathered
What are haustra
- Contraction of the teniae coli results in the shortening of the intestinal wall
- Sacculations form as the wall becomes “baggy” and gathered
- Visible on external surface
What are semilunar folds
- Haustra are internally separated by prominent ridges of mucosa
- Visible on the internal surface
- also PLICAE SEMILUNARIS
Peristalsis
Ripple-like wave of circular and longitudinal muscular contractions forcing material to propel forwards
Segmentation
Circular muscular contractions that mix and churn material forwards and backwards
Ileocecal junction
Marks junction between SI and LI when the ileum empties content into cecum via ileocecal valve
Ileocecal valve
- Formed by 2 semilunar shaped flaps that surround a slit-like orifice
- Located approximately 2cm above the opening of the appendix
- Acts to prevent REFLUX of chyme from the cecum back into ileum when digested material is acting against gravity to be propelled up the ascending colon
- Ileocolic lips create a passive flap valve that remains closed with tonic contractions
What is the cecum in relation to the ascending colon
First part of LI and is continuous with the ascending colon
Where is the cecum located
Right lower quadrant (RLQ)
Is the cecum intraperitoneal or retroperitoneal
Intraperitoneal as it can be lifted relatively freely and is entirely covered in a visceral layer of peritoneum
How is the cecum bound to the posterior abdominal wall
By cecal folds instead of having its own mesentery
Arterial supply of the cecum
Ileocolic artery (from the superior mesenteric)
What is the appendix
A 6-10cm blind intestinal diverticulum, containing masses of lymphoid tissue
Where is the appendix located
Right lower quadrant (RLQ)
McBurney’s point pain
Is the appendix intraperitoneal or retroperitoneal
INTRAPERITONEAL
How is the appendix held in place
By a short, triangular mesentery called the MESOAPPENDIX, arising from the posteromedial aspect of the cecum
Arterial supply of the appendix
The appendicular artery which travels in the mesoappendix and branches directly from the ileocolic artery
What is the ascending colon
2nd part of the LI and connects the cecum to the right colic flexure where it becomes the transverse colon
Where is the ascending colon located
Right quadrants (RLQ and RUQ)
Is the ascending colon intraperitoneal or retroperitoneal
Secondarily retroperitoneal
- link to embryology as only the anterior surface and sides are covered by peritoneum
Width of ascending colon in comparison to the cecum
NARROWER than cecum
Arterial supply of ascending colon
Right colic artery (branch of superior mesenteric)
What is the transverse colon (in relation to LI)
3rd part
Longest
Most mobile
Is the transverse colon intraperitoneal or retroperitoneal
Intraperitoneal
How is the transverse colon connected to the posterior abdominal wall
By transverse mesocolon, which allows it to hang down to level of umbilicus, approx L3/L4 vertebral level
RED LINE => ending of midgut and start of hindgut
How does the transverse colon attach to the diaphragm
At the left colic/splenic flexure via the phrenicocolic ligament
Arterial supply of transverse colon via
Middle colic artery - Proximal 2/3rds
Left colic artery - distal 1/3rd
Summary of proximal LI
What is the descending colon (in relation to LI)
4th part of LI and begins at left colic flexure where it connects the transverse colon -> sigmoid colon
Where is the descending colon located
In the left quadrants (LUQ and LLQ)
Is the descending colon intraperitoneal or retroperitoneal
Secondarily retroperitoneal
- link to embryology as only the anterior surface and sides are covered by peritoneum
Length of descending colon compared to ascending
Descending is longer
What is the left colic flexure related to
Spleen
What is the arterial supply of the descending colon
Left colic artery branching from inferior mesenteric artery
What is the sigmoid colon in relation to LI
5th part and connects descending colon to rectum
Where is the sigmoid colon located
Left Lower Quadrant (LLQ)
Where does the sigmoid colon extend from
Iliac fossa to approx S3 vertebral level
Is the sigmoid colon intraperitoneal or retroperitoneal
INTRAPERITONEAL
- Valvulus
Where do teniae coli terminate
At the rectosigmoid junction (NB SPOT!)
- approx 15cm from anus
Arterial supply of sigmoid colon
Sigmoid arteries (branching from inferior mesenteric)
Where does the rectum lie
Between the sigmoid colon and anal canal
What does the rectum follow
this fixed terminal part of the GIT follows the sacrococcygeal curve
External surface of the rectum
- No haustra
- No teniae coli
- No omental appendices
Is the PROXIMAL PART of the rectum intraperitoneal or retroperitoneal
Primarily retroperitoneal
Is the DISTAL PART of the rectum intraperitoneal, retroperitoneal or subperitoneal
Subperitoneal
What is the anal canal
Continuous with the rectum at the pelvic diaphragm where it makes a 90 degree posterior bend known as ANORECTAL FLEXURE
What is the anal canal divided into
An upper and lower part by PECTINATE LINE
