Small and Large Intestine Flashcards
What is the shape of the duodenum
C-shaped around the head of the pancreas
What is the duodenum continuous with
Pylorus of the stomach
Is the duodenum retro or intra peritoneal
Retroperitoneal
What is the major duodenal papilla and where is it found
Approx. 1/2 way along the internal wall of the duodenum
Opening for the bile duct and main pancreatic duct into the duodenum
What does the first half of the duodenum develop from
Embryological foregut
What supplies the first half of the duodenum
Branches from the coeliac trunk
What does the second half of the duodenum develop from
Embryological mid gut
What supplies the second half of the duodenum
Superior mesenteric artery
Which comes first the jejunum or ileum
Jejunum
What is continuous with the duodenum
Jejunum
Is the jejunum retro or intra peritoneal
Intraperitoneal
Is the ileum retro or intra peritoneal
Intraperitoneal
What is both the jejunum and ileum suspended from
Posterior abdominal wall by the mesentery of the small intestine
What are the jejunum and ileum derived from
Embryological midgut
Where does the jejunum lie
Left upper region
Where does the ileum lie
Right lower region
What features does the small intestine have for nutrient absorption
Vast surface area
Small intestine long
Mucosa folded (plicae circulares)
Mucosal folds bear villi
Microvilli
What is Meckel’s diverticulum
Blind ended diverticulum approx. 1m from its termination
What is the Meckel’s diverticulum a remnant of
Connection that was present between the midgut loop to the yolk sac
What is terminal ileum continuous with
Caecum
What is the junction called between the terminal ileum and caecum and where is it found
Ileocecal junction
R. iliac fossa
Define appendix
Small diverticulum that arises from the caecum
Contains lymphoid tissue
Connected to caecum by a small mesentery
What is the small mesentery called which connects the caecum to the appendix
Mesoappendix
What does the urge to defecate arise from
Contraction of rectal muscles
Relaxation of internal anal sphincter
Initial contraction of external anal sphincter
What is the nerve supply of the external anal sphincter
Pudendal nerve S2,3,4 - allows concious control
Describe defecation
Rectum is distended the rectosphinteric reflex is initiated and relaxes the internal sphincter
Then
- relaxation of the external sphincter
- contraction of abdominal wall muscles
- relaxation of pelvic wall muscles
Peristaltic waves facilitate movement of faeces through anal canal
What happens if defecation is not desired
Voluntary contraction of the external sphincter - usually enough to override the reflexes of anal distension initiates
Describe the Valsalva Manoeuvre
Defecation can be assisted by taking a deep breath and attempting to expel air against the glottis
What is the blood supply to the jejunum and ileum
Superior mesenteric artery
Embedded within the mesentery
What is more pronounced in the jejunum
Plicae
What is the internal ileum characterised by
Peyer’s patches - large submucosal lymph nodules
What is the role of the large intestine
Reabsorbs water from faecal material to form semi-solid faeces
What is the large intestine formed of
Caecum
Appendix
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Rectum
Anal canal
What is the outer longitudinal muscle layer of the large intestine organised like
Three bands - taeniae coli
Inner circular muscle layer forms budges - haustra
What is taeniae coli
Three bands of the outer longitudinal muscle layer of the large intestine
What are haustra
Bulges formed by the inner muscular layer of the large intestine
What are epiploic appendages
Fatty tags which mark the point at which blood vessels penetrate the intestinal wall
Describe the caecum
What are its features? What does it have?
Peritoneum - but no mesentery
Appendix
Describe the appendix
Contains lymphoid tissue
Varies in length and position of tip is variable
Connected to caecum by a small mesentery - mesoappendix
Describe the ascending colon
Runs vertically on right side of posterior abdominal wall - right paracolic gutter
Retroperitoneal (secondary)
What is the bend in the ascending colon called
Hepatic flexure (right colic flexure)
Describe the transverse colon
Intraperitoneal - suspended to posterior abdominal wall by transverse mesocolon
1st 2/3 = midgut
2nd 1/3 = hindgut
What is the bend in the transverse colon
Splenic flexure
Tethered to diaphragm by phrenicocolic ligament
Describe the descending colon
Runs left side of posterior abdominal wall in left paracolic gutter
Retroperitoneal (secondary)
Describe sigmoid colon
Sinuous shape
As it approaches midline makes a 90 degrees turn inferiorly = rectosigmoid junction
Intraperitoneal - sigmoid mesocolon
At what level does the coeliac trunk leave the aorta
T12
What does the coeliac trunk supply
Foregut
- oesophagus
- stomach
- first half of the duodenum
- liver
- gallbladder
- bile ducts
- pancreas
- spleen
What does the superior mesenteric supply
Midgut
- Second half of duodenum
- small intestine
- large intestine up to 2/3 away transverse colon
- branches which supply pancreas
At what level does the superior mesenteric artery leave the aorta
L1
What does the inferior mesenteric artery supply
Hindgut
- distal third of transverse colon
- descending and sigmoid colon
- rectum
- upper part of anal canal
At what level does the inferior mesenteric artery supply
L3
What arteries are embedded in the mesentery of the small intestine
Jejunal and ileal branches
Anastomose with each other to form loops of arteries - arcades which run the vasa recta - supply the intestinal wall
What are the branches of the superior mesenteric artery
Jejunal branches
Ileal branches
Ileocolic artery
Right colic artery
Middle colic artery
What does the ileocolic artery supply
Caecum
Appendix
Ascending colon
What does the right colic artery supply
Ascending colon
What does the middle colic artery supply
Transverse colon
What are the branches of the inferior mesenteric artery
Left colic artery
Sigmoid branches
Superior rectal artery (terminal branch)
What does the left colic artery supply
Transverse colon
Descending colon
What forms the marginal artery
Middle colic artery (SMA) and left colic artery (IMA) anastomose along the distal 1/3 of transverse colon and splenic flexure
What is the lower rectum supplied by
Internal iliac arteries
What is the parasympathetic nervous supply to the foregut and midgut
Parasympathetic fibres - Vagus nerve
What is the parasympathetic nervous supply to the hindgut
Pelvis splanchnic nerves
S2-4
What is the sympathetic innervation of the foregut
Greater splanchnic nerves T5-9
What is the sympathetic innervation of the midgut
Lesser splanchnic nerves T10-11
What is the sympathetic innervation of the hindgut
Least splanchnic nerves T12
What is the visceral innervation of the gut
Comes off the same as the sympathetic nerves