Describe the small intestines
Extends from pyloric orifice to the ileocaecal junction
Duodenum, jejunum and ileum
How do you know when the duodenum becomes the jejunum?
When retroperitoneal duodenum gains a mesentery and becomes intraperitoneal (just below and L of attachment of transverse mesocolon to post ab. wall
How does the jejunum differ from the ileum?
Wall of jejunum is thicker and more vascular with more plicae circulares and no Peyer’s patches.
Ileum is thinner, less vascular, no plicae circulares and large numbers of peyer’s patches
Where does the mesentery attach?
Obliquely across post. ab. wall from L of L2 vetebra to R sacroiliac joint
Describe the blood supply of the jejunum and ileum
Both by branches of superior mesenteric artery arranged in arcades
Jejunal, ileal (L side) and ileocolic (R side) branches
Name the branches of the superior mesenteric artery
Inferior pancreaticoduodenal, jejunal, ileal, ileocolic and R and middle colic arteries
What are the anastamoses of the ileal and jejunal blood supply called? Where are they most abundant?
Arcades
Many in ileum, fewer in jejunum
Describe the ileocolic artery
From R sided branch of superior mesenteric artery, passes to R iliac fossa and supplies terminal ileum and ascending colon (+caecum and appendix)
Describe the blood supply of the colon
Sup mes a.: Ileocolic= caecum, appendix and ascending colon R colic= ascending colon Middle colic= transverse colon Inf mes a.: L colic ascending and descending= transverse and descending colon 2-3 sigmoid= sigmoid colon Superior rectal= rectum
Where are Peyer’s patches found?
In lamina propria and submuscosa of terminal ileum
Describe the route of lymph from the small intestines
Peyer’s patches-> nodes in mesentery-> arterial arcades-> origin of sup. mes. a.-> cisterna chyli
Describe the sympathetic and parasympathetic supply of the small intestines
Symp: T9-T10-> celiac or sup. mes. ganglia-> small intestine (+pain)
Para: Vagus (+reflex)
What are the 3 bands of outer longitudinal muscle called in the large intestine?
Teniae coli
What are teniae coli?
3 bands of outer longitudinal muscle in the large intestine
What is the large intestine covered in?
Appendices epilocae (fatty tags)
What are appendices epilocae?
Fatty tags between colonic wall and the visceral peritoneum
What are the defining features of the large intestine?
Appendices epilocae (fatty tags), teniae coli (3 bands of outer longitudinal muscle) and haustra
What are haustrations also called?
Sacculations
Describe the caecum
Blind ended sac, continuous superiorly with ascending colon. Ileocaecal junction on medial wall. Vermiform appendix where teniae coli converge on posteriomedial wall
Where is pain from an inflamed appendix felt?
Initially in umbilical region (visceral, referred to belly button)
Later localises to R iliac region (parietal, somatosensory innervation localised to anatomical location of appendix)
Where does the ascending colon turn into the transverse colon?
At the visceral surface of the liver where is bends anteriorly and to the left (at the R colic flexure)
What is different about the ascending colon?
No mesentery, direct contact with fascia over post.ab. wall muscles. Therefore fixed in position
How does the L colic flexure maintain its position?
Via the phrenicocolic ligament where is attaches to the underside of the diaphragm
Where is the paracolic gutter? Significance?
Between abdominal wall and colon. Allows distension of bowels when chyme is passing through
Where is the infracolic space?
Between colon and mesentery of small intestine
What is the significance of the R paracolic gutter?
Continuos superiorly with the hepatorenal pouch and the aditus to the lesser sac and inferiorly with the rectouterine/rectovesical pouch
Describe the attachment of the sigmoid mesocolon
V shaped attachment to post. ab. wall with apex at bifurcation of L common iliac arteru and overlies L ureter
What is the anastomosis between the superior and inferior mesenteric arteries called?
Marginal artery, found on L side of transverse colon
Where does the inferior mesenteric vein drain?
To splenic vein behind body of pancreas
Describe the sympathetic supply of the large intestine
T11-L2-> sup mes ganglion-> proximal 2/3 colon
T11-L2-> inf mes ganglion-> distal 1/3 colon
Describe the parasympathetic supply of the large intestine
Prox 2/3= vagus
Distal 1/3= pelvis splanchnic nerves (S2-S4)
What level is the recto-sigmoid junction?
S3
Where is the anorectal junction? Also called what?
When rectum pierces pelvic floor muscles. Perineal flexure.
What muscle of the pelvic floor is involved in defaecation?
Pubrectalis, relaxes and angle between rectum and anus increases
What is the lower part of the rectum called?
Ampulla, dilated end
Describe the peritoneal covering of the recum
Sup 1/3= covers ant and lateral surfaces
Middle 1/3= covers ant surface
Inf 1/3= no peritoneal covering: subperitoneal
Why is there no peritoneal covering the posterior of the rectum?
Because it is contact with the sacrum
What is found lateral to the rectum?
Coils of small intestine
In males, what is the rectum related to anteriorly?
Base of urinary bladder, seminal vesicles, prostate and ductus deferens&ureters
In females what is the rectum related to anteriorly?
Uterus and vagina
Where does the anal canal begin?
At the level of the pelvic diaphragm
Describe the internal anal canal
6-10 anal columns with anal valves and anal sinuses above
Anal valves are situated along the pectinate line (junction between endoderm and ectoderm)
Describe the anal sphincters
Internal= involuntary circular fibres
External= voluntary skeletal muscle supplied by inf. rectal nerve (branch of pudendal nerve) and the perineal branch of S4
Subcutaneous, superficial and deep external parts (deep blends with pelvic floor)
What is found on each side of the anal canal?
Ischioanal fossae, full of fibrous tissue, nerves and fat
Lateral wall of fossae= obturator internus
What is found within obturator fascia?
Pudendal canal, hosuing the internal pudendal vessels and pudendal nerve
These give rise to the inferior rectal vessels and nerves
Describe the blood supply of the anal canal
Superior part= inferior mesenteric artery-> superior rectal artery
Inf part= internal iliac artery-> middle rectal arteries->pelvic floor and lower rectum
Internal pudendal a.-> inferior rectal a.-> lower anal canal and sphincters
Describe the drainage of the rectum and anal canal
Rectum& upper 1/2 anal canal-> internal rectal plexus-> superior rectal vain-> inferior mesenteric vein-> splenic vein-> hepatic portal vein
External plexus-> sup, middle, inf rectal veins-> some to inf mesenteric vein-> HPV and some to internal iliac and IVC
What does the external plexus of veins around the rectum and anal canal also communicate with?
Pelvic viscera venous plexuses, internal vertebral venous plexus, IVC and HPV
Describe the lymphatic drainage of the anal canal and rectum
Upper rectum= pararectal-> pre aortic
Anorectal region= internal iliac
Lower anal canal= superficial inguinal-> commmon iliac-> para aortic-> cisterna chyli
Describe the parasympathetic and sympathetic supply for the rectum and anal canal
SNS= T11-L2-> inf mes ganglion-> sup & inf hypogastric plexus PNS= S2-S4-> pelvic splanchnics-> inf hypogastric plexus
How does pain from upper anal canal and rectum travel?
With both symp and parasympathetic afferents
Describe the innervation of lower anal canal
Somatic nerves: inferior rectal branch of pudendal nerve (S2, 3, 4) and perineal branch of 4th sacral nerve
Clinical difference between internal and external haemorrhoids?
Internal= painless rectal bleeding External= pain and swelling