Anatomy - SI/LI

Question 1

where does the small intestine extend from?

Answer 1

pyloric orifice (stomach) -> iliocecal junction

Question 2

describe the location of the small intestines

Answer 2

epigastric/umbilical region
proximal 2/5th - jejunum (LUQ)
distal 3/5th - ilium (RLQ)

Question 3

name the differences between the jejunum and the ileum

Answer 3

jejunum has:
- larger diameter
- thicker wall
- less mesenteric fat
- more plicae circulatures
- less prominent arterial arcades
- longer vasa recta (straight arteries)

Question 4

describe the blood supply of the jejunum/ileum

Answer 4

jejunal/ileal arteries (from superior mesenteric)
~15-18 branches uniting to form arterial arcades
travele within SI mesentery

Question 5

describe the superior mesenteric artery

Answer 5

from abdominal aorta (L1) inferior to celiac trunk
supplies midgut structures:
- distal SI
- ascending colon
- proximal 2/3rds of transverse colon

Question 6

describe the venous drainage of the jejunum/ileum

Answer 6

superior mesenteric vein
begins in right iliac fossa and ascends in mesentery to the right of SMA
joins with splenic vein posterior to pancreas neck forming hepatic portal vein

Question 7

explain the lymphatic drainage of the small intestine

Answer 7

lacteals within villi (specialised lymphatic vessels absorbing emulsified fats)
drains to pre-aortic lymph nodes (celiac/foregut, SM/midgut, IM/hindgut)

IM -> SM -> celiac -> thoracic duct -> venous system (left brachiocephalic vein)

Question 8

describe the iliocecal junction

Answer 8

SI ends
ileum opens into LI where caecum/ascending colon join
2 flaps projecting into LI lumen (iliocecal fold) surrounding opening (sphincter function)

Question 9

what is meckel’s diverticulum?

Answer 9

remnant of proximal yolk sac extending into umbilical cord
rare congenital anomaly (causes ulceration/haemorrhaging)
may become inflamed and produce pain (mimicking appendicitis)

Question 10

describe some of the features of the large intestine

Answer 10

omental appendices - small/fatty projections

teniae coli - LM from caecum -> rectum (shorter than colon)

haustra - sacculations of colon wall

Question 11

describe the caecum and appendix

Answer 11

caecum - first part of LI (right groin), inferior to iliocecal opening, continuous with asc. colon

appendix - narrow/hollow tube conntected to caecum, large lymphoid tissue aggregations in walls

Question 12

which ways can the appendix be situated?

Answer 12

retrocecal (64%)
pelvic (32%)
subcecal (2%)
pre-ileal (1%)
postileal (0.5%)

Question 13

explain the anatomical location of the LI

Answer 13

ascending -> transverse at right colic/hepatic flexure (r.hypochondrium)
transverse -> descending at left colic/splenic flexure (l.hypochondrium)
sigmoid colon (pubic)

(transverse colon location can vary)

Question 14

explain the rectum

Answer 14

pelvic (extends from sigmoid)
rectosigmoid junction at L3
flexures: sacral, anorectal (anterior -> posterior, looks S shaped)
rectal ampulla (final part) expands to hold faeces until expulsion

Question 15

describe the anal canal

Answer 15

extends from rectum ampulla to anus
sphincters:
- internal (involuntary) usually contracted, relaxes in ampulla distension
- external (voluntary), relaxed when defecating

Question 16

describe the differences in the superior/inferior anal canal

Answer 16

superior has anal columns

inferior has irregular (pectinate) line

both have different developmental origins

Question 17

explain the blood supply of the colon

Answer 17

SMA (iliocolic, right colic and middle colic arteries)
IMA (left colic, sigmoid and superior rectal arteries)

Question 18

describe the blood supply of the rectum

Answer 18

IMA (superior rectal artery)
internal iliac artery (middle rectal and inferior rectal arteries) from internal pudendal artery

Question 19

explain the venous drainage of the colon

Answer 19

sigmoid/left colic -> superior rectal -> IMV -> splenic vein (posterior to pancreas)