GI Anatomy

Question 1

Name the layers of the abdominal wall from superficial to deep.

Answer 1

• skin
• fascia (Camper’s and Scarpa)
• muscles (external oblique, internal oblique, transversus abdominus) and their aponeuroses
• adipose tissue
• peritoneum

Question 2

Name the two abdominal lines that distinguish the rectus abdominus muscles.

Answer 2

• linea alba: midline
• linea semilunaris: lateral to muscles

Question 3

Name the insertions/attachments of the rectus abdominus muscles.

Answer 3

• originates at the pubic symphysis
• inserts at xiphoid process and 5th-7th costal cartilages
• attaches to linea alba by pyramidalis muscle

Question 4

Describe the formation of the rectus sheath and name its contents.

Answer 4

• formed of the aponeuroses of the external oblique, internal oblique, and transversus abdominus
• contains the rectus abdominus muscles, pyramidalis, superior and inferior epigastric vessels, and thoraco-abdominal/subcostal nerves (T7-12)

Question 5

Name and describe the umbilical peritoneal folds, and the depressions between them. What is the clinical significance of these depressions?

Answer 5

• five umbilical peritoneal folds exist:
  – mediaN: remnant of the urachus (joined foetal bladder to umbilical cord)
  – mediaL (x2): remnant of umbilical arteries
  – lateral (x2): covers inferior epigastric vessels
• three main depressions:
  – supravesicular: between mediaN and mediaL
  – mediaL inguinal fossa: between mediaL and lateral; also contains Hesselbach’s triangle
  – lateral inguinal fossa: lateral to the lateral
• clinical significance: potential hernia sites

Question 6

Name the three major unpaired arteries arising from the abdominal aorta that supply the abdomen and their vertebral level of origination

Answer 6

• coeliac axis; T12; supplies foregut
• superior mesenteric (SMA); L1; supplies midgut
• inferior mesenteric (IMA); L3; supplies hindgut

Question 7

Name the boundaries of the foregut, midgut, and hindgut.

Answer 7

• foregut: oral cavity to ampulla of Vater in the duodenum
• midgut: ampulla of Vater (duodenum) to proximal 2/3 of the transverse colon
• hindgut: proximal 2/3 of transverse colon to anus

Question 8

Name the branches of the coeliac axis and the viscera they supply.

Answer 8

• three main branches: left gastric, splenic, and common hepatic arteries
  – left gastric: gives oesophageal artery (supplies abdominal oesophagus) and anastomoses with the right gastric (supplying stomach lesser curvature)
  – splenic:
  — pancreatic arteries (dorsal, inferior, and great, supplying pancreatic body and tail)
  — short gastric: 5-7 arteries supplying the cardiac orifice and fundus of stomach; anastomoses with left gastric and left gastroepiploic
  — left gastroepiploic (aka left gastro-omental): anastomoses with right gastroepiploic to supply greater curvature of stomach
  – common hepatic:
  — hepatic artery proper: gives right gastric, right and left hepatic, and cystic (via right hepatic)
  — gastroduodenal: right gastroepiploic, superior pancreaticoduodenal (anastomoses with inferior pancreaticoduodenal to supply pancreatic head, uncinate process, and duodenum)

Question 9

Name the branches of the superior mesenteric (SMA) and the viscera they supply.

Answer 9

• inferior pancreaticoduodenal: anastomoses with superior pancreaticoduodenal to supply the head of pancreas, uncinate process, and duodenum
• jejunal, ileal: forms anastomotic arcades, from which smaller straight arteries (vasa recta) supply the jejunum and ileum, respectively
• middle, right colic: supplies transverse and ascending colon, respectively; these arteries anastomose
• ileocolic: final branch, which gives rise to further branches:
  – appendiceal (appendix)
  – caecal (caecum)
  – also anastomoses with right colic (ascending colon) and ileal (ileum)

Question 10

Name the branches of the inferior mesenteric (IMA) and name the viscera they supply.

Answer 10

• left colic: supplies distal 1/3 of transverse colon + descending colon; splits into:
  – ascending left colic
  – descending left colic: anastomoses with superior sigmoid artery
• sigmoid arteries: supplies descending and sigmoid colon. typically 2-4 branches, with the uppermost denoted the superior sigmoid artery (anastomoses with descending left colic)
• superior rectal: continuation of IMA, supplying the rectum
  – NB middle rectal is from internal iliac, and inferior rectal from internal pudendal

Question 11

Which artery is the typical site of peptic ulcer bleeds?

Answer 11

• gastroduodenal (a branch of the common hepatic, which is a branch of the coeliac axis)

Question 12

Which artery is ligated in the case of appendectomy?

Answer 12

• appendiceal (branch of the ileocolic, which is a branch of the SMA)

Question 13

To which particular structures should particular care be taken when ligating IMA branches?

Answer 13

• psoas major muscles, left ureter, and left internal spermatic vessels, as these have close anatomic relations to IMA and its branches

Question 14

Name and describe the two major anastomoses existing between the SMA and IMA.

Answer 14

• marginal artery (of Drummond): forms a continuous arterial circle along the inner border of the colon
  – SMA contributions: ileocolic, right colic, middle colic
  – IMA contribution: left colic, sigmoid branches
• arc of Riolan: less common than artery of Drummond (its existence is disputed)
  – SMA contribution: middle colic
  – IMA contribution: left colic

Question 15

Describe the arterial and venous supply of the oesophagus.

Answer 15

• thoracic oesophagus: oesophageal branches of the thoracic aorta and inferior thyroid artery; venous drainage into systemic circulation by azygous and inferior thyroid veins
• abdominal oesophagus: oesophageal branch of left gastric artery and left inferior phrenic artery; left gastric vein to portal circulation, azygous to systemic circulation

Question 16

Name the three major tributaries of the hepatic portal vein.

Answer 16

• the hepatic portal vein is formed by the union of the splenic and superior mesenteric veins
• the third major tributary, the inferior mesenteric vein, first drains into the splenic vein

Question 17

Define a porto-systemic anastomoses and give the four main examples.

Answer 17

• a connection between the veins of the portal system, and the veins of the systemic venous system
• oesophageal: left gastric (portal) + azygous (systemic)
• rectal: superior rectal + inferior rectal
• retroperitoneal: mesenteric veins (portal) + retroperitoneal veins (systemic)
• paraumbilical: hepatic portal veins (portal) + anterior abdominal wall veins (systemic)

Question 18

Describe the terms ‘intraperitoneal’ and ‘retroperitoneal’ and name the viscera in each category.

Answer 18

• intraperitoneal: enveloped by visceral peritoneum (covers organ both anteriorly and posteriorly). includes the stomach, liver, and spleen.
• retroperitoneal: covered only anteriorly by parietal peritoneum. remember SAD PUCKER:
  – Suprarenal (adrenal) glands
  – Aorta (and IVC)
  – Duodenum (except proximal 2cm)
  – Pancreas (head)
  – Ureters
  – Colon (ascending, descending only)
  – Kidneys
  – oEsophagus
  – Rectum

Question 19

Define the term ‘mesentery’.

Answer 19

• double layer of visceral peritoneum, connecting an intraperitoneal organ (e.g., liver, stomach, spleen) to the posterior abdominal wall.
• provides a pathway for nerves, blood vessels, and lymphatics to travel from the body wall to the viscera.

Question 20

Define the term ‘omentum’ and give the main examples of this.

Answer 20

• omentum: sheets of visceral peritoneum extending from the stomach and proximal duodenum to other abdominal organs
• greater omentum: greater curvature of stomach + proximal duodenum to anterior transverse colon
  – gastrophrenic ligament: to diaphragm
  – gastrosplenic: to spleen
  – gastrocolic: to colon
• lesser omentum: lesser curvature of stomach and proximal duodenum to liver
  – hepatogastric
  – hepatoduodenal

Question 21

Name and describe the four liver lobes.

Answer 21

• right lobe: largest
• left lobe: smaller and flattened. it is separated from the right lobe by the gallbladder fossa and IVC.
• caudate: sits between the fissure for the ligamentum venosum, and the IVC
• quadrate: located between the gallbladder and fissure for the ligamentum teres hepatis (aka ‘round ligament’)

Question 22

Name and describe the five hepatic ligaments.

Answer 22

• coronary: connects the superior liver to the diaphragm
• left/right triangular: lateral extensions of the coronary ligaments, connecting the left/right lobes to the diaphragm
• falciform: connects the liver to the anterior abdominal wall; it has the teres ligament on its free edge
• ligamentum teres hepatis (‘round ligament’): fibrous remnant of the umbilical vein, extending from the internal aspect of the umbilicus to the liver
• ligamentum venosum: remnant of the foetal ductus venosum)

Question 23

Describe the lymphatic drainage of the liver.

Answer 23

– hepatic nodes -> coeliac nodes -> cisterna chyli (if present) -> thoracic duct
– inferior diaphragmatic/phrenic nodes -> right posterior mediastinal nodes -> mediastinal lymphatic chain -> right lymphatic duct/thoracic duct

Question 24

At which vertebral level does the rectum begin? Give the five main flexures that mark the rectum.

Answer 24

• begins at S3
• sacral flexure: anteroposterior curve with concavity anteriorly, allowing curves of the sacrum and coccyx
• anorectal (perineal) flexure: anteroposterior curve with convexity anteriorly; formed by tone of puborectalis muscle, which contributes significantly to continence
• lateral flexures (superior/upper right, intermediate/middle left, inferior/lower right) are formed by transverse walls of the internal rectal wall

Question 25

Name the spaces formed by peritoneal reflections in males and females.

Answer 25

• male: rectovesical pouch (reflection of peritoneum from rectum to posterior bladder wall)
• female: rectouterine pouch (of Douglas) (reflection of peritoneum from rectum to posterior vagina and cervix)

Question 26

Describe the neurovascular supply (arteries, veins, nerves, and lymphatics) of the rectum.

Answer 26

• arteries: superior (IMA), middle (internal iliac), and inferior (internal pudendal) rectal arteries
• venous: superior (portal), middle and inferior (systemic) rectal veins
• innervation:
  – sympathetic: lumbar splanchnic nerves, superior + inferior hypogastric plexuses
  – parasympathetic: S2-4, pelvic splanchnic nerves, inferior hypogastric plexus
  – visceral afferent (sensory) fibres follow the parasympathetic supply
• lymphatics: pararectal nodes -> inferior mesenteric nodes; lower aspect drains directly to internal iliac nodes

Question 27

Describe the sphincters of the anal canal.

Answer 27

• internal sphincter: surrounds upper 2/3 of canal, formed from thickening of involuntary circular smooth muscle in bowel wall; it is autonomic (e.g., involuntary)
• external sphincter: surrounds lower 2/3 of canal therefore overlapping with internal sphincter; blends superiorly with puborectalis muscle; is voluntary

Question 28

Describe the makeup and histology of the pectinate (aka dentate) line of the anal canal.

Answer 28

• mucosa is organised into longitudinal folds (anal columns [of Morgagni]) -> anal columns joined at inferior end by anal valves which contain anal sinuses (mucous secreting glands) -> anal valves collectively form an irregular circle - the pectinate (dentate) line
• superior to pectinate line: derived from hindgut, therefore has same histology as rectum (columnar epithelium)
• inferior to pectinate line: derived from proctodeum. lined by non-keratinised stratified squamous epithelium, transitioning to keratinised squamous epithelium (anus to skin).

Question 29

Describe the neurovascular supply (arterial, venous, nervous, and lymphatic) of the anal canal.

Answer 29

• superior to pectinate line: superior rectal artery (IMA) and vein (IMV); inferior hypogastric plexus (visceral: sensitive to stretch); and internal iliac lymph nodes
• inferior to pectinate line: inferior rectal artery (internal pudendal) and vein (internal pudendal); inferior rectal nerves (pudendal; somatic - sensitive to pain, temperature, touch, and pressure); and superficial inguinal lymph nodes

Question 30

Describe the anatomical components of the inguinal canal.

Answer 30

• anterior wall: formed by aponeurosis of external oblique (EO)
• inferior wall: formed of inguinal ligament
• posterior wall: formed by transversalis abdominus (TA) fascia
• superior wall: formed by internal oblique (IO) and TA muscles
• contains 3 arteries, 3 nerves, and 3 others:
  – arteries: gonadal (testicular/ovarian), vas deferens, cremasteric
  – nerves: ilioinguinal [at risk during inguinal hernia surgery], genitofemoral, sympathetic nerves
  – others: vas deferens/round ligament, pampiniform plexus, and lymphatics

Question 31

Describe the anatomy of indirect and direct inguinal hernias.

Answer 31

• both are found superior and medial to the pubic tubercle, as opposed to femoral hernias
  – remember MILF: medial inguinal, lateral femoral
• indirect: occurs in infants due to failure of the closure of the processus vaginalis, and travels through both the deep and superficial inguinal rings
• direct: enters the inguinal canal at an area of transversalis abdominus (TA) fascia weakness, typically at Hesselbach’s triangle
• therefore, indirect and direct can be distinguished by reducing the hernia and putting pressure on the deep inguinal ring while having the patient cough
  – indirect hernias will not reappear
  – direct hernias will reappear

Question 32

Name the nine areas of the abdomen.

Answer 32

• upper: R hypochondrium, epigastrium, L hypochondrium
• middle: R lumbar, umbilical, L lumbar
• lower: R iliac, hypogastric, L iliac