3. Lower GI Anatomy

Question 1

Draw lower GI tract

Answer 1

Oesophagus
Stomach 
Pylorus
Duodenum
Jejunum
Ileum
Caecum (appendix)
Colon (ascending, transverse, descending)
Sigmoid colon
Rectum
(Spleen, Liver, Gallbladder)

Question 2

Draw the stomach and label features/parts

Answer 2

Oesophagus entry/cardiac orifice
Cardia
Fundus
Corpus/body
Lesser/greater curvature
Pylorus: antrum, canal, sphincter
Duodenum

Angular incisure (angle of stomach between lesser curve and pylorus)

Question 3

Describe omentum and ligaments of stomach

Answer 3

Lesser omentum>lesser curve and liver:hepatoduodenal (sphincter onwards & from gallbladder); hepatogastric, lesser curve & left lobe and right lobe up to gall bladder

Omentum is peritoneal reflection; is double layered; contains blood vessels

Question 4

Describe duodenum
Diameter
Parts and importance

Answer 4

Narrowing diameter from start to end
4 parts: duodenal cap/superior, descending part, horizontal/inferior part and ascending
Retroperitoneal apart from cap
Duodenal cap=site of duodenal ulcers

Question 5

Jejunum vs ileum (features)

Bloody supply from ? via ?

Answer 5

Blood supply from sup mesenteric via root of mesentery
Jejunum:
-proximal 2/5
-larger diameter, thicker walls
-prominent PLICAE CIRCULARES (bumps inside intestine)
-shallow arterial arcade, longer vasa recta

Ileum:

• distal 3/5
• narrower, thinner walls
• less PLICAE CIRCULARES
• extensive arterial arcade, shorter vasa recta
• more mesenteric fat

Question 6

Describe parts/features of large bowel (9 or 10/3)

Blood supply comes from (3)

Answer 6

Parts:
Appendix
Caecum/ileocecal junction w valve/sphincter
Ascending colon
Right hepatic/colic flexure 
Transverse colon
Left splenic/colic flexure (higher flexure bc liver big)
Descending colon
Sigmoid colon
Rectum 

Features:
Haustra: the shape-bumps like caused by a drawstring
Taeniae coli (ten-i col-i): muscle; like drawstring, can extend colon when needed; are 3 around whole of colon
Omental appendices/appendages: fatty deposits for energy

Blood supply:
Root of THE mesentery
Root of transverse mesocolon
Root of sigmoid mesocolon

Question 7

Describe GI tract distal to sigmoid colon

Answer 7

Sigmoid colon
Rectum
Once enters perineal layer>rectal ampulla part of rectum
Anal canal
Terminates as anus passes through perineum

Is surrounded by internal/external sphincters

Question 8

Describe lining of anal canal/draw

Answer 8

Pectinate line formed by anal valves (like VALLEYS); hindgut-proctodeum junc (GI mucosa>skin transition)

Upper mucosa (above pectinate line)
Anal columns
Anal valves between columns
Above columns are anal sinuses

Lower mucosa (below pectinate line)
Transition zone: lined with nonkeratinised stratified squamous epithelium
Anocutaneous ‘white’ line

Question 9

Describe peritoneum

1. What
2. Types
   * *doubke check this one**3. Peritoneal cavity
3. 3 peritoneal relationships

Answer 9

1. The thin, serous membrane that lines abdo & pelvic cavities
2. Parietal (lines wall/cavity); visceral (lines organs aka viscera)
3. Between 2 laters of peritoneum (bit of fluid; closed cavity in males; females-hole in peritoneum between fimbrae and ovaries>access to cavity)
4. Intraperitoneal (organ completely covered with visceral peritonum; attached to abdo wall via mesentery-stomach, jeju, ileum)
   Retroperitoneal (plastered to post wall by peritoneum-pancreas, asc/desc colon)
   Extraperitoneal (outside peritoneum e.g. fat/tissue)

Question 10

Draw GI tract before development with labelled features

Answer 10

Cylindrical balloon; GI tract pushed into balloon posterior>anterior direction so surrounded by the layers of balloon>dorsal mesentery/mesogastrium
Aorta is retroperitoneal
Ventral mesentery/mesogastrium=like pushing ruler Down on anterior of balloon

Question 11

Describe foregut development

Draw diagram where req

Answer 11

4-6 weeks:
Ai. Stomach is completely intraperitoneal, surrounded by ventral & dorsal mesogastrium; cross section=pokeball
B. Development: Anterior to stomach=liver (surrounded by ventral mesogastrium)
Post to stomach=spleen (surrounded by dorsal mesogast) not part of foregut
Gall bladder, ventral and dorsal pancreatic buds forming

6th week:
Ventral mesogastrium anterior to liver>falciform lig
“ between liver & stomach>lesser omentum

5th-10th week:
Stomach rotate clockwise 90o; greater curve on left, pylorus/lesser omentum on right
(Know about falciform lig, lesser om& epiploic foramen, lesser/greater sac, gastrosplenic lig, lienorenal/splenorenal lig)

Question 12

Describe development of GI tract
Draw diagram of mid/hind gut and label
(Min 1 diagram; up to 3)

Answer 12

Include:
Diagram 1
-Yolk sac; projecting into umbilicus; provide nourishment for embryo
-Mid gut lengthens rapidly; herniated out of umbilicus
-Vitelline duct at apex mid gut; attaches yolk sac to mid gut; vitelline arteries run into dorsal mesentery & fuse=SMA

Diagram 2 (development of caecum)

• Cephalic limb of midgut loop>jejunum, prox ileum
• vitelline duct
• caudal limb of midgut loop>distal ileum, caecum, appendix, ascending colon, prox 2/3 of transverse
• superior coils into duodenum
• inferior becomes colon

10th week:
Midgut rotate around SMA/vitelline 270o anticlock
Herniates out and enters back into abdo when abdo big enough to accommodate

PRIMITIVE mesentery of Asc/desc colon fuse w post abdo wall>retroperitoneal
‘’ of jeju, ileum, transverse, sigmoid don’t fuse>intraperitoneal