GI Anatomy

Question 1

State the layers of the gut tube

Answer 1

• Mucosa
• Submucosa
• External muscle layers
• Serosa

Question 2

Describe the layers of the mucosa

Answer 2

• Epithelial layer
  
  • Selectively permeable barrier - facilitate transport and digestion of food
  • Facilitate transport and digestion of food
  • Promote absorption
  • Produce hormones
  • Produce mucus
• Lamina propria
  
  • Lots of lymphoid nodules and macrophages
  • Produce antibodies - mainly IgA which is resistant to proteases
    - Protect against bacterial and viral invasion
• Muscularis mucosae
  
  • Layers of smooth muscle orientated in different directions
  • Keeps epithelium in contact with gut contents
    
    • Helps keep crypt contents dynamic

Question 3

Describe the contents of the submucosa, external muscle layers and serosa of the gut tube

Answer 3

• Submucosa
  
  • Contains dense connective tissue, blood vessels, glands, lymphoid tissue
  • Contains submucosal plexus (Meissner’s)
• External muscle layers
  
  • Inner circular muscle
    
    • Contains myenteric (Auerbach’s) plexus
  • Other longitudinal muscle
• Serosa
  
  • Blood, lymph vessels and adipose tissue
  • Continuous with mesenteries

Question 4

Describe the epithelial cell types of the major divisions of the alimentary tract

Answer 4

• Stratified squamous in oesophagus and distal anus
  
  • Lie in places of abrasion
• Everything in between is simple columnar
  - Lie in places of secretion and absorption

Question 5

Describe the function and location of enterocyte

Answer 5

• Simple columnar epithelial cell that absorbs
• Predominant cell of small intestine and colon
  
  • One cell thick
• Need to transport nutrients through
  
  • Apical membrane
  • Basolateral membrane
    
    • Blood vessels, lymphatics lie immediately below the enterocyte
• Has villi and microvilli to aid absorption

Question 6

Describe the function and location of goblet cells

Answer 6

• Scattered in between enterocytes
  
  • Increasing in number from duodenum to colon
• Wide top at apical surface and small base
• Mucus compresses nucleus to its base
• Produce mucus to protect epithelial from:
  
  • Friction - acts as lubricant
  • Chemical damage - acidic environment
    
    • Bacterial inflammation - forms physical barrier

Question 7

Describe the structure of glandular tissue in gut

Answer 7

• Organised secretory cells - acini and tubules
  
  • Acini tend to secret serous secretions
  • Tubules tend to secrete mucous
• Connected to a duct
• Eg. Salivary glands, pancreas, Brunners glands (mucous secreting gland)

Question 8

Describe the specialised cells found in crypts

Answer 8

• Stem cells found at bottom of crypts
  
  • Need to renew bowel epithelium every 2-4 days
  • Can lead to bowel perforation causing acid and bacteria to leak into peritoneum
• Paneth cells located at base of crypts
  
  • Secrete antibacterial proteins to protect stem cells
• Enteroendocrine cells predominantly located deeper in crypts and gastric glands
  
  • Secrete hormones that control the function of gut
    
    • Eg. Gastrin, CCK, secretin

Question 9

Describe where folds in the GI tract are found

Answer 9

• Permanent folds (plicae circulares) increase surface area for absorption
  
  • Duodenum has most folds and decreases further towards jejunum and ileum
• Temporary folds called rugae located in stomach to help it expand after eating

Question 10

Describe the muscles of the anterolateral abdominal wall and their innervation

Answer 10

• External oblique, internal oblique, transverse abdominis
• External oblique innervated by thoracoabdominal nerves and subcostal nerve
  
  • Hands in pocket pattern
• Internal oblique and transverse abdominis innervated by thoracoabdominal nerves, subcostal nerve and branches of the lumbar plexus

Question 11

Describe the rectus sheath

Answer 11

• Aponeurosis of the lateral muscles surrounding the rectus abdominis
• Above the arcuate line, internal oblique splits both anterior and posterior to rectus abdominis
• Below the arcuate line, all tendons go anterior to rectus abdominis
• Arcuate line have between umbilicus and pubic crest
  - Also point where inferior epigastric vessels pierce through rectus abdominis

Question 12

Define mesentery and give examples of organs which have mesenteries

Answer 12

• Double fold of peritoneum that attaches certain viscera to the posterior abdominal wall
• Jejunum, ileum, appendix, transverse colon, sigmoid colon, rectum
• Mesentery contains blood vessels, lymph vessels, nerves, fat

Question 13

Define peritoneal ligament and give examples

Answer 13

• Double fold of peritoneum that connects two viscera together
• Gastrocolic ligament
  
  • Stomach to transverse colon
• Gastrosplenic ligament
  - Stomach to spleen
• Also double fold of peritoneum that connects a viscera to the abdominal wall
  
  • Falciform ligament - liver to anterior abdominal wall
    
    • Triangular ligaments - liver to diaphragm

Question 14

Describe the function of sphincters in GI tract and give examples

Answer 14

• Sphincters - divide tube into sections
  
  • Control movement along the tube
  • Prevent reflux of material
• Some are very muscular - pyloric sphincter
• Involuntary sphincters include, upper oesophageal, lower oesophageal, pyloric, oddi, ileocaecal, internal anal
• Voluntary sphincter - external anal

Question 15

Describe the blood supply and venous drainage of the alimentary tract

Answer 15

• Arterial supply from branches of the aorta
  
  • Coeliac trunk - foregut
  • Superior mesenteric artery - midgut
  • Inferior mesenteric artery - hindgut
• Venous supply run alongside arteries and have same name
  
  • All venous drainage goes to liver via portal vein
    
    • Absorbed toxins from gut can be removed through liver capillaries