Grand Tour of the Alimentary Canal

Question 1

What are the control mechanisms involved in the control of salivary secretion?

Answer 1

• Salivary secretions are controlled by the prasympathetic and sympathetic systems
• The parasympathetic system will produce a profuse watery secretion in preparation for digesting food (rest and digest)
• The sympathetic system will produce a small volume of viscous salivary secretion (fight or flight response - mouth goes dry, but good for respiration)

Question 2

What are the effects of the parasympathetic and sympathetic systems on secretion and motility?

Answer 2

Parasympathetic - increase motility and secretion

Sympathetic - decrease motility and secretion

Question 3

What is the arterial supply and venous drainage of the GI tract?

Answer 3

Arterial supply:

• Coeliac trunk (Stomach, small intestine, pancrease, liver, L1)
• SMA (Small intestine, caecum, ascending colon, transverse colon, Lower border of L1)
• IMA (Descending colon, sigmoid colon, rectum, L3)

Venous drainage:

• Gastric veins (stomach)
• Splenic vein (pancreas)
• SMV (Small intestine to transverse colon)
• IMV (Descending to rectum)
• All of the above drain into the Hepatic Portal Vein
• Hepatic portal vein drains into Hepatic vein
• Hepatic vein drains into the IVC

Question 4

What is the portal venous system and its anastomosis with the systemic blood supply?

Answer 4

Portal venous system:

• Directs venous blood from parts of the GI tract to the Liver for processing before travelling on to the heart
• The portal venous system mixes venous blood with arterial blood via dense network of capillaries
• The hepatic portal vein is formed by the union of the SMA and splenic vein

Question 5

What is the anatomy of the GI tract and assign general physiological functions to each component?

Answer 5

Question 6

What are the common features of the alimentary wall structure?

Answer 6

Mucosa:

• Epithelium, lamina propria, muscularis mucosae
  1) Epithelium
• Mouth, eosophagus and anal canal = stratified squamous
• Stomach, small and large intestine = simple columnar
• Synthesises and secretes digestive enzymes
• Absorbs products of digestion

Submucosa

Muscularis externa (inner circular and outer longitudinal muscles)

Serosa (stomach, small and large intestine)/adventitia (oesophagus & rectum)

(MSMS)

Question 7

What is the organisation of the enteric nervous system?

Answer 7

• The ENS has independent control over gut function, i.e. reflexes which are generated within the GI tract are also integrated there and are acted upon by the GI system, such as motility, secretion and growth
• The ENS uses ‘short reflexes’