Grand tour of the alimentary canal

Question 1

What are the three salivary glands and what type of secretions do they produce?

Answer 1

• Submandibular
	- Produce a mix of serous and mucous secretion
	• Sublingual
	- Produces a mucous secretion
	• Parotid
	- Produces a serous secretion

Question 2

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

Answer 2

• Parasympathetic
- Cranial nerve VII (facial) and IX (glossopharyngeal)
- Stimulation: perfuse watery salivary stimulation
• Sympathetic
- Stimulation: small volume , viscous salivary secretion
- High mucous content (α1 adrenoreceptors)
- High amylase content (β2 adrenoceptors)

Question 3

Describe the effect of the sympathetic and parasympathetic nervous system on secretion and motility

Answer 3

• Parasympathetic: Vagus nerve (CN X) (except salivation which is facial (CN VII) and glossopharyngeal (CN IX)
	- Increased secretion
	- Increased motility
	• Sympathetic: Splanchnic nerve
	- Decreased secretion
	- Decreased motility
	- Does not decrease salivation

Question 4

What are the arterial supplies to the GI tract?

Answer 4

• Celiac trunk
• Superior mesenteric artery
• Inferior mesenteric artery

Question 5

What does the Celiac trunk supply?

Answer 5

• Stomach
  
  • Small intestine
  • Pancreas
  • Liver

Question 6

What does the superior mesenteric artery supply?

Answer 6

• Small intestine
  
  • Caecum
  • Ascending colon
    
    • Transverse colon

Question 7

What does the inferior mesenteric artery supply?

Answer 7

• Descending colon
  
  • Sigmoid colon
    
    • Rectum

Question 8

What are the venous supplies of the GI tract?

Answer 8

• Gastric veins
• Splenic veins
• Superior mesenteric vein
• Inferior mesenteric vein
• > Portal vein -> hepatic vein -> inferior vena cava

Question 9

Explain the concept of the portal venous system and its anastomosis with the systemic blood supply

Answer 9

• All the blood that has been round the gut tube goes to the liver before returning to the heart
  
  • The portal vein is formed by the union of the splenic vein and the superior mesenteric vein
  • The blood in the hepatic portal vein is high in nutrients but low in O2
  • The blood in the hepatic artery is low in nutrient but high in O2

Question 10

Describe the anatomy of the GI tract and assign general physiological functions to each of its components

Answer 10

• Mouth: Chewing and breaking up food, saliva is added as lubricant
  
  • Oesophagus: conduit between the mouth and stomach
  • Stomach: Digestion of proteins, foodstuff reduced to liquid form, storage and sterilisation
  • Pancreas: digestive enzymes for digestion of fats, carbohydrates and proteins
  • Liver: bile salts for digestion/ absorption of fats in the small intestine
  • Gallbladder: stores and concentrates bile
  • Small intestine: Final stages of chemical digestion and nutrient absorption
  • Large intestine: Water absorption, bacterial fermentation and formation of faeces

Question 11

Describe the common features of the alimentary canal wall structure

Answer 11

• Mucosa
	- Epithelium
	- Lamina propria
	- Muscularis mucosae
	• Submucosa
	• Mucosa externa
        * Serosa/ adventitia

Question 12

Describe the organisation of the enteric nervous sytem

Answer 12

• Sympathetic
- Abdominopelvic splanchnic nerves (greater, lesser and least)
- Paravertebral sympathetic ganglia
- Abdominal aortic plexus
• Parasympathetic
- Anterior and posterior vagal trunks
- Pelvic splanchnic nerves (S2, 3 and 4)