Grand Tour of the Alimentary Canal

Question 1

What are the 3 pairs of salivary glands?

Answer 1

• Parotid
• Sublingual
• Submandibular

Question 2

Which CNs are responsible for parasympathetic control of salivary secretion?

What are its effects on salivary secretion?

Answer 2

• CN VII (Facial), CN IX (Glossopharyngeal)

- Stimulates profuse watery secretion

Question 3

What are the effects of sympathetic innervation to the salivary glands?

Which receptors are implicated in this?

Answer 3

• Stimulates small volume, viscous salivary secretions

- a1 adrenoreceptors (high mucus content), b2 adrenoreceptors (high amylase content)

Question 4

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

Answer 4

Reflex control

→ Presence of food in mouth stimulates chemoreceptors/ pressure receptors (walls of mouth/tongue)
→ Stimulates autonomic nerves to the salivary glands
→ SALIVA!

Question 5

Describe nervous control of Alimentary system

Answer 5

• Long parasympathetic reflexes -> afferent pathway goes all the way back to the CNS and efferent autonomic nerve control
• Short ENS reflexes -> both afferent and efferent pathway entirely in the gut

Question 6

Which CNs are responsible for parasympathetic control of alimentary function?

What are its effects on alimentary function?

Answer 6

• Vagus Nerve (X)
  → EXCEPT salivation! (CN VII and IX)

Stimulatory:

• increased secretion
• increased motility

Question 7

What are the effects of sympathetic innervation on alimentary function?

Answer 7

Inhibitory (EXCEPT salivation):

• decreased secretion
• decreased motility

Question 8

What is the arterial supply to the GIT?

Answer 8

- Coeliac Trunk 
→ Stomach
→ Small Intestine
→ Pancreas
→ Liver

- SMA
→ Small Intestine
→ Caecum
→ Ascending colon
→ Transverse colon

• IMA
  → Descending colon
  → Sigmoid colon
  → Rectum

Question 9

What is the venous drainage of the GIT?

Answer 9

→ Gastric veins, Splenic vein, SMV, IMV
→ Hepatic Portal Vein
→ Hepatic Vein
→ IVC

Question 10

Describe the layers of the Alimentary Canal?

Answer 10

→ Mucosa -> epithelium, lamina propria, muscularis mucosa
→ Submucosa
→ Muscularis Externa -> Circular + Longitudinal muscle
→ Serosa or Adventitia

Question 11

What is the difference between Serosa and Adventitia?

Answer 11

→ Adventitia: surrounds structures outside the peritoneal cavity (ie. Oesophagus, Rectum)

→Serosa: surrounds structures inside the peritoneal cavity (ie. stomach, small intestine, large intestine)

Question 12

Describe the components of the ENS?

Answer 12

→ Submucosal (Meissner’s) Plexus

→ Myenteric (Auerbach’s) Plexus

Question 13

What type of epithelium is present in the Mouth, Oeseophagus and Anal Canal?

Answer 13

Stratified Squamous

adapted for constant rubbing and brushing against things

Question 14

What type of epithelium is present in the Stomach, Small and Large Intestine?

Answer 14

Simple Columnar

adapted for impermeability + is protective

Question 15

In which parts of the GIT are submucosal glands present? What do they secrete?

Answer 15

→ Oesophagus: mucus

→ Duodenum: bicarbonate ions