GI tract control

Question 1

How is maximum absorption of nutrients achieved?

Answer 1

• Regulating motility (rate at which food passes through the GI tract)
• Controlling secretion of digestive juices.

Question 2

How does the small intestine sense lumen contents?

Answer 2

Distention- mechanoreceptors
Osmolality- osmoreceptors
Acidity- chemoreceptors
Digestive products- chemoreceptors

Question 3

What does receptor activation of the small intestine cause?

Answer 3

• Neves= long and short reflexes
• Hormone release
• Paracrine transmission

Question 4

What is the enteric nervous system?

Answer 4

100 million nerve cells in myenteric and submucosal plexus.

Question 5

What is the enteric nervous system involved in and give an example?

Answer 5

Involved in short reflexes e.g. local distention leads to motility (muscle contraction).

Question 6

What does the parasympathetic system do?

Answer 6

• inc motility
• inc secretion
• interact with the enteric nervous system
• e.g. long reflexes
• ACh

Question 7

What does the sympathetic system do?

Answer 7

• decrease motility
• decrease blood flow
• noradrenaline

Question 8

Features of GI hormones

Answer 8

• All short chain peptides
• Secreted by enteroendocrine cells found in the mucosa into the blood.
• Target various regions of GI and glands.
• May have effects on the CNS.

Question 9

Examples of hormones acting in paracrine transmission.

Answer 9

Histamine (gastric secretion)
Prostagladin
Bradykinin

Question 10

Saliva is 99% water. What is the protein and ion composition of saliva and what is their function?

Answer 10

Proteins:

• mucins
• a-amylase (digestion of carbohydrates)
• anti-bacterials (antibacterial drugs cause dry mouth)
• growth factors

Ions:

• Na, Cl, HCO3 (produce osmotic gradient)
• pH=7

Question 11

What is the function of saliva?

Answer 11

lubrication
solvent
protect teeth and gums

Question 12

What are the 3 salivary glands and what secretion are they involved in?

Answer 12

Parotid- watery secretion
Sublinguals- mucus secretion
Submandibular- mixed secretion

Question 13

What is the structure of the salivary glands?

Answer 13

duct and acinus

Question 14

What type of saliva does the parasympathetic system induce?

Answer 14

Watery saliva
Low enzyme conc
4ml/min

Question 15

What type of saliva does the sympathetic system induce?

Answer 15

Small volume of saliva

Rich in enzymes

Question 16

What is the fundus in the stomach important for?

Answer 16

Acid secretion

Question 17

What is the antrum in the stomach important for?

Answer 17

Mixing food

Question 18

What is gastrin produced by and what does it do?

Answer 18

Produced by G cells.
Increases acid secretion and gastric motility.
Secretes pepsin.

Question 19

What is the composition of gastric juice?

Answer 19

• HCl (kills microbes, solubilisation)
• Pepsinogen-> pepsin (digestion)
• Intrinsic factor (absorption of vit B12)
• Mucus (protection, lubrication)

Question 20

What do parietal cells release?

Answer 20

HCl and intrinsic factor

Question 21

What is acid secretion stimulated by?

Answer 21

ACh
Gastrin
Histamine

Question 22

Structurally, what happens during acid secretion?

Answer 22

Receptor activation activates ion channels which causes changes in parietal cell structure:
tubulovesicles-> canaliculus (inc surface area and number of pumps).

Question 23

What are the three phases of gastric secretion control?

Answer 23

1. Cephalic phase (stimulatory
2. Gastric phase (stimulatory/ inhibitory)
3. Intestinal phase (inhibitory)

Question 24

Draw the gastric phase pathway

Answer 24

……

Question 25

What is an ulcer?

Answer 25

Acid/enzyme damage to stomach or intestinal wall

Question 26

How can ulcers be treated?

Answer 26

Vagotomy- decreases vagal stimulation (remove vagus nerve)
Histamine receptor antagonists
Proton pump inhibitors
Antibiotics to kill H. pylori