GI anatomy and physiology

Question 1

Describe how the movement is done throughout the GI tract?

Answer 1

1. Peristalsis which occurs through smooth muscle that’s electrically coupled to other cells

Question 2

Describe the intrinsic innervation enteric nervous system?

Answer 2

1. Controls the motility of gastric relaxation and contraction
2. Integrates autonomic nervous system and local systems: 5-HT
3. Functions independently of any other signals (some may say part of autonomic nervous system)

Question 3

What does the myenteric plexus mainly control?

Answer 3

Motility in GI tract

Question 4

What does the submucosal plexus mainly control?

Answer 4

Formation of secretions and blood flow in GI tract

Question 5

Describe how the intrinsic innervation autonomic innervation works in the parasympathetic and sympathetic?

Answer 5

1. Parasympathetic: Increases motility and secretion
   - ACh acting on muscarinic to increase salivation, mucosa (lining of stomach of mucus) and constriction
2. Sympathetic reduces GI function
   Noradrenaline relaxes the smooth muscle in GI

Question 6

Give examples of endocrine hormones in the blood stream and what they work on?

Answer 6

1. Gastrin and Cholesystokinin (CCK)

2. Both work on motility and secretion

Question 7

Give examples of paracrine hormones in the cell wall and what they work on?

Answer 7

1. Histamine and somatostatin

2. Modulate nerve action, affect secretion and motility

Question 8

What is the purpose behind salvia?

Answer 8

1. Aids swallowing
2. Begins digestion
3. Kills bacteria

Question 9

Describe how the parasympathetic and sympathetic nervous system work?

Answer 9

1. Parasympathetic produces watery salvia which increases secretion and blood flow
2. Sympathetic produces mixed salvia which increases secretion and decreases blood flow

Question 10

Describe the process of swallowing with the last step being the stomach?

Answer 10

1. Voluntary
2. Peristalsis occurs through the autonomic nervous system which is aided by mucous
3. Enters stomach via oesophageal sphincter

Question 11

What is the stomach lined with?

Answer 11

1. Rugae (epithelial cells) that contain deep gastric pits for producing acid to grind food in the stomach
2. Located in the mucosa layer

Question 12

What do the parietal cells do in the stomach?

Answer 12

Produce gastric acid

Question 13

What do the chief cells do in the stomach?

Answer 13

Produce pepsinogen and other digestive enzymes which break up the food in the stomach

Question 14

What does the gastric fluid consist of?

Answer 14

1. Pepsinogen
2. Salts
3. Hydrochloric acid
4. Water and intrinsic factors

Question 15

What is the importance of HCl?

Answer 15

1. Aids absorption of calcium and iron
2. Actives pepsinogen and optimises pepsin function
3. Aids breakdown of tissue
4. Eliminates pathogens, bacteria and viruses

Question 16

Describe how stomach acid is formed in the stomach?

Answer 16

1. Pariental cell forms carbonic anhydrase which forms the H+ and HCO3-
2. Cl- enters which replaces the HCO3- so that it can be transported via the K+/Cl- symporter
3. Proton pump (H+/K+ ATPase) transports H+ into the stomach lumen

Question 17

How is gastrin released and what is the role of it in acid secretion?

Answer 17

1. Released from cell from nerve, hormonal and food stimuli

2. Activates CCK2 receptors on ECL cells stimulating histamine release

Question 18

What is the role of histamine in acid secretion?

Answer 18

Agonist on H2 receptor on pariental cells that stimulate acid secretion

Question 19

What is the purpose of the gastric mucosa?

Answer 19

Protects stomach from acid and gastric enzyme by acting as a gel like alkaline bicarbonate

Question 20

What promotes mucosal secretion?

Answer 20

Prostaglandins

Question 21

Describe the three main gastric diseases (causes and symptoms)

Answer 21

1. GORD (Gastro oesophageal reflux disease)
   - Symptoms: heartburn, acid reflux, indigestion or irritation to gastric mucosa
2. Gastric bleeding
   - due to NSAID treatment
   - caused by irritants and cancer
3. Ulceration
   - Causes may be stress or certain foods
   - Caused by H. pylori infection

Question 22

What is the role of the stomach in gastric propulsion?

Answer 22

1. Stomach mixes and stores food for digestion in the intestine
2. Peristaltic waves propel food from the pyloric sphincter to the duodenum
3. Controls emptying of food depending on pH and content of food

Question 23

How is drug action affected by the stomach?

Answer 23

Depends on the rate of emptying and the pH of the stomach

Question 24

Describe how vomiting is, the symptoms and what occurs during it?

Answer 24

1. The sudden forceful evacuation of the contents in the stomach (and duodenum)
2. Symptoms: loss of appetite, nausea, vasoconstriction, sweating and dizziness
3. During vomiting:
   - Respiratory is relaxed
   - Stomach relaxes, duodenum contracts
   - Diaphragm and abdominal muscles contract powerfully

Question 25

What area of the brain controls the vomiting centre and what are the two main components?

Answer 25

1. Medulla of the brain stem 2. Chemoreceptor trigger zone (CTZ): senses enteric stimuli 3. Vomiting centre

Question 26

What are the two roles played by the pancreas?

Answer 26

1. Endocrine: - insulin and glucagon into the blood stream 2. Exocrine: - Alkaline fluid reduces pH in the duodenum - Digestive enzymes: Proteolytic and Lipolytic: digestion protein and fats 3. ACh, CCK, Gastrin increases secretion and somatostatin decreases

Question 27

What is the major role played by the small intestines?

Answer 27

The adsorption of nutrients and minerals as well as drug absorption

Question 28

How are monosaccharide and amino acids absorbed?

Answer 28

Absorbed by the small intestine regulated by Na dependent transporters

Question 29

How are fats and fat soluble vitamins absorbed ?

Answer 29

Micelles and bile salts

Question 30

What is the role of the large intestine?

Answer 30

1. The storage of waste disposable/indigestible food residues before elimination by defection 2. Absorbs water and electrolytes 3. Resident bacteria form vitamins such as vitamin B12, vitamin K, Riboflavin

Question 31

What is the role of mucous secretions in the large intestine?

Answer 31

Helps the movement of faeces easier throughout the defection period when the waste needs to be removed

Question 32

What role does dietary fibre play in motility and defecation?

Answer 32

1. Bulk stimulates movement in the GIT 2. Dietary fibre hydrates the bulk allowing softer faeces (basis of laxatives) 3. High fibre can protect against some GI issues