Upper GI tract (36)

Question 1

What is digestion?

Answer 1

the process of breaking down macromolecules to allow absorption

Question 2

Which structures make up the foregut?

Answer 2

• oesophagus
• stomach
• liver
• pancreas
• biliary system

Question 3

What are the layers of the gut wall?

Answer 3

• mucosa: epithelium, lamina propria, muscularis mucosae
• submucosa: connective tissue containing nerve plexus
• muscularis: smooth muscle containing nerve plexus
• serosa/adventitia: connective tissue

Question 4

What is the function of the oesophagus?

Answer 4

• conduit for food, drink and swallowed secretions from pharynx to stomach
• traverses 3 different body cavities: neck, thorax and abdomen

Question 5

What is the structure of the epithelium in the oesophagus?

Answer 5

• squamous, non-keratinising
• mucus secreting glands–> lubrication of food
• ‘wear and tear’ lining for extremes of temp.

Question 6

What is the is the structure of the muscle in the oesophagus?

Answer 6

• inner circular muscle

- longitudinal muscle

Question 7

What is the gastro-oesophageal junction?

Answer 7

• passes through diaphragmatic hiatus- diaphragm prevents reflux
• where pale pink mucosa (squamous) of oesophagus meets red mucosa of stomach (columnar)- EPITHELIAL TRANSITION
• gastric folds- rugae

Question 8

Why are gastric folds present?

Answer 8

inc. absorptive SA

Question 9

What are the 4 phases of swallowing?

Answer 9

• stage 0: oral phase- food broken down by teeth, saliva, tongue
• stage 1: pharyngeal phase- food goes from oral cavity to pharynx
• stage 2: upper oesophageal phase- upper sphincter opens + closes, sequential contractions of longitudinal muscle
• stage 3: lower oesophageal phase- lower sphincter opens and closes

Question 10

What is absorption?

Answer 10

the process of moving nutrients and water across a membrane

Question 11

What are the functions of the stomach?

Answer 11

• secrete acid and pepsin to break food into smaller particles
• hold food, releasing it in a controlled rate into duodenum
• kill parasites and certain bacteria

Question 12

What is the structure of the stomach?

Answer 12

• cardia- just below oesophagus
• fundus- bulbous bit
• body- most of stomach
• antrum
• pylorus- outlet
• pyloric sphincter

Question 13

What is the function of the circular muscle in the stomach?

Answer 13

• segmentation
• keeps food in stomach so can get broken down
• weaker contraction than peristalsis
• fluid chyme towards pyloric sphincter, solid chyme pushed back to body

Question 14

What is a gastric chief cell?

Answer 14

• protein- secreting epithelial cell, so rich in RER and Golgi
• secretion granules at apex- release protein into lumen
• secretes PEPSINOGEN (proenzyme)

Question 15

What is a parietal cell?

Answer 15

• helps to create HCl (which is important to pepsinogen–>pepsin)
• contain tubulovesicles, which house the H+/K+ ATPase pumps
• many mitochondria bc requires lots of ATP
• internal canaliculi- deep infoldings that inc. SA

Question 16

How does the parietal cell work?

Answer 16

• CO2 comes from capillaries, mixes with water, using enzyme CARBONIC ANHYDRASE–> HCO3- and H+ produced
• K+ comes into cell from capillaries and gets secreted into gastric lumen
• K+ gets exchanged w/ H+ using the pump, and comes into the cell
• H+ goes into lumen and combines w/ Cl- to give HCl

Question 17

What is the role of HCl?

Answer 17

converts pepsinogen to pepsin

Question 18

What is gastrin?

Answer 18

• hormone secreted by G cells in antrum of stomach

- stimulates parietal cell to produce HCl

Question 19

What are the phases of gastric secretion?

Answer 19

1. cephalic phase
2. gastric phase
3. intestinal phase

Question 20

What structures make up the mid gut?

Answer 20

• small intestine

- part of large intestine

Question 21

What structures make up the hind gut?

Answer 21

• colon

- rectum

Question 22

How many teeth do we have and what types?

Answer 22

32 in total

• 8 incisors
• 4 canines
• 8 premolars
• 12 molars

Question 23

What muscle is responsible for biting/largest jaw muscle?

Answer 23

masseter muscle

Question 24

What digestive enzymes are produced by the salivary glands?

Answer 24

• lingual lipase–> breaks down lipids

- salivary amylase–> breaks down carbohydrates

Question 25

What is the purpose of peristalsis?

Answer 25

to propel chyme towards the colon by moving it to pyloric sphincter

Question 26

What nerve supplies the stomach?

Answer 26

vagus

Question 27

How is stomach secretory activity stimulated in the cephalic phase?

Answer 27

sight/thought/taste/smell of food–> cerebral cortex–> hypothalamus and medulla oblongata–> vagus nerve (PNS)–> stomach
(N.B. here, gastric juice secreted before food even enters stomach)
ALSO hormonal stimulation- gastrin stimulates parietal cells

Question 28

How is stomach secretory activity stimulated in the gastric phase?

Answer 28

stomach distension (stretch) activates stretch receptor bc food occupying stomach--> stimulates vagus nerve- 'vasovagal reflex' or submucosal plexus (local)--> stomach
AND
food chemicals/rising pH activate chemoreceptors--> G cells secrete gastrin into blood--> travels to parietal cells in stomach

Question 29

How is stomach secretory activity stimulated in the intestinal phase?

Answer 29

enterogastric reflex

enterohormones send signal to brain–> vagus nerves

Question 30

How might you produce a useful drug to decrease acid secretion?

Answer 30

• block histamine- H2 receptor blockers
• somatostatin- suppresses G cell receptors
• block H+/K+ pump