Week 7 - Digestion and absorption

Question 1

What are the two types of contractile response that are superimposed upon the basal tone of the smooth muscle of the gut?

Answer 1

segmentation and peristaltic contractions

Question 2

What is segmentation?

Answer 2

small regions of smooth muscle first contract and then relax to promote the mixing of intestinal contents

circular smooth muscle contracts and relaxes

Question 3

What is the purpose of peristaltic contractions?

Answer 3

propulsion of food along the GI tract

Question 4

From what segments of the spinal cord do the preganglionic fibres of the gastrointestinal sympathetic innervation arise from?

Answer 4

T8 to L2

preganglionic - fibres from the CNS to the ganglion, use acytylcholine as their neurotransmitter

Question 5

Where do the cell bodies of the postganglionic fibres of the GI sympathetic innervation lie?

Answer 5

within the coeliac, superior and inferior mesenteric and hypogastric plexuses

postganglionic - fibres from the ganglion to the effector organ, in symathetic division these neurons are adrenergic (adrenaline and noradrenaline are the primary neurotransmitters)

Question 6

What is the effect of increased sympathetic discharge on gastrointestinal activity?

Answer 6

reduces the activity

sympathetic - ‘fight or flight’

chronic stress can cause digestive problems because increased stimulation of the sympathetic nervous sytem can produce almost complete inhibition of gut activity

Question 7

What do the sympathetic fibres of the GI tract innervate?

Answer 7

smooth muscle of arterioles - fibres cause vasocontriction and redirection of blood away from the splanchnic bed

innervate some of the circular muscle of the large and small intestine

glandular tissue and secretory cells

Question 8

What is the effect of parasympathetic input to the gut?

Answer 8

stimulates both motility and secretory activity

Question 9

What nerve relays parasympathetic innervation to the oesophagus, stomach, small intestine, liver, pancreas, caecum, appendix, ascending colon and transverse colon?

Answer 9

vagus nerve

Question 10

What area of the GI tract receives parasympathetic innervation from pelvic nerves via the hypogastric plexus?

Answer 10

the remainder of the colon not innervated by the vagus nerve

descending colon, sigmoid colon, rectum

Question 11

What is the enteric nervous system (ENS)?

Answer 11

one of the main divisions of the nervous system that governs the function of the gastrointestinal system

Question 12

What are the two main nerve plexuses that constitute the enteric nervous sytem?

Answer 12

myenteric plexus and submucosal plexus (both are intramural plexuses)

Question 13

How many endocrine hormones are known to exist in the gut?

Answer 13

8 including gastrin, secretin and CCK

endocrine - circulating hormones

Question 14

What syndrome is associated with extremely elevated levels of ghrelin in the blood?

Answer 14

Prader - Willi syndrome

ghrelin has a number of efects within the gut and elsewhere including stimulation of growth hormone secretion by the anterior pituitary and the stimulation of appetite

ghrelin secretion is enhanced during fasting and is at its lowest immediately after a meal

Question 15

What are the three phases of gastric secretion?

Answer 15

cephalic, gastric, intestinal

Question 16

What is the combined circulation to the stomach, liver, pancreas, intestine and spleen called?

Answer 16

splanchnic circulation

Question 17

What immunoglobulin is found in saliva?

Answer 17

IgA

Question 18

What are the three large pairs of salivary glands?

Answer 18

parotid, submandibular and sublingual

Question 19

How is Vitamin C absorbed?

Answer 19

by sodium-dependant active transport in the jejunum

Question 20

What binds to B12 in the gastric juice?

Answer 20

haptocorrin

B12 is released from food by the low pH of gastric juice and becomes bound to haptocorrin, a glycoprotein secreted by the salivary glands

Question 21

What happens to B12 in the duodenum?

Answer 21

binds to intrinsic factor

haptocorrin is digested so B12 pairs up with intrinsic factor which is secreted by the parietal cells of the gastric mucosa

Question 22

Where is the B12:IF complex absorbed?

Answer 22

lower ileum

Question 23

What does B12 bind to in the capillary endothelial cells?

Answer 23

transcobalamin II ready to be transported into the blood

Question 24

What is the function of the oesophagus?

Answer 24

lubricates the food

peristaltic waves move the food to the stomach

Question 25

What is the function of the gall bladder?

Answer 25

storage and concentration of bile

Question 26

What are the four layers of the gastrointestinal wall?

Answer 26

mucosa, submucosa, muscularis externa and serosa

Question 27

What layers make up the mucosa?

Answer 27

epithelium, lamina propria, muscularis mucosa

Question 28

What does saliva consist of?

Answer 28

water, mucoprotein, IgA, carbohydrates, inorganic ions, enzymes

Question 29

What are the two types of salivary glands?

Answer 29

**large paired -** parotoid, submandibular, sublingual ## Footnote **small glands**

Question 30

Where are the small glands in the mouth found?

Answer 30

mucosa and submucosa named after location **labial** - lips **buccal** - cheeks **lingual** - tongue

Question 31

What is the difference between the small glands and large paired salivary secreting glands?

Answer 31

small glands secrete continuosly large paired glands secrete only on stimulation

Question 32

Where are the large paired glands located?

Answer 32

outside the mouth and are connected by long ducts

Question 33

What is the basic architecture of the salivary glands?

Answer 33

a number of lobules surrounded by a fibrous capsule each lobule (acinus) is made up of balls of cells drained by ductules that join to form larger ducts leading into the mouth

Question 34

Where is the digestive enzyme salivary amylase stored?

Answer 34

zymogen granules in the serous acinar cells

Question 35

What is the effect of parasympathetic stimulation on the salivary glands?

Answer 35

promotes abundant watery saliva rich in amylase and mucins increase in blood flow - kallikrein promotes production of the vasodilator bradykinin

Question 36

When does the cephalic phase of digestion occur?

Answer 36

before food has arrived in the mouth **anticipation** of food - sight, smell, taste

Question 37

Where do the neurogenic signals that initiate the cephalic phase of gastric secretion originate from?

Answer 37

cerebral cortex appetite centers of the amygdala and hypothalamus

Question 38

What triggers the secretion of acetylcholine by nerve endings the cephalic phase of gastric secretion?

Answer 38

parasympathetic vagal stimulation

Question 39

What cell releases cholecystokinin?

Answer 39

I-cells of the duodenum

Question 40

Which hormone causes increased pancreatic enzyme secretion and gall bladder contraction? a) CCK b) Gastrin c) Lipase d) Secretin

Answer 40

a) CCK

Question 41

What is the role of pancreatic lipase?

Answer 41

cleaves triacylglycerides (TAG) in micelles **micelle -** small aggregates of mixed lipids and bile acids

Question 42

What are the two types of dietry lipid?

Answer 42

neutral fat and triglyceride

Question 43

What two processes must occur for triglycerides to be digested?

Answer 43

emulsification and enzymatic digestion

Question 44

Describe the action of pancreatic lipase on triglycerides

Answer 44

splits bonds linking fatty acids to 1st and 3rd carbon atoms of glycerol very limited action without **colipase**

Question 45

What cells are responsible for histamine secretion in the stomach?

Answer 45

ECL (enterochromaffin like cells)

Question 46

On what cells of the stomach does gastrin act?

Answer 46

parietal cells released by G cells of the pyloric antrum, duodenum and pancreas

Question 47

What are the two mechanisms of action of gastrin?

Answer 47

binds to CCK_B receptors on ECL cells to stimulate release of histamine induces insertion of K⁺/H⁺ ATPase pumps into apical membrane of parietal cells - leads to secretion of H⁺ into stomach cavity

Question 48

What stimuli causes G cells to release gastrin?

Answer 48

stomach distention vagal stimulation presence of partially digested proteins hypercalcemia