Digestion and Vomiting

Question 1

How much carbohydrates are consumed in a typical diet?

Answer 1

250-800g

Question 2

Where does digestion of carbohydrates begin?

Answer 2

In the mouth

Question 3

What happens to the food during mastication?

Answer 3

During mastication, the food is mixed with saliva which contains salivary amylase.

Question 4

What are the effects of salivary amylase?

Answer 4

It randomly hydrolyses a(1-4) glycosidic bonds within polysaccharides

Question 5

What are the products of carbohydrate digestion in the mouth?

Answer 5

Dextrins, maltose and glucose

Question 6

Why does carbohydrate digestion stop in the stomach?

Answer 6

The high acidity of the gastric secretions render the salivary amylase inactive once the pH drops below 4. There are also no carbohydrate splitting enzymes in the gastric juice

Question 7

What digests carbohydrates in the small intestine?

Answer 7

Pancreatic amylase and intestinal brush border enzymes

Question 8

What is the products of pancreatic amylase action?

Answer 8

hydrolyses dextrins into limit dextrins, maltose and isomaltose

Question 9

When does pancreatic amylase work?

Answer 9

It works before the food is passed into the duodenum and upper jejunum

Question 10

What are the products of the maltase?

Answer 10

Converts maltose into 2 glucose molecules

Question 11

What are the products of isomaltase?

Answer 11

Converts isomaltose into 2 glucose molecules

Question 12

What are the products of sucrase?

Answer 12

Converts sucrose into glucose and fructose

Question 13

What are the products of lactase?

Answer 13

Converts lactose into glucose and galactose

Question 14

What are the products of dextrinase?

Answer 14

Converts dextrins into glucose, maltose and isomaltose

Question 15

What are the products of glucoamylase?

Answer 15

Converts polysaccharides into glucose

Question 16

How much protein is consumed in the typical diet?

Answer 16

125g per day

Question 17

What are proteins composed of

Answer 17

Amino acids with a -COOH group on one end and -NH2 group on the other, and are linked together by peptide bonds

Question 18

Why does protein digestion not occur in the mouth?

Answer 18

There are no proteolytic enzymes in the saliva

Question 19

What is the effect of protein arrival in the stomach?

Answer 19

It stimulates G cells to release gastrin, which in turn cause the release of gastric juice containing HCl, pepsinogen and rennin

Question 20

What are the effects of HCl?

Answer 20

It causes the denaturing of proteins and converts pepsinogen into pepsin

Question 21

How does pepsin digests proteins?

Answer 21

It acts on the peptide bonds formed by -COOH group of protein to break them into proteases and peptones

Question 22

What does the low pH of the chyme cause the secretion of in the duodenum?

Answer 22

CCK and secretin hormones

Question 23

What is the effect of secretin?

Answer 23

It causes the secretion of bicarbonate by the pancreas to neutralize the pH

Question 24

What does CCK stimulate the release of?

Answer 24

Endopeptidases - trypsin, chymotrypsin ad elastase
Exopeptidases - carboxypeptidase and aminopeptidase

Question 25

What is the effect of endopeptidases?

Answer 25

It cleaves the internal peptide bonds and results in to formation of smaller peptides

Question 26

What is the effect of exopeptidases?

Answer 26

It cleaves of one amino acid at a time from either the -COOH or -NH2 terminal of the polypeptide

Question 27

What pancreatic peptidases secreted as?

Answer 27

They are secreted in their inactive form - trypsinogen, chymotrypsinogen and procarboxypeptidase

Question 28

How are the precursor pancreatic peptidases activated?

Answer 28

They are activated by proteolytic activation, initiated by enterokinase (secreted by the intestinal brush border) Enterokinase converts tyrpsinogen to trypsin Trypsin converts chymotrypsinogen and procarboxypeptidase into chymotrypsin and carboxypeptidase respectively

Question 29

How much fat is consumed in the typical diet?

Answer 29

25-100g

Question 30

Why are fat droplets formed?

Answer 30

Lipids are water insoluble and fail to mix with stomach and intestinal contents

Question 31

Which enzymes act on lipids in the mouth and stomach?

Answer 31

Lingual lipase and gastric lipase

Question 32

What are the products of lingual lipase and gastric lipase?

Answer 32

It converts lipids into glycerols and free fatty acids

Question 33

Where does most lipid digestion occur and by what?

Answer 33

In the duodenum by pancreatic lipase

Question 34

Why is lipid digestion aided by bile salts and what does it do?

Answer 34

Lipids are water insoluble and form fat droplets. Lipase molecules will only act on the surface. Bile salts cause emulsification, breaking the large lipid droplets into much smaller ones for efficient digestion

Question 35

What are the products and pancreatic lipase?

Answer 35

Breaks down triglyceride into 2 fatty acids and 1 monoglyceride

Question 36

Besides pancreatic lipase, what are the other 2 fat digestion enzymes secreted by the pancreas?

Answer 36

Phospholipase A2 Cholesterol esterase

Question 37

What is the effect of phospholipase A2?

Answer 37

It facilitates the digestion of phospholipids

Question 38

What is the effect of cholesterol esterase?

Answer 38

Promotes the degradation of cholesterol esters into cholesterol and free fatty acids

Question 39

What is vomiting/emesis?

Answer 39

Rapid and forceful evacuation of the stomach contents up to and out of the mouth

Question 40

What are the phases of vomiting?

Answer 40

Nausea, retching and vomiting

Question 41

What is nausea?

Answer 41

It is an unpleasant sensation that often precedes vomiting

Question 42

What accompanies nausea?

Answer 42

Increased salivation Shivering Increase HR Palpitations Stomach movements slow right down

Question 43

Why does a reflux of intestinal contents into the stomach occur?

Answer 43

It occurs due to reverse peristalsis and relaxation of the pyloric sphincter

Question 44

What is retching?

Answer 44

This follows nausea, and comprises of laboured sporadic respiratory movements against a closed glottis

Question 45

What accompanies retching?

Answer 45

Intense rhythmic contractions of the abdominal muscles, chest wall and diaphragm

Question 46

What pressure gradient is generated during retching?

Answer 46

The pyloric sphincter closes, the pressure within the abdomen rises and the pressure within the thorax lower. Altogether, this forces the contents of the stomach into the oesophagus

Question 47

Where are the mechano- and chemoreceptors involved in nausea and vomiting located?

Answer 47

stomach, jejunum and ileum

Question 48

What do mechano- and chemoreceptors detect?

Answer 48

emetic stimuli in the GIT

Question 49

What are the effects of mechanoreceptors?

Answer 49

Initiate emesis in response to distention and contraction

Question 50

What do chemoreceptors respond to?

Answer 50

They respond to a variety of toxins in the intestines

Question 51

Where does the vomiting centre receive input from?

Answer 51

GIT Cortical areas Chemoreceptor trigger zone located outside the BBB

Question 52

What is stimulated by the vomiting centre in order to induce vomiting?

Answer 52

salivary and respiratory centres pharyngeal, GIT and abdominal mecles

Question 53

Which neurotransmitters are involved in vomiting?

Answer 53

acetylcholine, histamine, dopamine, serotonin, enkepahlins, and substance P