Digestion and Vomiting Flashcards
How much carbohydrates are consumed in a typical diet?
250-800g
Where does digestion of carbohydrates begin?
In the mouth
What happens to the food during mastication?
During mastication, the food is mixed with saliva which contains salivary amylase.
What are the effects of salivary amylase?
It randomly hydrolyses a(1-4) glycosidic bonds within polysaccharides
What are the products of carbohydrate digestion in the mouth?
Dextrins, maltose and glucose
Why does carbohydrate digestion stop in the stomach?
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
What digests carbohydrates in the small intestine?
Pancreatic amylase and intestinal brush border enzymes
What is the products of pancreatic amylase action?
hydrolyses dextrins into limit dextrins, maltose and isomaltose
When does pancreatic amylase work?
It works before the food is passed into the duodenum and upper jejunum
What are the products of the maltase?
Converts maltose into 2 glucose molecules
What are the products of isomaltase?
Converts isomaltose into 2 glucose molecules
What are the products of sucrase?
Converts sucrose into glucose and fructose
What are the products of lactase?
Converts lactose into glucose and galactose
What are the products of dextrinase?
Converts dextrins into glucose, maltose and isomaltose
What are the products of glucoamylase?
Converts polysaccharides into glucose
How much protein is consumed in the typical diet?
125g per day
What are proteins composed of
Amino acids with a -COOH group on one end and -NH2 group on the other, and are linked together by peptide bonds
Why does protein digestion not occur in the mouth?
There are no proteolytic enzymes in the saliva
What is the effect of protein arrival in the stomach?
It stimulates G cells to release gastrin, which in turn cause the release of gastric juice containing HCl, pepsinogen and rennin
What are the effects of HCl?
It causes the denaturing of proteins and converts pepsinogen into pepsin
How does pepsin digests proteins?
It acts on the peptide bonds formed by -COOH group of protein to break them into proteases and peptones
What does the low pH of the chyme cause the secretion of in the duodenum?
CCK and secretin hormones
What is the effect of secretin?
It causes the secretion of bicarbonate by the pancreas to neutralize the pH
What does CCK stimulate the release of?
Endopeptidases - trypsin, chymotrypsin ad elastase
Exopeptidases - carboxypeptidase and aminopeptidase
What is the effect of endopeptidases?
It cleaves the internal peptide bonds and results in to formation of smaller peptides
What is the effect of exopeptidases?
It cleaves of one amino acid at a time from either the -COOH or -NH2 terminal of the polypeptide
What pancreatic peptidases secreted as?
They are secreted in their inactive form - trypsinogen, chymotrypsinogen and procarboxypeptidase
How are the precursor pancreatic peptidases activated?
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
How much fat is consumed in the typical diet?
25-100g
Why are fat droplets formed?
Lipids are water insoluble and fail to mix with stomach and intestinal contents
Which enzymes act on lipids in the mouth and stomach?
Lingual lipase and gastric lipase
What are the products of lingual lipase and gastric lipase?
It converts lipids into glycerols and free fatty acids
Where does most lipid digestion occur and by what?
In the duodenum by pancreatic lipase
Why is lipid digestion aided by bile salts and what does it do?
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
What are the products and pancreatic lipase?
Breaks down triglyceride into 2 fatty acids and 1 monoglyceride
Besides pancreatic lipase, what are the other 2 fat digestion enzymes secreted by the pancreas?
Phospholipase A2
Cholesterol esterase
What is the effect of phospholipase A2?
It facilitates the digestion of phospholipids
What is the effect of cholesterol esterase?
Promotes the degradation of cholesterol esters into cholesterol and free fatty acids
What is vomiting/emesis?
Rapid and forceful evacuation of the stomach contents up to and out of the mouth
What are the phases of vomiting?
Nausea, retching and vomiting
What is nausea?
It is an unpleasant sensation that often precedes vomiting
What accompanies nausea?
Increased salivation
Shivering
Increase HR
Palpitations
Stomach movements slow right down
Why does a reflux of intestinal contents into the stomach occur?
It occurs due to reverse peristalsis and relaxation of the pyloric sphincter
What is retching?
This follows nausea, and comprises of laboured sporadic respiratory movements against a closed glottis
What accompanies retching?
Intense rhythmic contractions of the abdominal muscles, chest wall and diaphragm
What pressure gradient is generated during retching?
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
Where are the mechano- and chemoreceptors involved in nausea and vomiting located?
stomach, jejunum and ileum
What do mechano- and chemoreceptors detect?
emetic stimuli in the GIT
What are the effects of mechanoreceptors?
Initiate emesis in response to distention and contraction
What do chemoreceptors respond to?
They respond to a variety of toxins in the intestines
Where does the vomiting centre receive input from?
GIT
Cortical areas
Chemoreceptor trigger zone located outside the BBB
What is stimulated by the vomiting centre in order to induce vomiting?
salivary and respiratory centres
pharyngeal, GIT and abdominal mecles
Which neurotransmitters are involved in vomiting?
acetylcholine, histamine, dopamine, serotonin, enkepahlins, and substance P
