GIT Physiology Flashcards
What type of amylase is the salivary one?
alpha-amylase
Where does pepsin act on its target molecule?
It hydrolyses the bound between a aromatic aa and a second aa
What is emulsifying?
Breaking up fats into droplets
What is vitamin C also known as?
L-Ascorbic acid
What is the function of Gastrin releasing peptide?
Acts in parallel with ACh from vagus to stimulate gastrin release from G cells
What is the effect of the release of secretin stimulated bicarbonate solution from the pancreas?
Neutralised acid and pepsin activity
This leads to reduced stimulation of stomatostatin release from duodenal D cells and stops the vago-vagal and duodenal-pyloric-antral reflexes inhibiting gastric emptying
What type of cells can sense sweet taste?
L cells
What type of cells express olfactory receptors?
EC cells
Why don’t most things taste good without fats?
Most odourants/favour molecules are fat soluble
If tri or dipeptides are absorbed in to the enterocytes what must happen to them?
Cleaves into single aa’s by small peptidases
How many transport systems are there for free aa’s?
7
What is the function of mucus and bicarbonate release in the duodenum?
Create a barrier to gastric acid
What is the result of L cells sensing sweetness?
Increased glucose absorption
To what level are proteins digested before they can be absorbed?
Tri-, Di-peptides and single aa’s
What does colon fermentation produce?
Short chain fatty acids
How is cholesterol esterase activated?
By bile
What is the function of Ghrelin?
It is released from the stomach in fasted state to increase appetite
Which enzyme is important for breaking cell-cell adhesion?
Pepsin
5 of the amino acid absorption systems require what for co-transport?
Na - similar to sodium-dependent glucose transporters (SGLT1)
If you don’t have a stomach what supplement do you require?
Intrinsic factor
Which cell secrete pepsinogen?
Chief cells
Do gastric lipases play a major role in lipid digestion?
No
What does the vagovagal reflex pathway control/regulate?
Swallowing
Acid secretion
Smooth muscle contraction in stomach and duodenum
What is the product of fibre fermentation?
Short chain fatty acids
What neural pathway activates the cephalic phase?
The vagus nerve
What are the basic functions of the GIT?
Digest food
Absorb nutrients
Excrete waste
Prevention of invasion by pathogens
Contain the microbiome
Where are the major sites of digestion?
Duodenum and upper jejunum
What is the last to empty from the stomach? What are the implications?
Fat
Massive increase in CCK release when it come through
Which enzyme digests sucrose? What are the products of its digestion?
Sucrase
Glucose and fructose
Which enzyme activates enzymes from the pancreatic juices?
Enterokinase
What is the name of the enzyme that digests sugars?
Amylase
What does the endocrine control system regulate?
Secretion of enzymes and solvents into the intestinal lumen
Helps regulate appetite
What are two disaccharides human digested commonly?
Lactose and sucrose
What enzymes cleave at the amino end of peptide chains?
Aminopeptidases
What is the major transporter for glucose absorption?
Sodium-dependent glucose transporter - Na provides the energy
Which hormone’s release is stimulated by tastants?
Serotonin (EC cells)
Where is conscious control required in the defecation process?
Relaxation of anal sphincter
Contraction of abdominal muscles
Does the salivary amylase make it through the stomach?
Yes and it is reactivated once the pH returns to neutral
What are micelles composed of?
Bile salts with lecithin and monoglycerides
How are fats absorbed into the epithelium?
Micelles come into contact with lipid membrane and lipids dissolve and enter cells
What do enterochromaffin cell-like cell release?
Histamine
What three factors stimulate gastric acid secretion in parietal cells?
Vagus stimulation via enteric nerves releasing ACh acting on parietal cells
Histamine for enterochromaffin cell-like cell
Gastrin from G cells in the antrum (of stomach) and duodenum (endocrine signalling - must travel through the portal system)
What does cholesterol esterase do?
Hydrolyse cholesterol esters and esters of fat soluble vitamins and phospholipids
What happens to fat in the stomach?
It floats to the top due to action of acid, pepsin and mechanical action
What happens if the lower oesophageal sphincter doesn’t close properly?
Oesophageal reflux
If chronic - can lead to GORD - gastrooesophageal reflux disease
What happens to fatty acids and monoglycerides inside epithelials cells?
They form triglycerides in the smooth endoplasmic reticulum
How does somatostatin act on parietal cells?
By paracrine action directly on parietal cells to dampen acid secretion and,
By inhibiting histamine (which stimulates parietal cell acid secretion) release in enterochromaffin cell-like cells
What mechanism of sensing are present in the intestine lumen?
Mechanical reception - distension and mucosal deformation
Chemical stimuli
What type of vessel do chylomicrons get exocytosed into for enterocytes?
Lymphatics
What happens when the GIT is activated during the cephalic stage of eating?
Salivation begins
Gastric acid pepsin secretion begins
The gastric body and fundus relax
What four functions must be regulated in the GIT?
Contractions of muscles to mix food
Secretion of digestive enzymes
Re-absorption of water
Coordination of separate regions
When food initially enters the duodenum, what is the fat content?
Low
What linkage can’t pancreatic and salivary amylase digest?
1:6alpha
What does the CNS control in relation to food?
Anticipation
Mood/activity - fight or flight responses
Does glucose and fructose require digestion in the GIT?
No, they are immediately absorbed
Triglycerides are covered by what to form chylomicrons?
Apolipoproteins
Where do aa go after being absorbed into enterocytes?
Blood > portal circulation > liver
Which enzyme acts at the carboxy end of polypeptides?
Pancreatic carboxypeptidases
Which transporter facilitates fructose transport into the epithelium?
GLUT5
What is the consistency of the food when it leaves the antrum?
Diluted paste
What enzymes digest maltotriose and maltose?
Isomaltase
Sucrose
Maltase
Which endocrine signal induces expression of alpha-amylase in the pancreas?
CCK
What is segmentation?
A motor pattern in the duodenum where there are alternate contrictions and relaxations to further mix food with digestive enzymes and bile and bring it into contact with the epithelium for absorption
Via what pathway does acid trigger the release of mucus and bicarbonate by Brunner’s cells?
Vagal afferent neurones trigger the vago-vagal reflex
What stimulates the urge to defecate?
Distension of the rectum
What is sacrose a polymer of?
Glucose and fructose
Distension of the stomach causes what?
Activation of enteric and vago-vagal reflexes that lead to more acid and pepsin release
What is fermented in the distal small intestine and colon?
Cellulose
How is it insured that pancreatic enzymes are only active once they reach the food?
With a multi-dependent activation cascade.
Why must pepsin have an inactivated form?
So it doesn’t digest the contents of the cells it’s stored in
Which sugar polymers are digested at the brush boarder?
Oligosaccharides
Disaccharides
Why must D cells in the duodenum release much greater amounts of somatostatin cf to those in the stomach for it to have it desired effect?
It must travel through the portal system and the whole body therefore it is diluted
At what point does the microbiota metabolism start?
Ileum and colon
What linkage does alpha-amylase hydrolyse?
1:4alpha
How does activation of sweet taste receptors increase glucose absorption?
It activates glucose-Na channels
Where is primary peristalsis generated from? How is it communicated to the GIT?
The brain
Vagus nerve
Why might initial acid digestion in the mouth be important?
Initiates preparation of lipid storage
Which enzyme can break I:6alpha linkages?
Isomaltase
What are the name of the intrinsic pacemaker cells in the muscles?
Interstitial cells of Cajal
Does fat digestion occur in the mouth?
Yes, starts with lingual lipase
What is the first thing that must happen when food enters the duodenum?
Neutralise acids
What does cholecystokinin excite? What is the effects? (there are three)
Afferent vagal nerves that act on the hypothalamus to suppress appetite
Enteric sensory neurones to activate motor action to mix food
Contraction of gall bladder for secretion and pancreatic digestive enzymes secretion
What is the function of the neurally regulated interdigestive motor complex?
Clear bacteria to prevent overgrowth
Amino acids and fatty acids stimulate release of what from which cells?
CCK (cholecystokinin) from I cells
Secretin from S cells (just AA’s)
T/F the majority of movement in the intestines after a meal is propulsion?
False, 90% is mixing
What is retropulsion?
Food pushed back towards pyloris to facilitate mixing with pancreatic duct secretions and bile - further digestion
Which transporter facilitate fructose transport from the epithelium to the interstitium?
GLUT2
What is the function of secretin?
Stimulate secretion of a bicarbonate solution from the pancreas
How is lipase activated?
Colipase activates it
Colipase is activated by trypsin
What does the enteric nervous system and institial cells of Cajal regulate?
Contractile activity and secretion of water and salt
Why do enteroendocrine cells often span the epithelium?
So they can release mediators into the lumen of the GIT or into the blood stream
Which endocrine hormone is required for secretion of pancreatic lipolytic enzymes?
CCK
What are the 4 responses to acid in the duodenum?
Activates D cells to release somatostatin
Activates to Brunner’s glands produce mucus and bicarbonate
Activates the vago-vagal reflex to stop gastric emptying
Duodenal-pyloro-antral reflex closes the pylorus to further prevent gastric emptying
Which is absorbed better, glucose or fructose?
Glucose
Are enzymes released in the pancreas active?
No, they’re in their inactivated form
Where do trypsin, elastase and chymotrypsins act on their substrates (it’s the same for each of them)?
At the interior bonds of peptides to produce short polypeptides
Where is pepsinogen I secreted?
Acid secreting region of the stomach
T/F Smooth muscle cells of the GIT have intrinsic pacemakers
True
How do active maltase and sucrase get to their site of action?
An inactivated pro form is placed on the mucosal membrane as combined glycoprotein until pancreatic proteases cleave them to activate them
What does digestion by pancreatic carboxypeptidases produce?
single aa’s
Where is pepsinogen II secreted?
Pylorus
What does the body and antrum of the stomach do before food enters?
Reflex to accommodate
T/F Cellulose and starch are resistant to digestion.
False, only cellulose
What emulsifies lipids in the GIT?
Bile salt and lecithin
What is the cephalic stage of eating?
The sight and smell of food initates aspects of the GIT including salivation. The site of food will affect how it tastes eg red lollies taste “sweeter”
What does pepsinogen become?
Pepsin
What activates pepsinogen secretion by chief cells?
Gastrin
What controls swallowing?
Somatic NS via vagus
Where is CCK released in sugar digestion?
Duodenal mucosa
What stimulates D cells to release somatostatin?
Vagal stimulation via the enteric ns releasing ACh
Gastrin released from G cells
Acid in the stomach
What is the response to food entering the fundus?
Inhibition of acid secretion in the body
How are short chain fatty acids absorbed?
In a H+ dependent manner in the distal small intestine and colon
What factor tones down gastric acid secretion by parietal cells? Which cells release it?
Somatostatin
D cells
What are enteroendocrine cells?
GIT signally cells that contain many different hormone signalling molecules
