GASTROINTESTINAL SYSTEM
Systems 2
Table of Contents
Gastrointestinal System 2
Lecture 1: Introduction to the Gastrointestinal System 2
Lecture 2: GI Tract Physiology 1 (Introduction) 2
Lecture 3: GI Tract Physiology 2 (Motility) 6
Lecture 4: GI Tract Physiology 3 (Digestion in the Mouth) 10
Lecture 5: Embryology 15
Lecture 6: Irritable Bowel Syndrome 19
Lecture 7: Anti-Emetic Drugs 20
Lectures 8 & 9: GI Tract Physiology 4 & 5 (Gastric Secretion) 24
Lecture 10: Radiology of the GI Tract 30
Lecture 11: Pharmacology of Gastric Acid Secretion 34
Lectures 12 & 13: GI Physiology 6 & 7 (Digestion in the Intestine) 36
Lecture 14: Upper and Lower GI Neoplasia 42
Lecture 15: GI Tract Physiology 8 (Absorption) 45
Lecture 16: Disorders of the Anorectal Canal 49
Lecture 17: Disorders of Hepatic, Biliary and Pancreatic Function 51
Lecture 18: Disorders of Absorption 52
Lecture 19: Chron’s Disease 53
Lecture 20: Normal Flora and Gastroenteritis 55
Lecture 21: Drugs and the GI Tract (Absorption and Availability) 56
Lecture 22: Drugs and the GI Tract (Excretion) 59
Lectures 23 & 24: Metabolic Functions of the Liver 1 & 2 64
Lecture 25: Ulcerative Colitis 73
Lecture 26: The Liver and Drug Metabolism 74
Lecture 27: Viral Hepatitis and Infections of the Liver 76
Lecture 28: Liver Function Tests 77
Lecture 29 : Case Studies in GI Tract Funciton 78
Lecture 30: Alcohol Related Liver Disease 80
Lecture 31: GI Microbiology 81
Lecture 32: Integrating Liver Biochemistry with Clinical Presentations 83
, Gastrointestinal System
Lecture 1: Introduction to the Gastrointestinal System
• What is an oral rehydration sachet? A sachet
with salts such as sodium chloride, potassium
chloride, trisodium citrate and glucose that you
dissolve in a litre of water, and then drink in
order to rehydrate as fast as possible. It is
particularly useful in treating secretory diarrhoea
• What is secretory diarrhoea? There is an
increase in the active secretion, or there is an inhibition of
absorption, meaning the stools get very liquid and voluminous.
There is little to no structural damage. The most common cause of this type of diarrhea is a cholera
toxin.
• Why do we add glucose to the oral rehydration sachet? Because it stimulates absorption of salts
such as NaCl (look at the graph).
Without the glucose, the salts would
not be as absorbed and so rehydration
would be hindered.
• Where, histologically, does chloride
secretion occur in the small intestine?
The crypts
• Where does absorption occur? The
villi
• Why does glucose promote sodium
absorption? Because they are co-
transported together via SGLT-1
(sodium glucose linked transporter 1).
• How does cholera cause secretory diarrhoea? A toxin causes cAMP activation à activates chloride
ions being pumped into the lumen of the gut via CFTR à sodium drawn out into the lumen à
massive amounts of water drawn out into the gut due to osmotic effect à watery diarrhoea à
dehydration
Lecture 2: GI Tract Physiology 1 (Introduction)
• Define the following terms
Term Definition
Digestion The process by which food and large molecules
are chemically degraded to produce smaller
molecules
Absorption The processes by which nutrient molecules are
absorbed by cells that line the GI tract and enter
the bloodstream
• In what way is the stomach a reservoir? It has 2 sphincters, one on each end of the stomach
(gastro-oesophageal and pyloric sphincters), and hence stores food whilst digesting it.
• When does food pass through the pyloric sphincter? When it becomes smaller than 2mm
Marc Huttman 2
,• Revise the histology of the GI tract (distinguish between different parts) and know the following
common architecture.
• What is the lamina propria? A layer of connective tissue in the mucosa, so it will have some small
blood vessels, nerves and muscle cells
• What does the muscularis mucosae do? It’s responsible for moving around the
mucosal folds when it contracts
• What are mucosal folds? They are NOT villi. They are the folds in the whole mucosa
of the GI tract. Imagine trees on a hilly landscape… the trees are the villi and the hills
on the landscape are the folds. Folds can be seen with the naked eye (see picture)
• Where do we find submucosal glands?
Submucosal gland Description
Oesophagus Oesophageal submucosal glands secrete mucus
for protection
Brunner’s glands in the duodenum • Secrete bicarbonate, HCO3-, to neutralise the
acid that’s coming from the stomach
• Briefly, how do bacteria in the colon help digestion? They break down indigestible materials and
create short chain fatty acids that are then absorbed
• What are the 2 nervous plexus systems found in the GI tract and where are they found?
Nervous plexus Where it’s found histologically Where it is located in GI tract
Submucosal plexus (Meissner’s In the submucosa, near to the Small and Large intestine
plexus) circular muscle of the
muscularis externa
Myenteric plexus (Auerbach’s Between the circular and All along the GI tract
plexus) longitudinal layers of the (oesophagus to rectum) – the
muscularis externa more important plexus
Marc Huttman 3
, • In what ways is the surface area of the GI tract amplified?
1. Folds of Kerckring/plicae circularis – large spiral or circular folds that on the lumen that I
mentioned before
2. Villi – finger like projections
3. Microvilli – even smaller finger light projections on the surface of the villus epithelium. They
can only be seen on an electron micrograph.
• Why are the microvilli kind of fuzzy on an electron micrograph? Because there is a glycocalyx
scaffolding that gives rise to an unstirred layer, which is important for the absorption of nutrients
• What do we mean by ‘unstirred layer’? A layer of substance that is not going to be subjected to the
churning up of the lumen of the intestine
• Are the apical and basal membrane of absorptive cells in the gut the same? No, they are very much
polarised. If they weren’t polarised, transport would not be able to occur
• Describe the following types of movement of molecules
Type of transport Description
Paracellular Between cells
Transcellular Through cells
• How are NaCl and water moved across the intestinal epithelium into the lumen?
1. Cl- ions are actively pumped across the basolateral membrane into the cell via NKCC1
2. Cl- ions then diffuse into the lumen across the apical membrane via CFTR
3. This puts a –ve charge in the lumen so Na+ follows the negative charge and flows into the lumen
paracellularly
4. A strong osmotic gradient is set up and so H2O flows into the lumen paracellularly, too.
Marc Huttman 4
Systems 2
Table of Contents
Gastrointestinal System 2
Lecture 1: Introduction to the Gastrointestinal System 2
Lecture 2: GI Tract Physiology 1 (Introduction) 2
Lecture 3: GI Tract Physiology 2 (Motility) 6
Lecture 4: GI Tract Physiology 3 (Digestion in the Mouth) 10
Lecture 5: Embryology 15
Lecture 6: Irritable Bowel Syndrome 19
Lecture 7: Anti-Emetic Drugs 20
Lectures 8 & 9: GI Tract Physiology 4 & 5 (Gastric Secretion) 24
Lecture 10: Radiology of the GI Tract 30
Lecture 11: Pharmacology of Gastric Acid Secretion 34
Lectures 12 & 13: GI Physiology 6 & 7 (Digestion in the Intestine) 36
Lecture 14: Upper and Lower GI Neoplasia 42
Lecture 15: GI Tract Physiology 8 (Absorption) 45
Lecture 16: Disorders of the Anorectal Canal 49
Lecture 17: Disorders of Hepatic, Biliary and Pancreatic Function 51
Lecture 18: Disorders of Absorption 52
Lecture 19: Chron’s Disease 53
Lecture 20: Normal Flora and Gastroenteritis 55
Lecture 21: Drugs and the GI Tract (Absorption and Availability) 56
Lecture 22: Drugs and the GI Tract (Excretion) 59
Lectures 23 & 24: Metabolic Functions of the Liver 1 & 2 64
Lecture 25: Ulcerative Colitis 73
Lecture 26: The Liver and Drug Metabolism 74
Lecture 27: Viral Hepatitis and Infections of the Liver 76
Lecture 28: Liver Function Tests 77
Lecture 29 : Case Studies in GI Tract Funciton 78
Lecture 30: Alcohol Related Liver Disease 80
Lecture 31: GI Microbiology 81
Lecture 32: Integrating Liver Biochemistry with Clinical Presentations 83
, Gastrointestinal System
Lecture 1: Introduction to the Gastrointestinal System
• What is an oral rehydration sachet? A sachet
with salts such as sodium chloride, potassium
chloride, trisodium citrate and glucose that you
dissolve in a litre of water, and then drink in
order to rehydrate as fast as possible. It is
particularly useful in treating secretory diarrhoea
• What is secretory diarrhoea? There is an
increase in the active secretion, or there is an inhibition of
absorption, meaning the stools get very liquid and voluminous.
There is little to no structural damage. The most common cause of this type of diarrhea is a cholera
toxin.
• Why do we add glucose to the oral rehydration sachet? Because it stimulates absorption of salts
such as NaCl (look at the graph).
Without the glucose, the salts would
not be as absorbed and so rehydration
would be hindered.
• Where, histologically, does chloride
secretion occur in the small intestine?
The crypts
• Where does absorption occur? The
villi
• Why does glucose promote sodium
absorption? Because they are co-
transported together via SGLT-1
(sodium glucose linked transporter 1).
• How does cholera cause secretory diarrhoea? A toxin causes cAMP activation à activates chloride
ions being pumped into the lumen of the gut via CFTR à sodium drawn out into the lumen à
massive amounts of water drawn out into the gut due to osmotic effect à watery diarrhoea à
dehydration
Lecture 2: GI Tract Physiology 1 (Introduction)
• Define the following terms
Term Definition
Digestion The process by which food and large molecules
are chemically degraded to produce smaller
molecules
Absorption The processes by which nutrient molecules are
absorbed by cells that line the GI tract and enter
the bloodstream
• In what way is the stomach a reservoir? It has 2 sphincters, one on each end of the stomach
(gastro-oesophageal and pyloric sphincters), and hence stores food whilst digesting it.
• When does food pass through the pyloric sphincter? When it becomes smaller than 2mm
Marc Huttman 2
,• Revise the histology of the GI tract (distinguish between different parts) and know the following
common architecture.
• What is the lamina propria? A layer of connective tissue in the mucosa, so it will have some small
blood vessels, nerves and muscle cells
• What does the muscularis mucosae do? It’s responsible for moving around the
mucosal folds when it contracts
• What are mucosal folds? They are NOT villi. They are the folds in the whole mucosa
of the GI tract. Imagine trees on a hilly landscape… the trees are the villi and the hills
on the landscape are the folds. Folds can be seen with the naked eye (see picture)
• Where do we find submucosal glands?
Submucosal gland Description
Oesophagus Oesophageal submucosal glands secrete mucus
for protection
Brunner’s glands in the duodenum • Secrete bicarbonate, HCO3-, to neutralise the
acid that’s coming from the stomach
• Briefly, how do bacteria in the colon help digestion? They break down indigestible materials and
create short chain fatty acids that are then absorbed
• What are the 2 nervous plexus systems found in the GI tract and where are they found?
Nervous plexus Where it’s found histologically Where it is located in GI tract
Submucosal plexus (Meissner’s In the submucosa, near to the Small and Large intestine
plexus) circular muscle of the
muscularis externa
Myenteric plexus (Auerbach’s Between the circular and All along the GI tract
plexus) longitudinal layers of the (oesophagus to rectum) – the
muscularis externa more important plexus
Marc Huttman 3
, • In what ways is the surface area of the GI tract amplified?
1. Folds of Kerckring/plicae circularis – large spiral or circular folds that on the lumen that I
mentioned before
2. Villi – finger like projections
3. Microvilli – even smaller finger light projections on the surface of the villus epithelium. They
can only be seen on an electron micrograph.
• Why are the microvilli kind of fuzzy on an electron micrograph? Because there is a glycocalyx
scaffolding that gives rise to an unstirred layer, which is important for the absorption of nutrients
• What do we mean by ‘unstirred layer’? A layer of substance that is not going to be subjected to the
churning up of the lumen of the intestine
• Are the apical and basal membrane of absorptive cells in the gut the same? No, they are very much
polarised. If they weren’t polarised, transport would not be able to occur
• Describe the following types of movement of molecules
Type of transport Description
Paracellular Between cells
Transcellular Through cells
• How are NaCl and water moved across the intestinal epithelium into the lumen?
1. Cl- ions are actively pumped across the basolateral membrane into the cell via NKCC1
2. Cl- ions then diffuse into the lumen across the apical membrane via CFTR
3. This puts a –ve charge in the lumen so Na+ follows the negative charge and flows into the lumen
paracellularly
4. A strong osmotic gradient is set up and so H2O flows into the lumen paracellularly, too.
Marc Huttman 4
