CASE 1
zondag 3 maart 2024 20:53
1. Anatomy GI tract
Overview
Oral cavity: Saliva glands (Parotid, sublingual and submandibular glands), Teeth and
Tongue
Oropharynx
Oesophagus
Stomach: Fundus, Body and pylorus
Small intestine: Duodenum (where Pancreas, Gall bladder enters), Jejunum and Ileum
Large intestine: Cecum, Ascending colon, Transverse colon, Descending colon and
Sigmoid colon
Rectum, anal channel anus
Histology of all organs in the GI tract
- Mucosa: most inner layer that lines the lumen. It secretes mucous, digestive
enzymes and hormones and to absorb end products of digestion. Consists of:
○ Epithelial cells
○ Lamina propria (blood vessels, lymph vessels (lacteals))
○ Muscularis mucosa
- Submucosa: consists of connective tissue and contains lots of blood and lymph
vessels. Also the nerve: submucosal plexus ( can be found here. The submucosal
layer gives it the elastic properties.
- Muscularis externa: is a layer of smooth muscle which is responsible for
segmentation and motility. It consists of:
○ Inner circular layer
○ Outer longitudinal layer, which also contains the myenteric nerve plexus
- Serosa: provides structure and consists of mesothelium (epithelial cells). When it
does not contain mesothelium but connective tissue it is called adventitia.
STOMACH
Function: chemical breakdown of food and the mixing with acid and enzymes
Like all organs, it contains simple columnar organs which contain many cells:
- G cells: produce gastrin which stimulates the parietal cells to secrete HCl and the
chief cells to secrete pepsinogen
- Parietal cells: release hydrochloric acid (H+ Cl-) which activates intrinsic factor (IF)
HCl makes the stomach acidic, this is needed to:
○ Kill bacteria
○ Denature proteins
○ Stimulates pepsinogen to pepsin
- Chief cells: pepsinogen is activated into pepsin in the presence of HCl. Pepsin is
responsible for the breakdown of proteins.
- Enteroendocrine cells: release regulatory hormones, serotonin and histamine that
in the presence of HCl and allow muscle contraction
Special: it contains an extra muscle layer, the inner most layer is the oblique muscle
which allows it to mix the chyme.
SMALL INTESTINE
Function: break down food, absorb nutrients needed for the body, and get rid of
unnecessary components. Contain:
- Goblet cells: secrete mucous
- Enteroendocrine cells: sensors of luminal nutrients and secrete a variety of peptide
hormones that regulate digestion
- Paneth cells: produce antimicrobial peptides and proteins and other components
that are important in host defence and immunity
Secretin is released and stimulates the release of bicarbonate (HCO3-) to counter the
acidic environment. Cholecystokinin (CCK) is released to allow zymogens to be released
to break down enzymes.
Small intestines are adapted to their function as they contain:
- Circular folds in the (sub)mucosa to slow down the movement and allow more
absorption
- Villi increase cell surface and they contain absorptive cells (enterocytes) and
lacteals (lymphatic bed) which are responsible for absorption
- Microvilli which contain brush border enzymes for the complete digestion of
carbohydrates and proteins
TENTAMEN PREP 4 Pagina 1
, carbohydrates and proteins
Special: the duodenum contains adventitia and the jejunum and ileum have serosa.
GALLBLADDER, LIVER AND PANCREAS
PANCREAS
Bicarbonate (HCO3-) neutralizes gastric acid
Peptidase: breaks down amino acids
Pancreatic amylase: partially break down starch
Pancreatic lipase: partially breaks down fats
Proteolytic enzymes:
Trypsinogen (active form = trypsin) in duodenum, breaks down proteins
Chymotrypsin (active from = chymotrypsin) also aids in digestion of proteins
LIVER AND GALL BLADDER
Bile forms in the liver and is stored in the gall bladder. Enters via the common hepatic
duct. Bile is needed for fat absorption and is made of:
- Pigments: for colour
- Bile salts for emulsification
LARGE INTESTINE
Function: absorbing water and electrolytes, producing and absorbing vitamins, and
forming and propelling faeces toward the rectum for elimination. Contains:
- Goblet cells: secrete mucous
- Enteroendocrine cells: sensors of luminal nutrients and secrete a variety of peptide
hormones that regulate digestion
Special: it contains 10 million bacteria which has special functions:
- Colonizing the colon
- Synthesizing vitamin B and K
- Metabolizing molecules
- Fermenting indigestible carbohydrates, release acid and gas
2. Digestion of carbohydrates
Carbohydrates are consumed as starch or disaccharides and starts at the oral cavity with
salivary amylase. Then it travels down the oesophagus to the stomach. In the stomach
salivary amylase loses its function due to low ph. Then in the small intestine pancreatic
juice contains pancreatic amylase to further breakdown the carbohydrates to
oligosaccharides and disaccharides, like:
- Maltose: 2x glucose (enzyme: maltase)
- Sucrose: 1x glucose and 1x fructose (enzyme: sucrase)
- Lactose: 1x glucose and 1x galactose (enzyme: lactase)
But only monosaccharides can be absorbed so the disaccharides are broken down into
monosaccharides: glucose, fructose and galactose.
- Glucose and galactose: absorbed via cotransport with sodium ions (Na+) in the
SGLT symporter into the lumen. Then they enter the blood via GLUT2 transporter.
(both active)
- Fructose: is sodium independent and enters the cell via the GLUT5 transporter by
diffusion. Then it enters the bloodstream also via the GLUT2 transporter.
Glucose can have various destinations, but galactose and fructose always travel to the
liver via the hepatic portal vein.
TENTAMEN PREP 4 Pagina 2
,3. Digestion of proteins
The digestion starts in the stomach. The protein is folded and this stimulates G cells to
secrete gastrin. Gastrin will stimulate the parietal cells to secrete HCl And the chief cells
to secrete pepsinogen. These are endopeptidases (protease) meaning they attack the
peptide bonds to break down larger polypeptide chains into smaller ones, but still quite
long. HCl creates an acidic environment pH 1-2 that:
1) Kills bacteria
2) Denatures proteins (unfolds)
3) Stimulates the transition of pepsinogen to pepsin
Now the smaller chains enter the small intestine. Here the release of secretin and
cholecystokinin CCK is stimulated and HCO3- (bicarbonate) is secreted to counter the
effects of HCl. The pH is now 5-6. CCK allows the release of zymogens (enzymes) that are
exopeptidases that release single amino acids from the peptide chain (most important
are carboxypeptidases (remove COO-) and aminopeptidases (remove NH2)). Elastase is
responsible for the chemical breakdown if elastin and trypsin and chymotrypsin further
break down the polypeptide. This all causes the breakdown to amino acids and some di-
or tripeptides. Which can now be absorbed.
There are 3 ways proteins can enter which are mainly secondary acive meaning they are
not directly dependent on metabolic activity, but their co-transport molecules are.
1. Co-transport in PEPT1 with H+ for di- and tri-peptide
2. Co-transport with Na+ for single amino acids
3. Transcytosis for longer peptides, they are transported intact in a vesicle.
The transport also depends on chemical composition: hydrophilic, hydrophobic (cannot
enter the blood easily) have to be bound to albumin which is produced in the liver.
4. Digestion of lipids
In the oral cavity, lingual lipase is added which starts the emulsification process of the
TENTAMEN PREP 4 Pagina 3
, In the oral cavity, lingual lipase is added which starts the emulsification process of the
fats with water. Then it moves down to the stomach where gastric lipase is added, which
targets the breakdown of triglycerides. Then in the small intestine bile is secreted and the
main digestion can occur. Fats are hydrophobic and lipophilic. When bile salts are added,
which are hydrophobic on one side and hydrophilic on the other it starts to form a coat
around it. Fat + bile salts = micelle. The pancreatic lipase starts to break down the
triglycerides into monoglycerides and fatty acids, without sticking to other fats due to the
coat surrounding it. The micelle now contains fatty acids and monoglycerides and can be
absorbed.
In the micelles are: bile salts, monoglycerides (MAG), fatty acids, phospholipids and
cholesterol (due to low pH).
Absorption:
Monoglycerides: are lipophilic and can enter via simple/facilitated diffusion via the CD43
or fatty acid transport protein (FATP). They move out of the micelle and diffuse across
the enterocyte.
Fatty acids and cholesterol: need a transporter to diffuse through the membrane
Once inside the MAG move to the smooth ER where they are recombined into
triglycerides. These are combined with cholesterol (by APO B48) to form chylomicrons
and are packed in secretory vesicles at the Golgi apparatus and leave the cell via
exocytosis.
Chylomicrons are large and cannot simply diffuse into the bloodstream, this is why they
pass to the lacteals (lymph vessels of the villi) where they enter the blood stream via the
thoracic duct.
OR
Monoglycerides are broken down into fatty acids, which can enter the blood stream and
are transported by albumin
Phospholipids are broken down and enter the chylomicrons (acyl group) and the choline
group is transported to the liver.
5. Faecal examination
Mr A. has health problems for a while now: he feels tired and is losing weight. During an
extensive clinical check-up, it has been found that the digestion of carbohydrates, protein
and fat is disturbed. Faecal examinations indicated incomplete digestion of all three
macronutrients. The consulted radiologist finds a tumour, located near the ductus
pancreaticus.
The pancreatic duct drains all the pancreatic enzymes into the intestines. When due to
the tumour the enzymes cannot access the intestines the macronutrients cannot be
broken down, or absorbed. Mr. A receives no nutrients and this is why he is tired and
loses weight.
Mr P. has comparable problems, but his faeces is pale and contains incomplete digested
fat, but no intact proteins and carbohydrates. He has a tumour nearby the pancreas.
The common bile duct passes through the pancreas before it empties into the first part of
the small intestine (duodenum). When the tumour is present near the pancreas (probably
the common bile duct) the bile cannot enter into the small intestines to break down fat.
TENTAMEN PREP 4 Pagina 4
zondag 3 maart 2024 20:53
1. Anatomy GI tract
Overview
Oral cavity: Saliva glands (Parotid, sublingual and submandibular glands), Teeth and
Tongue
Oropharynx
Oesophagus
Stomach: Fundus, Body and pylorus
Small intestine: Duodenum (where Pancreas, Gall bladder enters), Jejunum and Ileum
Large intestine: Cecum, Ascending colon, Transverse colon, Descending colon and
Sigmoid colon
Rectum, anal channel anus
Histology of all organs in the GI tract
- Mucosa: most inner layer that lines the lumen. It secretes mucous, digestive
enzymes and hormones and to absorb end products of digestion. Consists of:
○ Epithelial cells
○ Lamina propria (blood vessels, lymph vessels (lacteals))
○ Muscularis mucosa
- Submucosa: consists of connective tissue and contains lots of blood and lymph
vessels. Also the nerve: submucosal plexus ( can be found here. The submucosal
layer gives it the elastic properties.
- Muscularis externa: is a layer of smooth muscle which is responsible for
segmentation and motility. It consists of:
○ Inner circular layer
○ Outer longitudinal layer, which also contains the myenteric nerve plexus
- Serosa: provides structure and consists of mesothelium (epithelial cells). When it
does not contain mesothelium but connective tissue it is called adventitia.
STOMACH
Function: chemical breakdown of food and the mixing with acid and enzymes
Like all organs, it contains simple columnar organs which contain many cells:
- G cells: produce gastrin which stimulates the parietal cells to secrete HCl and the
chief cells to secrete pepsinogen
- Parietal cells: release hydrochloric acid (H+ Cl-) which activates intrinsic factor (IF)
HCl makes the stomach acidic, this is needed to:
○ Kill bacteria
○ Denature proteins
○ Stimulates pepsinogen to pepsin
- Chief cells: pepsinogen is activated into pepsin in the presence of HCl. Pepsin is
responsible for the breakdown of proteins.
- Enteroendocrine cells: release regulatory hormones, serotonin and histamine that
in the presence of HCl and allow muscle contraction
Special: it contains an extra muscle layer, the inner most layer is the oblique muscle
which allows it to mix the chyme.
SMALL INTESTINE
Function: break down food, absorb nutrients needed for the body, and get rid of
unnecessary components. Contain:
- Goblet cells: secrete mucous
- Enteroendocrine cells: sensors of luminal nutrients and secrete a variety of peptide
hormones that regulate digestion
- Paneth cells: produce antimicrobial peptides and proteins and other components
that are important in host defence and immunity
Secretin is released and stimulates the release of bicarbonate (HCO3-) to counter the
acidic environment. Cholecystokinin (CCK) is released to allow zymogens to be released
to break down enzymes.
Small intestines are adapted to their function as they contain:
- Circular folds in the (sub)mucosa to slow down the movement and allow more
absorption
- Villi increase cell surface and they contain absorptive cells (enterocytes) and
lacteals (lymphatic bed) which are responsible for absorption
- Microvilli which contain brush border enzymes for the complete digestion of
carbohydrates and proteins
TENTAMEN PREP 4 Pagina 1
, carbohydrates and proteins
Special: the duodenum contains adventitia and the jejunum and ileum have serosa.
GALLBLADDER, LIVER AND PANCREAS
PANCREAS
Bicarbonate (HCO3-) neutralizes gastric acid
Peptidase: breaks down amino acids
Pancreatic amylase: partially break down starch
Pancreatic lipase: partially breaks down fats
Proteolytic enzymes:
Trypsinogen (active form = trypsin) in duodenum, breaks down proteins
Chymotrypsin (active from = chymotrypsin) also aids in digestion of proteins
LIVER AND GALL BLADDER
Bile forms in the liver and is stored in the gall bladder. Enters via the common hepatic
duct. Bile is needed for fat absorption and is made of:
- Pigments: for colour
- Bile salts for emulsification
LARGE INTESTINE
Function: absorbing water and electrolytes, producing and absorbing vitamins, and
forming and propelling faeces toward the rectum for elimination. Contains:
- Goblet cells: secrete mucous
- Enteroendocrine cells: sensors of luminal nutrients and secrete a variety of peptide
hormones that regulate digestion
Special: it contains 10 million bacteria which has special functions:
- Colonizing the colon
- Synthesizing vitamin B and K
- Metabolizing molecules
- Fermenting indigestible carbohydrates, release acid and gas
2. Digestion of carbohydrates
Carbohydrates are consumed as starch or disaccharides and starts at the oral cavity with
salivary amylase. Then it travels down the oesophagus to the stomach. In the stomach
salivary amylase loses its function due to low ph. Then in the small intestine pancreatic
juice contains pancreatic amylase to further breakdown the carbohydrates to
oligosaccharides and disaccharides, like:
- Maltose: 2x glucose (enzyme: maltase)
- Sucrose: 1x glucose and 1x fructose (enzyme: sucrase)
- Lactose: 1x glucose and 1x galactose (enzyme: lactase)
But only monosaccharides can be absorbed so the disaccharides are broken down into
monosaccharides: glucose, fructose and galactose.
- Glucose and galactose: absorbed via cotransport with sodium ions (Na+) in the
SGLT symporter into the lumen. Then they enter the blood via GLUT2 transporter.
(both active)
- Fructose: is sodium independent and enters the cell via the GLUT5 transporter by
diffusion. Then it enters the bloodstream also via the GLUT2 transporter.
Glucose can have various destinations, but galactose and fructose always travel to the
liver via the hepatic portal vein.
TENTAMEN PREP 4 Pagina 2
,3. Digestion of proteins
The digestion starts in the stomach. The protein is folded and this stimulates G cells to
secrete gastrin. Gastrin will stimulate the parietal cells to secrete HCl And the chief cells
to secrete pepsinogen. These are endopeptidases (protease) meaning they attack the
peptide bonds to break down larger polypeptide chains into smaller ones, but still quite
long. HCl creates an acidic environment pH 1-2 that:
1) Kills bacteria
2) Denatures proteins (unfolds)
3) Stimulates the transition of pepsinogen to pepsin
Now the smaller chains enter the small intestine. Here the release of secretin and
cholecystokinin CCK is stimulated and HCO3- (bicarbonate) is secreted to counter the
effects of HCl. The pH is now 5-6. CCK allows the release of zymogens (enzymes) that are
exopeptidases that release single amino acids from the peptide chain (most important
are carboxypeptidases (remove COO-) and aminopeptidases (remove NH2)). Elastase is
responsible for the chemical breakdown if elastin and trypsin and chymotrypsin further
break down the polypeptide. This all causes the breakdown to amino acids and some di-
or tripeptides. Which can now be absorbed.
There are 3 ways proteins can enter which are mainly secondary acive meaning they are
not directly dependent on metabolic activity, but their co-transport molecules are.
1. Co-transport in PEPT1 with H+ for di- and tri-peptide
2. Co-transport with Na+ for single amino acids
3. Transcytosis for longer peptides, they are transported intact in a vesicle.
The transport also depends on chemical composition: hydrophilic, hydrophobic (cannot
enter the blood easily) have to be bound to albumin which is produced in the liver.
4. Digestion of lipids
In the oral cavity, lingual lipase is added which starts the emulsification process of the
TENTAMEN PREP 4 Pagina 3
, In the oral cavity, lingual lipase is added which starts the emulsification process of the
fats with water. Then it moves down to the stomach where gastric lipase is added, which
targets the breakdown of triglycerides. Then in the small intestine bile is secreted and the
main digestion can occur. Fats are hydrophobic and lipophilic. When bile salts are added,
which are hydrophobic on one side and hydrophilic on the other it starts to form a coat
around it. Fat + bile salts = micelle. The pancreatic lipase starts to break down the
triglycerides into monoglycerides and fatty acids, without sticking to other fats due to the
coat surrounding it. The micelle now contains fatty acids and monoglycerides and can be
absorbed.
In the micelles are: bile salts, monoglycerides (MAG), fatty acids, phospholipids and
cholesterol (due to low pH).
Absorption:
Monoglycerides: are lipophilic and can enter via simple/facilitated diffusion via the CD43
or fatty acid transport protein (FATP). They move out of the micelle and diffuse across
the enterocyte.
Fatty acids and cholesterol: need a transporter to diffuse through the membrane
Once inside the MAG move to the smooth ER where they are recombined into
triglycerides. These are combined with cholesterol (by APO B48) to form chylomicrons
and are packed in secretory vesicles at the Golgi apparatus and leave the cell via
exocytosis.
Chylomicrons are large and cannot simply diffuse into the bloodstream, this is why they
pass to the lacteals (lymph vessels of the villi) where they enter the blood stream via the
thoracic duct.
OR
Monoglycerides are broken down into fatty acids, which can enter the blood stream and
are transported by albumin
Phospholipids are broken down and enter the chylomicrons (acyl group) and the choline
group is transported to the liver.
5. Faecal examination
Mr A. has health problems for a while now: he feels tired and is losing weight. During an
extensive clinical check-up, it has been found that the digestion of carbohydrates, protein
and fat is disturbed. Faecal examinations indicated incomplete digestion of all three
macronutrients. The consulted radiologist finds a tumour, located near the ductus
pancreaticus.
The pancreatic duct drains all the pancreatic enzymes into the intestines. When due to
the tumour the enzymes cannot access the intestines the macronutrients cannot be
broken down, or absorbed. Mr. A receives no nutrients and this is why he is tired and
loses weight.
Mr P. has comparable problems, but his faeces is pale and contains incomplete digested
fat, but no intact proteins and carbohydrates. He has a tumour nearby the pancreas.
The common bile duct passes through the pancreas before it empties into the first part of
the small intestine (duodenum). When the tumour is present near the pancreas (probably
the common bile duct) the bile cannot enter into the small intestines to break down fat.
TENTAMEN PREP 4 Pagina 4
