All lectures
GI funcion and food digestion
GI tract: anatomy and basic function
Know staying time of food in the parts
- Stomach: needs to contain food for some time to expose food to gastric acid for optimal
digestion
- Small intestine: composed of duodenum, jejunum and ileum. Important for food digestion
and absorption.
- Large intestine (colon): digestion by microbiota, metabolite absorption and water
absorption. In terms of number the small intestine is the most important in absorbance of
water. However, without the colon absorbing water we would lose enormous amounts of
water through faeces. Food stays here approximately 1 day, because of the quite long staying
time microbes get the change to attach and influence the microbiome.
,Reabsorption of water:
,Different organs involved in digestion
Salivary glands
Three glands working on liberating fluids and digestive enzymes. It contains alfa-amylase which is
breaking down amylose, antimicrobial proteins. Function of saliva:
- Lubricating food because digestive enzymes are water soluble
- Initial phase food digestion (carbs)
- Protection induced by mucus which covers the walls of GI system
Alfa-amylase = first digestive enzyme for carbohydrates. It hydrolyses starch to maltose and
maltosetriose. Food is not in the mouth for a long time, therefore only a small part of the starch is
digested in the mouth. However, the enzyme keeps functioning in its way to the stomach until the pH
drops below 4 which breaks down the enzyme amylase. The moment you take in food, which has a
buffer capacity, the acidity in the food bolus will not be immediately very acidic. In total alfa-amylase
is responsible for 30-40% of starches.
Stomach
, In the stomach there are different types of cells, which can secrete different stuff.
In the gastric lumen there is a pH of approximately 1.5.
The acid in the stomach has several roles:
- Denaturation of proteins in food (but also of bacteria).
- Protection against bacteria
- Activates pepsinogen into pepsin (digestive enzyme for proteins)
The acidity in the gastric lumen would damage the epithelial cells. So, on top of those cells there is a
layer of mucus, which is a barrier, it is a viscous layer which stops the acid from reaching the
epithelial cells. Moreover, there is also bicarbonate flowing from your blood stream into the
stomach, this can bind to protons in gastric acids. This leads to this reaction, a buffer system:
H+ & HCO3- → H2CO3 → CO2 & H20
Small intestine
To optimize contact/surface area between body and food, there are folds with vili. When zooming in
you can see the brush border with mucus which contains glycocalyx, these are proteins which form a
sticky layer. Any food passing by is delayed by the action of the glycolyx, which delays food transit
time which gives enzymes more time. Glucocalyx contains:
- Peptidases
- Disaccharidases
- Mucus
Duodenum
There is secretion of pancreatic juice and bile and fluids from intestinal wall itself. Also digestion and
absorption takes place. Secretions is controlled by sphincters.
Jejenum and ileum
Are only very important in digestion and absorption, but do there is no fluid secretion anymore.
Pancreas
GI funcion and food digestion
GI tract: anatomy and basic function
Know staying time of food in the parts
- Stomach: needs to contain food for some time to expose food to gastric acid for optimal
digestion
- Small intestine: composed of duodenum, jejunum and ileum. Important for food digestion
and absorption.
- Large intestine (colon): digestion by microbiota, metabolite absorption and water
absorption. In terms of number the small intestine is the most important in absorbance of
water. However, without the colon absorbing water we would lose enormous amounts of
water through faeces. Food stays here approximately 1 day, because of the quite long staying
time microbes get the change to attach and influence the microbiome.
,Reabsorption of water:
,Different organs involved in digestion
Salivary glands
Three glands working on liberating fluids and digestive enzymes. It contains alfa-amylase which is
breaking down amylose, antimicrobial proteins. Function of saliva:
- Lubricating food because digestive enzymes are water soluble
- Initial phase food digestion (carbs)
- Protection induced by mucus which covers the walls of GI system
Alfa-amylase = first digestive enzyme for carbohydrates. It hydrolyses starch to maltose and
maltosetriose. Food is not in the mouth for a long time, therefore only a small part of the starch is
digested in the mouth. However, the enzyme keeps functioning in its way to the stomach until the pH
drops below 4 which breaks down the enzyme amylase. The moment you take in food, which has a
buffer capacity, the acidity in the food bolus will not be immediately very acidic. In total alfa-amylase
is responsible for 30-40% of starches.
Stomach
, In the stomach there are different types of cells, which can secrete different stuff.
In the gastric lumen there is a pH of approximately 1.5.
The acid in the stomach has several roles:
- Denaturation of proteins in food (but also of bacteria).
- Protection against bacteria
- Activates pepsinogen into pepsin (digestive enzyme for proteins)
The acidity in the gastric lumen would damage the epithelial cells. So, on top of those cells there is a
layer of mucus, which is a barrier, it is a viscous layer which stops the acid from reaching the
epithelial cells. Moreover, there is also bicarbonate flowing from your blood stream into the
stomach, this can bind to protons in gastric acids. This leads to this reaction, a buffer system:
H+ & HCO3- → H2CO3 → CO2 & H20
Small intestine
To optimize contact/surface area between body and food, there are folds with vili. When zooming in
you can see the brush border with mucus which contains glycocalyx, these are proteins which form a
sticky layer. Any food passing by is delayed by the action of the glycolyx, which delays food transit
time which gives enzymes more time. Glucocalyx contains:
- Peptidases
- Disaccharidases
- Mucus
Duodenum
There is secretion of pancreatic juice and bile and fluids from intestinal wall itself. Also digestion and
absorption takes place. Secretions is controlled by sphincters.
Jejenum and ileum
Are only very important in digestion and absorption, but do there is no fluid secretion anymore.
Pancreas
