DIGESTIVE SYSTEM PHYSIOLOGY 4:
DIGESTION AND ABSORPTION PHYSIOLOGY A: Finals Lec 5
DR. FELIPE BARBON | NOVEMBER 22, 2021
OBJECTIVES • Portal circulation is part of the splanchnic
1. Discuss how digestion and absorption occurs in circulation
each region of the GIT • Entry of absorbed substances from the GIT
2. How do bile salts aid in the digestion and including drainage from the spleen and pancreas
absorption of lipids?
3. Explain why most digestion and absorption
happens in the small intestine
4. Discuss the importance or the colonic bacterial
flora in the metabolism and protection of the body.
5. Correlate common clinical conditions affecting
physiology of the digestive system
References:
[1] Dr. Barbon’s Lecture 2021
DIGESTION AND ABSORPTION
DIGESTION
• Breakdown of nutrients into absorbable units
o Mechanical digestion – mastication (chewing) • Represents 25-30% of the CO (cardiac output)
breakdown the food particles into smaller units • Large reservoir – normally holds 30% of the total
facilitating the effects of digestive enzymes blood volume à This is why when the liver is
- also observed in the stomach (propulsion, damaged, you can die of excessive blood loss
retropulsion, antral pump, peristalsis) and
small intestine (segmentation) MOUTH
o Chemical digestion – Hydrolysis is the major
chemical reaction observed Is there digestion in the mouth?
YES, salivary amylase initially digests starch
ABSORPTION Mechanical digestion – mastication
• Transport of most of digestive products from the Chemical digestion – salivary amylase
GIT to the blood and some to the lymphatics (long
chain fatty acids) • There is presence of lingual lipase in the mouth but
is inactive because it needs an acidic environment
SPLANCHNIC CIRCULATION
Is there absorption in the mouth?
YES. That is why we have sublingual administration of
drugs. The tablet is placed below the tongue.
Agents normally absorbed in the oral mucosa:
• Glucose gel, some vitamins, drugs like
nitroglycerin (nitrates, coronary vasodilators),
ASA, verapamil, aspirin
• When absorbed à facial vein à subclavian vein à
superior vena cava
IMPORTANCE OF SALIVA
1. Digestion – amylase
o Salivary amylase (ptyalin) digests 20-40% of
• The different agents absorbed from the stomach, starch (converted to a disaccharide à
small intestine and colon will not go straight to the maltose)
vena cava. It will enter first the vena cava. o Digestion of starch is completed in the small
• Absorbed substances are initially screened by the intestine
liver (metabolic function). This is why the liver is 2. Enhancing the taste of food
affected during overdose and excessive intake of 3. Lubrication
toxic substances. 4. Aids in speech
• Substances absorbed from stomach, small 5. Neutralization of gastric acid
intestine, colon even pancreas and spleen à portal 6. Secretion of Transcobalamin 1, protect Vit. B12
vein à liver à hepatic veins à inferior vena cava (acid)
7. Protection – IgA, lysozyme, lactoferrin
Trans Makers: 1A-MARQUEZ|RARIO|BORDEOS| PENTINO | RAMOS Page 1 of 11
, DIGESTIVE PHYSIOLOGY 1 & 2: FUNCTIONAL ANATOMY AND MOTOR ACTIVITIES
8. Secretes Growth Factors When drinking alcohol, the “pulutan” is usually fatty foods
because fats can markedly decrease the rate of gastric
ESOPHAGUS emptying. So, alcohol stays longer in the stomach and not
• Only a passageway go directly to the small intestine which is the major site of
• No digestion and no absorption in the esophagus digestion and absorption. This prevents rapid alcohol
• If ever there is digestion happening, that is still due intoxication. This is also why they do not take
to the activity of the salivary amylase. It is only very carbohydrates while drinking alcohol.
minimal due to the rapid transit time of food.
SMALL INTESTINES
STOMACH ● major area for digestion absorption
• In the initial entry of food, the salivary amylase is Parts of small intestine :
still active because the food is not yet mixed with ● Duodenum - the shortest ( a foot in length or less than
gastric acid. Salivary amylase is active at a near one foot)
neutral pH (pH 6) ○ Ability to promote absorption is high for its size
• Once the ingested food is mixed with acid, the ● Jejunum - shorter than ileum
activity of the salivary amylase stops. Other ○ 40% of small intestine
enzymes promoting digestion in the stomach will ○ 6-7m in length
be active. ● Ileum - 60% of small intestine
What happens to food inside the stomach? ● Final products of digestion are formed in greatest
• Mechanical digestion – essential to mix contents quantities
with gastric acid and for regulation of gastric ○ The one receiving the enzymes coming from the
emptying pancreas and received by the duodenum.
- Make the food particles smaller in size about ○ Pancreatic enzymes will continue the digestion
1 mm2 to facilitate activity of enzymes initiated by salivary amylase and will be received
o Peristalsis (propulsion) in the duodenal area.
o Muscular contractions ○ The digestion of proteins initiated by pepsin in
o Reverse peristalsis (retropulsion) the stomach and will continue to the pancreatic
• Chemical digestion fortulitic enzyme and it will release in active form
o In the presence of acid (hydrochloric acid), but will be activated by enteropeptidase (in some
pepsinogen is converted to pepsin, which is books it is called enterokinase) in the small
responsible for the initial digestion of proteins intestine.
o Lingual lipase (from the salivary glands) and ○ The digestion or activation of lipase is seen in
gastric lipase (from the peptic cells or chief the stomach, initially absorption of fats also
cells) could digest about 30% of ingested fats happens in the stomach. Eventually it is
(pH <5) continued by the pancreatic lipases by the help
§ Digests only amphoteric fats (digested of colipase but the effect is delayed because it
even without bile salts) needs to wait for the emptying of bile salts that
o Pepsin could digest about 20% of ingested come from liver and gallbladder to emulsify the
proteins fats and it will continue the digestion.
§ Activity is optimum at pH <3 ○ Small intestinal enzyme that is responsible for
§ Inactivated reversibly at pH = 6.5 completion of digestion in the small intestine
§ Inactivated irreversibly at pH = 8 (final product).
○ Major enzymes needed to continue the digestion
• When there is food in the stomach,
to be received in the small intestine and the
the parietal cells are activated to
enzymes needed for completion of the digestion
release acid to keep the gastric pH
are coming from the small intestinal cells
acidic
specifically in the brush borders.
Is there absorption in the stomach? ● Mechanical and Chemical digestion
YES. But only very small amount is absorbed. ○ Mechanical - segmenting contraction or mixing
Agents normally absorbed in the stomach: movements allowing always fresh portions of
• Water intestinal contents to come into contact with the
• Ethyl alcohol (about 10%) brush borders. In the brush borders it has
• Copper enzymes responsible for chemical digestion.
• Iodide ● Contents are moved slowly allowing sufficient time
• Fluoride for digestion and absorption
• Molybdenum ○ Normally we don’t observe peristalsis in the
• Aspirin small intestine, the common motor activity in the
small intestine is segmentation.
○ If there is peristalsis in the small intestine the
person is suffering from diarrhea, faster of flow ,
rapid of transient time or short transient time.
Trans Makers: 1A-MARQUEZ|RARIO|BORDEOS| PENTINO | RAMOS Page 2 of 11
DIGESTION AND ABSORPTION PHYSIOLOGY A: Finals Lec 5
DR. FELIPE BARBON | NOVEMBER 22, 2021
OBJECTIVES • Portal circulation is part of the splanchnic
1. Discuss how digestion and absorption occurs in circulation
each region of the GIT • Entry of absorbed substances from the GIT
2. How do bile salts aid in the digestion and including drainage from the spleen and pancreas
absorption of lipids?
3. Explain why most digestion and absorption
happens in the small intestine
4. Discuss the importance or the colonic bacterial
flora in the metabolism and protection of the body.
5. Correlate common clinical conditions affecting
physiology of the digestive system
References:
[1] Dr. Barbon’s Lecture 2021
DIGESTION AND ABSORPTION
DIGESTION
• Breakdown of nutrients into absorbable units
o Mechanical digestion – mastication (chewing) • Represents 25-30% of the CO (cardiac output)
breakdown the food particles into smaller units • Large reservoir – normally holds 30% of the total
facilitating the effects of digestive enzymes blood volume à This is why when the liver is
- also observed in the stomach (propulsion, damaged, you can die of excessive blood loss
retropulsion, antral pump, peristalsis) and
small intestine (segmentation) MOUTH
o Chemical digestion – Hydrolysis is the major
chemical reaction observed Is there digestion in the mouth?
YES, salivary amylase initially digests starch
ABSORPTION Mechanical digestion – mastication
• Transport of most of digestive products from the Chemical digestion – salivary amylase
GIT to the blood and some to the lymphatics (long
chain fatty acids) • There is presence of lingual lipase in the mouth but
is inactive because it needs an acidic environment
SPLANCHNIC CIRCULATION
Is there absorption in the mouth?
YES. That is why we have sublingual administration of
drugs. The tablet is placed below the tongue.
Agents normally absorbed in the oral mucosa:
• Glucose gel, some vitamins, drugs like
nitroglycerin (nitrates, coronary vasodilators),
ASA, verapamil, aspirin
• When absorbed à facial vein à subclavian vein à
superior vena cava
IMPORTANCE OF SALIVA
1. Digestion – amylase
o Salivary amylase (ptyalin) digests 20-40% of
• The different agents absorbed from the stomach, starch (converted to a disaccharide à
small intestine and colon will not go straight to the maltose)
vena cava. It will enter first the vena cava. o Digestion of starch is completed in the small
• Absorbed substances are initially screened by the intestine
liver (metabolic function). This is why the liver is 2. Enhancing the taste of food
affected during overdose and excessive intake of 3. Lubrication
toxic substances. 4. Aids in speech
• Substances absorbed from stomach, small 5. Neutralization of gastric acid
intestine, colon even pancreas and spleen à portal 6. Secretion of Transcobalamin 1, protect Vit. B12
vein à liver à hepatic veins à inferior vena cava (acid)
7. Protection – IgA, lysozyme, lactoferrin
Trans Makers: 1A-MARQUEZ|RARIO|BORDEOS| PENTINO | RAMOS Page 1 of 11
, DIGESTIVE PHYSIOLOGY 1 & 2: FUNCTIONAL ANATOMY AND MOTOR ACTIVITIES
8. Secretes Growth Factors When drinking alcohol, the “pulutan” is usually fatty foods
because fats can markedly decrease the rate of gastric
ESOPHAGUS emptying. So, alcohol stays longer in the stomach and not
• Only a passageway go directly to the small intestine which is the major site of
• No digestion and no absorption in the esophagus digestion and absorption. This prevents rapid alcohol
• If ever there is digestion happening, that is still due intoxication. This is also why they do not take
to the activity of the salivary amylase. It is only very carbohydrates while drinking alcohol.
minimal due to the rapid transit time of food.
SMALL INTESTINES
STOMACH ● major area for digestion absorption
• In the initial entry of food, the salivary amylase is Parts of small intestine :
still active because the food is not yet mixed with ● Duodenum - the shortest ( a foot in length or less than
gastric acid. Salivary amylase is active at a near one foot)
neutral pH (pH 6) ○ Ability to promote absorption is high for its size
• Once the ingested food is mixed with acid, the ● Jejunum - shorter than ileum
activity of the salivary amylase stops. Other ○ 40% of small intestine
enzymes promoting digestion in the stomach will ○ 6-7m in length
be active. ● Ileum - 60% of small intestine
What happens to food inside the stomach? ● Final products of digestion are formed in greatest
• Mechanical digestion – essential to mix contents quantities
with gastric acid and for regulation of gastric ○ The one receiving the enzymes coming from the
emptying pancreas and received by the duodenum.
- Make the food particles smaller in size about ○ Pancreatic enzymes will continue the digestion
1 mm2 to facilitate activity of enzymes initiated by salivary amylase and will be received
o Peristalsis (propulsion) in the duodenal area.
o Muscular contractions ○ The digestion of proteins initiated by pepsin in
o Reverse peristalsis (retropulsion) the stomach and will continue to the pancreatic
• Chemical digestion fortulitic enzyme and it will release in active form
o In the presence of acid (hydrochloric acid), but will be activated by enteropeptidase (in some
pepsinogen is converted to pepsin, which is books it is called enterokinase) in the small
responsible for the initial digestion of proteins intestine.
o Lingual lipase (from the salivary glands) and ○ The digestion or activation of lipase is seen in
gastric lipase (from the peptic cells or chief the stomach, initially absorption of fats also
cells) could digest about 30% of ingested fats happens in the stomach. Eventually it is
(pH <5) continued by the pancreatic lipases by the help
§ Digests only amphoteric fats (digested of colipase but the effect is delayed because it
even without bile salts) needs to wait for the emptying of bile salts that
o Pepsin could digest about 20% of ingested come from liver and gallbladder to emulsify the
proteins fats and it will continue the digestion.
§ Activity is optimum at pH <3 ○ Small intestinal enzyme that is responsible for
§ Inactivated reversibly at pH = 6.5 completion of digestion in the small intestine
§ Inactivated irreversibly at pH = 8 (final product).
○ Major enzymes needed to continue the digestion
• When there is food in the stomach,
to be received in the small intestine and the
the parietal cells are activated to
enzymes needed for completion of the digestion
release acid to keep the gastric pH
are coming from the small intestinal cells
acidic
specifically in the brush borders.
Is there absorption in the stomach? ● Mechanical and Chemical digestion
YES. But only very small amount is absorbed. ○ Mechanical - segmenting contraction or mixing
Agents normally absorbed in the stomach: movements allowing always fresh portions of
• Water intestinal contents to come into contact with the
• Ethyl alcohol (about 10%) brush borders. In the brush borders it has
• Copper enzymes responsible for chemical digestion.
• Iodide ● Contents are moved slowly allowing sufficient time
• Fluoride for digestion and absorption
• Molybdenum ○ Normally we don’t observe peristalsis in the
• Aspirin small intestine, the common motor activity in the
small intestine is segmentation.
○ If there is peristalsis in the small intestine the
person is suffering from diarrhea, faster of flow ,
rapid of transient time or short transient time.
Trans Makers: 1A-MARQUEZ|RARIO|BORDEOS| PENTINO | RAMOS Page 2 of 11
