MEDICO EXPRESS BLOCK 4 BOOK
MEDICO EXPRESS
2ND YEAR MBBS
BIOCHEM GIT BLOCK 4 BOOK
Give the composition and importance of saliva and Biochemistry Biochemistry of GIT
GIT- related clinical disorder (xerostomia) Give the /GIT secretions &
B- composition and importance of gastric juice with special digestion and
001 reference to mechanism of HCl secretion and related absorption of dietary
clinical disorders (achlorhydria, gastric ulcer Give the carbohydrates
composition and importance of pancreatic juice, bile
and succus entericus and related clinical disorders
(pancreatitis, cystic fibrosis, cholelithiasis). Describe
digestion and absorption of dietary carbohydrates along
with inherited and acquired disorders (lactose
intolerance, sucrase-isomaltase deficiency).
Composition of Saliva
pH: 6.4 to 6.9
Electrolytes: Sodium, potassium, bicarbonate, phosphate, calcium and magnesium.
Antibodies: IgA and IgG
Enzymes: amylase and lipase
Other Components: water, mucins, glycoproteins.
Importance of Saliva:
Lubrication
Stimulation of taste buds
Oral hygienic
Regulation of water intake
Digestion
Xerostomia: It is a condition in which enough saliva is not produced resulting in dry mouth.
Normal salivary flow decreases with age in both men and women, although many patients with
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xerostomia are postmenopausal who also complaint of burning tongue or mouth. Factors
causing xerostomia can be both, physiological and pathological.
Some common causes are:
1. Chronic anxiety
2. Dehydration
3. Sjogren Syndrome
Composition of gastric juice:
Gastric juice is composed of HCl, lipase and pepsin, Water, Inorganic constituents ,
Organic matter
Importance of gastric juice:
Gastric juice kills the microorganisms ingested.
Gastric juice initiates the digestion of proteins.
Gastric juice converts the ingested food into a semi soluble mass called chyme.
Gastric acids produce mucin which acts as lubricating agent
Intrinsic factor is involved in absorption of Vit B12
PAST SEQ: Give chemical composition of Gastric juice. Give three functions of HCI
Mechanism of HCL secretion:
When stimulated, the parietal cells secrete an acid solution that contains about 160 mmol/L of
hydrochloric acid, which is nearly isotonic with the body fluids
The mechanism of secretion is as follows:
1. Water inside the parietal cell becomes dissociated into H+ and hydroxide (OH− ) in the cell
cytoplasm. The H+ is then actively secreted into the canaliculus in exchange for K+ , an active
exchange process that is catalyzed by H+ -K+ ATPase. Potassium ions transported into the cell by
the sodium Na+ -K+ ATPase pump on the basolateral (extracellular) side of the membrane tend
to leak into the lumen but are recycled back into the cell by the H+ -K+ ATPase. The basolateral
Na+ -K+ ATPase creates low intracellular Na+ , which contributes to Na+ reabsorption from the
lumen of the canaliculus. Thus, most of the K+ and Na+ in the canaliculus is reabsorbed into the
cell cytoplasm, and hydrogen ions take their place in the canaliculus.
2. The pumping of H+ out of the cell by the H+ -K+ ATPase permits OH− to accumulate and form
bicarbonate (HCO3 − ) from CO2, either formed during metabolism in the cell or while entering
the cell from the blood. This reaction is catalyzed by carbonic anhydrase. The HCO3 − is then
transported across the basolateral membrane into the extracellular fluid in exchange for chloride
ions, which enter the cell and are secreted through chloride channels into the canaliculus, giving
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a strong solution of hydrochloric acid in the canaliculus. The hydrochloric acid is then secreted
outward through the open end of the canaliculus into the lumen of the gland
3. Water passes into the canaliculus by osmosis because of extra ions secreted into the canaliculus.
Thus, the final secretion from the canaliculus contains water, hydrochloric acid at a
concentration of about 150 to 160 mEq/L, potassium chloride at a concentration of 15 mEq/L,
and a small amount of sodium chloride.
Express Hit: HCL is produced by the parietal cells of the stomach. The H+K+ ATPase
pump in the cell membrane is responsible for producing as much as 2L of acidic gastric
fluid per day.
Express Hit: HCL is a strong acid and dissociate immediately while acetic acid is a weak
acid and takes time to dissociate
Express Hit: HCL produced by parietal cell of stomach cause a conformational change in
the pepsinogen that enables it to cleave itself forming active pepsin
Clinical Conditions:
Achlorhydria:
The parietal cells lining the stomach are involved in the production of HCl.
Achlorhydria refers to a condition in which the production of HCl is diminished.
It occurs due to dysplasia of gastric mucosa or in response to an underlying medical
condition.
Stomach ulcer:
A stomach ulcer occurs when gastric acid removes the protective stomach lining.
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A peptic ulcer is an excoriated area of stomach or intestinal mucosa caused principally
by the digestive action of gastric juice or upper small intestinal secretions
The usual cause of peptic ulceration is an imbalance between the rate of secretion of
gastric juice and the degree of protection afforded by the gastroduodenal mucosal
barrier and the neutralization of the gastric acid by duodenal juices
The acid produces open sores that can bleed and cause stomach pain.
Causes of a stomach ulcer:
Infection with the bacterium Helicobacter pylori
Alcohol consumption
Smoking
Long term use of NSAIDs
Composition of pancreatic juice:
It is released by the pancreas and it is alkaline in nature.
It constitutes of several enzymes like, trypsinogen, chymotrypsinogen, amylase and
lipase, Elastase, Collagenase, Ribonuclease
It also contain Inorganic and organic constituents
PAST SEQs. Give the composition of pancreatic juice
Importance of pancreatic juice:
Pancreas secretes pancreatic juice which consists of several enzymes which are involved
in digestion.
Pancreatic lipase hydrolyzes fats and trypsin is involved in the digestion of proteins.
Pancreatic juice has high content of bicarbonate ions which is essential to neutralize the
acidic gastric chyme.
Q.1. what are functions of pancreatic phospholipase A2 and alpha-amylase? How dietary hexoses are
actively absorbed from intestinal lumen?
Functions:
Phospholipase catalyzes the hydrolysis of lecithins and cephalins
Alpha amylase: hydrolysis of starch
Absorption of hexoses
Fructose by Glut 5 independent of sodium ions
Galactose by GLUT 5
Composition of bile:
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MEDICO EXPRESS
2ND YEAR MBBS
BIOCHEM GIT BLOCK 4 BOOK
Give the composition and importance of saliva and Biochemistry Biochemistry of GIT
GIT- related clinical disorder (xerostomia) Give the /GIT secretions &
B- composition and importance of gastric juice with special digestion and
001 reference to mechanism of HCl secretion and related absorption of dietary
clinical disorders (achlorhydria, gastric ulcer Give the carbohydrates
composition and importance of pancreatic juice, bile
and succus entericus and related clinical disorders
(pancreatitis, cystic fibrosis, cholelithiasis). Describe
digestion and absorption of dietary carbohydrates along
with inherited and acquired disorders (lactose
intolerance, sucrase-isomaltase deficiency).
Composition of Saliva
pH: 6.4 to 6.9
Electrolytes: Sodium, potassium, bicarbonate, phosphate, calcium and magnesium.
Antibodies: IgA and IgG
Enzymes: amylase and lipase
Other Components: water, mucins, glycoproteins.
Importance of Saliva:
Lubrication
Stimulation of taste buds
Oral hygienic
Regulation of water intake
Digestion
Xerostomia: It is a condition in which enough saliva is not produced resulting in dry mouth.
Normal salivary flow decreases with age in both men and women, although many patients with
MEDICO EXPRESS BLOCK 4 BOOK -FOLLOW MEDICO EXPRESS E LERNING ON INSTAGRAM
JOIN OUR WHATSAPP GOUP 03346072846
,MEDICO EXPRESS BLOCK 4 BOOK
xerostomia are postmenopausal who also complaint of burning tongue or mouth. Factors
causing xerostomia can be both, physiological and pathological.
Some common causes are:
1. Chronic anxiety
2. Dehydration
3. Sjogren Syndrome
Composition of gastric juice:
Gastric juice is composed of HCl, lipase and pepsin, Water, Inorganic constituents ,
Organic matter
Importance of gastric juice:
Gastric juice kills the microorganisms ingested.
Gastric juice initiates the digestion of proteins.
Gastric juice converts the ingested food into a semi soluble mass called chyme.
Gastric acids produce mucin which acts as lubricating agent
Intrinsic factor is involved in absorption of Vit B12
PAST SEQ: Give chemical composition of Gastric juice. Give three functions of HCI
Mechanism of HCL secretion:
When stimulated, the parietal cells secrete an acid solution that contains about 160 mmol/L of
hydrochloric acid, which is nearly isotonic with the body fluids
The mechanism of secretion is as follows:
1. Water inside the parietal cell becomes dissociated into H+ and hydroxide (OH− ) in the cell
cytoplasm. The H+ is then actively secreted into the canaliculus in exchange for K+ , an active
exchange process that is catalyzed by H+ -K+ ATPase. Potassium ions transported into the cell by
the sodium Na+ -K+ ATPase pump on the basolateral (extracellular) side of the membrane tend
to leak into the lumen but are recycled back into the cell by the H+ -K+ ATPase. The basolateral
Na+ -K+ ATPase creates low intracellular Na+ , which contributes to Na+ reabsorption from the
lumen of the canaliculus. Thus, most of the K+ and Na+ in the canaliculus is reabsorbed into the
cell cytoplasm, and hydrogen ions take their place in the canaliculus.
2. The pumping of H+ out of the cell by the H+ -K+ ATPase permits OH− to accumulate and form
bicarbonate (HCO3 − ) from CO2, either formed during metabolism in the cell or while entering
the cell from the blood. This reaction is catalyzed by carbonic anhydrase. The HCO3 − is then
transported across the basolateral membrane into the extracellular fluid in exchange for chloride
ions, which enter the cell and are secreted through chloride channels into the canaliculus, giving
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,MEDICO EXPRESS BLOCK 4 BOOK
a strong solution of hydrochloric acid in the canaliculus. The hydrochloric acid is then secreted
outward through the open end of the canaliculus into the lumen of the gland
3. Water passes into the canaliculus by osmosis because of extra ions secreted into the canaliculus.
Thus, the final secretion from the canaliculus contains water, hydrochloric acid at a
concentration of about 150 to 160 mEq/L, potassium chloride at a concentration of 15 mEq/L,
and a small amount of sodium chloride.
Express Hit: HCL is produced by the parietal cells of the stomach. The H+K+ ATPase
pump in the cell membrane is responsible for producing as much as 2L of acidic gastric
fluid per day.
Express Hit: HCL is a strong acid and dissociate immediately while acetic acid is a weak
acid and takes time to dissociate
Express Hit: HCL produced by parietal cell of stomach cause a conformational change in
the pepsinogen that enables it to cleave itself forming active pepsin
Clinical Conditions:
Achlorhydria:
The parietal cells lining the stomach are involved in the production of HCl.
Achlorhydria refers to a condition in which the production of HCl is diminished.
It occurs due to dysplasia of gastric mucosa or in response to an underlying medical
condition.
Stomach ulcer:
A stomach ulcer occurs when gastric acid removes the protective stomach lining.
MEDICO EXPRESS BLOCK 4 BOOK -FOLLOW MEDICO EXPRESS E LERNING ON INSTAGRAM
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, MEDICO EXPRESS BLOCK 4 BOOK
A peptic ulcer is an excoriated area of stomach or intestinal mucosa caused principally
by the digestive action of gastric juice or upper small intestinal secretions
The usual cause of peptic ulceration is an imbalance between the rate of secretion of
gastric juice and the degree of protection afforded by the gastroduodenal mucosal
barrier and the neutralization of the gastric acid by duodenal juices
The acid produces open sores that can bleed and cause stomach pain.
Causes of a stomach ulcer:
Infection with the bacterium Helicobacter pylori
Alcohol consumption
Smoking
Long term use of NSAIDs
Composition of pancreatic juice:
It is released by the pancreas and it is alkaline in nature.
It constitutes of several enzymes like, trypsinogen, chymotrypsinogen, amylase and
lipase, Elastase, Collagenase, Ribonuclease
It also contain Inorganic and organic constituents
PAST SEQs. Give the composition of pancreatic juice
Importance of pancreatic juice:
Pancreas secretes pancreatic juice which consists of several enzymes which are involved
in digestion.
Pancreatic lipase hydrolyzes fats and trypsin is involved in the digestion of proteins.
Pancreatic juice has high content of bicarbonate ions which is essential to neutralize the
acidic gastric chyme.
Q.1. what are functions of pancreatic phospholipase A2 and alpha-amylase? How dietary hexoses are
actively absorbed from intestinal lumen?
Functions:
Phospholipase catalyzes the hydrolysis of lecithins and cephalins
Alpha amylase: hydrolysis of starch
Absorption of hexoses
Fructose by Glut 5 independent of sodium ions
Galactose by GLUT 5
Composition of bile:
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