Transcript Chapter 15 (GI Trat Fluid).

King Saud University
College of Science
Department of Biochemistry
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Chapter 15
Gastrointestinal Tract Fluid
Professor A. S. Alhomida
1
Secretions of the
Gastrointestinal (GI) Tract
1. Primary Organs
• Salivary
• Gastric
• Pancreatic
• Intestinal
2. Accessory Organs
• Teeth
• Tongue
• Gallbladder
• Liver
Length of GI tract
vs height
2
GI Tract Anatomy
3
Stomach
cardia
fundus
pylorus
body
4
Daily Secretion of Digestive Fluids
Fluid
Volume
(mL/day)
pH
Saliva
Stomach (gastric secretion)
1000-1200
2000-3000
6.0-7.0
1.0-3.5
Pancreas (exocrine
secretion)
Bile secretion
Brunner’s gland secretion
Succus entericus
(intestinal juice)
Large intestine
1200-2000
8.0-8.3
600-700
50
2000-3000
7.8
8.0-8.9
7.8-8.0
60
7.5-8.05
Enzymes of GI Tract
6
Hormones of GI Tract
7
Digestive Process
1. Ingestion- taking food in
•
Bolus- an amount of food passing through tract
2. Propulsion- moves food through tract
•
•
Swallowing- voluntary
Peristalsis- involuntary muscular waves moves food
forward
3. Mechanical digestion- physical chewing, mixing,
churning
•
Segmentation- rhythmic local constrictions of intestine for
mixing
8
Digestive Process, cont’d
4. Chemical digestion- catabolism/ breakdown of
polymers into monomers by enzymes
•
Begins in mouth, essentially complete in small intestine
5. Absorption- passage of digested end products across
wall into blood
•
•
•
Monomers, vitamins, minerals and water
Pass through mucosal cells lining tract
Small intestine major absorption site
6. Defecation- eliminates indigestible substances and
other wastes from body via anus in form of feces
9
Digestive Process
10
Functions of Saliva
1. Maintenance of oral hygiene
•
Lysozyme, peroxidases (XEROSTOMIA)
2. Maintain mineralization of teeth
•
(Ca2+ and pH)
3. Lubrication
•
Speaking and swallowing (mucin)
4. Digestive function
•
Amylase (Ptyalin) & Lipase
5. Solvation
•
Enables one to taste foodstuffs
11
Three Major salivary glands
% Total
Type
1. Submandibular (submaxillary): 70%
2. Parotid:
serous (protein)
3. Sublingual:
mucin (mucus)
sero-mucin
25%
5%
Total
1,500 mL/day
12
Salivary Gland Structure
13
Salivary Gland Structure
Acinus  intercalated ducts  striated ducts  excretory duct
14
Salivary Flow Rate
Na
Cl
100
Na
80
80
60
60
40
HCO3
Cl
20
HCO3
K
K
0
1
2
3
Flow rate (mL/min)
40
20
0
4
Plasma
15
Saliva
Ion concentration (mM)
120
100
Ion concentration (mM)
140
Composition of Human Saliva
16
Salivary Gland Diseases
1.
Functional disorders
• Sialorrhea (Increase in saliva flow)
• Psychosis, mental retardation, certain nuerologicval diseases,
rabies,
• Mercury poisoning
• Xerostomia (Decrease in saliva flow)
• Mumps, sardoidosis, Sjogrens, syndrome, lupus, postirradiation
17
Salivary Gland Diseases
2.
3.
4.
Obstructive disorders
Non-neoplastic disorders
Neoplastic disorders
18
Salivary Calculi
1. It sometimes is formed in the ducts and similar
composition to tartar (Ca(PO4)2 or CaCO3
2. It is usually stated that a nucleus around which the
precipitation body of these salts occur
3. Calcium oxalate may be the precipitated salt which
together with mucin and globulin may form the calculi
4. Increased acidity is necessary for oxalate calculus
formation
19
Pancreatic Structure
1. Endocrine cells
•
They are arranged in small islets within the
pancreas, secrete directly into the circulation:
•
•
•
•
Insulin
Glucagon
Somatostain
Polypeptids
20
Pancreatic Structure, Cont’d
2. Exocrine cells
•
They are organized into acini that produce four
types of digestive enzymes:
•
•
•
•
Peptidases
Lipases
Amylases
Nucleases
21
Pancreatic Structure, Cont’d
3. Ductal cells
•
Each day they secrete about 1200-1500 mL of
pancreatic juice containing a high concentration of
HCO3
•
•
The HCO3- neutralizes gastric acid and regulates the pH
of the upper intestine
Failure to naturalize the chyme as it enters the intestine
will result duodenal ulcers
22
Pancreatic Juice Composition
23
Pancreas Structure
24
Pancreatic Secretion
25
Ion Concentration (mM)
pH
8.2
340
pH
7.8
Osm 300
7.4
260
160
Osmolality
Pancreatic Secretion
+
Na
HCO3-
120
80
ClK+
40
0
0
300
100
Secretion rate (mL/hr)
500
26
Functions of Gastric
Secretions
1.
2.
3.
4.
Digestion of proteins (pepsinogen and HCl)
Protection of stomach (HCO3 and mucus)
Absorption of vitamin B12 (intrinsic factor)
Destroy bacteria and other microorganisms
(HCl)
27
Gastric Juice Composition
28
Gastric Secretions
29
Gastric Pit
mucus neck & surface cells
Mucus & HCO3
Peptic cells
(chief, zymogen)
Pepsinogen secretion
parietal cells
(oxyntic)
H+ secretion &
intrinsic factor
30
HCl Section Mechanism
1. HCl is secreted into the parietal cell canaliculi by a
three step process:
•
•
•
Active transport process is begun by transport of K+ and
Cl- into the canaliculi. Cl- is transported by either a pump
or through a channel. The flow of Cl- creates a –ve
potential inside the canaliculi, causing K+ to flow +vely
into the canaliculi
H+ is exchanged for K+ by H+-K+ ATPase pump
Water enters the canaliculi down the osmotic gradient
created by the movement of HCl into the canaliculi
31
HCl Section Mechanism, Cont’d
+
2. The H entering the canaliculi is supported by
+
dissociation of carbonic acid (H2CO3) into H and
bicarbonate (HCO3 ) within the parietal cell:
•
•
•
H2CO3 is formed from the Rxn catalyzed by carbonic
anyhydrase:
CO2 + H2O →
H2CO3
HCO3- diffuses back into the plasma in exchange for Cl-
3. Most the HCl that is secreted into the stomach is
neutralized and reabsorbed within the small intestine
32
HCl Section Mechanism, Cont’d
4. Active transport process involved in the generation
of HCl requires a large amount of ATP which is
generated by mitochondria in parietal cell
5. The pH of the parietal cell secretion can be as low as
0.8
+
+
6. The H -K ATPase pump can irreversible inhibited
by the drug omeprazole (antacid) which is used now
for the treatment of duodenal and gastric ulcers
33
HCl Section Mechanism, Cont’d
34
Regulation of Gastric Secretion
1. Cephalic
•
•
•
Food in mouth increases secretion of HCl (efferent vagus)
Anger and tension increases secretion HCl
Fear and depression increases secretion HCl
2. Gastric
•
•
•
Stimulated by distension (vago-vagal), hypertonicity
Alcohol and AAs (gastrin)
Inhib by H+ (-ve feedback, somatostatin)
3. Intestinal
•
Peptides (gastrin), AA’s, fats
CCK-PZ)
35
Regulation of Gastric Secretion
36
Gastric Ulcers
1. Ulcer (sore) in inner lining of stomach
• Chronic bleeding into GI tract
• Anemia may result
• Perforated ulcer
• Stomach contents spill into abdomen
2. Caused by Helicobacter pylori (bacterium)
• Antibiotics cure problem
37
Gastric Ulcers, Cont’d
• An ulcer is a crater-like lesion on
the skin or mucous membrane
caused by an inflammatory,
infectious, or malignant condition
• To avoid irritating an ulcer a
person can try eliminating certain
substances from their diet such as
caffeine, alcohol, aspirin, and
avoid smoking
• Patients can take certain medicines
to suppress the acid in the stomach
38
Small Intestine
1. Major digestive organ
2. Longest part of alimentary canal (3-6 hour journey)
3. Three subdivisions
•
Duodenum
•
•
•
Jejunum
•
•
Shortest but lots going on
Hepatopancreatic ampulla- bile duct and main pancreatic duct enter
Middle portion
Ileum
•
Last part joins large intestine at ileocecal valve
39
Small Intestine
40
Intestinal Juice
1.
2.
3.
4.
5.
Glands make 1-3 L daily
Stimulated by entrance of acidic chime
Slightly alkaline to neutralize chyme
Largely water with some mucus
Relatively enzyme poor because enzymes are
bound to the brush border
41
Intestinal Juice Composition
42
Carbohydrate and Protein
Digestion
43
Fat and Nucleic Acid Digestion
44
Large Intestine
1. Shorter but larger diameter than small
intestine
2. Major function in feces elimination and water
reabsoprtion
3. 12-24 hours
45
Large Intestine
46
Bacterial Flora
1.
2.
3.
4.
5.
Most bacteria killed by stomach acid or enzymes
Some survive or come up from the anus
Ferment indigestible carbohydrates (cellulose and others)
Release acids and gases (about 500 mL/day)
Also release B complex vitamins and most of the body’s
vitamin K need (for clotting)
47
Bile
• Function of Bile
• Bile is required for the digestion and absorption of fats and
for excretion of water-insoluble substances as cholesterol
and bilirubin
• Formation of Bile
• It is formed from two sites:
• Hepatocytes
• Ductal cells
48
Bile, Cont’d
• Storage of Bile
• Although it is secreted continuously, but it is stored
in the gallbladder during the interdigestive period
• Release of Bile
• It is released into the duodenum during the digestive
period
49
Bile Fluid
1. Flows toward bile duct branches in portal
triads
2. Constantly made by hepatocytes
3. List of contents but bile salts and
phospholipids important in digestion
4. Bile cholesterol is important because it is one
of the few ways in which cholesterol stores
can be regulated
50
Bile Salts
•
Role of Bile Salts in Emulsifying Fat
1. Break up large glob into smaller globs
2. Makes for large surface area for lipid
digesting enzymes
3. Facilitate fat and cholesterol absorption
• Most of bile (but not bile salts) will leave with
feces
• Bile salts are actually recycled for reuse
51
Human Bile Composition
52
Bile Salts Role in Digestions
53
Bile Acids (Salts) Biosynthesis
1. Primary Acids
2. Secondary acids
54
Bile Acids (Salts) Biosynthesis,
Con’td
55
Recycling of Bile Salts
1. The total circulating pool of bile salts is about 3.6 g
2. Because 4-8 g of bile salts are required to digest
and absorb a meal (more if the meal is high in fat),
the total pool of bile salts must circulate twice
during the digestion of each meal
3. The bile salts usually circulate 6-8 times daily
56
Recycling of Bile Salts, Cont’d
57
Gallbladder
1. Pear-shaped muscular sack
•
Attached to surface of liver
2. Stores excess bile
•
•
Liver produces 1000 mL/day
Water is reabsorbed
•
Consistency of thick mucus
58
Gallbladder, Cont’d
3. Bile duct empties into duodenum
4. Stores bile not immediately needed for
digestion
5. Concentrates stored bile
6. Releases bile when foods high in lipids enter
the small intestine
59
Gallbladder, Cont’d
60
Gallstones
1. Gallstone = crystallized bile
•
•
80% of stones are cholesterol
20% bilirubin
2. Treatment
•
•
•
Surgical removal (cholecystectomy)
• 500,000 surgeries/year
Oral dissolution
Sound waves
• break stones into small, passable pieces
61
Gallstones
1.
Obstruction of the cystic
duct leading to severe
abdominal pain (biliary
colic)
2. Infection or inflammation
of the gallbladder
(cholecystitis)
3. Blockage of the biliary
ducts leading to the
duodenum (biliary
obstruction)
62
THE END
Any questions?
63