SECRETIONS OF GASTRO SECRETIONS OF GASTRO INTESTINAL TRACTINTESTINAL TRACT

TYPESTYPES

Secretions are of two main types:Secretions are of two main types: MucusMucus EnzymesEnzymes

Secretions are produced in response Secretions are produced in response to presence of food in alimentary to presence of food in alimentary tract.tract.

MECHANISM OF MECHANISM OF STIMULATION OF GLANDSSTIMULATION OF GLANDS

1)1) Stimulation of Enteric Nervous Stimuli By;Stimulation of Enteric Nervous Stimuli By;

I.I. Tactile StimulationTactile StimulationII.II. Chemical IrritationChemical IrritationIII.III. Distention of the Gut.Distention of the Gut.

2)2) Autonomic Parasympathetic Stimulation:Autonomic Parasympathetic Stimulation:I.I. Increases the rate of glandular secretionIncreases the rate of glandular secretion..

3)3) Sympathetic Stimulation:Sympathetic Stimulation:I.I. Usually reduces the secretionsUsually reduces the secretions..

4)4) Hormonal Stimulation:Hormonal Stimulation:I.I. May increase or decrease the secretions.May increase or decrease the secretions.

Chemically Gastrointestinal hormones one polypeptides orChemically Gastrointestinal hormones one polypeptides or polypeptide devirativer.polypeptide devirativer.

MECHANISM OF SECRETION MECHANISM OF SECRETION OF GLANDSOF GLANDS

Secretion Of Organic Substance;Secretion Of Organic Substance;1)1) Nutrient material is provided by the blood.Nutrient material is provided by the blood.2)2) Mitochondria forms ATP.Mitochondria forms ATP.3)3) Rough Endoplasmic reticulum & Golgi complex Rough Endoplasmic reticulum & Golgi complex

forms organic substance by nutrients using forms organic substance by nutrients using ATP.ATP.

4)4) Secretory vesicles formed are stored until Secretory vesicles formed are stored until nervous or hormonal signals are arrived to nervous or hormonal signals are arrived to extrude them through cells.extrude them through cells.

Postulated Mechanism of Secretion;Postulated Mechanism of Secretion;1)1) Cel ions are actively secreted to the cells Cel ions are actively secreted to the cells

interior.interior.2)2) Followed by passive movement of Na+ ions to Followed by passive movement of Na+ ions to

cells interior.cells interior.3)3) Resulting osmosis of water causes increased Resulting osmosis of water causes increased

volume & hydrostatic pressure.volume & hydrostatic pressure.4)4) Pressure causes excretion of water, Pressure causes excretion of water,

electrolytes and organic substance through the electrolytes and organic substance through the cell.cell.

Salivary Glands;Salivary Glands;

1)1) Parotia.Parotia.

2)2) Submandibular.Submandibular.

3)3) Sublingual.Sublingual.

4)4) Buccal.Buccal.

Daily Secretion of Saliva is 1000ml,which consist of;Daily Secretion of Saliva is 1000ml,which consist of;1)1) Serous Secretion.Serous Secretion.

Containing Ptyalin (x-amylase)Containing Ptyalin (x-amylase)i-e; Enzymatic Secretion for digestion of starches.i-e; Enzymatic Secretion for digestion of starches.

2)2) Mucus Secretion.Mucus Secretion.Containing mucin for lubrication & protective purposes.Containing mucin for lubrication & protective purposes.PH of Saliva is : 6.0 – 7.0PH of Saliva is : 6.0 – 7.0

3)3) Ion Secretion.Ion Secretion.Contains large quantites of potassium & bicarbonate ions Contains large quantites of potassium & bicarbonate ions and chloride ions.and chloride ions.Potassium and bicarbonate ions and chloride ions so that Potassium and bicarbonate ions and chloride ions so that during resting conditions sodium and chloride ions are during resting conditions sodium and chloride ions are 15,/Eq/L each,15,/Eq/L each,Potassium about 30mEq/L and Bicarbonate 50-70 mEq /L.Potassium about 30mEq/L and Bicarbonate 50-70 mEq /L.

Saliva helps to prevent detriorative Saliva helps to prevent detriorative processes;processes;

1)1) Washes the buccal cavity.Washes the buccal cavity.

2)2) Thiocyanate ions and proteolytic Thiocyanate ions and proteolytic enzymes.enzymes.

Destroy bacteria.Destroy bacteria. Digest food particles.Digest food particles.

3)3) Antibodies present in saliva prevent Antibodies present in saliva prevent dental carries.dental carries.

Entirely mucus in character,Entirely mucus in character,

Two types of glands:Two types of glands:

1)1) Simple mucus glands,Simple mucus glands,

In main body of Esophagus.In main body of Esophagus.

2)2) Compound mucus glands,Compound mucus glands,

at the initial & gastric ends of at the initial & gastric ends of Esophagus.Esophagus.

Two types of glands,Two types of glands,1)1) Oxyntic glands.Oxyntic glands.2)2) Pyloric glands.Pyloric glands.The Oxyntic Glands Secrete :The Oxyntic Glands Secrete : 1)1) Hydrochloric Acid.Hydrochloric Acid.2)2) Pepsinogen.Pepsinogen.3)3) Intrinsic Factor.Intrinsic Factor.4)4) Mucus.Mucus.

Form the prosimal 80 % of stomach.Form the prosimal 80 % of stomach.Pyloric Glands Secrete :Pyloric Glands Secrete :1)1) MucusMucus2)2) Gastrin.Gastrin. These forms distal 20 % of the stomachThese forms distal 20 % of the stomach..

Oxyntic glands are composed of three Oxyntic glands are composed of three types of cells,types of cells,

1)1) Mucous neck cellsMucous neck cells

Secrete mainly mucus.Secrete mainly mucus.

2)2) Peptic (Chief) cellsPeptic (Chief) cells

Secrete pepsinogen.Secrete pepsinogen.

3)3) Parietal (Oxyntic) CellsParietal (Oxyntic) Cells

Secrete HCL and intrinsic factorSecrete HCL and intrinsic factor..

There are 160 mill moles of HCL in There are 160 mill moles of HCL in parietal cell secretion,parietal cell secretion,

PH is about: 0.8PH is about: 0.8

1500 calories of energy is required 1500 calories of energy is required for achieving this acidity for achieving this acidity concentration which is about 3 concentration which is about 3 million times that of artericel blood.million times that of artericel blood.

Parietal cell contains large branching canalicuki Parietal cell contains large branching canalicuki having villus like projections which the HCL is having villus like projections which the HCL is formed.formed.

STEP 1:STEP 1:

Cl- ions are actively secreted from cell Cl- ions are actively secreted from cell cytoplasm to the canaliculus.cytoplasm to the canaliculus.

Na+ ions are transported out of canaliculus,Na+ ions are transported out of canaliculus,

Create a –ive potential of -40 to -70 mv in Create a –ive potential of -40 to -70 mv in canaliculus.canaliculus.

Result in transport of K+ ions to the canaliculusResult in transport of K+ ions to the canaliculus..

STEP 2:STEP 2:Dissociation of Water.Dissociation of Water.Provided H+ ions to be transported to canaliculus Provided H+ ions to be transported to canaliculus

for the formation of HCL.for the formation of HCL.Na+ are actively reabsorbed.Na+ are actively reabsorbed.STEP 3:STEP 3:Water passes by osmosis inside the canaliculus.Water passes by osmosis inside the canaliculus.Thus FINAL COMPOSITION is:Thus FINAL COMPOSITION is:1)1) Water.Water.2)2) HCL 150-160 mEq /L.HCL 150-160 mEq /L.3)3) Potassium chloride: 15 mEq /L.Potassium chloride: 15 mEq /L.4)4) Small amount of Nacl.Small amount of Nacl.

STEP 4:STEP 4:

Co2 combines with Hydroxyl ions to form Co2 combines with Hydroxyl ions to form bicarbonate ions:bicarbonate ions:

Co2 + Oh ------Co2 + Oh ------Hco 3Hco 3

Which is transported out of cell in exchange Which is transported out of cell in exchange of Cl- ions.of Cl- ions.

Secreted by the peptic cells in slightly different Secreted by the peptic cells in slightly different forms but all performs the same function.forms but all performs the same function.

Activation of Pepsinogen:Activation of Pepsinogen: Pepsinogen is zymogen form of enzyme pepsin.Pepsinogen is zymogen form of enzyme pepsin. Activated by HCL.Activated by HCL. Pepsinogen having molecular weight 42,5000 is Pepsinogen having molecular weight 42,5000 is

split to form pepsin of molecular weight 35000.split to form pepsin of molecular weight 35000.

Pepsin is an active proteolytic enzyme requiring Pepsin is an active proteolytic enzyme requiring acidic medium for its function.acidic medium for its function.

Intrinsic factor is essential for absorption Intrinsic factor is essential for absorption of Vit.B12.of Vit.B12.

Secreted with HCL by parietal cells.Secreted with HCL by parietal cells.

Thus destruction of parietal cells causes.Thus destruction of parietal cells causes. Achlorydria as well as Achlorydria as well as Pernicious anemia.Pernicious anemia.

Secretion of Mucus & GastrinSecretion of Mucus & GastrinPyloric glands containPyloric glands contain Mostly Mucous cells.Mostly Mucous cells. Few peptic cells.Few peptic cells. No parietal cells.No parietal cells.

So the Secretions are;So the Secretions are; A small amount of pepsinogen.A small amount of pepsinogen. Large amount of mucus.Large amount of mucus. Hormone: Gastrin------Plays a role in controlling gastric Hormone: Gastrin------Plays a role in controlling gastric

secretio.secretio. The stomach wall is also lined by surface mucous cells.The stomach wall is also lined by surface mucous cells.

Ecl cells- EnteroChromafin like cells are the cells that Ecl cells- EnteroChromafin like cells are the cells that are lying deep to oxyntic glands & secrete Histamine in are lying deep to oxyntic glands & secrete Histamine in direct contact with the parietal cells.direct contact with the parietal cells.So ECL cells can control HCL secretion by producing So ECL cells can control HCL secretion by producing histamine and histamine secretion can be controlled histamine and histamine secretion can be controlled by;by;

1)1) Gastrin Secretion.Gastrin Secretion.2)2) Acetylcholine-released from vagal nerve endings.Acetylcholine-released from vagal nerve endings.3)3) Hormonal substances-secreted by enteric nervous Hormonal substances-secreted by enteric nervous

system.system.

Gastrin secreted by G cells of the pyloric Gastrin secreted by G cells of the pyloric glands is a polypepticle having 2 forms;glands is a polypepticle having 2 forms;

1)1) G34-containing 34 amino acids.G34-containing 34 amino acids.2)2) G-17-containing 17 amino acids.G-17-containing 17 amino acids.

The meats or protein containing foods causes The meats or protein containing foods causes release of gastrin which then reaches the ECL release of gastrin which then reaches the ECL cells & releases Histamine that causes Hcl cells & releases Histamine that causes Hcl secretionsecretion..

GASTRIC SECRETION DURING GASTRIC SECRETION DURING THE INTERDIGESTIVE PERIODTHE INTERDIGESTIVE PERIOD

Interdigestive Period;Interdigestive Period;The duration in which little or no The duration in which little or no digestion is occurring.digestion is occurring.

The secretions during this period;The secretions during this period;

non- oxyntic type-containing almost no non- oxyntic type-containing almost no acid.acid.

Little pepsin.Little pepsin. Large amount of mucus.Large amount of mucus.