The digestive system consists of: 1.Alimentary canal from mouth to the anal canal. 2.Associated glands: salivary gland, liver, pancreases. 3.Accessory.

The digestive system consists of:The digestive system consists of:

1.1.Alimentary canal from mouth to the Alimentary canal from mouth to the anal canal . anal canal .2.2.Associated glands: salivary gland, liver, Associated glands: salivary gland, liver, pancreases. pancreases.3.3.Accessory organs: tongue, teeth, muscle Accessory organs: tongue, teeth, muscle of mastication etc …. of mastication etc ….

Digestive systemDigestive systemBy prof.Dr.sobhy el-kafafyBy prof.Dr.sobhy el-kafafy

The main physiological function of GIT are:

1.1.DigestionDigestion..

2.2.AbsorptionAbsorption..

3.3.Secretion of digestive juiceSecretion of digestive juice..

4.4.Immune functionImmune function..5.5.Endocrine functionEndocrine function..

Salivary secretionSalivary secretion• Three pairs of main salivary glands. • Parotid, submandibular and sublingual• Many small glands in the

buccal mucosa.

Composition of saliva:The volume: 1000 – 1500 ml/dayColourless, viscous fluid, slightly acidic pH 6.6-7.1, it is hypotonic•99.5% water.•0.2% inorganic constituents.•0.3% organic constituents.

Inorganic constituents:•NaCl and KCL.•Na2 H CO3: NaH2 CO3 and NaH2PO4: Na2HPO4.•Calcium salts as Ca bicarbonate and phosphate. - Tartar. - Salivary calculi.•Potassium thiocyanate, it has bactericidal action.

Organic constituents:•Ptyalin (α-amylase), lysozyme and lingual lipase.•Albumin, globulins and mucus,.

•Salivary amylase: Hydrolyses cooked starch to polysaccharides.•Lysozyme: has antibacterial action.

• Types of salivary gland:

Gland Type of secretion

%of total secretion

Parotid Serous 25

Submandibular Mixed 70

Sublingual mucous 5

1.1.Moistening of food.Moistening of food.

2.2.Cleaning of the mouth by: Cleaning of the mouth by: • mechanical wash. mechanical wash. • antibacterial action by lysozyme.antibacterial action by lysozyme.• the bactericidal effect by thiocyanante. the bactericidal effect by thiocyanante.

• antibodies.antibodies.

Functions of saliva:Functions of saliva:

33 . .facilitation of speechfacilitation of speech..

44 . .digestion of starchdigestion of starch..

55 . .it dissolves food materials it dissolves food materials to facilitate taste sensation to facilitate taste sensation..

66 . .water balancewater balance..

77 . .buffering action for acids buffering action for acids and alkalis and alkalis..

8. Neutralization of the excessive cold or hot food.

9. Body temperature regulation.

10. Excretion of iodides and mercury.

Control of salivary secretionControl of salivary secretion

NervousNervous mechanism onlymechanism only: 2 types : 2 types of reflexes:of reflexes:• The inborn (unconditioned) reflex.The inborn (unconditioned) reflex.• Acquired (conditioned) reflex.Acquired (conditioned) reflex.1- Unconditioned reflexes:1- Unconditioned reflexes:

(inborn, do not depend on previous (inborn, do not depend on previous training)training)

2-Conditioned reflex:2-Conditioned reflex: acquired, depend on training acquired, depend on training and pervious experience and pervious experience (Pavlov experiment).(Pavlov experiment).

Mastication (chewing)Mastication (chewing)•Mastication is the mechanical Mastication is the mechanical processing of food, breakingprocessing of food, breaking it into pieces by grinding and mixing it into pieces by grinding and mixing it with saliva, ready to swallow.it with saliva, ready to swallow.•Mastication is started voluntarily Mastication is started voluntarily but continue as an involuntary but continue as an involuntary reflex.reflex.

Deglutition (swallowing)Deglutition (swallowing)•Deglutition is the transfer of Deglutition is the transfer of food from the mouth to the food from the mouth to the stomach. stomach.

•Start of deglutition is Start of deglutition is voluntary, but it is completed voluntary, but it is completed by reflex actions (involuntary) by reflex actions (involuntary)

Phases of deglutition:Phases of deglutition:

The first phase:The first phase:Voluntary during which Voluntary during which passage of the bolus of food passage of the bolus of food through the anterior pillars of through the anterior pillars of the fauces takes place.the fauces takes place.

The second phaseThe second phase::It is involuntary, very rapid, takes It is involuntary, very rapid, takes about 1-2 seconds. This phase about 1-2 seconds. This phase passes by the following passes by the following sequences of events:sequences of events:

1- The posterior pillars of the 1- The posterior pillars of the fauces shut off the mouth.fauces shut off the mouth.

2- Protective reflexes prevent the 2- Protective reflexes prevent the passage of food into the larynx by:passage of food into the larynx by:a.a.Elevation of the soft palate.Elevation of the soft palate.

b.b.Elevation of the larynx and closure of Elevation of the larynx and closure of its opening (glottis) by epiglottis and its opening (glottis) by epiglottis and approximation of the vocal cords. approximation of the vocal cords.

c.c.Inhibition of respiration (reflex apnea).Inhibition of respiration (reflex apnea).

The third phase:The third phase:

Passage of food along the Passage of food along the esophagus to the esophagus to the stomach occurs, it is stomach occurs, it is involuntary.involuntary.

The stomachThe stomachThe stomachThe stomach

The functions of the stomach are:1.1. Storage of large quantities of food.Storage of large quantities of food.

2.2. Mixing of food with gastric Mixing of food with gastric secretions.secretions.

3.3. Regulation of the rate of evacuation Regulation of the rate of evacuation of chime.of chime.

4.4. The acidic gastric juice facilitates the The acidic gastric juice facilitates the absorption of calcium and iron.absorption of calcium and iron.

5.5.Digestive function. Digestive function. 6.6. Release intrinsic factor for vit. B12 Release intrinsic factor for vit. B12

absorption.absorption.

7.7.Secretion of mucin, which is Secretion of mucin, which is protective for the mucosa.protective for the mucosa.

The gastric glands are composed of The gastric glands are composed of different types of cells:different types of cells:

1.1.The mucous neck cells, which The mucous neck cells, which secrete mucin.secrete mucin.

2.2.The The chiefchief or or pepticpeptic cellscells secret secret digestive enzyme (pepsin).digestive enzyme (pepsin).

3.3.The The parietalparietal or or oxynticoxyntic cells secret cells secret HClHCl, and , and intrinsicintrinsic factor. factor.

Composition of gastric secretion:About 3 liters/day, pH 1-2 approximately Constituents:water 99%Enzymes pepsin, gelatinase. LipaseCations Na+, K+, Mg++, Ca++

Anions Cl- ,HPO-, SO4-

HCl 0.4%Mucin Intrinsic factor

Functions of HCl:Functions of HCl:1.1. Activation of pepsinogen.Activation of pepsinogen.

2.2. gives the optimum pH needed for its gives the optimum pH needed for its action.action.

3.3. Antibacterial action.Antibacterial action.

4.4. Absorption of calcium and iron.Absorption of calcium and iron.

5.5. Hydrolysis of some food.Hydrolysis of some food.

6.6. Stimulate the release of secretin H.Stimulate the release of secretin H.

Function of the enzymes:Pepsin:- optimum pH = 2.0 pepsin converts proteins into acid metaproteins, proteoses, and peptones.

- pepsionogen is activated by HCl to pepsin, any minute amounts of pepsin formed can activate the rest of pepsinogen to pepsin.

Gastric lipase:Gastric lipase:It is a lipolytic enzyme. (weak).It is a lipolytic enzyme. (weak).

Mucin:Mucin:Protection for the stomach wall,lubrication Protection for the stomach wall,lubrication

of food transport and neutralization of of food transport and neutralization of HCl.HCl.

Intrensic factor:Intrensic factor:

It is a glycoprotein necessary for It is a glycoprotein necessary for absorption of (Vit. B12).absorption of (Vit. B12).

Regulation of gastric secretionRegulation of gastric secretion

Gastric secretion is regulated by both Gastric secretion is regulated by both nervousnervous and and hormonalhormonal mechanisms. mechanisms.

Nervous mechanism:Nervous mechanism:

• Conditioned reflexes:Conditioned reflexes:

Stimulus: is seeing, hearing, smelling, .…Stimulus: is seeing, hearing, smelling, .…(primary center is the cerebral cortex) (primary center is the cerebral cortex)

• Unconditioned reflexes:Unconditioned reflexes:

Stimulus: is presence of food in the mouth.Stimulus: is presence of food in the mouth.

Hormonal control:

gastric and intestinal phase.

a. gastric: (gastrin H)

Gastrin H: Stimulus for its release from the pylorus is:

• distension of the stomach by food.

• secretagogues: vegetables extracts, peptones, and alcohol.

b. Intestinal phase:b. Intestinal phase:Intestinal gastrin Intestinal gastrin HH: : Secreted from duodenum in response Secreted from duodenum in response

to:to:

• distension of the intestine.distension of the intestine.

• chemical stimuli.chemical stimuli.

Gastrin H. increases gastric Gastrin H. increases gastric secretion and motility.secretion and motility.

Regulation of stomach emptying:Regulation of stomach emptying:

1- Gastric factors:1- Gastric factors:

•Volume of the gastric contents.Volume of the gastric contents.

•Gastrin hormone.Gastrin hormone.

2- Duodenal factors:2- Duodenal factors:

•Enterogastric reflex.Enterogastric reflex.

•Hormonal factors:Hormonal factors:-Cholecystokinin H.-Cholecystokinin H. -- Secretin H.Secretin H.

Definition: It is outward expulsion of the gastric contents

through the oral cavity.

Mechanisms of vomiting: steps:

• Contraction of the diaphragm, anterior abdominal wall muscles and the pelvic floor, this leads to rise of the intra-abdominal pressure.

• Relaxation of body and funds of the stomach and esophageal sphincters.

• Contraction of the pyloric portion of the stomach.

• The protective reflexes that prevent passage of vomitus in respiratory passage.

Causes of vomiting:Causes of vomiting:The causes of vomiting can be grouped into:The causes of vomiting can be grouped into:

1- Central causes:1- Central causes:• Direct stimulationDirect stimulation of the vomiting centre as: of the vomiting centre as:

increased intracreanial pressure.increased intracreanial pressure.

• Indirect stimulationIndirect stimulation of vomiting centre by of vomiting centre by certain substances circulating in the blood as:certain substances circulating in the blood as:

- exogenous drugs: tartar emetic, emetine, - exogenous drugs: tartar emetic, emetine, morphine,…morphine,…

- endogenous toxins: blood urea,….- endogenous toxins: blood urea,….

2- Peripheral causes2- Peripheral causes: : by afferent by afferent impulses from:impulses from:- - G.I.T. tract: from the pharynx to the colon. G.I.T. tract: from the pharynx to the colon.

- Affection of other abdominal organs: kidneys,- Affection of other abdominal organs: kidneys,……

- - Extrabdominal organs: cardiac, vestibular Extrabdominal organs: cardiac, vestibular apparatus,….apparatus,….

3- Psychogenic vomiting:3- Psychogenic vomiting:Without any organic diseases or by conditioned Without any organic diseases or by conditioned

reflexesreflexes

Pancreatic secretionPancreatic secretion• The exocrine pancreatic secretion is

considered as the most important source for the digestive enzymes.

• Digesting the three major types of food.

• It is the most alkaline juice in the human body pH is 8.3 (bicarbonate)

Composition of pancreatic secretion

• 1200ml/day pH is 8.3.1200ml/day pH is 8.3.

the main enzymes are:the main enzymes are:

1- Proteolytic enzymes:1- Proteolytic enzymes: ProenzymeProenzyme Active enzymeActive enzyme

EnterokinaseEnterokinase- Trypsinogen trypsin - Trypsinogen trypsin

trypsin trypsin - ChymotrypsinogenChymotrypsinogen chymotrypsin chymotrypsin

trypsintrypsin- - ProcarboxypolypeptidasProcarboxypolypeptidas carboxypolypeptidasecarboxypolypeptidase..

2- Pancreatic amylase2- Pancreatic amylase: hydrolyses of : hydrolyses of uncooked and cooked starches, uncooked and cooked starches, glycogen and carbohydrates to form glycogen and carbohydrates to form disaccharides. Chloride ions serve as a disaccharides. Chloride ions serve as a coenzyme.coenzyme.

3-Lipolytic enzymes: 3-Lipolytic enzymes: pancreatic lipasepancreatic lipase is is the main enzyme for digestion of fat the main enzyme for digestion of fat (neutral fat into glycerol and fatty acid), (neutral fat into glycerol and fatty acid), and and cholesterol esterasecholesterol esterase for hydrolysis of for hydrolysis of cholesterol esters.cholesterol esters.

Other constituents of pancreatic juice:Other constituents of pancreatic juice:

-Water-Water

- Cations as Na- Cations as Na++, K, K++, Ca, Ca++, Mg, Mg++..

-Anions as HCO-Anions as HCO--33, CL, CL

--, SO, SO

--

44, HPO, HPO--4 4 ..

-Albumin and globulin.-Albumin and globulin.

Regulation of pancreatic secretion:Regulation of pancreatic secretion: Both Both nervousnervous and and hormonalhormonal mechanisms mechanisms

hormonal regulation is the more importanthormonal regulation is the more important

1- Nervous regulation:1- Nervous regulation: - - by both conditioned and unconditioned by both conditioned and unconditioned

reflexes, reflexes,

- nervous type of secretion is rich in - nervous type of secretion is rich in enzymes but deficient in alkali and water. enzymes but deficient in alkali and water.

2- Hormonal regulation:2- Hormonal regulation:

A. Secretin HA. Secretin H: : presences of acidchime in the duodenum, release presences of acidchime in the duodenum, release

and activate secretin H. and activate secretin H. copious pancreatic secretion very alkaline poor in copious pancreatic secretion very alkaline poor in

enzymes.enzymes.

Importance of secretin H:Importance of secretin H:• secretin H. stimulates alkaline pancreatic secretin H. stimulates alkaline pancreatic

secretion for neutralization of Hcl.secretion for neutralization of Hcl.• bicarbonate secretion provide the suitable pH for bicarbonate secretion provide the suitable pH for

the enzyme.the enzyme.

Extrapancreatic action of secretin H.

a.stimulation of bile secretion form the livers

(choleretic).

b.increase the intestinal movements.

c.inhibit gastric motility and secretion.

B. Cholecystokinin H: (C.C.K.)

- released from the mucosa of the upper

small intestine.

- stimulus is digestive products of protein

and fats.

- Cholecystokinin pancreatic

secretion rich in enzymes and poor in

bicarbonates.

Extra pancreatic action of C.C.K.Extra pancreatic action of C.C.K.

- Evacuation of gall bladder. (cholagouge)- Evacuation of gall bladder. (cholagouge)

- Increase intestinal movements.- Increase intestinal movements.

- Inhibit gastric motility and secretion- Inhibit gastric motility and secretion

Liver and billiary system

Liver functions: Liver functions:

1.1. Secretion of bile.Secretion of bile.

2.2. Destruction of aged RBCs and excretion of bile Destruction of aged RBCs and excretion of bile

pigments.pigments.

3.3. Metabolic functions for carbohydrates, lipids and Metabolic functions for carbohydrates, lipids and

proteins.proteins.

4.4. Filtering the portal blood.Filtering the portal blood.

5.5. Production of red blood cells in fetal liver.Production of red blood cells in fetal liver.

6.6. The liver detoxifies toxic agent.The liver detoxifies toxic agent.

7.7. Storage of iron, vitamins.Storage of iron, vitamins.

8.8. Endocrine function: erythropiotin.Endocrine function: erythropiotin.

9.9. Synthesis of fibrinogen, prothrombin,…Synthesis of fibrinogen, prothrombin,…

10.10. blood reservoir.blood reservoir.

Composition of bile: Composition of bile: Volume 700ml/day, Specific gravity 1050, pH 7-8Volume 700ml/day, Specific gravity 1050, pH 7-8

The main constituents of bile are:The main constituents of bile are:• Water.Water.

• Bile salts 0.5 g/day.Bile salts 0.5 g/day.

• Bile pigments.Bile pigments.

• Cholesterol, fatty acids and lecithin.Cholesterol, fatty acids and lecithin.

• Electrolytes: NaElectrolytes: Na++, K, K++, Ca, Ca++++/ CL/ CL--, HCO, HCO--33..

• Mucin-like substances.Mucin-like substances.

Functions of bile salts:Functions of bile salts:• Digestive: reduce the surface tension of Digestive: reduce the surface tension of

fat molecule emulsification. fat molecule emulsification.

• Bile salts dissolve the insoluble fatty Bile salts dissolve the insoluble fatty acids in water.acids in water.

• Absorption: of fatty acids, bile salts Absorption: of fatty acids, bile salts facilitate the absorption of fat-soluble facilitate the absorption of fat-soluble vitamins (D, E, K,A).vitamins (D, E, K,A).

•Solvents: prevent the precipitation Solvents: prevent the precipitation of cholesterol and fatty acid.of cholesterol and fatty acid.

•Choleretic:bile salts are the best Choleretic:bile salts are the best choleretic.choleretic.

•Anti-putrefactive.Anti-putrefactive.

•Activate pancreatic lipase.Activate pancreatic lipase.

•Mechanism of bile secretion:Mechanism of bile secretion: (choleretics)(choleretics)

1- Humoral mechanisms:1- Humoral mechanisms:• bile salts: is the best choleretics.bile salts: is the best choleretics.

• secretin secretin H.H.

2- Nervous factors: parasympathetic supply 2- Nervous factors: parasympathetic supply (vagus N.).(vagus N.).

3- 3- Increase blood flow.Increase blood flow.

Functions of the gall bladder:Functions of the gall bladder:  

• Storage of bile.Storage of bile.

• Concentration of bile.Concentration of bile.

• Acidification of bileAcidification of bile

• Secretion of white bile (mucus).Secretion of white bile (mucus).

• Buffer of biliary pressure.Buffer of biliary pressure.

• Evacuation of bile when needed.Evacuation of bile when needed.

Gall bladder evacuants: (cholagogues)

Gall bladder evacuants are called cholagogues.

• Hormonal factor: cholecystokinin (CCK).

• Nervous factor: the vagus nerve is motor to the wall of gall bladder.

Functions of the small intestine:Functions of the small intestine: Digestive.Digestive. Absorption.Absorption. Endocrinal.Endocrinal. Movement. Movement.

Digestion in the small intestinal:Digestion in the small intestinal:- luminal digestion.- luminal digestion.

- membrane digestion.- membrane digestion.

The small intestineThe small intestine

Intestinal secretion

Enzymes:• Peptidases: split polypeptides into amino acids,

dipeptidases splits dipeptids into amino acids.

• Disaccharidases:Maltase: maltose glucose + glucose.

Sucrase: Sucrose glucose +fructose.

Lactase: lactose glucose + galactose.

• Lipase: fats monoglycerides+fatty acids.

• Nucleases:nucleic acids pentoses + purine.

• Enterokinase: trypsinogen trypsin.

Regulation of intestinal secretion:

- Local nervous reflexes in response to distention and irritation.

- G.I.T. hormones as, secretin and CCK hormone.

- Vagal stimulation secretes mucus.

Intestinal motility: Two types of movements: segmenting

(mixing) and peristaltic (propulsive).

1- Segmenting movement: ( for mixing )

2- Peristaltic movements:(propulsive movements)

• Normal peristalsis: it is a wave of contraction preceded by a wave of relaxation, speed 0.5 to 2 cm/second.

• Peristaltic rush: Fast peristalsis

• Antiperistalsis: - Between duodenum and stomach.

- Between ileum and coecum.

3- Movements of villi: enhance rate of absorption.

Functions of the large intestine:1- Digestion:

In herbivore cellulose is hydrolyzed into glucose.

2- Absorption:The large intestine can absorb water, glucose, crystalloids, in slower rate than the small intestine about 250 ml/day.

3- Secretion of mucus: it has the following functions:

- Protects the wall.- Holding fecal matter together and lubricates the faeces.- Neutralizes the acid produced by bacterial fermentation.

4- Bacterial action:

Vitamin K, Vit. B complex, and some amino acids.

5- Storage of faeces.

6- Defecation.

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