Digestive System Question And Answers

Question 1. Describe the composition and functions of saliva. Add a note on the regulation of salivary secretion. (or) Regulation of salivary secretion.
Answer:

Saliva:

• Saliva Composition:
  • Saliva constitutes of
    1. Water-99.5%
    2. Solids -0.5%
       1. Organic substances:
          1. Enzymes:
             • Ptyalin or amylase
             • Lysozyme
             • Kallikerin
             • Lingual lipase Maltase
             • Phosphatase
          2. Other:
          3. Proteins – mucin and albumin.
          4. Blood group antigens.
          5. IgA
          6. Free amino acids
          7. Urea, uric acid, creatinine, xanthine.
       2. Inorganic substances:

1. 1. 1. 1. • \(\mathrm{Na}^{+}, \mathrm{K}^{+}, \mathrm{Ca}^{2+}\)
            • HCO3^–,PO₄^3-, bromide, F^–, CI^–
              

Read And Learn More: BDS Previous Examination Question And Answers

Saliva Functions:

1. Lubrication of food:

• The saliva moistens and dissolves the food that enters in the mouth.
• Saliva also moistens the oral mucusa.
• Mucin present in saliva lubricates the food thus assists mastication and facilitates swallowing.

2. Appreciation of taste:

• Saliva serve as a solvent to dissolve the solid food substances.
• These dissolved particles stimulate the taste buds.

3. Digestive function:

1. Salivary amylase/ptyalin.
   • It is a carbohydrate splitting enzyme.
   • It acts in a neutral or slightly acidic medium
   • Amylase digest starch but not completely.
   • Major part of it is digested in stomach.
   • Amylase converts starch into dextrin and maltose.
2. Maltase.
   • It converts maltose into glucose.
3. Lingual lipase:
   • It converts triglycerides of milk fat into fatty acid and diacylglycerol.

4. Excretion:

• Saliva excretes substances like mercury, potassium iodide, lead and thiocyanate. Saliva also excretes certain viruses such as those causing rabies and mumps.

5. Cleansing action:

• Continuous secretion of saliva washes off the food residues, bacteria and desquamated epithelial cells.
• Mucin in saliva lubricates the oral mucosa and protects the mouth.

6. Regulation of water balance:

7. Regulation of pH balance:

• Proline rich proteins present in saliva binds to toxic substances like tannin and maintain oral pH at 7.0.
• At this pH, saliva is saturated with calcium which protects enamel.

8. Protective:

• Lysosyme kills some bacteria such as staphylococcus, streptococcus and brucella.
• IgA provides defence against bacteria and viruses.
• Lactoferrin – arrests bacterial multiplication.

9. Speech:

• Saliva moisten and lubricate the soft parts of mouth and lips and aids in speech.

Regulation of salivary secretion:

• Salivary glands are under the control of autonomic nervous system which includes both sympathetic and parasympathetic nerve.

2. Stimulation of sympathetic nerve includes 2 types of reflex.

1. Conditioned reflex.
   • Here salivary secretion increases by sight, smell, hearing or thought of food.
   • It is due to impulses arising from eyes, nose, ear, etc.
2. Unconditional reflex.
   • Here, salivary secretion increases when any substances is placed in the mouth.
   • This stimulates the sympathetic fibers.
   • These fibers activates the acinar cells and cause vasoconstriction to secrete noradrenaline.

Question 2. Enumerate any four functions of saliva. Describe the nerve supply to salivary gland and regulation of salivary secretion.
Answer:

Nerve supply to salivary glands:

Salivary glands receive efferent nerve fibers from both parasympathetic and sympathetic divisions of autonomic nervous system.

1. Parasympathetic nerve supply:

1. To parotid gland.

Postganglionic fibers pass through auriculo temporal nerve to supply the gland.

2. To submandibular and sublingual gland.

2. Sympathetic nerve supply:

Around middle meningeal artery to supply parotid gland.

Around facial artery to supply submandibular and sublingual gland.

Question 3. Describe the mechanism of gastric secretion.
Answer:

Mechanism of gastric secretion:

1. Secretion of pepsinogen:

2. Secretion of hydrochloric acid:

• According to davenport theory, it is an active process occurring in parietal cells.
• In parietal cells carbon dioxide is derived from.

1. Blood

2. Metobolic activites of the cell.

↓
Co2 combines with water to form carbonic acid in presence of carbonic anhydrase enzyme.

Carbonic acid splits into [H₂CO₃→ H‾+HCO₃‾]

1. Hydrogen ion- pumped into cnaliculi.

2. Bicarbonate ion.

Bicarbonate enters the blood and combines with sodium ion of sodium chloride and form sodium bicarbonate.

HCO₃‾ + Na+ →→ NaHCO₃

Hydrogen ion combines with chloride ion to form hydrogen chloride. H+ CT-→HCI

Question 4. Discuss the composition, function and regulation of gastric juice.
Answer:

Composition of gastric juice:

1. Water-99.5%
2. Solids-0.5%
   1. Organic substances.
      1. Enzymes.
         • Pepsin helps to digest protein.
         • Renin-curdles milk.
         • Gastric lipase – splits fats
         • Gelatinase digests gelatine.
         • Urease converts urea to ammonia.
         • Carbonic anhydrase – present in small amount
         • Lysozyme-bacteriocidal.
      2. Mucus.
         1. Forms
            • Soluble-vehicle for HCI and enzymes.
            • Insoluble- protects gastric mucosa form HCI.
         2. Intrinsic factor.
            • Helps in absorption of Vit. B12.
      3. Inorganic substances.
         1. Hydrochloric acid.
         2. Cations – Na⁺, K⁺, Ca2⁺
         3. Anions -CI, HCO₃‾, PO₃^3‾, SO₄^2‾

Functions of gastric juice:

1. Digestive function:
   1. Pepsin.
      • Digest protein and convert it into proteases, peptones and polypeptides.
      • It causes curdling and digestion of milk.
   2. Gastric lipase.
      • Hydrolyses fats into fatty acid and glycerols.
   3. Gelatinase-digest gelatine.
   4. Gastric amylase- degrade starch.
2. Hemopoietic function:
   • Gastric juice contains intrinsic factor of castle which is essential for absorption of Vit. B12
   • Vit B12 is one of the maturation factor or erythropoiesis.
3. Protective function:
   • Gastric juice contains mucus which.
     • Protects stomach wall from irritation.
     • Prevents digestive action of pepsin on the stomach wall.
     • Protects gastric mucosa from hydrochloric acid.
4. Functions of hydrochloric acid:
   • Activates pepsinogen into pepsin.
   • Bacterolytic action.
   • Provides acidic media for hormones.

Regulation: of gastric juice:

• The regulation of secretion of gastric juice is broadly brought about by two mechanism.

1. Nervous mechanism:

• It includes.

1. Local myenteric reflex:

Vasovagal reflex.

2. Hormonal mechanism:

• When the food enters tomach, gastrin, a GI hormone is secreted by the G cells present in pyloric glands of stomach.
• This gastrin stimulates the secretion of pepsinogen and hydrochloric acid by the gastric juice.

Question 5. Name phase of gastric secretion and describe in detail. (or) Phases of gastric secretion.
Answer:

Phases of gastric secretion:

1. Cephalic phase:

• Secretion of gastric juice by the stimuli arising from head region is called cephalic phase.
• It occurs even before food enters the stomach.

Gastric Juice secreted:

• Gastric juice secreted during this phase is rich in enzymes and hydrochloric acid.
• 30-50% juice is secreted.

Regulation:

• This phase is regulated by two reflexes.

1. Unconditioned reflex:

Conditioned reflex.

It is stimulation of gastric juice via vagus nerve in response to sight, smell, thought or taste of the food.

2. Gastric phase:

• Once the food enters the stomach, the secretion of gastric juice increases, this is called gastric phase.

Gastric juice secreted:

• Gastric juice secreted during this phase is rich in pepsinogen and hydrochloric acid.
• 50-60% of the total juice is secreted during this phase.

Regulation:

• This phase is regulated by both nervous and hormonal mechanism.

3. Intestinal phase:

• This phase occurs when food enters the duodenum.

Regulation:

1. Initial phase.
   • As the food enters the intestine, it stimulates the duodenal mucosa to release gastrin.
   • This gastrin is transported to stomach where it stimulates the secretory activity of gastric glands.
2. Later stage.
   • After the initial increase in secretion of gastric juice, there is decrease or complete stoppage of secretion of gastric juice.
   • This secretion is inhibited by.
     • Enterogastric reflex.
     • GI hormone.

Question 6. Proteolytic enzymes of pancreas.
Answer:

Proteolytic enzymes:

1. Trypsinogen:

• It is a single long polypeptide chain with molecular weight of 25,000
• It contains 229 amino acids
• It is converted into active trypsin by enterokinase.

Trypsinogen Actions:

• It converts proteins into proteoses and polypeptides by hydrolysis.
• Curdles milk.
• Accelerates blood clotting.
• Activates other enzymes of pancreas.
• It has autocatalytic action.

2. Chymotrypsinogen:

• It is a polypeptide with a molecular weight of 25,700.
• It has 246 amino acids.
• It is activated by trypsin.

Chymotrypsinogen Actions:

• Digests protein to small polypeptides.
• Causes more rapid digestion of milk.

3. Carboxypeptidases:

• They are activated by trypsin.

Carboxypeptidases Actions:

• They break the terminal bond of protein.
• Carboxypeptidase A splits the proteins into amino acids having aromatic side chains.
• Carboxypeptiase B splits the proteins into amino acids having basic side chains.

4. Nucleases:

• They split nucleic acids into mononucleotides.

5. Proelastase:

• Proelastase is activated by trypsin.

Proelastase Actions:

• Causes digestion of elastin and other polypeptides.

6. Collagenase:

• It is also activated by trypsin.
• It digests collagen.
• All these enzymes are secreted in inactive state.
• The inactive granules are activated in the duodenum where they act on proteins.

Question 7. Describe exocrine function of pancreas how are they regulated.
Answer:

Pancreas:

• The pancreas is a double function organ containing both exocrine’ as well as `endocrine’ cells.
• The endocrine function involves the production of the hormones.
• The exocrine function involves the secretion of digestive juice pancreatic juice.
• This pancreatic juice is discharged from apices of the cells into the lumen of the pancreatic ducts.
• The pancreatic juice passes via intercalated and excretory ducts to be collected by two ducts: `duct of Wirsung’ and duct of santorini’.
• The cells of the duct contains zymogen granules, which possess digestive enzymes.

Pancreas Regulation:

1. Pancreas Nervous regulation:

• Reflex stimulation of vagus nerve causes increase in pancreatic juice secretion.
• This is seen with.
  1. Conditioned reflexes,
     Example: sight, smell of food.
  2. Unconditioned reflexes.
     Example: taste of food.
• The afferent impulses during these reflexes reach the dorsal nucleus of vagus.
• From here, the efferent impulses reach the pancreas via efferent fibers of vagus nerve.
• This results in release of acetylcholine which stimulates the acinar cells of pancreas to release the enzymes.

2. Pancreas Humoral regulation:

• GIT hormones on liberation into portal venous blood via systemic circulation reach pancreatic tissue to stimulate the secretion of pancreatic juice.
• They are.
  1. Secretin:
     • Discovered by Bayliss and Starling.
     • It is produced by S cells of mucous membrane in duodenum and jejunum.
       Action:
     • Acts on the cells of pancreatic ductules via cyclic AMP.
     • It causes secretion of large amount of watery juice with high concentration of bicarbonate ion.
     • It also stimulates bile secretion and potentiates the effect of CCK-PZ on the pancreas.
  2. Cholecystokinin-pancreozymin (CCK – PZ):
     • It causes contraction of gall bladder to release bile.
     • Causes secretion of pancreatic juice rich in enzymes.
     • It also increases the secretion of enterokinase.
     • It increases the motility of small and large intestine.
  3. Gastrin:
     • It is produced by the pyloric antrum, duodenum and in some conditions, pancreatic islet tumours.
     • It stimulates pancreatic secretion rich in enzymes.
  4. Vasoactive intestinal polypeptide (VIP):
     • It stimulates pancreatic secretion mainly rich in HCO3, water and to some extent enzymes.
     • It stimulates intestinal secretion of electrolytes and water.

Question 8. Give in detail the functions of liver.
Answer:

Functions of liver:

1. Storage function:

• Liver stores glycogen, fat, protein, vitamin A and B12, iron folic acid and amino acid.

2. Synthetic function:

• Liver synthesizes.
  1. Most of the plasma proteins specially albumin.
  2. Some clotting factors like fibrinogen, prothrombin, factor V, VII, IX and X.
  3. Enzymes like alkaline phosphatase, SGPT, SGOT.
  4. Cholesterol.

3. Secretory function:

• Liver secretes bile.
• Bile contains bile salts, bile pigments, cholesterol, fatty acids and lecithin.
• This helps in.
  1. Activation of lipase.
  2. Breakdown of fats.

4. Metabolic function:

• Liver helps in the metabolism of
  1. Carbohydrate.
     • Liver is a site of glycogenolysis, glycogenesis and gluconeogenesis.
  2. Protein:
     • Liver synthesize plasma proteins, blood clotting factors, enzymes, urea and lipoprotein from amino acids.
  3. Fat.
     • It is site for synthesis of triglycerides, lipoproteins, cholesterol, phospholipids and aceto-acetic acid.

5. Excretory function:

• Liver excretes.
  1. Cholesterol, bile pigments.
  2. Heavy metals like lead, arsenic.
  3. Detoxified drugs
  4. Bacteria like typhoid.
  5. Hormones like thyroid, steroid hormone.

6. Hemopoietic function:

• In fetal life, liver produces RBC.
• It stores.
  1. Vit. B12 – for erythropoiesis.
  2. Iron – for haemoglobin, for production of thrombocytes.

7. Hemolytic function:

• Liver is a part of reticuloendothelial system.
• Thus, senile RBC are destroyed in liver.

8. Heat production:

• As metabolic reactions takes place in liver enormous amount of heat is produce in liver.

9. Inactivation of hormones and drugs:

• Liver catabolizes hormones like growth hormone, parathormone, cortisol, insulin, glucagon, testosterone and estrogen.
• Inactivates fat soluble drugs.
• Converts fat soluble drugs into water soluble substances.

10. Body defence:

• Kupffer cells destroy the bacteria that enter the portal blood by phagocytosis.
• The cells of liver are involved in the production of interleukin and TNF which activates immune system of the body.

11. Detoxification:

• Liver cells are involved in removal of toxic property of various harmful substances.
• It occurs by.
  1. Metabolic degradation.
  2. Conjugation with glucuronic acid/sulfates.

Question 9. Describe different phases of deglutition and their regulation. Answer:

Deglutition:

• It is process by which chewed food is emptied from the mouth into the stomach.

Stages/Phases of Deglutition:

1. Oral phase:

• It is voluntary stage.
• After mastication chewed food, moistened and lubricated by saliva, is rolled into bolus.
• The bolus is placed over posterodorsal surface of the tongue.
• At this, the anterior part of tongue is retracted and depressed while the posterior part is elevated and retracted.
• This pushes bolus into the pharynx.

2. Pharyngeal stage:

• It shows involuntary, complex, closely coordinated movements in the pharynx that pushes the bolus into the oesophagus.
• It lasts for 1-2 seconds.
  • Soft palate is elevated and thrown against posterior pharyngeal wall closing the posterior nares.
    • This prevents the reflux of food into the nasal cavities.
  • Larynx rises with elevation of hyoid bone vocal cords are approximated and breathing is arrested.
    • This prevents entry of food into the larynx.
  • Palatopharyngeal folds approximate to shut off the oral cavity.
    • This prevents the entry of bolus back into the oral cavity.
  • The upward movement of the larynx stretches to opening of the oesophagus.
    • Due to contraction of pharyngeal muscles, peristaltic contractions start in the pharynx.
    • Elevation of larynx also lifts the glottis away from the food passage.
    • Due to all these, the bolus moves easily into the esophagus.

3. Esophageal stage:

• This stage for liquid food lasts for 1-2 seconds and for dry food it lasts for 10 seconds.
• It is also involuntary stage.
• When bolus reaches the oesophagus, the peristaltic waves are intiated, which propel the bolus into the stomach.

Types of peristaltic contractions:

1. Primary peristaltic contractions:
   • It starts as soon as bolus reaches the upper part of oesophagus.
   • As a result of this contraction, a pressure develops to propel the bolus.
   • Initially this pressure is negative which immediately becomes positive.
2. Secondary peristaltic contractions:
   • Due to the distention of upper esophagus by the bolus, secondary peristaltic contractions occurs.
   • These contractions passes down, and propels the bolus into stomach.

Regulation:

Entry of bolus into the oropharyngeal region.
↓
Stimulation of receptors present in the.

1. Mucous membrane covering mouth and pharynx
2. Posterior pharyngeal wall.
3. Soft palate and
4. Epiglottis.

Impulses from these receptors pass via glossopharyngeal nerve to the deglutition center present at the floor of the fourth ventricle in medulla.
↓
Efferent fibers pass through motor fibers of V, VII, IX, X and XII nerves to the pharyngeal musculature and tongue.
↓
This causes.

1. Initiation of pharyngeal stage.
2. Upward movement of soft palate to close nasopharynx.
3. Upward movement of larynx to close respiratory passage.
4. Entry of bolus into oesophagus.

Question 10. What are the stages of deglutition? Describe them in detail with a note on dysphagia.
Answer:

Dysphagia:

• It is the condition of difficulty in swallowing.

Dysphagia Causes:

• Mechanical obstruction of oesophagus.
• Decreased movement of oesophagus.
• Muscular disorders.

Question 11. Explain how starch, sucrose and lactose are hydrolyzed in the gastrointestinal tract. Add a note on glucose absorption.
Answer:

Digestion of carbohydrates in the gastrointestinal tract.

1. Digestion in the mouth:

• While food is chewed in the mouth before it is swallowed it mixes with saliva.
• The chewed food is subjected to the action of salivary a-amylase (ptyalin)
• This a-amylase aids in digestion of starch to produce dextrin and maltose.

2. Digestion in the stomach:

• The action of salivary amylase on starch and glycogen continues in the stomach.
• The HCI present in the gastric juice may hydrolyse some sucrose.

3. Digestion in the small intestine:

• Pancreatic amylase rapidly converts all form of starch into dextrin, maltose and maltroise.
• Its digestive activity is increased by presence of bile salts.
• Succus entericus contains enzymes for splitting disaccharides into monosaccharides.

They are:

1. Sucrase-converts sucrose into glucose and fructose at pH 5-7.
2. Maltase-converts maltose into glucose at pH 5.S-6.2.
3. Lactase-converts lactose into glucose and galactose at pH 5.4-6.0.
4. Dextrinase-converts dextrin into glucose.

Absorption of glucose:

• Glucose is transported from the lumen of small intestine into the epithelial cells in the mucous membrane of small intestine by means of sodium co-transport.
• Glucose first combines with a ‘carrier’ and form glucose-carrier complex.
• This moves the glucose across the lipid barrier of cell membrane and releases the glucose inside the cell.
• The glucose and Na+ have the same carrier called sodium-dependent glucose transporter – 1.
• To concentrate the glucose within the cell, the carrier is coupled to a source of energy which is obtained by the binding process of sodium ion and the glucose molecule to the carrier protein.
• Sodium ion now moves laterally into the intercellular space utilizing the energy liberated by breakdown of ATP.
• The glucose is transported by glucose transporter – 2 into the interstitial space and then to blood capillaries.

Factors effecting glucose absorption:

• Thyroid – increases absorption.
• Adrenal cortex deficiency – decreases absorption.
• In diarrhoea – absorption decreases.

Fate of glucose:

• 5% stored as glycogen in liver and muscle.
• 50-60%-catabolised in tissues.
• 30-40%-converted to fat and stored.

Question 12. Describe the composition, functions and regulation of secretion of pancreatic juice.
Answer:

Pancreatic Juice Composition:

• Pancreatic juice contains
  1. Water-99.5%
  2. Solids -0.5%
     1. Organic substances – enzymes
        • Proteolytic enzymes – trypsinogen, carboxypepditase, elastase
        • Nucleases – deoxyribonucleases
        • Amylolytic – pancreatic amylase
        • Lipolytic pancreatic lipase, phospholipase
     2. Inorganic substances
        • Cations
          • Sodium, potassium, calcium, magnesium, zinc
        • Anions
          • Bicarbonate, chloride, phosphate, sulphate

Pancreatic Juice Functions:

• Digestive function
  • Enzymes present in the pancreatic juice helps in digestion of proteins, lipids and carbohydrates
• Neutralizing action
  • As soon as acidic chyme enters intestine from stomach, large quantity of pancreatic juice with its alkaline bicarbonate content is release into intestine
  • This alkaline bicarbonate neutralizes the acidic chyme
  • Thus, intestine is protected from the destructive action of acidic chyme

Pancreatic Juice Regulation:

Pancreatic Juice Stages:

1. Cephalic phase

Regulated by two reflexes:

• Unconditioned reflex- occurs when food is placed in mouth
• Conditioned reflex – occurs due to sight, smell, hearing or thought of food

Nervous Pathway:

2. Gastric phase

3. Intestinal phase

• Entry of chyme into intestine constitute intestinal phase
• By its entry, hormones are release which may stimulate/ inhibit pancreatic secretion.

Question 13. Composition and functions of saliva.
Answer:

Saliva Functions:

1. Lubrication of food.

• Mucin present in saliva lubricates the food and aids in mastication.

2. Appreciation of taste.

• Saliva dissolve the food particles which stimulate the taste buds.

3. Digestive function.

1. Salivary amylase.
   • Converts starch into dextrin and maltose.
2. Maltase
   • Converts maltose into glucose.
3. Lingual lipase.
   • Converts triglycerides into fatty acid and diacylglycerol.

4. Excretion.

• Saliva excretes substances like mercury, potassium, iodide, lead and thiocyanate.

5. Cleansing action.

• Saliva washes off the food residues, bacteria and desquamated epithelial cells.

6. Regulation of water balance.

• Saliva regulates water balance by decreasing its secretion when the body water content decreases.
• This induces thirst.

7. Regulation of pH balance.

• Proline rich proteins present in saliva maintain oral pH at 7.0.

8. Protective.

• Lysosyme kills bacteria.
• IgA- protects against bacteria and virus.
• Lactoferrin – Bacteriostatic.

9. Speech.

• Saliva moisten and lubricate the soft parts of mouth and lips and aids in speech.

Question 14. Functions of stomach.
Answer:

stomach Functions:

1. Mechanical function:

1. Storage function:
   • Stomach serves as a reservoir for the food ingested.
   • Food remains in the stomach for 22-3 hours and passes gradually into the intestine.
   • This provides enough time for proper digestion and absorption of food substances in the small intestine.
2. Formation of chyme:
   • The peristaltic movements of stomach mix the bolus with gastric juice and convert it into chyme.

2. Digestive function:

1. Enzymes present in the gastric juice of stomach helps in the digestion of various nutritive substances.
   • Pepsin digest proteins.
   • Amylase digests starch.
   • Lipase – hydrolyses fatty acid.
   • Gelatinase digests gelatin.
   • Urease converts urea into ammonia.

3. Protective function:

• Thick mucus is present in gastric juice.
• This mucus.
  1. Protect stomach wall from irritation.
  2. Prevents digestive action of pepsin on stomach wall.
  3. Protects gastric mucosa from HCI.

4. Hemopoietic function:

• Intrinsic factor is present in gastric juice.
• This is necessary for absorption of Vit B₁₂ from the small intestine.
• Vit  B₁₂ is one of the maturation factor for erythropoiesis.

5. Excretory function:

• Many substances like toxins, alkaloids, metals are excreted through gastric juice.

Question 15. Composition and functions of pancreatic juice.
Answer:

Pancreatic Juice Composition:

• Pancreatic juice contains:
  1. Water-99.5%.
  2. Solids -0.5%.
     1. Organic substances: enzymes
        1. Proteolytic.
           • Trypsinogen.
           • Carboxypeptidase
           • Elastase
        2. Nucleases-deoxyribonuclease
        3. Amylolytic pancreatic amylase
        4. Lipolytic.
           • Pancreatic lipase
           • Phospholipase
     2. Inorganic substances.
        1. Cations.
           • Sodium, potassium, calcium, magnesium, zinc.
           • Na⁺ and K⁺ remains constant on changing rate of secretion.
     3. Anions:
        • HCO₃^–, CI^–, phosphate, sulphate.
        • At high secretory rates, CI^– conc. falls and HCO₃^–, conc. rises and total concentration of these two anions remains constants.

Functions of pancreatic juice:

1. Digestive function:

• Enzymes present in the pancreatic juice help in the digestion of proteins, lipids and carbohydrates.
  1. Proteolytic enzymes.
     1. Trypsinogen – converts proteins into proteoses and polypeptides.
     2. Chymotrypsinogen – digest proteins into polypeptides
     3. Nucleases converts nucleic acids into nucleotides
     4. Elastase digest elastin.
     5. Collagenase digests collagen.
  2. Lipolytic enzymes.
     • Hydrolyzes triglycerides into monosaccharide and fatty acids.
  3. Amylolytic enzymes.
     • Pancreatic amylase – converts starch into dextrin and maltose.

2. Neutralizing action:

• As soon as acidic chyme enters intestine from stomach, large quantity of pancreatic juice with its
• alkaline bicarbonate content is release into intestine.
• This alkaline bicarbonate neutralizes the acidic chyme.
• Thus, intestine is protected from the destructive action of acidic chyme.

Question 16. Name the bile slats and describe their functions.
Answer:

Bile salts:

• Bile acids namely glycocholic acid and taurocholic acid combine with sodium or potassium ions to form bile salts.
• Bile salts thus formed are:
  1. Sodium or potassium glycocholate.
  2. Sodium or potassium tauracholate.

Bile salts Functions:

1. Emulsification of fats.

• Bile salts decreases the surface tension of the fats by their detergent action.
• Due to this, the lipid granules are broken into minute particles which can be easily digested by lipolytic enzymes and absorbed in small intestine.

2. Absorption of fats.

• Bile salts combine with lipids to form micelles which are water soluble complexes from which the lipids can be more easily absorbed.

3. Choleretic action.

• Bile salts stimulate the secretion of bile from liver.

4. Cholague action.

• Bile salts increases the release of bile from gall bladder by stimulating the secretion of hormone cholecystokinin.

5. Laxative action.

• Bile salts act as laxatives by stimulating peristaltic movements of the intestine.

6. Prevention of gallstone formation.

• Bile salts prevent the formation of gallstone by keeping the cholesterol and lecithin in solution.

Question 17. Functions of bile.
Answer:

bile Functions:

1. Functions of bile salts of bile.

• Help in digestion and absorption of fats.
• Help in absorption of fat soluble vitamins.
• Act as laxatives.
• Prevent gallstone formation.
• Have choleretive and cholagogue action.

2. Neutralization of acid.

• Bile contains alkali which neutralized the acidic chyme.

3. Excretion.

• Bile excretes.
• Bile pigments.
• Drugs, toxins, hormones.
• Cholesterol, lecithin.
• Alkaline phosphates.

4. Antiseptic.

• Bile inhibits the growth of bacteria by its detergent action.

5. Lubrication function.

• The mucin in bile acts as a lubricant for the chyme in intestine.

Question 18. Functions of liver.
Answer:

Functions:

1. Storage function.

• Liver stores glycogen, fat, protein, vitamin A and B12, iron, folic acid and amino acid.

2. Synthetic function.

• Liver synthesizes.
  1. Most of the plasma proteins.
  2. Some of the clotting factors.
  3. Enzymes.
  4. Cholesterol.

3. Secretory function.

• Liver secretes bile.

4. Metabolic function.

• Liver helps in the metabolism of carbohydrates, proteins and fats.

5. Excretory function.

• Liver excretes.
  1. Cholesterol, bile pigments.
  2. Heavy metals like lead, arsenic.
  3. Detoxified drugs.
  4. Bacteria.
  5. Hormones like thryroid, steroid hormone.

6. Hemopoietic function.

• In fetal life, liver produces RBC.
• It stores.
  1. Vit B₁₂ – for erythropoiesis.
  2. Iron- for haemoglobin.
• It produces thrombopoietin for production of thrombocytes.

7. Hemolytic function.

• Senile RBC are destroyed in liver.

8. Heat production.

• Liver is a site for many metabolic reactions thus enormous amount of heat is produced.

9. Inactivation of hormones and drugs.

• Catabolises hormones.
• Inactivates fat soluble drugs.

10. Body defence.

• Kupffer cells destroy the bacteria entering portal circulation.

11. Detoxification.

• Liver cells are involved in removal of toxic property of various harmful substances.

Question 19. Functions of gall bladder.
Answer:

1. Storage of bile.

• Bile secreted from liver is stored in gall bladder and released into intestine only intermittently.

2. Concentration of bile.

• The mucosa of gall bladder rapidly reabsorbs water and electrolytes.
• But bile salts, bile pigments, cholesterol and lecithin are not reabsorbed.
• Thus, concentration of these substances increases in bile.

3. Alteration of pH bile.

• Rapid absorption of HCO3, Na+ and CT, decreases the bile pH from 8.6 to 7.4.

4. Secretion of mucin.

• Gall bladder secretes mucin which makes the bile viscous.

5. Regulation of pressure in biliary system.

• During fasting, rate of secretion of bile is low and pressure in the biliary system in small.
• When the pressure of bile in bile duct is above 7 cm H2O, bile passes without resistance along the cystic duct into the gall bladder.

Question 20. Mention of functions of large intestine.
Answer:

Functions of large intestine:

1. Absorptive function:

1. Large intestine help in absorption of.
   1. Water main site for its absorption are caecum and ascending colon.
   2. Electrolytes.
      • Na+, K+, Cl-
      • Na+ is actively absorbed from the colon and water follows along the osmotic gradient thus generated.
   3. Organic substances like glucose and vitamins
   4. Alcohol and drugs.

2. Formation of faeces:

• After the absorption of nutrients, water and other substances, the unwanted substances in the large intestine form faeces.

3. Excretory function:

• Large intestine excrete heavy metals like mercury, lead, bismuth and arsenic.

4. Secretary function:

• Large intestine secretes
• Mucin.
• Lubricates the intestinal mass.
• Neutralizes the acid formed.
• Inorganic substances like chloride and bicarbonates.

5. Synthetic function:

• The colonic bacterial flora synthesizes vitamin B12, K and folic acid.

Question 21. Describe the small intestine movements.
Answer:

Movements of small intestine:

1. Mixing movements:

1. Segmentation movements.
   • These movements occurs in rhythmic fashion.
   • Segmental contractions occur at regularly spaced intervals along a section of intestine.
   • The segments of intestine in between the constricted segments are relaxed.
   • This results in ring appearance resembling the chain of sausages.
   • The constricted part later relaxes and relaxed part constricts.
   • This process is repeated over and over again aids in mixing of chyme with digestive juices.
   • Pendular movement.
   • Loops of intestine sweep forward and backward or upward and downward resembling the movements of pendulum in the clock.
   • This facilitates mixing of bolus with the digestive enzymes.

2. Propulsive movements:

1. Peristaltic movement.
   • Peristalsis is a coordinated reaction in by a wave of relaxation passes down a hollow viscus.
   • These waves propel the intestinal contents towards ileo-caecal vale.
   • The peristaltic contractions are always weak and usually disappear after travelling for few centimetres.
   • So the chyme requires several hours to travel from duodenum to the end of small intestine.
   • The peristaltic wave increases to a great extend immediately after a meal.
2. Peristaltic rush.
   • It occurs due to excessive irritation of intestinal mucosa or extreme distention of the intestine.
   • This peristaltic rush sweeps the contents of intestine into the colon with few minutes.

3. Peristalsis in fasting – migrating motor complex:

• It occurs during the long periods of fasting.
• It occurs once in every 1/2 to 2 hours.
• The migrating motor complex sweeps the excess digestive secretions into the colon and prevents the accumulation of the secretions in stomach and intestine.

4. Movements of villi:

• The movements of villi are shortening and elongation which helps in emptying lymph from the central lacteal into the lymphatic system.
• The surface area of villi is increased during elongation which aids in absorption of digested food particles from the lumen of intestine.

Question 22. Give an account of the factors influencing gastric emptying. Answer:

Factors influencing gastric emptying:

1. Volume of gastric content.

• Gastric emptying is directly proportional to the volume.
• More the content, rapidly it is emptied into the intestine.

2. Consistency of gastric content.

• Rate of gastric emptying is directly proportional to the square root of volume of liquid meal remaining in the stomach.
• Liquids leave the stomach rapidly.
• Solids move out of the stomach only after being converted into fluid or semifluid.

3. Chemical composition.

4. pH of the gastric content.

• The gastric chyme with low pH leaves the stomach slowly.

5. Osmolar concentration of gastric content.

• The gastric content, which is isotonic to blood, leaves the stomach rapidly than the hypotonic and hypertonic content.

6. Products of protein digestion and acid in duodenum act via stimulating receptors in the duodenal mucosa and decrease gastric emptying.

7. Size of duodenal osmoreceptors.

1. Hypo-osmolar chyme.
   • Causes distension of osmoreceptors.
   • Mildly inhibit the rate of gastric emptying.
2. Hyperosmolar chyme.
   • Causes shrinkage of osmoreceptors.
   • Markedly inhibit the gastric emptying.

Question 23. Write a note on peristalsis.
Answer:

Definition:

• Peristalsis is a coordinated reaction in which a wave of contraction preceded by a wave of relaxation passes down a hollow viscus.

Features:

• It can occur in either direction from a stimulated point but it normally lies out rapidly in oral direction, while continuing for considerable distance towards the anus.
• They are usually superimposed upon rhythmic segmental contractions.
• It is always weak and usually disappears after travelling for few centimetres.
• So the chyme requires several hours to travel from duodenum to the end of small intestine.
• The peristaltic wave increases to a great extend immediately after a meal.

Function:

• The peristaltic waves propel the intestinal contents towards ileo-caecal valve.

Regulation:

• Stimulus for the peristaltic waves is distension.
• As a result of distension, peristaltic waves pass along the intestine towards the rectum.
• The local stretch releases serotonin, which activates sensory neurons that stimulates the myenteric plexus called “myenteric reflex”.

Question 24. Mass peristalsis.
Answer:

Mass peristalsis:

• They are simultaneous contractions of the smooth muscle occurring at the same time over a large portion of the colon.

Features:

• They occur more in the descending and sigmoid colon.
• It occurs only a few times every day.
• The duration is about 10 minutes in the morning before or after breakfast.

Function:

• They propels the faeces from colon towards anus.
• They are the predominant contraction force during defecation.

Regulation:

• It is regulated by gastrocolic reflex and parasympathetic stimulation.

Question 25. Gastrin.
Answer:

• Gastrin is a peptide with 34 amino acid residues.

Sources of secretion:

• G cells of pyloric glands of stomach.
• TG cells in stomach, duodenum and jejunum.
• Islets in fetal pancreas.

Actions:

• Stimulates gastric secretion and motility.
• Promotes growth of gastric mucosa.
• Stimulates release of pancreatic hormones.
• Stimulates secretion of pancreatic juice.

Factors effecting gastrin secretion:

1. Factors that increase gastrin secretion.

• Peptides and amino acids
• Distension of pyloric antrum.
• Increased vagal discharge.
• Calcium.
• E-pinephrine.

2. Factors that inhibit gastrin release.

• Acid in the antrum by release of so matostatin.
• Hormones like.
• Secretin.
• Gastric inhibitory peptide (GIP)
• Vasoactive intestinal peptide (VIP).
• Glucagon
• Calcitonin.

Question 26. Composition and functions of gastric juice
Answer:

Composition Of Gastric Juice:

1. Water-99.5%
2. Solids -0.5%
   1. Organic substances
      1. Enzymes
         • Pepsin – helps to digest proteins
         • Renin-curdles milk
         • Gastric lipase – splits fats
         • Gelatinase-digests gelatin
         • Urease-converts urea to ammonia
         • Carbonic anhydrase – present in small amount
         • Lysozyme-bacteriocidal
      2. Mucus
         Forms:
         • Soluble vehicle for HCl and enzymes
         • Insoluble – protects gastric mucosa to form HCI
      3. Intrinsic factor
         • Helps in absorption of vit B12
   2. Inorganic substances
      1. Hydrochloric acid

Functions Of Gastric Juice:

1. Digestive function

1. Pepsin
   • Digest proteins and converts it into proteases, peptones and polypetides
   • It causes curdling and digestion of milk
2. Gastric lipase
   • Hydrolyses fats into fatty acid and glycolysis
3. Gelatinase
   • Digests gelatine
4. Gastric amylase – degrades starch

2. Haemopoietic function

• Gastric juice contains intrinsic factor of castle which is essential for absorption of Vit B₁₂
• Vitamin B₁₂ is one of the maturation factor of erythropoeisis

3. Protective function

• Gastric juice contains mucus which
• Protects stomach wall from irritation
• Prevents digestive action of pepsin on the stomach wall
• Protects gastric mucosa from hydrochloric acid

4. Functions of hydrochloric acid

• Activates pepsinogen into pepsin
• Bacteriolytic action
• Provides acidic media for hormones

Question 27. Describe the composition, function and regulation of succus entericus.
Answer:

Succus entericus:

• Secretions of small intestine is called succus entericus

Composition:

1. water-98.5%
2. solids-1.5%
   1. inorganic substances -0.7%
      • sodium.
      • calcium
      • magnesium
      • potassium
      • chloride
      • bicarbonate
      • phosphate sulphate
   2. organic substances – 0.8%
      • enzymes
      • Enterokinase
      • Amylolytic
      • Lipolytic
      • Proteolytic
      • mucous
      • intrinsic factor
      • defensins

Functions:

• Digestion
  • Amylolytic enzymes like dissacharidases splits dissacharides into monosaccharides
  • Proteolytic enzymes converts peptides into aminoacids
  • Lipolytic enzymes converts triglycerides into fatty acids
• Protective function
  • Mucous protects intestinal wall from acid chyme, prevents ulcer
  • Defensins – have antimicrobial property
• Other function
  1. Enterokinase activates trypsinogen into trypsin
  2. Intrinsic factor – helps in erythropoiesis

Regulation:

• Nervous regulation
  • Entry of chyme into small intestine
  • Mucosa is stimulated
  • Development of local reflexes
  • Stimulation of glands of intestine
• Hormonal regulation
  • Entry of chyme into small intestine
  • Secretion of enterocrinin, secretin and cholecystokinin
  • Stimulates intestinal glands
  • Promotes secretion of succus entericus

Question 28. Movements of large intestine.
Answer:

1. Mixing movements – segmentation contractions

• Large circular constrictions which appear in the colon are called mixing segmentations contractions
• Types:
  • Type I
    • Low pressure
    • Frequency-10-12/min
    • Duration – 5 sec
    • Aids in mixing of contents of colon
  • Type II
    • Large pressure
    • Frequency-1-2/min
    • Duration 30 sec
    • Aids in mixing of contents of colon Facilitates absorption

2. Propulsive movements – mass peristalsis

• It propels the faeces from colon towards anus
• Occurs few times every day
• Duration – 10 min in morning before or after breakfast
• Types
  • Type III
    • Small pressure
    • Longer duration
    • Propel contents towards rectum
  • Type IV
    • Occurs over large portion of colon simultaneously
    • Lasts for 3-4 min
    • Serve to empty the colon rapidly

Question 29. Describe the mechanism of secretion of HCI by the gastric mucosa.
Answer:

• HCI secretion is active process occurring in the canaliculi of parietal cells in gastric glands
• Carbon dioxide is formed from metabolic activity combines with water and forms carbonic acid in presence of carbonic anhydrase
  • Carbonic acid quickly splits into hydrogen ion and bicarbonate ion
• H+ ion is pumped into the lumen of canaliculi in exchange of ATP
  • Clion enters the canaliculi actively
  • It is derived from NaCl in blood
• NaCl -> Na+ + Cl
  • Bicarbonate ion combines with sodium ion to form sodium bicarbonate
• Na+ HCO₃ -> NaHCO₃
  • Thus H+ ion and Clion combines in the lumen of canaliculi to form HCl

Question 30. Saliva.
Answer:

Properties:

1. Volume 1000-1500 ml of saliva is secreted per day.
2. pH-slightly below 7.0 under resting state, and 8.0 during active secretion.
3. Specific gravity – 1.002 – 1.012.
4. Tonicity hypotonic to plasma.

Composition:

• Water 88.5%
• Solids 0.5%
• Organic substances
• Enzymes
• Proteins
• IgA
• Free amino acids
• Urea, uric acid, creatinine.
• Inorganic substances.

Functions:

• Lubrication of food
• Appreciation of taste
• Digestion
• Excretion
• Cleansing action
• Regulation of water balance
• Regulation of pH balance.
• Protection
• Speech.

Question 31. Cephalic phase of gastric secretion.
Answer:

Cephalic phase:

• Secretion of gastric juice by the stimuli arising from head region is called cephalic phase.
• It occurs even before food enters the stomach.
• Gastric juice secreted during this phase is rich in enzymes and hydrochloric acid.
• About 30-50% of total juice is secreted during this phase.
• It is regulated by conditioned and unconditioned reflex.

Question 32. Functions of stomach.
Answer:

1. Mechanical function:

• Storage function.
• Stomach stores the ingested food and gradually pass it into intestine.
• Formation of chyme.
• The peristaltic movements of stomach mix the bolus with gastric juice and convert it into chyme.

2. Digestive function:

• Enzymes present in the gastric juice of stomach helps in the digestion of various nutritive substances.

3. Protective function:

• Thick mucus present in gastric juice protects the stomach wall from injury and from the action of pepsin and hydrochloric acid.

4. Hemopoietic function:

• Gastric juice contains intrinsic factor essential for the absorption of Vit B12 from intestine.

5. Excretory function:

• Many substances like toxins, alkaloids, metals are excreted through gastric juice.

Question 33. Proteolytic enzymes of pancreas.
Answer:

Question 34. Mention the enzymes of pancreatic juice.
Answer:

Enzymes of pancreatic juice:

1. Proteolytic enzymes:

• Trypsinogen.
• Chymotrypsinogen
• Procarboxypeptidase
• Proelastase

2. Nuclease enzyme:

• Deoxyribonuclease

3. Amylolytic enzymes:

• Pancreatic amylase

4. Lipolytic enzymes:

• Pancreatic lipase
• Phospholipase.

Question 35. Pancreozymin.
Answer:

• It is polypeptide in nature.
• Its secretion is stimulated by the entry of semi digested food into the duodenum.
• It is secreted by I cells in duodenal and jejunal mucosa.

Actions:

• It causes contraction of gall bladder to release bile.
• Causes secretion of pancreatic juice rich in enzymes.
• It also increases the secretion of enterokinase.
• It increases the motility of small and large intestine.

Question 36. Bile.
Answer:

• Bile is formed in liver.
• It is both secretory and excretory in nature.
• It enters the digestive tract along with pancreatic juice through the common opening called ampulla of water.

Properties:

• Volume-800- 120 ml/day
• Color – golden yellow/greenish fluid.
• pH-8-8.6 (alkaline)
• Specific gravity – 1.010-1.011

Composition:

1. Water- 87.6%
2. Solids 2.4%
   1. Organic substances.
      • Bile salts.
      • bile pigments
      • Cholesterol
      • Fatty acids
      • Lecithin
      • Mucin.
   2. Inorganic substances.
      • Na⁺,Ca²⁺,K⁺

Question 37. List functions of liver.
Answer:

Functions of liver:

• Storage function.
• Synthetic function
• Secretory function
• Metabolic function
• Excretory function
• Hemopoietic function
• Hemolytic function
• Heat production.
• Inactivation of hormones and drugs
• Body defence.
• Detoxification.

Question 38. Functions of bile:
Answer:

Functions of bile:

1. Functions of bile salts of bile.
   • Help in digestion and absorption of fat
   • Help in absorption of fat soluble vitamins
   • Act as laxatives
   • Prevent gall stone formation.
   • Have cholerectic and cholagague action.
2. Neutralizes the acid of chyme.
3. Excretes substances like bile pigments, drugs toxins, etc.
4. Inhibits the growth of bacteria.
5. Mucin in bile lubricates the chyme.

Question 39. Bile salts.
Answer:

• Bile salts are formed by combining bile acids with sodium or potassium ion.

Functions:

• Emulsification of fats
• Absorption of fats
• Choleretic and cholagogue action
• Act as laxative
• Prevent gallstone formation.

Fate:

• Out of the total bile salts which enter the duodenum, 90-95% are reabsorbed actively from the terminal ileum in the portal vein and return to the liver, to be excreted again.
• This is called entero-hepatic circulation.
• Remaining 5-10% enter the colon and is excreted in stools.

Question 40. Gall blader.
Answer:

• The bile secreted from liver is stored in gall bladder.
• The capacity of gall bladder is approx 50 ml.

Functions:

• Storage of bile.
• Concentration of bile
• Alteration of pH of bile.
• Secretion of mucin
• Maintains pressure in biliary system.

Question 41. Peristalsis.
Answer:

Definition:

• Persistalsis is a coordinated reaction in which a wave of contraction preceded by a wave of relaxation passes down a hollow viscus.

Function:

• The peristaltic waves propel the intestinal contents towards ileo-caecal valve.

Regulation:

• It is regulated by “myenteric reflex”.

Question 42. Movements of small intestine.
Answer:

1. Mixing movements:

• They are responsible for proper mixing of chyme with digestive juices they are.
• Segmentation contractions.
• Here chyme is segmented and mixed together with digestive juices.
• Pendular movement.
• Small protions of intestine sweep forward and backward like pendulum.

2. Propulsive movements:

• They are involved in pushing the chyme in the aboral direction of intestine.
• They are.
• Peristaltic movements.
• Peristaltic rush.

3. Peristalsis in fasting:

• It occurs in stomach and small intestine during the long periods of fasting.

4. Movements of villi:

• It includes elongation and shortening which help in emptying lymph from the central lacteal into the lymphatic system.

Question 43. Pharyngeal stage of deglutition.
Answer:

• It is a reflex process.

Events:

Question 44. Deglutition.
Answer:

Definition:

• It is a process by which chewed food is empotied from the mouth into the stomach.

Stages:

1. Oral stage:

• It constitutes the passage of food through the oral cavity towards the pharynx by the tongue.
• It is voluntary.

2. Pharyngeal stage;

• It is involuntary, complex, closely coordinated movements in the pharynx that pushes the bolus into the oesophagus.

3. Oesophageal stage:

• It is involuntary.
• As soon as bolus reaches the oesophagus, peristaltic waves are initiated which propel the bolus into stomach.

Question 45. Mastication.
Answer:

• It is the mechanical process occurring in GI tract which breaks up larger food particles into smaller pieces.

Significance:

• Makes easy swallowing of food
• Mixes the food with saliva thoroughly
• Lubricates and moistens dry food.
• Increases surface area of food particles for better digestion.
• Appreciation of taste.

Muscles of mastication:

• Masseter
• Temporal
• Pterygoids
• Buccinator

Question 46. Name two hormones acting on pancreas.
Answer:

Question 47. Jaundice.
Answer:

Definition:

• Jaundice is a yellow discoloration of the skin, eyes, mucous membrane and deeper tissues due to increased accumulation of bilirubin in the plasma and tissue fluids.

Value:

• Normal serum bilirubin level -0.2-0.8 mg/dl
• In jaundice – more than 2 mg/dl.

Types:

Question 48. Hemolytic jaundice.
Answer:

Cause:

• Excessive breakdown of RBCs.

Laboratory investigation:

1. Van den bergh test – indirect positive.

2. Blood.

1. Blood smear.
   • It shows anaemia, reticulocytosis and abnormal RBC.
2. Plasma.
   • Plasma proteins normal.
3. Bilirubin – unconjugated.
4. Serum alkaline phosphatise level-normal.

3. Urine.

1. Bilirubin – absent.
2. Urobilinogen – increased.

4. Faeces.

1. Stercobilinogen – increased
2. Faecal fat-normal.

5. Liver.

• Liver function normally

Question 49. Bile pigments.
Answer:

• Bile pigments are the excretory products in bile.

Bile pigments:

1. Bilirubin.

2. Biliverdin.

Formation and circulation:

Senile RBC are destroyed and haemoglobin is released.
↓
Hemoglobin into.

1. Globin

2. Heme.

• Heme split into.

1. 1. Iron-stores in iron pool.
   2. Biliverdin.

Biliverdin is reduced to unconjugated bilirubin.
↓
Bilirubin is released into blood and transported to liver through albumin.
↓
Here, it becomes conjugated.

Fate:

1. 50% of bilirubin

• Converted into urobilinogen.

2. Remaining 50%.

• Absorbed into blood
• Re-enters the liver.
• Re-excreted in bile.

Question 50. Phases of gastric secretion.
Answer:

1. Cephalic phase

• It occurs even before food enters the stomach

2. Gastric phase

• Once the food enters the stomach, the secretion of gastric juice increases, this is called gastric phase

3. Intestinal phase

• Occurs when food enters duodenum

Question 51. Name any four gastrointestinal hormones.
Answer:

Gastrointestinal hormones are:

• Gastrin
• Secretin
• Cholecystokinin
• Gastric inhibitory peptide
• Vasoactive intestinal polypeptide
• Pancreatic polypeptide
• Somatostatin
• Peptide YY