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Digestive system (Digestive juice)/Function/Composition

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Secretory Function of Alimentary Tract
Digestive juice:
1. Saliva
2. Gastric juice
3. Intestinal juice
4. Pancreatic juice
5. Bile

Published in: Health & Medicine
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Digestive system (Digestive juice)/Function/Composition

  1. 1. DIGESTION Digestive juice secretions Md. Saiful Islam Dept. of Pharmaceutical Sciences North South University Facebook Group: Pharmacy Universe YouTube Channel: Pharmacy Universe
  2. 2. Secretory Function of Alimentary Tract Digestive juice: • 1. Saliva • 2. Gastric juice • 3. Intestinal juice • 4. Pancreatic juice • 5. Bile
  3. 3. Salivary Glands; Characteristics of Saliva. • Salivary Glands; Characteristics of Saliva. • The principal glands of salivation are the parotid, submandibular, and sublingual glands; in addition, there are many very small buccal glands. • Daily secretion of saliva normally ranges between 800 and 1500 milliliters, • Saliva contains two major types of protein secretion: (1) a serous secretion that contains ptyalin (an a-amylase), which is an enzyme for digesting starches, and (2) mucus secretion that contains mucin for lubricating and for surface protective purposes. • The parotid glands secrete almost entirely the serous type of secretion, while the submandibular and sublingual glands secrete both serous secretion and mucus. • The buccal glands secrete only mucus. Saliva has a pH between 6.0 and 7.0, a favorable range for the digestive action of ptyalin.
  4. 4. Function of Saliva for Oral Hygiene. • Under basal awake conditions, about 0.5 milliliter of saliva, almost entirely of the mucous type, is secreted each minute; but during sleep, secretion becomes very little.This secretion plays an exceedingly important role for maintaining healthy oral tissues. The mouth is loaded with pathogenic bacteria that can easily destroy tissues and cause dental caries. Saliva helps prevent the deteriorative processes in several ways. • First, the flow of saliva itself helps wash away pathogenic bacteria as well as food particles that provide their metabolic support. • Second, saliva contains several factors that destroy bacteria. One of these is thiocyanate ions and another is several proteolytic enzymes—most important, lysozyme—that (a) attack the bacteria, (b) aid the thiocyanate ions in entering the bacteria where these ions in turn become bactericidal, and (c) digest food particles, thus helping further to remove the bacterial metabolic support. • Third, saliva often contains significant amounts of protein antibodies that can destroy oral bacteria, including some that cause dental caries. In the absence of salivation, oral tissues often become ulcerated and otherwise infected, and caries of the teeth can become rampant.
  5. 5. Composition A. Water: 99.5% B. Solid:0.5% 1. Organic • Enzyme (Ptyalin, Lysosome) • Mucin • Urea • Cholesterol • Amino acid 2. Inorganic ( Various ion) 3. Cellular constituent (Yeast, bacteria) 4. Gases (N2, O2)
  6. 6. Function: • It keeps the mouth moist and helps in speech. • It facilitates swallowing • It helps in preparing food stuff into bolus • It acts as a lubricant • By dissolving food stuff, saliva helps in taking the taste of food. • It breaks down boiled starch into maltose due to the presence of enzyme ptyalin. • It excretes urea heavy metals, certain drugs. • It helps in acid-base balance • It has bacteriolytic property
  7. 7. Structure of stomach The stomach is an expanded section of the gastrointestinal tract between the esophagus and the duodenum of the small intestine. • The stomach is on the left side of the abdominal cavity with the most superior part laying against the diaphragm • The major regions of the stomach are the cardia, fundus, body and the pylorus. • Additionally it has the greater and lesser curvatures, which are the right and left sides of the stomach, respectively. • The esophageal sphincter is contained within the cardia region. The esophageal sphincter controls the flow of material coming into the stomach. • The fundus is the section of the stomach that is formed by the upper curvature . • the body is the main area of the stomach. • The final part of the stomach is the antrum where the pylorus, the exit of the stomach and entrance to the duodenum of the small intestine is located. • Within the pylorus is the pyloric sphincter that controls what leaves the stomach into the duodenum.
  8. 8. Gastric Anatomy
  9. 9. • The inside of the stomach is composed of four layers, from the innermost layer to the outermost layer: • muscosa, submuscosa, muscularis externa, and the serosa. • The muscosa is where stomach acid is produced and secreted into the stomach. • The submuscosa is layer composed of connective tissue that separates the muscosa from the muscularis externa. • The muscularis externa is composed of three layers of smooth muscle: inner oblique, middle circular, and outer longitudinal. These are the muscles that are primarily responsible for mixing material that has come into stomach with digestive enzymes and moving the material through the stomach. • The final layer is the serosa, which is a layer of connective tissue that attaches and is continuous with the peritoneum, the lining of the abdominal cavity.
  10. 10. • There are three types of gastric gland present in the stomach: 1. Cardiac gland: Mucus secreting cell 2. Gastric gland or oxyntic gland: a. Mucus neck cell: Secrets mainly mucus but also some pepsinogen b. Peptic/Chief cell: Secret large quantities of pepsinogen, gastric renin. c. Parietal/Oxyntic cell: Secret HCl and intrinsic factor. d. Enterochromaffin like cell: Secret gastrin and histamin 3. Pyloric gland: secret mucin and hormone gastrin Gastric secretion
  11. 11. Gastric Glands and secretions
  12. 12. Composition and function of gastric secretions 1. HCl  converts pepsinogen to pepsin for chemical digestion  provides optimal pH environment for pepsin  destroys some bacteria  stimulates the small intestinal mucosa to release secretin and CCK (Cholecystokinin from Greek chole, "bile"; cysto, "sac"; kinin, "move) is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein)  promotes the absorption of Ca2+ and Fe2+ in small intestine
  13. 13. 2. Pepsinogen (precursor of pepsin)  digestion of proteins 3. Mucus  forms a protective barrier: Mucus-bicarbonate barrier 4. Intrinsic factor  combines with vitamin B12 to make it absorbable 5. Gastrin Stimulates gastric acid secretion 6. Histamine Stimulates gastric acid secretion
  14. 14. Gastric acid secretion • The Figure shows schematically the functional structure of a parietal cell (also called oxyntic cell), demonstrating that it contains large branching intracellular canaliculi. The hydrochloric acid is formed at the villus-like projections inside these canaliculi and is then conducted through the canaliculi to the secretory end of the cell.
  15. 15. The chemical mechanism of hydrochloric acid formation consists of the following steps: 1.Chloride ion is actively transported from the cytoplasm of the parietal cell into the lumen of the canaliculus, and sodium ions are actively transported out of the canaliculus into the cytoplasm of the parietal cell. These two effects together create a negative potential of -40 to –70 millivolts in the canaliculus, which in turn causes diffusion of positively charged potassium ions and a small number of sodium ions from the cell cytoplasm into the canaliculus. Thus, in effect, mainly potassium chloride and much smaller amounts of sodium chloride enter the canaliculus. 2. Water becomes dissociated into hydrogen ions and hydroxyl ions in the cell cytoplasm. The hydrogen ions are then actively secreted into the canaliculus in exchange for potassium ions: this active exchange process is catalyzed by H+,K+- ATPase.
  16. 16. In addition, a separate sodium pump actively reabsorbs the sodium ions. Thus, most of the potassium and sodium ions that had diffused into the canaliculus are reabsorbed into the cell cytoplasm, and hydrogen ions take their place in the canaliculus, giving a strong solution of hydrochloric acid in the canaliculus. The hydrochloric acid is then secreted outward through the open end of the canaliculus into the lumen of the gland. 3. Water passes into the canaliculus by osmosis because of extra ions secreted into the canaliculus. Thus, the final secretion from the canaliculus contains water, hydrochloric acid, potassium chloride and a small amount of sodium chloride. 4. Finally, carbon dioxide, either formed during metabolism in the cell or entering the cell from the blood, combines under the influence of carbonic anhydrase with the hydroxyl ions (from step 2) to form bicarbonate ions. These then diffuse out of the cell cytoplasm into the extracellular fluid in exchange for chloride ions that enter the cell from the extracellular fluid and are later secreted into the canaliculus.
  17. 17. Secretion and Activation of Pepsinogen Several slightly different types of pepsinogen are secreted by the peptic and mucous cells of the gastric glands. When pepsinogen is first secreted, it has no digestive activity. However, as soon as it comes in contact with hydrochloric acid, it is activated to form active pepsin. In this process, the pepsinogen molecule, having a molecular weight of about 42,500, is split to form a pepsin molecule, having a molecular weight of about 35,000. Pepsin functions as an active proteolytic enzyme in a highly acid medium (optimum pH 1.8 to 3.5), but above a pH of about 5 it has almost no proteolytic activity and becomes completely inactivated in a short time. So, Hydrochloric acid is as necessary as pepsin for protein digestion in the stomach;
  18. 18. Secretion of Intrinsic Factor. • The substance intrinsic factor, essential for absorption of vitamin B12 in the ileum, is secreted by the parietal cells along with the secretion of hydrochloric acid. • If the acid-producing parietal cells of the stomach are destroyed, which frequently occurs in chronic gastritis, the person develops not only achlorhydria (lack of stomach acid secretion) but often also pernicious anemia because of failure of maturation of the red blood cells in the absence of vitamin B12 stimulation of the bone marrow.
  19. 19. Pyloric Glands—Secretion of Mucus and Gastrin • The pyloric glands are structurally similar to the oxyntic glands but contain few peptic cells and almost no parietal cells. • Instead, they contain mostly mucous cells that are identical with the mucous neck cells of the oxyntic glands. • These cells secrete a small amount of pepsinogen, and an especially large amount of thin mucus that helps to lubricate food movement, as well as to protect the stomach wall from digestion by the gastric enzymes. • The pyloric glands also secrete the hormone gastrin, which plays a key role in controlling gastric secretion.
  20. 20. Regulation of Pepsinogen Secretion • Regulation of pepsinogen secretion by the peptic cells in the oxyntic glands is much less complex than regulation of acid secretion; it occurs in response to two types of signals: 1) stimulation of the peptic cells by acetylcholine released from the vagus nerves or from the gastric enteric nervous plexus, and 2) stimulation of peptic cell secretion in response to acid in the stomach. Therefore, the rate of secretion of pepsinogen, the precursor of the enzyme pepsin that causes protein digestion, is strongly influenced by the amount of acid in the stomach. In people who have lost the ability to secrete normal amounts of acid, secretion of pepsinogen is also decreased, even though the peptic cells may otherwise appear to be normal.
  21. 21. Regulation of gastric secretion :Phases of Gastric Secretion 1. Cephalic Phase 2. Gastric Phase 3. Intestinal Phase
  22. 22. 1. The taste or smell of food, tactile sensations of food in the mouth, or even thoughts of food stimulate the medulla oblongata (green arrow). 2. Parasympathetic action potentials are carried by the vagus nerves to the stomach (pink arrow). 3. This impulse stimulate secretion by parietal and chief cells and stimulate gastrin secretion by endocrine cells. 5. Gastrin is carried through the circulation back to the stomach (purple arrow), where it stimulates secretion by parietal and chief cells. Cephalic Phase Gastrin Circulation Secretions stimulated Taste or smell of food Tactile sensation in mouth Medulla oblongata Vagus nerves Stomach 1 2 3 5 4 Regulation of gastric secretion :Phases of Gastric Secretion
  23. 23. The taste or smell of food, tactile sensations of food in the mouth, or even thought of food sends nerve signals to the medulla oblongata (green arrow). Taste or smell of food Tactile sensation in mouth Thought of food Medulla oblongata Cephalic Phase
  24. 24. Parasympathetic action potentials are carried by the vagus nerves to the stomach (pink arrow). Vagus nerves Cephalic Phase
  25. 25. Cephalic Phase This impulse stimulate secretion by parietal and chief cells and stimulate gastrin secretion by endocrine cells. Gastrin Stomach
  26. 26. Cephalic Phase Gastrin is carried through the circulation back to the stomach (purple arrow), where it stimulates secretion by parietal and chief cells. Gastrin Circulation Secretions stimulated
  27. 27. Cephalic Phase:Summary • Stimulated by sight, smell, and taste of food. • Activation of vagus: – Stimulates chief cells to secrete pepsinogen. – Directly stimulates G cells to secrete gastrin. – Directly stimulates ECL cells to secrete histamine. – Indirectly stimulates parietal cells to secrete HCl. • Continues into the 1st 30 min. of a meal.
  28. 28. Stomach Local reflexes stimulated by stomach distention Distention Secretions stimulated Vagus nervesMedulla oblongata 1. Distention of the stomach activates a parasympathetic reflex. Action potentials are carried by the vagus nerves to the medulla oblongata (green arrow). 2. The medulla oblongata stimulates stomach secretions (pink arrow). 3. Distention of the stomach also activates local reflexes that increase stomach secretions (purple arrow). Gastric Phase 1 2 3
  29. 29. Local reflexes stimulated by stomach distention Distention Vagus nervesMedulla oblongata Distention of the stomach activates a parasympathetic reflex. Action potentials are carried by the vagus nerves to the medulla oblongata (green arrow). Gastric Phase Stomach
  30. 30. Gastric Phase Secretions stimulated The medulla oblongata stimulates stomach secretions (pink arrow). Vagus nerves Stomach Decreased gastric secretions
  31. 31. Gastric Phase Local reflexes stimulated by stomach distention Distention of the stomach also activates local reflexes that increase stomach secretions (purple arrow). Stomach Distention
  32. 32. • Arrival of food in stomach stimulates the gastric phase. • Gastric secretion stimulated by: – Distension. – Chemical nature of chyme (amino acids and short polypeptides). • Stimulates G cells to secrete gastrin. • Stimulates chief cells to secrete pepsinogen. • Stimulates ECL cells to secrete histamine. – Histamine stimulates secretin of HCl. Gastric Phase
  33. 33. 1. Chyme in the duodenum with a pH less than 2 or containing fat digestion products (lipids) inhibits gastric secretions by three mechanisms. 2. Sensory vagal action potentials to the medulla oblongata (green arrow) inhibit motor action potentials from the medulla oblongata (pink arrow). 3. Local reflexes inhibit gastric secretion (orange arrows). 4. Secretin, gastric inhibitory polypeptide, and cholecystokinin produced by the duodenum (brown arrows) inhibit gastric secretions in the stomach. Intestinal Phase Secretin, gastric inhibitory peptide, cholecystokinin Circulation pH<2 or lipids Local reflexes Decreased gastric secretions Medulla oblongata Vagus nerves Vagus nerves 1 2 3 4
  34. 34. Chyme in the duodenum with a pH less than 2 or containing fat digestion products (lipids) inhibits gastric secretions by three mechanisms. pH<2 or lipids Intestinal Phase
  35. 35. Intestinal Phase They cause impulses to go to the medulla oblanga to decrease parasympathetic stimulation of the gastric glands. pH<2 or lipids Medulla oblongata Vagus nerves Vagus nerves Mechanism One Decreased gastric secretions
  36. 36. Intestinal Phase Secondly they set up local reflexes, via neuron in the wall of the gut, that inhibit gastric secretion (orange arrows). pH<2 or lipids Local reflexes Decreased gastric secretions Mechanism Two
  37. 37. Thirdly, they cause the release of 3 local hormones: Secretin, gastric inhibitory polypeptide, and cholecystokinin from the duodenum (brown arrows) which travel via circulation to the gastric gland and inhibit gastric secretions in the stomach. Secretin, gastric inhibitory peptide, cholecystokinin pH<2 or lipids Decreased gastric secretions Circulation Mechanism Three Intestinal Phase
  38. 38. Control Of Gastric Secretions: The Intestinal Phase
  39. 39. 3.Pancreatic juice Composition A.Water: 98.5% B.Solid:1.5% a. Organic: i. Proteolytic enzyme: Trypsin,chemotrypsin ii. Carbohydrate splitting enzyme: Pancreatic amylase iii. Fat splitting enzyme: Pancreatic lipase,phospholipase b. Inorganic: Various ions • Function: 1. Due to the presence of high concentration of different enzyme, pancreatic juice digest all three types of food-Proteins, carbohydrate and fats. 2. Pancreatic juice contain large quantities of bicarbonate which plays an important role neutralizing the acid emptied by the stomach into the duodenum
  40. 40. 4. Intestine Juice Composition I) Water – 98.5% II) Solid – .5% a) Inorganic e.g. Na+, K+, Ca++ etc. b) Organic-Various enzymes -Mucin Functions: • It helps in digestion of food like protein, fat, carbohydrate. • Due to the presence of mucin, it protects intestinal mucosa. • Due to its abundant water content it- -helps in the transport of food particles, ready for absorption. -provides the ready supply of water, needed for hydrolysis of food particles. -dissolves substances like vitamins. -It helps in water balance -It helps in absorption.
  41. 41. 5. BILE Functions of Bile • Digestive function: – Bile helps in the digestion of fat and to a lesser extent of proteins and carbohydrate. • Absorptive function: – Bile helps in the absorption of fat and other substances like fat soluble vitamins, iron, Ca++ etc. – Laxative function: Bile salts increases peristalsis and thereby help in defecation.
  42. 42. THANK YOU

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