1. M.Pharm (Pharmacology)
Digestive System
Disha Parikh
M.Pharm (Pharmacology)

2. The digestive system comprises of alimentary canal or gastrointestinal tract (GIT) and some accessory organs.
The tract starts from mouth and ends at anus
GIT mainly involves:
Mouth
Pharynx
Oesophagus
Stomach
Small intestine
Large intestine
Rectum
Anus
The Accessory organs are:
Pancreas
Liver
Gall bladder

4. The activity of digestive system involves the following:
Ingestion: Taking the food into the alimentary canal (eating or drinnking)
Propulsion: Mixing and moving the contents along the tract.
Digestion: it consist of:
Mechanical breakdown of food: Mastication (the processes of grinding & tearing of food and mixing with saliva involve movement of jaws, cheeks, lips and tongue)
Chemical digestion: large food molecules are converted to small molecules by the enzymes present in digestive juices produced by digestive glands and accessory organs.
Absorption: the process by which the digested food substances pass through the walls of GIT into the blood circulation and is used by the body cells.
Elimination: the undigested and unabsorbed food is excreted out of GIT in form of faeces by the process of defecation.

5. Oral Cavity

6. The first enlarged part of tract is the oral cavity.
The oral cavity is lined throughout with mucous membrane, containing startified squamous epithelium conataing small mucus secreting glands.
The part of mouth between the gums and the cheeks is called vestibule.
The dome shaped roof of the oral cavity is called palate.
The front part is hard palate and behind is the soft palate.
The muscular fold hanging from the middle of the soft palate is called uvula.
At the arch of the soft palate the pharyngeal tonsils are present which act as gate keepers and protect against the infection.

8. TONGUE:
The voluntary muscular structure present at the floor of the mouth.
It is attached to the base by the thin membranous covering called frenulum.
The surface of the tongue consist of stratified squamous epithelim with numerous papillae (little projections acting as sensory receptors) and taste buds (sense of taste).
The papillae are of following types:
Filiform papillae: narrow and conical in shape distributed all over the tongue. Taste buds are absent in filiform papillae.
Fungiform papillae: present at the tip and edges of the tongue consist of few taste buds. More in no. as compared to filiform papillae.
Circumvallate papillae: these are the largest papillae present at the base of the tongue. They are arranged as inverted ‘V’ shape at the base of the tongue.
The taste buds are present on the sides of the papillae.

9. The tongue plays an important role in mastication (chewing), deglutition (swallowing), speech and taste.

10. M:Molars, P: Pre-molars, C: Canines, I: Incisors
TEETH
There are =32 teeth in mouth that are fixed in the socket in the upper jaw (maxilla) and the lower jaw (mandible).
The order of the teeth from front to back is incisors, canines, pre-molars and molars.
Right : M P C I I C P M :Left
Upper jaw: :Upper jaw
Lower jaw: :Lower jaw
M:Molars, P: Pre-molars, C: Canines, I: Incisors

11. Function of the teeth:
The incisor and canine are the cutting teeth and are used for the bitting off the pieces of the food.
The premolar and molar are broad and flat surface teeth used for the grinding and chewing of the food.
Structure of tooth:
Enamel The hard outer layer of the crown. Enamel is the hardest substance in the body.
Dentine Not as hard as enamel, forms the bulk of the tooth and can be sensitive if the protection of the enamel is lost.
Pulp Soft tissue containing the blood and nerve supply to the tooth. The pulp extends from the crown to the tip of the root.
Cementum The layer of bone-like tissue covering the root. It is not as hard as enamel.

12. 3 pairs of salivary glands are present: Parotid gland
Submaxiliary or Submandibular gland
Sublingual gland
Parotid gland: situated besides the second upper molar and below the ear. The gland is present on either sides. It secretes ptyaline (digestion of starch). The duct opens on either side of cheeks
Submaxiliary gland: they are situated on each side at bottom of the mouth. The duct opens on the tongue. About 70% of saliva is produced by it.
Sublingual gland: they are situated bellow the tongue. The duct opens on both the sides of the fernulum.

13. SALIVA:
It is the secretion form the salivary glands which contains water, inorganic salts, NaCl, KCl, enzymes such as ptyalin (salivary amylase), phosphatase, lipase ; lysozymes and mucin.
The pH of saliva is slightly acidic (6-7).
Functions of saliva:
Chemical Digestion: saliva contains amylase enzyme which converts compound sugars to simple sugars.
Starch
Amylase
Maltose
Maltase
Glucose
Lubrication of food: dry food is lubricated by saliva which can be easily swallowed. Also prevent damage due to rough food.
Cleaning: adequate flow of saliva cleans the mouth, keep it soft and moist.
Non- specific defense: lysosomes present in saliva may combat with the invading microbs.
Taste: the taste of the food can be only sensed if the food gets mixed with the saliva.

14. Protection: it dilute hot and pungent substances and prevent injury to the mouth.
Other functions:
It helps in mastication and formation of bolus.
It facilitates in speech .
It helps in sensation of thirst thus maintain water balance.
It acts as buffer by maintaining the level of bicarbonate and phosphate in blood. It maintains the consistency of blood pH.

15. Pharynx

16. It is the tubular space between mouth and oesophagus.
Subdivided into 3 parts:
Nasopharynx
Oropharynx
Laryngopharynx
The oropharynx and laryngopharynx are the passages common between both respiratory and digestive system.
The base of the skull forms the roof of the pharynx.
The adenoid or the tonsil is the lymph node present at the back of nasopharynx.
When it gets inflamed, it obstructs the breathing.
Such a breathing through mouth is called paranoid facies.
Tonsils help in trapping the bacteria and destroy them.

17. Oesophagus

18. It is the long hollow tube of 25 cm length and 2 cm in diameter.
It lies in the thorax region behind the trachea and heart.
It continues with the pharynx and just below the diaphragm it joins the stomach.
The upper and the lower ends of the oesophagus are closed by the sphincters.
The upper sphincter prevents the entry of the air during inspiration and aspiration of oesophageal contents.
The lower oesophageal sphincter prevents the reflux of the acid and gastric contents back into the oesophagus.

19. Histologically oesophagus have 3 layers
Muscular
Sub mucosal
Mucosal
The muscular layer consist of striated muscle in upper one third region and smooth muscle in lower one third region.
The middle region consist of both muscles.
Mucosa
Sub-mucosa
Muscularis

20. Stomach

21. It is the J shape organ lying in the abdomen under the diaphragm.
The major part is to the left of the midline.
It has the capacity of 1-2 liters.
It mechanically digest the food by gastric contractions and biochemically by the gastric juice it secretes.

23. The gastric glands are of 3 types:
Peptic glands: it secretes pepsin (digestion of protein)
Oxyntic glands: it secretes HCl.
Mucus gland: secretes alkaline mucus
The oxyntic glands are situated in the fundus of the stomach.
The peptic and mucus glands are situated in pylorus of the stomach.
The stomach has the rich supply of blood vessels and nerves.
It is supplied with the autonomic nerves both sympathetic and parasympathetic.
Sympathetic nerve inhibits the secretory activity of stomach whereas parasympathetic stimulates the same.

24. Gastric juice:
The mucosal layer of the stomach secretes the gastric juice.
It is clear and colorless fluid containing 0.4% HCl and enzymes such as pepsin, gastric renin and gastric lipase.
The pH of gastric juice is highly acidic.
Mechanism of gastric secretion:
The fundus part secretes the acidic juice while the pyloric part secretes alkaline juice.
In fasting condition the stomach secretes 10-60ml of juice per hour whereas 500ml juice per hour during meals.
The mechanism of juice secretion was studied using animals (dogs).
Sham feeding experiment
Pavlov’s pouch

25. Sham feeding experiment

26. Pavlov’s pouch experiment

27. Secretion of gastric juice has following phases:
Cephalic/Nervous phase:
The flow of juice occurs before the food enters the stomach.
It is due to the stimulation of the vagus (parasympathetic) nerves which is initiated by sight, smell or taste of the food.
When the vagus nerve is cut (vagotomy) these phase stops. Sympathetic stimulation occurs during emotional stress which inhibits gastric activity.
Gastric phase:
When the food enters the stomach the pyloric antrum and duodenum secretes gastrin (hormone) which passes into the blood circulation
This gastrin comes to the blood vessels that supplies to the stomach.
The gastrin will stimulate gastric glands to secrete more gastric juice thus gastric secretion is a continuous process.
Gastrin secretion is suppressed when the pH of the pyloric antrum falls to 1.5.

28. Intestinal Phase:
When the partially digested food (chyme) enters the intestine 2 hormones secretin and cholecystokonine and gastric inhibiting peptide are secreted.
They all inhibit the gastric acid secretion and reduce gastric motility.
As a result the chyme gets more time to mix with the bile and pancreatic juice.
This phase is most marked following a meal with a high fat content.
Functions of gastric juice:
The enzyme pepsin along with HCl digests proteins to is peptones and proteoses.
Renin acts on milk protein caseinogen to form casein which is then digested by pepsin
HCl carry out hydrolysis of food and also act as antiseptic
Gastric juice excrete out toxins, heavy metals and certain drugs such as opium.
It contains blood extrinsic (Castel’s) factor responsible for absorption of vit B12 (cynocobalamine)

29. Functions of stomach:
Mechanical functions: act as reservoir of the food. Movement of the stomach helps in mixing of the food with the digestive juices. It propels the food further in the duodenum.
Secretion: it secretes the digestive juice which converts the food into the chyme which can be further digested
Antiseptic: HCl destroys the microbs and prevents infection
Digestion: the gastric juice helps in digestion of proteins and fats.
Absorption: water, alcohol, glucose and certain drugs are absorbed from the walls of the stomach. Vit B12 is also absorbed through extrinsic factor.
Excretion: helps in excretion of toxins and drugs.
Reflux action:
Gastro-salivary reflux

30. Small intestine

31. It is the coiled up tubular structure consisting 3 parts:
Duodenum
Jejunum
Ileum
It is 5-7 m long
Duodenum:
c- shaped first part of intestine
The descending part consist of opening for bile and pancreatic duct.
They open jointly as common bile duct
Bile is secreted from liver and stored in gall bladder
Pancreatic juice is secreted from pancreas
The main function of duodenum is partial digestion of food
Jejunum:
It is the continuation of duodenum forms the 2/5th part of small intestine
It is coiled structure and performs the movement of peristalsis because of its muscular coat
It is bound behind the mesentery which carries blood vessels, autonomic nerves.

32. It consist of innumerable glands for the digestion of food also performs the function of absorption.
Ileum: it follows jejunum ,its is 3/5th fold of small intestine. It ends at caecum.
It is coiled up portion and contains many villi
It consist of payer’s patches which are minute lymphoid structures which serves as defense against microbial invasion
It also consist of digestive glands but less than jeunum
Histology of small intestine:
It consist of serosa layer and muscularis externa and submucosal layer
The muscularis externa consist of smooth muscle layer arranged in two layers:
1.Outer layer: consist of longitudinal muscles
2. Inner layer: consist of circular muscle
The submucosal layer consist of brunner gland which secrets alkaline mucus
The muscularis interna is not well defined

33. The ileum consist of villi which performs the function of absorption
These are the minute finger like projections which increase the surface area for the absorption
The villi consist of folds columnar cells containing lymphatics in the center called lacteals surrounded by blood vessels
The blood vessels absorb carbohydrates and proteins and lymphatics absorb fats.
In addition ileum consist of goblet cells that secret mucus

34. Movements of small intestine:
Peristalsis:
It the wave of contraction proceeded by relaxation. Helps in propelling the food further in ileum and jejunum the speed is 2-25 cm/sec
Segmental: circular muscles contracts at regular intervals thus divides the intestine into segments. Helps in mixing the food with digestive juices and absorption of digested food
Pendular: movement in pendular fashion a rate 5cm/sec. it is like segmental helps in mixing the food with digestive juices and also absorption.
Functions:
Pancreatic secretions: secretion from pancreas into duodenum. The pH is (alkaline). Contains various digestive enzyme for digestion of following:
Carbohydrate digestion: amylase and maltase enzymes digest carbohydrate.

35. Fat digestion: lipase (steapsin) cause breakdown of fat
Fat digestion: lipase (steapsin) cause breakdown of fat. Bile helps in emulsification of fat reducing the big fat globules into small fat globules.
Protein digestion: enterokinase enzyme converts trypsiongen to tripsin, these trypsin converts chymotrypsinogen to chymotripsin. The tripsin and chymotrypsin then act on proteins for its breakdown to peptones and proteoses
Then carboxypeptidase enzyme will act at carbonyl end of protein to convert it to peptides and amino acids
Succus entericus: it is the intestinal juice that contains enzymes erepsin, lipase, amylase, sucrase and lactase
Erepsin converts dipeptides and polypeptides to amino acids.

36. Large Intestine

38. It 1. 5 cm in length and wider then small intestine
It 1.5 cm in length and wider then small intestine. It does not contain villi.
Functions of large intestine:
Absorption of water and formation of solid stool
Absorption of saline, glucose, amino acids and some drugs
Secretion of mucus for lubrication
Excretion: Some heavy metals gets directly excreted from blood to colon
Synthesis of vitamins: the microflora of large intestine helps in synthesis of folic acid, vit B12 and vit K.
Microbial digestion: Microbs digest other pathogenic products and fight against infection
Microflora: They include E.coli, Eenterobacter aerogenes, Streptococcus faecalis and Clostridium perfringens. These microbs are commensals. However become pathogenic if transferred to other part of body e.g. E.coli may cause urinary bladder infection if it gains access in urinary bladder.
Movements: Peristalsis and Mass peristalsis (pushes the stool into rectum)

39. Rectum
Straight tube present at center of the pelvis behind the urinary bladder. It has mucosal coat. When intra-rectal pressure goes to 40-50mmHg the feces passes out of anus (defecation).
Anus
It is the lower end of rectum dilates during defecation and the contracts

40. Pancreas

41. It is a pale grey gland situated transversely on the posterior upper abdominal wall.
It has a head, body and a tail. The tail touches the spleen.
It is a mixed type of gland consisting of Exocrine and Endocrine part.
The exocrine part consist of lobules full of secretory glands secreting pancreatic juice.
The pancreatic juice is carried to the duodenum via pancreatic duct. Just before entering to the duodenum the pancreatic duct joins to common bile duct to form hepatopancreatic ampulla. The opening of the ampulla at the duodenum is controlled by a sphincter called as sphincter of oddi.

42. The pancreatic juice contains various enzymes for the digestion of carbohydrate, proteins and lipids.
The endocrine part consist of islets of Langerhans which consist of α and β cells. These cells secrete glucagon and insulin hormones to maintain blood sugar levels.

43. Liver

44. The liver is the wedge shaped organ present beneath the diaphragm and to the side of the stomach.
It has the superior convex and inferior concave surfaces with anterior sharp and posterior blunt boarders.
It has major two parts right lobe and left lobe with the apex in the left. The right lobe is larger then the left lobe.
The two lobe are joined by a ligamentous band called as falciform ligament.
On the inferior of the organ the two bands subdivides the organs into 4 compartments
1. Right lobe 2. left lobe 3. Quadrate lobe 4. caudate lobe

45. Blood vessels of liver:
The liver is made up of lobules and the lobules consist of liver cells.
Between the lobules there is connective tissue containing blood vessels, nerves, bile ducts and lymphatics etc.
Circulation:
Portal vein: it enters the liver carrying blood from the stomach, spleen, pancreas, and small & large intestine.
Hepatic artery: it is the branch of abdominal aorta which carries arterial blood.
The hepatic artery and portal vein takes the blood to the liver and drains into the central veins of liver lobules. These veins combine to form hepatic veins which drains into inferior vena cava.
There are bile cannaliculi in between the hepatic cells which secretes bile , these bile is drained to hepatic ducts that passes through the liver and terminate into gall bladder.

46. Functions of Liver:
Carbohydrate metabolism:
Imp role in maintaining the plasma glucose levels
It is the site for glycogenesis (formation of glycogen from glucose), glycogenolysis (destruction og glycogen to glucose), neoglycogenesis (formation of glucose from sources other then carbohydrates such as proteins and fats)
Protein metabolism:
Deamination: the removal of nitrogen from amino acid not required for new protein; urea is formed from these nitrogen which is excreted in urine.
Transamination: removal of nitrogen from aminoacid and attaching it to other carbohydrate molecule forming new non-essential aminoacid.
Synthesis of plasma proteins: albumin, globulins, clotting factors such as plasminogen etc are also synthesized.

47. Fat metabolism:
The fats are synthesized and stored in the liver. The oxidation of fats occurs through beta oxidation and the liberated energy is utilized by the tissues.
Defense against the microbs:
Reticulo-endothelial cells (Kuffer Cells) manufacture antibodies in form of agglutinins, precipitins and bacteriolysins against the invades microb.
Detoxification:
Various drugs, ethanol and heavy metals are detoxified and are finally excreted through bile via gall bladder.
Production of heat: due to its high metabolic rate it produces a great deal of heat
Secretion of bile: the hepatocytes synthesize the bile which include bile salts ( sodium taurocolate & glycolate and bile pigments such as bilirubin & biliverdin)

48. Storage:
The substance include:
Glycogen
Fat soluble vitamins-A,D,E,K
Iron, copper
Some water soluble vitamins e.g. Vit B12

49. Gall Bladder

50. It is the sac like structure which is serves as the reservoir of the bile. It is anteriorly under the liver and on the right to the abdominal surface.
It opens through the cystic duct which joins the common hepatic duct to form the common bile duct. The common bile duct carries the bile juice and opens jointly into the pancreatic duct in the duodenum.
It contacts under the influence of cholecystokinin and autonomic nerves. The bile and pancreatic juices are poured simultaneously in to duodenum.

51. Functions:
It acts as a reservoir of bile
It concentrates bile and helps in absorption of water and inorganic salts
It secretes mucus and excretes cholesterol
It maintains pressure in the billiary tract
Bile juice:
Bile is the secretory and excretory product of the liver.
The common bile duct takes the bile juice to the duodenum.
The bile juice is continuously synthesized in liver but the entry in the duodenum starts only after the ingestion of the food.
Composition of bile juice:
It is a yellowish fluid containing many substances but no enzyme.
The substances include:
Water
Mineral salts such as chloride, carbonates, phosphates of sodium, potassium and calcium
Bile salts such as sod. Taurocolate and sod. Glycolate derieved from bile acids such as colic acid and chenodeoxycholic acid
Bile pigments such as bilirubin, biliverdin
cholesterol

52. Functions:
Fat digestion: It reduces surface tension an helps in fat digestion. It activates the enzyme lipase which helps in breakdown of the fat. Helps in digestion of fat, protein and carbohydrates.
Absorption: helps in digestion of various substance such as iron, calcium and fat soluble vitamins-A,D,E & K.
Laxative action: it stimulates peristalsis and produce laxative action (rapid defecation)
Buffer action: contains mucin which act as buffer to maintain the pH
Excretion: heavy metals, bacteria, cholesterol and lecithin are excreted in bile
Optimum pH: it maintains the pH which helps in action of the digestive enzymes.
Cholagogue: bile itself stimulates the biliary secretion. This is known as cholagogue action
Secretogogue: it stimulates secretin, a local hormone which stimulates the pancreatic, biliary and intestinal secretion

53. Disorders of digestive system

54. Constipation:
Delay in defecation and formation of hard stool. It might be due to:
Continuously ignoring/ preventing
Decreased colonic motility
Ageing
Emotions
Low bulk diet
Atonic or spastic colon
Chronic amoebiasis
Diarrhea:
Frequent defecation, usually with high fluid fecal matter (watery stool)
It may be due to:
Increase intestinal motility
Fluid overload in colon
Salt overload in colon
Infection
Allergy
toxemia
Nausea: felling of vomiting prior to vomit

55. Vomiting: sudden spasmodic expulsion of the contents of stomach
Vomiting: sudden spasmodic expulsion of the contents of stomach. It may be due to central effect, reflex, toxic , obstruction
Anorexia: loss of appetite might be due to anxiety or dipression
Gastritis: acute or chronic inflammation of gastric mucosa arising due to irritant substance, infection, emotions or obstruction
Heart Burn: sour burning sensation in upper oesophagus due to evacuation of acidic contents in mouth leading to burning sensation behind the sternum
Cholecystitis: inflammation of gall bladder
Gastroenteritis: inflammation in upper GIT manifested with the symptoms such as nausea, anorexia, vomiting abdominal discomfort, diarrhea. It may be due to bacterial and fungal infection or poisoning.
Dysphagia: difficulty in swallowing
Aerophagy: swallowing of air in the stomach unknowingly

56. Peptic ulcer disease: it is ulceration of mucus membrane , these ulcers may penetrate in muscularis mucosa. It occurs in the areas that are bath by the acid and pepsin in stomach and/or duodenum (duodenal ulcers). May occur due to excessive vagal nerve stimulation resulting in excessive acid secretion, disturbed mind or consumption of irritating food.
Appendicitis: inflammation in appendix.
Peritonitis: Inflammation of peritoneum of the abdomen
Flatulence: accumulation of gas in the stomach or intestine due to aerophagy, intestinal fermentation, deficient absorption or constipation
Hemorrhoids (piles): swelling or dilation or varicose veins present in the mucus membrane of the rectum or skin of the annus
Fatty liver: accumulation of fats, triglycerides or cholesterol in the liver

57. Hepatitis: inflammation of liver
Hepatitis: inflammation of liver. Histologically there is necrosis of hepatic cells. Occurs due to vital or amoebic infection
Cirrhosis of liver: hardening of the liver. Liver functions are adversely affected. Often produce ascities (free fluid accumulation in abdomen)
Endoscopy: it is the diagnostic technique to view the hollow organs from inside using light and magnification.