2The digestive system comprises of alimentary canal or gastrointestinal tract (GIT) and some accessory organs.The tract starts from mouth and ends at anusGIT mainly involves:MouthPharynxOesophagusStomachSmall intestineLarge intestineRectumAnusThe Accessory organs are:PancreasLiverGall bladder
4The 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.
6The 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.
8TONGUE: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.
9The tongue plays an important role in mastication (chewing), deglutition (swallowing), speech and taste.
10M:Molars, P: Pre-molars, C: Canines, I: Incisors TEETHThere 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 :LeftUpper jaw: :Upper jawLower jaw: :Lower jawM:Molars, P: Pre-molars, C: Canines, I: Incisors
11Function 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.
123 pairs of salivary glands are present: Parotid gland Submaxiliary or Submandibular glandSublingual glandParotid 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 cheeksSubmaxiliary 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.
13SALIVA: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.StarchAmylaseMaltoseMaltaseGlucoseLubrication 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.
14Protection: 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.
16It is the tubular space between mouth and oesophagus. Subdivided into 3 parts:NasopharynxOropharynxLaryngopharynxThe 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.
18It 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.
19Histologically oesophagus have 3 layers MuscularSub mucosalMucosalThe 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.MucosaSub-mucosaMuscularis
21It 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.
23The gastric glands are of 3 types: Peptic glands: it secretes pepsin (digestion of protein)Oxyntic glands: it secretes HCl.Mucus gland: secretes alkaline mucusThe 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.
24Gastric 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 experimentPavlov’s pouch
27Secretion 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 circulationThis 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.
28Intestinal 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 pepsinHCl carry out hydrolysis of food and also act as antisepticGastric 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)
29Functions 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 digestedAntiseptic: HCl destroys the microbs and prevents infectionDigestion: 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
31It is the coiled up tubular structure consisting 3 parts: DuodenumJejunumIleumIt is 5-7 m longDuodenum:c- shaped first part of intestineThe descending part consist of opening for bile and pancreatic duct.They open jointly as common bile ductBile is secreted from liver and stored in gall bladderPancreatic juice is secreted from pancreasThe main function of duodenum is partial digestion of foodJejunum:It is the continuation of duodenum forms the 2/5th part of small intestineIt is coiled structure and performs the movement of peristalsis because of its muscular coatIt is bound behind the mesentery which carries blood vessels, autonomic nerves.
32It 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 villiIt consist of payer’s patches which are minute lymphoid structures which serves as defense against microbial invasionIt also consist of digestive glands but less than jeunumHistology of small intestine:It consist of serosa layer and muscularis externa and submucosal layerThe muscularis externa consist of smooth muscle layer arranged in two layers:1.Outer layer: consist of longitudinal muscles2. Inner layer: consist of circular muscleThe submucosal layer consist of brunner gland which secrets alkaline mucusThe muscularis interna is not well defined
33The ileum consist of villi which performs the function of absorption These are the minute finger like projections which increase the surface area for the absorptionThe villi consist of folds columnar cells containing lymphatics in the center called lacteals surrounded by blood vesselsThe blood vessels absorb carbohydrates and proteins and lymphatics absorb fats.In addition ileum consist of goblet cells that secret mucus
34Movements 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/secSegmental: circular muscles contracts at regular intervals thus divides the intestine into segments. Helps in mixing the food with digestive juices and absorption of digested foodPendular: 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.
35Fat 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 proteosesThen carboxypeptidase enzyme will act at carbonyl end of protein to convert it to peptides and amino acidsSuccus entericus: it is the intestinal juice that contains enzymes erepsin, lipase, amylase, sucrase and lactaseErepsin converts dipeptides and polypeptides to amino acids.
38It 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 stoolAbsorption of saline, glucose, amino acids and some drugsSecretion of mucus for lubricationExcretion: Some heavy metals gets directly excreted from blood to colonSynthesis 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 infectionMicroflora: 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)
39RectumStraight 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).AnusIt is the lower end of rectum dilates during defecation and the contracts
41It 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.
42The 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.
44The 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 compartments1. Right lobe 2. left lobe 3. Quadrate lobe 4. caudate lobe
45Blood 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.
46Functions of Liver:Carbohydrate metabolism:Imp role in maintaining the plasma glucose levelsIt 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.
47Fat 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 heatSecretion of bile: the hepatocytes synthesize the bile which include bile salts ( sodium taurocolate & glycolate and bile pigments such as bilirubin & biliverdin)
48Storage:The substance include:GlycogenFat soluble vitamins-A,D,E,KIron, copperSome water soluble vitamins e.g. Vit B12
50It 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.
51Functions:It acts as a reservoir of bileIt concentrates bile and helps in absorption of water and inorganic saltsIt secretes mucus and excretes cholesterolIt maintains pressure in the billiary tractBile 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:WaterMineral salts such as chloride, carbonates, phosphates of sodium, potassium and calciumBile salts such as sod. Taurocolate and sod. Glycolate derieved from bile acids such as colic acid and chenodeoxycholic acidBile pigments such as bilirubin, biliverdincholesterol
52Functions: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 pHExcretion: heavy metals, bacteria, cholesterol and lecithin are excreted in bileOptimum 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 actionSecretogogue: it stimulates secretin, a local hormone which stimulates the pancreatic, biliary and intestinal secretion
54Constipation:Delay in defecation and formation of hard stool. It might be due to:Continuously ignoring/ preventingDecreased colonic motilityAgeingEmotionsLow bulk dietAtonic or spastic colonChronic amoebiasisDiarrhea:Frequent defecation, usually with high fluid fecal matter (watery stool)It may be due to:Increase intestinal motilityFluid overload in colonSalt overload in colonInfectionAllergytoxemiaNausea: felling of vomiting prior to vomit
55Vomiting: 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 , obstructionAnorexia: loss of appetite might be due to anxiety or dipressionGastritis: acute or chronic inflammation of gastric mucosa arising due to irritant substance, infection, emotions or obstructionHeart Burn: sour burning sensation in upper oesophagus due to evacuation of acidic contents in mouth leading to burning sensation behind the sternumCholecystitis: inflammation of gall bladderGastroenteritis: 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 swallowingAerophagy: swallowing of air in the stomach unknowingly
56Peptic 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 abdomenFlatulence: accumulation of gas in the stomach or intestine due to aerophagy, intestinal fermentation, deficient absorption or constipationHemorrhoids (piles): swelling or dilation or varicose veins present in the mucus membrane of the rectum or skin of the annusFatty liver: accumulation of fats, triglycerides or cholesterol in the liver
57Hepatitis: inflammation of liver Hepatitis: inflammation of liver. Histologically there is necrosis of hepatic cells. Occurs due to vital or amoebic infectionCirrhosis 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.