The Digestive System

2. DIGESTION • The process of conversion of complex food substances to simple absorbable forms is called digestion. • Digestion is carried out by our digestive system by mechanical and biochemical methods.
3. PHASES OF DIGESTION • The activities of the digestive system can be grouped under five main headings. • Ingestion :-This is the taking of food into the alimentary tract, i.e. eating and drinking. • Propulsion :-This mixes and moves the contents along the alimentary tract. • Digestion :-This consists of: • Mechanical breakdown of food by mastication(chewing). • Chemical digestion of food into small molecules by enzymes present in secretions produced by glands and accessory organs of the digestive system

1. THE DIGESTIVE SYSTEM PRESENTER – SHOAIB AKHTAR MODERATOR – MR.GAURAV PANDEY

2. DIGESTION The process of conversion of complex food substances to simple absorbable forms is called digestion. Digestion is carried out by our digestive system by mechanical and biochemical methods.

3. PHASES OF DIGESTION The activities of the digestive system can be grouped under five main headings. Ingestion :- This is the taking of food into the alimentary tract, i.e. eating and drinking. Propulsion :- This mixes and moves the contents along the alimentary tract. Digestion :- This consists of: M echanical breakdown  of food by mastication(chewing). Chemical digestion  of food into small molecules by enzymes present in secretions produced by glands and accessory organs of the digestive system

4. CONT… Absorption :- This is the process by which digested food substances pass through the walls of some organs of the alimentary canal into the blood and lymph capillaries for circulation and use by body cells. Elimination :- Food substances that have been eaten but cannot be digested and absorbed are excreted from the alimentary canal as   faeces by the process of defaecation.

5. DIGESTIVE SYSTEM The human digestive system consists of the alimentary canal and the associated glands.

6. ALIMENTARY CANAL Alimentary Canal The alimentary canal begins with an anterior opening the mouth, and it opens out posteriorly through the anus. The  alimentary canal  includes the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus. The oral cavity has a number of teeth and a muscular tongue

7. ACCESSORY DIGESTIVE ORGANS Accessory Digestive Organs Contains the following organs: Teeth , Tongue, Gallbladder, Salivary Glands, Liver, and Pancreas

8. TEETH Teeth are concerned with mastication. Depending on the age at which they arise, teeth can be classified into two types: PERMANENT TEETH: The teeth of adult life. TEMPORARY OR MILK TEETH : The teeth of childhood

9. CONT… PERMANENT TEETH : They are 32 in number and 16 are present in each jaw. Upper and lower half jaw contain 8 teeth. They are 2incisor, 1 canine, 2 premolar ,3 molars. TEMPORARY TEETH : They are 20 in number . Each jaw contain 10 teeth. Each half of the jaw has 2incisors, 1 canine, and 2 molars.

10. FUNCTION OF TEETH Incisors and Canine :- cutting teeth, help in biting off pieces of food. Premolar and molar :- broad and flat surface, help in grinding or chewing food

11. TONGUE Tongue lies in the floor of the mouth and it is attached to hyoid bone. Tongue contain: A root at which blood vessels and nerves pass. A tip which is pointed when the tongue is protruded when the tongue is in the mouth. Two margins which are in contact with lower teeth. An upper surface which contain a small elevation called dorsum. A lower surface which contain a soft ligamentous structure called frenulum.

12. CONT… The two important structure of tongue are:- Taste buds which are on the lateral aspects of tongue. Small projections called papillae present on the upper surface .

13. FUNCTION OF TONGUE Chewing(mastication) Swallowing(deglutition) Speech Taste

14. CONT…

15. STRUCTURE OF ALIMENTARY CANAL The walls of the alimentary tract are formed by four layers of tissue:  adventitia or serosa – outer covering muscle layer  submucosa mucosa – lining

16. ADVENTITIA OR SEROSA This is the outermost layer. In the thorax it consists of loose  fibrous tissue and in the abdomen the organs are covered by a serous membrane (serosa) called  peritoneum PERITONEUM Peritoneum is the serous membrane lining the abdominopelvic cavity. Visceral peritoneum covers the external surfaces of most digestive organs and is continuous with the parietal peritoneum that lines the body wall.

17. PERISTALTIC WAVE In much of the digestive tract such as human GIT smooth muscles tissue contracts in sequence to produce peristaltic waves. This propels a ball of food (called bolus while in oesophagus and upper GIT and chyme in stomach) along the tract. Contraction of longitudinal muscle ahead of bolus Contraction of circular muscle behind bolus. Contraction in circular muscle layer forces bolus forward.

18. CONT…

19. MUSCLE LAYER This smooth muscle layer has inner circular and outer longitudinal layer of muscle fiber separated by myenteric plexus. Neural innervation control the contraction of these muscle and hence mechanical breakdown and peristalsis of food within the lumen .

20. SUBMUCOSA This layer consist of loose areolar connective tissue containing collagen . It surrounds muscularis mucosa and consist of flat fibrous connective tissue and larger vessels and nerves. The blood vessels are arterioles ,venules and capillaries.

21. MUCOSA It is the innermost layer of digestive tract and has specialized epithelial cells supported by an underlying connective tissue layer called lamina propria. Lamina propria contain blood vessels, nerves, lymphoid tissue that support mucosa. Beneath the lamina propria is a muscularis mucosa it comprises layer of smooth muscles which can contract to change shape of the lumen.

22. SALIVARY GLAND There are three pair of salivary gland in the mouth . They are paratoid submandibular and sublingual glands. Parotid glands These are situated one on each side of the face below and in front of each ear . Each gland has a parotid duct opening into the mouth at the level of the second upper molar tooth. Submandibular glands These lie one on each side of the face under the angle of the jaw. The two submandibular ducts open on the floor of the mouth, one on each side of the frenulum of the tongue.

23. CONT… Sublingual glands These glands lie under the mucous membrane of the floor of the mouth in front of the submandibular glands. They have numerous small ducts that open into the floor of the mouth

24. SALIVA It is a mixed secretion of all the three pairs of salivary gland .it is an alkaline fluid containing water to the extent of 99%. The solid content of saliva are : Mucin which is a glycoprotein. Pytaline ,an enzyme which convert starch into maltose.

25. FUNCTION It convert starch into a soluble sugar called maltose It acts as a solvent for food and helps in its swallowing. It moistens, lubricates and clean the mouth. It excretes organic and inorganic substance and some drugs.

26. PHARYNX Pharynx lies between the mouth and oesophagus. Pharynx contain three parts : Nasopharynx Oropharynx Laryngopharynx

27. OESOPHAGUS Hollow muscular tube. It lies between trachea in front and vertebrae column at the back. About 25cm(10 inc.)long and 2cm(0.8 inc.)wide Convey solid food and liquid to the stomach. It is innervated by fibers from the oesophagal plexus. The oesophagus contain sphincter at its upper and lower ends. These sphincters relax during swallowing

28. DEGLUTITION The act of swallowing In the mouth food is masticated and mixed well with saliva. The action of tongue and cheeks convert food into a round mass called bolus. This bolus is swallowed Swallowing occurs in the following three stages. Stage 1 : closing of the lips and raising of the tongue against the palate forces the bolus into Oropharynx . Now the Nasopharynx is closed by soft palate and larynx is closed by epiglottis . This prevent the entry of food into respiratory passage.

29. CONT… Stage 2 : By the contraction of the muscle of pharynx, the bolus is forced into oesophagus. Stage 3 : In the oesophagus ,contraction of its muscular wall carries the food down to stomach. It must be noted that the first stage is a voluntary act but it is performed automatically .But the second stage and third stages are involuntary acts.

30. STOMACH The stomach is a J-shaped dilated portion of the alimentary canal and it receives food from oesophages . Temporary storage Chemical digestion: pepsin break protein into polypeptides Mechanical digestion : three smooth muscle layer are added and the content are liquefied Limited absorption Production and secretion of intrinsic factor needed for absorption of vitamin B12.

31. PARTS OF STOMACH Two surfaces : an anterior and a posterior surface Two border : an upper border called lesser curvature , a lower border called greater curvature . Two ends : upper end called cardiac end it is guarded by cardiac sphincter . Lower end called pyloric end , it is guarded by pyloric sphincter. Fundus : a dome shaped upper part lying to the left of cardiac end. Body : the main part of stomach Pyloric antrum : the lower part

32. CONT…

33. WALLS OF STOMACH It contain four coats: Peritoneal coat (made of serous covering ) Muscular coat (made of longitudinal , circular and oblique fibers) Submucous coat (made of areolar tissue) Mucuous coat (made of mucous membrane)

34. SECRETION OF STOMACH The mucous membrane of stomach contain glands which secrete gastric juice continuously. About 2 liters of gastric juice are secreted daily by specialized secretory glands in the mucosa Gastric juice contain  water  mineral salts hydrochloric acid  intrinsic factor

35. FUNCTION OF GASTRIC JUICE Water  further liquefies the food swallowed. Hydrochloric acid Acidifies the food and stops the action of salivary amylase kills ingested microbes provides the acid environment needed for the action of pepsins. Pepsinogens are activated to pepsins by hydrochloric acid and by pepsins already present in the stomach. These enzymes begin the digestion of proteins. Pepsins act most effectively at a very low Ph.

36. CONT… Intrinsic factor  (a protein) is necessary for the absorption of vitamin B12 from the ileum   Mucus prevents mechanical injury to the stomach wall by lubricating the contents. It also prevents chemical injury by acting as a barrier.

37. SMALL INTESTINE The small intestine is continuous with the stomach at the pyloric sphincter. 2.5 cm in diameter, 5 metres long and leads into the large intestine at the ileocaecal valve . In the small intestine the chemical digestion of food is completed and absorption of most nutrients takes place. The small intestine comprises three continuous parts.

38. Food can be digested by a combination of two methods – mechanical digestion and chemical digestion In  mechanical  digestion, food is physically broken down into smaller fragments via the acts of chewing (mouth), churning (stomach) Mechanical Digestion Chewing (Mouth) Food is initially broken down in the mouth by the grinding action of teeth (chewing or mastication) The tongue pushes the food towards the back of the throat, where it travels down the esophagus as a bolus

39. The epiglottis prevents the bolus from entering the trachea, while the uvula prevents the bolus from entering the nasal cavity Churning (Stomach) The stomach lining contains muscles which physically squeeze and mix the food with strong digestive juices ('churning’) Food is digested within the stomach for several hours and is turned into a creamy paste called chyme Eventually the chyme enters the small intestine (duodenum) where absorption will occur

40. In  chemical  digestion, food is broken down by the action of chemical agents (such as enzymes, acids and bile) Stomach Acids The stomach contains gastric glands which release digestive acids to create a low pH environment (pH ~2) The pancreas releases alkaline compounds (e.g. bicarbonate ions), which neutralize the acids as they enter the intestine. 

41. Bile The liver produces a fluid called bile which is stored and concentrated within the gall bladder prior to release into the intestine Bile contains bile salts which emulsify fat.

42. Enzymes Amylase release by salivary glands help in carbohydrate digestion in mouth. Amylase secreted by pancreas help in carbohydrate digestion in small intestine. Proteases digest protein in stomach Lipases release from the pancreas help in digestion of smaller fat droplets. Nucleases release by pancreas which digest nucleic acid (DNA, RNA) into smaller nucleosides.

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