Digestive System Medical Class Lecture.pptx

Anatomy and Physiology of Digestive systems.

1. Digestive System Unit-X

2. Objectives At the completion of this unit, the learners will be able to: Define the digestive system and list its functions Ident if y the va r iou s or g ans of digest i v e sys t em Desc ribe the a nato m y & p h ysi ol o g y of digesti v e or g ans Discuss the role of accessory organs in digestion Discuss digestion of f o o d in --Mouth --Stomach -- Small intes t ines -- La r ge intes t ines Discuss the absorption of nutrients in the digestive system Disc uss the p r ocess of de f ecat i on.

3. The digestive system includes m a n y o r g a ns , a nd e a ch o r g a n h a s m a n y v a r i o us r eg i on s . The main t r a ct t h r o u g h the d i g e s t i v e s y s te m ( f r o m the mouth, t h r o u gh the s t o m a c h a n d i n t e s t i n e s ) i s ca l led the g a s t r o i n t e s t i n a l t r a ct ( G I) or the ali m e n t a r y c a n a l .

4. Func t ions o f D igestive Sy s tem Ingestio n — taki n g f ood a n d l i q u id D i gestio n — mecha n ica l a n d chem i cal A b sorpti o n — i nt o b l ood a n d l ymph De f ecati o n — el i mi n ati o n of f eces

5. Digestive System Digestive system has two subdivisions: Digestive tract Up to 9 me t ers (3 f eet) long It con sis t s of mouth, P h a r ynx, Eso p h a g u s, Sto m ac h , S m a l l i n te sti n e , a n d Larg e i n te sti n e . Accessory organs It includes Teeth,Tongue, Salivary glands, Liver, Gallbla d de r , an d Panc r ea s .

6. Digestive system

7. M out h → Sto mac h

8. Salivar y Glands

9. Salivar y Glands D i vi d ed i n to ma j or a n d mi n or g l a n ds Major Salivary Glands P a r otid -- - p a i r ed a n d the l a rgest Submandibular --- one on each side of the face under the an g l e of j a w Sub l i n g u al --- single a n d the s m a l lest Minor salivary glands Th e r e a r e ab o ut 4 5 mi n or sal i va r y gl a nd s situated i n the mucosa of lips, cheeks, palate, floor of mouth, and retromolar region.

10. Composition of Saliva T o t al amo u nt i s 15 ml/d a y 99 % water and 1 % dissolved substances (organic and i n organ i c). P t yali n e or saliva r y a m ylas e , s e c r e t ed f r om pa r o t id Lingual lipase acting on triglycerides Mucin, a glycoprotein is secreted by sublingual and s u b ma n di b u la r gl a nd. 3 In o rg a n i c s u b s ta n ces i n cl u de N a + , K + , C a ++ , HCO - and C l -

11. Functions of Saliva Lubricatio n and spe e ch Appreciation of taste—only saliva soluble food can stimulate the taste buds. Digestion---- starch is converted into maltose De f ense -- - L ysozy m e and IgA Cl i n i ca l T erms: Sia l o r rhea ( h ypersal i vatio n ) Xerostomia...dry mouth Sjogren's (SHOW-grins) syndrome is an autoimmune disorder characterized b y t w o most common symptoms — d r y e y es and d r y mouth.

12. General A nat o my o f D igestive T r act Most of the digestive tract consists of four layers, in order from inner to outer surface: 1. Mucosa Is a m uco us membr a ne l i n i ng the l u men. It h a s th r ee l a y ers as Epithelium : coming in direct contact with food Lami n a p r o p ri a : Loose con nect i v e tis s ue l a y er Mu s cu l ar i s m ucosa : s m ooth m uscle t h i n l a y er (i n ner ci r cu l ar a n d o u ter l o n g it u d i nal l a y er)

13. Layers of GI Tract cont.. The lamina propria (lamina=thin plate; propria = own) is areolar/loose connective tissue having blood and lymphatic vessels for absorption. It o v erl i es m uco sa

14. GI layers con t … 2 . Su b m uco s a F ormed b y a r eol ar con ne c t i v e t i ss u e t hat bind s m u c osa to m usc ularis extern a . It has a network of (auto) neurons called submucosal plexus (Meissner Plexus ), glands and lymphatic tissues. 3. M u scu lar is Ex t erna Consists of two layers of smooth muscles as inner circular and ou t er long i t u d i nal l a y ers . In between the two layers is a myenteric Plexus/ Auerbach plexus The involuntary contraction of circular and longitudinal smooth muscles help break down and propulsion of food along t h e G I t rac t .

15. GI Layers cont … 4. Se r osa Serosa means serous membrane, the outermost layer. It i s a ls o called t he visceral perito n eum. It begins in the lower 3 to 4 cm of the esophagus and ends wit h the s i g moid col o n. The oral cavity, pharynx, most of the esophagus and the r ectum a r e s u r ro u nded b y a con nect i v e tis s ue l a y er ca l led adventitia. The esophagus, stomach, and intestines have a nervous net w ork cal l ed the enteric ne r v ous sy s tem wh i ch r egu l ates d i gesti v e tract motil i t y , s ec r etio n , a n d b l ood fl o w .

16. Neurons of Enteric Nervous System (ENS) Neu r o n s of t h e ENS a r e a r ra n ged i n to t w o g r o u ps. A. Submucosal Plexus or Meissner Plexus B. Myenteric Plexus or Auerbach plexus found between circular and longitudinal smooth muscles of muscularis externa.

17. The Stomach It se r v es as a s h ort - t er m s t o r a g e r ese r v oir , a ll o w i ng a meal t o be cons u m ed q ui c k ly and deal t w i t h o v e r an e x t e n d e d peri o d of t im e . In the stomach a substantial enzymatic digestion is initiated, particularly of p r o t e i ns b y pe ps i n. L o w pH ( p H 2 - 3) . C o n t r a c t i o n s of g a s t r i c smoot h m u sc l e m i x f oo d wi t h g a s t r i c s e c r e t i o n s , r e s u l t i ng in liq u e f a c ti on o f f oo d , a p r e r e q u i s i t e f or del i v e r y of t h e i n g e s t a t o t h e sma l l i n t e s t i n e . As food is liquefied, it is slowly released i nt o the small i n t e s ti n e f or f u r t her processing. Co p y r ig h t © W ordPr e ss The wet mass of broken up food and digestive chemicals is called chyme .

18. Gastric secretions G a s t ric sec r etion i s a co l or l ess , wate r y , aci d i c , p r oduced i n the s t omach . P h ysical p r o p e r ties; It is a watery fluid, that has a pale color, pH is 1-3. the v o l ume sec r eted per d a y i s 2 - 3 L . Chemical composition; It is 97-99% water , it contains inorganic salts ,and organic components that include, mucin, digestive enzyme s , h o rmones

19. Gastric Glands and secretions The gastric secretion is produced by the epithelial cells of the gastric g l ands. Go b let cells o r m u cus ce ll s : m uco us cel l s, w h ic h c o v er the ent i r e l u menal surfac e . These cells secrete a bicarbonate-rich mucus that coats and lubricates the gastric surface, and serves an important role in protecting the epithelium from hydrochloric acid and pepsin a n d other chem i cal d a mag e .

20. Gastric Glands and secretions Parietal or oxyntic cells : They secret HCl into the st o mach lu m en wh e r e i t es t ablishes an ex t r em e l y a c idic environment. This acid is important for activation of pepsinogen and inactivation of ingested microorganisms such as bacteria. T h e y also s e c r et the in t rinsic facto r , a g l yco p r o t ein w h ic h i s n e ces s a r y f or in t es t ina l absor p ti o n of vitamin B 12 .

21. Gastric Glands and secretions cont.. Chief cells : they secrete pepsinogen(zymogen). Once secreted, pepsinogen is activated by stomach acid into the active protease pepsin, which initiates digestion of p r o t ei n s i n t h e s t o m ach. In young animals, chief cells also secrete rennin a p r o t ease t h at h elp s coagulate milk all o win g i t t o be r e t ained m or e t h an b rief l y i n t h e s t o m ach. T h e ep it h eli u m cells a l so p r o d uce i m p o r tant h o rmo n e gastrin, a peptide that is important in control of acid sec r e t io n and gastric m o tili t y , and so m atos t atin.

22. Produce alkaline mucus that covers mucosa layer Synthesize and secrete the protease precursor known as pepsinogen. Synthesize and secrete the HCl acid responsible for the acidic pH in the gastric lumen. Exocrine gland cells of gastric pits

23. Gastric secretion phases Gastric acid secretion can be divided into three phases: Cephalic phase mediated by the CNS and triggered by sight, smelling, chewing or even the thought of food. Mediated by the vagus and accounts for 10-30% of the acid secretion. Gastric phase trig g e r ed b y t h e p r es e nce of f o o d i n t h e st o mach ( b o t h chemical and mechanical sensing are involved). Accounts for 70 - 90 % of acid s e c r e t i o n Intestinal phase Presence of chyme, most probably amino acids, in the intestine triggers approximately 5% of the gastric acid secretion .

24. Gastric and Peptic Ulcers Pept i c u l cers: Erosions of the mucous membranes of the stomach or duodenum p r oduced b y action of HC l . Zol l i nge r - Ell i son synd r ome: Ulcers of the duodenum are produced by excessive gastric acid secretions. Hel i cob acter p ylo r i: Bacteria that reside in GI tract and may produce ulcers. Acute gastritis: Histamine released by tissue damage and inflammation stimulate further acid sec r etion.

25. Stomach

26. Stomach

27. Stomach

28. The Stomach Co p y r ig h t © R oz ain i Othman

29. Function of the Stomach The stomach performs three main functions: Store ingested food. Secretes hydrochloric acid (HCl) and enzymes that begin protein digestion. The ingested food is pulverized and mixed with gastric secretions to produce a thick liquid mixture known as chyme.

30. Functional Anatomy of Liver and Biliary System Liver is the largest gland in the body Hepatic Lobes: Ri g ht l o be Lef t l o be Q u a d rate l o be C a ud ate l o be Hepatic Lobules: Hep a tic Lob u l e i s t he structural a n d fu n ctio n al u n i t of liver. Th e r e a r e 5 , 00 to 1 , 000 l o b u le s i n the li v er

31. Hepatic lobule is a honeycomb like structure which is made u p of h e pat o cyte s . Hepatic Plates: Hepatocytes are arranged in columns which form h e patic p lates. Each p lat e i s made u p of t w o co lu m ns of h e pat o cyte s . In b e t w een t w o col u mns of each plate lie s a b ile canaliculus. In b e t w e e n t h e plate s , a bl o od space c a lle d si n u s oid is present. Si n u s oid i s li n ed b y t h e end o t h elial cells a l o n g wi t h mac r op hages i n b e t w e e n t h e cells.

32. P osterior vi e w

33. Gallst o ne Gallstone is a solid crystal deposit that is formed by cho l e s te r ol, calc i um io n s an d b i l e p i gments i n t he gallbladder or bile duct. Cholelithiasis is the presence of gallstones in gallbladder. Choledocholithiasis is the p r esence of ga l lstone s i n the b i l e d u ct s .

34. The Small Intestine The average length in an adult human male is 7 m. It is approximately 2.5–3 cm in diameter. Consists of: Duodenum Jejunum Ileum Co p y r ig h t © W ordPr e ss The small intestine is the main site for digestion and absorption of nutrients.

35. Enzymatic Transport into the Duodenum Most digestion occurs in the upper portion of the small intestine, called the duodenum. Co p y r ig h t © R oz ain i Othman

36. Absorption of nutrients The structure of the small intestine, in place to aid absorption of nutrients, consists of three levels: on the macro-scale , folds or plicae intrude into the lumen ; on the meso-scale villi cover the surface; and on the micro-scale microvilli cover the villi on a cellular level.

37. The ileocecal valve of the ileum (small intestine) passes material into the large intestine at the cecum. Partly digested food moves through the cecum into the colon, where water and some nutrients and electrolytes are removed. The colon is responsible for reabsorption of 1.0 to 1.5 liters of electrolyte-rich fluid entering it each day from the proximal intestine. The remaining material, solid waste called stool, moves through the colon, is stored in the rectum, and leaves the body through the anal canal and anus. The Large Intestine The large intestine is about 1.5 m long. It absorbs mainly water and minerals and produces and eliminates fecal matter. Copyright © Nasir Alar; AlarGastro.com

38. vers u s The large intestine primarily absorbs water, and compacts and dries out the fecal bolus: villi would be a hindrance to movement of the semi-solid fecal mass, and would likely be injured by its passage. Hence there are no villi in the large intestine, and in addition, there are numerous goblet cells whose secretions (mucins) act as lubrication for the mov in g m a t e r ial . Co p y r ig h t © Thoma s Ca c eci

39. References Ross a n d Wi l son, A n ato m y & P h ysiol o gy i n Hea l t h a n d Ill nes s,12 Ed it i on Ross & Wi l son. (200 0) A n ato m y & P h ysiol o gy i n Health & Illness. Edi n burgh: Ch u r chil l , 1 th Ed it i on PR Asha l atha & G D ee p , A n ato m y & P h ysiol o gy f or Nurses 4 th Edition