GIT 1 gastro intestinal tract physiology topic

Medical

1. Introduction and Physiological anatomy of Gastro Intestinal tract Every cell of living system needs energy Unicellular organisms: Exists in the sea of nutrients Can satisfy their nutritional need just by Proteins present at the cell membrane

2. Multi cellular organisms In multi cellular organisms, a groups of cells converted to a tissue , to perform specific function A number of systems are evolved in vertebrates including humans To provide nutrients to all the systems The Gastro intestinal tract is accounted for extraction of nutrients from the food

3. The Food The most of the food we eat are macromolecules , it can not cross the cell membrane easily so it must be converted to monomers Gastrointestinal tract is to make the food in absorbable form by help of chewing and mixing with various enzymes in mouth to small intestine

4. Digestive process is accomplished by mechanical and enzymatic breakdown (chemical) of food into simpler chemical compounds .

5. Digestive system

6. Components of GIT Primary Digestive Organs Accessory Digestive Organs Oral Cavity, Pharynx Teeth Oesophagus Tongue, Salivary glands Stomach Pancreas Duodenum Jejunum Liver Ileum Gall bladder Jejunum Cecum Colon Rectum and anal canal

7. WALL OF GASTROINTESTINAL TRACT In general, wall of the GI tract is formed by four layers which are from inside out: 1. Mucus layer 2. Submucus layer 3. Muscular layer 4. Serous or fibrous layer .

8. Mucus layer is the innermost layer of the wall of GI tract. Mucosa has three layer of structures: i . Epithelial lining ii. Lamina propria iii. Muscularis mucosa.

9. Epithelial Lining Epithelial lining is in contact with the contents of GI tract. The inner surface of mouth, surface of tongue, inner surface of pharynx and esophagus have stratified squamous epithelial cells. However , mucus membrane lining the other parts such as stomach, small intestine and large intestine has columnar epithelial cells.

10. Lamina Propria Lamina propria is formed by connective tissues, which contain fibro blasts, macrophages, lymphocytes and eosinophils . Muscularis Mucosa Muscularis mucosa layer consists of a thin layer of smooth muscle fibers. It is absent in mouth and pharynx. It is present from esophagus onwards .

11. SUBMUCUS LAYER Submucus layer is also present in all parts of GI tract, except the mouth and pharynx. It contains loose collagen fibers , elastic fibers, reticular fibers and few cells of connective tissue. Blood vessels, lymphatic vessels and nerve plexus are present in this layer .

12. MUSCULAR LAYER Muscular layer in lips, cheeks and wall of pharynx contains skeletal muscle fibers . The esophagus has both skeletal and smooth muscle fibers. Wall of the stomach and intestine is formed by smooth muscle fibers.

13. Smooth muscle fibers in stomach are arranged in three layers : i . Inner oblique layer ii. Middle circular layer iii. Outer longitudinal layer. Smooth muscle fibers in the intestine are arranged in two layers : i . Inner circular layer ii. Outer longitudinal layer. Auerbach nerve plexus is present in between the circular and longitudinal muscle fibers

14. NERVE SUPPLY TO GASTROINTESTINAL TRACT GI tract has two types of nerve supply: Intrinsic nerve supply Extrinsic nerve supply Intrinsic nerves to GI tract form the enteric nervous system that controls all the secretions and movements of GI tract . Nerve fibers of this system are interconnected and form two major networks called-1. Auerbach plexus 2 . Meissner plexus.

15. Auerbach Plexus Auerbach plexus is also known as myenteric nerve plexus. It is present in between the inner circular muscle layer and the outer longitudinal muscle layer. Major function of this plexus is to regulate the movements of GI tract. Excitatory neurotransmitter substances like acetylcholine, serotonin etc. inhibitory neurotransmitters such as vasoactive intestinal polypeptide (VIP), neurotensin and enkephalin .

16. Meissner Nerve Plexus. situated in between the muscular layer and sub mucosal layer of GI tract. Function of Meissner plexus is the regulation of secretory functions of GI tract. These nerve fibers cause constriction of blood vessels of GI tract.

17. EXTRINSIC NERVE SUPPLY Extrinsic nerves that control the enteric nervous system are from autonomic nervous system . Both sympathetic and parasympathetic divisions of autonomic nervous system innervate the GI tract. Sympathetic nerve fibers inhibit the movements and decrease the secretions of GI tract by secreting the neurotransmitter noradrenaline. It also causes constriction of sphincters.

18. Paras ympathetic Nerve Fibers Parasympathetic nerve fibers accelerate the movements and increase the secretions of GI tract. The neurotransmitter secreted by the parasympathetic nerve fibers is acetylcholine (Ach ).

19. Structure of wall of the GIT

20. Structure of wall of the GIT

21. Salivary functions and its regulation Saliva is the mixed glandular secretion which constantly bathes the teeth and the oral mucosa First secretion encounter the food It is vital for oral health It is constituted by the secretions of the three paired major salivary glands; Parotid, sub mandibular and sublingual It also contains the secretions of the minor salivary glands

22. Structure of salivary Glands

23. Parotid gland Parotid Is large accounts for 50% sec. of saliva (when stimulated) Situated in front of ear behind the ramus of mandible Gland drain in to oral cavity opposite to second molar tooth Secretions are basically serous

24. Submandibular and sub lingual gland The submandibular gland is variable in size being about half the size of the parotid lies above the mylohyoid in the floor of the mouth. It opens into the floor of the mouth underneath the anterior part of the tongue The sublingual is the smallest of the paired major salivary glands, It is situated in the floor of the mouth beneath the sublingual folds of mucous membrane .

25. Structure of salivary gland

26. Composition of saliva Water 99.55% solid 0.45% pH 7.04 Na, K, Ca , Mg, Cl , HCO3 - and phosphate Organic substances includes IgA, Lysozymes, albumin, glucose, lactate , salivary amylase, lingual lipase urea and ammonia etc . Normal salivary flow rates are 0.3-0.4 ml/min when unstimulated and 1-1.5 litre /day when stimulated Approximately 0.5 – 0.6 litres of saliva is secreted perday

27. Functions of saliva Initiate the digestion of starch Protects oral cavity (IgA and lysozymes) Provide lubrication for food to make bolus Facilitate the taste When salivary flow is reduced, dryness of the mouth occurs and information from osmoreceptors are translated to increase the water intake Helps in speaking, swallowing, chewing Buffer the gastric secretions reflux in to the oesophagus

28. Function of Parasympathetic Fibers Stimulation of parasympathetic fibers of salivary glands causes secretion of saliva with large quantity of water. Function of Sympathetic Fibers Stimulation of sympathetic fibers causes secretion of saliva , which is thick and rich in organic constituents such as mucus.

29. Control of salivary secretion Basically controlled by parasympathetic, sympathetic stimulation causes proteinaceous secretion without affecting the volume

30. Xerostomia (salivary flow< 0.2 ml/min) The presence of saliva is vital to the maintenance of healthy hard (teeth) and soft (mucosa) oral tissues. Severe reduction of salivary output results in a rapid deterioration in oral health Patients suffering from dry mouth can experience difficulty with eating, swallowing, speech, the wearing of dentures, trauma to and ulceration of the oral mucosa, taste alteration, poor oral hygiene, a burning sensation of the mucosa, oral infections including Candida and rapidly progressing dental caries After radio therapy, old age and multidrug therapy