Advanced Physiology (part 1, Digestive system)

2. فیزیولوژی تکمیلی Advanced Physiology(part 1, Digestive system) By: A. Riasi (PhD in Animal Nutrition & Physiology)

3. Introduction • The primary function of digestive system • Intracellular and extracellular process in digestive system • Three specific regions in most animals digestive system: • Foregut • Midgut • Hindgut

4. Introduction • Digestive systems perform four basic digestive process: • Motility • Propulsive movements • Mixing movements • Secretion • Digestion • Absorption

5. Introduction

6. Introduction • The digestive system of animals consists of: • The digestive tract (gastrointestinal tract) • Accessory digestive organs • Additional function of the digestive tract: • Osmoregulation • Endocrine secretion • Immune function • Elemination of toxins

7. Introduction • Regulation of digestive function is complex and synergetic • The smooth muscle cells of digestive system are single unit type • The nervous system control digestive system function • Intrinsic nerve plexuses • Extrinsic nerves

8. Introduction The four layers are the same from esophagus to anal canal

9. Introduction

10. Introduction

11. Introduction The enteric nervous system of a rat’s stomach

12. Introduction • Receptor activation alters digestive activity through neural reflexes and hormonal pathways • Three different types of sensory receptors: • Chemoreceptors • Mechanoreceptors (pressure receptors) • Osmoreceptors

13. Different parts of digestive tract and the functions

14. Mouth • Obtaining and receiving food

15. Mouth • Taste buds are composed of groups of about 40 columnar epithelial cells bundled together along their long axes.

16. Salivary glands • Acini is a secretary unit of salivary gland • Each acini secrete a fluid into collecting ducts • Water • Electrolytes • Mucus • Enzymes

17. Salivary glands • Three major parts of salivary glands • Parotid glands • Submaxillary glands • Sublingual glands

18. Salivary glands

19. Salivary glands In the histological sections of salivary gland shown above, the cells stained pink are serous cells, while the white, foamy cells are mucus-secreting cells.

20. + Other input Cerebral cortex + Salivary center in medulla + Conditioned reflex + Pressure receptors and chemoreceptors in mouth Autonomic nerves Simple reflex + Salivary galnds + Salivary secretion • Control of salivary secretion

21. Salivary secretion in sheep

22. Swallowing • Eating and swallowing are complex neuromuscular activities consisting essentially of two stages: • Oropharyngeal stage • Esophageal stage

23. Esophagus • Anatomically and functionally, the esophagus is the least complex section of the digestive tube • It contains the crop in poultry

24. Esophagus • There are two physiologic sphincters: • Upper and lower esophageal sphincters. • In ruminants, a nasopharyngeal sphincter is present.

25. Esophagus in birds

26. Stomach In monogastric mammals, the stomach is divided into three section:

27. Stomach

28. Stomach • Microscopic anatomy of the stomach • Muscularis: has an additional oblique layer • Epithelial lining composed of goblet cells • Gastric pits contain gastric glands

29. A remarkable ability for significant changes in volume

30. Stomach • Two distinct areas for secretion of gastric digestive juice: • Oxyntic mucosa (contain three type of cells) • Mucous cells • Chief cells • Parietal cells or oxyntic cells • Pyloric gland area (PGA): • Mucous cells • Chief cells

31. Gastric secretion cells:

32. Gastric secretion cells • Exocrine cells • Paracrine cells • Endocrine cells

33. Mechanism of HCl secretion

35. Control of gastric secretion • Cephalic phase (Mediated by vagus nerve and acetylcholin) • Gastric phase (gastrin has the main effect) • Intestinal phase (intestinal gastrin has the main effect)

36. The duodenal factors trigger either neural or hormonal responses • Neural response is mediated through two reflexes: • Intrinsic nerve plexus (short reflex) • Autonomic nerves (long reflex) (These reflexes are called the enterogastric reflex) • The hormonal response involves the release duodenal’s several hormones: • Secretin • CCK • Gastric inhibitory peptide or glucose-dependent insulinotrophic peptide • Avian pancreatic polypeptide (APP) (These hormones are known as enterogastrones)

38. Gastric emptying and mixing

39. Factors that influence the rate of gastric emptying A- Stomach factors • Amount of chyme in the stomach (more effect) • Vagus nerve • Stomach hormone gastrine • The degree of fluidity of the chyme B- Duodenum factors • Fat (more effect) • Acid • Hypertonicity • Distention

40. Bird stomach • Proventriculus-gizzard processes of digestion in birds • There are two type of glands into the proventriculus: • Simple mucosal glands that secrete mucus • Submucosal glands that secrete HCl and pepsinogen Interestingly, unlike in mammals, both HCl and pepsinogen are synthesized with in the same cell (chief or oxynticopeptic cell)

41. Bird stomach • The mucosal lining of the gizzard is covered by koilin • In birds myoglobin content of the gizzard is approximately 100-fold greater than the breast muscle, and mitochondrial numbers are also elevated.

42. Ruminant stomach • Rumen development

43. Ruminant stomach • Rumen development Undeveloped Rumen Developed Rumen

44. Ruminant stomach • Pre-ruminant period

45. Ruminant stomach • Pre-ruminant period

46. Absorptive surface area is enhanced by increasing: Papillae length Papillae width Papillae density • Ruminant stomach

47. Milk only Milk and grain Milk and hay • Ruminant stomach

48. Ruminant stomach • The interior surface of the rumen forms numerous papillae

49. Ruminant stomach The 4 layers of the rumen epithelium: stratum corneum (SC), stratum granulosum (SG), stratum spinosum (SS) and stratum basal (SB).

50. Ruminant stomach Light micrographs of rumen papillae biopsied during the high forage and hogh grain diets (Adapted from Steele et al. 2009)