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Gastroinstestinal System Lecture 2

Physiology II. Gastroinstestinal System Lecture 2. Dr Than Kyaw 30 April 2012. Ruminant and monogastric Digestion. Ruminant digestion Monogastric digestion Enzymes and hormones Digestion products Absorption and utilization. Compound stomach.

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Gastroinstestinal System Lecture 2

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  1. Physiology II Gastroinstestinal SystemLecture 2 Dr Than Kyaw 30 April 2012

  2. Ruminant and monogastricDigestion • Ruminant digestion • Monogastric digestion • Enzymes and hormones • Digestion products • Absorption and utilization

  3. Compound stomach (multichambered , polygastric, ruminant stomach) • Consume fibrous foods - forages (grasses) - roughages - other fibrous food sources • Plant materials other simple stoach animals are unable to digest. • Fermented in the rumen with the help of microbes (microflora) Cellulose and semicellose To valuable products

  4. 4 compartments • Rumen (paunch) • - Bacterial and chemical breakdown of fiber (anaerobic) • - Occupy most of the left-side of the abdomen • - Has thick, muscular wall • - Papillae on walls: up to 1 cm. in length, bacteria more concentrated • - Rumen capacity • - 50 to 65 gallons (dairy cattle) • - 5 to 10 gallons (sheep)

  5. Right longitudinal grove Dorsal coronary groove Dorsal sac Posterior Dorsal blind sac Posterior ventral blind sac Ventral coronary groove Ventral sac

  6. Papillae in Rumen Papillae in Rumen Interior surface of rumen - numerous papillae - vary in shape and size - short and pointed to long and foliate.

  7. 4 compartments • Reticulum (honey combs) • interior surface – looks like honeycomb • helps to remove foreign matter from the food material.

  8. Reticulum - full Reticulum - cleaned Epithelium of reticulum - thrown into folds that form polygonal cells - honey-comb appearance - Numerous small papillae

  9. 4 compartments • Omasum (book stomach) • - round and muscular • - “Grinds” the food material and prepares the food material for chemical breakdown.

  10. Omasum - full Inner surface of omasum - Broad longitudinal folds or leaves (lay term - 'book'). - Omasal folds - packed with finely ground ingesta - Estimated to be 1/3 of the total surface area of the forestomachs.

  11. 4 compartments Abomasum – inside view • Abomasum (true stomach) • very similar to the stomach of non-ruminants • the majority of chemical breakdown of food material occurs. • mixes in digestive enzymes (pepsin)

  12. Size of young and adult ruminants Important to know the development of ruminant stomach for feeding young and adult

  13. Compartment size of young and adult ruminants

  14. Rumen microbes (micro flora) • Bacteria: Over 60 spp • - digest sugars, starch, fiber, and protein for the cow. • Protozoa: About 35 spp (size: 20 – 200 μ) • - some spp swallow and digest bacteria, starch granules, and some fiber. • Bacteria and protozoa • – differ greatly in size, shape, and structure

  15. Rumen microbes (micro flora) • Fungi • - verysmall fraction • - important in splitting plant fibers open to provide • easy digestion by bacteria

  16. Protozoa of rumen A Protozoan A fungal spore A Protozoan dividing into two Bacteria attaching under side of the protozoan A Protist found in rumen

  17. Some protozoan and bacteria have symbotic relationship Protozoan covered with chains of bacteria

  18. Bacteria attacking a strand of Fiber taken from a cow’s rumen.

  19. Rumen microbes (micro flora) • - One trilion microbes/oz of ruminal fluid • multiply in double in 11 minutes • Almost all rumen microbes – anaerobic • 2/3 of feed digestion • 90% of fiber digestion In rumen

  20. Rumen microbes (micro flora) • - Rumen bacteria – good source of protein for the host • Microbes - 55% of protein and may provide up to half of total dietary need • Urea – can be utilized by microbes (synthesis of microbial protein) • Vitmins K and B-complex synthesis • adapted to a pH between roughly 5.5 and 6.5 • Abomasum pH: 2 to 4

  21. 3 primary zones based on their specific gravity • Gas rises to fill the upper regions • Grain and fluid-saturated roughage ("yesterday's hay") sink to the bottom • Newly arrived roughage floats in a middle layer.

  22. Ingesta flow • Digestion

  23. Compound stomach • Ruminal motility • - mix the ingesta • - aid in eructation of gas • - propel fluid and fermented foodstuffs into the omasum • - Supression of motility - ruminal impaction • Cycles of contraction - 1 to 3 times/min • - During feeding - highest frequency • - During resting - lowest

  24. Ruminal motility Two types of contractions Primary contractions - Originate in the reticulum - Pass caudally around the rumen - Involves a wave of contraction followed by a wave of relaxation, so as parts of the rumen are contracting, other sacs are dilating Secondary contractions - occur in only parts of the rumen - usually associated with eructation.

  25. Rumination Rumination (cud chewing) - regurgitation of ingesta from the reticulum - remastication - resalivation and - redeglutition (reswallowing) Provides - effective mechanical breakdown of roughage - increases substrate surface area to fermentative microbes.

  26. Rumination Sequences Result - Contraction of reticulum - Relaxation esophageal sphincter - Inspiratory movement with closed glottis - Negative pressure in the thorax - Dilation of thoracic esophagus and cardia - Reverse peristalsis Roughage + Fluid to mouth Flow of ingesta Rumination time = about 8 h/d 1 circle of rumination = 1 min

  27. Eructation – Enormous quantity of gas by fermentation – About 30-50 liters/h in adult cattle 5 l/h in a sheep or goat - Eructation or belching - continually get rid of fermentation gases - eructation is associated with almost every secondary ruminal contraction - Eructated gas travels up the esophagus at 160 to 225 cm/s

  28. Eructation • - Any interferences with eructation – life threatening • Expanding rumen rapidly interferes with breathing • Animals suffering ruminaltympany (bloat) die from asphyxiation.

  29. Fermentation in the rumen Carbohydrate fermentation • Fibrous feed (cellulose, hemicellulose, xylans) • Readily fermentable CHO (starch, sugars) • Principle end products - VFAs Volatile fatty acids - CO2 - CH4 - Heat

  30. Volatile Fatty Acids Microbial Fermentation • VFA’s Carbohydrates × Glucose Butyric acid (4c) Acetic acid (2c) Propionic acid (3c) - Rumen, cecum, colon

  31. VFA Formation 2 acetate + CO2 + CH4 + heat 1 Glucose 2 propionate + water 1 butyrate + CO2 + CH4 - VFAs absorbed passively from rumen to portal blood - Provide 70-80% of ruminant’s energy needs

  32. Uses of VFA • Acetate • Energy • Fatty acid synthesis • Propionate • Energy • Gluconeogenic – glucose synthesis • Butyrate • Energy • Rumen epithelial cells convert to ketone Proportions produced depends on diet - Fibrous feed – less propionic/a - carbohydrate feed – more propionic/a

  33. Absorption of VFAs • No evidence for active transport • VFA metabolism in the rumen wall • Cells use most of the butyrate for their own energy needs • Acetate and propionate are ‘exported’ to blood

  34. Fermentation of plant protein • Amino/a • Ammonia • Organic acids • Proteolytic • organisms • Plant proteins • Resynthesized to different microbial proteins • Rumen microbes – also able to utilze non-protein nitrogens • - urea, biurets, amines

  35. Fermentation of lipids • Plant contains limited amount of lipids • Lipids found in most plant = galactosyldiglycerides • Microbes do not alter lipids very much • Can synthesize some lipids • Cannot tolerate if dietary fat contains 5 – 7% of total diet

  36. Digestion in simple stomach Discussed in Lecture (1) Stomach produces: • - HCl(stomach pH about 2, pareitel cell) - pepsinogen (pepsin, Chief cell) - gastric lipase (fat digestion) - mucus (protect the stomach epithelium) - gastrin (hormone – G-cell; stimulate gastric secrretions - signals S/I to prepare for arrival of food)

  37. Digestion in simple stomach Pepsinogen • Digest mainly protein to polypeptides • Kill pathogens Proteinin bolus HCl pepsin (Pro-enzyme/ Precursor of pepsin) Peptide - Liquids - removed quickly (about 30 m) - Solid portion (chyme) - takes hours

  38. Small intestine 3 parts - Duodenum - Jejunum - Ileum. • Smooth m/s • - circular (segmental contraction) • - longitudinal (contract a wave-like action – peristalsis) • - further digestion and absorption of nutrients • - micro villi on the epithelium

  39. Small intestine Digesta pHFunctions Duodenum 2.7 - 4 Enzymes pH change Flow rate regulation very little absorption Jejunum 4 – 7 Enzymes Absorption Ileum 7 - 8 Absorption Limited fermentation • Rate of pH increase through small intestine is faster in monogastrics.

  40. Enhanced Surface Area for Increased Nutrient Absorption Intestinal villi Note: provision of Large surface areas by the micro villi for absorption

  41. Gastrointestinal Hormones • Gastrin • Origin: stomach, abomasum • Stimulus: food in stomach • Function: stimulates HCl & pepsinogen secretion, increases stomach motility • Secretin • Origin: duodenum • Stimulus: acid • Function: stimulates pancreatic secretions; slows stomach motility and acid production

  42. Gastrointestinal Hormones • Cholecystokinin (CCK) • Origin: duodenum • Stimulus: fat & protein in duodenum • Function: stimulates bile and pancreatic secretions • Also regulates appetite and feed intake • Gastric Inhibitory Protein (GIP) • Origin: duodenum • Stimulus: fats and bile • Function: inhibit stomach motility and secretion of acid and enzymes

  43. Pancreas and its secretions • - long, thin delicate organ • pinkish gray, glandular • Secretions of pancreas • Exocrine • - enzymes and carbonates  • Endocrine • - hormones

  44. Pancreas and its secretions • Enzymes • 1. Amylase: -- carbohydrate digestion (starch, dextrin) • mainly to disaccharides (maltose) • -- amylase low in ruminants • 2. Lipase: fat digestion • - triglycerides to monoglycerides and free fatty acids

  45. Pancreas and its secretions • 3. Proteases*: protein digestion • Trypsinogen - converted to trypsin (by enterokinase) • Chymotrypsinogen - converted to chymotrypsin (by trypsin) • Procarboxypeptidase - converted to carboxypeptidase (by trypsin) • 4. Nucleases • Digest nucleic acids and nucleotides • Lecithinase • Lecithin to lysolecithin • Inorganic compound • NaH2CO3– neutralize acids • Secretion - pH is 7.2-7.8 * Enzymes are ususally released in inactive forms in the source organs. Why? - They are capable of doing autodigestion.

  46. Pancreas and its secretions • Endocrine • - islets of Langerhans • - insulin ( beta cells) • - glucagon (alpha cells) • - somatostatin (delta cells)

  47. 1. Insulin Main functions -- Fat Break down inhibited -- promote fat deposition and glycogenesis -- enhance glucose transport across cell membrane and facilitate diffusion Blood Glucose uptake of glucose Muscle, Liver (Stored as glycogen) Insulin uptake of amino/a Amino acids Used for protein synthesis by all cells Insulin - All essential amino/a (balanced ration) are needed for protein synthesis

  48. 2. Glucagon Glycogen Glycogenolysis Opposite effect of insulin glucagon Blood glucose Fat (Lipolysis) glucagon Blood glucose

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