Fisiología y anatomía del sistema digestivo

Descripción fisiologica del sistema digestivo

1. 1 The Digestive System The ENTERIC (GI) system Mouth to anus Long tube with different structures and functions Accessory glands salivary glands pancreas liver gallbladder

2. 2 Objectives: Digestive System Understand the digestive system is a series of tubes with different epithelia and cells = mouth to the anus Describe the 4 layers in the tubes (mucosa, submucosa, muscularis externa, adventitia or serosa Describe the structure and functions of each organ: mouth, esophagus, stomach, duodenum, small intestine, and large intestine. Describe the structure and function of the accessory organs (salivary, pancreas, liver, and gallbladder) Understand and describe the control mechanisms: nervous system (intrinsic and extrinsic) and hormonal – paracrine and endocrine mechanisms Describe the secretory cells in the tubes and accessory glands Understand why motility (via muscle contraction) of the tubes is important Explain where and how the processes of digestion, absorption, and excretion occur

3. The Plan Introduction – 1. General concepts Follow food as it moves thru the digestive tract and discuss the anatomy and physiology or each area 2. Mouth thru esophagus 3. Stomach 4. Duodenum and accessory glands – liver, gall bladder and pancreas 5. Small intestine and large intestine 3

4. 4 Readings – Digestive 1 McKinley, O ’ Loughlin, and Bidle, Anatomy and Physiology An integrative Approach, p 1015-1061. Overview of the Digestive System 1015-1019

5. The Gastrointestinal Tract For better or for worse, the gut are exquisitely designed to acquire every calorie out of every meal

6. Physiological Processes of the Digestive Tract - simplified 1. 2. 3. 4.

7. 7 What does the digestive system do? Think about it: First 2 functions you think of What happens when you first smell fresh apple pie? What does your stomach do? How long is the intestine? Does your GI tract move; make noise? Does your nervous system control the GI tract? Why do you eat food?

8. 8 What happens when you first smell fresh bread? The body gets ready for digestion : Salivary glands release Serous and mucous fluid Amylase – breaks down carbohydrates Lipase – lipid digestion Stomach begins to churn (muscles) and acid & enzymes are released Pancreas and gall bladder activate These are controlled by the CNS – the extrinsic nervous system.

9. 9 What happens when you first taste fresh bread? ( food in your mouth ) Salivary glands release Serous and mucous fluid Digestion begins Amylase – breaks down carbohydrates Lipase for lipid digestion Chewing (mastication) and mixing of food with tongue Stomach muscles contract, acid and enzymes released Pancreas and gall bladder secrete

10. 10 What happens when you swallow the chewed bread? Tongue helps move food bolus to the oropharynx (mouth) Skeletal muscles in the pharynx move food to esophagus Esophagus = a conduit to stomach muscles contract to allow peristalsis glands secrete to moisten food (oro)pharynx esophagus

11. 11 What happens to the bread in the stomach ? Stomach functions: Storage of food Mixing via muscle contractions Release of H + & Cl - and pH lowers kills bacteria Degrades foods = chyme Cells release pepsinogen – a zymogen Pepsinogen converted to pepsin in low pH – cleaves proteins Digestion continues via Acid and pepsin Amylase, lipase stomach

12. 12 What happens to bread (chyme) in the small intestine Acidic Fluids flow into the small intestine: digestive enzymes and bicarbonate (HCO 3 - ) added from Pancreas Liver makes bile for lipid absorption Water added and reabsorbed Digestion accelerates and pH neutralized to pH ~ 7 Absorption of building blocks through enterocytes to the liver via the portal blood system Undigested material remains small intestine

13. 13 What happens to chyme in the large intestine ? Dehydration of indigestible material Compaction of indigestible material Elimination of undigested material large intestine

14. 14 Accessory glands for the digestive system – (see small intestine) Salivary glands Moistening/lubricating fluid with enzymes Amylase helps break down starch; lipase - lipids Pancreas Release of digestive enzymes Release of bicarbonate (HCO 3 - ) solution Endocrine functions = insulin & glucagon Liver Makes bile -- helps dissolve fats Receives and stores building blocks (aa, CHO, etc.) from intestine Makes blood proteins Detoxifies drugs Gallbladder Stores and concentrates bile (from liver)

15. Digestive System (Figure 26.1) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Accessory Digestive Organs Gastrointestinal (GI) Tract Teeth Tongue: mechanical proces sing , moistening, and mixing with salivary secretions Salivary glands: secretion of lubricating fluids with enzymes to breakdown carbohydrates and lipids Liver: synthesis of bile, storage of nutrients, many other functions Gallbladder: Storage, concentration and secretion of bile Pancreas: exocrine portion secrete buffers and digestive enzymes and endocrine portion secretes hormones Anus Large intestine: dehydration and compaction of materials in preparation for elimination (3 ’ ) Small intestine: enzymatic digestion and absorption of nutrients (20 ’ ) Stomach: chemical breakdown of materials by acidic and enzymatic processing and mechanical mixing via muscular contractions ( 12 ” ) Esophagus: conduit to the stomach (15 ” ) Oral cavity Pharynx: muscular propulsion of materials into the esophagus Summary

16. 16 Retroperitoneal Posterior to the parietal peritoneum Embedded in connective tissue duodenum pancreas parts of the lg intestine Intraperitoneal (with in) Bordered by a single cell - mesothelium Peritoneal cavity Omentum (from ‘ epipleein ’ Gk.) meaning to float on; Mesentery is a double layer of peritoneum Fig 24.2 Concepts and characteristics

17. 17 Mesentery Supports 20 ’ of small intestine – hold in place yet allows movement Allows blood vessels and nervous system to enter and leave

18. 18 Design of the tube: Structure Control mechanisms: Neural - intrinsic = Enteric NS - extrinsic = CNS Control mechanisms: Hormonal - signaling molecules - secretions - motility of muscles Digestion and Absorption General concepts for the Digestive System food H 2 O, ions H 2 O, ions ‘ Inside tube is outside body ’

19. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. #1 Mucosa Epithelium Lamina propria Muscularis mucosae #2 Submucosa Submucosal nerve plexus #3 Muscularis Inner circular layer Myenteric nerve plexus Outer longitudinal layer #4 Serosa or Adventitia Vein, artery, lymph vessel (within mesentery) (a) Tunics Lumen Design of the Four Layers in the GI System fig 26.2 changes

20. 20 #3 Muscularis externa mesothelium Lamina propria #2 Submucosa Muscularis mucosa Different surfaces #4 Serosa 4 layers – different diagram Submucosal gland From salivary glands, pancreas or liver mesentery #1 Mucosa – epithelium, lamina propria, muscularis mucosa

21. 21 Peristalsis, segmentation, and … Peristalsis – process that moves chyme forward – in 1 direction Segmentation – irregular contractions forcing chyme in both directions NO NET PROGRESS Passes nutrients back and forth to optimize absorption Interstitial cells of Cajal – motor neurons in the myenteric plexus Intrinsic control Slow, constant contractions Fig 24.4 LUMEN Ganglia!

22. Control Mechanisms 1. Neuronal (neurocrine) A. Short or Intrinsic Reflex – neurons within the GI system (ENS = enteric nervous system) Signal from the lumen to the ENS and back The only organ system capable of using a reflex response without the CNS B. Long or Extrinsic Reflex – neurons in the CNS – (outside the ENS) Signal from the lumen to the CNS and back to the GI tract 2. Hormonal – enteroendocrine cells in the GI epithelium and endocrine glands Paracrine Endocrine 22

23. Neural controls of the GI System Extrinsic = CNS Intrinsic = ENS More neurons in the gut than in the spinal cord

24. 24 Control mechanisms : #1a. Neural – Intrinsic Enteric NS = short reflex Sensory neurons receive signals from the lumen. They contain: Mechanoreceptors - for stretch Chemoreceptors - pH, osmolarity, food breakdown products Signals go to intrinsic Parasympathetic neurons – ’ rest and digest ’ Cause cell/gland secretions and muscle contractions Sympathetic fibers – shut enteric system down Mostly inhibit parasympathetic neurons Control blood flow Interneurons important for local reflexes Motor neurons drive smooth muscle PNS: neurons intrinsic to the digestive system (GI) = Enteric nervous system - ‘ the little brain ’

25. 25 Control mechanisms : #1b. Neural – Extrinsic CNS = long reflex Input from 5 senses in CNS signal GI system Starts gland and cell secretions in mouth and stomach Starts muscle contractions in stomach OR Signals in GI are sent to the CNS Sensory information(from GI) = afferent to CNS and response = efferent back to GI system = REFLEX CNS sends signals to enteric neurons controls GI gland and cell secretions controls GI muscle contractions– indirectly through CNS influences can be modified by autonomic NS Parasympathetic and sympathetic Emotions (CNS) effect enteric system Butterflies when flying 1 st time Talking in front of a class – mouth is dry Really scared – urination or diarrhea

26. 26 The Enteric Nervous System Myenteric plexus (Auerbach ’ s) Intrinsic versus Extrinsic Controls Submucosal plexus (Meissner ’ s) Intrinsic Nervous system Extrinsic NS signals

27. 27 Signaling mechanisms 1. Autocrine – signal goes back to cell of origin 2. Paracrine – signal goes short distance to nearby cells 3. Endocrine mechanisms lumen Blood vessel REVIEW Enteroendocrine cell

28. 28 Control mechanisms: #2. Hormonal Hormonal mechanisms Enteroendocrine cells ‘ taste ’ chemicals in the lumen Enteroendocrine release peptide hormones Released into CT and then blood vessels Function via paracrine & endocrine mechanisms Controls secretion of gland cells (stomach, pancreas, etc.) Controls - enhance or inhibit muscle contraction Influence intrinsic and extrinsic nervous system inputs Endocrine hormones, eg. insulin, glucagon, etc

29. 29 Glands - Exocrine glands – release of products through duct systems Endocrine glands – release of products into the circulation (blood vessels) to circulate to target cells enteroendocrine cells secrete peptides GI is the largest endocrine gland – Review

30. 30 Secretions: cells & glands Enteroendocrine cells (stomach, duodenum …) Respond to events in the lumen (mechanical or chemical) = ‘ taste buds ’ of the gut Secrete peptides – paracrine & endocrine (into the circulation) Example: G cells release gastrin – a peptide Gastrin – to near cells and enters into blood vessels and controls Cell secretion Muscle motility Some also respond to CNS neural inputs Exocrine Glands (gland cells secrete into ducts) Salivary glands make H 2 0 and enzymes Liver makes bile Pancreas makes digestive enzymes and bicarbonate (HCO 3 - ) Duodenal glands make bicarbonate (HCO 3 - ) to neutralize HCl

31. 31 Motility = muscle movement Skeletal muscle = voluntary control from CNS Tongue and pharynx Upper 2/3 esophagus Anal region sphincter Smooth muscle = involuntary control Intrinsic control from enteric parasympathetic neurons on: Muscularis mucosa: smooth muscle Muscularis externa: inner circular and outer longitudinal bands Extrinsic control from the CNS neurons CNS neurons stimulate ENS parasympathetic neurons Control muscles in the enteric nervous system Modified by sympathetic neurons

32. Smooth Muscle Motility Necessary functions: Mixing of food, acid and enzymes in the stomach Slow release of chyme into the small intestine Controls movement through small intestine and thus rate of digestion Movement and removal of indigestible material Structure – smooth muscle cells Closely positioned elongated cells w/o direct synapses Gap junctions allow synchronous contractions of many cells Actions Depolarization allows Ca ++ influx or release of intracellular Ca ++ Contraction of smooth muscle cells Causative agents Release of neurotransmitter from ENS neurons Signal molecules (histamine, serotonin, etc.) 32

33. 33 Sensory receptors Stimulus (sight, smell, etc) 1. Muscle contraction or relaxation 2. Exocrine gland secretion : enzymes, mucous, acid, bicarbonate 3. Endocrine secretion : peptides, insulin Digestive system Responses Enteric nervous system Sensory receptors of neurons Enteric neurons (ganglia/ plexus) (Parasympathetic) increase in activity Stimulus: (stretch, pH, osmolarity, products of digestion) Smooth muscles or secretory cells Green arrows = short (intrinsic) reflex Blue arrows = long (extrinsic) reflex (Sympathetic) decrease in activity

34. 34 Digestion, Absorption & Elimination Digestion – break down of foodstuffs to basic building blocks (aa, sugars, fats, nucleotides) Absorption – passage of building blocks from intestine via portal system to the liver Elimination – release of waste products and recovery of fluids

35. 35 Summary: Digestive System Series of tubes with different epithelia and cells = mouth to the anus 4 layers to the tubes (mucosa, submucosa, muscularis externa, adventitia or serosa Accessory organs (salivary, pancreas, liver, and gallbladder) Controls: nervous system (extrinsic and intrinsic) and hormones – paracrine and endocrine mechanisms Secretory cells in the tubes and accessory glands Motility (muscle) of the tubes is important Digestion, absorption, and excretion occur

36. 36 What does the digestive system do? First 2 functions you think of What happens when you first smell fresh apple pie? What does your stomach do? How long is the intestine? Does your GI tract move, make noise? Does your nervous system control the GI tract? Why do you eat food?

37. For those who want more .. The next 3 images are alternative examples to explain the difference between the intrinsic (short) reflex and the extrinsic (long) reflex. I have put an explanation of each figure in the ‘ notes ’ feature presented in PowerPoint below the images

38. 38 Interactions in the Digestive System Important Fig 24.5

39. 39 Credit to Dr. G. Mawe Intrinsic neurons Sensory Neurons Associated with the Gut Sensory Neurons Associated with the Gut

40. 40 Credit to Dr. G. Mawe efferents efferents Efferent Intrinsic neurons