1. SISTEMA DIGESTIVO
Es un tubo abierto: extensión del medio ambiente! E S
absorción
Digestión:
mecánica (trituración)
química (enzimas hidrolíticas)

2. EL TRACTO DIGESTIVO

3. Anatomía del sistema digestivo
Digestive tract
Alimentary tract or canal
GI tract
Accessory organs
Primarily glands
Regions
Mouth or oral cavity
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Anus

4. Oral Cavity Mouth or oral cavity Lips (labia) and cheeks
Vestibule: Space between lips or cheeks and alveolar processes
Oral cavity proper
Lips (labia) and cheeks
Palate: Oral cavity roof
Hard and soft
Palatine tonsils
Tongue: Involved in speech, taste, mastication, swallowing

5. Teeth Two sets Types Primary, deciduous, milk: Childhood
Permanent or secondary: Adult (32)
Types
Incisors, canine, premolar and molars

6. Tooth structure:

7. Salivary Glands Produce saliva Three pairs
Prevents bacterial infection
Lubrication
Contains salivary amylase
Breaks down starch
Three pairs
Parotid: Largest
Submandibular
Sublingual: Smallest

9. Production of Salivary juice

10. SALIVARY SECRETIONS Serous secretion that contains ptyalin, which is an enzyme for digesting starches.
2. Mucous secretion that contains mucin for lubricating and for surface protective purposes.
3. Saliva also contains IgA antibodies and lysozyme, which help to destroy any microorganisms in the oral cavity.

11. Swallowing reflex: Soft Palate & Esophagus
Figure 21-13: The swallowing reflex

12. Deglutition (Swallowing)
Three phases
Voluntary
Bolus of food moved by tongue from oral cavity to pharynx
Pharyngeal
Reflex: Upper esophageal sphincter relaxes, elevated pharynx opens the esophagus, food pushed into esophagus
Esophageal
Reflex: Epiglottis is tipped posteriorly, larynx elevated to prevent food from passing into larynx

13. Histología del tracto digestivo

14. Peritoneum and Mesenteries
Visceral: Covers organs
Parietal: Covers interior surface of body wall
Retroperitoneal: Behind peritoneum as kidneys, pancreas, duodenum
Mesenteries
Routes which vessels and nerves pass from body wall to organs
Greater omentum
Lesser omentum

15. Pharynx and Esophagus Esophagus Pharynx
Transports food from pharynx to stomach
Passes through esophageal hiatus (opening) of diaphragm and ends at stomach
Hiatal hernia
Sphincters
Upper
Lower
Pharynx
Nasopharynx
Oropharynx: Transmits food normally
Laryngopharynx: Transmits food normally

16. Functions Ingestion: Introduction of food into stomach
Mastication: Chewing
Propulsion
Deglutition: Swallowing
Peristalsis: Moves material through digestive tract

17. Stomach Anatomy: Openings Regions Gastroesophageal: To esophagus
Pyloric: To duodenum
Regions
Cardiac
Fundus
Body
Pyloric

18. Stomach Histology: Layers Serosa or visceral peritoneum: Outermost
Muscularis: Three layers
Outer longitudinal
Middle circular
Inner oblique
Submucosa
Mucosa

21. Stomach Histology Rugae: Folds in stomach when empty
Gastric pits: Openings for gastric glands
Contain cells
Surface mucous: Mucus
Mucous neck: Mucus
Parietal: Hydrochloric acid and intrinsic factor
Chief: Pepsinogen
Endocrine: Regulatory hormones

22. Hydrochloric Acid Production

23. Gastric Phase: The Stomach
Figure 21-15: The mucus-bicarbonate barrier of the gastric mucosa

25. Phases of Gastric Secretion

28. Movements in Stomach

30. Small Intestine Site of greatest amount of digestion and absorption
Divisions
Duodenum
Jejunum
Ileum: Peyer’s patches or lymph nodules
Modifications
Circular folds or plicae circulares, villi, lacteal, microvilli
Cells of mucosa
Absorptive, goblet, granular, endocrine

31. Small Intestine Secretions
Mucus
Protects against digestive enzymes and stomach acids
Digestive enzymes
Disaccharidases: Break down disaccharides to monosaccharides
Peptidases: Hydrolyze peptide bonds
Nucleases: Break down nucleic acids
Duodenal glands
Stimulated by vagus nerve, secretin, chemical or tactile irritation of duodenal mucosa

32. Duodenum Anatomy and Histology

33. Duodenum and Pancreas

35. Large Intestine, H2O Absorption & Defecation
Figure 21-27: Anatomy of the large intestine

36. Large Intestine Digestion & Absorption
Bacterial fermentation: Vit. K , lactate & butyrate
Water and electrolyte secretion &/or absorption
Figure 21-28: NaCl reabsorption by colonocytes

37. Intestinal Phase: Large Intestine Digestion & Absorption
Figure 21-29: NaCl secretion by colonic crypt cells

38. Phases of Digestion: Overview
Figure 21-11: Overview of functions in different regions of the digestive system

39. Regulating Digestion: CNS and Enteric Nervous System (ENS)
Figure 21-9: The enteric nervous system

40. Cephalic and Oral Phases of Digestion
Cephalic: anticipation of food
CNS  ANS long reflex
Enteric  cells short reflex
GI motility
GI secretions
Mouth: starts digestion
Grind, mix & liquefy
Saliva: water, enzymes, mucus & lysozyme

41. Cephalic and Oral Phases of Digestion
Figure 21-12: Long and short reflexes in the stomach

42. Liver Lobes Ducts Major: Left and right Minor: Caudate and quadrate
Common hepatic
Cystic
From gallbladder
Common bile
Joins pancreatic duct at hepatopancreatic ampulla

45. Functions of the Liver Bile production Storage
Salts emulsify fats, contain pigments as bilirubin
Storage
Glycogen, fat, vitamins, copper and iron
Nutrient interconversion
Detoxification
Hepatocytes remove ammonia and convert to urea
Phagocytosis
Kupffer cells phagocytize worn-out and dying red and white blood cells, some bacteria
Synthesis
Albumins, fibrinogen, globulins, heparin, clotting factors

46. Blood and Bile Flow

47. Duct System

48. Gallbladder Bile is stored and concentrated
Stimulated by cholecystokinin and vegal stimulation
Dumps into small intestine
Production of gallstones possible
Drastic dieting with rapid weight loss

49. Pancreas Anatomy Secretions Endocrine Pancreatic juice (exocrine)
Pancreatic islets produce insulin and glucagon
Exocrine
Acini produce digestive enzymes
Regions: Head, body, tail
Secretions
Pancreatic juice (exocrine)
Trypsin
Chymotrypsin
Carboxypeptidase
Pancreatic amylase
Pancreatic lipases
Enzymes that reduce DNA and ribonucleic acid

50. Bicarbonate Ion Production

51. Gastric hormones:

52. Movement in small intestine:
Mixing: Segmental contraction that occurs in small intestine
Secretion: Lubricate, liquefy, digest
Digestion: Mechanical and chemical
Absorption: Movement from tract into circulation or lymph
Elimination: Waste products removed from body

53. Large Intestine: Extends from ileocecal junction to anus
Consists of cecum, colon, rectum, anal canal
Movements sluggish (18-24 hours)

54. Large Intestine Cecum Colon Rectum Anal canal
Blind sac, vermiform appendix attached
Colon
Ascending, transverse, descending, sigmoid
Rectum
Straight muscular tube
Anal canal
Internal anal sphincter (smooth muscle)
External anal sphincter (skeletal muscle)
Hemorrhoids: Vein enlargement or inflammation

55. Secretions of Large Intestine
Mucus provides protection
Parasympathetic stimulation increases rate of goblet cell secretion
Pumps
Exchange of bicarbonate ions for chloride ions
Exchange of sodium ions for hydrogen ions
Bacterial actions produce gases called flatus

56. Histology of Large Intestine

57. Movement in Large Intestine
Mass movements
Common after meals
Local reflexes in enteric plexus
Gastrocolic: Initiated by stomach
Duodenocolic: Initiated by duodenum
Defecation reflex
Distension of the rectal wall by feces
Defecation
Usually accompanied by voluntary movements to expel feces through abdominal cavity pressure caused by inspiration

58. Reflexes in Colon and Rectum:

59. Digestion, Absorption, Transport
Breakdown of food molecules for absorption into circulation
Mechanical: Breaks large food particles to small
Chemical: Breaking of covalent bonds by digestive enzymes
Absorption and transport
Molecules are moved out of digestive tract and into circulation for distribution throughout body

60. Liver Histology
portal
triad
Figure 24.20a, b

61. …each day around 600 ml of bile is produced…
Bile acid
Phospholipids
Cholesterol
Bilirubin
Waste products
Electrolytes
Mucin

62. Functions of the Liver Bile production Storage
Salts emulsify fats, contain pigments as bilirubin
Storage
Glycogen, fat, vitamins, copper and iron
Nutrient interconversion
Detoxification
Hepatocytes remove ammonia and convert to urea
Phagocytosis
Kupffer cells phagocytize worn-out and dying red and white blood cells, some bacteria
Synthesis
Albumins, fibrinogen, globulins, heparin, clotting factors
The liver is the largest gland in the body and performs an astonishingly large number of tasks that impact all body systems. One consequence of this complexity is that hepatic disease has widespread effects on virtually all other organ systems. At the risk of losing sight of the forest by focusing on the trees, I will only briefly mention the vasculare and metabolic functions of the liver. It is a storage of cabohydrate, lipid copper and iron as well as it is able to interconvert nutrients. It detoxificate the bloocd by removing ammonia and converting it to ureal. The vascular functions include formation of lymph and it is part of phagocytic system. The Kupfeer cells phagocytize old blood cells and the liver also syntezise important components of the wound healing.
But we have focused on the very first one, the secretory and excretory functions of the liver, because it is the only one that directly affects digestion - the bile production which plays a critical role in the digestion and absorption of dietary lipids. However, the understanding the vascular and metabolic functions of the liver is critical to appreciating the gland as a whole.

63. Exocrine Pancreas – Enzymes
Trypsinogen
Chymotrysinogen
Carboxypeptidases
Pro-elastase
Phospholipase
pancreatic lipase
Pancreatic amylase
Pancreatic juice is composed of two secretory products critical to proper digestion: digestive enzymes and bicarbonate. The enzymes are synthesized and secreted from the exocrine ascinar cells, whereas bicarbonate is secreted from the epithelial cells lining small pancreatic ducts.
Digestive Enzymes
The pancreas secretes a magnificent battery of enzymes that collectively have the capacity to reduce virtually all digestible macromolecules into forms that are capable of, or nearly capable of being absorbed. Three major groups of enzymes are critical to efficient digestion:
Proteases
Digestion of proteins is initiated by pepsin in the stomach, but the bulk of protein digestion is due to the pancreatic proteases. Several proteases are synthesized in the pancreas and secreted into the lumen of the small intestine. The two major pancreatic proteases are trypsin and chymotrypsin, which are synthesized and packaged into secretory vesicles as an the inactive proenzymes trypsinogen and chymotrypsinogen.
As you might anticipate, proteases are rather dangerous enzymes to have in cells, and packaging of an inactive precursor is a way for the cells to safely handle these enzymes. The secretory vesicles also contain a trypsin inhibitor which serves as an additional safeguard should some of the trypsinogen be activated to trypsin; following exocytosis this inhibitor is diluted out and becomes ineffective - the pin is out of the grenade.
Once trypsinogen and chymotrypsinogen are released into the lumen of the small intestine, they must be converted into their active forms in order to digest proteins. Trypsinogen is activated by the enzyme enterokinase, which is embedded in the intestinal mucosa.
Once trypsin is formed it activates chymotrypsinogen, as well as additional molecules of trypsinogen. The net result is a rather explosive appearance of active protease once the pancreatic secretions reach the small intestine.
Trypsin and chymotrypsin digest proteins into peptides and peptides into smaller peptides, but they cannot digest proteins and peptides to single amino acids. Some of the other proteases from the pancreas, for instance carboxypeptidase, have that ability, but the final digestion of peptides into amino acids is largely the effect of peptidases in small intestinal epithelial cells. More on this later.
Pancreatic Lipase
The major form of dietary fat is triglyceride, or neutral lipid. A triglyceride molecule cannot be directly absorbed across the intestinal mucosa. Rather, it must first be digested into a 2-monoglyceride and two free fatty acids. The enzyme that performs this hydrolysis is pancreatic lipase, which is delivered into the lumen of the gut as a constituent of pancreatic juice.
Sufficient quantities of bile salts must also be present in the lumen of the intestine in order for lipase to efficiently digest dietary triglyceride and for the resulting fatty acids and monoglyceride to be absorbed. This means that normal digestion and absorption of dietary fat is critically dependent on secretions from both the pancreas and liver.
Pancreatic lipase has recently been in the limelight as a target for management of obesity. The drug orlistat (Xenical) is a pancreatic lipase inhibitor that interferes with digestion of triglyceride and thereby reduces absorption of dietary fat. Clinical trials support the contention that inhibiting lipase can lead to significant reductions in body weight in some patients.
Amylase
The major dietary carbohydrate for many species is starch, a storage form of glucose in plants. Amylase is the enzyme that hydrolyses starch to maltose (a glucose-glucose disaccharide), as well as the trisaccharide maltotriose and small branchpoints fragments called limit dextrins. The major source of amylase in all species is pancreatic secretions, although amylase is also present in saliva of some animals, including humans.
Other Pancreatic Enzymes
In addition to the proteases, lipase and amylase, the pancreas produces a host of other digestive enzymes, including ribonuclease, deoxyribonuclease, gelatinase and elastase.
Bicarbonate and Water
Epithelial cells in pancreatic ducts are the source of the bicarbonate and water secreted by the pancreas. The mechanism underlying bicarbonate secretion is essentially the same as for acid secretion parietal cells and is dependent on the enzyme carbonic anhydrase. In pancreatic duct cells, the bicarbonate is secreted into the lumen of the duct and hence into pancreatic juice.

64. Bicarbonate Ion Production

70. Digestive System Regulation
Nervous regulation
Involves enteric nervous system
Types of neurons: sensory, motor, interneurons
Coordinates peristalsis and regulates local reflexes
Chemical regulation
Production of hormones
Gastrin, secretin
Production of paracrine chemicals
Histamine
Help local reflexes in ENS control digestive environments as pH levels

72. Lipoproteins Types Chylomicrons VLDL LDL HDL Enter lymph
Transports cholesterol to cells
HDL
Transports cholesterol from cells to liver

74. Water and Ions: Water Ions
Can move in either direction across wall of small intestine depending on osmotic gradients
Ions
Sodium, potassium, calcium, magnesium, phosphate are actively transported

75. Effects of Aging
Decrease in mucus layer, connective tissue, muscles and secretions
Increased susceptibility to infections and toxic agents
Ulcerations and cancers

76. Chemical Events in Digestion: Carbohydrates
1. Shows carbohydrate digestion.
2. Note the small intestine’s role in conversion to mono- and di-saccharides.

77. Chemical Events in Digestion: Lipids
3. Lipid digestion is shown here.
4. Note the conversion to monoglycerides in the small intestine due to bile salts and pancreatic lipase.

78. Chemical Events in Digestion: Proteins
5. Digestion of proteins.
6. Note stomach’s conversion to polypeptides.
7. Small intestine converts to short peptides and amino acids for intestinal absorption.

79. Gastric Secretion
Thin, strongly acidic (pH: 1 to 3), almost colorless liquid. It is secreted by the glands in the lining of the stomach.
Essential constituents are the digestive enzymes pepsin and renin, hydrochloric acid, and mucus.
Certain cells of the stomach lining secrete intrinsic factor which is necessary for the absorption of vitamin B12.

80. Secretion rates of Gastric juice

82. Path followed by bile juice in liver and gall bladder

83. Pancreatic Secretion

84. Production of Pancreatic Secretion

85. Pancreatic Secretion
1. Clear, alkaline secretion of the pancreas containing enzymes that aid in the digestion of proteins, carbohydrates, and fats.
2. There are mainly two types of pancreatic secretions:
- Bicarbonate Secretion,
- Enzyme Secretion.

86. Secretion of Pancreatic juice

87. Chemistry of Digestion: Fats
Figure 21-8: Fat digestion