Exam 3

  1. Digestion
    Mechanical and chemical breakdown of foods into forms that cell membranes can absorb
  2. Mechanical digestion
    Breaks large pieces into small pieces w\o altering the chem make-up of the pieces
  3. Chemical digestion
    Breaks down larger chemicals to smaller chemicals
  4. Besides digestive what does the digestive system do?
    Ingestion, propulsion, absorption & defecation
  5. Alimentary canal
    • Muscular tube about 8 meters long
    • Extending from the mouth to the anus
    • Passes through the thoracic and abdominopelvic cavities
    • Develops from the endoderm of the embryo & the accessory organs develop as buds from the canal
  6. Structure of the Wall
    • Four layers
    • Mucosa
    • Submucosa
    • Muscular
    • Serosa
    • Developed to different degrees in different layers
  7. Mucosa
    • Protects the layers beneath it
    • Provides secretions
    • Absorbs nutrients & other food components (e.g., water & electrolytes)
  8. Mucosa
    • Surface epithelium
    • Lamina propria (underlying connective tissue)
    • Muscularis mucosae (smooth muscle)
    • Projections into lumen increase surface area for absorption
    • Glands that secrete digestive enzymes and mucous
  9. Submucosa
    • To nourish surrounding tissues
    • To secrete chemicals
    • To carry away absorbed materials
  10. Submucosa
    • Loose connective tissue
    • Glands
    • Blood vessels
    • Lymphatic vessels
    • Nerves
  11. Muscular Layer
    To move the contents of the canal
  12. Muscular Layer
    • Circular fibers:
    • Smooth muscle
    • Inner layer
    • Closed spirals around tube
    • Change diameter of tube
    • Longitudinal fibers:
    • Open spirals
    • Outer layer
    • Run lengthwise
    • Shorten the tube upon contraction
  13. Serosa
    • Protect underlying tissue
    • Secrete serous fluid to lubricate and moisten the outer surface
  14. Serosa
    • Visceral peritoneum:
    • Underlying connective tissue
    • Outer layer of epithelium
  15. What do Parasympathetic impulses do?
    increase activities of digestive system
  16. What do Sympathetic impulses do?
    inhibit certain digestive actions
  17. Mouth
    • Ingests food
    • Mechanically breaks up solid particles
    • Adds saliva
    • Prepares food for chemical digestion
    • Speech organ
    • Sensory reception organ
  18. Cheeks
    • Outer layers of skin
    • Pads of subcutaneous fat
    • Muscles associated with expression and chewing
    • Inner linings of moist, stratified layers of squamous epithelium
  19. Lips
    • highly mobile structures that surround the mouth opening
    • Skeletal muscles
    • Sensory receptors determine temp & texture of food.
    • Outer border marks separation of facial skin & mucous membranes of alimentary canal
  20. Tongue
    • Thick, muscular organ
    • Occupies the floor of the mouth
    • Nearly fills the oral cavity when the mouth is closed
    • Covered by mucous membrane
    • Mixes food particles with saliva during chewing
    • Moves food particles toward the pharynx during swallowing
  21. Other Parts of the Tongue
    • Lingual frenullum
    • Papillae
    • Lingual tonsils
  22. Palate
    • forms the roof of the oral cavity
    • Hard palate
    • Soft palate
  23. Hard palate
    formed by palatine processes of maxillary bones & horizontal parts of the palatine bones
  24. Soft palate
    forms a muscular arch that extends to the cone-shaped uvula
  25. Other Parts of the Palate
    • Palatine tonsils
    • Pharyngeal tonsils
  26. Teeth
    • Hardest structures in the body
    • Develop in sockets w/in the alveolar processes of the mandibular & maxillary bones
    • Break food into smaller pieces to begin mechanical digestion
    • Loss most often due to gingivitis or endodontitis
  27. Sets of Teeth
    • 20 primary (deciduous) teeth erupt through gingiva (gums) at regular intervals btw 6 months and two to four months of age
    • Usually shed in the same order in which they erupted
    • Roots are resorbed and, then pushed out of their sockets by the secondary teeth
    • 32 secondary (permanent) teeth erupt between 6 & 25 yrs
    • “Wisdom” teeth erupt last and may be “impacted”
  28. Types of Teeth
    • Incisors
    • Cuspids
    • Bicuspids
    • Molars
  29. Incisors
    • Front four teeth
    • Chisel-shaped
    • Sharp edges bite off pieces of food
  30. Bicuspids
    • Aka, premolars
    • Two teeth on each side of each jaw
    • Flattened surfaces
    • Grind food
  31. Cuspids
    • Aka, canine teeth
    • One tooth on each side of each jaw
    • Cone-shaped
    • Grasp and tear food
  32. Molars
    • Three teeth on each side of each jaw
    • Flattened surfaces
    • Grind food
  33. Crown and Center of Teeth
    • Projects beyond gum
    • Covered with glossy, white enamel
    • Hardest substance in body
    • Composed primarily of calcium salts
    • Not replaced if eroded, abraded, or damaged
    • Worn away with age
  34. Interior Portion of Teeth
    • Dentin
    • Central cavity
    • Root canal
  35. Dentin
    • Most of tooth beneath enamel
    • Living cellular tissue that is similar to, but harder than, bone
  36. Central cavity
    • Aka, pulp cavity
    • Surrounded by dentin
    • Contains blood vessels, nerves, and connective tissue (aka, pulp)
  37. Root canal
    • Tubular canal through which blood vessels & nerves reach the central cavity
    • Extends from base of tooth
  38. Neck
    Between crown and root
  39. Root of Teeth
    • Anchored to alveoli process of jaw
    • Enclosed by cementum, a thin layer of bone-like material
    • Periodontal ligament (periodontal membrane
    • Composed of collagen
    • Firmly attaches tooth to alveolar process
    • Between the cementum and alveolar process
    • Contains blood vessels and nerves near surface of the cementum-covered root
  40. Salivary Secretions
    Serous cells
    Produce a watery fluid containing salivary amylase, which breaks starch and glycogen into disaccharides
  41. Salivary Secretions
    Mucous cells
    Secrete mucous, which binds food particles and acts as a lubricant during swallowing
  42. Salivary Secretions
    Sympathetic impulses
    Stimulate secretion of a small amount of a viscous saliva
  43. Salivary Secretions
    Parasympathetic impulses
    • Reflexively stimulate secretion of large amounts of a watery saliva when thinking or sensing good food
    • Reflexively inhibits secretion of watery saliva whenthinking or sensing unpleasant food
  44. Major Salivary Glands
    • Parotid glands
    • Submandibular glands
    • Sublingual glands
  45. Parotid glands
    • Largest major salivary gland
    • Located anterior and inferior to ear between the skin of the cheek and the masseter muscle
    • Duct transports fluid and enters mouth opposite the upper second molar on each side of the jaw
    • Secrete clear watery, serous fluid
    • Rich in salivary amylase
  46. Submandibular glands
    • Located in the floor of the mouth within the lower jaw
    • Duct transports fluid and enters mouth near the lingual frenulum
    • Secrete fluid that is about equally serous and mucus
  47. Sublingual glands
    • Smallest major salivary gland
    • Located on the floor of the mouth near the base of the tongue
    • Many separate ducts
    • Secrete primarily thick, stringy mucus
  48. Pharynx and Esophagus
    • The pharynx is a cavity posterior to the mouth from which the tubular esophagus leads to the stomach
    • Neither structure is directly involved in digestion
    • Both the pharynx and esophagus muscular walls function in swallowing
  49. Structure of the Pharynx
    Connects the nasal and oral cavities with the larynx and esophagus
  50. The pharynx can be divided into the following parts:
    • Nasopharynx
    • Oropharynx
    • Laryngopharynx
  51. Nasopharynx
    • Located superior to the soft palate
    • Communicates with the nasal cavity
    • Provides a passageway for air during breathing
    • Connects pharynx with middle ear through auditory tubes
  52. Oropharynx
    • Located posterior to the mouth
    • Opens posterior to the soft palate into the nasopharynx and projects downward to the upper border of the epiglottis
    • Passageway for food moving downward frm the mouth
    • Passageway for air moving into and out of the nasal cavity
  53. Laryngopharynx
    • Located immediately inferior to the oropharynx
    • Extends from the upper border of the epiglottis to the lower border of the cricoid cartilage of the larynx
    • Passageway to the esophagus
  54. Muscles of the Pharynx
    • Constrictor muscles
    • Longitudinal muscles exterior to constrictor muscles
    • Skeletal muscles that can be under voluntary control to start swallowing, but they are reflexive control during swallowing
  55. Constrictor muscles
    • Circular muscles that pull the walls of the pharynx inward during swallowing
    • Superior constrictor muscles are attached to the bony processes of the skull and mandible and curve around the upper part of the pharynx
    • Middle constrictor muscles arise from the projections of the hyoid bone and fan around the middle of the pharynx
    • Inferior constrictor muscles arise from cartilage of the larynx and pass around the lower portion of the pharyngeal cavity
    • Some inferior constrictor muscles are usually contracted in order to prevent air from entering the esophagus during breathing
  56. Swallowing Mechanism
    • Three stages:
    • 1.Voluntary stage
    • 2.Swallowing begins when food reaches the pharynx stimulates sensory receptors which trigger the swallowing reflex
    • 3.Peristalsis transports food in the esophagus to the stomach
  57. Voluntary stage
    • Food is chewed and mixed with saliva
    • Food is rolled into bolus and forced into the pharynx by the tongue
  58. Swallowing begins
    • Soft palate and uvula raise to prevent food from entering the nasal cavity
    • Hyoid bone and larynx elevate
    • Epiglottis a flaplike structure attached to the larynx closes off top of the trachea so food is less likely to enter the trachea
    • Tongue presses against the soft palate and uvula to seal off the oral cavity from the pharynx so food doesn’t back up
    • After all attached cavities and tubes are blocked, muscle actions to move the food begin
    • The longitudinal muscles of pharynx contract pulling the pharynx up toward the food
    • The lower inferior constrictor muscles relax and the esophagus opens
    • The superior constrictor muscles contract to stimulate start of a peristaltic wave in other pharyngeal muscles
    • Food enters the esophagus
    • Breathing is momentarily inhibited by the swallowing
    • reflex.....step 3
  59. Esophagus
    • A straight collapsible tube that is about 25 cm long
    • A passageway for food to move from the pharynx to the stomach
    • Muscles in the wall push food from the pharynx to the stomach
    • Located posterior to trachea
    • Descends through the thorax and mediastinum
    • Passes through the esophageal hiatus of the diaphragm
    • Continuous with stomach
    • Mucous glands in the submucosa layer moisten and lubricate the epithelial lining of the tube
    • Lower esophageal (cardiac) sphincter muscles encircle the esophagus immediately above where it joins the stomach
  60. Stomach
    • Receives food from the esophagus
    • Mixes food with gastric secretions
    • Initiates digestion of proteins
    • Carries on limited absorption
    • Moves food into the small intestine
  61. Stomach
    • A J-shaped, pouch-like organ, about 25-30 cm long
    • Maximum capacity is about 1 liter
    • Located inferior to the diaphragm in the upper-left portion of the abdominal cavity
    • Inner lining has rugae, thick folds of mucosal & submucosal tissue that flatten out when wall is distended
  62. Muscle Layers of Stomach
    • inner circular layer
    • outer longitudinal layer
    • A third inner layer of oblique fibers:
    • In some parts of the stomach
    • Most highly developed near the lower esophageal
    • sphincter and in the body of the stomach
    • Strengthen stomach wall
    • Help mix and churn stomach contents
  63. Parts of the Stomach
    • Cardiac region
    • Fundus
    • Body of stomach
    • Pyloric region
    • Pyloric region
  64. Cardiac region
    • Adjacent to lower esophageal sphincter
    • Where swallowed food enters stomach
  65. Fundus
    • Top of stomach
    • Superior to cardiac region
    • Storage area
    • Sometimes fills with swallowed air
  66. Body of stomach
    Central and largest region
  67. Pyloric region
    Funnel-shaped area that narrows to become the pyloric canal
  68. Funnel-shaped area that narrows to become the pyloric canal
    • Circular muscular layer around the pyloric canal immediately above where it joins the small intestine
    • A valve that controls gastric emptying
  69. Gastric Glands
    • Tubular glands embedded in thick mucosa of stomach
    • Gastric pits:
    • Small openings at the surface of the mucosa
    • Located at the ends of gastric glands
    • Structure & composition of secretions vary in different areas of the stomach
  70. Three types of secretory cells in the glands
    • Mucous cell
    • Chief cells (aka, peptic cells)
    • Parietal cells (aka, oxyntic cells)
  71. Mucous cell
    • In the necks of the glands
    • Near the opening of the gastric pits
  72. Chief cells (aka, peptic cells)
    Secrete digestive enzymes
  73. Parietal cells (aka, oxyntic cells)
    Secrete a solution containing hydrochloric acid
  74. Gastric Secretions
    Protein secretions:
    • Pepsinogen
    • Pepsin
    • Gastric lipase
  75. Pepsinogen
    • From the chief cells
    • Inactive, nonerosive, precursor form of pepsin
  76. Pepsin
    • Formed from pepsinogen in the presence of hydrochloric acid
    • Most active under acidic conditions
    • Is a protein splitting enzyme
    • Begins digestion of almost all dietary proteins
    • Breaks down pepsinogen to form more pepsin
  77. Gastric lipase
    • Small quantities in gastric juice
    • A fat-splitting enzyme that works mostly on butterfat
    • Weak activity due to acidity of gastric juice
  78. Gastric Secretions
    Non-protein secretions
    • Hydrochloric acid
    • Mucus
    • Intrinsic factor
  79. Hydrochloric acid
    • From the parietal cells
    • Needed to convert pepsinogen to pepsin
  80. Mucus
    • From the mucous cells of the gastric glands:
    • Thin mucus
    • Produced in large amounts
    • From cells of the mucous membrane, associated with the inner lining of the stomach and between the gastric glands:
    • More viscous mucus
    • Alkaline secretion
    • Coats the inside wall of the stomach
    • Prevents pepsin from digesting proteins of stomach tissues
    • Protective to stomach wall
  81. Intrinsic factor
    • From the parietal cells
    • Is required for vitamin B12absorption from the small intestine
  82. Regulation of Gastric Secretions
    • Somatostatin
    • Acetylcholine
    • Gastrin
    • Histamine
  83. Somatostatin
    • Produced by specialized cells closely associated with parietal cells
    • Inhibits acid secretion
  84. Acetylcholine
    • Released from nerve endings upon stimulation by parasympathetic nerve impulses from the vagus nerve
    • Suppresses secretion of somatostatin
    • Stimulates release of large amounts of gastric juice from the gastric glands
  85. Gastrin
    • Peptide hormone
    • Produced by certain cells, mostly in the pyloric region
    • Secretion stimulated by same impulses as acetylcholine secretion
    • Induced increased secretory activity of gastric glands
  86. Histamine
    • Release stimulated by parasympathetic impulses and gastrin
    • Released from gastric mucosal cells
    • Stimulates additional gastric secretions
  87. Three Phases of Gastric Secretions
    • Cephalic phase
    • Gastric phase
    • Intestinal phase
  88. Cephalic phase
    • Induced by taste, smell, sight, or thought of food and before food enters the stomach
    • Parasympathetic reflex signal from vagus nerve
    • Stimulates secretion of gastric juices
    • Level of hunger reflected in amount of secretion
    • Responsible for 30 – 50 % of the secretory response to a meal
  89. Gastric phase
    • Starts when food enters the stomach
    • Presence of food and resulting distension of the stomach wall trigger release of the hormone gastrin
    • Gastrin stimulates release of more gastric juice
    • Higher pH in stomach due to mixing of food with stomach secretions induces release of additional gastric juice
    • Decreasing pH inhibits, then stops, secretion of gastrin
    • Responsible for 40 – 50 % of the secretory response to a meal
    • Acid release into stomach is accompanied by removal of hydrogen ions from the blood and release of equivalent number of bicarbonate ions into the blood Excess bicarbonate ions excreted in urine during the alkaline tide
  90. Intestinal phase
    • Begins when food leaves the stomach and enters the small intestine
    • Intestinal gastrin secretion induced by food contacting the intestinal wall
    • Intestinal gastrin stimulates secretions from the gastric glands
    • Acid in the upper part of the small intestine triggers a sympathetic nerve impulse that inhibits secretion of gastric juice from the stomach wall
    • Cholecystokinin:
    • A peptide hormone
    • Release stimulated by presence of fats in the upper region of the small intestine
    • Released from cells in the intestinal wall
    • Decreases gastric motility
    • Intestinal somatostatin:
    • A hormone
    • Release stimulated by presence of proteins and fats in the upper region of the small intestine
    • Released from cells in the intestinal wall
    • Inhibits release of gastric juice
    • Gastric secretions and motility decrease as small intestine fills with food
  91. Gastric Absorption
    • Gastric enzymes begin breaking down proteins, but the stomach is not well-adapted to absorb digestive products
    • The stomach does absorb:
    • Some water
    • Certain salts
    • Certain lipid-soluble drugs
    • Alcohol
    • Most nutrients are absorbed in the small intestine
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Exam 3