Chapter 22: Digestive System22.2: Introduction- Anatomy Overview: GI Tract- Anatomy Overview: Accessory Organs and Structures22.3: The Digestive System Has Anatomical and Functional Patterns- The Digestive Tract Consists of 4 Layerso- Motility is a Major Digestive Processo Motility is due to smooth muscle contractions that occur throughout the digestive tract and carries ingested food bolus from our esophagus to our rectumo Two patterns of contractions Peristalsis  creates wavelike movements through coordinated contractions- Contraction behind a bolus and relaxation in front of the bolus Segmentation  Simultaneous contraction of smooth muscle in front and behind the bolus, creating back and forth motion- mixes the bolus with digestive secretions- Digestion can be Mechanical or Chemicalo Mechanical digestions  beings in oral cavity, does not break chemical bonds, simply helps to increase surface area  helps increase efficiency chemical digestiono Chemical digestion Carbohydrase  breaks down complex carbohydrates into simple sugars Nucleases  breaks DNA and RNA down into nucleic acids  Lipases  breaks down lipids into free fatty acids and glycerol- Secretion and Absorption are the Last of the Major Digestive Processeso Secretion refers to movement of a substance into the lumen  example: HClo Absorption refers to movement of a substance out of he lumen and into cells  Highly selective process by specific region22.4: Regional Specializations- Digestive Tract Begins with Oral Cavityo Functions of oral cavity Protection of mouth/digestive system against chemical abrasions Increase surface area of food Coating food with saliva Initiate swallowing, delivering food to stomach- Mastication Mechanically Digests Food into Smaller Particleso Mastication  chewing, breaks up large food particles into smaller particleso 32 teeth  8 incisors, 4 canines, 8 premolars, and 12 molars o Medulla oblongata  controls chewing through sensory signals- Saliva is the Major Secretion in the Oral Cavityo Three glands secrete saliva  parotid, submandibular, and sublingualo Composition of saliva  water, electrolytes, mucous, leukocytes, epithelial cells, glycoproteins, enzymes, IgA, and lysozymeso Functions and Features of saliva 6.5-7.5 pH Moistens and liquefies food Salivary amylase  5% breakdown of carbs Anti-microbial lysozymes and IgA Secretion is stimulated by cranial nerves in response to stimuli- Motility: Swallowing Connects the Oral Cavity to the Stomacho Pharynx  tube that connects inner ear, oral cavity, and larynx Provides passageway for movement of food/air/liquid into esophagus and tracheao Deglutition, or swallowing, has three phases: Voluntary phase- Mouth, tongue, teeth, and secretions form a food bolus  tongue pushes bolus against hard palate where it is detected by receptors Pharyngeal phase- Food contacts sensor  info sent to medulla  motor info travels back and soft palate elevation occurs  nasopharynx/oropharynx passage way closes Esophageal phase- Passage of food/water from pharynx to stomach - Food bolus moves via peristalsis- Upper esophagus  voluntarily controlled - Lower esophagus  involuntarily controlledo Gastroesophageal reflux disease (GERD) Lower esophageal sphincter doesn’t close properly  acid secretions from stomach reflux/leak back into esophagus and cause inflammation  heartburn Untreated can cause ulceration of esophagus wall  massive blood loss and esophageal cancer22.5: Regional Specialization: The Stomach- Functions of the Stomacho Short-term storage reservoiro Mix and grind stomach contents with HCl and enzyme pepsino Continue chemical and enzymatic digestiono Move stomach contents into small intestine for further processing- Secretion in the Stomach: The Gastric Pito Enzymatic digestion begins in stomach, converting food bolus into acidic chymeo Cell types and their unique digestive secretion Chief cells  secrete pepsin  preproenzyme  pepsinogen  pepsine  contain hormonal receptors that stimulate pepsin release EC Cells  Secrete histamine  Binds H2 receptors on parietal cells to stimulateHCl secretion D cells  Secrete somatostatin  inhibits gastrin and histamine secretion Parietal cells  Secrete HCl  secretes bicarbonate  maintains acidic pH in stomach  secrete intrinsic factor G cells  secrete gastrin in response to food  stimulate HCl, pepsin, and histamine secretion- Parietal Cells used Active Transport to Secrete HCl into the Stomach Lumeno Parietal cells secrete H+ into stomach lumen via H+/K+ ATPaseo Cl- ions are transported into lumen via conductance channelso HCl is formed in lumeno Various nerve signals, hormones, and other chemicals control HCl release- Gastric Ulcerso Break in normal tissue lining stomach or small intestine  caused by imbalance between secretion of acid and pepsin, and the defenses provided by mucosal liningo Risk factors include chronic inflammation, excessive use of anti-inflammatory meds, and smokingo Causes abdominal pain, nausea, indigestion, vomiting blood, blood in stool, weight losso Antacids, antibiotics, and dietary changes used to treat it- Stomach Motility Involves Strong Contractions1.) Food mixes in stomach to form chyme2.) Tonic smooth muscles contract, stimulating cells of Cajal  generate action potentials3.) Phasic smooth muscle contractions4.) Upper stomach expands5.) Mixing waves push chyme toward pyloric sphincter6.) Stomach distension stimulates gastrin release7.) Pyloric sphincter relaxes, food is pushed into duodenum22.6: Regional Specialization: The Small Intestine- Major functions of small intestineo Mix liver and pancreatic secretions with chymeo Continue digestion of carbs, proteins, and initiate fat digestiono Absorb nutrientso Move chyme towards large intestineo Produce hormones that regulate digestive tracto Produce large number of immune cells to protect against pathogens associated with food- Other featureso 90% of all digestion occurs in small intestineo Composed of three parts: duodenum, jejunum, and ileum- Nutrient Digestion and Absorption Occurs at Brush Borderso Brush border: major site of nutrient digestion and absorptiono Folds increase surface area 600-fold- Unique epithelial cell types line Small Intestineo Absorptive Cells  extensive microvilli that produce digestive enzymeso Goblet cells 