Anatomy and Physiology Chapter 21 - Digestive System I, II Martini’s Visual Anatomy and Physiology First Edition Martini w Ober Chapter 21 - Digestive System I, II Lectures 7 & 8 100 min, 52 slides

Lecture Overview (Lectures 7 & 8) Introduction to the digestive system General characteristics of the alimentary canal The mouth and tongue Salivary glands Pharynx and esophagus Stomach Pancreas

Digestive System Functions of Digestive System ingestion mechanical digestion chemical digestion propulsion absorption excretion defecation Digestion is the mechanical and chemical breakdown of food into a form that cells can absorb

Major Organs of Digestive System Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 Organs can be divided into the: Digestive tract (primary) (alimentary canal); tube extending from mouth to anus (about 30 ft.) Accessory organs; teeth, tongue, salivary glands, liver, gallbladder, and pancreas

The Greater and Lesser Omenta Omentum: One of the folds of the peritoneum that connect the stomach with other abdominal organs. Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

The Mesentery Mesentery: Any of several folds of the peritoneum that connect the intestines to the dorsal abdominal wall, especially such a fold that envelops the jejunum and ileum. Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

The Abdominal Cavity & Peritoneum Notice that the pancreas, duodenum, and rectum are retroperitoneal Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Alimentary Canal Continuous tube modified along its length to carry out specialized, regional functions. Mouth, pharynx, esophagus, and anal canal are lined by nonkeratinized stratified squamous epithelium Stomach and intestines are lined by simple columnar epithelium. Why? 105 min; 54 slides

Alimentary Canal Wall Know the 4 layers of the alimentary canal Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Alimentary Canal Wall

Movements Through the Alimentary Canal mixing movements (segmentation) peristalsis - The wavelike muscular contractions of the alimentary canal or other tubular structures by which contents are forced onward toward the opening. (Triggered by pacesetter cells.)

Innervation of the Alimentary Canal The alimentary canal has extensive sympathetic and parasympathetic innervation - mainly in the muscularis externa - regulates its tone and the strength, rate, and velocity of muscular contractions submucosal plexus – controls secretions/blood flow myenteric plexus – controls gastrointestinal motility/sphincters parasympathetic division of ANS – increases activities of digestive system and relaxes sphincters sympathetic division of ANS – generally inhibits digestive actions and contracts sphincters

Mouth (Oral or Buccal cavity) (Labium) ingestion mechanical digestion prepares food for further chemical digestion The lips (labia) are formed by the orbicularis oris muscle covered with keratinized skin. The red margin is what we normally think of as the lips. This is very thin and poorly keratinized with no sweat or sebaceous glands (must be kept moist by saliva). Palatoglossal arches in front; palatopharyngeal arches behind. Between these two arches are the fauces, containing the palatine tonsils. (Labium) Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

Tongue Very muscular; muscles run in several directions Covered by mucous membranes Blast from the past - Root of tongue is anchored to the hyoid bone Tastebuds Friction for food handling Secretes lingual lipase Filiform papillae roughen surface of tongue to provide friction for food handling. Fungiform papillae. 10-12 Circumvallate (vallate) papillae aligned in a V-shaped row on back of tongue. Foliate papillae are pleat-like folds on posterolateral portion of tongue. (Fungiform, circumvallate, and foliate papillae contain taste buds.) Lingual tonsils are located on posterior of tongue. Sensory fibers are CN IX and chorda tympani branch of CN VII. CN XII innervates tongue muscle.

Palate roof of oral cavity (adenoids) Important in separating the nasopharynx from the pharynx during swallowing Muscles of the soft palate include: 1. Tensor Palati, 2. Levator Palati, 3. Palatoglossus, 4. Palatopharyngeus, and the 5. Superior Constrictor

Secondary (Permanent) Teeth Total of 32 secondary (permanent) teeth 1 16 Watch for incoming ICBMs!!! 32 17 Know the order of these Dental formula: 2.1.2.3 / 2.1.2.3

Primary (Deciduous, Baby, Milk) Teeth (Mastication = chewing) 8 incisors 4 cuspids 8 molars 20 total Dental formula: 2.1.0.2 / 2.1.0.2 All primary teeth are lost, generally between ages 6 and 12

Section of a Tooth What type of articulation is this? Oh no! Not again! What type of articulation is this? Know this diagram for exam

Functions of Saliva Moistens food Binds food particles Dissolves food for tasting Begins chemical digestion of complex CHO (amylase) Cleans teeth and mouth (pH = 6.5 – 7.5) Anti-microbial (IgA and lysozyme) Saliva is hypotonic, alkaline containing K+, HCO3-, Ca2+, Mg2+, PO43-. Ca/Po4 prevents demineralization of tooth enamel.

Salivary Glands Parasympathetic – CN VII and IX; sympathetic via cervical sympathetic chain.

Secretions of Salivary Glands Secretions are slightly acidic and continual due to basal parasympathetic stimulation, but increase after - presence, or anticipation of, food; - parasympathetic stimulation (watery, large volume) - sympathetic stimulation (viscous, small volume) Parotid glands clear primarily water, serous fluid rich in amylase mumps virus typically attacks here Food in mouth stimulates the nucleus of the tractus soliarius and this stimulates the salivatory nuclei in the pons/medulla send signals to salivary glands via the facial and glossopharyngeal nerves Submandibular glands primarily serous fluid some mucus, amylase Sublingual glands primarily mucus most viscous

Pharynx Superior, middle, and inferior constrictor muscles. Motor and sensory fibers in CN IX and CN X. Pharynx aids swallowing by grasping food and moving it toward the esophagus.

Three Phases of the Swallowing Reflex Only voluntary phase is the buccal (oral) phase, i.e., the initiation of swallowing, then… soft palate and uvula raise hyoid bone and larynx elevate Pharyngeal phase epiglottis closes off top of trachea longitudinal muscles of pharynx contract reflexive inferior constrictor muscles relax and esophagus opens Esophageal phase peristaltic waves push food through pharynx

Swallowing Mechanism Muscles that elevate the hyoid/larynx: digastric, stylohyoid, mylohyoid, and geniohyoid.

Esophagus Veins drain into hepatic portal vein (via gastric veins) Esophagus is about 25 cm long. Straight course through the mediastinum. Solid foods pass from the oropharynx to the stomach in about 8 sec.; fluids in about 1-2 sec. Innvervated by CN X (via connection with myenteric plexus). Lower esophageal (cardiac) sphincter prevents reflux (backup) of stomach acid into the esophagus. Esophagus conveys food from pharynx to stomach by peristalsis

Stomach Rugae flatten as stomach fills Stomach can hold about 1-1.5 liters of material Gastric glands M G cells D cells Greater curvature Stomach Functions: - Mixing - Reservoir - Secretion of gastric juice - Digestion, anti-bacterial action, facilitates absorption of vitamin B12 - Secretion of gastrin, somatostatin Range of stomach volume is about 50 ml (empty) to about 4L (very distended). Rugae flatten as stomach fills

Blood Supply and Drainage of Stomach Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Lining and Gastric Glands of Stomach Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Gastric Secretions mucus (cardia) from goblet cells and mucous glands protective to stomach wall hydrochloric acid from parietal cells needed to convert pepsinogen to pepsin ‘p’ in parietal and ‘p’ in pH pepsinogen from chief cells inactive form of pepsin intrinsic factor from parietal cells required for vitamin B12 absorption pepsin from pepsinogen in presence of HCl protein splitting enzyme mucus, gastrin, somatostatin from pyloric glands protective to stomach wall gastrin and somatostatin are hormones H.Pylori is difficult to eradicate, so three medications are used simultaneously. This is called "Triple Therapy". The best treatment at present is called OAC, taken for 7 days: O = Omeprazole (which decreases the acid level in the stomach) A = Amoxicillin (a penicillin antibiotic). C = Clarithromycin (an antibiotic related to erythromycin) OMC is used in those who are penicillin allergic, where M = Metranidazole. INFANTS ONLY rennin (chymosin) gastric lipase

Secretion of H+ by Parietal Cells Important functions of the stomach pH (1.5 – 2.0) - kills microorganisms - denatures proteins - breaks down plant material and CT in meats - activates pepsin Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Three Phases of Stomach Control Cephalic phase triggered by smell, taste, sight, or thought of food begin secretion and digestion Gastric phase triggered by distension, presence of food, and rise in pH in stomach enhances secretion and digestion Intestinal phase triggered by distension of small intestine and pH change controls rate of gastric emptying; may slow emptying NOTE that all these phases control activity in the STOMACH Know what each phase does (shown in red)

Cephalic Phase of Gastric Secretion Emotional states can exaggerate or inhibit this phase Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Gastric Phase of Gastric Secretion Secretion stimulated by: 1) ACh 2) histamine 3) gastrin. Small peptides and amino acids cause secretion of gastrin. Below pH 2, gastrin secretion is inhibited. Proteins, alcohol, and caffeine can markedly increase secretions by stimulating gastric chemoreceptors Histamine stimulates acid secretion by parietal cells Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Intestinal Phase of Gastric Secretion Enterogastric reflex (inhibits gastric activity) –reduces gastric motility, stimulates contraction of pyloric sphincter (pylorus) Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Overview of Gastric Control/Secretion Key + Stimulation - Mucous Cells Inhibition Emptying of Stomach ( [H+ ]) Stomach Molility (Segmentation/Peristalsis) ECL Cells Histamine Endocrine Factor + + + Exocrine Factor + (cephalic/gastric phases) Parasympathetic NS G cells Gastrin + Both + D cells Somatostatin Intrinsic Factor + B12 Parietal Cells pH < 3.0 - + H+ + Cl- HCO3- (alkaline tide) + + + + + (intestinal phase) Stretch of stomach Fats in Small Intestine pH > 3.0 (dilution of H+) Peptides Chief Cells Pepsinogen Pepsin Protein Breakdown Food in Stomach Fat Breakdown Lipases

Mixing and Emptying Actions

Gastric Absorption Gastric absorption is very limited due to: - blanket of mucus covering cells - epithelial cells lack specialized transport mechanisms - tight junctions between adjacent epithelial cells - gastric lining is relatively impermeable to water - chyme usually contains only partially digested material Some substances can be absorbed by the stomach: some water certain salts certain lipid-soluble drugs, e.g., aspirin alcohol (slowed by presence of fats)

Pancreas Exocrine (digestive) and endocrine (metabolic) functions Completes digestion of proteins that was started in the stomach

Blood Supply and Drainage of Pancreas Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

Pancreatic Juice pancreatic amylase – splits glycogen into disaccharides pancreatic lipases – break down triglycerides pancreatic nucleases – digest nucleic acids bicarbonate ions – make pancreatic juice alkaline (pH = 8) and neutralize acid coming from stomach Pancreatic proteolytic enzymes…

Pancreatic Proteolytic Enzymes Enteropeptidase (Enterokinase) (brush border of sm. intestine) Know this chart Trypsinogen Trypsin Chymotrypsinogen Chymotrypsin Pancreas Procarboxypeptidase Carboxypeptidase Proelastase Elastase (Proenzymes, Zymogens) (Active enzymes) Dipeptides, tripeptides, amino acids Proteins Purpose of proteolytic enzymes is continued breakdown of proteins that began in the stomach

Regulation of Pancreatic Secretions acidic chyme stimulates release of secretin secretin stimulates release of watery pancreatic juice with bicarbonate and phosphate (= buffers; to  pH) CCK and parasympathetic NS stimulate production and secretion of pancreatic enzymes and zymogens The acini of the pancreas secrete enzymes/zymogens; the ducts secrete buffers (bicarbonate, phosphates)

Regulation of Pancreas/Intestinal Digestion Key + Stimulation Acidic Chyme Enters Duodenum + (brush border) + + Enterokinase Cholecystokinin (CCK) Secretin + Trypsinogen Trypsin + + + Gallbladder Contraction Relaxation of hepatopancreatic sphincter Chymotrypsinogen Procarboxypeptidase Proelastase Trypsinogen Carboxypeptidase Elastase Pancreas Bile and Pancreatic ducts (proenzymes, zymogens) Proteins Bile Lipases HCO3-, PO43- (emulsification) Nucleases (DNA, RNA) Amylase (glycogen, starches) Di- and tripeptides Triglycerides Cholesterol Fat Soluble Vitamins  pH to ≈ 8 (req. for enzyme action) Nucleotides Mono-, di-, trisaccharides Action of brush border enzymes Fatty acids, monoglycerides Lacteals Portal Vein Amino acids Conversion to chylomicrons Subclavian vein Monosaccharides

Review Alimentary canal (direct contact with food) Mouth, pharynx, esophagus, stomach, small and large intestines, anal canal Accessory structures (no direct contact with food, but provide secretions) Salivary glands, liver, gall bladder, pancreas Four layers of the alimentary canal Mucosa – absorption, secretion, protection Submucosa – nutrition and transport Muscularis – movement Serosa – protection, lubrication

Review Wave-like movement of alimentary canal is called peristalsis Results from stretching Bowel sounds Innervation of the alimentary canal (enteric nervous system) Parasympathetic – increases activity Sympathetic – decreases activity Mouth Mastication – mechanical processing of food and mixing with saliva

Review Tongue Palate (roof of oral cavity) Lined by mucous membranes Thick, skeletal muscle Papillae function in food handling and taste Lingual frenulum Lingual tonsils Lingual glands secrete lingual lipase Palate (roof of oral cavity) Hard palate (Palatine proc. of maxillary bones) Soft palate Uvula is suspended from this Uvula closes opening to nasal cavity (nasopharynx)

Review Tonsils Teeth Lingual (back of tongue) Palatine (lateral to tongue) Pharyngeal (posterior wall of pharynx; adenoids) Teeth Primary teeth (deciduous teeth; baby teeth) 6 months to 2-4 years 20 total Secondary (permanent teeth) 6 yrs to 17-25 years 32 total

Review Teeth (continued) Incisors – sharp for biting Cuspids (canine) – for grasping/tearing Bicuspids and molars – grinding Structure Crown – above gum line Root – below gum line Outer covering is enamel hardest substance in body NOT replaceable Inner substance is dentin (alive) Pulp cavity Periodontal ligament

Review Alimentary canal (direct contact with food) Mouth, pharynx, esophagus, stomach, small and large intestines, anal canal Accessory structures (no direct contact with food) Salivary glands, liver, gall bladder, pancreas Four layers of the alimentary canal Mucosa – absorption, secretion, protection Submucosa – nutrition and transport Muscularis – movement Serosa – protection, lubrication

Review Wave-like movement of alimentary canal is called peristalsis Results from stretching Bowel sounds Innervation of the alimentary canal (enteric nervous system) Parasympathetic – increases activity Sympathetic – decreases activity Mouth Mastication – mechanical processing of food and mixing with saliva

Review Tongue Palate (roof of oral cavity) Lined by mucous membranes Thick, skeletal muscle Papillae function in food handling and taste Lingual frenulum Lingual tonsils Lingual glands secrete lingual lipase Palate (roof of oral cavity) Hard palate (Palatine proc. of maxillary bones) Soft palate Uvula is suspended from this Uvula closes opening to nasal cavity (nasopharynx)

Review Tonsils Teeth Lingual (back of tongue) Palatine (lateral to tongue) Pharyngeal (posterior wall of pharynx; adenoids) Teeth Primary teeth (deciduous teeth; baby teeth) 6 months to 2-4 years 20 total Secondary (permanent teeth) 6 yrs to 17-25 years 32 total

Review Teeth (continued) Incisors – sharp for biting Cuspids (canine) – for grasping/tearing Bicuspids and molars – grinding Structure Crown – above gum line Root – below gum line Outer covering is enamel hardest substance in body NOT replaceable Inner substance is dentin (alive) Pulp cavity Periodontal ligament

Review Salivary glands produce saliva which Moistens food Binds food particles Begins chemical digestion of CHO Dissolves food (for taste) Cleanses mouth and teeth; antibacterial Three pairs of salivary glands Parotid; front of ear, watery fluid rich in amylase Submandibular; floor of mouth, viscous fluid Sublingual; below tongue, thick, stringy secretion

Review Salivary glands Pharynx Sympathetic stimulation – small quantity of viscous saliva Parasympathetic stimulation – large volume of watery saliva Pharynx Cavity connecting mouth with esophagus Nasopharynx, oropharynx, laryngopharynx Muscles Inner circular – constriction Outer longitudinal – movement of food bolus

Review Swallowing Esophagus Initiation is voluntary; act of swallowing is NOT – it’s a reflex Three stages Chewing and rolling of food into oropharynx (voluntary, buccal) Swallowing reflex (pharyngeal) Epiglottis closes over larynx Muscles in lower pharynx relax Esophagus opens and food moves in Peristalsis in esophagus transports food to stomach (esophageal) Esophagus Muscular tube connects to cardiac region of stomach Esophageal hiatus Lower esophageal (cardiac) sphincter

Review Stomach Cardiac, fundus, body, pylorus Mixes food and begins digestion of protein Limited absorption (alcohol) Moves food into small intestine Pyloric sphincter (entrance to small intestine) Rugae and gastric pits Gastric glands Mucous cells (goblet) – secrete mucous Chief cells (peptic) – secrete digestive enzymes, esp. pepsinogen Parietal cells (oxyntic) – secrete HCl (Parietal, pH) Infants only - Gastric lipase and rennin

Review Regulation of gastric activity Cephalic phase (primarily neural) Prior to food entry into stomach Increased motility and production of gastric juice Gastric phase Neural: Food entering stomach / pH rising Hormonal: gastrin release Local: histamine release (stimulates parietal cells) Intestinal phase Neural: distension of duodenum (enterogastric reflex) Hormonal: CCK, GIP, and secretin, gastrin Reduction (slowing) of gastric emptying

Review Pancreas Both exocrine and endocrine functions Main source of intestinal digestive enzymes Pancreatic amylase (starches) Pancreatic lipase (fats) Nucleases Proteolytic proenzymes / enzymes Regulation of pancreatic activity Acid chyme stimulates secretin Secretin stimulates watery buffering secretion Parasympathetic NS and CCK stimulate production and secretion of digestive enzymes