Ch. 23 The Digestive System

I. Basic Concepts & Processes Shared By Most Digestive Organs A. Two Groups of Organs: Alimentary canal = Organs: Students Do Accessory digestive organs =

B. Digestive Processes (Text p. 1040) Ingestion 2. Propulsion Peristalsis 3. Mechanical digestion Mastication Segmentation 4. Chemical digestion 5. Absorption 6. Defecation Ingestion Propulsion Mechanical Digestion Absorption Defacation

Propulsion& Segmentation From mouth (a) Peristalsis: successive waves of contraction move food distally (1-way). (b) Segmentation: Food mixing/slow food propulsion occurs. Figure 23.3

C. Control of Digestive Processes Mechanical and Chemical stimuli STUDENTS DO 2. Nervous System Control: a) Extrinsic: via CNS & autonomic nerves Use long reflexes (brain to gut) Intrinsic = Enteric Nerves In digestive organs-- Use short reflexes Submucosal nerve plexus: within submucosa Myenteric nerve plexus within muscularis externa #3 • Myenteric nerve plexus • Submucosal nerve plexus

4. Hormonal Controls Stomach Gastrin: Small Intestine Secretin: Cholecystokinin (CCK)

D. Blood Supply: Splanchnic Circulation Branches of Abdominal Aorta Students Do Celiac Trunk Superior mesenteric Inferior mesenteric Hepatic Portal Vein

E. Peritoneum Students Do Peritoneum, Greater Omentum, Mesentery Dorsal mesentery Parietal peritoneum Visceral peritoneum Ventral mesentery Peritoneal cavity Alimentary canal organ Liver Figure 23.5a

F. Histology of Alimentary Canal Mucosa Epithelium Lamina Propria Areolar Lympoid Follicles: = collection of small lymphoid nodules Part of MALT = Mucus-Associated Muscularis Mucosae Submucosa Many vessels Glands (Duodenal in s.i.) Mucosa Muscularis Muscosae Lympoid Follicles

Lympathic tissue (Lymph Nodules in s.i.) Submucosal nerves plexus 3. Muscularis externa Circular (inner) Sphincters Longitudinal Myenteric nerve 4. Serosa = Visceral Peritoneum Areolar Mesothelium (simple squ.) Submucosa

Histology of Alimentary Canal … #6 Glands in submucosa Mucosa • Epithelium • Lamina propria • Muscularis mucosae Submucosa Muscularis externa • Longitudinal muscle • Circular muscle Serosa Nerve Lumen Gland in mucosa • Epithelium Artery • Connective tissue Vein Mucosa-associated lymphoid tissue (MALT) Lymphatic vessel Mesentery

II. Digestive System Organs of the Head and II. Digestive System Organs of the Head and Thorax: Anatomy & Function A. The Mouth & Associated Organs Students Do Following 1. Mouth Anatomy Tissue Lining: Palate: Hard &Soft Uvula: 2. Overall Functions: Ingestion, Mechanical Digestions Chemical digestion: amylase Swallowing (Deglutition)

2. The Tongue STUDENTS DO Composition: Functions: 3 Bolus Lingual Tonsil Lingual Lipase

3. The Salivary Glands Students Do 3 pairs of Glands Functions Composition of Saliva 1. Lubrication 2. hydration of food 3. chemical digestion 4. protection from microbes (clinical medium) Tongue Parotid gland Parotid duct Ducts of sublingual gland Submandibular duct Masseter muscle Sublingual gland Body of mandible (cut) Submandibular gland

B. Pharynx Regions: Students Do Stratified squamous e.t. skeletal muscle Propulsion Oropharynx Laryngopharynx

C. Esophagus = propulsion only Muscular tube Esophageal hiatus Upper & Lower Esophageal Sphincters (Lower = Gastroesophageal Sphincter) Histology: stratified squamous

D. Digestive Processes: Mouth to Esophagus--SWALLOWING (Text p D. Digestive Processes: Mouth to Esophagus--SWALLOWING (Text p. ) STUDENTS DO FOLLOWING 1) MOUTH: Voluntary (Buccal) Phase - tongue presses against hard palate; bolus oropharynx. Bolus of food Tongue Pharynx Epiglottis Glottis Trachea

Uvula Bolus Epiglottis Esophagus 2) Pharyngeal (-Esophageal) Phase: uvula and larynx block airways. Upper esophageal sphincter relaxes and pharynx muscles force bolus into esophagus. Upper esophageal sphincter closes Figure 23.13, step 2

Gastroesophageal sphincter opens Bolus 3) Esophageal Phase:. And Bolus moved to stomach by peristalsis; Gastroesophageal (a.k.a. cardiac) sphincter opens, food  stomach. Figure 23.13, step 3

III. Digestive Organs of the Abdomen-Pelvis A. The Stomach: 1 III. Digestive Organs of the Abdomen-Pelvis A. The Stomach: 1. Overall Functions a) Store Food b) Mechanical D. c) Chemical D. Proteins d) Intrinsic Factor 2. Gross Anatomy Cardia Fundus Serosa Body Lesser curvature Rugae of mucosa a) Regions Body Cardia Pyloric Fundus b) Rugae Pyloric sphincter Pyloric Region Greater curvature Duodenum Figure 23.14a

A. The Stomach … 2. Gross Anatomy … Cardia Fundus c) Curvatures Greater Lesser d) Sphincters Cardiac Pyloric Serosa Body Lesser curvature Rugae of mucosa Pyloric sphincter Pyloric Region Greater curvature Duodenum (a) Figure 23.14a

Lesser omentum Greater omentum 2. Gross Anatomy … e) Mesentaries Lesser omentum From liver to lesser curvature Greater omentum Drapes from greater curvature Anterior to small intestine Lesser omentum Greater omentum

The Stomach: … Gross Anatomy … Cardia f) Muscular tunic has extra 3rd layer – inner most oblique layer = churning action Slide: difficult to see; is thin Fundus Serosa Body Lesser curvature Rugae of mucosa Pyloric sphincter (valve) at pylorus Pyloric canal Greater curvature Pyloric antrum Duodenum (a) Figure 23.14a

3. Microscopic Anatomy of the Stomach

ii) Gastric Pits lead to the  Gastric Glands which produce 3. Microscopic Anatomy of Stomach … a) Mucosa i) Simple Columnar E.T. in loops w/ Goblet cells Esophagus ii) Gastric Pits lead to the  Gastric Glands which produce Gastric Juice– mostly from Fundus and Body iii) Cells of Gastric Glands Muscus Neck Cells Alkaline mucus– bicarbonate rich Function: protect cells from pH1.5 – 3.5 gastric juice In all stomach regions Stomach Gastric Pits Mucous neck cells Gastric Glands Figure 23.12b

STOMACH

a) Mucosa iii) Gastric Gland Cells … Gastric pits Gastric pit Parietal Cells Function: Hydrochloric Acid (HCl) for activation of enzyme pepsinogen and intrinsic factor for B12 absorption in small intestine) HCl also kills bacteria Slide: Round, large, pinkish cells Surface epithelium (mucous cells) Gastric gland Mucous neck cells Pepsinogen Pepsin Parietal cell HCl Chief cell Enteroendocrine cell (b) Enlarged view of gastric pits and gastric glands

a) Mucosa iii) Gastric Gland Cells … Gastric pits Gastric pit Chief Cells Function: produce enzyme Pepsinogen HCl Activates it to Pepsin Most numerous cells Slide: Small, purplish cells Enteroendocrine cells G cells: Function: produce hormones Gastrin, Histamine which promote secretion of gastric juices w/ HCl and Pepsinogen Surface epithelium (mucous cells) Gastric gland Mucous neck cells Parietal cell Chief cell Enteroendocrine cell (b) Enlarged view of gastric pits and gastric glands

Stomach

4. Digestive Processes Occurring in the Stomach a) Introduction i) Secretions: Up to 3L gastric juices per day secreted ii) Nervous Control: Parasympathetic NS via Vagus Nerve: stimulates glands Sympathetic NS: depress secretary action Enteric Plexuses iii) Hormonal Control Gastrin, most important hormone Stimulates secretion of enzymes, HCl, & intestinal enzymes iv) Stimulus: Head, Stomach, and Small Intestine

4. Digestive Processes occurring in the Stomach … b. Regulation of Gastric Secretion 3 Phases i) Cephalic (reflex) phase: a few min. Gets stomach ready for digestive processes Long Reflexes from CNS to Enteric Ganglia Conditioned Reflex Stimulatory events Cephalic phase Sight and thought of food 1 Cerebral cortex Conditioned reflex Stimulation of taste and smell receptors 2 Hypothalamus and medulla oblongata Vagus nerve Stomach secretory activity Figure 23.17 (1) Sight and Thoughts  Hypothalamus  Medulla nuclei  Vagus Nerve  Ach/Stomach  increased secretions

a. Cephalic Phase … (2) Taste and Smell  Hypothalamus  Medulla vagal nuclei  vagus nerve  Ach/ stomach  ↑ secretion of gastric juices Inhibitory Events: From Cerebrum-- Depressed or not hungry then  Parasympathetic NS. Not stimulated  Cephalic Phase inhibited Stimulatory events Cephalic phase Sight and thought of food 1 Cerebral cortex Conditioned reflex Stimulation of taste and smell receptors 2 Hypothalamus and medulla oblongata Vagus nerve Stomach secretory activity Figure 23.17 Figure 23.17

b. Gastric Phase– 3-4 hours, after food first enters stomach 2. Regulation of … b. Gastric Phase– 3-4 hours, after food first enters stomach Produces 2/3 gastric juice produced Stomach distention  Myenteric Reflex (local)  AND Vagovagal Reflex =  (2) Food Chemicals (proteins) & Rising pH  Chemoreceptors  activate G cells (enteroendocrine cells)  Gastrin (hormone)  increased HCl secretion by Parietal Cells  Vagus  Medulla  Vagus  at Stomach AcH released  increased gastric juices Stimulatory events Inhibitory events Stomach distension activates stretch receptors 1 Vagovagal reflexes Medulla Vagus nerve Gastrin secretion declines G cells 1. Excessive acidity (pH <2) in stomach Excessive acidity (pH <2) in stomach 1 Stomach distension activates stretch receptors 1 Vagovagal reflexes Medulla Vagus nerve Gastrin secretion declines G cells Gastric phase Local reflexes Overrides parasym- pathetic controls Sympathetic nervous system activation Emotional upset 2 Ach Local reflexes Overrides parasym- pathetic controls Sympathetic nervous system activation 2. Emotional upset Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors 2 G cells Gastrin release to blood Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors 2 G cells Gastrin release to blood Stomach secretory activity Stomach secretory activity Stimulate Entero- gastric reflex Local reflexes 1 Inhibit Figure 23.17 Presence

Negatie Feedback Loop: (2) Food Chemicals … The increase in acidity activates pepsinogen to pepsin so that proteins can be digested Inhibitory Events Negatie Feedback Loop: Acidity: Low H+ (High pH) stimulates release of Gastrin High H+ (low pH) inhibits release of Gastrin Emotional distress– activates sympathetic N.S. Stimulatory events Inhibitory events Stomach distension activates stretch receptors 1 Vagovagal reflexes Medulla Vagus nerve Gastrin secretion declines G cells Excessive acidity (pH <2) in stomach 1 Stomach distension activates stretch receptors 1 Vagovagal reflexes Medulla Vagus nerve Gastrin secretion declines G cells Excessive acidity (pH <2) in stomach 1 Gastric phase Local reflexes Overrides parasym- pathetic controls Sympathetic nervous system activation Emotional upset 2 Ach Local reflexes Overrides parasym- pathetic controls Sympathetic nervous system activation Emotional upset 2 Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors 2 Stimulate G cells Gastrin release to blood Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors 2 G cells Gastrin release to blood Inhibit Stomach secretory activity Stomach secretory activity Entero- gastric reflex Local reflexes 1 Figure 23.17 Presence

c. Intestinal Phase In Duodenum Begins when stomach begins to empty chyme to duodenum Two parts: Excitatory and Inhibitory EXCITATORY PART Brief effect (1) Partially digested food (including fats), low pH, & hypertonic solution  release Intestinal Gastrin  Stomach glands continue to secrete gastric fluids briefly Stomach secretory activity Stimulatory events Presence of low pH, partially digested foods, fats, or hypertonic solution in duodenum when stomach begins to empty 1 Intestinal (enteric) gastrin release to blood Intestinal phase Brief effect Stimulate Figure 23.17 Inhibit

(2) Distension of Duodenum, …  Release of intestinal Hormones c. Intestinal Phase … INHIBITORY PART Distension of Duodenum, very low pH, fats, part dig. proteins, & irritants  Enterogastric Reflex inhibits gastric secretion and closes the Pyloric Sphincter Function: to move a small bit of chyme into duodenum and to protect it from over-distension (2) Distension of Duodenum, …  Release of intestinal Hormones Cholecystokinin (CCK) Secretin TO BE CONTINUED UNDER SM. INTESTINE Figure 23.17 Intestinal Phase … Stomach secretory activity Inhibitory events Entero- gastric reflex Local reflexes Distension of duodenum; presence of fatty, acidic, hypertonic chyme, and/or irritants in the duodenum 1 Vagal nuclei in medulla Pyloric sphincter Release of intestinal hormones (secretin, cholecystokinin, vasoactive intestinal peptide) Distension; presence of fatty, acidic, partially digested food in the duodenum 2 Stimulate Inhibit

B. Small Intestine 1. Gross Anatomy 2–4 m long; Subdivisions Duodenum– 10 inches Jejunum– 8 feet Ileum– 12 feet Duodenum Most chemical dig. & absorption occurs here Receives bile from liver & enzymes and bicarbonate from pancreas Small intestine Duodenum Jejunum Ileum

ii) Plicae Circulares—deep folds of mucosa and submucosa a. Duodenum … i) Hepatopancreatic Ampulla: Bulb-like point where Bile duct & main pancreatic duct join Major Duodenal Papilla: Volcano-shaped opening into Duodenum H. Ampulla attached and releases contents to Papilla  Duodenum Hepatopancreatic Sphincter: at Ampulla/Papilla junction ii) Plicae Circulares—deep folds of mucosa and submucosa Bile duct and sphincter Major duodenal papilla Plicae Circulares Main pancreatic duct and sphincter Hepatopancreatic ampulla and sphincter Duodenum

Jejunum Attached to Duodenum Location In central and lower part of Abdominal Cavity Coiled Ileum Attached to Jejunum Location– same Both framed by Large Intestine

2. Microscopic Anatomy Small Intestine

a. Mucosa w/ folds & loops 2. Microscopic Anatomy … a. Mucosa w/ folds & loops i) Villi—loops of mucosa (epithelia = scattered goblets among absorptive cells) Blood vessels, nerves, and lacteal Cells with Microvilli: small loops at apical side of cells; form brush border Digestive Enzymes embedded in microvilli Function of folds and loops:

Small Intestine

ii) Intestinal Glands (Crypts) in Mucosa = tubular glands b/n villi 2. Microscopic Anatomy … ii) Intestinal Glands (Crypts) in Mucosa = tubular glands b/n villi Secretory cells epithelium produce intestinal juice: water, some mucus, slightly alkaline (pH =7.4-7.8) and low in enzymes Enteroendocrine cells (secrete CCK, secretin among others) iii) Lamnia Propria - agregations of intestinal nodules (MALT) Absorptive cells Goblet cell Lacteal Vilus Intestinal crypt Enteroendocrine cells Venule Lymphatic vessel Submucosa Duodenal gland

b) Submucosa of small intestine Areolar Tissue Peyer’s patches = aggregated lymphoid follicles; increase towards end sm. int. They protect distal areas against bacteria Have lymphocytes Duodenal (Brunner’s) glands: of duodenum secrete alkaline (bicarbonate)mucus to neutralize the acidic chime coming in from stomach c. Muscularis Externa d. Serosa Submucosa Duodenal gland Peyer’s Patches

Small Intestine

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Review Questions The mucosa of the lower pharanx and esophagus has _________ __________ epithelia. ___________, i.e. swallowing, involves over 22 muscle groups and moves a _________ from the oral cavity to the stomach. stratified squamous Deglutition bolus

Review Questions amylase Enzymes in saliva include _________, which is responsible for starch breakdown. 2I, 1C, 2PM, 3M

enteric nerve plexuses Review Questions Short reflexes of the GI tract are housed and completed within _____ ____ ______ while _______ reflexes involve the CNS. enteric nerve plexuses long

Review Questions In the small intestine, ___________ __________, __________, and ___________ all contribute to expanding the surface area for adequate __________. plicae circulares villi microvilli absorption

Review Questions From the esophagus to the anus, the GI tract contains how many layers? Which 2 layers contain smooth muscle? 4: mucosa, submucosa, muscularis externa, serosa Mucosa & muscularis externa

Participating… gastric The _________ phase is responsible for the production of most gastric secretions by releasing the hormone _________. What other 2 hormones promote gastric secretions? gastrin ACh and Histamine

Review Questions Parietal gastric ________ cells of _______ glands produce HCl and ___________ __________. __________ cells produce pepsinogen. What is intrinsic factor for? intrinsic factor Chief B12 absorption

Figure 23.17 Stimulatory events Inhibitory events Cephalic phase Sight and thought of food 1 Cerebral cortex Lack of stimulatory impulses to parasym- pathetic center Cerebral cortex Loss of appetite, depression 1 Conditioned reflex Stimulation of taste and smell receptors 2 Hypothalamus and medulla oblongata Vagus nerve Stomach distension activates stretch receptors 1 Vagovagal reflexes Medulla Vagus nerve Gastrin secretion declines G cells Excessive acidity (pH <2) in stomach 1 Gastric phase Local reflexes Overrides parasym- pathetic controls Sympathetic nervous system activation Emotional upset 2 Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors 2 G cells Gastrin release to blood Stomach secretory activity Entero- gastric reflex Local reflexes Distension of duodenum; presence of fatty, acidic, hypertonic chyme, and/or irritants in the duodenum 1 Presence of low pH, partially digested foods, fats, or hypertonic solution in duodenum when stomach begins to empty 1 Intestinal (enteric) gastrin release to blood Vagal nuclei in medulla Brief effect Intestinal phase Pyloric sphincter Release of intestinal hormones (secretin, cholecystokinin, vasoactive intestinal peptide) Distension; presence of fatty, acidic, partially digested food in the duodenum 2 Stimulate Inhibit Figure 23.17

Figure 23.17 Stimulatory events Inhibitory events Cephalic phase Sight and thought of food 1 Cerebral cortex Lack of stimulatory impulses to parasym- pathetic center Cerebral cortex Loss of appetite, depression 1 Conditioned reflex Stimulation of taste and smell receptors 2 Hypothalamus and medulla oblongata Vagus nerve Stomach distension activates stretch receptors 1 Vagovagal reflexes Medulla Vagus nerve Gastrin secretion declines G cells Excessive acidity (pH <2) in stomach 1 Gastric phase Local reflexes Overrides parasym- pathetic controls Sympathetic nervous system activation Emotional upset 2 Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors 2 G cells Gastrin release to blood Stomach secretory activity Entero- gastric reflex Local reflexes Distension of duodenum; presence of fatty, acidic, hypertonic chyme, and/or irritants in the duodenum 1 Presence of low pH, partially digested foods, fats, or hypertonic solution in duodenum when stomach begins to empty 1 Intestinal (enteric) gastrin release to blood Vagal nuclei in medulla Brief effect Intestinal phase Pyloric sphincter Release of intestinal hormones (secretin, cholecystokinin, vasoactive intestinal peptide) Distension; presence of fatty, acidic, partially digested food in the duodenum 2 Stimulate Inhibit Figure 23.17

b) Intrinsic = Enteric Nervous System (Gut Brain) CNS is linked via extrinsic long ANS fibers Intrinsic nerve plexuses • Myenteric nerve plexus • Submucosal nerve plexus

Gingivae (gums) Hard palate Soft palate Uvula Posterior wall of oropharynx Palatine tonsil

100 million bacteria/mL of saliva! Serous & Mucous Cells Water content Enzyme = Mucin Control of Salivation: Parasym. Sys. via chemo- & mechano-receptors 100 million bacteria/mL of saliva!

Hiatal hernia

Homeostatic Imbalance Peptic or gastric ulcers: erosion of stomach wall Helicobacter pylori bacteria Bacteria Mucosa layer of stomach (a) A gastric ulcer lesion (b) H. pylori bacteria

Regulation of Gastric Secretion Figure 23.17 Stimulatory events Inhibitory events Sight and thought of food 1 Cephalic phase Cerebral cortex Lack of stimulatory impulses to parasym- pathetic center Cerebral cortex Loss of appetite, depression 1 Conditioned reflex Stimulation of taste and smell receptors 2 Hypothalamus and medulla oblongata Vagus nerve Stomach distension activates stretch receptors 1 Vagovagal reflexes Medulla Vagus nerve Gastrin secretion declines G cells Excessive acidity (pH <2) in stomach 1 Gastric phase Local reflexes Overrides parasym- pathetic controls Sympathetic nervous system activation Emotional upset 2 Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors 2 G cells Gastrin release to blood Stomach secretory activity Entero- gastric reflex Local reflexes Distension of duodenum; presence of fatty, acidic, hypertonic chyme, and/or irritants in the duodenum 1 Presence of low pH, partially digested foods, fats, or hypertonic solution in duodenum when stomach begins to empty 1 Intestinal (enteric) gastrin release to blood Vagal nuclei in medulla Brief effect Intestinal phase Pyloric sphincter Release of intestinal hormones (secretin, cholecystokinin, vasoactive intestinal peptide) Distension; presence of fatty, acidic, partially digested food in the duodenum 2 Stimulate Inhibit

Regulation of Gastric Secretion Stimulatory events Inhibitory events Sight and thought of food 1 Cerebral cortex Lack of stimulatory impulses to parasym- pathetic center Cerebral cortex Loss of appetite, depression 1 Cephalic phase Conditioned reflex Stimulation of taste and smell receptors 2 Hypothalamus and medulla oblongata Vagus nerve Stomach distension activates stretch receptors 1 Vagovagal reflexes Medulla Vagus nerve Gastrin secretion declines G cells Excessive acidity (pH <2) in stomach 1 Gastric phase Local reflexes Overrides parasym- pathetic controls Sympathetic nervous system activation Emotional upset 2 Food chemicals (especially peptides and caffeine) and rising pH activate chemoreceptors 2 G cells Gastrin release to blood Stomach secretory activity Entero- gastric reflex Local reflexes Distension of duodenum; presence of fatty, acidic, hypertonic chyme, and/or irritants in the duodenum 1 Presence of low pH, partially digested foods, fats, or hypertonic solution in duodenum when stomach begins to empty 1 Intestinal (enteric) gastrin release to blood Vagal nuclei in medulla Brief effect Intestinal phase Pyloric sphincter Release of intestinal hormones (secretin, cholecystokinin, vasoactive intestinal peptide) Distension; presence of fatty, acidic, partially digested food in the duodenum 2 Stimulate Inhibit Figure 23.17

3. Gastric Motility & Emptying Stretch-Relaxation Response: Relaxes to recieve food, then contracts Contractile Activity: Pacemaker cells (in smooth muscle) initiate bi-directional peristalsis 3X a min = BER (basic electrical rhythm) Stimulated by neural and hormonal factors Stomach & Duodenum coordinated: 3 mL chyme  duodenum/time Emptying time: 4 hours normally, if much fat up to 6 hours each Pyloric valve closed Pyloric valve slightly opened 3. Retropulsion: Small amounts of chyme enter duodenum, most moves backward = more mixing 1 Propulsion: Peristaltic waves move from fundus toward pylorus. 2. Grinding: Most vigorous peristalsis/ mixing action occur near pylorus. Figure 23.19