Obj 6 Digestive System PDF

Objective 6: Digestive System PN 1241 Chapters 23 & 24 6. Discuss the structure and function of the digestive system 6.1 Define key terms related to the digestive system. 6.2 Discuss the primary processes of the digestive system. 6.3 Identify the main structures of the digestive system. 6.4 Discuss...

Objective 6: Digestive System PN 1241 Chapters 23 & 24 6. Discuss the structure and function of the digestive system 6.1 Define key terms related to the digestive system. 6.2 Discuss the primary processes of the digestive system. 6.3 Identify the main structures of the digestive system. 6.4 Discuss the four layers of the gastrointestinal tract and the linings of the abdominopelvic cavity. 6.5 Discuss the stimuli and control mechanisms of the gastrointestinal tract. 6.6 Discuss the structure and functions of the: a) mouth b) tongue c) salivary glands d) teeth e) pharynx f) esophagus g) stomach h) liver i) gall bladder j) pancreas k) small intestine l) large intestine 6.7 Discuss the process of digestion. 6.8 Discuss the process of absorption. 6.9 Discuss the enzymes involved in digestion and what foods they act upon. 6.10 Identify the end products of the digestion of proteins, fats, carbohydrates and nucleic acid. 6.11 Discuss the five major nutrient categories. 6.12 Discuss carbohydrates, lipids, and proteins. 6.13 Discuss vitamins and minerals. 6.14 Discuss metabolism, catabolism and anabolism. 6.15 Discuss the metabolic pathways for carbohydrates, lipids and proteins. 6.16 Discuss basal metabolic rate. Function of Digestive System Main functions of the digestive system Take in food Break it down into nutrient molecules Absorb molecules into the bloodstream Rid body of any indigestible remains © 2016 Pearson Education, Inc. Part 1 – Overview of Digestive System Organs of the digestive system fall into two groups: 1. Alimentary canal (gastrointestinal or GI tract or gut) Continuous muscular tube that runs from the mouth to anus Digests food: breaks down into smaller fragments Absorbs fragments through lining into blood Organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus © 2016 Pearson Education, Inc. Part 1 – Overview of Digestive System 2. Accessory digestive organs Teeth Tongue Gallbladder Digestive glands: produce secretions that help break down foodstuffs Salivary glands Liver Pancreas © 2016 Pearson Education, Inc. Figure 23.1 Alimentary canal and related accessory digestive organs. Mouth (oral cavity) Tongue* Parotid gland Sublingual gland Submandibular gland Salivary glands* Pharynx Esophagus Stomach Pancreas* (Spleen) Liver* Gallbladder* Transverse colon Duodenum Small intestine Jejunum Ileum Descending colon Ascending colon Cecum Sigmoid colon Rectum Appendix Anus © 2016 Pearson Education, Inc. Anal canal Large intestine Digestive Processes Processing of food involves 6 essential activities: 1. 2. Ingestion: eating Propulsion: movement of food through the tract, which includes: Swallowing Peristalsis: major means of propulsion of food that involves alternating waves of contraction and relaxation 3. Mechanical breakdown: processes that physically mix or bread foods down into smaller fragments Segmentation: local constriction of intestine that mixes food with digestive juices; makes absorption more efficient by repeatedly moving different parts of food mass over the intestinal wall © 2016 Pearson Education, Inc. Digestive Processes 4. 5. 6. Digestion: catabolic stets that involves enzymes that break down food molecules Absorption: passage of digested end products from intestinal mucosa into blood or lymph Defecation: elimination of undigested substances via anus in form of feces © 2016 Pearson Education, Inc. Ingestion Food Mechanical breakdown Pharynx Chewing (mouth) Churning (stomach) Segmentation (small intestine) Figure 23.2 Gastrointes tinal tract activities. Esophagus Propulsion Swallowing (oropharynx) Peristalsis (esophagus, stomach, small intestine, large intestine) Digestion Stomach Absorption Lymph vessel Small intestine Blood vessel Large intestine Mainly H2O Feces Defecation Anus © 2016 Pearson Education, Inc. Organization of Digestive System Relationship of Digestive Organs to Peritoneum Peritoneum: serous membranes of abdominal cavity that consists of: Visceral peritoneum: membrane on external surface of most digestive organs Parietal peritoneum: membrane that lines body wall Peritoneal cavity Fluid-filled space between two peritoneums Serous fluid lubricates mobile organs © 2016 Pearson Education, Inc. Relationship of Digestive Organs to Peritoneum (cont.) Mesentery: double layer of peritoneum; layers are fused back to back Extends from body wall to digestive organs Provides routes for blood vessels, lymphatics, and nerves Holds organs in place and also stores fat © 2016 Pearson Education, Inc. Histology of the Alimentary Canal All digestive organs have the same four basic layers, or tunics 1. 2. 3. 4. Mucosa Submucosa Muscularis externa Serosa © 2016 Pearson Education, Inc. Histology of the Alimentary Canal (cont.) 1. Mucosa Tunic layer that lines lumen Functions: different layers perform one or all three Secretes mucus, digestive enzymes, and hormones Absorbs end products of digestion Protects against infectious disease 2. Submucosa Contains blood and lymphatic vessels, lymphoid follicles, and nerve fibers that supply surrounding GI tract tissues Has abundant amount of elastic tissues that help organs to regain shape after storing large meal © 2016 Pearson Education, Inc. Histology of the Alimentary Canal (cont.) 3. Muscularis externa Muscle layer responsible for segmentation and peristalsis Contains inner circular muscle layer and outer longitudinal layers Circular layer thickens in some areas to form sphincters that act as valves to control food passage from one organ to the next and prevent backflow 4. Serosa Outermost layer which is made up of the visceral peritoneum Summary: Digestive System | Learn Anatomy (visiblebody.com) © 2016 Pearson Education, Inc. Part 2 – Functional Anatomy of the Digestive System Mouth and Associated Organs Mouth is where food is chewed and mixed with enzyme-containing saliva that begins process of digestion, and swallowing process is initiated Associated organs include: Mouth Tongue Salivary glands Teeth © 2016 Pearson Education, Inc. Mouth Also called the oral (buccal) cavity Bounded by lips, cheeks, palate, and tongue Oral orifice is anterior opening Walls of mouth lined with stratified squamous epithelium Tough cells that resist abrasion Cells of gums, hard palate, and part of tongue are keratinized for extra protection Lips & cheeks Lips (labia) – made of orbicularis oris muscle Cheeks – made of buccinators muscle Oral cavity proper – area within teeth and gums © 2016 Pearson Education, Inc. Mouth (cont.) Palate Palate forms the roof of the mouth and has two distinct parts: 1. Hard palate (anterior): formed by palatine bones and palatine Mucosa is slightly corrugated to help create friction against tongue 2. Soft palate: fold formed mostly of skeletal muscle Closes off nasopharynx during swallowing Palatine tonsils are located here Uvula: fingerlike projection that faces downward from free edge of soft palate © 2016 Pearson Education, Inc. Figure 23.8b Anatomy of the oral cavity (mouth). Upper lip Gingivae (gums) Palatine raphe Superior labial frenulum Hard palate Palatoglossal arch Soft palate Palatopharyngeal arch Uvula Posterior wall of oropharynx Palatine tonsil Tongue Sublingual fold with openings of sublingual ducts Lingual frenulum Opening of submandibular duct Oral vestibule Gingivae (gums) Lower lip Inferior labial frenulum Anterior view © 2016 Pearson Education, Inc. Tongue occupies floor of mouth Composed of interlacing bundles of skeletal muscle Contains taste buds Functions include: Gripping, repositioning, and mixing of food during chewing Formation of bolus, mixture of food and saliva Initiation of swallowing, speech, and taste muscles change shape of tongue and alter tongue’s position Lingual frenulum: attachment to floor of mouth; limits posterior movement of tongue © 2016 Pearson Education, Inc. Epiglottis Palatopharyngeal arch Palatine tonsil Lingual tonsil Palatoglossal arch Terminal sulcus Foliate papillae Vallate papilla Medial sulcus of the tongue Figure 23.9 Dorsal surface of the tongue, and the tonsils. Dorsum of tongue Fungiform papilla Filiform papilla © 2016 Pearson Education, Inc. Salivary Glands Functions of saliva: Cleanses mouth Dissolves food chemicals for taste Moistens food; compacts into bolus Begins breakdown of starch with enzyme amylase Most saliva produced by major salivary glands located outside oral cavity: parotid, submandibular & sublingual Minor salivary glands are scattered throughout oral cavity © 2016 Pearson Education, Inc. Salivary Glands (cont.) Major salivary glands include: Parotid: anterior to ear opens next to second upper molar Submandibular: medial to body of mandible Duct opens at base of lingual frenulum Sublingual: anterior to submandibular gland under tongue Opens via 10–12 ducts into floor of mouth © 2016 Pearson Education, Inc. Figure 23.10a The salivary glands. Tongue Teeth Parotid gland Ducts of sublingual gland Parotid duct Frenulum of tongue Masseter muscle Sublingual gland Body of mandible (cut) Mylohyoid muscle (cut) Posterior belly of digastric muscle Anterior belly of digastric muscle Submandibular duct Submandibular gland © 2016 Pearson Education, Inc. Salivary Glands (cont.) Salivary glands are composed of two types of secretory cells: Serous cells: produce watery secretion, enzymes, ions, bit of mucin Mucous cells: produce mucus Parotid and submandibular glands contain mostly serous cells, but sublingual gland consists mostly of mucous cells © 2016 Pearson Education, Inc. Salivary Glands (cont.) Control of salivation 1500 ml/day can be produced Minor glands continuously keep mouth moist Major salivary glands are activated by parasympathetic nervous system when: Ingested food stimulates chemoreceptors and mechanoreceptors in mouth Strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia) Smell/sight of food or upset GI can act as stimuli © 2016 Pearson Education, Inc. The Teeth Teeth lie in sockets in gum-covered margins of mandible and maxilla Mastication: process of chewing that tears and grinds food into smaller fragments Dentition: Primary dentition consists of 20 deciduous teeth, or baby teeth, that erupt between 6 and 24 months of age 32 deep-lying permanent teeth enlarge and develop while roots of milk teeth are resorbed from below, causing them to loosen and fall out Occurs around 6–12 years of age All but 3rd molars (wisdom teeth) are in by end of adolescence Third molars may or may not emerge around 17–25 years of age © 2016 Pearson Education, Inc. The Teeth (cont.) Teeth are classified according to shape: Incisors: chisel shaped for cutting Canines: fanglike teeth that tear or pierce Premolars (bicuspids): broad crowns with rounded cusps used to grind or crush Molars: broad crowns, rounded cusps: best grinders During chewing, upper and lower molars lock together, creating tremendous crushing force © 2016 Pearson Education, Inc. The Teeth (cont.) Tooth structure Each tooth has two major regions: Crown: exposed part above gingiva (gum) Covered by enamel, the hardest substance in body Heavily mineralized with calcium salts and hydroxyapatite crystals Enamel-producing cells degenerate when tooth erupts, so no healing if tooth decays or cracks; needs artificial repair by filling Root: portion embedded in jawbone Connected to crown by neck © 2016 Pearson Education, Inc. The Teeth (cont.) Cement: calcified connective tissue Covers root; attaches it to periodontal ligament Periodontal ligament Forms fibrous joint called gomphosis Anchors tooth in bony socket (alveolus) Gingival sulcus: groove where gingiva borders tooth Dentin: bonelike material under enamel Maintained by odontoblasts of pulp cavity Summary: The Oral Cavity | Digestive Anatomy (visiblebody.com) © 2016 Pearson Education, Inc. Pharynx and Esophagus The Pharynx Food passes from mouth into oropharynx and then into laryngopharynx Allows passage of food, fluids, and air Stratified squamous epithelium lining contains mucus-producing glands External muscle layers consists of two skeletal muscle layers Inner layer runs longitudinally Outer encircles wall of pharynx (Pharyngeal constrictors) Moves food toward the esophagus © 2016 Pearson Education, Inc. The Esophagus Flat muscular tube that runs from laryngopharynx to stomach Is collapsed when not involved in food propulsion Pierces diaphragm at esophageal hiatus Joins stomach at cardial sphincter cardiac sphincter Keeps orifice closed when food is not being swallowed Mucus cells on both sides of sphincter help protect esophagus from acid reflux © 2016 Pearson Education, Inc. Digestive Processes of the Mouth Pharynx and esophagus are channels to pass food from mouth to stomach by peristalsis Major function of both organs is propulsion that starts with deglutition (swallowing) Deglutition involves coordination of 22 muscle groups and two phases: Buccal phase: voluntary contraction of tongue compacts food and makes a bolus that initiates swallowing Pharyngeal-esophageal phase: involuntary phase that primarily involves vagus nerve Controlled by swallowing center in medulla and pons © 2016 Pearson Education, Inc. Slide 6 Bolus of food Nasopharynx Tongue Uvula Oropharynx Bolus Epiglottis Upper esophageal sphincter Trachea Esophagus 1 Buccal phase: 2 Pharyngeal-esophageal phase begins: The upper esophageal sphincter is contracted (closed). The tongue blocks the mouth. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. The soft palate and its uvula rise, closing off the nasopharynx. The larynx rises so that the epiglottis blocks the trachea. The upper esophageal sphincter relaxes; food enters the esophagus. Upper esophageal sphincter Bolus 3 Pharyngeal-esophageal phase continues (steps 3 − 5 ): The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts after food enters. Relaxed muscles Relaxed muscles Circular muscles contract Bolus of food Longitudinal muscles contract Circular muscles contract Gastroesophageal sphincter opens Gastroesophageal sphincter closed Stomach Figure 23.14 Deglutition (swallowing). 4 Peristalsis moves food through the esophagus to the stomach. © 2016 Pearson Education, Inc. 5 The gastroesophageal sphincter surrounding the cardial orifice opens. After food enters the stomach, the sphincter closes, preventing regurgitation. The Stomach a temporary storage tank that starts chemical breakdown of protein digestion Located in upper left quadrant, nearly hidden by liver and diaphragm Converts bolus of food to paste-like chyme Empty stomach has ~50 ml volume but can expand to 4 L When empty, stomach mucosa forms many folds called rugae © 2016 Pearson Education, Inc. Gross Anatomy of the Stomach (cont.) Major regions of the stomach: Cardiac sphincter: at end of esophagus before stomach; prevents acid reflux Fundus: dome-shaped region beneath diaphragm Body: mid-portion; continuous with pyloric part Pyloric part: Pylorus is continuous with duodenum through pyloric valve (sphincter controlling stomach emptying) © 2016 Pearson Education, Inc. Cardia Fundus Esophagus Muscularis externa Longitudinal layer Circular layer Oblique layer Duodenum Serosa Body Lumen Lesser curvature Rugae of mucosa Greater curvature Pyloric sphincter Pyloric Figure 23.15a Anatomy of the stomach. (valve) at pylorus canal © 2016 Pearson Education, Inc. Pyloric antrum Gross Anatomy of the Stomach (cont.) Greater curvature: convex lateral surface of stomach Lesser curvature: concave medial surface of stomach Mesenteries extend from curvatures and tether stomach to other digestive organs Lesser omentum Runs from lesser curvature to liver Greater omentum: drapes from bottom of greater curvature over intestine, spleen, and transverse colon © 2016 Pearson Education, Inc. Gross Anatomy of the Stomach (cont.) Autonomic nervous system supplies stomach Sympathetic fibers from thoracic region are relayed through the celiac plexus Parasympathetic fibers are supplied by vagus nerve © 2016 Pearson Education, Inc. Microscopic Anatomy of the Stomach Stomach wall contains regular four tunics but muscularis and mucosa are modified: Muscularis externa has circular and longitudinal smooth muscle layers but also has extra layer of smooth muscle Inner oblique layer - allows stomach to pummel food, which increases physical breakdown Mucosa layer Consists mostly of mucous cells Dotted with gastric pits, which lead into gastric glands that produce gastric juices Rugae – folds in mucosa © 2016 Pearson Education, Inc. Microscopic Anatomy of the Stomach (cont.) Types of secreting cells in gastric glands secretory cells include: Mucous neck cells Parietal cells Chief cells Enteroendocrine cells Harsh digestive conditions require stomach to be protected Mucosal barrier protects stomach Glands in fundus and body produce most gastric juices © 2016 Pearson Education, Inc. Microscopic Anatomy of the Stomach (cont.) Mucous neck cells Secrete thin, acidic mucus of unknown function Parietal cells Hydrochloric acid (HCl) Makes stomach contents acidic (pH 1.5–3.5); breaks down protein, activates pepsin, breaks down plant cell walls, and kills many bacteria Intrinsic factor required for absorption of vitamin B12 in small intestine © 2016 Pearson Education, Inc. Microscopic Anatomy of the Stomach (cont.) Chief cells Secretions include: Pepsinogen: activated by HCl to convert to pepsin Lipases Fat digesting enzyme Digests ~15% of lipids Enteroendocrine cells Secrete hormone gastrin; chemical messenger © 2016 Pearson Education, Inc. Digestive Processes in the Stomach Processes carried out by stomach 1. Carries out breakdown of food 2. Serves as holding area for food 3. Delivers chyme to small intestine 4. Denatures proteins by HCl 5. Pepsin carries out breakdown of proteins © 2016 Pearson Education, Inc. Digestive Processes in the Stomach (cont.) 6. Lipid-soluble alcohol and aspirin are absorbed into blood 7. Only stomach function essential to life is secretion of intrinsic factor for vitamin B12 absorption B12 needed for red blood cells to mature Lack of intrinsic factor causes pernicious anemia Treated with B12 injections Summary: Propulsion and Peristalsis | Digestive Anatomy (visiblebody.com) © 2016 Pearson Education, Inc. Regulation of Gastric Secretion Gastric mucosa secretes >3 L of gastric juice/day and are regulated by: Neural mechanisms Vagus nerve stimulation increases secretion Sympathetic stimulation decreases secretion Hormonal mechanisms Gastrin stimulates secretion of enzymes and HCl secretion Gastrin antagonists are secreted by small intestine © 2016 Pearson Education, Inc. Regulation of Gastric Secretion (cont.) Gastric secretions are broken down into three phases: 1. 2. 3. Cephalic (reflex) phase Gastric phase Intestinal phase © 2016 Pearson Education, Inc. Regulation of Gastric Secretion (cont.) 1. Cephalic (reflex) phase Conditioned reflex triggered by aroma, taste, sight, thought 2. Gastric phase Lasts 3–4 hours and provides two-thirds of gastric juice released Stimulation of gastric phase Distension activates stretch receptors, initiating both long and short reflexes Chemical stimuli, such as partially digested proteins, caffeine, and low acidity, activate secretion of gastrin © 2016 Pearson Education, Inc. Regulation of Gastric Secretion (cont.) Stimulation of gastric phase (cont.) Release of gastrin then initiates HCl release from parietal cells and activates enzyme secretion Prods parietal cells to secrete HCl Buffering action of ingested proteins causes pH to rise, which activates more gastrin secretion Inhibition of gastric phase Low pH (below 2) inhibits gastrin secretion Occurs between meals Occurs during digestion as negative feedback mechanism The more protein, the more HCl acid is secreted, causing decline in pH, which inhibits gastrin secretion © 2016 Pearson Education, Inc. Regulation of Gastric Secretion (cont.) 3. Intestinal phase Begins with a brief stimulatory component but is primarily inhibition Stimulation of intestinal phase Partially digested food enters small intestine, causing a brief release of intestinal (enteric) gastrin Encourages gastric glands of stomach to continue secretory activities Stimulatory effect is brief and overridden by inhibitory stimuli as intestine fills © 2016 Pearson Education, Inc. Regulation of Gastric Secretion (cont.) Inhibition of intestinal phase Four main factors in duodenum cause inhibition of gastric secretions: Distension of duodenum due to entry of chyme Presence of acidic chyme Presence of fatty chyme Inhibitory effects protect intestine from being overwhelmed by too much chyme or acidity Inhibition is achieved in two ways: Enterogastric reflex and hormones © 2016 Pearson Education, Inc. Regulation of Gastric Secretion (cont.) Enterogastric reflex Duodenum inhibits acid secretion in stomach by: Enteric nervous system Sympathetic nervous system and vagus nerve Hormones Duodenal cells release important hormones that inhibit gastric secretion Secretin Cholecystokinin (CCK) Gastric inhibitory peptide (GIP) Regulation of Gastric Motility and Emptying Regulation of gastric emptying Duodenum can prevent overfilling by controlling how much chyme enters Duodenal receptors respond to stretch and chemical signals Enterogastic reflex and enterogastrones (hormones) inhibit gastric secretion and duodenal filling Stomach empties in ~4 hours, but increase in fatty chyme entering duodenum can increase time to 6 hours or more Carbohydrate-rich chyme moves quickly through duodenum © 2016 Pearson Education, Inc. Liver, Gallbladder and Pancreas Liver, gallbladder, and pancreas are accessory organs associated with small intestine Liver: digestive function is production of bile Bile: fat emulsifier Gallbladder: chief function is storage and concentration of bile Pancreas: supplies most of enzymes needed to digest chyme, as well as bicarbonate to neutralize stomach acid Summary: Accessory Organs | Digestive Anatomy (visiblebody.com) © 2016 Pearson Education, Inc. The Liver Largest gland in body; weighs ~3 lbs Consists of four primary lobes Falciform ligament Separates larger right and smaller left lobes Suspends liver from diaphragm and anterior abdominal wall Round ligament (ligamentum teres) Remnant of fetal umbilical vein along free edge of falciform ligament Lesser omentum anchors liver to stomach © 2016 Pearson Education, Inc. Figure 23.23a Gross anatomy of the human liver. Sternum Bare area Nipple Liver Falciform ligament Left lobe of liver Right lobe of liver Round ligament (ligamentum teres) Gallbladder © 2016 Pearson Education, Inc. The Liver (cont.) Hepatic artery and vein = liver blood vessels Bile ducts: Common hepatic duct leaves liver Cystic duct connects to gallbladder Common Bile duct formed by union of common hepatic duct and cystic ducts Carries bile from GB and empties it in the duodenum © 2016 Pearson Education, Inc. The Liver (cont.) Liver lobules Hexagonal (6 sided) structural and functional units Composed of hepatocytes (liver cells) that filter and process nutrient-rich blood Portal triad in each of the 6 corners of lobule contains: Branch of hepatic artery, which supplies oxygen Branch of hepatic portal vein, which brings nutrient-rich blood from intestine Bile duct, which receives bile © 2016 Pearson Education, Inc. The Liver (cont.) Microscopic anatomy of the liver (cont.) Liver sinusoids: leaky capillaries located between hepatic cells Blood from both hepatic portal vein and hepatic artery proper percolates from triad regions through sinusoids and empties into central vein Stellate macrophages (hepatic macrophages) in liver sinusoids remove debris and old RBCs © 2016 Pearson Education, Inc. The Liver (cont.) Liver functions: Produce ~900 ml bile per day Process blood-borne nutrients Example: store glucose as glycogen and make plasma proteins (albumin, fibrinogen, globulins & clotting factors) Store fat-soluble vitamins (A,D, E & K) Perform detoxification of waste and drugs Example: converting ammonia to urea Metabolism of fats, proteins and CHO © 2016 Pearson Education, Inc. The Liver (cont.) Bile: Yellow-green, alkaline solution containing: Bile salts: cholesterol derivatives that function in fat emulsification and absorption Bilirubin: pigment formed from heme Bacteria break down in intestine to stercobilin that gives brown color of feces © 2016 Pearson Education, Inc. The Gallbladder Gallbladder is a thin-walled muscular sac beneath right lobe of liver Functions to store and concentrate bile Contains many honeycomb folds that allow it to expand as it fills Muscular contractions release bile via cystic duct, which flows into bile duct that empties into duodenum of SI © 2016 Pearson Education, Inc. The Pancreas mostly retroperitoneal; deep to greater curvature of stomach; between spleen and small intestine Exocrine function: produce pancreatic juice Acini: clusters of secretory cells to produce pancreatic juices Ducts: secrete to duodenum via main pancreatic duct; smaller duct cells produce water and bicarbonate Endocrine function: secretion of insulin and glucagon by pancreatic islet cells © 2016 Pearson Education, Inc. The Pancreas (cont.) Composition of pancreatic juice 1200–1500 ml/day is produced containing: Watery, alkaline solution (pH 8) to neutralize acidic chyme coming from stomach Electrolytes, primarily HCO3− Digestive enzymes: Proteases (for proteins): secreted in inactive form to prevent self-digestion of pancreas Amylase breaks down carbohydrates Lipases breaks down lipids Nucleases break down nucleic acids © 2016 Pearson Education, Inc. Bile and Pancreatic Secretion into the Small Intestine (cont.) Regulation of bile and pancreatic secretions Bile and pancreatic juice secretions are both stimulated by neural and hormonal controls Hormonal controls include: Cholecystokinin (CCK) - stimulates gallbladder to release bile Secretin – produced in response to acid © 2016 Pearson Education, Inc. Figure 23.27 Relationship of the liver, gallbladder and pancreas to the duodenum. Liver Right and left hepatic ducts Common hepatic duct Bile duct and sphincter Accessory pancreatic duct Gallbladder Mucosa with folds Cystic duct Pancreas Tail of pancreas Main pancreatic duct and sphincter Head of pancreas Jejunum Duodenum Major duodenal papilla Hepatopancreatic ampulla and sphincter © 2016 Pearson Education, Inc. The Small Intestine Small intestine is the major organ of digestion and absorption 2–4 m long (7–13 ft) from pyloric sphincter to ileocecal valve, point at which it joins large intestine From pyloric sphincter to ileocecal valve ; point at which joins large intestine Small diameter of 2.5–4 cm (1.0–1.6 inches) © 2016 Pearson Education, Inc. Gross Anatomy (cont.) Subdivisions: Duodenum: 10.0” long; curves around head of pancreas Jejunum: 8 ft long; attached posteriorly by mesentery Ileum: 12 ft long; attached posteriorly by mesentery; joins large intestine at ileocecal valve © 2016 Pearson Education, Inc. Figure 23.1 Alimentary canal and related accessory digestive organs. Mouth (oral cavity) Tongue* Parotid gland Sublingual gland Submandibular gland Salivary glands* Pharynx Esophagus Stomach Pancreas* (Spleen) Liver* Gallbladder* Transverse colon Duodenum Small intestine Jejunum Ileum Descending colon Ascending colon Cecum Sigmoid colon Rectum Appendix Anus © 2016 Pearson Education, Inc. Anal canal Large intestine Microscopic Anatomy Modifications of small intestine for absorption Small intestine’s length and other structural modifications provide huge surface area for nutrient absorption Surface area is about size of a tennis court Modifications include: Circular folds - folds of mucosa & submucosa that force chyme to slowly spiral through lumen, allowing more time for nutrient absorption Villi - Fingerlike projections of mucosa with a core that contains dense capillary bed and lymphatic capillary called a lacteal for absorption of fat Microvilli - give fuzzy appearance called the brush border that contains membranebound enzymes brush border enzymes, used for final carbohydrate and protein digestion © 2016 Pearson Education, Inc. Microscopic Anatomy (cont.) Histology of the small intestine wall (cont.) Mucosa-associated lymphoid tissue (MALT) protects intestine against microorganisms and includes: Individual lymphoid follicles Peyer’s patches (aggregated lymphoid nodules) Found in great numbers in distal part of small intestine, where bacterial numbers increase large numbers of plasma cells that secrete IgA Duodenal glands secrete alkaline mucus to neutralize acidic chyme © 2016 Pearson Education, Inc. Intestinal Juice 1–2 L secreted daily in response to distension or irritation of mucosa Major stimulus for production is hypertonic and acidic chyme Consists largely of water but also contains mucus Mucus is secreted by duodenal glands and goblet cells of mucosa © 2016 Pearson Education, Inc. Digestive Processes in the Small Intestine Chyme from stomach contains partially digested carbohydrates and proteins and undigested fats Takes 3–6 hours in small intestine to absorb all nutrients and most water Sources of enzymes for digestion: Substances such as bile, bicarbonate, digestive enzymes are imported from liver and pancreas Brush border enzymes bound to plasma membrane perform final digestion of chyme © 2016 Pearson Education, Inc. Digestive Processes in the Small Intestine Regulating chyme entry Chyme entering duodenum is usually hypertonic; therefore chyme delivery has to be slow to prevent osmotic loss of water from blood Chyme has to be mixed with bile and pancreatic juice to continue digestion Enterogastic reflex and enterogastrones (hormones) control movement of food into duodenum to prevent it from being overwhelmed Digestive Processes in the Small Intestine (cont.) Motility of the small intestine After a meal: Segmentation is most common motion of small intestine; mixes/moves content toward ileocecal valve Promotes mechanical breakdown and mixing of chyme Intensity is altered by long and short reflexes and hormones Parasympathetic increases motility; sympathetic decreases it © 2016 Pearson Education, Inc. Digestive Processes in the Small Intestine (cont.) Between meals: Peristalsis increases Meal remnants, bacteria, and debris are moved toward large intestine Complete trip from duodenum to ileum takes ~2 hours © 2016 Pearson Education, Inc. Digestive Processes in the Small Intestine (cont.) Ileocecal valve control: Ileocecal sphincter relaxes and admits chyme into large intestine when: Ileocecal valve flaps close when chyme exerts backward pressure Prevents regurgitation into ileum © 2016 Pearson Education, Inc. Table 23.2-1 Overview of the Functions of the Gastrointestinal Organs © 2016 Pearson Education, Inc. Table 23.2-2 Overview of the Functions of the Gastrointestinal Organs (continued) © 2016 Pearson Education, Inc. The Large Intestine Gross Anatomy Large intestine has three unique features not seen elsewhere: Teniae coli: three bands of longitudinal smooth muscle in muscularis Haustra: pocketlike sacs caused by tone of teniae coli Epiploic appendages: fat-filled pouches of visceral peritoneum that hang from surface of LI Main function is absorption of water, electrolytes and vitamins; defacation © 2016 Pearson Education, Inc. Gross Anatomy (cont.) Subdivisions of large intestine 1. 2. Cecum: first part of large intestine Appendix: masses of lymphoid tissue attached to cecum Part of MALT of immune system Bacterial storehouse capable of recolonizing gut when necessary Twisted shape of appendix makes it susceptible to blockages 3. Colon: has several regions Ascending colon: travels up right side of abdominal cavity to level of right kidney Ends in right-angle turn called right colic (hepatic) flexure Transverse colon: travels across abdominal cavity Ends in another right-angle turn, left colic (splenic) flexure Descending colon: travels down left side of abdominal cavity Sigmoid colon: S-shaped portion that travels through pelvis © 2016 Pearson Education, Inc. Gross Anatomy (cont.) Subdivisions of large intestine (cont.) 4. 5. Rectum: rectal valves stop feces from being passed with gas (flatus) Anal canal: last segment of large intestine that opens to body exterior at anus Has two sphincters Internal anal sphincter: smooth muscle (involuntary) External anal sphincter: skeletal muscle (voluntary) © 2016 Pearson Education, Inc. Figure 23.31a Gross anatomy of the large intestine. Left colic (splenic) flexure Right colic (hepatic) flexure Transverse mesocolon Transverse colon Epiploic appendages Superior mesenteric artery Descending colon Haustrum Ascending colon IIeum Cut edge of mesentery IIeocecal valve Tenia coli Sigmoid colon Cecum Appendix Rectum Anal canal External anal sphincter © 2016 Pearson Education, Inc. Microscopic Anatomy Large intestine contains thicker mucosa Does not contain circular folds, villi, or digestive secretions Contains many mucus-producing goblet cells numerous bacterial flora present for vitamin synthesis © 2016 Pearson Education, Inc. Digestive Processes in the Large Intestine Residue remains in large intestine 12–24 hours No food breakdown occurs except what enteric bacteria digest Vitamins – synthesizes B complex and some vitamin K needed by liver to produce clotting factors Water and electrolytes (Na+ and Cl-) are reclaimed Major functions of large intestine is propulsion of feces to anus and defacation © 2016 Pearson Education, Inc. Digestive Processes in the Large Intestine (cont.) Motility of the large intestine Haustral contractions: most contractions of colon, where haustra sequentially contract in response to distension Slow segmenting movements, mostly in ascending and transverse colon Gastrocolic reflex: initiated by presence of food in stomach Results in mass movements: slow, powerful peristaltic waves that are activated three to four times per day typically during or just after eating Descending colon and sigmoid colon act as storage reservoir Feces dries out © 2016 Pearson Education, Inc. Digestive Processes in the Large Intestine (cont.) Defecation Mass movements force feces toward rectum Distension initiates spinal defecation reflex Parasympathetic signals Stimulate contraction of sigmoid colon and rectum Relax internal anal sphincter Conscious control allows relaxation of external anal sphincter © 2016 Pearson Education, Inc. Digestive Processes in the Large Intestine (cont.) Defecation (cont.) Muscles of rectum contract to expel feces Assisted by Valsalva’s maneuver Closing of glottis, contraction of diaphragm and abdominal wall muscles cause increased intra-abdominal pressure Levator ani muscle contracts, causing anal canal to be lifted superiorly and allowing feces to leave body © 2016 Pearson Education, Inc. Part 3 – Physiology of Digestion and Absorption 23.10 Mechanisms of Digestion and Absorption Digestion breaks down ingested foods into their chemical building blocks Only these molecules are small enough to be absorbed across wall of small intestine Summary: Absorption and Elimination | Digestive Anatomy (visiblebody.com) © 2016 Pearson Education, Inc. Mechanism of Digestion & Absorption Digestion: catabolic process that breaks macromolecules down into monomers small enough for absorption Enzymes carry out hydrolysis, whereby water is added to break chemical bonds Absorption is process of moving substances from lumen of gut into body Most nutrients are absorbed before chyme reaches ileum © 2016 Pearson Education, Inc. Processing of Nutrients Digestion of Carbohydrates Only monosaccharides can be absorbed Starch digestion begins in mouth with salivary amylase Further broken down into lactose, maltose, and sucrose Final breakdown into monosaccarides (glucose, fructose, galactose) © 2016 Pearson Education, Inc. Processing of Nutrients Steps of starch digestion in intestine 1. 2. 3. Pancreatic amylase breaks down starch or glycogen that escaped salivary amylase Brush border enzymes lactase, maltase, & sucrase further break these into lactose, maltose, & sucrose; then further broken into monosaccharides (glucose, fructose, galactose) Monosaccharides use active transport with Na+ and /or facilitated diffusion for absorption Digestion of Proteins Source of protein not only is dietary, but also includes digestive enzymes and proteins from breakdown of mucosal cells Proteins are broken into amino acids Large polypeptides small polypeptides and small peptides Then amino acid monomers Digestion begins in stomach when pepsinogen is converted to pepsin © 2016 Pearson Education, Inc. Digestion of Proteins Steps in protein digestion 1. 2. 3. Pancreatic proteases trypsin and chymotrypsin break down protein into smaller peptides Brush border enzymes break dipeptides into amino acids Amino acids are absorbed via active transport carriers (Na+ or H+) and /or facilitated diffusion Digestion of Lipids Fats need pre-treatment with bile salts that break large fat globules into smaller ones Need a fatty element, Micelle to aid digestion Without the Micelle the fats would float on top of chyme and not be absorbed Short chain fatty acids can diffuse directly into blood © 2016 Pearson Education, Inc. Digestion of Nucleic Acids Nuclei of ingested cells in food contain DNA and RNA Pancreatic nucleases breakdown nucleic acid to nucleotide monomers Further broken down into free nitrogenous bases, pentose sugars, and phosphate ions Breakdown products are actively transported by special carriers in epithelium of villi © 2016 Pearson Education, Inc. Absorption of Vitamins, Electrolytes, and Water Vitamin absorption In small intestine Fat-soluble vitamins (A, D, E, and K) are absorbed by diffusion Water-soluble vitamins (C and B) are absorbed by passive or active transport Vitamin B12 (large, charged molecule) binds with intrinsic factor and is absorbed In large intestine: vitamin K and B vitamins from bacterial metabolism are absorbed © 2016 Pearson Education, Inc. Absorption of Vitamins, Electrolytes, and Water (cont.) Absorption of electrolytes Iron and calcium are absorbed in duodenum Iron and calcium absorption is related to need Ionic iron is stored in mucosal cells with ferritin When needed, transported in blood by transferrin Ca2+ absorption is regulated by vitamin D and parathyroid hormone (PTH) © 2016 Pearson Education, Inc. Absorption of Vitamins, Electrolytes, and Water (cont.) Absorption of water 9 L water, most from GI tract secretions, enter small intestine 95% is absorbed in the small intestine by osmosis Most of rest is absorbed in large intestine © 2016 Pearson Education, Inc. Part 1 – Nutrients Most nutrients are used as fuel for cellular activity, but some are for cell structures and molecular synthesis Nutrient: substance in food needed for growth, maintenance, repair Macronutrients: three major nutrients that make up the bulk of ingested food Carbohydrates, lipids, and proteins © 2016 Pearson Education, Inc. Part 1 – Nutrients Micronutrients: two other nutrients that are required, but only in small amounts Vitamins and minerals Water is required, so technically it is a nutrient Essential nutrients: nutrients that must be eaten because body cannot synthesize these from other nutrients 45–50 nutrients are considered essential © 2016 Pearson Education, Inc. Part 1 – Nutrients Nonessential nutrients are also vital to life, but if not enough is available, liver can usually convert another nutrient into one needed Energy value of foods is measured in kilocalories (kcal) © 2016 Pearson Education, Inc. 24.1 Role of Carbohydrates, Lipids, and Proteins * review table 24-1, p. 930 Carbohydrates Dietary sources: starch & sugar Primarily from plants, such as starch (complex carbohydrates) in grains and vegetables Sugars (mono- and disaccharides) in fruits, sugarcane, sugar beets, honey, and milk Insoluble fiber: cellulose in vegetables provides roughage Soluble fiber: pectin in apples and citrus fruits reduces blood cholesterol levels Small amount in milk sugar, glycogen in meats Recommended adult intake: 45-65 % of daily calorie intake © 2016 Pearson Education, Inc. Carbohydrates (cont.) Uses in body Glucose: fuel most used by cells to make ATP Small amounts used for nucleic acid synthesis © 2016 Pearson Education, Inc. Carbohydrates (cont.) Dietary requirements Should consist mostly of complex carbohydrates (whole grains and vegetables) Simple carbohydrates should be limited High amounts of sugars can lead to obesity, as well as nutritional deficiencies © 2016 Pearson Education, Inc. Lipids Dietary sources Triglycerides (neutral fats): most abundant form Found in saturated fats in meat, dairy foods, tropical oils, or hydrogenated oils (trans fats) Unsaturated fats found in seeds, nuts, olive oil, and most vegetable oils Cholesterol found in egg yolk, meats, organ meats, shellfish, and milk products Liver makes ~85% cholesterol Liver can convert some fatty acids into others, but essential fatty acids (examples: linoleic and linolenic acid found in most oils) must be eaten © 2016 Pearson Education, Inc. Lipids (cont.) Uses in body Adipose tissue offers protection, insulation, fuel storage Phospholipids are used in myelin sheaths and all cell membranes Cholesterol stabilizes membranes; precursor of bile salts, steroid hormones, and basis of Vit D Prostaglandins → smooth muscle contraction, BP control, inflammation © 2016 Pearson Education, Inc. Lipids (cont.) Dietary requirements Unsaturated fats: 2-3 TBSP a day Saturated fats: limit saturated fats Cholesterol: no more than 300 mg/day (about 1-1/2 egg yolks) Goal is to keep total cholesterol < 5.2 20-35% of calorie intake © 2016 Pearson Education, Inc. Proteins Dietary sources Animal products (eggs, milk, fish, most meats), as well as soybeans, are considered complete proteins Contain all needed essential amino acids Legumes, nuts, and cereals contain incomplete proteins (lack some essential amino acids) Legumes and cereal grains together contain all essential amino acids © 2016 Pearson Education, Inc. Proteins (cont.) Uses in body Structural materials Example: keratin (skin), collagen and elastin (connective tissue), and muscle proteins Functional molecules Example: enzymes and some hormones Three factors help determine whether amino acids are used to synthesize proteins or burned as energy: 1. All-or-none rule All amino acids needed must be present for protein synthesis to occur; if not all are present, then amino acids are used for energy © 2016 Pearson Education, Inc. Proteins (cont.) Uses in body (cont.) 2. Adequacy of caloric intake Protein is used as fuel if insufficient carbohydrate or fat is available 3. Hormonal controls Anabolic hormones (GH, sex hormones) accelerate protein synthesis and growth Adrenal glucocorticoids (released during stress) promote protein breakdown and conversion of amino acids to glucose © 2016 Pearson Education, Inc. Proteins (cont.) Uses in body (cont.) Nitrogen balance Homeostatic state where rate of protein synthesis equals rate of breakdown and loss Positive nitrogen balance: protein synthesis exceeds breakdown (normal in children, pregnant women, tissue repair) Negative nitrogen balance: protein breakdown exceeds synthesis (example: stress, burns, infection, injury, poor dietary proteins, starvation) © 2016 Pearson Education, Inc. Proteins (cont.) Dietary requirements Needs reflect age, size, metabolic rate, nitrogen balance Rule of thumb: daily intake of 0.8 g per kg body weight (those over 19 yrs old) © 2016 Pearson Education, Inc. Role of Vitamins and Minerals Vitamins Organic compounds that are crucial in helping body use nutrients Most function as coenzymes Most must be ingested, except: Vitamin D (made in skin) Some B and K synthesized by intestinal bacteria Beta-carotene (e.g., from carrots) converted in body to vitamin A No one food group contains all vitamins Richest sources are whole grains, vegs, legumes and fruit © 2016 Pearson Education, Inc. Vitamins (cont.) Two types of vitamins based on solubility: Water-soluble vitamins B complex and C are absorbed with water B12 absorption requires intrinsic factor Not stored in the body Any not used within 1 hour are excreted Fat-soluble vitamins A, D, E, and K are absorbed with lipid digestion products Stored in body, except for vitamin K Excessive consumption can cause health problems © 2016 Pearson Education, Inc. Vitamins (cont.) Dangerous free radicals are generated during normal metabolism Vitamins C, E, and A and mineral selenium are antioxidants that neutralize these free radicals Broccoli, cauliflower, brussel sprouts are all good sources of vitamins A and C Mega doses of vitamins are useless and may actually cause serious health problems, depending on vitamin involved © 2016 Pearson Education, Inc. Minerals Seven minerals are required in moderate amounts: Calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium Others are required in trace amounts Not used for energy Work with nutrients to ensure proper body functioning Uptake and excretion are balanced to prevent toxic overload Richest sources are: meats, vegs, nuts and legumes © 2016 Pearson Education, Inc. Minerals (cont.) Examples of uses in body Calcium, phosphorus, and magnesium salts harden bone Iron is essential for oxygen binding to hemoglobin Iodine is necessary for thyroid hormone synthesis Sodium and chloride are major electrolytes in blood © 2016 Pearson Education, Inc. Part 2: Metabolism Metabolism: sum of all chemical reactions to sustain life Anabolism and Catabolism Anabolism: synthesis of large molecules from small ones (example: synthesis of proteins from amino acids) Catabolism: hydrolysis of complex structures to simpler ones (example: breakdown of proteins into amino acids) © 2016 Pearson Education, Inc. Carbohydrate Metabolism Carbohydrate metabolism is essentially glucose metabolism All food carbohydrates are transformed to glucose Glucose then transformed to CO2 and water in a variety of processes When cellular energy is high, glucose breakdown is inhibited Glucose is converted to glycogen (glycogenesis) OR to fat (Lipogenesis) When blood glucose levels fall, glycogenolysis occurs so the glucose stores can be converted into glucose The liver can form glucose from non-carbohydrate sources, fat or protein (gluconeogenesis) © 2016 Pearson Education, Inc. Lipid Metabolism Lipids provide a greater energy yield than glucose or protein catabolism Most products of fat digestion are transported in lymph as chylomicrons Broken down by into fatty acids and glycerol © 2016 Pearson Education, Inc. Lipogenesis Lipogenesis: triglyceride synthesis that occurs when cellular ATP and glucose levels are high Dietary glycerol and fatty acids not needed for energy are stored as triglycerides 50% is stored in adipose tissue; other 50% is deposited in other areas Glucose is easily converted to fat © 2016 Pearson Education, Inc. Lipolysis (cont.) Lipolysis: breakdown of stored fats into glycerol and fatty acids; reverse of lipogenesis Fatty acids are actually preferred by liver, cardiac muscle, resting skeletal muscle for fuel Lipolysis is accelerated when carbohydrate intake is inadequate When there are excessive fats used for energy, the livers produces ketone bodies and releases to blood Excessive ketone bodies will lead to metabolic acidosis © 2016 Pearson Education, Inc. Protein Metabolism Proteins deteriorate, so they need to be continually broken down and replaced Amino acids are recycled into new proteins or different compounds Proteins are not stored in body When dietary proteins are in excess, amino acids are: Oxidized for energy or Converted to fat for storage © 2016 Pearson Education, Inc. Protein Synthesis Amino acids are most important anabolic nutrients Form all proteins as well as bulk of functional molecules Protein synthesis that occurs on ribosomes is hormonally controlled (example: growth hormone, thyroid hormone, sex hormones) Synthesis requires complete set of amino acids Essential amino acids must be acquired in diet During our lifetime, depending on body size, we can synthesize 225– 450 kg (500–1000 lbs) of protein © 2016 Pearson Education, Inc. Basal Metabolic Rate (BMR) Thyroxine is major hormone to control BMR Reflects energy body needs to perform its most essential activities at rest Measured after a 12-hour fast, reclining position, relaxed mentally and physically, room temperature 20–25C Recorded as kilocalories per square meter of body surface per hour (kcal/m2/h) Example: 70 kg adult BMR = 66 kcal/h © 2016 Pearson Education, Inc. Basal Metabolic Rate (BMR) (cont.) BMR is influenced by: Age and gender: BMR decreases with age Males have disproportionately higher BMR Body temperature: BMR increases with temperature Stress: BMR increases with stress Thyroxine: increases oxygen consumption, cellular respiration, and BMR © 2016 Pearson Education, Inc. 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