THE DIGESTIVE SYSTEM Chapter 24 An Introduction to

THE DIGESTIVE SYSTEM Chapter 24 An Introduction to

THE DIGESTIVE SYSTEM Chapter 24 An Introduction to the Digestive System Learning Outcomes 24-1 Identify the organs of the digestive system, list their major functions, describe the histology of the digestive tract, and outline the mechanisms that regulate digestion. 24-2 Discuss the anatomy of the oral cavity, and list the functions of its major structures and regions. 24-3 Describe the structure and functions of the pharynx. 24-4 Describe the structure and functions of the esophagus.

24-5 Describe the anatomy of the stomach, including its histological features, and discuss its roles in digestion and absorption. 2015 Pearson Education, Inc. An Introduction to the Digestive System Learning Outcomes 24-6 Describe the anatomical and histological characteristics of the small intestine, explain the functions and regulation of intestinal secretions, and describe the structure, functions, and regulation of the accessory digestive organs. 24-7 Describe the gross and histological structure of the large intestine, including its regional specializations and role in nutrient absorption.

24-8 List the nutrients required by the body, describe the chemical events responsible for the digestion of organic nutrients, and describe the mechanisms involved in the absorption of organic and inorganic nutrients. 24-9 Summarize the effects of aging on the digestive system. 24-10 Give examples of interactions between the digestive system and other organ systems studied so far. 2015 Pearson Education, Inc. An Introduction to the Digestive System The Digestive System Acquires nutrients from environment Anabolism Uses raw materials to synthesize essential compounds

Catabolism Decomposes to function 2015 Pearson Education, Inc. substances to provide energy cells need An Introduction to the Digestive System Catabolic Reactions Require two essential ingredients 1. 2. Oxygen Organic molecules broken down by intracellular enzymes 2015 Pearson Education, Inc.

For example, carbohydrates, fats, and proteins 24-1 The Digestive Tract The Digestive Tract Also called gastrointestinal (GI) tract or alimentary canal Is a muscular tube Extends from oral cavity to anus Passes through pharynx, esophagus, stomach, and small and large intestines 2015 Pearson Education, Inc. FIGURE 24-1 THE COMPONENTS OF THE DIGESTIVE SYSTEM (PART 1 OF 2). Major Organs of the Digestive Tract

Oral Cavity (Mouth) Ingestion, mechanical processing with accessory organs (teeth and tongue), moistening, mixing with salivary secretions Pharynx Muscular propulsion of materials into the esophagus Esophagus Transport of materials to the stomach Stomach Chemical breakdown of materials by acid and enzymes; mechanical processing through muscular contractions Small Intestine Enzymatic digestion and absorption of water, organic substrates, vitamins, and ions Large Intestine Dehydration and compaction of indigestible materials in preparation for elimination Anus

FIGURE 24-1 THE COMPONENTS OF THE DIGESTIVE SYSTEM (PART 2 OF 2). Accessory Organs of the Digestive System Teeth Mechanical processing by chewing (mastication) Tongue Assists mechanical processing with teeth, sensory analysis Salivary Glands Secretion of lubricating fluid containing enzymes that break down carbohydrates Liver Secretion of bile (important for lipid digestion), storage of nutrients, many other vital functions Gallbladder Storage and concentration of

bile Pancreas Exocrine cells secrete buffers and digestive enzymes; Endocrine cells secrete hormones 24-1 The Digestive Tract Six Functions of the Digestive System 1. 2. 3. 4. 5. 6. Ingestion Mechanical processing Digestion Secretion Absorption Excretion

2015 Pearson Education, Inc. 24-1 The Digestive Tract Ingestion Mechanical Processing Crushing and shearing Makes materials easier to propel along digestive tract Digestion Occurs when materials enter digestive tract via the mouth

The chemical breakdown of food into small organic fragments for absorption by digestive epithelium Secretion Is the release of water, acids, enzymes, buffers, and salts By epithelium of digestive tract By glandular organs 2015 Pearson Education, Inc. 24-1 The Digestive Tract Absorption Movement of organic substrates, electrolytes, vitamins, and water

Across digestive epithelium Into interstitial fluid of digestive tract Excretion Removal of waste products from body fluids Process called defecation removes feces 2015 Pearson Education, Inc. 24-1 The Digestive Tract The Lining of the Digestive Tract Safeguards surrounding tissues against: 1. 2. 3. 2015 Pearson Education, Inc. Corrosive effects of digestive acids and enzymes

Mechanical stresses, such as abrasion Bacteria either ingested with food or that reside in digestive tract 24-1 The Digestive Tract The Digestive Organs and the Peritoneum Lined with serous membrane consisting of: Superficial mesothelium covering a layer of areolar tissue Serosa, or visceral peritoneum Covers organs within peritoneal cavity Parietal 2015 Pearson Education, Inc.

peritoneum Lines inner surfaces of body wall 24-1 The Digestive Tract Peritoneal Fluid Is produced by serous membrane lining Provides essential lubrication Separates parietal and visceral surfaces Allows sliding without friction or irritation About 7 liters produced and absorbed daily, but very little in peritoneal cavity at one time Ascites swelling 2015 Pearson Education, Inc.

excess peritoneal fluid causing abdominal 24-1 The Digestive Tract Mesenteries Are double sheets of peritoneal membrane Suspend portions of digestive tract within peritoneal cavity by sheets of serous membrane That connect parietal peritoneum With visceral peritoneum Areolar tissue between mesothelial surfaces Provides an access route to and from the digestive tract For passage of blood vessels, nerves, and lymphatic vessels

Stabilize positions of attached organs Prevent intestines from becoming entangled 2015 Pearson Education, Inc. 24-1 The Digestive Tract Mesentery Development During embryonic development Digestive tract and accessory organs are suspended in peritoneal cavity by: 2015 Pearson Education, Inc. Dorsal mesentery Ventral mesentery Later disappears along most of digestive tract except at the lesser omentum and at the falciform ligament

FIGURE 24-2A MESENTERIES. Neural tube Notochord Mesoderm Coelomic cavity Dorsal mesentery Peritoneal cavity Developing liver Ventral mesentery Digestive tract Visceral peritoneum Digestive tract 4 weeks Parietal

peritoneum 5 weeks a During embryonic development, the digestive tube is initially suspended by dorsal and ventral mesenteries. In adults, the ventral mesentery is lost, except where it connects the stomach to the liver (at the lesser omentum) and the liver to the anterior body wall and diaphragm (at the falciform ligament). 24-1 The Digestive Tract The Lesser Omentum Stabilizes position of stomach Provides access route for blood vessels and other structures entering or leaving liver The Falciform Ligament

Helps stabilize position of liver Relative 2015 Pearson Education, Inc. to diaphragm and abdominal wall 24-1 The Digestive Tract The Dorsal Mesentery Enlarges to form an enormous pouch, called the greater omentum Extends inferiorly between: The body wall and the anterior surface of small intestine Hangs like an apron From lateral and inferior borders of stomach Adipose Tissue in Greater Omentum

Conforms to shapes of surrounding organs Pads and protects surfaces of abdomen Provides insulation to reduce heat loss Stores lipid energy reserves 2015 Pearson Education, Inc. 24-1 The Digestive Tract The Mesentery Proper Is a thick mesenterial sheet Provides stability

Permits some independent movement Suspends all but first 25 cm (10 in.) of small intestine Is associated with initial portion of small intestine (duodenum) and pancreas Fuses with posterior abdominal wall, locking structures in position 2015 Pearson Education, Inc. 24-1 The Digestive Tract The Mesocolon A mesentery associated with a portion of the large intestine Transverse mesocolon supports transverse colon Sigmoid mesocolon supports sigmoid colon During development, mesocolon of ascending colon, descending colon, and the rectum:

Fuse to dorsal body wall Lock regions in place 2015 Pearson Education, Inc. FIGURE 24-2B MESENTERIES. Transverse mesocolon Lesser omentum Transverse colon Ascending colon Mesentery proper (mesenterial sheet) Greater omentum (cut) Mesocolon of ascending and

descending colons fused to posterior portion of the parietal peritoneum Descending colon Small intestine Sigmoid colon b A diagrammatic view of the organization of mesenteries in an adult. As the digestive tract enlarges, mesenteries associated with the proximal portion of the small intestine, the pancreas, and the ascending and descending portions of the colon fuse to the body wall. FIGURE 24-2D MESENTERIES. Falciform ligament Diaphragm Lesser omentum

Liver Stomach Pancreas Transverse mesocolon Duodenum Mesentery proper Transverse colon Sigmoid mesocolon Rectum Urinary bladder Greater omentum Parietal peritoneum

Small intestine Uterus d A sagittal section showing the mesenteries of an adult. Notice that the pancreas, duodenum, and rectum are retroperitoneal. 24-1 The Digestive Tract Histological Organization of the Digestive Tract Four major layers of the digestive tract 1. 2. 3. 4. 2015 Pearson Education, Inc. Mucosa Submucosa Muscularis externa

Serosa 24-1 The Digestive Tract The Mucosa Is the inner lining of digestive tract Is a mucous membrane consisting of: Epithelium, moistened by glandular secretions Lamina propria of areolar tissue Mucosal epithelium is simple or stratified Depending 2015 Pearson Education, Inc. on location, function, and stresses 24-1 The Digestive Tract

The Digestive Epithelium Oral cavity, pharynx, and esophagus Mechanical stresses Lined by stratified squamous epithelium Stomach, small intestine, and most of large intestine Absorption Simple columnar epithelium with mucous cells Enteroendocrine cells Are scattered among columnar cells of digestive epithelium Secrete hormones that:

2015 Pearson Education, Inc. Coordinate activities of the digestive tract and accessory glands 24-1 The Digestive Tract Lining of Digestive Tract Folding increases surface area for absorption Longitudinal folds, disappear as digestive tract fills Permanent transverse folds (plicae circulares) 2015 Pearson Education, Inc. 24-1 The Digestive Tract The Lamina Propria Consists of a layer of areolar tissue that contains: Blood

vessels Sensory nerve endings Lymphatic vessels Smooth muscle cells Scattered areas of lymphatic tissue Muscularis mucosae Narrow band of smooth muscle and elastic fibers in lamina propria Smooth muscle cells arranged in two concentric layers 2015 Pearson Education, Inc. Inner layer encircles lumen (circular muscle) Outer layer contains muscle cells parallel to tract (longitudinal layer) 24-1 The Digestive Tract The Submucosa

Is a layer of dense irregular connective tissue Surrounds muscularis mucosae Has large blood vessels and lymphatic vessels May contain exocrine glands Secrete 2015 Pearson Education, Inc. buffers and enzymes into digestive tract 24-1 The Digestive Tract Submucosal Plexus Also called Meissners plexus Innervates the mucosa and submucosa Contains:

Sensory neurons Parasympathetic ganglionic neurons Sympathetic postganglionic fibers 2015 Pearson Education, Inc. 24-1 The Digestive Tract The Muscularis Externa Is dominated by smooth muscle cells Are arranged in: Inner circular layer Outer longitudinal layer

2015 Pearson Education, Inc. Involved in: Mechanical processing Movement of materials along digestive tract Movements coordinated by enteric nervous system (ENS) Sensory neurons Interneurons Motor neurons 24-1 The Digestive Tract

The Muscularis Externa ENS Innervated primarily by parasympathetic division of ANS Sympathetic postganglionic fibers The mucosa The myenteric plexus (Auerbachs plexus) The Serosa Serous membrane covering muscularis externa Except 2015 Pearson Education, Inc.

in oral cavity, pharynx, esophagus, and rectum Where adventitia, a dense sheath of collagen fibers, firmly attaches the digestive tract to adjacent structures 24-1 The Digestive Tract The Movement of Digestive Materials By muscular layers of digestive tract Consist of visceral smooth muscle tissue Along digestive tract Has rhythmic cycles of activity Controlled by pacesetter cells Cells 2015 Pearson Education, Inc.

undergo spontaneous depolarization Triggering wave of contraction through entire muscular sheet 24-1 The Digestive Tract Pacesetter Cells Located in muscularis mucosae and muscularis externa Surrounding lumen of digestive tract Peristalsis Consists of waves of muscular contractions Moves a bolus along the length of the digestive

tract 2015 Pearson Education, Inc. 24-1 The Digestive Tract Peristaltic Motion 1. Circular muscles contract behind bolus While circular muscles ahead of bolus relax 2. Longitudinal muscles ahead of bolus contract Shortening 3. adjacent segments

Wave of contraction in circular muscles Forces 2015 Pearson Education, Inc. bolus forward 24-1 The Digestive Tract Segmentation Cycles of contraction Churn and fragment the bolus Mix contents with intestinal secretions Does not follow a set pattern

Does not push materials in any one direction 2015 Pearson Education, Inc. 24-1 The Digestive Tract Control of Digestive Functions Local Factors Prostaglandins, histamine, and other chemicals released into interstitial fluid affect adjacent cells within small segment of digestive tract Neural Mechanisms

Movement of materials along digestive tract Secretory functions May Coordinate response to changing conditions For example, variations in local pH, chemical, or physical stimuli Affect only a portion of tract 2015 Pearson Education, Inc. Control

Motor neurons Control smooth muscle contraction and glandular secretion Located in myenteric plexus 24-1 The Digestive Tract Neural Mechanisms Short reflexes responsible for local reflexes Control small segments of digestive tract Operate entirely outside of CNS control

Long reflexes Are 2015 Pearson Education, Inc. Sensory neurons Motor neurons Interneurons Higher level control of digestive and glandular activities

Control large-scale peristaltic waves Involve interneurons and motor neurons in CNS May involve parasympathetic motor fibers that synapse in the myenteric plexus Glossopharyngeal, pelvic nerves vagus, or 24-1 The Digestive Tract Hormonal Mechanisms At least 18 peptide hormones that affect: Most aspects of digestive function Activities of other systems

Are produced by enteroendocrine cells in digestive tract Reach target organs after distribution in bloodstream 2015 Pearson Education, Inc. FIGURE 24-5 THE REGULATION OF DIGESTIVE ACTIVITIES. 2 Neural Control Mechanisms The movement of materials along the digestive tract, as well as many secretory functions, is primarily controlled by local factors. Short reflexes are triggered CNS by chemoreceptors or stretch receptors in the walls of the digestive tract; the Long controlling neurons are located in the myenteric plexus. These reflexes are reflex often called myenteric reflexes. Long reflexes involving interneurons and motor neurons in the CNS provide a higher Myenteric level of control over digestive and glandular activities, generally

plexus controlling large-scale peristalsis that moves materials from one region of the Short digestive tract to another. Long reflexes reflex Peristalsis and may involve parasympathetic motor fibers segmentation Stretch receptors, in the glossopharyngeal (N IX), vagus movements chemoreceptors (N X), or pelvic nerves that synapse in the myenteric plexus. Buffers, acids, enzymes released 1 Secretory cells 3

Hormonal Control Mechanisms Local Factors Local factors are the primary stimulus for digestion. They coordinate the responses to changes in the pH of the contents of the lumen, physical distortion of the wall of the digestive tract, or the presence of chemicals either specific nutrients or chemical messengers released by cells of the mucosa. Enteroendocrine cells Hormones released Carried by bloodstream The digestive tract produces at least 18 hormones that affect almost every aspect of digestion, and some of them

also affect the activities of other systems. These hormones are peptides produced by enteroendocrine cells, endocrine cells in the epithelium of the digestive tract. We will consider these hormones as we proceed down the length of the digestive tract. 24-2 The Oral Cavity Functions of the Oral Cavity 1. Sensory analysis Of 2. material before swallowing Mechanical processing Through

actions of teeth, tongue, and palatal surfaces 3. Lubrication Mixing 4. with mucus and salivary gland secretions Limited digestion Of 2015 Pearson Education, Inc. carbohydrates and lipids 24-2 The Oral Cavity Oral Mucosa

Lining of oral cavity Has stratified squamous epithelium Of cheeks, lips, and inferior surface of tongue Is relatively thin, nonkeratinized, and delicate Inferior to tongue is thin and vascular enough to rapidly absorb lipid-soluble drugs Cheeks are supported by pads of fat and the buccinator muscles 2015 Pearson Education, Inc. 24-2 The Oral Cavity Labia

Also called lips Anteriorly, the mucosa of each cheek is continuous with that of the lips Vestibule Space between the cheeks (or lips) and the teeth 2015 Pearson Education, Inc. 24-2 The Oral Cavity Gingivae (Gums) Ridges of oral mucosa Surround base of each tooth on alveolar processes of maxillary bones and mandible 2015 Pearson Education, Inc.

FIGURE 24-6A THE ORAL CAVITY. Hard palate Palatoglossal arch Soft palate Nasal cavity Pharyngeal tonsil Opening of parotid duct Entrance to auditory tube Upper lip Nasopharynx Uvula Cheek Dorsum of tongue Lower lip

Palatine tonsil Fauces Palatopharyngeal arch Oropharynx Gingiva Vestibule Body of tongue Lingual tonsil Epiglottis Root of tongue Hyoid bone Laryngopharynx a A sagittal section of the oral cavity FIGURE 24-6B THE ORAL CAVITY. Hard palate Soft palate

Fauces Uvula Palatoglossal arch Palatopharyngeal arch Palatine tonsil Lingual frenulum Gingiva Vestibule Frenulum of lower lip Openings of submandibular ducts b An anterior view of the oral cavity 24-2 The Oral Cavity The Tongue

Manipulates materials inside mouth Functions of the tongue 1. 2. 3. 4. 2015 Pearson Education, Inc. Mechanical processing by compression, abrasion, and distortion Manipulation to assist in chewing and to prepare material for swallowing Sensory analysis by touch, temperature, and taste receptors Secretion of mucins and the enzyme lingual lipase 24-2 The Oral Cavity Salivary Glands

Three pairs secrete into oral cavity 1. 2. 3. Parotid salivary glands Sublingual salivary glands Submandibular salivary glands Each pair has distinctive cellular organization And produces saliva with different properties 2015 Pearson Education, Inc. 24-2 The Oral Cavity

Parotid Salivary Glands Inferior to zygomatic arch Produce serous secretion Enzyme salivary amylase (breaks down starches) Drained by parotid duct Which 2015 Pearson Education, Inc. empties into vestibule at second molar 24-2 The Oral Cavity Sublingual Salivary Glands

Covered by mucous membrane of floor of mouth Produce mucous secretion Acts as a buffer and lubricant Sublingual ducts Either 2015 Pearson Education, Inc. side of lingual frenulum 24-2 The Oral Cavity Submandibular Salivary Glands

In floor of mouth Within mandibular groove Secrete buffers, glycoproteins (mucins), and salivary amylase Submandibular ducts Open immediately posterior to teeth Either side of lingual frenulum 2015 Pearson Education, Inc. 24-2 The Oral Cavity Saliva Glands produce 1.01.5 liters of saliva each day 70 percent by submandibular glands

25 percent by parotids 5 percent by sublingual glands 2015 Pearson Education, Inc. Saliva 99.4 percent water 0.6 percent includes: Electrolytes (Na+, Cl, and HCO3) Buffers Glycoproteins (mucins) Antibodies Enzymes Waste products 24-2 The Oral Cavity

Functions of Saliva Lubricating the mouth Moistening and lubricating materials in the mouth Dissolving chemicals that stimulate taste buds and provide sensory information Initiating digestion of complex carbohydrates by the enzyme salivary amylase (ptyalin or alphaamylase) 2015 Pearson Education, Inc. 24-2 The Oral Cavity Control of Salivary Secretions By autonomic nervous system Parasympathetic

and sympathetic innervation Parasympathetic accelerates secretion by all salivary glands Salivatory nuclei of medulla oblongata influenced by: Other brain stem nuclei Activities of higher centers 2015 Pearson Education, Inc. 24-2 The Oral Cavity The Teeth

Tongue movements pass food across occlusal surfaces of teeth Chew (masticate) food 2015 Pearson Education, Inc. 24-2 The Oral Cavity Dentin A mineralized matrix similar to that of bone Does not contain cells Pulp Cavity Receives blood vessels and nerves through the root canal

2015 Pearson Education, Inc. 24-2 The Oral Cavity Root Of each tooth sits in a bony socket (alveolus) A layer of cementum covers dentin of the root Providing protection and anchoring periodontal ligament Crown Exposed portion of tooth Projects beyond soft tissue of gingiva

Dentin covered by layer of enamel 2015 Pearson Education, Inc. 24-2 The Oral Cavity Alveolar Processes Of the maxillae Form maxillary arcade (upper dental arch) Of the mandible Form 2015 Pearson Education, Inc. mandibular arcade (lower dental arch) 24-2 The Oral Cavity

Types of Teeth 1. 2. 3. 4. Incisors Cuspids (canines) Bicuspids (premolars) Molars 2015 Pearson Education, Inc. 24-2 The Oral Cavity Incisors Blade-shaped teeth

Located at front of mouth Used for clipping or cutting Have a single root 2015 Pearson Education, Inc. 24-2 The Oral Cavity Cuspids (Canines) Conical Sharp ridgeline Pointed tip Used for tearing or slashing Have a single root 2015 Pearson Education, Inc. 24-2 The Oral Cavity

Bicuspids (Premolars) Flattened crowns Prominent ridges Used to crush, mash, and grind Have one or two roots 2015 Pearson Education, Inc. 24-2 The Oral Cavity Molars Very large, flat crowns With prominent ridges Used for crushing and grinding

Have three or more roots 2015 Pearson Education, Inc. 24-2 The Oral Cavity Dental Succession During embryonic development, two sets of teeth form Primary dentition, or deciduous teeth Secondary dentition, or permanent dentition 2015 Pearson Education, Inc. 24-2 The Oral Cavity Deciduous Teeth

Also called primary teeth, milk teeth, or baby teeth 20 temporary teeth of primary dentition Five on each side of upper and lower jaws 2 incisors 1 cuspid 2 deciduous molars 2015 Pearson Education, Inc. 24-2 The Oral Cavity Secondary Dentition

Also called permanent dentition Replaces deciduous teeth 32 permanent teeth Eight on each side, upper and lower 2 incisors 1 cuspid 5 molars 2015 Pearson Education, Inc. 24-2 The Oral Cavity Mastication Also called chewing Food is forced from oral cavity to vestibule and back

Crossing 2015 Pearson Education, Inc. and recrossing occlusal surfaces 24-2 The Oral Cavity Muscles of Mastication Close the jaws Slide or rock lower jaw from side to side Chewing involves mandibular: Elevation and depression Protraction and retraction Medial and lateral movement 2015 Pearson Education, Inc. 24-3 The Pharynx

The Pharynx (Throat) A common passageway for solid food, liquids, and air Regions of the pharynx: Nasopharynx Oropharynx Laryngopharynx Food passes through the oropharynx and laryngopharynx to the esophagus 2015 Pearson Education, Inc. 24-4 The Esophagus The Esophagus

A hollow muscular tube About 25 cm (10 in.) long and 2 cm (0.80 in.) wide Conveys solid food and liquids to the stomach Begins posterior to cricoid cartilage Enters abdominopelvic cavity through the esophageal hiatus Is innervated by fibers from the esophageal plexus 2015 Pearson Education, Inc. 24-4 The Esophagus Resting Muscle Tone

In the circular muscle layer in the superior 3 cm (1.2 in.) of esophagus prevents air from entering Histology of the Esophagus Wall of esophagus has three layers 1. 2. 3. 2015 Pearson Education, Inc. Mucosal Submucosal Muscularis 24-4 The Esophagus Histology of the Esophagus Mucosa contains: Nonkeratinized

Mucosa and submucosa form: Large and stratified squamous epithelium folds that extend the length of the esophagus Muscularis mucosae consists of: Irregular 2015 Pearson Education, Inc. layer of smooth muscle 24-4 The Esophagus Histology of the Esophagus Submucosa contains

esophageal glands Which produce mucous secretion Reduces friction between bolus and esophageal lining Muscularis externa has: Usual inner circular and outer longitudinal layers 2015 Pearson Education, Inc. 24-4 The Esophagus Swallowing

Also called deglutition Can be initiated voluntarily Proceeds automatically Is divided into three phases 1. 2. 3. Buccal phase Pharyngeal phase Esophageal phase 2015 Pearson Education, Inc. 24-5 The Stomach Major Functions of the Stomach 1. 2. 3. 4.

Storage of ingested food Mechanical breakdown of ingested food Disruption of chemical bonds in food material by acid and enzymes Production of intrinsic factor, a glycoprotein required for absorption of vitamin B12 in small intestine 2015 Pearson Education, Inc. 24-5 The Stomach Anatomy of the Stomach The stomach is shaped like an expanded J Short lesser curvature forms medial surface Long greater curvature forms lateral surface

Anterior and posterior surfaces are smoothly rounded Shape and size vary from individual to individual and from one meal to the next Stomach typically extends between levels of vertebrae T7 and L3 2015 Pearson Education, Inc. 24-5 The Stomach Regions of the Stomach 1. 2. 3. 4. Cardia Fundus Body Pylorus

2015 Pearson Education, Inc. 24-5 The Stomach Smooth Muscle Muscularis mucosae and muscularis externa Contain extra layers of smooth muscle cells Oblique layer in addition to circular and longitudinal layers 2015 Pearson Education, Inc. 24-5 The Stomach Histology of the Stomach

Simple columnar epithelium lines all portions of stomach Epithelium is a secretory sheet Produces mucus that covers interior surface of stomach Gastric pits, shallow depressions that open onto the gastric surface Mucous cells, at the base, or neck, of each gastric pit, actively divide, replacing superficial cells 2015 Pearson Education, Inc. FIGURE 24-13A THE STOMACH LINING. Layers of the Stomach Wall Mucosa Gastric pit (opening to gastric gland) Mucous epithelium Lamina propria Muscularis mucosae

Submucosa Artery and vein Muscularis externa Oblique muscle Circular muscle Lymphatic vessel Longitudinal muscle Myenteric plexus Serosa a Stomach wall 24-5 The Stomach

Gastric Glands In fundus and body of stomach Extend deep into underlying lamina propria Each gastric pit communicates with several gastric glands Parietal cells Chief cells 2015 Pearson Education, Inc. 24-5 The Stomach Parietal Cells

Secrete intrinsic factor and hydrochloric acid (HCl) Chief Cells Are most abundant near base of gastric gland Secrete pepsinogen (inactive proenzyme) Pepsinogen Is converted by HCl in the gastric lumen To

pepsin (active proteolytic enzyme) 2015 Pearson Education, Inc. 24-5 The Stomach Pyloric Glands Located in the pylorus Produce mucous secretion Scattered 2015 Pearson Education, Inc. with enteroendocrine cells G cells produce gastrin D cells release somatostatin, a hormone that inhibits release of gastrin

24-5 The Stomach Regulation of Gastric Activity Production of acid and enzymes by the gastric mucosa can be: Controlled by the CNS Regulated by short reflexes of ENS Regulated by hormones of digestive tract Three phases of gastric control 1. 2. 3. 2015 Pearson Education, Inc. Cephalic phase Gastric phase Intestinal phase

24-5 The Stomach Digestion and Absorption in the Stomach Stomach performs preliminary digestion of proteins by pepsin Some digestion of carbohydrates (by salivary amylase) Lipids (by lingual lipase) 2015 Pearson Education, Inc. 24-5 The Stomach Digestion and Absorption in the Stomach Stomach contents Become more fluid

pH approaches 2.0 Pepsin activity increases Protein disassembly begins Although digestion occurs in the stomach, nutrients are not absorbed there 2015 Pearson Education, Inc. 24-6 The Small Intestine The Small Intestine Plays key role in digestion and absorption of nutrients 90 percent of nutrient absorption occurs in the small intestine 2015 Pearson Education, Inc.

24-6 The Small Intestine The Duodenum The segment of small intestine closest to stomach 25 cm (10 in.) long Mixing bowl that receives chyme from stomach and digestive secretions from pancreas and liver Functions of the duodenum: To receive chyme from stomach To neutralize acids before they can damage the absorptive surfaces of the small intestine 2015 Pearson Education, Inc. 24-6 The Small Intestine

The Jejunum Is the middle segment of small intestine 2.5 meters (8.2 ft) long Is the location of most: Chemical digestion Nutrient absorption Has few plicae circulares Small villi 2015 Pearson Education, Inc. 24-6 The Small Intestine The Ileum

The final segment of small intestine 3.5 meters (11.48 ft) long Ends at the ileocecal valve A sphincter that controls flow of material from the ileum into the cecum of the large intestine 2015 Pearson Education, Inc. 24-6 The Small Intestine Histology of the Small Intestine Circular folds (plicae circulares) Transverse folds in intestinal lining Are permanent features

Do not disappear when small intestine fills Intestinal villi A series of fingerlike projections in mucosa of small intestine Covered by simple columnar epithelium Covered with microvilli 2015 Pearson Education, Inc. 24-6 The Small Intestine Histology of the Small Intestine

Intestinal glands (Crypts of Lieberkhn) Mucous cells between columnar epithelial cells Eject mucins onto intestinal surfaces Openings from intestinal glands To intestinal lumen at bases of villi Entrances for brush border enzymes 2015 Pearson Education, Inc. 24-6 The Small Intestine Intestinal Glands Brush border enzymes Integral membrane

proteins On surfaces of intestinal microvilli Break down materials in contact with brush border 2015 Pearson Education, Inc. 24-6 The Small Intestine Intestinal Glands Enteropeptidase A brush border enzyme Activates pancreatic proenzyme trypsinogen Enteroendocrine cells Produce intestinal hormones such as gastrin,

cholecystokinin, and secretin 2015 Pearson Education, Inc. 24-6 The Small Intestine Intestinal Glands Duodenal glands Also called submucosal glands or Brunners glands Produce copious quantities of mucus 2015 Pearson Education, Inc. When chyme arrives from stomach 24-6 The Small Intestine Intestinal Secretions

Watery intestinal juice 1.8 liters per day enter intestinal lumen Moisten chyme Assist in buffering acids Keep digestive enzymes and products of digestion in solution 2015 Pearson Education, Inc. 24-6 The Small Intestine Intestinal Movements Chyme arrives in duodenum Weak peristaltic contractions move it slowly toward jejunum Myenteric

reflexes Not under CNS control Parasympathetic stimulation accelerates local peristalsis and segmentation 2015 Pearson Education, Inc. 24-6 The Small Intestine The Gastroenteric Reflex Stimulates motility and secretion Along entire small intestine The Gastroileal Reflex

Triggers relaxation of ileocecal valve Allows materials to pass from small intestine into large intestine 2015 Pearson Education, Inc. 24-6 The Pancreas The Pancreas Lies posterior to stomach From duodenum toward spleen

Is bound to posterior wall of abdominal cavity Is wrapped in thin, connective tissue capsule 2015 Pearson Education, Inc. 24-6 The Pancreas Regions of the Pancreas Head Broad In loop of duodenum Body Slender

Extends toward spleen Tail Short 2015 Pearson Education, Inc. and rounded 24-6 The Pancreas Histological Organization Lobules of the pancreas Are separated by connective tissue partitions (septa) Contain blood vessels and tributaries of pancreatic ducts In each lobule:

2015 Pearson Education, Inc. Ducts branch repeatedly End in blind pockets (pancreatic acini) 24-6 The Pancreas Histological Organization Pancreatic acini Blind pockets Are lined with simple cuboidal epithelium Contain scattered pancreatic islets Pancreatic islets Endocrine

tissues of pancreas Scattered (1 percent of pancreatic cells) 2015 Pearson Education, Inc. FIGURE 24-18B THE PANCREAS. Pancreatic duct Connective tissue septum Exocrine cells in pancreatic acini Endocrine cells in pancreatic islet b Diagram of the cellular organization of the pancreas. 24-6 The Pancreas Functions of the Pancreas

Endocrine cells of the pancreatic islets Secrete insulin and glucagon into bloodstream Exocrine cells Acinar cells and epithelial cells of duct system secrete pancreatic juice 2015 Pearson Education, Inc. 24-6 The Pancreas Physiology of the Pancreas

1000 mL (1 qt) pancreatic juice per day Controlled by hormones from duodenum Contain pancreatic enzymes Pancreatic Enzymes include: Pancreatic alpha-amylase Pancreatic lipase Nucleases Proteolytic enzymes 2015 Pearson Education, Inc. 24-6 The Pancreas Pancreatic Alpha-Amylase A carbohydrase Breaks down starches

Similar to salivary amylase Pancreatic Lipase Breaks down complex lipids Releases products (e.g., fatty acids) that are easily absorbed 2015 Pearson Education, Inc. 24-6 The Pancreas Nucleases Break down nucleic acids Proteolytic Enzymes

Break certain proteins apart Proteases break large protein complexes Peptidases break small peptides into amino acids 70 percent of all pancreatic enzyme production Secreted as inactive proenzymes Activated after reaching small intestine 2015 Pearson Education, Inc. 24-6 The Liver 2015 Pearson Education, Inc. Is the largest visceral organ (1.5 kg; 3.3 lb) Lies in right hypochondriac and epigastric regions Extends to left hypochondriac and umbilical regions Performs essential metabolic and synthetic functions

24-6 The Liver Anatomy of the Liver Wrapped in tough fibrous capsule Covered by visceral peritoneum Divided into lobes 2015 Pearson Education, Inc. 24-6 The Liver Hepatic Blood Supply 1/3 of blood supply

Arterial blood from hepatic artery proper 2/3 venous blood from hepatic portal vein, originating at: Esophagus Stomach Small intestine Most of large intestine 2015 Pearson Education, Inc. 24-6 The Liver Histological Organization of the Liver Liver lobules

The basic functional units of the liver Each lobe is divided by connective tissue About 100,000 liver lobules 1 mm diameter each Hexagonal in cross section With six portal areas (portal triads) One at each corner of lobule 2015 Pearson Education, Inc. 24-6 The Liver

A Portal Area Contains three structures 1. 2. 3. Branch of hepatic portal vein Branch of hepatic artery proper Small branch of bile duct 2015 Pearson Education, Inc. FIGURE 24-20C LIVER HISTOLOGY. Branch of hepatic artery proper Branch of hepatic portal

vein (containing blood) Hepatocytes Sinusoids Bile duct Portal area LM 320 c A sectional view showing the vessels and ducts within a portal area 24-6 The Liver Hepatocytes Adjust circulating levels of nutrients Through

selective absorption and secretion In a liver lobule form a series of irregular plates arranged like wheel spokes Many Kupffer cells (stellate reticuloendothelial cells) are located in sinusoidal lining As blood flows through sinusoids: Hepatocytes absorb solutes from plasma and secrete materials such as plasma proteins 2015 Pearson Education, Inc. 24-6 The Liver The Bile Duct System Liver secretes bile fluid Into

a network of narrow channels (bile canaliculi) Between opposing membranes of adjacent liver cells 2015 Pearson Education, Inc. 24-6 The Liver Right and Left Hepatic Ducts Collect bile from all bile ducts of liver lobes Unite to form common hepatic duct that leaves the liver Bile Flow From common hepatic duct to either: The common bile duct, which empties into duodenal

ampulla The cystic duct, which leads to gallbladder 2015 Pearson Education, Inc. 24-6 The Liver The Common Bile Duct Is formed by union of: Cystic duct Common hepatic duct Passes within the lesser omentum toward stomach Penetrates wall of duodenum

Meets pancreatic duct at duodenal ampulla 2015 Pearson Education, Inc. 24-6 The Liver The Physiology of the Liver 1. 2. 3. Metabolic regulation Hematological regulation Bile production 2015 Pearson Education, Inc. 24-6 The Liver Metabolic Regulation The liver regulates:

1. 2. 3. 4. 5. 2015 Pearson Education, Inc. Composition of circulating blood Nutrient metabolism Waste product removal Nutrient storage Drug inactivation 24-6 The Liver Composition of Circulating Blood All blood leaving absorptive surfaces of digestive tract Enters hepatic portal system Flows into the liver

Liver cells extract nutrients or toxins from blood Before they reach systemic circulation through hepatic veins Liver removes and stores excess nutrients Corrects nutrient deficiencies by mobilizing stored reserves or performing synthetic activities 2015 Pearson Education, Inc. 24-6 The Liver Metabolic Activities of the Liver

Carbohydrate metabolism Lipid metabolism Amino acid metabolism Waste product removal Vitamin storage Mineral storage Drug inactivation 2015 Pearson Education, Inc. 24-6 The Liver Hematological Regulation Largest blood reservoir in the body Receives 25 percent of cardiac output

Functions of Hematological Regulation Phagocytosis and antigen presentation Synthesis of plasma proteins Removal of circulating hormones Removal of antibodies Removal or storage of toxins Synthesis and secretion of bile 2015 Pearson Education, Inc. 24-6 The Liver The Functions of Bile

Dietary lipids are not water soluble Mechanical processing in stomach creates large drops containing lipids Pancreatic lipase is not lipid soluble Interacts only at surface of lipid droplet Bile salts break droplets apart (emulsification) Increases surface area exposed to enzymatic attack Creates tiny emulsion droplets coated with bile salts 2015 Pearson Education, Inc. 24-6 The Gallbladder The Gallbladder

Is a hollow, pear-shaped, muscular sac Stores and concentrates bile prior to excretion into small intestine Is located in the fossa on the posterior surface of the livers right lobe Regions of the Gallbladder 1. 2. 3. Fundus Body Neck 2015 Pearson Education, Inc. 24-6 The Gallbladder The Cystic Duct

Extends from gallbladder Union with common hepatic duct forms common bile duct 2015 Pearson Education, Inc. 24-6 The Gallbladder Physiology of the Gallbladder Stores bile Releases bile into duodenum, but only under stimulation of intestinal hormone cholecystokinin (CCK) CCK Hepatopancreatic sphincter remains closed Bile exiting liver in common hepatic duct cannot flow through common bile duct into duodenum Bile enters cystic duct and is stored in gallbladder

2015 Pearson Education, Inc. 24-6 The Gallbladder Physiology of the Gallbladder Full gallbladder contains 4070 mL bile Bile composition gradually changes in gallbladder Water is absorbed Bile salts and solutes become concentrated 2015 Pearson Education, Inc. 24-6 Coordination of Secretion and Absorption Neural and Hormonal Mechanisms Coordinate activities of digestive glands

Regulatory mechanisms center around duodenum Where 2015 Pearson Education, Inc. acids are neutralized and enzymes added 24-6 Coordination of Secretion and Absorption Neural Mechanisms of the CNS Prepare digestive tract for activity (parasympathetic innervation) Inhibit gastrointestinal activity (sympathetic innervation) Coordinate movement of materials along digestive tract (the enterogastric, gastroenteric,

and gastroileal reflexes) Motor neuron synapses in digestive tract release neurotransmitters 2015 Pearson Education, Inc. 24-6 Coordination of Secretion and Absorption Intestinal Hormones Intestinal tract secretes peptide hormones with multiple effects In several regions of digestive tract In accessory glandular organs 2015 Pearson Education, Inc. 24-6 Coordination of Secretion and Absorption Hormones of Duodenal Enteroendocrine Cells

Coordinate digestive functions Gastrin Secretin Gastric inhibitory peptide (GIP) Cholecystokinin (CCK) Vasoactive intestinal peptide (VIP) Enterocrinin 2015 Pearson Education, Inc. 24-6 Coordination of Secretion and Absorption Gastrin Is secreted by G cells in duodenum When

exposed to incompletely digested proteins Promotes increased stomach motility Stimulates acids and enzyme production Secretin Is released when chyme arrives in duodenum Increases secretion of bile and buffers by liver and pancreas 2015 Pearson Education, Inc. 24-6 Coordination of Secretion and Absorption Gastric Inhibitory Peptide (GIP) Is secreted when fats and carbohydrates enter small intestine

Cholecystokinin (CCK) Is secreted in duodenum When chyme contains lipids and partially digested proteins Accelerates pancreatic production and secretion of digestive enzymes Relaxes hepatopancreatic sphincter and gallbladder Ejecting 2015 Pearson Education, Inc. bile and pancreatic juice into duodenum 24-6 Coordination of Secretion and Absorption Vasoactive Intestinal Peptide (VIP)

Stimulates secretion of intestinal glands Dilates regional capillaries Inhibits acid production in stomach Enterocrinin Is released when chyme enters small intestine Stimulates mucin production by submucosal glands of duodenum 2015 Pearson Education, Inc. FIGURE 24-23 THE FUNCTIONS OF MAJOR DIGESTIVE TRACT HORMONES. Ingested food Hormone Action

Food in stomach Acid production by parietal cells KEY stimulates inhibits Gastrin Stimulation of gastric motility; mixing waves increase in intensity GIP Chyme in duodenum Release of insulin from pancreas Release of pancreatic enzymes and buffers

Secretin and CCK Bile secretion and ejection of bile from gallbladder VIP facilitates Dilation of intestinal capillaries facilitates Material arrives in jejunum Nutrient absorption NUTRIENT UTILIZATION BY ALL TISSUES 24-6 Coordination of Secretion and Absorption

Intestinal Absorption It takes about five hours for materials to pass from duodenum to end of ileum Movements of the mucosa increase absorptive effectiveness Stir and mix intestinal contents Constantly change environment around epithelial cells 2015 Pearson Education, Inc. 24-7 The Large Intestine The Large Intestine

Is horseshoe shaped Extends from end of ileum to anus Lies inferior to stomach and liver Frames the small intestine Also called large bowel Is about 1.5 meters (4.9 ft) long and 7.5 cm (3 in.) wide 2015 Pearson Education, Inc. 24-7 The Large Intestine Functions of the Large Intestine Reabsorption of water Compaction of intestinal contents into feces Absorption of important vitamins produced by

bacteria Storage of fecal material prior to defecation 2015 Pearson Education, Inc. 24-7 The Large Intestine Parts of the Large Intestine 1. Cecum The 2. Colon The 3. pouchlike first portion largest portion Rectum The

2015 Pearson Education, Inc. last 15 cm (6 in.) of digestive tract 24-7 The Large Intestine The Cecum Is an expanded pouch Receives material arriving from the ileum Stores materials and begins compaction 2015 Pearson Education, Inc. 24-7 The Large Intestine Appendix Also called vermiform appendix Is a slender, hollow

appendage about 9 cm (3.6 in.) long Is dominated by lymphoid nodules (a lymphoid organ) Is attached to posteromedial surface of cecum Mesoappendix connects appendix to ileum and cecum 2015 Pearson Education, Inc. 24-7 The Large Intestine The Colon Has a larger diameter and thinner wall than small intestine The wall of the colon Forms

a series of pouches (haustra) Haustra permit expansion and elongation of colon 2015 Pearson Education, Inc. 24-7 The Large Intestine Colon Muscles Three longitudinal bands of smooth muscle (taeniae coli) Run along outer surfaces of colon Deep to the serosa Similar to outer layer of muscularis externa Muscle tone in taeniae coli creates the haustra

2015 Pearson Education, Inc. 24-7 The Large Intestine Serosa of the Colon Contains numerous teardrop-shaped sacs of fat Fatty appendices or epiploic appendages Four Regions of the Colon 1. 2. 3. 4. Ascending colon Transverse colon Descending colon Sigmoid colon

2015 Pearson Education, Inc. 24-7 The Large Intestine Ascending Colon Begins at superior border of cecum Ascends along right lateral and posterior wall of peritoneal cavity To inferior surface of the liver and bends at right colic flexure (hepatic flexure) 2015 Pearson Education, Inc. 24-7 The Large Intestine Transverse Colon

Crosses abdomen from right to left; turns at left colic flexure (splenic flexure) Is supported by transverse mesocolon Is separated from anterior abdominal wall by greater omentum 2015 Pearson Education, Inc. 24-7 The Large Intestine Descending Colon Proceeds inferiorly along left side to the iliac fossa (inner surface of left ilium) Is retroperitoneal, firmly attached to abdominal wall 2015 Pearson Education, Inc. 24-7 The Large Intestine

Sigmoid Colon Is an S-shaped segment, about 15 cm (6 in.) long Starts at sigmoid flexure Lies posterior to urinary bladder Is suspended from sigmoid mesocolon Empties into rectum 2015 Pearson Education, Inc. 24-7 The Large Intestine Blood Supply of the Large Intestine

Receives blood from tributaries of: Superior mesenteric and inferior mesenteric arteries Venous blood is collected from: Superior mesenteric and inferior mesenteric veins 2015 Pearson Education, Inc. 24-7 The Large Intestine The Rectum

Forms last 15 cm (6 in.) of digestive tract Is an expandable organ for temporary storage of feces Movement of fecal material into rectum triggers urge to defecate The Anal Canal Is the last portion of the rectum Contains small longitudinal folds called anal columns 2015 Pearson Education, Inc. 24-7 The Large Intestine Anus

Also called anal orifice Is exit of the anal canal Has keratinized epidermis like skin Anal Sphincters Internal anal sphincter Circular muscle layer of muscularis externa Has smooth muscle cells, not under voluntary control External anal sphincter Encircles distal portion of anal canal A ring of skeletal muscle fibers, under voluntary control 2015 Pearson Education, Inc.

FIGURE 24-24C THE LARGE INTESTINE. Rectum Anal canal Anal columns Internal anal sphincter External anal sphincter Anus c The rectum and anus 24-7 The Large Intestine Histology of the Large Intestine Lacks villi Abundance of mucous cells Presence of distinctive intestinal glands Are

deeper than glands of small intestine Are dominated by mucous cells 2015 Pearson Education, Inc. 24-7 The Large Intestine Histology of the Large Intestine Does not produce enzymes Provides lubrication for fecal material Large lymphoid nodules are scattered throughout the lamina propria and submucosa The longitudinal layer of the muscularis externa is reduced to the muscular bands of taeniae coli 2015 Pearson Education, Inc. FIGURE 24-25A THE MUCOSA AND GLANDS OF THE COLON.

Teniae coli Omental appendices Haustrum Simple columnar epithelium Aggregated lymphoid nodule Layers of the Large Intestine Mucous cells Mucosa Intestinal crypt Muscularis mucosae Muscularis mucosae

Submucosa Submucosa Muscularis externa Circular layer Longitudinal layer (teniae coli) Serosa a Diagrammatic view of the colon wall FIGURE 24-25B THE MUCOSA AND GLANDS OF THE COLON. Simple columnar epithelium Mucous cells Intestinal crypt

Muscularis mucosae Submucosa The colon LM 110 b Colon histology showing detail of mucosal layer 24-7 The Large Intestine Physiology of the Large Intestine Less than 10 percent of nutrient absorption occurs in large intestine Prepares fecal material for ejection from the body 2015 Pearson Education, Inc.

24-7 The Large Intestine Absorption in the Large Intestine Reabsorption of water Reabsorption of bile salts In the cecum Transported in blood to liver Absorption of vitamins produced by bacteria Absorption of organic wastes 2015 Pearson Education, Inc. 24-7 The Large Intestine Vitamins

Are organic molecules Important as cofactors or coenzymes in metabolism Normal bacteria in colon make three vitamins that supplement diet 2015 Pearson Education, Inc. 24-7 The Large Intestine Three Vitamins Produced in the Large Intestine 1. Vitamin K (fat soluble) Required by liver for synthesizing four clotting factors, including prothrombin 2.

Biotin (water soluble) Important 3. in glucose metabolism Vitamin B5 (pantothenic acid) (water soluble) Required in manufacture of steroid hormones and some neurotransmitters 2015 Pearson Education, Inc. 24-7 The Large Intestine Organic Wastes Bacteria convert bilirubin to urobilinogens and stercobilinogens Urobilinogens

absorbed into bloodstream are excreted in urine Urobilinogens and stercobilinogens in colon convert to urobilins and stercobilins by exposure to oxygen 2015 Pearson Education, Inc. 24-7 The Large Intestine Organic Wastes Bacteria break down peptides in feces and generate: Ammonia 1. Indole and skatole 2.

Nitrogen compounds responsible for odor of feces Hydrogen sulfide 3. 2015 Pearson Education, Inc. As soluble ammonium ions Gas that produces rotten egg odor 24-7 The Large Intestine Organic Wastes Bacteria feed on indigestible carbohydrates (complex polysaccharides) Produce 2015 Pearson Education, Inc. flatus, or intestinal gas, in large intestine

24-7 The Large Intestine Movements of the Large Intestine Gastroileal and gastroenteric reflexes Move materials into cecum while you eat Movement from cecum to transverse colon is very slow, allowing hours for water absorption Peristaltic waves move material along length of colon Segmentation movements (haustral churning) mix contents of adjacent haustra 2015 Pearson Education, Inc.

24-7 The Large Intestine Movements of the Large Intestine Movement from transverse colon through rest of large intestine results from powerful peristaltic contractions (mass movements) Stimulus is distension of stomach and duodenum; relayed over intestinal nerve plexuses Distension of the rectal wall triggers defecation reflex Two positive feedback loops Both loops triggered by stretch receptors in rectum 2015 Pearson Education, Inc. 24-7 The Large Intestine

Two Positive Feedback Loops 1. Short reflex Triggers 2. peristaltic contractions in rectum Long reflex Coordinated by sacral parasympathetic system Stimulates mass movements 2015 Pearson Education, Inc. 24-7 The Large Intestine Rectal Stretch Receptors

Also trigger two reflexes important to voluntary control of defecation A long reflex Mediated by parasympathetic innervation in pelvic nerves Causes relaxation of internal anal sphincter A somatic reflex Motor commands carried by pudendal nerves Stimulates contraction of external anal sphincter (skeletal muscle) 2015 Pearson Education, Inc. FIGURE 24-26 THE DEFECATION REFLEX. L2a Stimulation of somatic motor neurons

KEY stimulates L2b L1 Increased peristalsis throughout large intestine Stimulation of parasympathetic motor neurons in sacral spinal cord inhibits S1 L S Stimulation of myenteric plexus in sigmoid colon and rectum

Long Reflex Short Reflex The first loop is a short reflex that triggers a series of peristaltic contractions in the rectum that move feces toward the anus. S2 Stimulation of stretch receptors Start Increased local peristalsis DISTENSION OF RECTUM Relaxation of internal anal sphincter; feces move into anal canal Voluntary relaxation of the

external sphincter can override the contraction direction by somatic motor neurons (L2a). Involuntary contraction of external anal sphincter If external sphincter is voluntarily relaxed, defecation occurs. The long reflex is coordinated by the sacral parasympathetic system. This reflex stimulates mass movements that push feces toward the rectum from the descending colon and sigmoid colon. 24-7 The Large Intestine Elimination of Feces

Requires relaxation of internal and external anal sphincters Reflexes open internal sphincter, close external sphincter Opening external sphincter requires conscious effort 2015 Pearson Education, Inc. 24-8 Digestion Nutrients A balanced diet contains: Carbohydrates Lipids Proteins Vitamins Minerals Water

2015 Pearson Education, Inc. 24-8 Digestion The Processing and Absorption of Nutrients Breaks down physical structure of food Disassembles component molecules Molecules released into bloodstream are: Absorbed by cells Broken down to provide energy for ATP synthesis Or used to synthesize carbohydrates, proteins, and lipids 2015 Pearson Education, Inc. 24-8 Digestion

Digestive Enzymes Are secreted by: Salivary glands Tongue Stomach Pancreas 2015 Pearson Education, Inc. 24-8 Digestion Digestive Enzymes Break molecular bonds in large organic molecules Carbohydrates, proteins, lipids, and nucleic acids In a process called hydrolysis

Are divided into classes by targets Carbohydrases break bonds between simple sugars Proteases break bonds between amino acids Lipases separate fatty acids from glycerides 2015 Pearson Education, Inc. 24-8 Digestion Digestive Enzymes Brush border enzymes break nucleotides into: Sugars Phosphates Nitrogenous 2015 Pearson Education, Inc. bases TABLE 24-1 DIGESTIVE ENZYMES AND

THEIR FUNCTIONS FIGURE 24-27 CHEMICAL EVENTS OF DIGESTION (PART 1 OF 3). REGION and Hormonal Controls CARBOHYDRATES Salivary amylase ORAL CAVITY ESOPHAGUS STOMACH Stimulus: Anticipation or arrival of food Hormone: Gastrin Source: G cells of stomach Proenzyme released: Pepsinogen by chief cells, activated to pepsin by HCl SMALL INTESTINE Stimulus: Arrival of chyme in duodenum Hormone: CCK Proenzymes released: Chymotrypsinogen, procarboxypeptidase, proelastase,

trypsinogen. Enteropeptidase activates trypsin, which activates other enzymes Enzymes released: Pancreatic amylase, pancreatic lipase, nuclease, enteropeptidase INTESTINAL MUCOSA Brush border Disaccharides Trisaccharides Pancreatic alpha-amylase Disaccharides Lactase Trisaccharides Maltase, Sucrase

FACILITATED DIFFUSION AND COTRANSPORT Monosaccharides Cell body FACILITATED DIFFUSION ROUTE TO BLOODSTREAM Carbohydrates and amino acids are absorbed and transported by intestinal capillaries. Lipids form chylomicrons that diffuse into lacteals and are delivered to the left subclavian vein by the thoracic duct. Capillary Monosaccharides FIGURE 24-27 CHEMICAL EVENTS OF DIGESTION (PART 2 OF 3). REGION and Hormonal Controls

LIPIDS Lingual lipase ORAL CAVITY ESOPHAGUS STOMACH Stimulus: Anticipation or arrival of food Hormone: Gastrin Source: G cells of stomach Proenzyme released: Pepsinogen by chief cells, activated to pepsin by HCl SMALL INTESTINE Stimulus: Arrival of chyme in duodenum Hormone: CCK Proenzymes released: Chymotrypsinogen, procarboxypeptidase, proelastase, trypsinogen. Enteropeptidase activates trypsin, which activates other enzymes Enzymes released: Pancreatic amylase, pancreatic lipase, nuclease, enteropeptidase

INTESTINAL MUCOSA Bile salts and pancreatic lipase Monoglycerides, Fatty acids in micelles DIFFUSION Brush border Monoglycerides, Fatty acids Triglycerides Cell body Chylomicrons EXOCYTOSIS ROUTE TO BLOODSTREAM

Carbohydrates and amino acids are absorbed and transported by intestinal capillaries. Lipids form chylomicrons that diffuse into lacteals and are delivered to the left subclavian vein by the thoracic duct. Lacteal Chylomicrons TABLE 24-1 DIGESTIVE ENZYMES AND THEIR FUNCTIONS (PART 3 OF 3). FIGURE 24-27 CHEMICAL EVENTS OF DIGESTION (PART 3 OF 3). REGION and Hormonal Controls PROTEINS ORAL CAVITY ESOPHAGUS STOMACH Stimulus: Anticipation or arrival of food Hormone: Gastrin

Source: G cells of stomach Proenzyme released: Pepsinogen by chief cells, activated to pepsin by HCl SMALL INTESTINE Stimulus: Arrival of chyme in duodenum Hormone: CCK Proenzymes released: Chymotrypsinogen, procarboxypeptidase, proelastase, trypsinogen. Enteropeptidase activates trypsin, which activates other enzymes Enzymes released: Pancreatic amylase, pancreatic lipase, nuclease, enteropeptidase INTESTINAL MUCOSA Pepsin Polypeptides Trypsin Chymotrypsin Elastase

Carboxypeptidase Short peptides, Amino acids Dipeptidases Brush border FACILITATED DIFFUSION AND COTRANSPORT Cell body Amino acids FACILITATED DIFFUSION AND COTRANSPORT ROUTE TO BLOODSTREAM Carbohydrates and amino acids are absorbed and transported by intestinal capillaries. Lipids form chylomicrons that diffuse into lacteals and are delivered to the left subclavian vein by the thoracic duct.

Capillary Amino acids 24-8 Digestion Water Absorption Cells cannot actively absorb or secrete water All movement of water across lining of digestive tract: Involves 2015 Pearson Education, Inc. passive water flow down osmotic gradients FIGURE 24-28 DIGESTIVE SECRETION AND WATER REABSORPTION. Digestive Secretions

Dietary Input Food and drink 2000 mL Saliva 1500 mL Gastric secretions 1500 mL 5000 mL Liver (bile) 1000 mL Pancreas (pancreatic juice) 1000 mL Water Reabsorption 9000 mL Small intestine reabsorbs 7800 mL Intestinal secretions 2000 mL

1200 mL Colon reabsorbs 1250 mL 150 mL lost in feces 1400 mL Colonic mucous secretions 200 mL 24-8 Digestion Ion Absorption Osmosis does not distinguish among solutes Determined

only by total concentration of solutes To maintain homeostasis: Concentrations of specific ions must be regulated Sodium ion absorption Rate increased by aldosterone (steroid hormone from adrenal cortex) 2015 Pearson Education, Inc. 24-8 Digestion Ion Absorption Calcium ion absorption Involves

active transport at epithelial surface Rate increased by parathyroid hormone (PTH) and calcitriol Potassium ion concentration increases: As other solutes move out of lumen Other ions diffuse into epithelial cells along concentration gradient 2015 Pearson Education, Inc. 24-8 Digestion Ion Absorption Cation absorption (magnesium, iron) Involves specific carrier proteins Cell must use ATP to transport ions to interstitial fluid

Anions (chloride, iodide, bicarbonate, and nitrate) Are absorbed by diffusion or carrier-mediated transport Phosphate and sulfate ions Enter 2015 Pearson Education, Inc. epithelial cells by active transport 24-8 Digestion Vitamins Are organic compounds required in very small quantities

Are divided into two major groups 1. 2. 2015 Pearson Education, Inc. Fat-soluble vitamins Water-soluble vitamins TABLE 24-2 THE ABSORPTION OF IONS AND VITAMINS. 24-9 Effects of Aging on the Digestive System Age-Related Changes Division of epithelial stem cells declines Digestive epithelium becomes more susceptible to damage by abrasion, acids, or enzymes Smooth muscle tone and general motility decrease

Peristaltic contractions become weaker Cumulative damage from toxins (alcohol, other chemicals) Absorbed by digestive tract and transported to liver for processing 2015 Pearson Education, Inc. 24-9 Effects of Aging on the Digestive System Age-Related Changes Rates of colon cancer and stomach cancer rise with age Oral and pharyngeal cancers common among

elderly smokers Decline in olfactory and gustatory sensitivities Leads 2015 Pearson Education, Inc. to dietary changes that affect entire body FIGURE 24-29 DIAGRAMS THE FUNCTIONAL RELATIONSHIPS BETWEEN THE DIGESTIVE SYSTEM AND THE OTHER BODY SYSTEMS WE HAVE STUDIED SO FAR. I N T E G R A T O R Digestive System Body System Provides vitamin D3 needed for the absorption of calcium and phosphorus Provides lipids for storage by adipocytes in subcutaneous layer Skull, ribs, vertebrae, and pelvic

girdle support and protect parts of digestive tract; teeth are important in mechanical processing of food Absorbs calcium and phosphate ions for incorporation into bone matrix; provides lipids for storage in yellow marrow Page 174 Skeletal Integumentary Skeletal Digestive System Integumentary S Y S T E M Body System Liver regulates blood glucose and fatty acid levels, metabolizes lactate from active muscles

ANS regulates movement and secretion; reflexes coordinate passage of materials along tract; control over skeletal muscles regulates ingestion and defecation; hypothalamic centers control hunger, satiation, and feeding Provides substrates essential for neurotransmitter synthesis Provides nutrients and substrates to endocrine cells; endocrine cells of pancreas secrete insulin and glucagon; liver produces angiotensinogen Increased thoracic and abdominal pressure through contraction of respiratory muscles can assist in defecation Secretions of digestive tract (acids and enzymes) provide innate defense against pathogens Nervous

Endocrine Cardiovascular Tonsils and other lymphoid nodules defend against infection and toxins absorbed from the digestive tract; lymphatic vessels carry absorbed lipids to venous system Absorbs fluid to maintain normal blood volume; absorbs vitamin K; liver excretes heme (as bilirubin), synthesizes coagulation proteins Page 647 Page 776 Lymphatic Distributes hormones of the digestive tract; carries nutrients, water, and ions from sites of absorption; delivers nutrients and toxins to liver

Page 558 Page 824 Pressure of digestive organs against the diaphragm can assist in exhalation and limit inhalation Respiratory Endocrine Cardiovascular Page 380 Epinephrine and norepinephrine stimulate constriction of sphincters and depress digestive activity; hormones coordinate activity along digestive tract Respiratory Muscular Protects and supports digestive organs in abdominal cavity; controls

entrances and exits of digestive tract Lymphatic Nervous Muscular Page 285 Page 874 Reproductive For all systems, the digestive system absorbs organic substrates, vitamins, ions, and water required by all cells. Urinary The DIGESTIVE SYSTEM Page 1090

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