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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Digestive System Part A.

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1 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Digestive System Part A

2 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Digestive System: Overview  The alimentary canal or gastrointestinal (GI) tract digests and absorbs food  Alimentary canal – mouth, pharynx, esophagus, stomach, small intestine, and large intestine  Accessory digestive organs – teeth, tongue, gallbladder, salivary glands, liver, and pancreas

3 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Digestive System: Overview Figure 23.1

4 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Digestive Process  The GI tract is a “disassembly” line  Nutrients become more available to the body in each step  There are six essential activities:  Ingestion, propulsion, and mechanical digestion  Chemical digestion, absorption, and defecation

5 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Digestive Process Figure 23.2

6 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Gastrointestinal Tract Activities  Ingestion – taking food into the digestive tract  Propulsion – swallowing and peristalsis  Peristalsis – waves of contraction and relaxation of muscles in the organ walls  Mechanical digestion – chewing, mixing, and churning food

7 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Peristalsis and Segmentation Figure 23.3

8 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Gastrointestinal Tract Activities  Chemical digestion – catabolic breakdown of food  Absorption – movement of nutrients from the GI tract to the blood or lymph  Defecation – elimination of indigestible solid wastes

9 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings GI Tract  External environment for the digestive process  Regulation of digestion involves:  Mechanical and chemical stimuli – stretch receptors, osmolarity, and presence of substrate in the lumen  Extrinsic control by CNS centers  Intrinsic control by local centers

10 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Receptors of the GI Tract  Mechano- and chemoreceptors respond to:  Stretch, osmolarity, and pH  Presence of substrate, and end products of digestion  They initiate reflexes that:  Activate or inhibit digestive glands  Mix lumen contents and move them along

11 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Control of the GI Tract  Intrinsic controls  Nerve plexuses near the GI tract initiate short reflexes  Short reflexes are mediated by local enteric plexuses (gut brain)  Extrinsic controls  Long reflexes arising within or outside the GI tract  Involve CNS centers and extrinsic autonomic nerves

12 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Control of the GI Tract Figure 23.4

13 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Peritoneum and Peritoneal Cavity  Peritoneum – serous membrane of the abdominal cavity  Visceral – covers external surface of most digestive organs  Parietal – lines the body wall  Peritoneal cavity  Lubricates digestive organs  Allows them to slide across one another

14 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Peritoneum and Peritoneal Cavity Figure 23.5a

15 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Peritoneum and Peritoneal Cavity  Mesentery – double layer of peritoneum that provides:  Vascular and nerve supplies to the viscera  A means to hold digestive organs in place and store fat  Retroperitoneal organs – organs outside the peritoneum  Peritoneal organs (intraperitoneal) – organs surrounded by peritoneum

16 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Peritoneum and Peritoneal Cavity Figure 23.5b

17 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Blood Supply: Splanchnic Circulation  Arteries and the organs they serve include  The hepatic, splenic, and left gastric: spleen, liver, and stomach  Inferior and superior mesenteric: small and large intestines  Hepatic portal circulation:  Collects nutrient-rich venous blood from the digestive viscera  Delivers this blood to the liver for metabolic processing and storage

18 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Histology of the Alimentary Canal  From esophagus to the anal canal the walls of the GI tract have the same four tunics  From the lumen outward they are the mucosa, submucosa, muscularis externa, and serosa  Each tunic has a predominant tissue type and a specific digestive function

19 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Histology of the Alimentary Canal Figure 23.6

20 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Mucosa  Moist epithelial layer that lines the lumen of the alimentary canal  Its three major functions are:  Secretion of mucus  Absorption of the end products of digestion  Protection against infectious disease  Consists of three layers: a lining epithelium, lamina propria, and muscularis mucosae

21 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Mucosa: Epithelial Lining  Consists of simple columnar epithelium and mucus- secreting goblet cells  The mucus secretions:  Protect digestive organs from digesting themselves  Ease food along the tract  Stomach and small intestine mucosa contain:  Enzyme-secreting cells  Hormone-secreting cells (making them endocrine and digestive organs)

22 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  Lamina Propria  Loose areolar and reticular connective tissue  Nourishes the epithelium and absorbs nutrients  Contains lymph nodes (part of MALT) important in defense against bacteria  Muscularis mucosae – smooth muscle cells that produce local movements of mucosa Mucosa: Lamina Propria and Muscularis Mucosae

23 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Mucosa: Other Sublayers  Submucosa – dense connective tissue containing elastic fibers, blood and lymphatic vessels, lymph nodes, and nerves  Muscularis externa – responsible for segmentation and peristalsis  Serosa – the protective visceral peritoneum  Replaced by the fibrous adventitia in the esophagus  Retroperitoneal organs have both an adventitia and serosa

24 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Enteric Nervous System  Composed of two major intrinsic nerve plexuses  Submucosal nerve plexus – regulates glands and smooth muscle in the mucosa  Myenteric nerve plexus – Major nerve supply that controls GI tract mobility  Segmentation and peristalsis are largely automatic involving local reflex arcs  Linked to the CNS via long autonomic reflex arc

25 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Mouth  Oral or buccal cavity:  Is bounded by lips, cheeks, palate, and tongue  Has the oral orifice as its anterior opening  Is continuous with the oropharynx posteriorly  To withstand abrasions:  The mouth is lined with stratified squamous epithelium  The gums, hard palate, and dorsum of the tongue are slightly keratinized

26 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Anatomy of the Oral Cavity: Mouth Figure 23.7a

27 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Lips and Cheeks  Have a core of skeletal muscles  Lips: orbicularis oris  Cheeks: buccinators  Vestibule – bounded by the lips and cheeks externally, and teeth and gums internally  Oral cavity proper – area that lies within the teeth and gums  Labial frenulum – median fold that joins the internal aspect of each lip to the gum

28 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Oral Cavity and Pharynx: Anterior View Figure 23.7b

29 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Palate  Hard palate – underlain by palatine bones and palatine processes of the maxillae  Assists the tongue in chewing  Slightly corrugated on either side of the raphe (midline ridge)

30 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Palate  Soft palate – mobile fold formed mostly of skeletal muscle  Closes off the nasopharynx during swallowing  Uvula projects downward from its free edge  Palatoglossal and palatopharyngeal arches form the borders of the fauces

31 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tongue  Occupies the floor of the mouth and fills the oral cavity when mouth is closed  Functions include:  Gripping and repositioning food during chewing  Mixing food with saliva and forming the bolus  Initiation of swallowing, and speech

32 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tongue  Intrinsic muscles change the shape of the tongue  Extrinsic muscles alter the tongue’s position  Lingual frenulum secures the tongue to the floor of the mouth

33 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tongue  Superior surface bears three types of papillae  Filiform – give the tongue roughness and provide friction  Fungiform – scattered widely over the tongue and give it a reddish hue  Circumvallate – V-shaped row in back of tongue  Sulcus terminalis – groove that separates the tongue into two areas:  Anterior 2/3 residing in the oral cavity  Posterior third residing in the oropharynx

34 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tongue Figure 23.8

35 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Salivary Glands  Produce and secrete saliva that:  Cleanses the mouth  Moistens and dissolves food chemicals  Aids in bolus formation  Contains enzymes that break down starch  Three pairs of extrinsic glands – parotid, submandibular, and sublingual  Intrinsic salivary glands (buccal glands) – scattered throughout the oral mucosa

36 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Salivary Glands  Parotid – lies anterior to the ear between the masseter muscle and skin  Parotid duct – opens into the vestibule next to the second upper molar  Submandibular – lies along the medial aspect of the mandibular body  Its ducts open at the base of the lingual frenulum  Sublingual – lies anterior to the submandibular gland under the tongue  It opens via ducts into the floor of the mouth

37 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Salivary Glands Figure 23.9a

38 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Saliva: Source and Composition  Secreted from serous and mucous cells of salivary glands  A % water, hypo-osmotic, slightly acidic solution containing  Electrolytes – Na +, K +, Cl –, PO 4 2–, HCO 3 –  Digestive enzyme – salivary amylase  Proteins – mucin, lysozyme, defensins, and IgA  Metabolic wastes – urea and uric acid

39 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Control of Salivation  Intrinsic glands keep the mouth moist  Extrinsic salivary glands secrete serous, enzyme- rich saliva in response to:  Ingested food which stimulates chemoreceptors and pressoreceptors  The thought of food  Strong sympathetic stimulation inhibits salivation and results in dry mouth

40 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Teeth  Primary and permanent dentitions have formed by age 21  Primary – 20 deciduous teeth that erupt at intervals between 6 and 24 months  Permanent – enlarge and develop causing the root of deciduous teeth to be resorbed and fall out between the ages of 6 and 12 years  All but the third molars have erupted by the end of adolescence  There are usually 32 permanent teeth

41 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Deciduous Teeth Figure

42 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Permanent Teeth Figure

43 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Classification of Teeth  Teeth are classified according to their shape and function  Incisors – chisel-shaped teeth adapted for cutting or nipping  Canines – conical or fanglike teeth that tear or pierce  Premolars (bicuspids) and molars – have broad crowns with rounded tips and are best suited for grinding or crushing  During chewing, upper and lower molars lock together generating crushing force

44 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Dental Formula: Permanent Teeth  A shorthand way of indicating the number and relative position of teeth  Written as ratio of upper to lower teeth for the mouth  Primary: 2I (incisors), 1C (canine), 2M (molars)  Permanent: 2I, 1C, 2PM (premolars), 3M 2I1C2PM3M X2 (32 teeth) 2I1C2PM3M

45 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tooth Structure  Two main regions – crown and the root  Crown – exposed part of the tooth above the gingiva (gum)  Enamel – acellular, brittle material composed of calcium salts and hydroxyapatite crystals is the hardest substance in the body  Encapsules the crown of the tooth  Root – portion of the tooth embedded in the jawbone

46 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tooth Structure  Neck – constriction where the crown and root come together  Cementum – calcified connective tissue  Covers the root  Attaches it to the periodontal ligament

47 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tooth Structure  Periodontal ligament  Anchors the tooth in the alveolus of the jaw  Forms the fibrous joint called a gomaphosis  Gingival sulcus – depression where the gingiva borders the tooth

48 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tooth Structure  Dentin – bonelike material deep to the enamel cap that forms the bulk of the tooth  Pulp cavity – cavity surrounded by dentin that contains pulp  Pulp – connective tissue, blood vessels, and nerves  Root canal – portion of the pulp cavity that extends into the root  Apical foramen – proximal opening to the root canal  Odontoblasts – secrete and maintain dentin throughout life

49 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tooth Structure Figure 23.11

50 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tooth and Gum Disease  Dental caries – gradual demineralization of enamel and dentin by bacterial action  Dental plaque, a film of sugar, bacteria, and mouth debris, adheres to teeth  Acid produced by the bacteria in the plaque dissolves calcium salts  Without these salts, organic matter is digested by proteolytic enzymes  Daily flossing and brushing help prevent caries by removing forming plaque

51 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Tooth and Gum Disease: Periodontitis  Gingivitis – as plaque accumulates, it calcifies and forms calculus, or tartar  Accumulation of calculus:  Disrupts the seal between the gingivae and the teeth  Puts the gums at risk for infection  Periodontitis – serious gum disease resulting from an immune response  Immune system attacks intruders as well as body tissues, carving pockets around the teeth and dissolving bone

52 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Digestive System Part B

53 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Pharynx  From the mouth, the oro- and laryngopharynx allow passage of:  Food and fluids to the esophagus  Air to the trachea  Lined with stratified squamous epithelium and mucus glands  Has two skeletal muscle layers  Inner longitudinal  Outer pharyngeal constrictors

54 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Esophagus  Muscular tube going from the laryngopharynx to the stomach  Travels through the mediastinum and pierces the diaphragm  Joins the stomach at the cardiac orifice

55 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Esophageal Characteristics  Esophageal mucosa – nonkeratinized stratified squamous epithelium  The empty esophagus is folded longitudinally and flattens when food is present  Glands secrete mucus as a bolus moves through the esophagus  Muscularis changes from skeletal (superiorly) to smooth muscle (inferiorly)

56 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Digestive Processes in the Mouth  Food is ingested  Mechanical digestion begins (chewing)  Propulsion is initiated by swallowing  Salivary amylase begins chemical breakdown of starch  The pharynx and esophagus serve as conduits to pass food from the mouth to the stomach

57 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Deglutition (Swallowing)  Involves the coordinated activity of the tongue, soft palate, pharynx, esophagus and 22 separate muscle groups  Buccal phase – bolus is forced into the oropharynx  Pharyngeal-esophageal phase – controlled by the medulla and lower pons  All routes except into the digestive tract are sealed off  Peristalsis moves food through the pharynx to the esophagus

58 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Deglutition (Swallowing) Figure (a) Upper esophageal sphincter contracted (b) Upper esophageal sphincter relaxed (c) Upper esophageal sphincter contracted (e) (d) Bolus of food Uvula Bolus Relaxed muscles Tongue Pharynx Epiglottis Glottis Trachea Bolus Epiglottis Bolus of food Longitudinal muscles contract, shortening passageway ahead of bolus Gastroesophageal sphincter closed Circular muscles contract, constricting passageway and pushing bolus down Stomach Gastroesophageal sphincter open Esophagus

59 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Stomach  Chemical breakdown of proteins begins and food is converted to chyme  Cardiac region – surrounds the cardiac orifice  Fundus – dome-shaped region beneath the diaphragm  Body – midportion of the stomach  Pyloric region – made up of the antrum and canal which terminates at the pylorus  The pylorus is continuous with the duodenum through the pyloric sphincter

60 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Stomach  Greater curvature – entire extent of the convex lateral surface  Lesser curvature – concave medial surface  Lesser omentum – runs from the liver to the lesser curvature  Greater omentum – drapes inferiorly from the greater curvature to the small intestine

61 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Stomach  Nerve supply – sympathetic and parasympathetic fibers of the autonomic nervous system  Blood supply – celiac trunk, and corresponding veins (part of the hepatic portal system)

62 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Stomach Figure 23.14a

63 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of the Stomach  Muscularis – has an additional oblique layer that:  Allows the stomach to churn, mix, and pummel food physically  Breaks down food into smaller fragments  Epithelial lining is composed of:  Goblet cells that produce a coat of alkaline mucus  The mucous surface layer traps a bicarbonate- rich fluid beneath it  Gastric pits contain gastric glands that secrete gastric juice, mucus, and gastrin

64 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of the Stomach Figure 23.15

65 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Glands of the Stomach Fundus and Body  Gastric glands of the fundus and body have a variety of secretory cells  Mucous neck cells – secrete acid mucus  Parietal cells – secrete HCl and intrinsic factor

66 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Glands of the Stomach Fundus and Body  Chief cells – produce pepsinogen  Pepsinogen is activated to pepsin by:  HCl in the stomach  Pepsin itself via a positive feedback mechanism  Enteroendocrine cells – secrete gastrin, histamine, endorphins, serotonin, cholecystokinin (CCK), and somatostatin into the lamina propria

67 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Stomach Lining  The stomach is exposed to the harshest conditions in the digestive tract  To keep from digesting itself, the stomach has a mucosal barrier with:  A thick coat of bicarbonate-rich mucus on the stomach wall  Epithelial cells that are joined by tight junctions  Gastric glands that have cells impermeable to HCl  Damaged epithelial cells are quickly replaced

68 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Digestion in the Stomach  The stomach:  Holds ingested food  Degrades this food both physically and chemically  Delivers chyme to the small intestine  Enzymatically digests proteins with pepsin  Secretes intrinsic factor required for absorption of vitamin B 12

69 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Gastric Secretion  Neural and hormonal mechanisms regulate the release of gastric juice  Stimulatory and inhibitory events occur in three phases  Cephalic (reflex) phase: prior to food entry  Gastric phase: once food enters the stomach  Intestinal phase: as partially digested food enters the duodenum

70 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Cephalic Phase  Excitatory events include:  Sight or thought of food  Stimulation of taste or smell receptors  Inhibitory events include:  Loss of appetite or depression  Decrease in stimulation of the parasympathetic division

71 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Gastric Phase  Excitatory events include:  Stomach distension  Activation of stretch receptors (neural activation)  Activation of chemoreceptors by peptides, caffeine, and rising pH  Release of gastrin to the blood

72 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Gastric Phase  Inhibitory events include:  A pH lower than 2  Emotional upset that overrides the parasympathetic division

73 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Intestinal Phase  Excitatory phase – low pH; partially digested food enters the duodenum and encourages gastric gland activity  Inhibitory phase – distension of duodenum, presence of fatty, acidic, or hypertonic chyme, and/or irritants in the duodenum  Initiates inhibition of local reflexes and vagal nuclei  Closes the pyloric sphincter  Releases enterogastrones that inhibit gastric secretion

74 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Release of Gastric Juice Figure 23.16

75 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Regulation and Mechanism of HCl Secretion  HCl secretion is stimulated by ACh, histamine, and gastrin through second-messenger systems  Release of hydrochloric acid:  Is low if only one ligand binds to parietal cells  Is high if all three ligands bind to parietal cells  Antihistamines block H 2 receptors and decrease HCl release

76 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Regulation and Mechanism of HCl Secretion Figure 23.17

77 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Response of the Stomach to Filling  Stomach pressure remains constant until about 1L of food is ingested  Relative unchanging pressure results from reflex- mediated relaxation and plasticity  Reflex-mediated events include:  Receptive relaxation – as food travels in the esophagus, stomach muscles relax  Adaptive relaxation – the stomach dilates in response to gastric filling  Plasticity – intrinsic ability of smooth muscle to exhibit the stress-relaxation response

78 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Gastric Contractile Activity  Peristaltic waves move toward the pylorus at the rate of 3 per minute  This basic electrical rhythm (BER) is initiated by pacemaker cells (cells of Cajal)  Most vigorous peristalsis and mixing occurs near the pylorus  Chyme is either:  Delivered in small amounts to the duodenum or  Forced backward into the stomach for further mixing

79 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Gastric Contractile Activity Figure 23.18

80 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Gastric Emptying  Gastric emptying is regulated by:  The neural enterogastric reflex  Hormonal (enterogastrone) mechanisms  These mechanisms inhibit gastric secretion and duodenal filling  Carbohydrate-rich chyme quickly moves through the duodenum  Fat-laden chyme is digested more slowly causing food to remain in the stomach longer

81 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Gastric Emptying Figure 23.19

82 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Small Intestine: Gross Anatomy  Runs from pyloric sphincter to the ileocecal valve  Has three subdivisions: duodenum, jejunum, and ileum  The bile duct and main pancreatic duct:  Join the duodenum at the hepatopancreatic ampulla  Are controlled by the sphincter of Oddi  The jejunum extends from the duodenum to the ileum  The ileum joins the large intestine at the ileocecal valve

83 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Small Intestine: Microscopic Anatomy  Structural modifications of the small intestine wall increase surface area  Plicae circulares: deep circular folds of the mucosa and submucosa  Villi – fingerlike extensions of the mucosa  Microvilli – tiny projections of absorptive mucosal cells’ plasma membranes

84 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Small Intestine: Microscopic Anatomy Figure 23.21

85 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Small Intestine: Histology of the Wall  The epithelium of the mucosa is made up of:  Absorptive cells and goblet cells  Enteroendocrine cells  Interspersed T cells called intraepithelial lymphocytes (IELs)  IELs immediately release cytokines upon encountering Ag

86 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Small Intestine: Histology of the Wall  Cells of intestinal crypts secrete intestinal juice  Peyer’s patches are found in the submucosa  Brunner’s glands in the duodenum secrete alkaline mucus

87 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Intestinal Juice  Secreted by intestinal glands in response to distension or irritation of the mucosa  Slightly alkaline and isotonic with blood plasma  Largely water, enzyme-poor, but contains mucus

88 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Liver  The largest gland in the body  Superficially has four lobes – right, left, caudate, and quadrate  The falciform ligament:  Separates the right and left lobes anteriorly  Suspends the liver from the diaphragm and anterior abdominal wall

89 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Liver  The ligamentum teres:  Is a remnant of the fetal umbilical vein  Runs along the free edge of the falciform ligament

90 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Liver: Associated Structures  The lesser omentum anchors the liver to the stomach  The hepatic blood vessels enter the liver at the porta hepatis  The gallbladder rests in a recess on the inferior surface of the right lobe

91 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Liver: Associated Structures  Bile leaves the liver via:  Bile ducts, which fuse into the common hepatic duct  The common hepatic duct, which fuses with the cystic duct  These two ducts form the bile duct

92 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Gallbladder and Associated Ducts Figure 23.20

93 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Liver: Microscopic Anatomy  Hexagonal-shaped liver lobules are the structural and functional units of the liver  Composed of hepatocyte (liver cell) plates radiating outward from a central vein  Portal triads are found at each of the six corners of each liver lobule  Portal triads consist of a bile duct and  Hepatic artery – supplies oxygen-rich blood to the liver  Hepatic portal vein – carries venous blood with nutrients from digestive viscera

94 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Liver: Microscopic Anatomy  Liver sinusoids – enlarged, leaky capillaries located between hepatic plates  Kupffer cells – hepatic macrophages found in liver sinusoids

95 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Liver: Microscopic Anatomy  Hepatocytes’ functions include:  Production of bile  Processing bloodborne nutrients  Storage of fat-soluble vitamins  Detoxification  Secreted bile flows between hepatocytes toward the bile ducts in the portal triads

96 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Anatomy of the Liver Figure 23.24c, d

97 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Composition of Bile  A yellow-green, alkaline solution containing bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes  Bile salts are cholesterol derivatives that:  Emulsify fat  Facilitate fat and cholesterol absorption  Help solubilize cholesterol  Enterohepatic circulation recycles bile salts  The chief bile pigment is bilirubin, a waste product of heme

98 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings The Gallbladder  Thin-walled, green muscular sac on the ventral surface of the liver  Stores and concentrates bile by absorbing its water and ions  Releases bile via the cystic duct, which flows into the bile duct

99 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Bile Release  Acidic, fatty chyme causes the duodenum to release:  Cholecystokinin (CCK) and secretin into the bloodstream  Bile salts and secretin transported in blood stimulate the liver to produce bile  Vagal stimulation causes weak contractions of the gallbladder

100 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Bile Release  Cholecystokinin causes:  The gallbladder to contract  The hepatopancreatic sphincter to relax  As a result, bile enters the duodenum

101 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Bile Release Figure 23.25

102 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Digestive System Part C

103 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Pancreas  Location  Lies deep to the greater curvature of the stomach  The head is encircled by the duodenum and the tail abuts the spleen

104 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Pancreas  Exocrine function  Secretes pancreatic juice which breaks down all categories of foodstuff  Acini (clusters of secretory cells) contain zymogen granules with digestive enzymes  The pancreas also has an endocrine function – release of insulin and glucagon

105 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Acinus of the Pancreas Figure 23.26a

106 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Composition and Function of Pancreatic Juice  Water solution of enzymes and electrolytes (primarily HCO 3 – )  Neutralizes acid chyme  Provides optimal environment for pancreatic enzymes  Enzymes are released in inactive form and activated in the duodenum

107 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Composition and Function of Pancreatic Juice  Examples include  Trypsinogen is activated to trypsin  Procarboxypeptidase is activated to carboxypeptidase  Active enzymes secreted  Amylase, lipases, and nucleases  These enzymes require ions or bile for optimal activity

108 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Pancreatic Secretion  Secretin and CCK are released when fatty or acidic chyme enters the duodenum  CCK and secretin enter the bloodstream  Upon reaching the pancreas:  CCK induces the secretion of enzyme-rich pancreatic juice  Secretin causes secretion of bicarbonate-rich pancreatic juice  Vagal stimulation also causes release of pancreatic juice

109 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Regulation of Pancreatic Secretion Figure 23.28

110 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Digestion in the Small Intestine  As chyme enters the duodenum:  Carbohydrates and proteins are only partially digested  No fat digestion has taken place

111 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Digestion in the Small Intestine  Digestion continues in the small intestine  Chyme is released slowly into the duodenum  Because it is hypertonic and has low pH, mixing is required for proper digestion  Required substances needed are supplied by the liver  Virtually all nutrient absorption takes place in the small intestine

112 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Motility in the Small Intestine  The most common motion of the small intestine is segmentation  It is initiated by intrinsic pacemaker cells (Cajal cells)  Moves contents steadily toward the ileocecal valve  After nutrients have been absorbed:  Peristalsis begins with each wave starting distal to the previous  Meal remnants, bacteria, mucosal cells, and debris are moved into the large intestine

113 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Control of Motility  Local enteric neurons of the GI tract coordinate intestinal motility  Cholinergic neurons cause:  Contraction and shortening of the circular muscle layer  Shortening of longitudinal muscle  Distension of the intestine

114 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Control of Motility  Other impulses relax the circular muscle  The gastroileal reflex and gastrin:  Relax the ileocecal sphincter  Allow chyme to pass into the large intestine

115 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Large Intestine  Has three unique features:  Teniae coli – three bands of longitudinal smooth muscle in its muscularis  Haustra – pocketlike sacs caused by the tone of the teniae coli  Epiploic appendages – fat-filled pouches of visceral peritoneum

116 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Large Intestine  Is subdivided into the cecum, appendix, colon, rectum, and anal canal  The saclike cecum:  Lies below the ileocecal valve in the right iliac fossa  Contains a wormlike vermiform appendix

117 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Large Intestine Figure 23.29a

118 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Colon  Has distinct regions: ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, and sigmoid colon  The transverse and sigmoid portions are anchored via mesenteries called mesocolons  The sigmoid colon joins the rectum  The anal canal, the last segment of the large intestine, opens to the exterior at the anus

119 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Valves and Sphincters of the Rectum and Anus  Three valves of the rectum stop feces from being passed with gas  The anus has two sphincters:  Internal anal sphincter composed of smooth muscle  External anal sphincter composed of skeletal muscle  These sphincters are closed except during defecation

120 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Mesenteries of Digestive Organs Figure 23.30b

121 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Mesenteries of Digestive Organs Figure 23.30c

122 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Mesenteries of Digestive Organs Figure 23.30d

123 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Large Intestine: Microscopic Anatomy  Colon mucosa is simple columnar epithelium except in the anal canal  Has numerous deep crypts lined with goblet cells  Anal canal mucosa is stratified squamous epithelium  Anal sinuses exude mucus and compress feces  Superficial venous plexuses are associated with the anal canal  Inflammation of these veins results in itchy varicosities called hemorrhoids

124 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Structure of the Anal Canal Figure 23.29b

125 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Bacterial Flora  The bacterial flora of the large intestine consist of:  Bacteria surviving the small intestine that enter the cecum and  Those entering via the anus  These bacteria:  Colonize the colon  Ferment indigestible carbohydrates  Release irritating acids and gases (flatus)  Synthesize B complex vitamins and vitamin K

126 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Functions of the Large Intestine  Other than digestion of enteric bacteria, no further digestion takes place  Vitamins, water, and electrolytes are reclaimed  Its major function is propulsion of fecal material toward the anus  Though essential for comfort, the colon is not essential for life

127 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Motility of the Large Intestine  Haustral contractions  Slow segmenting movements that move the contents of the colon  Haustra sequentially contract as they are stimulated by distension  Presence of food in the stomach:  Activates the gastrocolic reflex  Initiates peristalsis that forces contents toward the rectum

128 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Defecation  Distension of rectal walls caused by feces:  Stimulates contraction of the rectal walls  Relaxes the internal anal sphincter  Voluntary signals stimulate relaxation of the external anal sphincter and defecation occurs

129 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Defecation Figure 23.32

130 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Digestion: Carbohydrates  Absorption: via cotransport with Na +, and facilitated diffusion  Enter the capillary bed in the villi  Transported to the liver via the hepatic portal vein  Enzymes used: salivary amylase, pancreatic amylase, and brush border enzymes

131 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Digestion: Proteins  Absorption: similar to carbohydrates  Enzymes used: pepsin in the stomach  Enzymes acting in the small intestine  Pancreatic enzymes – trypsin, chymotrypsin, and carboxypeptidase  Brush border enzymes – aminopeptidases, carboxypeptidases, and dipeptidases

132 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Digestion: Proteins Figure 23.34

133 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Digestion: Fats  Absorption: Diffusion into intestinal cells where they:  Combine with proteins and extrude chylomicrons  Enter lacteals and are transported to systemic circulation via lymph  Glycerol and short chain fatty acids are:  Absorbed into the capillary blood in villi  Transported via the hepatic portal vein  Enzymes/chemicals used: bile salts and pancreatic lipase

134 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Digestion: Fats Figure 23.35

135 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Fatty Acid Absorption  Fatty acids and monoglycerides enter intestinal cells via diffusion  They are combined with proteins within the cells  Resulting chylomicrons are extruded  They enter lacteals and are transported to the circulation via lymph

136 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Fatty Acid Absorption Figure 23.36

137 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Digestion: Nucleic Acids  Absorption: active transport via membrane carriers  Absorbed in villi and transported to liver via hepatic portal vein  Enzymes used: pancreatic ribonucleases and deoxyribonuclease in the small intestines

138 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Electrolyte Absorption  Most ions are actively absorbed along the length of small intestine  Na + is coupled with absorption of glucose and amino acids  Ionic iron is transported into mucosal cells where it binds to ferritin  Anions passively follow the electrical potential established by Na +

139 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Electrolyte Absorption  K + diffuses across the intestinal mucosa in response to osmotic gradients  Ca 2+ absorption:  Is related to blood levels of ionic calcium  Is regulated by vitamin D and parathyroid hormone (PTH)

140 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Water Absorption  95% of water is absorbed in the small intestines by osmosis  Water moves in both directions across intestinal mucosa  Net osmosis occurs whenever a concentration gradient is established by active transport of solutes into the mucosal cells  Water uptake is coupled with solute uptake, and as water moves into mucosal cells, substances follow along their concentration gradients

141 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Malabsorption of Nutrients  Results from anything that interferes with delivery of bile or pancreatic juice  Factors that damage the intestinal mucosa (e.g., bacterial infection)  Gluten enteropathy (adult celiac disease) – gluten damages the intestinal villi and reduces the length of microvilli  Treated by eliminating gluten from the diet (all grains but rice and corn)

142 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings  3 rd week – endoderm has folded and foregut and hindgut have formed  The midgut is open and continuous with the yolk sac  Mouth and anal openings are nearly formed  8 th week – accessory organs are budding from endoderm Embryonic Development of the Digestive System

143 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure Embryonic Development of the Digestive System

144 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Developmental Aspects  During fetal life, nutrition is via the placenta, but the GI tract is stimulated toward maturity by amniotic fluid swallowed in utero  At birth, feeding is an infant’s most important function and is enhanced by  Rooting reflex (helps infant find the nipple) and sucking reflex (aids in swallowing)  Digestive system has few problems until the onset of old age  During old age the GI tract activity declines, absorption is less efficient, and peristalsis is slowed

145 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Cancer  Stomach and colon cancers rarely have early signs or symptoms  Metastasized colon cancers frequently cause secondary liver cancer  Prevention is by regular dental and medical examinations

146 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Cancer  Colon cancer is the 2 nd largest cause of cancer deaths in males (lung cancer is 1 st )  Forms from benign mucosal tumors called polyps whose formation increases with age  Regular colon examination should be done for all those over 50


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