Chapter 24 The Digestive System Part A.

Chapter 24 The Digestive System Part A

Digestive System Takes in food
Breaks food down into nutrient molecules Absorbs these molecules into the blood stream Rids the body of indigestible remains

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: a long tube Accessory digestive organs – teeth, tongue, gallbladder, salivary glands, liver, and pancreas; not part of the tube but help with digestion

Figure 22.1

Mechanism for nourishing the body
Digestion Mechanism for nourishing the body Most nutrients in food require either degradation ( break apart) or release prior to absorption Digestion occurs in GI Tract Digestion Mechanical chewing and peristalsis Chemical enzymes, HCl

The GI tract is a “disassembly” line
Nutrients become more available to the body in each step

There are six essential activities: Ingestion Propulsion
Digestive Process There are six essential activities: Ingestion Propulsion Mechanical digestion Chemical digestion Absorption Defecation Figure 22.2

Essential Activities of Digestion
Ingestion – taking food in Propulsion – swallowing and peristalsis Peristalsis – waves of contraction and relaxation of muscles in organ walls, esophagus and intestine Mechanical digestion – chewing; mixing; churning food

Movement of digestive materials
Visceral (organ) smooth muscle shows rhythmic cycles of activity Pacemaker cells Peristalsis Waves that move a bolus (rounded mass of food that is swallowed) Segmentation Churn and fragment a bolus

Figure Peristalsis Figure 22.4

bolus Figure 22.3a, b

Chemical digestion – catabolic breakdown of food Absorption – movement of nutrients from GI tract to blood or lymph Defecation – elimination of indigestible solid wastes

Figure 22.2 Figure 22.2

GI Tract External environment for the digestive process; open to outside at both ends Regulation of digestion involves: Mechanical and chemical stimuli Extrinsic control by CNS centers Intrinsic control by local centers

Receptors of the GI Tract
Mechano- and chemoreceptors respond to: Stretch by food in lumen Osmolarity(solute concentration) and pH Presence of substrate or End products of digestion They initiate reflexes that: Activate or inhibit digestive glands Mix lumen contents and move them along

Control of the digestive system
Movement of materials along the digestive tract is controlled by: Neural mechanisms Parasympathetic and local reflexes Hormonal mechanisms Enhance or inhibit smooth muscle contraction Local mechanisms Coordinate response to changes in pH or chemical stimuli

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

Nervous Control of the GI Tract
Figure 22.4

Figure 22.5 The Regulation of Digestive Activities

Digestive System Organs and Peritoneum
Peritoneum – serous membrane of the abdominal cavity Visceral – covers external surface of most digestive organs Parietal – lines the body wall Figure 22.5a

Peritoneal cavity Lubricates digestive organs Allows them to slide across one another Figure 22.5a

Mesentery – double layer of peritoneum Vascular(blood) 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 Figure 22.5b

The digestive system organs and the peritoneum
Mesenteries Sheets of serous membranes that support portions of the digestive tract Greater omentum lies anterior to abdominal viscera Provides padding, protection, insulation, and energy reserves Lesser omentum

Figure Mesenteries Figure 24.2b

Figure Mesenteries Figure 24.2c

Figure Mesenteries Figure 24.2d

Chapter 24 The Digestive System Part B

Blood Supply: Splanchnic Circulation
Arteries that branch off abdominal aorata and the organs they serve include The hepatic: liver, splenic:spleen, and left gastric: stomach Inferior and superior mesenteric: small and large intestines Hepatic portal circulation: Collects nutrient-rich venous blood from the digestive viscera (organs) Delivers it to the liver for metabolic processing and storage

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 Note: serosa is technically not present on the esophagus Each tunic has a predominant tissue type and specific digestive function

Histology of the Alimentary Canal
Figure 24.6

Figure 24.3 The Structure of the Digestive Tract

Mucosa Moist epithelial layer -- 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: lining epithelium lamina propria muscularis mucosae

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 tract Stomach and small intestine mucosa contain: Enzyme-secreting cells Hormone-secreting cells

Mucosa: Lamina Propria and Muscularis Mucosae
Loose areolar and reticular connective tissue Nourishes the epithelium and absorbs nutrients Contains lymph nodes (part of MALT-Mucosa Associated Lymphatic Tissue) important in defense against bacteria Muscularis mucosae– smooth muscle cells that produce local movements of mucosa

Mucosa: Other Sublayers
Submucosa – dense connective tissue containing: elastic fibers blood and lymphatic vessels lymph nodes 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

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 Linked to the CNS via long autonomic reflex arc Parasympatheitic enhances Sympathetic inhibits Enteric nevous system or “gut brain” 100 million neurons-more than the spinal cord

Chapter 24 The Digestive System Part C

Mouth Oral or buccal cavity: To withstand abrasions:
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

Mouth Figure 24.7a

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 Figure 24.7b

Lips and Cheeks Figure 24.7b

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) 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

Cleft palate

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 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

Homeostatic Imbalance
Ankyloglossia – congenital situation where the lingual frenulum is extremely short Commonly referred to as being “tongue-tied” Corrected surgically by cutting the frenulum

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

Tongue Figure 24.8a

Taste and taste buds Most of the 10,000 or so taste buds are found on the tongue Taste buds are found in papillae of the tongue mucosa Fungiform and circumvallate papillae contain taste buds

Taste is 80% smell Five taste sensations
There are five basic taste sensations Sweet – sugars, saccharin, alcohol, and some amino acids Salt – metal ions Sour – hydrogen ions Bitter – alkaloids such as quinine and nicotine Umami – elicited by the amino acid glutamate Taste is 80% smell

Salivary Glands Produce and secrete saliva that:
Cleanses the mouth Moistens and dissolves food chemicals Aids in bolus formation Contains enzymes that breakdown starch Three pairs of extrinsic glands – parotid submandibular sublingual Intrinsic salivary glands (buccal glands) – scattered throughout the oral mucosa

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

Salivary Glands II Figure 24.9a

Mumps – inflammation of the parotid glands caused by myxovirus Signs and symptoms – moderate fever and pain in swallowing acidic foods In adult males, mumps carries 25% risk that testes may become infected, leading to sterility

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–, PO42–, HCO3– Digestive enzyme – salivary amylase Proteins – mucin, lysozyme, defensins, and IgA Metabolic wastes – urea and uric acid

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

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

Teeth Figure

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 = 170N

Tooth Structure Two main regions – crown and the root
Crown – exposed part of the tooth above the gingiva (gum) encapsulaed by enamel Enamel – acelluar, brittle material composed of calcium salts and hydroxyapatite crystals;the hardest substance in the body Root – portion of the tooth embedded in the jawbone

Tooth Structure Neck – constriction where the crown and root come together Cementum – calcified connective tissue Covers the root Attaches it to the periodontal ligament Periodontal ligament Anchors the tooth in the alveolus of the jaw Forms the fibrous joint called a gomaphosis Gingival sulcus – depression where the gingival borders the tooth

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

Tooth Structure Figure 24.11

Root canal therapy – blows to the teeth can cause swelling and consequently pinch off the blood supply to the tooth. The nerve dies and may become infected with bacteria the cavity is sterilized and filled with an inert material The tooth is capped

Tooth and Gum Disease Dental caries or cavities – 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

Dental Caries

Tooth and Gum Disease: Periodontitis
Gingivitis –plaque accumulates, calcifies and forms calculus, or tartar Accumulation of tartar: 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 Attack of the immune system against intruders: Also carves pockets around the teeth and Dissolves bone away Can cause heart problems including heart attack!!

Periodontitis

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

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

Heartburn (gastroesophageal reflux disease or GERD) – burning, radiating substernal pain caused by acidic gastric juice regurgitated into the esophagus Caused by excess eating or drinking, and conditions that force abdominal contents superiorly (e.g., extreme obesity, pregnancy, and running) Hiatus hernia – structural abnormality in which the superior part of the stomach protrudes slightly above the diaphragm Prolonged episodes can lead to esophagitis, ulcers, and cancer

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)

Digestive Processes in the Mouth
Food is ingested Mechanical digestion begins (chewing) or mastication 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

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

Figure 24.13a-c

Figure 24.13d, e

Stomach Figure 24.14a

Digestion in the Stomach
Holds ingested food Degrades it both physically and chemically Chemical breakdown of proteins begins and food is converted to chyme Delivers chyme to the small intestine Enzymatically digests proteins with pepsin Secretes intrinsic factor required for absorption of vitamin B12

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 Gastric pits containing gastric glands that secrete: Gastric juice Mucus Gastrin

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 (oxyntic) cells – secrete HCl and intrinsic factor Chief (zymogenic) cells – produce pepsinogen Pepsinogen is activated to pepsin by: HCl in the stomach Pepsin itself by a positive feedback mechanism Enteroendocrine cells – secrete gastrin, histamine, endorphins, serotonin, cholecystokinin (CCK), and somatostatin into the lamina propria

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

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

Cephalic Phase Excitatory events include: Inhibitory 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

Gastric Phase Excitatory events include: Inhibitory 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 Inhibitory events include: A pH lower than 2 Emotional upset which overrides the parasympathetic division

Intestinal Phase Excitatory phase – low pH and partially digested food enters the duodenum Inhibitory phase – distension of duodenum, presence of fatty, acidic, or hypertonic chyme, and/or irritants in the duodenum Closes the pyloric sphincter Releases enterogastrones that inhibit gastric secretion

Release of Gastric Juice
Figure 24.16

Regulation and Mechanism of HCl Secretion
HCl secretion is stimulated by ACh, histamine, and gastrin Release of hydrochloric acid: Is low if only one ligand binds to parietal cells Is prolific if all three ligands bind to parietal cells Antihistamines and cimetidine (Tagamet) block H2 receptors and decrease HCl release; proton pump inhibitors like Prilosec interupt HCl production at pump and stop production.

Regulation and Mechanism of HCl Secretion
Figure 24.17

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

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

Gastric Contractile Activity
Figure 24.18

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 moves through the duodenum quickly Fat-laden chyme is digested more slowly causing food to remain in the stomach longer

Regulation of Gastric Emptying
Figure 24.19

Vomiting (emesis) – the stomach empties via a different route (oral) Causes include extreme stretching, irritants such as bacterial toxins, excessive alcohol, spicy foods, and certain drugs The emetic center of the medulla initiates a number of motor responses Diaphragm and abdominal wall muscle contract Cardiac sphincter relaxes and soft palate closes off the nasal passages Excessive vomiting can cause dehydration and upset electrolyte and pH balance

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

Microscopic Anatomy of the Small Intestine
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

Microscopic Anatomy of the Small Intestine
Figure 24.21a-c

Small Intestine: Histology of the Wall
The epithelium of the mucosa is made up of: Absorptive cells and goblet cells Interspersed T cells (intraepithelial lymphocytes), and Enteroendocrine cells Intestinal crypts cells secrete intestinal juice Peyer’s patches are found in the submucosa lymphoid tissue; fights infection causing bacteria Brunner’s glands in the duodenum secrete alkaline mucus

Intestinal Juice Secreted by intestine glands in response to distension or irritation of the mucosa It is slightly alkaline and isotonic with blood plasma Is largely water, enzyme-poor, but contains mucus

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 The ligamentum teres: Is a remnant of the fetal umbilical vein Runs along the free edge of the falciform ligament

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 Bile leaves the liver via Bile ducts which fuse into the common hepatic duct The common hepatic duct fuses with the cystic duct These two ducts form the bile duct

Liver: Associated Structures
Figure 24.20

The Liver p.286

Microscopic Anatomy of the Liver
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

Figure 24.24c, d

Liver sinusoids – enlarged, leaky capillaries located between hepatic plates Kupffer cells – hepatic macrophages found in liver sinusoids Hepatocytes’(liver cells) functions include: Production of bile Processing blood borne nutrients Storage of fat-soluble vitamins Detoxification Secreted bile flows between hepatocytes toward the bile ducts in the portal triads

Figure 24.24c, d

Hepatitis – inflammation of the liver often due to viral infection Viruses causing hepatitis are catalogued has HVA through HVF HVA and HVE are transmitted enterically and cause self-limiting infections Hepatitis B is transmitted via blood transfusions, contaminated needles, and sexual contact, and increases the risk of liver cancer Hepatitis C produces chronic liver infection Nonviral hepatitis is caused by drug toxicity and wild mushroom poisoning

Cirrhosis – diffuse and progressive chronic inflammation of the liver Typically results from chronic alcoholism or severe chronic hepatitis The liver becomes fatty and fibrous and its activity is depressed Scar tissue obstructs blood flow in the hepatic portal system causing portal hypertension

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

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

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 Cholecystokinin causes: The gallbladder to contract The hepatopancreatic sphincter to relax As a result, bile enters the duodenum

Regulation of Bile Release
Figure 24.25

Gallstones – crystallization of cholesterol which can obstruct the flow of bile Current treatments include: dissolving the crystals with drugs, pulverizing them with ultrasound, vaporizing them with lasers, and surgical removal of the gallbladder cholecystectomy : surgery to remove gall bladder Obstructive jaundice – yellowish skin caused by bile pigments deposited in the skin Due to blocked bile ducts

Pancreas Location Exocrine function
Lies deep to the greater curvature of the stomach The head is encircled by the duodenum and the tail abuts the spleen 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

Pancreas Figure 24.26a

Composition and Function of Pancreatic Juice
Water solution of enzymes and electrolytes (primarily HCO3) Neutralizes acid chyme Provides optimal environment for pancreatic enzymes Enzymes are released in inactive form and activated in the duodenum

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

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

Regulation of Pancreatic Secretion
Figure 24.28

Digestion in the Small Intestine
As chyme enters the duodenum Carbohydrates and proteins are only partially digested No fat digestion has taken place 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

Incorporated in the plasma membrane of the microvilli are a number of enzymes that complete digestion: aminopeptidases attack the amino terminal (N-terminal) of peptides producing amino acids. disaccharidases These enzymes convert disaccharides into their monosaccharide subunits. maltase hydrolyzes maltose into glucose. sucrase hydrolyzes sucrose (common table sugar) into glucose and fructose. lactase hydrolyzes lactose (milk sugar) into glucose and galactose. Fructose simply diffuses into the villi, but both glucose and galactose are absorbed by active transport. Fatty acids and monoglycerides. These become resynthesized into fats as they enter the cells of the villus. The resulting small droplets of fat are then discharged by exocytosis into the lymph vessels, called lacteals, draining the villi.

Motility of 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

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 Other impulses relax the circular muscle The gastroileal reflex and gastrin: Relax the ileocecal sphincter Allow chyme to pass into the large intestine

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 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

Large Intestine Figure 24.29a

Silv. p.686 The Large Intestine

Appendicitis – inflammation of the appendix resulting from blockage that traps infectious bacteria in its lumen If the appendix ruptures, feces containing bacteria spray over the abdominal contents causing peritonitis Treatment is surgical removal of the appendix

Chapter 24 The Digestive System Part F

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

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

Mesenteries of Digestive Organs
Figure 24.30b

Figure 24.30c

Figure 24.30d

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

Mechanical Digestion Haustral contractions
propel and mix from pouch to pouch

Large Intestine: Microscopic Anatomy
Figure 24.29b

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

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

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

Diverticulosis – small herniation (diverticula) of the mucosa of the colon walls caused by lack of bulk in the colon Most common in the sigmoid colon in people over 70 Diverticulitis – inflamed diverticula that can be life threatening if the diverticula rupture

Figure 24.23 The Large Intestine
Figure 24.23b, c

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 Figure 24.32

The Defecation Reflex Figure 24.25

Figure 24.27 Digestive Secretion and Absorption of Water

Diarrhea – watery stool resulting from any condition that rushes food residue through the large intestine too quickly This causes insufficient time for water absorption Prolonged diarrhea may result in dehydration and electrolyte imbalance Constipation – hard stool that is difficult to pass resulting from residues staying in the intestine too long May result from lack of fiber in the diet

Food Poisoning: Salmonella
Salmonella is spread by: Contaminated eggs and egg products Infected food handlers with feces-contaminated hands Salmonella can cause: Bacteremia 4 to 7 days after infection Endocarditis, thrombi, bone infections, arthritis, and meningitis Diagnosis is by positive stool samples Salmonellosis is treated symptomatically

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

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

Chemical Digestion: Proteins
Figure 24.34

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

Chemical Digestion: Fats
Figure 24.35

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

Fatty Acid Absorption Figure 24.36

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

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+

Electrolyte Absorption
K+ diffuses across the intestinal mucosa in response to osmotic gradients Ca2+ absorption: Is related to blood levels of ionic calcium Is regulated by Vitamin D and parathyroid hormone (PTH)

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

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)

Embryonic Development of the Digestive System
3rd 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 8th week – accessory organs are budding from endoderm

Embryonic Development of the Digestive System
Figure 24.37

Peritonitis – inflammation of the peritoneum caused by a piercing wound, perforating ulcer, or burst appendix Often, infected membranes tend to stick together localizing the infection Generalized or widespread peritonitis is dangerous and often lethal Treatment includes removing infectious debris and massive doses of antibiotics

Cleft palate – palatine bones, palatine process of the maxillae (or both) fail to fuse Tracheoesophageal fistula – opening between the esophagus and trachea Cystic fibrosis – impairs pancreatic activity

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 (aid 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

Overview of GI Tract Upper GI Tract Mouth and pharnyx provide entryway
Lead to Esophagus Esophagus wall consists of same layers found in remainder of GI tract epithelium (mucosa), submucosa (submucosal plexus), muscularis externa (circular and longitudinal muscles + myenteric plexus); serosa Secretory glands found throughout GI except colon exocrine glands (ducted) and endocrine (ductless) glands

Upper GI Tract Continued
Sphincters circular muscles located throughout digestive tract Lower Esophageal Sphincter allows passage of food into stomach Pyloric Sphincter Controls release of chyme from stomach to duodenum Ileocecal sphincter Stomach J shaped organ volume ranges from 50 to 1500 mL (2 -52 oz)

Lower GI tract and Accessory Organs
Small Intestine Duodenum (< 1 ft), jejunum and ileum (~9 ft) main site for nutrient digestion and absorption duodenum receives secretions from liver, gallbladder and pancreas Liver hepatocytes make bile from cholesterol right and left hepatic bile ducts join to form common hepatic duct unites with cystic duct leading to gallbladder

Lower GI tract and Accessory Organs
Gallbladder capacity to hold mL of bile functions to concentrate and store bile Common hepatic bile duct goes to duodenum (Sphincter of Oddi) Pancreas 2 types of active tissue Acini or ducted exocrine tissue produces digestive enzymes secreted into small ducts within pancreas which leads to common hepatic bile duct empties into duodenum via Sphincter of Oddi Ductless endocrine tissue secretes hormones, glucagon and insulin into blood

Structure of SI Epithelial surface (mucosa) structured to maximize surface area Large folds of mucosa (folds of Kerckring) Villi projections lined with 100s of absorptive cells contain blood capillaries and central lacteal Microvilla extensions of plasma membrane of absorptive cells possess surface coat of glycocalyx forms brush border most digestive enzymes produced by SI found here.

Structure of SI Crypts of Lieberkuhn pits located between villi
epithelial cells in these crypt migrate upward and out of crypts toward tips of villi turnover every 3-5 days Cells include paneth cells secrete proteins with unknown function globlet cells secrete mucus Enterochromaffin cells with endocrine functions

Structure of SI Gut Associated Lymphoid Tissue (GALT) Ileocecal valve
mucosa and submucosa Leukocytes (white blood cells) Found between intestinal absorptive cells T-lymphocytes, Natural Killer cells, Microfold cells Peyer’s Patches Aggregates of lymphoid tissue underneath M cells T-lymphocytes, B-lymphocytes and macrophages provide defense against bacteria and foreign bodies Ileocecal valve allows unabsorbed materials to leave ileum and enter cecum

Colon Cecum Ascending, transverse and descending sections
Sigmoid sections Haustra or pouches created by contraction of 1 or 3 muscular strips (tenaie coli) along with contraction of circular muscles Absorbs water and lytes

Regulation Of Digestive Process
Regulatory Peptides (GI hormones and neuropeptides) Gastrin (hormone) produced mainly by gastric (G) cells in stomach (pyloric gland) released upon entry of food into stomach stimulates HCl release gastric and intestinal motility pepsinogen release Cholecystokinin (CCK, hormone) produced by SI cells released upon entry of chyme into stomach amino acids, fat targets pancreas and gallbladder

Regulatory Peptides Secretin (hormone)
produced by cells of SI secreted in response to chyme (acid) into duodenum targets pancreas (HCO-3) may inhibit GI motility Gastric Inhibitory Polypeptide (GIP; hormone) produced by SI cells Inhibits gastric secretions and motility Simulates intestinal and insulin secretions

Regulatory Peptides Somatostatin Produced by pancreatic and SI cells
Paracrine released by endocrine cells but diffuse through extracellular space to gastric juice Inhibits gastrin secretion Increases release of GIP, secretin, motilin Inhibits gastric acid release, gastric motility, pancreatic exocrine secretions and gall bladder secretions

Regulatory Peptides Motilin
Small intestine Contraction of intestinal smooth muscle Vasoactive intestinal peptide (VIP; Neurocrine) Neurons within gut Stimulates intestinal secretions, relaxes most GI sphincters, inhibits gastric acid secretion and stimulates HCO3- Gastrin-releasing pepetide (GRP; Neurocrine) Released from nerves, stimulates release of HCL, gastrin and CCK

Neural Regulation Enteric Nervous System located in wall of GI tract
begins in esophagus and ends at anus controls peristaltic activity/GI motility (myenteric plexus) affected by parasympathetic and sympathetic nervous systems Acetylcholine increase GI motility Norepinephrine and epinephrine inhibit GI activity Also influences GI secretions (submucosal plexus)

Process of Digestion Oral Cavity and Salivary Glands
mastication of food mixed with salivary gland secretions parotid glands water, lytes and enzymes submandibular and sublingual glands water, lytes, enzymes and mucus Enzymes alpha amylase and lingual lipase

Process of Digestion Esophagus Entry of food results in peristalsis
acetylcholine LES LES pressure decreases upon swallowing Neural and hormonal regulation functions to prevent gastric reflux

Process of Digestion Stomach Body extends from LES to angular notch
includes fundus serves as reservoir as well as producer of gastric juice Antrum (Pyloric Portion) extends from angular notch to duodenum grinds and mixes food with digestive juice (chyme) provides strong peristalsis

Stomach Gastric Juices produced by 3 different gastric glands
Cardiac glands (fundus) mucus cells (HCO3- and mucus) and endocrine cells no parietal (oxyntic cells) Parietal glands (body) mucus cells, oxyntic cells (secrete HCl and IF), chief cells (secrete pepsinogen upon stimulation by acetylcholine) Pyloric glands (antrum) both mucus and oxyntic cells G cells that produce gastrin Acetylcholine stimulates chief, oxyntic and other gastric cells

Gastric Juices HCl Mucus Intrinsic Factor (IF)
activates inactive zymogen pepsinogen to active pepsin denatures proteins serves as bactericide nutrient release Mucus lubricates and protects gastric lining Intrinsic Factor (IF) necessary for vitamin B12 absorption

HCl Release from oxyntic cells stimulated by
acetylcholine, gastrin, CCK, histamine Histamine secreted from mast cells paracrine that binds to H2 receptors on parietal cells to stimulate HCl release mechanism used in drug therapy to lower acid Drugs (tagamet) prevent histamine from binding to H2 receptors decreases acid release Parietal cells contain Potassium chloride transport system Hydrogen (proton) potassium ATPase exchange system Proton pump Result: secretion of hydrogen and chloride Proton pump targetted/exploited in drug therapy to lower acid Prilosec binds to proton pump

Gastric Emptying GI hormones and neuropeptides affect a pacemaker (between fudnus and body of stomach) determines frequency and rate of contractions 1-5 mL (<1 tsp) chyme allowed to enter duodenum every 30 seconds Fat appears to slow gastric emptying Inhibitors Secretin, GIP, Somatostatin, CCK

Small Intestine Chyme has low pH Digestive juices
SI protected by pancreatic secretions and secretions from Brunner’s glands (located in mucosa and submucosa of the first few centimeters of the duodenum) Secretin and CCK Digestive juices Glands within crypts of Lieberkuhn Pancreas Responsible for enzymes that digest 50% CHO, 50% protein, 90% lipids

Digestive Juice Pancreatic Proteases
trypsinogen, chymotrypsinogen, procarboxypeptidases, proelastase, collagenase secreted in vesicles must be activated trypinsogen converted to trypsin by enteropeptidase (enterokinase) and by free trypsin hydrolyze peptide bonds either internally or from ends mono, di and some tri can be absorbed Brush border aminopeptidases to hydrolyze further

Digestive Juice CHO Lipids Pancreatic alpha amylase
hydrolyzes alpha 1-4 bonds Alpha dextrinase to hydrolyze 1-6 branches Brush border enzymes (isomaltase, maltase, sucrase, lactase) Lipids Pancreatic lipase hydrolyzes TG to yield MG, FFA and glycerol Phospholipase and cholesterol esterase Bile required and sometimes pancreatic colipase (binds TG and pancreatic lipase displacing bile)

Bile Synthesis Made in liver cells from cholesterol
cholesterol oxidized chenodeoxycholic acid and cholic acid conjugated to glycine or taurine glycocholic acid and taurocholic acid conjugation of bile acids with amino acids improves its ability to form micelles cholesterol and PLs secreted into bile bile acid dependent frx Water, Lytes and bilirubin secreted in bile

Bile Storage Gallbladder Concentrates bile by removing 90% of water
Stores bile Stimulated to release bile by CCK CCK secreted in response to amino acids and lipids Bile is secreted into duodenum

Function of Bile Digestion Absorption Bile acids are amphipathic
Contain polar (hypdrophic) and non-polar (hydrophobic) areas Decrease surface tension of fat Hydrophobic part surrounds and dissolves into the ingested fat molecule and helps break apart Permits emulsification of fat Increases exposed surface area of lipids Allow digestive enzymes (lipase) to get close to fat Absorption Micelle Formation

Micelles Contain ~ 40 bile salt molecules
Hydrophobic centers, hydrophilic periphery Fatty acids, MAGs, cholesterol, fat soluble vitamins enter micelles Mixed Micelles Micelles travel to brush border Contents diffuse through unstirred water layer and into enterocytes Bile acids released back to lumen for reuse

Enterohepatic Circulation
> 90% of bile acids secreted in duodenum are reabsorbed into ileum Enters portal vein for transport via blood back to liver Reabsorbed bile acids are secreted in bile along with newly made bile acids New bile mixed with recirculated bile is sent via cystic duct for storage in gallbladder Pool of bile (2-4 g) may recycle 1-2 times/meal

Secondary Bile Acids Bile acids not reabsorbed in ileum may be deconjugated by bacteria in colon deconjugated bile acids form secondary bile acids cholic acid is converted to deoxycholic acid which may be reabsorbed chenodeoxycholic acid is converted to lithocholic acid which is excreted in feces ~ 0.5 g of bile salts are lost in feces daily Some fibers bind bile salts and acids and prevent conversion to secondary bile acids (possible risk factor in colon cancer?)

Decreasing Blood Cholesterol
Only route of cholesterol excretion is in feces By increasing excretion of bile in feces, one can lower blood cholesterol levels necessitates use of body cholesterol for synthesis of new bile acids drugs (powdered resins) bind bile and enhance excretion from body (cholestyramine) soluble fiber behaves like resins

Role of Intestinal Brush Border in Digestion
CHO Digestion Isomaltase 1-6 bonds in oligosaccharides and dextrins Sucrase alpha 1-4 bonds in sucrose and maltose Glucoamylase, glucosidase, maltase alpha 1-4 bonds in oligosaccharides, maltotriose and maltose Maltase, Lactase and Sucrase

Role of Intestinal Brush Border in Digestion
Protein Digestion Aminopeptidases hydrolyze N terminal amino acids from oligopeptides, tripeptides and dipeptides Tripeptidases = 1 free aa + dipeptide Dipeptidases = 2 free aa

Absorption Begins in duodenum Continues throughout jejunum and ileum
May be accomplished by simple diffusion facilitated diffusion active transport pinocytosis or endocytosis paracellular absorption Mechanism depends on nutrient solubility; electrical gradient; size

Colon Greater absorption of sodium, chloride and water
90-95% of water and sodium reabsorbed Secretion of bicarbonate into colon neutralize acids produced by colonic anaerobic bacteria via action on CHO Progressive dehydration of unabsorbed materials 1 L of chyme reduced to < 200 mL of defecated material

Colon Bacteria Protein digestion Probiotics and Prebiotics
synthesize small amounts of vitamin K, biotin and folate CHO digestion (fiber) Produce acids in colon include short chain fatty acids acetate, butyrate (preferred energy source for colon cells; regulate cell growth), propionate may be absorbed by colonocyte Protein digestion Ammonia (must be controlled in those with liver disease) Probiotics and Prebiotics Increase populations with no adverse health effects and decrease populations with adverse health effects (pathogenic strains)

Silv. p.686 The Large Intestine

NaCl Absorption by the Colon
Silv. p.687 NaCl Absorption by the Colon

Digestive Secretions: (7 L / Day From Tissues into Lumen)
Salivary glands Pancreas Water Enzymes Mucus Ions: H+, K+, Na+ HCO3-, Cl- Mass Balance (H2O)

Enzymatic digestion in the human digestive system

Motility: Smooth Muscle Contractions
Tonic – support Phasic – move products Parastalsis – moves  Segmentation – mixes Figure 21-4: Contractions in the GI tract

Digestion of fats

Regulating Digestion: CNS and Enteric Nervous System (ENS)

Gastric Phase: The Stomach
Figure 21-15: The mucus-bicarbonate barrier of the gastric mucosa

Chapter 24 Pathology

Digestive Health: Protection & Problems
Immune defense: M-cells, Peyer's patches, lymphocytes Irritable bowel disease – chronic inflammation Diarrhea: leads to dehydration (4 million deaths/yr) Osmotic-solutes prevent H2O reabsorption Secretory- bacterial toxins ("flush out' pathogens) Vomiting (emesis) can lead to alkalosis Ulcers- Helicobacter pylori "heart-burn"  acid reflux disease (GERD)

Peptic Ulcer Lesions in the wall of the stomach or duodenum.
Primarily caused by bacteria. Treated with antacids AND antibiotics.

Appendicitis Usually caused by fecal obstruction
or anatomical “kinking” of the appendix. A rupture leads to peritonitis.

(Inflammation of the Peritoneum)
Peritonitis (Inflammation of the Peritoneum) Usually results from an infection caused by a external or internal penetrating wound. Bacteria enter the sterile areas of the body surrounding the digestive system. May become lethal if not treated with high doses of antibiotics.

(Inflammation of the liver)
Hepatitis (Inflammation of the liver) Caused by drugs, chemicals, viruses, alcohol, etc. Viral “Hepatitis A” is usually caused by the ingestion of food. Viral “Hepatitis B” and “Hepatitis C” are “blood-borne” pathogens.

Hepatitis – inflammation of the liver often due to viral infection Viruses causing hepatitis are catalogued has HVA through HVF HVA and HVE are transmitted enterically and cause self-limiting infections Hepatitis B is transmitted via blood transfusions, contaminated needles, and sexual contact, and increases the risk of liver cancer Hepatitis C produces chronic liver infection Nonviral hepatitis is caused by drug toxicity and wild mushroom poisoning

Diverticulitis Small herniations of the mucosa in the large intestine.
These areas can become inflamed and possibly rupture. Prevention is the treatment of choice. A diet high in fiber will help prevent diverticulitis.

Diverticulosis

Emesis (Vomiting) Can be caused by microbes, allergies,
gluttony, poisons, etc.

Diarrhea Movement of fecal material through the GI Tract too rapidly.
May be caused by microbes, spicy foods, stress, etc.

Constipation Infrequent defecation of fecal material.
Usually caused by a diet low in fiber and water.

Cirrhosis of the Liver Condition where liver cells are
destroyed and replaced by fibrous connective tissue. Alcoholism is a common cause of cirrhosis.

Gall Stones (Biliary Calculi) Crystalization of cholesterol and bile
salts. Blocks the bile duct or fills the gall bladder.

Jaundice Build-up of bile in the skin and
conjunctiva causing a yellowing of the skin. May be caused by damage to the liver, gall bladder, or any of the ducts that service these organs.

Jaundice

Bulemia Nervosa Condition where a patient binges on
food and then purges with either laxatives or vomiting. Considered a psychological disorder where the patient has a fear of gaining weight. Treated with psychotherapy.

Anorexia Nervosa Psychological disorder where the patient
has a false perception of their own weight. Patient denies their own appetite. Patients are usually % below normal body weight. Extreme cases are lethal. Closely associated with bulimia nervosa.

Flatulence Excessive intestinal gas resulting
from bacteria in the intestines, diet, or swallowing air.

Cystic Fibrosis Genetic disorder where excess mucous is produced.
Causes a blocking of the pancreatic duct, therefore enzymes cannot enter the duodenum from the pancreas. Treated by giving digestive enzymes orally.

NaCl Secretion by the Colon
Silv. p.688 NaCl Secretion by the Colon

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 Colon cancer is the 2nd largest cause of cancer deaths in males (lung cancer is 1st) Forms from benign mucosal tumors called polyps whose formation increases with age Regular colon examination should be done for all those over 50

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)

Food Poisoning: Salmonella
Salmonella is spread by: Contaminated eggs and egg products Infected food handlers with feces-contaminated hands Salmonella can cause: Bacteremia 4 to 7 days after infection Endocarditis, thrombi, bone infections, arthritis, and meningitis Diagnosis is by positive stool samples Salmonellosis is treated symptomatically

Hiatal hernia structural abnormality in which the superior part of the stomach protrudes slightly above the diaphragm Prolonged episodes can lead to esophagitis, ulcers, and cancer

Age related changes in the digestive system include:
Thinner, more fragile epithelium Reduction in epithelial stem cells Weaker peristaltic contractions Effects of cumulative damage Increased cancer rates

Digestive Disorders Anorexia Nervosa Appendicitis Barrett’s esophagus
Buliemia Nervosa Cancer Cavities Celiac Disease (gluten enteropathy) Cirrhosis of the Liver Constipation Crohn’s Disorder Cystic Fibrosis Diarrhea Diverticulitis Emesis Gall Stones GERD Gingivitis Hepatitis Hiatal Hernia Jaundice Lactose Intolerance Mumps Peptic Ulcer Periodontitis Peritonitis

Chapter 24 The Digestive System Part A.

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Chapter 24 The Digestive System Part A.

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