DIGESTIVE SYSTEM. Gastroenterology - the study of the digestive sytem.
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Transcript of DIGESTIVE SYSTEM. Gastroenterology - the study of the digestive sytem.
Structures of Digestive System•1. Gastrointestinal tract (GI)▫Also called the alimentary canal▫Long continuous tube from the mouth to the anus (~ 9 meters long)▫Includes mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anus
•2. Accessory Organs▫Teeth, tongue, salivary glands, liver, gall bladder, pancreas (most do not come in direct contact with the food)
Functions of Digestive System
•1. Ingestion - eating/drinking•2. Secretion - ~ 7L of H2O, acid, buffers, enzymes per day•3. Mixing/Propulsion - alternate contraction & relaxation of smooth muscle lining the GI tract▫Mixes food & secretions, propels them toward the anus
•4. Digestion▫Mechanical - begins in the mouth with teeth chewing & grinding food▫- continues in the stomach with churning & mixing food with digestive enzymes▫Chemical – carbohydrates, proteins and lipids are broken down ▫- digestive enzymes speed up this process
•5. Absorption – fluids and molecules from chemical digestion pass through the lining of the small intestine into the bloodstream•6. Defecation - elimination of waste material (feces…more commonly known as “poop”)
Walls of the Digestive Tract•1. mucosa – innermost mucus membrane layer•2. submucosa – surrounds mucosa•3. muscularis - outside the submucosa (2 layers of smooth muscle)•4. serosa – below the diaphragm (secretes serous fluid for lubrication)
Upper GI Tract
•Includes:▫mouth (salivary glands, tongue, teeth, hard & soft palate)▫Pharynx▫Esophagus▫Stomach
Salivary Glands
•3 main glands that produce and secrete saliva▫1. parotid gland – largest; anterior & inferior to the ear▫2. sublingual gland – under the tongue▫3. submandibular gland – floor of the mouth
Composition of Saliva•99.5% H2O•0.5% solutes, including Na+, K+, Cl-, HCO3
-, PO4-3, bacteria inhibitors, enzymes
and mucus•Salivary amylase – breaks down starches•Lingual lipase – breaks down lipids•HCO3
-, PO4-3 act as buffers to keep pH
between 6.35-6.85•Mucus – acts as lubrication for food
Upper GI Tract SecretionsSubstance
Secretion
Classif-ication
Secreted By
Secreted Into
Acts On Function
Saliva Salivary Amylase
Enzyme
Salivary glands
Mouth starch Breaks down starch to polysac-charides
Lingual Lipase
Enzyme
Salivary glands
Mouth Lipids (in stomach)
Breaks down lipids
Mucus ~~~~~~
Salivary glands
mouth Food Moistens food
Functions of Saliva
•1. cleansing the mouth•2. solvent for taste•3. lubricate food•4. breakdown starches•5. inhibits bacterial growth
Salivation
•Controlled by the nervous system•Touch, taste, smell, sight & sound of food cause increases in salivation•Normal conditions – moistens mouth & esophagus and cleanses teeth• stress – secretions stop (mouth gets dry)•Eating – secretions increase
Function of the Tongue in Digestion
•Move food in the mouth and to back of mouth for swallowing (degluttition)•Contains taste buds – found on the papillae (bumps) of the tongue•Gustation - taste
Mechanical Digestion in the Mouth
•Mastication – chewing▫Food is manipulated by the tongue, ground by the teeth and mixed with saliva to form a bolus (chewed up, soft mass)
Chemical Digestion in the Mouth
•Salivary amylase – breaks down polysaccharides (starch) into maltose▫Continues in the stomach ~ 1 hour after being swallowed
•Lingual lipase – breaks down (triglycerides) lipids into fatty acids▫Becomes activated in the acidic stomach environment, so happens after food is swallowed
Teeth
•Two sets▫Deciduous (baby teeth) – 20▫Permanent (including wisdom) -32•3 types of teeth▫Incisors - sharp edges (biting,cutting)▫Cuspids – pointed (grasp, tear)▫Molars - flat (grinding)
Parts of teeth•Crown - visible portion of tooth•Enamel - hardest substance in the
body; surrounds dentin in the crown•Root -portion that is in the sockets of
mandible and maxilla•Pulp - central core of tooth; blood
vessels & nerves•Dentin – surrounds pulp cavity; a living
cellular substance similar to bone•Neck –region between crown and root•Root canal - pulp cavity
Other parts of the Mouth
•Hard palate - roof of the mouth•Soft palate - skeletal muscle & connective tissue; ends in the uvula•Uvula - moves food away from the nasal cavity & into the oral pharynx
Pharynx
•3 parts of pharynx▫Nasopharynx – upper region; contains tonsils & adenoids; functions in respiration▫Oropharynx – behind oral cavity; first region where food enters when swallowed▫Laryngopharynx - behind larynx
Stages of Swallowing
•1. Voluntary Stage – bolus to back of mouth and into oropharynx•2. Pharyngeal Stage – bolus from oropharynx into esophagus
Involuntary Airway closes, breathing is interrupted Soft palate & uvula close off nasopharynx Epiglottis blocks respiratory tract
•3. Esophageal Stage - bolus goes from esophagus into stomach▫Peristalsis - rhythmic contractions that move the bolus along the digestive tract▫When bolus is at the end of the esophagus, the cardiac sphincter relaxes and food enters the stomach
Functions of the Stomach
•1. mix saliva, food & gastric juices to form chyme (semisolid mixture)•2. hold food until it moves into the small intestine•3. secretes gastric juice into stomach•4. secretes gastrin into blood
Mechanical Digestion in the Stomach
•Food enters stomach through a valve called the gastroesophageal sphincter, which keeps food from going back into the esophagus•Mixing waves in the body of the stomach & the pylorus move the chyme into the duodenum
Chemical Digestion in the Stomach
•Gastric Juice consists of:▫1. Mucus – protects stomach lining▫2. Pepsinogen - breaks down proteins▫3. Gastric lipase – breaks down fats▫4. HCl – kills bacteria; stimulates secretion of gastrin (a hormone)▫5. Intrinsic factor - necessary to absorb Vitamin B12 in the small intestine
Upper GI Tract SecretionsSubstance
Secretion
Classif-ication
Secreted By
Secreted Into
Acts On Function
Gastric Juice
Pepsin (Pepsinogen)
Enzyme Gastric Glands
stomach Proteins Breaks proteins into peptides
Gastric Lipase
Enzyme Gastric Glands
Stomach Lipids Breaks down lipids
HCl Acid Gastric Glands
Stomach Contents of stomach
Decreases pH; kills bacteria
Mucus ~~~~~~
Gastric Glands
Stomach Walls of stomach
Protects from acid
Gastrin Hormone Gastric Glands
Blood Gastric glands; sphincters
Stimulates gastric glands & cardiac sphincter; inhibits pyloric & ileocecal
Intrinsic Factor
~~~~~~
Gastric Glands
Stomach Vitamin B12
Lets B12 get absorbed
3 Phases of Stomach Digestion•1. Cephalic Phase▫Controlled by nerve stimuli▫Sight, smell, sound or taste of food causes increased nerve impulses▫Stomach secretes pepsinogen, HCl and mucus into the chyme▫Gastrin is secreted into the bloodstream▫Stomach churning increases
•2. Gastric Phase▫Stomach stretches to accommodate food
▫pH in stomach increases▫Gastric juices are secreted▫Gastrin – hormone secreted by the stomach Stimulates gastric glands Strengthens the contraction of the cardiac sphincter
Relaxes pyloric & ileocecal sphincters▫pH below 2 - secretions inhibited▫pH above 2 – secretions stimulated
•3. Intestinal Phase▫Activated by the small intestine▫Inhibitory effect on the stomach▫Slowing of stomach emptying▫2 hormones secretedSecretin – decreases gastric secretionsCCK (cholecystokinin) - inhibits stomach emptying
▫Stomach empties in 2-4 hours…first carbs, then proteins, lastly fats
Small Intestine•Duodenum (approx 10 inches)▫Recieves chyme from the stomach▫Pancreatic juice & bile enter here
•Jejunum (approx 3 feet)▫Begins where duodenum turns downward
•Ileum (approx 6 feet)▫Ends at ileocecal sphincter, which prevents feces from backing into small intestine
mesentary – thin tissue that prevents small intestines from twisting or tangling
Functions of Small Intestine
1. Digestion2. Absorption
- food remains in intestine for 3-5 hours- Intestinal glands secrete intestinal juice, which contains enzymes:- sucrase, lactase, maltase, peptidase & enterokinase
Digestive Secretions – Lower GISubstance
Secretion
Classif-ication
Secreted By
Secreted Into
Acts On Function
Intestinal Juice
Sucrase Enzyme Small Intestine
Small Intestine
Sucrose (breaks into - )
Glucose & fructose
Intestinal Juice
Lactase Enzyme Small Intestine
Small Intestine
Lactose (breaks into-)
Glucose & galactose
Intestinal Juice
Maltase Enzyme Small Intestine
Small Intestine
Maltose (breaks into -)
2 or 3 molecules of glucose
Intestinal Juice
Peptidase
Enzyme Small Intestine
Small Intestine
Peptides (breaks into -)
Amino acids
Intestinal Juice
Entero-kinase
Enzyme Small Intestine
Small Intestine
Trypsin-ogen (breaks into -)
trypsin
Characteristics of Small Intestine that increase surface area for absorption
•1. Length - ~ 10 feet long•2. Villi – finger-like folds in mucosa•3. Microvilli – hair-like projections in villi•4. Circular folds – causes chyme to “spiral”
instead of moving straight through
- 90% of absorption occurs in small intestine- nutrients, electrolytes, water, Vitamins A, B, C,
D, E and K are absorbed (Vitamin B12 must be bound to intrinsic factor in order to be absorbed)
Hormones of the Small Intestine•These secretions act to stimulate the pancreas▫1. Secretin – tells the pancreas to secrete sodium bicarbonate ions to increase pH
▫2. CCK (Cholecystokinen) – tells the pancreas to secrete digestive enzymes & gall bladder to secrete bile
Digestive Secretions – Lower GISubstance Secretion Classifi-
cationSecreted by
Secreted Into
Acts On Function
Intestinal Juice
Secretin Hormone
Small intestine
Circulatory system (blood)
Stomach & pancreas
Inhibit gastric secretions, stimulate pancreatic buffers
Intestinal Juice
Chole-cystokinin (CCK)
Hormone
Small intestine
Circulatory system (blood)
Stomachpancreas & gall bladder
Inhibit stomach emptying, stimulate pancreatic enzymes, stimulate release of bile
Pancreas
•Produces and secretes insulin, which regulates blood sugar
•Produces pancreatic juice which is secreted into the small intestine
Pancreatic Juice
•Contains water, salts, sodium bicarbonate and enzymes▫sodium bicarbonate – keeps pH between 7.1-8.2 to buffer the acidic chyme from the stomach, stop the action of pepsin, and activate digestive enzymes in the small intestine
Pancreatic Enzymes•There are pancreatic enzymes that act to
break down carbohydrates, proteins and lipids.▫Pancreatic amylase - acts on carbohydrates▫Trypsin & chymotrypsin – act on proteins,
but are secreted in an inactive form so as to protect the pancreas from their effects (trypsinogen & chymotrypsinogen) Trypsinogen & entrokinase react to form
trypsin Trypsin and chymotrypsinogen react to form
chymotrypsin▫Pancreatic lipase - act on lipids
Digestive Secretions – Lower GISubstance
Secretion Class-ification
Secreted By
Secreted Into
Acts On Function
Pancreatic Juice
Pancreatic Amylase
Enzyme
Pancreas Small Intestine
Carbohy-drates
Break into disacch-arides
Pancreatic Juice
Trypsin (trypsino-gen)
Enzyme
Pancreas Small Intestine
Proteins Break into peptides
Pancreatic Juice
Chymotryp-sin (chymotry-psinogen)
Enzyme
Pancreas Small Intestine
Proteins Break into peptides
Pancreatic Juice
Pancreatic Lipase
Enzyme
Pancreas Small Intestine
Lipids Break into fatty acids
Liver•Heaviest gland, 2nd largest organ in the body•Multi-lobed organ•Hepatocytes – liver cells•Functions of liver▫1. produces bile - a yellow-greenish fluid consisting
of water, bile salts (helps break down fats), bile pigments (gives urine & feces their color) and cholesterol (a by-product of lipid metabolism)
▫2. stores glycogen▫3. filtration of blood absorbed from small intestine▫4. detoxification – alters chemical composition of
harmful substances to make them less harmful
Gall Bladder
•Function is to store and concentrate bile
•Fats in chyme cause CCK to be secreted into the blood…CCK, in turn, causes secretion of bile
Summary of Carbohydrate Digestion
•1. Salivary Amylase - secreted in mouth; breaks starches into maltose (a disaccharide)
•2. Pancreatic Amylase - secreted into small intestine; breaks polysaccharides into disaccharides
•3. Secreted into small intestine; breaks disaccharides into monosaccharides▫Sucrase – sucrose into glucose and fructose▫Lactase – lactose into glucose and galactose ▫Maltase - maltose into glucose (2-3
molecules)
Summary of Protein Digestion•1. Pepsin – produced & secreted in
stomach in inactive form of pepsinogen; breaks proteins into peptides
•2. Trypsin & Chymotrypsin - secreted from pancreas into small intestine in inactive form of trypsinogen and chymotrypsinogen; breaks proteins into peptides
•3. Peptidases – produced & secreted in small intestine; breaks peptides into amino acids
Summary of Lipid Digestion
•All three break lipids into fatty acids
•1. Lingual lipase – secreted in the mouth
•2. Gastric lipase - produced & secreted in the stomach
•3. Pancreatic lipase - secreted from pancreas into small intestine
Large Intestine•Approx. 5 ft long, 2 ½ inches in diameter•Begins at ileocecal sphincter (where
material passes from small intestine into large intestine)
•Cecum – inferior to ileocecal sphincter; basically a blind pouch
•Colon – longest portion; ascending, transverse, descending
•Sigmoid – S-shaped curve•Rectum - last 8 inches•Anal Canal - last inch of rectum; opens to
outside at the anus
•No villi present nor enzymes secreted•Goblet cells – secrete mucus for
lubrication•Haustra – a series of pouches that give the
colon a “puckered” appearance
•Functions of Large Intestine▫1. abosorb water▫2. produce and excrete solid waste
Formation and Expulsion of Feces
•Water and electrolytes are absorbed•Bacteria (normally present) - break down any
remaining carbs and proteins▫ - they also produce hydrogen, carbon dioxide
and methane gases, which contribute to flatus (gas in the colon)
• Feces – consists of water, salts, sloughed off cells, bacterial, unabsorbed or indigestible parts of food & mucus
•Defecation – discharge of feces from the rectum▫ - under voluntary control of external anal
sphincter