Digestive System
Lesson Objectives
• List four functions of the digestive system.• Describe the four layers of the digestive tract.• Describe the structure and functions of the
organs of the digestive tract.• Describe the structure and functions of the
accessory organs of the digestive tract.
Digestive System
Other names:-Alimentary Canal-Gastrointestinal (GI) Tract
Functions of the Digestive System
Ingest foodDigest it
–Mechanical –Chemical
Absorb nutrientsExcrete waste
Overview of the Digestive SystemMouthPharynxEsophagusStomachSmall intestineLarge intestineRectum, anusAccessory organs--Salivary glands --liver--gallbladder--pancreas
Four Layers of the Digestive TractMucosal layer (innermost)
hormones, enzymes, mucus
Submucosal layernerves, glands, blood vessels
Muscle layer- Circular and longitudinal
Mixing, mashing action - Peristaltic action
“wave-like” motion
- Enteral nervous system
Serosal layer (outermost)- Peritoneal membranes
Peritoneal Membranes• Anchor organs• Behind the
digestive organs–Mesentery and
mesocolon
• In front of organs–Greater or lesser
omentum
Peritoneal Membranes
Greater omentum- “Lacy Apron” Mesentery
Peristalsis
• Waves of muscle contraction, relaxation
• Pushes food from mouth toward anus
• Peristaltic movements differ from organ to organ
Oral Cavity = Mouth• Teeth: Mastication
– 2 sets: • Deciduous: 20 “Milk teeth”• Permanent: 32
• Tongue: Swallowing– Forms bolus (food ball)
• Salivary glands - Parotid - Submandibular (below jaw) - Sublingual (below tongue)
Buccal cavity= gums to cheeks/lips
The Tooth
Three parts:1.Crown = above gum(gingiva)2.Neck= connects crown to root 3.Root= embedded in jaw (dentin), has pulp(sensation)
Shape
Shape and location indicate function
molar = grind
Cuspids (Canines) = tear and graspIncisors = tear and grasp
Premolars (bicuspids) = grind
TongueTwo Roles1.Positioning of Food
a) Bolus (food ball)
2.Taste Sensationa) Taste buds (poison)
Parts: Frenulum: anchorSublingual blood supply
Eating and Swallowing• Mouth
– Hard and soft palates– Uvula (for swallowing)
• Pharynx (throat)– Laryngopharynx – Oropharynx
• Epiglottis: covers trachea
• Esophagus - Esophageal sphincters
Pharyngoesophageal Lower esophageal
Borborygmus?
•What is Borborygmus???
Functions of the Stomach
• Regulates rate of gastric emptying• Secretes gastric juice, HCl• Secretes gastric hormones • Digests limited amount of food• Absorbs limited substances
Parts of the Stomach • Fundus• Body• Rugae• Lesser curvature• Greater curvature• Pylorus• Pyloric sphincter
Muscles of the Stomach
• Longitudinal• Oblique• Circular• Mixing and
mashing chyme• Peristalsis
Stomach Structure: Mucosa• Mucous cells• Parietal cells
- HCl - Intrinsic factor
• Chief cells - Digestive enzymes
• Chyme: paste-like mixture
Small Intestine: Parts and Functions
Parts (Dow Jones Industrials)(DJ Illy)
-Duodenum-Jejunum-IleumFunctions
-Digests-Absorbs-Secretes hormones and digestive enzymes
Villi and Microvilli
• Folds increase area for absorption
• Inside composed of capillaries and lacteals
• Deliveres to hepatic portal system and lymphatics
Duodenum
• 10 inches• Receives Chyme of
stomach• Accessory organ
secretions enter here• Where MOST
DIGESTION and ABSORPTION OCCURS
The RestJejunum (2nd Part)•8 Feet Ileum (3rd Part)
•12 feet
•Connects to Cecum of L.I.– Ileocecal valve
•Contains Peyer’s patches
-Control bacterial numbers of L.I.
Large Intestine
• 5 feet• Cecum
– Vermiform appendix
• Colon-Ascending-Transverse-Descending-Sigmoid
• Rectum• Anal Canal Anus
Functions of the Large Intestine
• Absorption of water and electrolytes-Constipation: absorb too much water-Diarrhea: not absorbing enough water
• Synthesis of vitamins by intestinal bacteria• Temporary storage of waste• Elimination of waste (feces) and gas (flatus)
Landmarks of Large Intestine
• Hepatic flexure: curve near liver (right side)• Splenic flexure: curve near spleen (left side)• Anal canal has 2 sphincters• Internal sphincter
– (involuntary)
• External sphincter– (voluntary), potty training
Clinical Conditions: Stomach
A. Gastric ulcerB. Hiatal herniaC. Nasogastric tubeD. Gastric resectionE. Pyloric stenosisF. Vagolytic effectsGastrostomy tube
Clinical Conditions: Large IntestineA. Intestinal
obstructionB. ColostomyC. HemorrhoidsD. Enema
Accessory Digestive Organs
• Liver
• Gallbladder
• Pancreas
Liver Functions • Synthesis of bile salts and secretion of bile• Synthesis of plasma proteins• Storage of glucose, fat-soluble vitamins• Detoxification
– Main organ for drug detoxification
• Excretion of bilirubin, cholesterol, drugs• Metabolism of carbohydrates, protein, fats• Phagocytosis: Kupffer cells (hepatic
macrophages)
Hepatic Portal System• Liver processes end
products of digestion
• Discharging blood through hepatic veins and into Inferior Vena Cava
Biliary Tree
• Ducts connect liver, gallbladder, pancreas to duodenum
• Hepatic ducts• Cystic duct• Common bile duct
– Ampulla of Vater– Sphincter of Oddi
Gallbladder
• Pear-shaped sac -underside of the liver -concentrates and stores bile
• Attached to common bile duct by cystic duct• Fat in the duodenum stimulates release of the
hormone cholecystokinin (CCK)-CCK causes gallbladder to contract, eject bile into common bile duct and duodenum
Bile• Formed from blood
in the liver lobules • Assists in digestion of
fat• Stored in gallbladder• Composition
-Water-Cholesterol-Bile pigments-Salts
Clinical Conditions
• Celiac Disease– Unable to absorb certain
nutrients
• Gallstones • Bleeding
– Loss of clotting factors (liver failure)
• Esophageal varices– Bleeding into esophagus
• Acute pancreatitis
Lesson 23-2 Objectives
• Explain the physiology of digestion and absorption.
• Describe the effects of amylases, proteases, and lipases.
• Describe the role of bile in the digestion of fats.
• Describe five categories of nutrients.
Nutrition Basics• Mechanical Digestion: change in size• Chemical Digestion: change in
chemical composition
• Food-Carbohydrates-Proteins-Fats-Vitamins and Minerals
• Specific Enzymes for each type– Ending of –ase indicates enzymes
Fats: Digestion and Absorption
• Fats are insoluble in water.• Emulsification
-Bile splits big fat globules into small ones.-Bile salts make fat water- soluble.
• Digestion-Accomplished by lipases-End products: Fatty acids and glycerol, absorbed by lacteals
Carbohydrates: Digestion and Absorption
• Monosaccharides-Simple sugars, end products of digestion absorbed by villi
• Disaccharides-Digested by disaccharidases to monosaccharides
• Polysaccharides-Digested by amylases to disaccharides
Proteins: Digestion and Absorption
• Gastric HCl unravels strands of protein
• Proteases digest protein into amino acids, which are absorbed into villi
• Common proteases-Pepsin, stomach-Trypsin, pancreas-Chymotrypsin, pancreas-Enterokinase, duodenum
Digestion and Absorption: Summary
• Trace the flow of food from the mouth to the anus.
• Point out entrance of each accessory organ into the digestive tract.
Nutrition: Concepts to Know
• Nutrition: Study of the relationship of food to body function
• Five categories of nutrients– Carbohydrates– Proteins– Lipids– Vitamins– Minerals
Nutrition Concepts: Carbohydrates
Simple Sugars
• Monosaccharides• Disaccharides
Complex Carbohydrates
• Polysaccharides• Consist primarily of
starch and fiber• Most carbohydrate
consumption should be in this form.
Nutrition Concepts: Proteins
• Essential amino acid: Not synthesized by the body; must be consumed
• Nonessential amino acid: Synthesized in the body; not essential to consume
• Complete protein: Contains all the essential amino acids
• Incomplete protein: Does not contain all essential amino acids
Nutrition Concepts: Fats
• Saturated fatty acid: Solid at room temperature
• Unsaturated fatty acid: Oil; liquid at room temperature
• Essential fatty acid: Not synthesized by the body and must be consumed; linoleic acid is an important component of cell membranes
Nutrition Concepts: Vitamins
• Small organic molecules that help regulate cell metabolism
• Fat-soluble vitamins– Vitamins A, D, E, and K– Can be stored in the body
• Water-soluble vitamins– Vitamins B and C– Most are not stored by the body
Nutrition Concepts: Minerals
• Inorganic substances needed for normal body function
• Sodium, chloride• Potassium• Calcium, phosphorus, magnesium• Iron• Iodine• Trace elements
Appetite Control
• Hypothalamus– Feeding center– Satiety center
• Theories of satiety– Glucostat hypothesis– Lipostat hypothesis