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