DIGESTIVE SYSTEM AND BODY METABOLISMChapter 14
ANATOMY Two main parts
Alimentary canal Performs the following
functions: Ingestion Digestion Absorption Defecation
Accessory digestive organs Teeth Tongue Digestive glands
ALIMENTARY CANAL AKA Gastrointestinal (GI) Tract
Continuous, hollow tube winding through the ventral cavity
Open at both ends Contains the following organs:
Mouth Pharynx Esophagus Stomach Small and Large Intestines
PARTS OF ALIMENTARY CANAL Oral Cavity
Lined by mucous membrane Teeth: mechanical digestion Salivary glands: moisten food so it can be swallowed Tongue: helps mix saliva with food; involved in mechanical
digestion Uvula: “dangly thing;” projection of the soft palate
Pharynx Connects digestive and respiratory systems
Epiglottis: flat of skin that closes to prevent food from going into trachea Walls composed of two layers of muscle
Inner layer-longitudinal Outer layer-circular (constrictor muscles) Alternating contractions push food into esophagus (below)
Called peristalsis
ORAL CAVITY ANATOMY
PARTS OF ALIMENTARY CANAL, CONT. Esophagus
Runs from pharynx to stomach About 10 inches long
From esophagus to large intestine, walls are made of four layers: Mucosa Submucosa Muscularis externa Serosa
MUCOSA // SUBMUCOSA Innermost layer Moist Functions in secretion
and absorption Epithelium and
smooth muscle Esophagus: stratified
squamous epithelium Resists friction
The rest: simple columnar epithelium Better for absorption
Beneath mucosa Made of connective
tissue Contains blood
vessels, nerves, lymphatic tissue
MUSCULARIS EXTERNA // SEROSA Muscular layer Contains two layers
Circular and Longitudinal muscles
Outermost layer Serous membrane
Layer of flat fluid-producing cells Visceral peritoneum Visceral peritoneum
continuous with parietal peritoneum Lines
abdominopelvic cavity via mesentery
ALIMENTARY CANAL-BASIC STRUCTURE
STOMACH C-shaped; on LEFT side of abdominal cavity Has four regions
Cardiac region: where food enters from esophagus Lower esophgeal sphincter: prevents backflow into
esophagus Fundus: expanded part lateral to cardiac region Body: middle part; largest part Pylorus: funnel-shaped; next to small intestine
Pyloric sphincter: valve that controls emptying of stomach Inside curve: lesser curvature Outside curve: greater curvature Folds in stomach lining: rugae
STOMACH, CONT. Stomach is site of secretion Glands:
Parietal cells-secrete HCl Chief cells-secrete pepsinogen Mucous glands;coat inside to protect from HCl
Gastric ulcer: erosion of mucous layer/lining of stomach
Perforated ulcer: hole in stomach Most digestive activity is in pylorus
After processing, food is called chyme (looks like thick cream)
SMALL INTESTINE The major digestive
organ Large muscular tube,
divided into 3 sections: Duodenum
10 inches long Attaches to stomach
Jejunum About 8 feet long
Ileum About 12 feet long
SMALL INTESTINE, CONT. Location of most
chemical digestion Pyloric sphincter
controls food movement
Villi Fingerlike projections
of mucosa Increase surface area
for absorption Microvilli Lacteal
LARGE INTESTINE Larger in diameter but shorter in length Functions:
Water absorption Elimination of wastes (feces)
Subdivisions: Cecum
Sac-like; appendix is attached Good location for bacteria growth/inflammation
Colon Ascending (up); Transverse (across); Descending
(down); sigmoid colon; rectum; anal canal Anal canal: contains voluntary and involuntary
sphincters
ACCESSORY ORGANS Pancreas
Pink, triangular Produces enzymes to
break down food Produces hormone insulin
Liver Largest gland in the
body Under diaphragm,
toward right side of body
Produces bile Yellowish-green solution
that helps digest fats Emulsification (acts like
detergent) Breaks large fat globules
into smaller ones Gallbladder
Bile is stored here until it is needed
NUTRIENTS Carbohydrates
Sugars and Starches Come mainly from plants
Sugars-from fruits, sugar cane, milk Starches-from grains, legumes, root veggies
Cellulose-in plant cell walls Not digested by humans Provides fiber, helps defecation
Lipids Fats
Saturated-animal products and coconut Unsaturated-seeds, nuts, vegetable oils
NUTRIENTS, CONT. Proteins
Made of amino acids Found in animal products
Complete proteins-eggs, milk, meat Incomplete proteins-beans, peas, nuts, cereals
Missing some essential amino acids Vitamins
Required in small amounts Need a balanced diet to have all necessary
vitamins Minerals
Inorganic substances such as calcium, sodium, potassium, etc.
METABOLISM Term referring to all chemical reactions in the
body Includes:
Catabolism Breaking down
Anabolism Building larger molecules
Energy is released and captured to make ATP which is used for all the body’s activities
ENERGY BALANCE Energy can’t be created or destroyed-it can only change
form Energy intake = Energy output*
Energy output = heat + work + storage) Storage isn’t important except in growth periods/fat deposit
Energy in food measured in kilocalories (kcal)
Basal Metabolic Rate (BMR) Amount of kcal needed by body when it is at rest
Total Metabolic Rate (TMR) Total amount of kcal needed by body to sustain all
ongoing activities When total calories = TMR body weight is constant