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DIGESTIVE SYSTEM
Professor Andrea GarrisonBiology 11
Illustrations ©2010 Pearson Education, Inc.
Digestive System 2
Digestive System
• Digestive system = digestive tract plus associated glands and organs
• Function = digestion– Breaks down food to simple
molecules that can be absorbed by the lining of the intestine
Digestive System 3
Glands in lining of stomach and intestine
Digestive System 4
Stages of Digestion
Digestive System 5
Stages of Digestion
Digestive System 6
Stages of Digestion
Digestive System 7
Stages of Digestion
Digestive System 8
Ingestion
Digestive System 9
Digestion
• Mechanical digestion– Breaks chunks of food into small pieces• Allows chemical digestion to be effective
• Chemical digestion– Digestive enzymes and assisting chemicals break
food into smaller molecules for absorption
Digestive System 10
Glands in lining of stomach and intestine
Digestive System 11
Digestion in Mouth
• Mouth– Ingestion– Mechanical digestion
• Food is chewed– Pressure on gums creates
reflex• Bolus is formed by tongue,
teeth, cheeks
Digestive System 12
Digestion in Mouth
• Mouth– Chemical digestion
• Taste buds detect sweet, sour, salty, bitter
• Clue to spoiled food• Smell, sight, taste of food
prepares stomach
Digestive System 13
Digestion in Mouth
• Mouth– Chemical digestion
• Salivary glands secrete saliva– Parotid glands– Sublingual glands– Submandibular glands
• Saliva – 99% water– 1% salts and proteins
» Mucins produce mucus
» Amylase breaks down starch
Digestive System 14
Swallowing
• Bolus pushed to pharynx to esophagus– Food swallowed via reflex in pharynx
Digestive System 15
Swallowing
• Bolus pushed to pharynx to esophagus– Food swallowed via reflex in pharynx
Digestive System 16
Swallowing • Bolus pushed to pharynx to esophagus– Food swallowed via reflex in pharynx
Digestive System 17
Peristalsis• Food moves through
digestive tract from esophagus to anus via peristalsis– Waves of involuntary
muscle contractions– Push materials forward– Different rates in
different regions of digestive tract
– Triggered by stretch of muscular walls as material moves in
Digestive System 18
Esophagus
• Muscular tube from pharynx to stomach
• Esophageal sphincter at top
• Penetrates diaphragm
Digestive System 19
Stomach
• Sphincters keep food and gastric juices in stomach until desired release– Cardiac sphincter
• Prevents backflow into esophagus
– Pyloric sphincter• Controls movement
into small intestine
Digestive System 20
Stomach -- Digestion
• Serves for:– Food storage– Formation of
chyme• Slurry of food,
mucus, gastric enzymes
– Initiation of protein digestion
Digestive System 21
Stomach -- Digestion
• Muscles of stomach wall contract to mix the chyme
Digestive System 22
Stomach -- Digestion
• Gastric glands secrete mucus, pepsin, acid– Very acidic– Deactivates salivary amylase– Acid + pepsin breaks down
proteins → amino acid chains
Digestive System 23
Small Intestine
• Peristalsis in stomach and relaxation of pyloric sphincter
• Chyme enters small intestine a little bit at a time
Small intestine
Digestive System 24
Small Intestine
• 3 sections– Duodenum -- first 10 inches– Jejunum -- 8 feet– Ileum --12 feet
Small intestine
Digestive System 25
Small Intestine -- Digestion
• Chyme– Carbs have barely
started digestion– Protein segments
from stomach digestion
– Fats not yet digested
Digestive System 26
Small Intestine -- Digestion
• Role of liver– Produces bile to
assist in fat digestion
• Role of gall bladder– Stores bile from liver
• Role of pancreas– Produces
bicarbonate – Produces digestive
enzymes
Digestive System 27
Small Intestine -- Digestion• Duodenum receives
– Chyme – Mucus from intestinal
cells– Secretin and CCK from
glands in intestinal lining• Stimulate liver,
gallbladder and pancreas
– Bile from liver via gallbladder
– Bicarbonate from pancreas
– Digestive enzymes from pancreas
Digestive System 28
Small Intestine -- Digestion
• Bicarbonate neutralizes acid• Bile emulsifies fats– Increases surface area for digestive
enzymes
Fat
Digestive System 29
Small Intestine -- Digestion
• Pancreatic enzymes work once pH neutralized– Pancreatic amylase• Digests carbohydrates to monosaccharides (sugars)
– Proteases • Digest proteins to amino acids
– Lipases• Digest fats to fatty acid + glycerol
Digestive System 30
Small Intestine -- Digestion
(protease)
Digestive System 31
Small Intestine -- Digestion
(protease)
Digestive System 32
Small Intestine -- Digestion
Digestive System 33
Small Intestine -- Digestion
Digestive System 34
Small Intestine
• Most of absorption occurs here
• Maximizes surface area– Folds, folds, more
folds– Villi and microvilli
most abundant in duodenum and jejunum, also present in ileum
Digestive System 35
Small Intestine
Digestive System 36
Small Intestine
Digestive System 37
Small Intestine
Digestive System 38
Absorption• Most of water• Amino acids & sugars
– actively transported into cells and then to blood capillaries
• Fats – Diffuse into cells– Built back into triglycerides – Attached to proteins
(lipoproteins)– Expelled via exocytosis– Absorbed into lymphatic
vessel and carried to blood
Digestive System 39
Ulcer-causing Bacteria
Digestive System 40
What’s left?
• Mostly wastes– Never absorbed into cells of body• Exception is bile, made from breakdown products of
red blood cells
• Some water– Will be absorbed in large intestine
Digestive System 41
Ileocecal Sphincter
• Peristalsis moves materials into large intestine
• Small intestine joins large intestine at ileocecal sphincter
Digestive System 42
Large Intestine
• Large intestine– Colon
• Ascending colon• Transverse colon• Descending colon• Sigmoid colon
– Rectum – Anus
Ascending colon
Transverse colon
Sigmoid colon Descending
colon
Anus Rectum
Digestive System 43
Large Intestine -- Absorption
• Large anaerobic bacteria population (E. coli)– Breaks down remaining nutrients– Synthesize some B vitamins and vitamin K• absorbed in large intestine
Digestive System 44
Large Intestine -- Absorption
• Most remaining water absorbed– Prevents dehydration– Peristalsis too fast• Diarrhea
– Peristalsis too slow• constipation
Digestive System 45
Egestion
• Peristalsis moves wastes into rectum• Stretch of rectal walls triggers urge to defecate• Wastes removed from body through anus– 2 sphincters• Internal anal sphincter -- involuntary• External anal sphincter -- voluntary
