The Digestive System
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Be Amaaaaaazed!
• Your digestive, entrance to exit is
approximately 30 feet long.
• In your lifetime, your digestive system may
handle about 50 tons of food.
• Salivary glands make about 1.7 liters of
saliva in one day
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Parts of the Digestive System
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Mouth
Esophagus
Stomach
Small Intestine
Large Intestine
Pancreas
Liver
Gallbladder
Rectum
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Digestion
• Function: moves and breaks down food into
smaller usable nutrients.
• Types
– Mechanical (physical) mouth, stomach
• Chew, tear, grind, mash, mix
– Chemical mouth, stomach, intestines
• Breakdown of:
– Carbohydrate
– Protein
– Lipid
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Digestion
• Phases
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Ingestion (mouth)
Movement (through system)
Digestion (mechanical/ chemical)
Absorption (intestines)
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Layers of Gastrointestinal Tract
• AKA: Alimentary canal
Layers:
• Mucosa:
– inner layer; lines the gastrointestinal tract; simple
columnar epithelium
Deep
• Submucosa:
to
– blood vessels; glands; nerve plexuses; loose conn. ts.
Superficial
• Muscularis:
– Two layers (long, circular) Peristalsis
• Serosa:
– Outer layer of connective tissue
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Pathway
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Anatomy of the Mouth and
Throat
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The Major Salivary Glands
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Swallowing
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Esophagus
• From pharynx to stomach
• Salivary glands release mucus
for lubrication, antimicrobial
agents, and amylase to digest
starch.
• Epiglottis covers respiratory
tract during swallowing
• Peristalsis: propulsion of
food
• Cardio esophageal sphincter:
between esophagus and
stomach
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Stomach
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Usually “J” shaped
Left side, anterior to the spleen
Pyloric sphincter: between esophagus and sm. intestine
Functions: store food ; initiate digestion of proteins ; kill bacteria
with the strong acidity (pH 2); make chyme (rugae)
– The stomach digests only proteins, but not fats and carbohydrates
– There is basically no absorption in the stomach
• Enzymes:
– Release of gastrin (hormone) upon sight, smell, taste of food increases enzyme
production
– Pepsinogen HCL pepsin: begins digestion of proteins
– Intrinsic factor: necessary for B12 absorption
– Rennin: in infants, digests milk
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Stomach issues
• Peptic ulcer: acid penetrates
alkaline mucus; sharp pains
– Perforated: erodes
through peritoneal cavity
• Stomach cancer: often
advanced before diagnosis;
gastroscopy
• Gastric stapling: shrinks
stomach
• Gastric bypass: connects
proximal small intestine to
small pouch of superior
stomach
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Anatomy of the Stomach
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Small Intestine
• Extends from pyloric sphincter
 ileocecal valve (12 feet.)
• Duodenum, Jejunum, Ileum
• Columnar epithelium for secretion/
absorption
• Villi/ microvilli increase surface area
• Functions
– Digestion & Absorption carbs,
lipids, proteins, water
– *** requires pancreatic juices
and bile from liver to perform
function
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Structure of the Villi in the
Small Intestine
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Pancreas
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Function
– Endocrine & exocrine functions
– Makes and secretes insulin (dec. blood sugar) &
glucagon (inc. blood sugar)
– Contain bicarbonate ions to neutralize stomach chime
– Empties pancreatic juice through pancreatic ducts into
duodenum
Enzymes:
– Amylase: starch & glycogen  dissacharides
– Lipase: fats fatty acids & monoglycerides
– Trypsin: proteins amino acids
– Nucleases: nucleic acids nucleotides
Disorders:
– Cystic fibrosis slows pancreatic enzyme production;
must take supplements
– Pancreatic cancer: surgery unless it has spread; 95%
mortality rate 5 years
– Diabetes (Type I, II)
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Liver
(hepatocytes)
Functions:
• Produces bile hepatic duct duodenum of sm.
intestine emulsify fats
– Gallbladder: connected to liver & duodenum; stores
bile
• Regulates carb metabolism (stores glucose, converts
glucose into adipose)
• Makes clotting factors for blood (fibrinogens)
• Stores iron, blood, glycogen, vitamins A, D, K, B12
• Filters & detoxifies blood; makes urea from amino acids
Disorders:
• Gallstones: bile contents crystallize
• Hepatitis: inflammation of liver caused by virus
– Passed by food contamination or bodily fluid sharing
– Types A,B,C,D,E
• Cirrhosis: scarring & hardening of liver
• Liver transplants: can donate portions; Hepatitis C
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Large Intestine
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Cecum: sm. intestine meets large
Colon: Ascending Transverse Descending
Sigmoid
– Rectum
– Anal Canal
• Food remains for 18-24 hours
Functions:
• Secretes mucus: lubricate and feces stick together
• Water absorption
• Flatus: gas produced by bacteria
Disorders:
• Appendix: appendicitis
• Constipation: slow movement, >> water
absorption
• Diarrhea: >>speed of movement; >> secretion,
<< water absorption
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Anatomy of the Large Intestine
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Carbohydrate summary
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Carbs: Poly di mono
Salivary & pancreatic amylase
Mouth, small intestine
Monosaccharides absorbed by small
intestine and sent to liver for conversion
into glucose
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Lipid Summary
• Bile salts emulsify
• Lipase from pancreas converts to fatty acids
• Transported with a water soluble protein in blood
(lipoprotein)
• LDL: low density lipoprotein transports
cholesterol to cells for use
– Membranes; steroid hormones (testosterone,
estrogen)
• HDL: high density lipoprotein: transports old
cholesterol
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Protein Summary
• Stomach: Somewhat digested to short-chain polypeptides by pepsin
• Duodenum, jejunum: Digested to amino acids, di-peptides, tripeptides by pancreatic juice enyzmes (trypsin)
– Transport of amino acids across epithelial layer
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Control of the Digestive System
Digestive system is controlled by:
• automatic activity/ autonomic nerves
• hormones
• innervation of the gastrointestinal tract
parasympathetic: rest and digest
sympathetic: fight and flight
Autonomic Branch Effect on GI system
Effect on GI system
parasympathetic
Inc. motility, open
valves
sympathetic
Dec. motility, close
valves
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Can you
identify
these parts?
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Esophagus
Liver
Gall bladder
Duodenum
Ascending colon
Cecum
Appendix
Rectum/ anal canal
Ileum
Jejunum
Sigmoid colon
Small intestine
Transverse colon
Descending colon
Pancreas
Stomach
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The End
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