Digestive System Chapter 16

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Factoids: • HOW LONG ARE YOUR INTESTINES? At least 25 feet in an adult. Be glad you're not a full-grown horse -- their coiled-up intestines are 89 feet long! • Chewing food takes from 5-30 seconds • Swallowing takes about 10 seconds • Food sloshing in the stomach can last 3-4 hours • It takes 3 hours for food to move through the intestine • Food drying up and hanging out in the large intestine can last 18 hours to 2 days! • Americans eat about 700 million pounds of peanut butter. • Americans eat over 2 billion pounds of chocolate a year. • In your lifetime, your digestive system may handle about 50 tons!! 2

• 1) Ingestion

Functions

• When foods enter

• 2) Mechanical processing • Physical manipulation

• 3) Digestion • Chemical breakdown

• 4) Secretion • Release of water, acids, enzymes, buffers

• 5) Absorption • Movement of small molecules into interstitial fluids

• 6) Excretion • Removal of waste from body

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Subdivisions • Alimentary canal • Digestive functions • Food passes through

• Accessory organs • Assists digestion • Food does not pass through

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Alimentary Canal • “Gastrointestinal (GI) tract” • Coiled, hollow tube • Includes: • • • • • • • •

Mouth Pharynx Esophagus Stomach Small intestine Large intestine Rectum Anus 5

Alimentary Canal • In a Cadaver: • 9 m (30 ft) • Shorter when alive • Muscle tone

• The Digestive System CrashCourse Biology 11 min

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Structure of Alimentary Tract • Four basic tissue layers: • 1) Mucosa • • • •

Inner most layer Lines lumen Epithelium Narrow band of smooth muscle (outer region)

• 2) Submucosa • Beneath the mucosa • Loose connective tissue • Blood vessels, nerves, and lymph vessels 7

Structure of Alimentary Tract • 3) Muscularis externa • Smooth muscle • Inner circular layer • Outer longitudinal layer

• Autonomic reflexes

• 4)Serosa • Outermost layer • Serous membrane • Visceral peritoneum • Parietal peritoneum

• Makes up mesentary • None in oral cavity, pharynx, esophagus, rectum 8

Peristalsis • Stalsis = constriction • Wavelike pattern of muscle contractions • Circular 1st • Longitudinal 2nd

• Segmentation – mechanical mixing • No pattern • Does not propel materials 9

Mouth • Oral (buccal) cavity • • • • • • • •

Lips (labia) Cheeks Hard palate Soft palate Uvula Vestibule Tongue Lingual frenulum 10

3 Pairs of Salivary Glands • 1) Parotid – under skin of lateral, posterior surface of mandible • Mumps virus can infect

• 2) Sublingual - beneath mucous membrane on floor of mouth • 3) submandibular - floor of mouth on surfaces of mandible 11

Saliva • 1-1.5 L each day • Mixture of mucus, serous fluids, buffers • Moistens and binds food • Dissolves for tasting • Helps form bolus

• Amylase (enzyme) • Begins the digestion of starch

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Teeth • Two sets • Deciduous (baby, milk, primary) • 6 mo to 2 yrs • 20

• Permanent • 6-12 years • 32 • Wisdom teeth later

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Pharynx • “Throat” • Passage for food and air • Food passes thru oro and laryngo portions

• Muscular • Short tube-like

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Swallowing (deglutition) • Food pushed into pharynx • Tongue blocks mouth • Larynx rises • Epiglottis closes windpipe • Goes down esophagus

• Pharynx and esophagus • No digestive function

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Esophagus • • • •

“Gullet” 25 cm (10”) long 2 cm (.75”) wide Stratified squamous epithelium • Mucous glands • Peristalsis

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Esophagus

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Stomach • C-shaped • Regions • Cardiac • Where esophagus conects • Near heart

• Fundus • The bulge • Lateral and superior to cardiac region

• Body • B/w fundus and lower curve • Middle

• Pylorus • Connects to intestine

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Stomach • 3 layers • Usually holds 1-1.5 L • Can hold upto 4 L

• Valves at each end: • Cardiac sphincter • Pyloric sphincter

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Stomach • Rugae • Large folds in wall of stomach

• Greater curvature • Convex • Lateral surface

• Lesser curvature • Concave • Medial surface 20

Stomach • Visceral peritoneum is continuous with mysenteries: • Lesser omentum • From liver to lesser curvature

• Greater omentum • Covers abdominal organs • Lacy apron • Fat • Lymph nodes

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Greater Omentum

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Stomach • Gastric pits • Pits • Gastric juice produced • Parietal cells • Produce HCl • pH 1.5-2.0 • Kills microorganisms • Breaks down plant cell walls anc connective tissues in meat

• Chief cells • Secrete pepsinogen (protein) • Converted to pepsin (enzyme) when contacts HCl

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Gastric Pits • Intrinsic factor • Needed to absorb vitamin B-12

• Mucous cells • Alkaline fluid • Lines and protects stomach

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Chyme • churned food and gastric juice • Soupy

• Most digestive activity occurs in pyloric region • Stimulated by gastrin (hormone) • Begins protein digestion • Only alcohol and aspirin absorbed • 2 year old bypass 4:30 25

Heartburn (GERD) • Cardiac sphincter fails to close • Gastric juice backs up • No mucus = pain • Inflammation

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Hiatal hernia • Structural abnormality • Stomach moves above diaphragm • No longer supports cardiac sphincter • Weakens sphincter

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Peptic Ulcers • Lining of stomach eroded • Often bacteria infect • Page 546

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Food Propulsion • Pyloric sphincter barely opens • Releases 3 ml of chyme

• ~ 4 hours for stomach to empty

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Pyloric Sphincter • Controls movement of food into small intestine from stomach

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Small Intestine • 95% of nutrient absorption • Most digestion completed here • Muscular tube • ~ 6m (20’) long • ~2.5 cm (1”) diameter

• 3 subdivisions: • 1) duodenum • 2) jejunum • 3) ilium 31

1) Duodenum • ~ 25 cm (10”) • Closest to stomach • C-shaped • Curves around pancreas

• Retroperitoneal

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1) Duodenum • “mixing bowl” • Chemical digestion really begins • Mixes chyme from stomach and digestive secretions from pancreas and liver 33

2) Jejunum • Where duodenum reenters peritoneal cavity • 2.5m (8’) long • Most digestion and absorption • Drastic weight control = removal of big portion 34

3) Ilium • Longest • 3.5m (12’)

• Ends at ileocecal valve • Controls flow into large intestine

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Small Intestine • Plicae circulares • Folds in wall • Contain villi • Covered by simple columnar epithelium and microvilli • “brush border”

• All increase surface area 36

Surface Area • Increased from 3.6 ft2 to >2200 ft2 !!!!!!!!

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Villi • Finger-like projections • Velvety appearance • Capillary bed and Lymphatic capillary (Lacteal) inside each

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Small Intestine Absorption • • • •

Along entire length Most by active transport Enter capillaries in villi Blood takes nutrients to liver via Hepatic portal vein • Lipids • Too big • Absorbed into lacteals 39

Small Intestine Propulsion • ~ 5 hours in here! • Segmentation mixes with mucous and enzymes • Peristalsis occurs • When food enters stomach • Gastrin is released • Triggers ileocecal valve to relax • Food enters large intestine 40

Vomiting (emesis) • Increased saliva • Buffers acid

• Reverse peristalsis • Duodenum, proximal jejunum empty into stomach

• Contraction of abdominal muscles • Soft palate and uvula block entrance to nasopharynx 41

Accessory Organs • Pancreas • Grainy looking gland • Triangular • Behind and below stomach • Retroperitoneal

• 15 cm (6”) • 80g (3 oz)

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Pancreas • Primarily exocrine gland • Produces pancreatic juice: (~1 L / day) • • • •

Enzymes Buffers Glucagon Insulin

• Alkaline • Helps neutralize chyme

• Breaks down all nutrients • Secreted into duodenum

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When the Pancreas Fails • Pancreatitis • Blockage of ducts • Bateria, viruses, drug reaction

• Diabetes mellitus • Requires insulin

• Nutrient malabsorption • Requires oral administration of pancreatic enzymes

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Accessory Organs • Liver • Largest visceral organ • ~ 1kg (3.5 1b)

• Right hypochondriac and epigastric region • Four lobes • Held in place by mesentery • Falciform ligament • Divides L and R lobes • Remnant of umbilical vein 45

Liver Functions (p.556) • Produces bile • Yellowish-green liquid • Contains: Water, bile salts, bilirubin, cholesterol, and electrolytes • Does not contain enzymes • Aids digestion and absorption of fats

• Stores glycogen • Regulates blood composition • Receives 25% • Removes pathogens, damaged RBCs, alcohol 46

Accessory Organs • Gall bladder • Small, thin walled sac • Holds 40-70 ml

• Greenish • Stores and concentrates bile • Gallstones form when bile is too concentrated

• Food present: • Gallbladder contracts • Pumps out bile

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Large Intestine • Larger diameter ~ 7.5 cm (3”) • Shorter ~ 1.5m (5’)

• No villi • Many goblet cells • Mucus

• Major functions: • Absorb water • Compact and store feces before defecation • Absorb vitamins 48

Subdivisions of Large Intestine • 1) Cecum • 1st part • Ileocecal valve • Compaction begins • Contains (vermiform) appendix • ~ 9 cm (3.5”)

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Subdivisions of Large Intestine • 2) Colon • Thinner walls • Contains haustra • Pouches • Allow distension and elongation

• 4 parts: • • • •

Ascending Transverse Descending Sigmoid (S-shaped)

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Subdivisions of Large Intestine • 3) Rectum • End of digestive tract • ~15 cm (6”)

• Expandable • Stores feces • Anal canal • Last portion

• Anus • The exit

• Internal anal sphincter • Smooth muscle

• External anal sphincter • Skeletal muscle

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Activity of Large Intestine • Takes ~12-24 hours • Contains bacteria • • • •

Metabolize some nutrients Generate vitamins: K, Biotin, B5 Breakdown toxins Release gases (flatus): • ~ 500 ml of gas/day • Methane • Hydrogen sulfide 52

Peristalsis in Large Intestine • Long, slow contractions • 3-4 times a day • Forces contents toward the rectum • During or after eating • Bulk or fiber increases contractions and softens stool 53

Diverticulosis • Diverticula (pockets) form • Diet lacks fiber • Colon narrows

• Diverticulitis • Diverticula become inflamed • Can be life threatening • Colitis –inflammation of other parts of colon 54

Disassembly Line • Ingestion • Propulsion • Peristalsis

• Mechanical digestion • Preparation

• Chemical digestion • Change substance

• Absorption • Small intestine

• Defecation • Indigestible material 55

Mouth • Mouth: • Mechanical digestion • Big pieces to small pieces • Same substance

• Mixed with saliva

• Chemical digestion • Different substance • Salivary amylase • Starch into maltose

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Pancreatic Juice • Dumps into the small intestine • Contains enzymes • Pancreatic amylase • Digestion of starch

• Trypsin, chymotrypsin, carboxypeptidase • Digestion of protein

• Pancreatic lipases • Digestion of lipids

• Pancreatic nucleases • Digestion of nucleic acids 57

Carbohydrates • Broken into: • Polysaccharides • Disaccharides • Building blocks • Monosaccharides

• Where: (p. 562) • Mouth • Small intestine • Small intestine

salivary amylase pancreatic amylase maltase, sucrase, lactase

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Review: Carbohydrates • Broken into: • Monosaccharides

• 3 common: • 1) Glucose • Most important • Blood sugar

• 2) Fructose • Sugar in fruit

• 3) Galactose • Milk sugar

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Proteins • Broken into: • Polypeptides • Building blocks • Amino acids

(p. 562)

• Where: • Stomach • Small intestine • Small intestine

pepsin trypsin, chymotrypsin, carboxypeptidase (from pancreas)

peptidases

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Fats • Broken into: • Building blocks • Fatty acids • Glycerol

• Where: • Small intestine • Small intestine

bile pancreatic lipase

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