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The Digestive System
Chapter 14
Digestive Tract
• General
– digestive system
– alimentary canal
• anterior end - mouth
• posterior end - anus
– GI tract
– primary structures
• mouth --> pharynx --> esophagus --> stomach
--> small intestine --> large intestine --> anus
– accessory structures
• tongue , salivary glands, teeth , pancreas ,
liver , gall bladder
• Processes of digestion
– ingestion
– propulsion - peristalsis
– mechanical - large --> smaller
• chew, churn, mixing
– chemical
• enzymes & acid
– absorption - into blood or lymph
• monosaccharides, fatty acids, & amino acids
– defecation - elimination of undigestables
• feces
• Mouth
Alimentary Canal Organs
– oral cavity
– lips
– cheeks
– roof of mouth
• hard palate - anterior
• soft palate - posterior
– tonsils
– uvula
– tongue
• lingual frenulum - anchor tongue to floor of mouth
• taste buds
• Gums (gingivae)
– gum inflammation - gingivitis periodontal
disease
• teeth
– crown - exposed part of tooth
– enamel - covers crown
– neck - connects crown w/ gums
– root - embedded in gum
– Dentin- bonelike under enamel
– Pulp cavity- under dentin supplies
nutrients to tooth tissues– tooth decay
• cavities, dental plaque, (sugar bacteria
debris) , lactic acid - breaks down enamel
Tooth
– two sets of teeth
• deciduous teeth - 6 months to 2 yrs --->
• 6 - 12 yrs
• permanent teeth - 32 teeth
– types of teeth
•
•
•
•
incisors - 8
premolars - 8
canines - 4
molars - 12
• Mastication
– (bolus) lump of food “ball”
• salivary glands
– reflex response
– paired glands
• parotids under ears
• submaxillaries (sub mandibular)
• sublinguals
– amount
• 1-2 liters
Salivary Glands
parotid
sublingual
submandibular
25-1
• saliva composition
– 99% water - moisten
– 1 % solutes: containing;
• electrolytes
• mucin - slippery
• antibodies - IgA
• lysozyme - enzyme breaks down
bacteria
• unknown - blocks viral entry (AIDS)
• salivary amylase - enzyme breaks down
starch --> disaccharide + water -->
monosaccharides
• Pharynx
– throat
• esophagus
– 10 inch tube
– passageway
– serosa
• outer layer peritoneum
• visceral and parietal
– layers
• muscularis externa - smooth muscle
• submucosa - connective tissue blood & lymph vessels
• mucosa - innermost
– ends are stratified squamos
– simple columnar, goblet cells
Pharynx
pharyngeal constrictors
upper esophageal sphincter
25-13
Esophagus
X-ray: Swallowing in Esophagus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Upper
esophagus
Peristaltic
contraction
Figure 25.11b
Bolus of ingested
matter passing
down esophagus
(b)
© The McGraw-Hill Companies, Inc.,/Jim Shaffer, photographer
25-15
Greater omentum is mesentery that
extends from
greater curvature of stomach and loosely
covers small intestine; "fatty hairnet“
Lesser omentum is mesentery
that extends from
lesser curvature of stomach to liver
• Stomach on left side J or C shaped
• Can hold up to 4 liters of liquidified food
• Food in stomach for 2-6 hrs
– a muscular organ
• chemical breakdown of proteins
• churning & acid, food --> chyme
– anatomy
•
•
•
•
•
cardiac sphincter - circular muscle
fundus - top
body - middle
pylorus - bottom sac holds 30 ml of chyme
pyloric sphincter - circular muscle squirts out 3 ml of
chyme into duodenum
– Gastrin- hormone stimulates gastric glands to
secrete HCl
• Gastric glands
– gastric juices
• 2 to 3 liters a day
– HCL pH of 1-2
– pepsin (peptidase)- enzyme breaks down protein --->amino
acids
– rennin - enzyme breaks down milk protein
– autodigestion is prevented
• mucus lining renewed 3-5 days
– problems
• vomiting - presence of irritants
• hiatal hernia - structural abnormality,
superior part of stomach protrudes
above diaphragm
• ulcer - acid eats away stomach wall
– Gastritis- inflammation of lining
• Small intestine
– 21 ft in cadaver, 6 ft in living
• completes digestion, absorbs nutrients 3-6 hrs
– duodenum - 1st part of small intestine 10 inches
chyme(pH 4-5) enters here from stomach
• pancreatic juice & bile enter here,
• pancreatic juice - made by pancreas
– amylase - starch --> glucose
– Trypsin (protease) - proteins --> amino acids
– lipases - lipids --> fatty acids
– Nucleases- breakdown nucleic acids
-sodium bicarbonate pH 8- neutralize chyme’s acid pH
• bile - made by liver secreted by gall bladder,
emulsifies fat.,
– sodium bicarbonate- helps neutralize acid
– jejunum
• 8 ft allows pancreatic juice and bile time to work
• Ileum- last part of small intestine
– intestinal glands
• secrete intestinal juice
–
–
–
–
–
–
– villi
maltase: maltose --> 2 glucoses (monosaccharides)
sucrase: sucrose --> glucose & fructose
lactase: lactose --> glucose & galactose
intestinal lipase --> lipids --> fatty acids
peptidases - protein --> amino acids
Nucleases
– microvilli (capillary within)
– secrete brush border enzymes to
– absorb nutrients
– lacteals
– within each villi absorb fatty acids into lymph
Gross Anatomy of Small Intestine
• Large intestine 5 – 6 feet
– ileocecal sphincter to the anus
– anatomy
• caecum - sac attached to ileocecal
• appendix - attached to caecum
• colon
–
–
–
–
ascending
transverse
descending
sigmoid
• rectum - store feces valves separate gas & feces
• anal canal
– sphincters
» internal: smooth muscle
» external : striated
– anus - opening
• Transport of fecal material
– mucus - slide
– mass movement - haustral movement
– defecation reflex
– bilirubin gives feces color
• bile –reddish brown
• absorption of vitamins and fluid
• metabolism of waste products
• mixture of gases - flatus - 500 ml
– H2, N2, CO2, H2S, methane
• bacteria synthesize vitamins
– B12 red blood cells, K clotting
• reabsorption of most water
• disorders
– diarrhea, constipation, diverticulitis, colitis
Colon X-ray
cecum
ascending colon
transverse colon
rectum
descending colon
sigmoid colon
Accessory Digestive Organs
• Pancreas
– anatomy
– endocrine functions
• insulin - lowers glucose in blood
• glucagon - raises glucose in blood
– exocrine functions
• pancreatic juice composed of: water,
enzymes(lipase, trypsins, amylase) electrolytes
and sodium bicarbonate
• pancreatic duct- goes to duodenum
• Liver
– largest gland of body
– disorders
• hepatitis
• cirrhosis
• jaundiced
• gall bladder
– Cystic(bile) duct
– stores and concentrates bile
– releases bile- emulsifies fats
– sodium bicarbonate
– gall stones
• cholesterol may crystallize stones block flow
of bile
Nutrition & Metabolism
• Nutrients
– Six classes are required
•
•
•
•
•
•
carbohydrates - 125-175 g
proteins - 50 g
lipids - 80 - 100 g
vitamins
electrolytes / minerals
water
4calories/gram
4calories/gram
9calories/gram
• Importance of water
– solvent chemical reactions & body temp.
• metabolism
– BMR : amount of energy in kilocalories ; weight
in kilograms x 1 male x .9 female
– anabolism : make larger molecule, amino acids -> proteins
– catabolism : break down digestion
• carbohydrate metabolism
– carbohydrate --> monosaccharide
– phases of cellular respiration
• lipid metabolism
– lipids --> fatty acids
• protein metabolism
– proteins --> amino acids
• General metabolic functions
– glycogenesis : making of glucogen
– glycogenolysis : breaking down of
glycogen to glucose
– glucogenesis : fats or proteins made into
glucose
• cholesterol metabolism
– 15 % from diet & 85 % made by liver
• LDL’s - low density lipoproteins transport
cholesterol to body cells
• HDL’s - high density lipoproteins transport
cholesterol to liver and out of body.
Body Energy Balance
• regulation
of food intake
Chemical energy (high-energy electrons)
• nutrient levels
CO2
Chemical energy
• hormones,
body temp.
CO2
• glucose in blood & psychological
Mitochondrion
Electron transport
Glycolysis
• body
temperatureKrebs
regulation
chain and oxidative
Glucose
Cytosol
of cell
• heat
acid promoting
Pyruvic
cycle
phosphorylation
– vasoconstricting
» shivering, pyrogens
H2O
•Mitochondrial
heat loss
cristae
– radiation --> blood vessels skin dilating
– evaporation --> sweat
Via oxidative
phosphorylation
ATP
ATP
ATP
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