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DIGESTIVE SYSTEM
ALIMENTARY CANAL / GI TRACT & ACCESSORY ORGANS
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I. Digestive System Functions
> Ingestion
> Propulsion
> Digestion breakdown of foodstuff
– Mechanical
– Chemical
> Absorption
> Defecation
the taking in of food
movement caused by force
intake of nutrients from food
elimination of indigestible waste
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• Oral Cavity: Mechanical & Chemical Digestion
> Teeth mastication/chew food (mechanical breakdown)
> Tongue mixes food with saliva & initiates swallowing– contains taste buds/taste receptors
> Salivary Glands saliva is mixture of mucus & serous fluids– contains salivary amylase (chemical digestion)– moistens food and helps create a bolus– helps dissolve food so can taste it
> Epiglottis blocks opening to trachea to allow food to enter into esophagus instead of air passageway
> Hard & Soft Palate separates oral cavity & nasal cavity– when you swallow soft palate rises to close nasal
passage
• Pharynx: this is subdivided into three parts: > nasopharynx respiratory passageway> oropharynx most posterior part of oral cavity> laryngopharynx most superior part of esophagus
II. Organs of the Alimentary Canal (GI tract)
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• Esophagus: muscular tube for transport (peristalsis)
• Stomach: Mechanical & Chemical digestion
> Regions:
– Cardia
– Fundus
– Body
– Pylorus
> Rugae folds in the walls of the stomach
> Mucosa line with simple columnar epithelium with millions of gastric pits creating gastric juice
– Mucous cells produce alkaline mucus to protect walls
– Gastric pits (with glands)
« Chief cells produce pepsinogens« Parietal cells produce HCl« Mucous neck cells produce acidic mucus (not sure of
purpose)
> Sphincter muscles on both ends of the stomach regulate entry and exit of food stuffs
– Cardiac Sphincter
– Pyloric Sphincter
> Stomach does aid in absorption of small amount of lipid soluble substances (aspirin, alcohol)
II. Organs of the Alimentary Canal (GI tract) cont'd
- produces chyme
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• Small Intestine:> Functions:
– Chemical digestion– Absorption of nutrients
> Regions:– Duodenum– Jejunum– Ileum
> What enters the duodenum?– Pancreatic juices (enzymerich & bicarbonaterich)– Bile (from liver & gall bladder)
> Brush Border Enzymes– Produced by small intestine– Completes chemical digestion of carbs, proteins, &
nucleic acids
> Structural modifications: increases surface area
– Plicae circulares: Deep folds of mucosa« Force chyme to spiral through lumen...slowing
movement & allows more time for nutrient absorption
– Villi: Fingerlike projections of mucosa« Blood capillary network & lymphatic capillary (lacteal)
– Microvilli: Tiny projections of plasma membrane of mucosa cells
II. Organs of the Alimentary Canal (GI tract) cont'dMesentery
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• Large Intestine:> Functions:
– Water absorption– Elimination of indigestible
material
> Regions: – Cecum (appendix)
« Ileocecal Valve– Colon
« Ascending« Transverse« Descending« Sigmoid
– Rectum– Anal canal
> Defacation Reflex
II. Organs of the Alimentary Canal (GI tract) cont'd
« Internal Involuntary Sphincter« External Voluntary Sphincter
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> Mucosa innermost layer– epithelial tissue lined with
goblet cells that produce mucus
> Submucosa connective tissue containing...– blood vessels, nerves, &
lymphatic tissue
> Muscularis externa layers of smooth muscle
> Serosa outermost layer– peritoneum & mesentery
• From the esophagus large intestine the wall of the GI tract is composed of the following tissues:
III. Layers of the Alimentary Canal (GI tract)
• Pancreas flat gland that extends from the spleen to the duodenum
> Produces pancreatic juice– Emptied in duodenum – Alkaline solution– Consists of enzymes that aid in chemical digestion of all
categories of food:
« Proteases
« Pancreatic Amylase
« Lipases
« Nucleases
Proteins -> smaller peptides
Complex Sugars -> Dissacharides
Fats -> Glycerol & Fatty Acids
Cleaves nucleic acids (DNA/RNA)
IV. Accessory Digestive Organs
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• Liver large organ with 4lobes / located just under diaphragm
> Produces bile– a yellowgreen substance containing bile salts, bile
pigments, cholesterol, phospholipids, & electrolytes
> Bile salts help break large fat globules into smaller ones– helps increase surface area so lipases can break fat
down at faster rate
> Exits the liver via hepatic ductEmulsification
IV. Accessory Digestive Organs cont'd
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• Gallbladder small saclike organ embedded on underside of liver
> Bile leaving liver backs up into gallbladder via cystic duct
> Bile is concentrated in gallbladder– Secreted into duodenum via
common bile duct (when fatty foods are present)
• Salivary glands Parotid, Sublingual, Submandibular
> Contains mucus which helps moisten food
> Contains salivary amylase which starts starch digestion
> Contains lysozyme and antibodies (protective function)
> Dissolves food chemicals (can taste food)
• Teeth mechanical breakdown by mastication
IV. Accessory Digestive Organs cont'd
Oral Cavity
Stomach
Lumen of Small Intestine
Epithelium ofSmall Intestine
Carbohydrates
Proteins
NucleicAcids Fats/lipids
Salivary AmylaseStarch
PancreaticAmylase
disaccharides
brush borderenzymes
monosaccharides
Pepsin
Pancreatic Proteases
brush borderenzymes
amino acids
smallpeptides
Proteins
brush borderenzymes
PancreaticNucleases
DNA/RNA
nucleotides
PancreaticLipases
glycerol & fatty acids
Triglycerides/Fats
*All (except some lipids) absorbed in blood...to liver...to rest of body
*Some lipid breakdown products absorbed in blood, some in lymph...all end up in liver...then to rest of body
CHEMICAL DIGESTION & ABSORPTION
large polypeptides
Starch
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V. Metabolism: all chemical reactions that help maintain life
A. Anabolism
B. Catabolism
1. Carbohydrate metabolism:
2. Fat Metabolism:
3. Protein Metabolism:
reaction building molecules
reaction that breaks down molecules
> digestion = catabolic process> enzymatic breakdown of food via
hydrolysis
Metabolism by body cells