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DIGESTIVE SYSTEM
ALIMENTARY CANAL / GI TRACT & ACCESSORY ORGANS
Mar 1610:34 PM
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I. Digestive System Functions
> Ingestion
> Propulsion
> Digestion breakdown of food stuff
– 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> Tongue mixes food with saliva & initiates swallowing
– contains taste buds
> Salivary Glands saliva is mixture of mucus & serous fluids (containing salivary amylase) moistens food and helps create a bolus, helps dissolve food so can taste it
> Teeth mastication/chew food (mechanical digestion)
> 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)
Mar 218:05 AM
4Mar 168:07 AM
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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
– chief cells produce pepsinogens– parietal cells produce HCl– mucous neck cells produce alkaline mucus
> Sphincter muscles on both ends of the stomach regulate entry and exit of food stuffs
> Stomach does aid in small amount of fat soluble substances (aspirin, alcohol)
II. Organs of the Alimentary Canal (GI tract) cont'd
Mar 1810:31 AM
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Mar 1610:33 PM
• Small Intestine> Functions:
– chemical digestion– absorption of nutrients
> Regions:– duodenum– jejunum– ileum
> Pancreatic juices and bile enter small intestine (duodenum)> help with complete break down of food particles
> Structural modifications:– Microvilli
– Villi
– Plicae circulares
II. Organs of the Alimentary Canal (GI tract) cont'd
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Mar 199:51 PM
Mar 199:53 PM
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• Large Intestine:> Functions:
– water absorption– elimination of indigestible
material
> Regions: – cecum (appendix)– colon
« ascending« transverse« descending« sigmoid
– rectum– anal canal
II. Organs of the Alimentary Canal (GI tract) cont'd
Mar 199:58 PM
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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, consists of enzymes that aid in chemical digestion of all categories of food:
– Proteases
– Pancreatic Amylase
– Lipases
– Nucleases
> secreted in an alkaline solution
> emptied into duodenum (vagus nerve & hormones: secretin, CCK)
Proteins -> smaller peptides
Complex Sugars -> Dissacharides
Fats -> Glycerol & Fatty Acids
Cleaves nucleic acids (DNA/RNA)
IV. Accessory Digestive Organs
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Mar 237:35 PM
• 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
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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
Apr 82:48 PM