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ap digestive 25 & 26

Digestive system

tube that is wrapped around the body
aka = gastrointestinal tract (GI)/alimentary canal

digestive system functions

1. Ingestion = (MAIN) eating
2. Mastication = chew
3. Propulsion = smoth muscle to move food (mechanical)
4. Secretion = acid & enzymes to help digestive
5. Digestion - Mechanical and chemical = breaking big molecules to small
6. Absorption = (MAIN)
Elimination = (MAIN)

organs of digestion: main organs - path

Mouth ---> oropharynx ---> esophagus ---> stomach ---> small intestine ---> large intestine ---> rectum ---> anal canal

organs of digestion: accessory organs

Salivary glands, tongue, teeth, liver, gallbladder, pancreas, and appendix


1. Lips
2. Cheeks - buccal cavity
3. Hard palate - roof
4. Soft palate - roof
5. Uvula - goes up nasopharynx so food doesn't go into nasal cavity

Tongue (3)

1. Contains taste buds - sweet, salt, sour, bitter
2. Intrinsic muscles -
a. Change shape
3. Extrinsic muscles
a. Move tongue around
b. Helps with formation of bolus and swallowing

Salivary glands (3)

liquid like secretion
1. Parotid glands
2. Submandibular glands
Sublingual glands

salivary gland: parotid glands

Water, serous fluid
Rich in amylase ---> digests carbs

salivary gland: Submandibular glands

Primarily serous fluid
Some mucus

salivary gland: Sublingual glands

"below tongue", under tongue
Primarily mucus
Most viscous - b/c temperature - blood close to surface


1. Prevents bacterial infection = protective
a. Lyzozyme = immune system
b. IgA = immune system
2. Lubrication
3. Contains salivary amylase = carb digestion
4. Helps to form bolus for swallowing


1. Organs of mastication = easier to digest
2. Gingiva or gums
3. Deciduous & permanent


1. Smooth muscle
2. Posterior walls of oropharynx and laryngopharynx contains muscles that contribute to swallowing
3. Function = to move food


1. Transports food from pharynx to stomach
2. Peristalsis = wave like contraction, squeezes & pushes down bolus over & over again
3. Passes through esophageal hiatus
a. Hiatal hernia: widening of hiatus. too big and the stomach can go into the respiratory tract
4. Lower Esophageal Sphincter (aka cardiac sphincter)
a. Incompetent - GERD (everytime you eat acid goes up into esophagus). doesn't work = heart burn


circular muscle on the outside

Wall of GI Tract

1. Mucosa
a. Lines the lumen
b. Secretes digestive enzymes
c. Goblet cells secrete mucus
2. Submucosa
a. Contains blood vessels, lymphatic vessels, and nerves
3. Muscularis
a. Circular layer
b. Longitudinal layer
4. Serosa
Secretes serous fluid

Wall of GI Tract: mucosa

a. Lines the lumen
b. Secretes digestive enzymes
c. Goblet cells secrete mucus

Wall of GI Tract: submucosa

a. Contains blood vessels, lymphatic vessels, and nerves

Wall of GI Tract: muscularis

a. Circular layer
b. Longitudinal layer

Wall of GI Tract: serosa

Secretes serous fluid


1. Divisions
a. Fundus
b. Body
c. Pylorus
2. Sphincter muscles
a. Cardiac sphincter (lower esophageal sphincter)
b. Pyloric sphincter

stomach divisions

a. Fundus
b. Body
c. Pylorus

stomach: sphincter muscles

a. Cardiac sphincter (lower esophageal sphincter)
b. Pyloric sphincter

Gastric Mucosa

1. Gastric glands
Chief cells
Endocrine cells
Parietal cells
Kills bacteria
Stops carbohydrate digestion by inactivating salivary amylase
Denatures proteins
Helps convert pepsinogen to pepsin
Intrinsic factor

Functions of Stomach

1. Reservoir for food
2. Chemical digestion - stomach acid & pepsin
3. Mechanical digestion - peristalsis & segmentation
4. Secretes intrinsic factor
5. Limited absorption
6. Produces gastrin
7. Protection

Mechanical digestion

1. Physical breakdown of food into smaller particles
2. Teeth and churning action of stomach and intestines

Chemical digestion

1. Reactions that break macromolecules into their subunits
2. Enzymes from saliva, stomach, pancreas and intestines
3. Results
a. Polysaccharides into monosaccharides
b. Proteins into amino acids
c. Fats into glycerol and fatty acids

Small Intestine

1. Divisions
a. Duodenum
i. openings to ducts from liver and/or pancreas.
b. Jejunum
c. Ileum
i. Ileocecal valve
2. Major site of digestion and absorption

Small Intestine Mucosa

1. Increase surface area
a. Plicae (circular folds)
b. Villi - contain capillaries and lacteals.
c. Microvilli - extensions of cell membranes of absorptive cells

Large Intestine

1. Cecum
2. Colon
3. Ascending colon
4. Transverse colon
5. Descending colon
6. Sigmoid colon
7. Rectum


1. Internal anal sphincter
2. External anal sphincter


1. Mesentery
2. Omentum
a. Cushions and insulates
b. Contains macrophages
3. Retroperitoneal
4. Peritonitis


1. Bile Ducts
a. Right and left hepatic ducts
b. Cystic duct
c. Common bile duct
2. Lobules
3. Sinusoids

Composition of Bile

1. Water
2. Bile salts
3. Bile pigments
4. Cholesterol
5. Electrolytes

Functions of Liver

1. Detoxification
2. Bile synthesis & secretion
3. Metabolism of proteins, fats, and carbohydrates
4. Storage of substances - glycogen, vitamins, iron
5. Production of plasma proteins
6. Produces urea after breaking down amino acids
7. Helps regulate the blood cholesterol level

Gall Bladder

1. Storage of bile
2. Concentration of bile
3. Ejection of bile into duodenum


1. Endocrine and exocrine gland
2. Functions of the pancreas
a. Digestive enzymes
b. Hormones
i. Insulin
ii. Glucagon
3. Hypoglycemia
4. Hyperglycemia

Regulation of Motility

1. Nervous stimulation
a. Sight or smell of food
b. Parasympathetic stimulation
2. Hormones
a. Gastrin
b. GIP
c. Secretin
d. Cholecystokinin(CCK)

Enterogastric Reflex

Regulates the rate at which chyme leaves the stomach


1. Gastrin
a. Causes release of
i. HCl
ii. Pepsinogen
b. Maintain mucosa
2. GIP
a. Inhibit motility & secretions


1. Release stimulated by acidic chyme
2. Pancreatic secretion of bicarbonate and water
3. Potentiates CCK

Cholecystokinin (CCK)

1. Stimulated by chyme containing fat
2. Stimulates bile secretion
3. Stimulates pancreatic secretion of enzymes
4. Inhibits gastric motility & secretion

Pancreatic Enzymes

1. Proenzymes
2. Pancreatic amylase - splits glycogen into disaccharides
3. Pancreatic lipase - breaks down triglycerides
4. Trypsin, chymotrypsin, and carboxypeptidase - digest proteins
5. Nucleases - digest nucleic acids
6. Bicarbonate ions - make pancreatic juice alkaline

7. Effect of pH

Carbohydrate Digestion

1. Begins in mouth
2. Completed in small intestine
3. Polysaccharides Disaccharides & Monosaccharides

Protein Digestion

1. Begins in stomach
2. Completed in small intestine
3. Polypeptides ---> amino acids

Fat Digestion

1. Begins and completed in small intestine
2. Requires bile - need to bring fat into water to digest = bile salts, emulsify)
3. Triglycerides ---> monoglycerides, glycerol, free fatty acids
Lipases = use to digest

Absorption of Fats

1. Chylomicrons = lipoprotein. protein makes water soluble, but makes too big to go into capillary bed, so it goes into lacteal and then to liver
2. Lacteals = lymphatic vessel carries chylomicrons away from small intestine
Note: in the cells most fats are reassembled (intestinal lining), unlike any other macromolecule


1. Simple diffusion or osmosis
2. Active transport (water molecule always using ATP = sodium
3. Sodium cotransport = using the energy that moves sodium move glucose or AA at the same time. AA & glucose never want to saturate so use cotransport.

Hepatic Portal System

1. -The portal venous blood contains all of the products of digestion absorbed from the GI tract.
2. -All nutrients are processed/viewed in the liver (by hepatocytes) before being released back into the central veins.
3. Liver is the most metabolic organ


1. Defecation = based on stretch reflex
2. Constipation = mostly diet, lack of fiber. insoluble - intestine can contract against. soluble fiber - holds onto moisture
3. Diarrhea = moves too fast thru digestive system. protective = get rid of toxin (vomit if in stomach), if in intestine then diarrhea.


protein digesting enzymes


Absorption of fats
lipoprotein. protein makes water soluble, but makes too big to go into capillary bed, so it goes into lacteal and then to liver

internal anal sphinter - type of muscle


external anal sphincter - type of muscle

skeletal muscle

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