- in the digestive tract (outside a cell)

- digestion by enzymes produced by the digestive tract cells

- digestion taking place inside a cell

- eg. bacteria phagocytosed by wbc, and digested by enzymes fr. lysosomes

- a muscular tube that extends fr. oral cavity to anus

- it passes through the mouth, most of pharynx, esophagus, stomach, small intestine, and large intestine

- teeth

- tongue

- salivary glands

- liver

- gallbladder

- pancreas

Digestive System Processes

(ismdad)

- ingestion = of food

- secretion = salivary enzymes

- mechanical processing/propulsion (swallowing, peristalsis)

- chewing (mouth)

- churning (stomach)

- segmentation (small intestine)

- digestion (chemical) - stomach

- absorption - small intestine

- defecation - large intestine, anus

- sensory analysis of material before swallowing

- mechanical processing

- lubrication through mixing w/ mucus and salivary gland secretions

- limited enzymatic digestion of carbohydrates and lipids

1. Primary - 20 decicuous teeth that erupt at intervals bet. 6-24 months

2. Permanent dentitions have formed by age 21

- usually 32 permanent teeth

- basic structure of a tooth

- release saliva

- small amount to keep mouth and pharynx moist and clean

- when food enters mouth -> secretion increases:

- lubricate, dissolve and begin chemical digestion

- 3 pairs of major salivary glands: sublingual, submandibular, and parotid

- chewing or mastication

- food manipulated

- 99.5% water

- small amount of dissolved ions

- lysozyme (a bacteriolytic enzyme)

- salivary amylase

- salivary amylase

- act on starches

- continues to act until inactivated by stomach acid

- lingual lipase

- secreted by lingual glands acts on triglycerides

- becomes activated in acidic environment of stomach

1. Inner lining (mucosa)

- epithelium - protection, secretion, absorption

2. Connective tissue (submucosa)

- contains blood vessels, lymphatic vessels and nerves

- binds mucosa to muscle layer

3. Muscle layers (muscularis)

- mostly involuntary smooth muscle

- circular and longitudinal fibers

- voluntary skeletal muscle found in mouth, pharynx, upper esophagus, and anal sphincter

4. Serosa

- connective tissue memb.

- visceral peritoneum

- inner lining

- epithelium: protection, secretion, absorption

- connective tissue

- contains blood v, lymphatic v

- muscle layers

- mostly involuntary smooth muscle: circular and longitudinal fibers

- voluntary skeletal muscle found in mouth, pharync, upper esophagus, and anal spinchter

- secretes mucous and transports food

- no enzymes produced, no absorption

- swallowing

- stages: voluntary, pharyngeal, esophageal

- two sphincters:

- upper esophageal sphincter regulates movement into esophagus

- lower esophageal sphincter regulates movement into stomach

- peristalsis moves food through the esophagus to the stomach

- circular muscles contract, then longitudinal muscles contract

- serves as mixing chamber and holding reservoir

- 4 main regions: cardia, fundus, body, pylorus

- the secretions of the mucous, parietal, and chief cells form gastric juice which totals 2-3 l/d

- some chemical and mechanical digestion

- gastric pits containing gastric glands

- secretes gastric juice, mucus, and gastrin

1. mucous neck cells (mucus)

- alkaline mucus

- the mucous surface layer traps a bicarbonate-rich fluid beneath it

2. parietal cells

- intrinsic factor and HCl

3. chief cells (enzymes)

- pepsinogen and gastric lipase

- mixing waves helps creates chyme

- 3 layers: oblique muscle layer

- parietal cells

- secrete HCl that kills many microbes, denatures proteins

- chief cells

- secrete pepsinogen activated by:

- HCl in the stomach

- pepsin itself via a + feedback mechanism

- activated by acidic gastric juice

- digest triglycerides into fatty acids and diglycerides

- holding reservoir

- gastric juice converts the food to acid chyme

- secretes intrinsic factor

- required for absorption of vit. B12

- small amount of nutrient absorption

- some H2O, ions, short chain fatty acids, certain drugs (aspirin) and alcohol

- sphincters

- esophageal sphincter prevents reflux of chyme

- pyloric sphincter regulates movement of chyme into small intestine

- stomach pH approaches 2.0

- mucosal barrier has:

- a thick coat of bicarbonate-rich mucus on the stomach wall

- epithelial cells that are joined by tight junctions

- damaged epithelial cells are quickly replaced

- pepsin is secreted as inactive pepsinogen

- activated only in the presence of HCL or pepsin

- mucosal barrier has: a thick coat of bicarbonate-rich mucus on the stomach wall; epithelial cells that are joined by tight junctions

- damaged epithelial cells are quickly replaced

- pepsin is secreted as inactive pepsinogen: activated only in the presence of HCl or pepsin

- the largest gland in the body

- has 4 lobes

- suspended fr. the diaphragm and anterior abdominal wall by ligament

- 

- mostly water, bile salts, cholesterol and bile pigments

- are cholesterol that emulsify fat and facilitate fat and cholesterol absorption

- stored and concentrated in the gallbladder

- released bile via the cystic duct, w/c flows into the bile duct

- carbohydrate metabolism

- maintenance of blood glucose levels

- lipid metabolism

- fatty acid breakdown - ATP synthesis

- synthesis of fats such as cholesterol and lipoproteins

- protein metabolism

- a.a. breakdown

- synthesis of plasma proteins and other blood proteins

- processing drugs and hormones

- detoxification

- synthesis and secretion of bile

- glycogen and triglyceride storage

- phagocytosis

- activation of vit. D

- foodstuff: enzyme and source : site of action

starch/disaccharides: salivary/panc. amylase: mouth/small intestine

- lactose, maltose, sucrose

- lactose -> galactose and glucose

- maltose -> glucose

- sucrose -> glucose and fructose

- overall function to complete absorption, produce certain vitamins, and form and expel feces

- 4 major regions: cecum, colon, rectum, and anal canal

- colon divided into ascending, transverse, descending and sigmoid

- the secretion of digestive juices in humans are under both nervous and hormonal control

- nervous control of secretion is short-lived, while hormonal control is more sustained

1. cephalic phase

- smell, sight, thought or initial taste of food prepares mouth and stomach for food to be eaten

2. gastric phase

- promotes gastric secretion and gastric motility once food enters stomach

3. intestinal phase

- begins when food enter small intestine

- slows exit of chyme fr. stomach

- stimulates continued digestion in the small intestine

- neural regulation

- smell, taste, sight or thought of food activates neural centers

- stimulates cerebral cortex, hypothalamus and brain stem

- stimulate secretion of saliva and gastric juice

- both neural and hormonal regulation

- neural regulation: events that stimulate neural mechanisms

- stomach distension activation of stretch receptors

- activation of chemoreceptors in stomach due to increase in pH during ingestion; also peptides and caffeine

- release of gastrin to the blood

- start a neural negative feedback loop

- hormonal regulation - regulated by the hormone gastrin, produced by gastric glands

- gastrin secretion is stimulated by:

- stomac distension

- partially digested protein

- high pH

- caffeine and acetylcholine

- both neural and hormonal regulation

- neural regulation

- enterogastric reflex caused by distention of duodenum due to influx of gastric chyme

- stretch receptors send impulses to medulla oblongata to:

- inhibit gastric mobility

- increase contraction of pyloric sphincter and decrese gastric emptying

- hormonal regulation

- both secretin and cholecystokinin are secreted by the small intestine glands in response to acidic, fatty chyme entering the duodenum

- CCK and secretin enter the bloodstream and circulate to the pancrease:

- induces the secretion of enzyme-rich pancreatic juice

- secretin causes secretion of bicarbonate

- acidic chyme: entering the duodenum causes the specific endocrine cells of the duodenal wall to release secretin

- secretin enters the bloodstream, and circulates to the pancreas

- secretin stimulates the flow of bicarbonate-rich pancreatic juice

- chewing or mastication

- food manipulated by tongue, ground by teeth, and mixed w/ saliva

- forms bolus

- G cells: secretes gastrin (hormone)

- digest proteins

- breaks down proteins into smaller peptides

- works most effectively at very acidic pH

- the longest section of alimentary canal

- has 3 subdivisions: duodenum, jejunum, and ileum

- most important site of chemical digestion

- absorption of nutrients (90%) and most of the water

1. duodenum

- receives chyme fr. stomach

- neutralize acids before they can damage the absorptive surfaces

- receives digestive secretions fr. pancreas and liver

- bile duct and pancreatic duct

2. jejunum

- location of most of the chemical digestion and nutrient absorption

3. ileum

- ends at the ileocecal valve that controls flow of material fr. the ileum into the large intestine

- epithelium of the mucosa is made up of:

- absorptive cell

- digests and absorbs nutrients

- goblet cell

- secretes mucus

- enteroendocrine cell

- secretes the hormones secretin, cholecystokinin, or GIP

- paneth cell

- secretes lysozyme and is capable of phagocytosis

- allows small amounts of chyme to pass into the duodenum to begin the intestinal phase of digestion

- collective effort of pancreatic juice, bile, and intestinal juice in the small intestine

- enzymatic hydrolysis

- emulsification

- pH regulation

- liver, gall bladder and pancreas

- pancreatic juice secreted into pancreatic duct and accesory duct and to small intestine

- panc. duct joins common bile duct and enters duodenum at hepatopancreatic ampulla

- panc. juice is a watery sol. of enzymes and electrolytes (primarily HCO3-)

- 1% of cells are endocrine cells of the pancreatic islets (islets of langerhans)

- secrete hormones such as glucagon and insulin

- 99% of cells are exocrine cells (acini)

- secrete pancreatic juice

- neutralizes acid chyme

- provides optimal environment for panc. enzymes

- enzymes produced: amylase, lipases and nucleases

- some enzymes are released in inactive form and activated in the duodenum (proteases)

- trypsin: secreted as trypsinogen

- chymotrypsin: chymotrypsinogen

- carboxypeptidase: procarboxypeptidase

- are the structural and functional units of the liver

- composed of hepatocytes

- production of bile

- processing bloodborne nutrients

- storage of fat-soluble vitamins

- detoxification

- foodstuff: enzyme&source: site of action

unemulsified triglycerides: lingual/gastric/panc. lipase/bile salts: mouth/stomach/small int./small int.

- monoglycerides (or diglycerides w/ gastric lipase) & fatty acids

- foodstuff: enzyme&source: site of action

large polypep.: pepsin (stomach glands): stomach

to

small polypep.: panc. enzymes (trypsin, chymotripsin, carboxypeptidase): small int.

to

amino acids (some dipep. and tripep.): brush border enzymes (aminopeptidase): small int. 

- energy stored in Na+ conc. gradients is used to drive glucose across the memb. against its conc. gradient

- ATP energy pumps Na+ back out

- bile salts provide a transport mechanism for fats w/in the watery chyme of the small int.

- emulsification does not break chemical bonds, but vastly increases the surface area exposed to digestive enzymes

- formed when fatty globules are combined with proteins

- vesicles containing this migrate to the basal memb., are extruded fr. the epithelial cell, and enter a lacteal

- allows modification of nutrients absorbed fr. the digestive tract by the liver cells