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What are the two groups of organs of the digestive tract?
- Alimentary canal (gastrointestinal tract)
- Accessory digestive organs
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The organs of the alimentary canal include
Mouth, pharynx, esophagus, stomach, small intestine and large intestine
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What are the accessory organs of the digestive system?
What are the diestive glands?
- Teeth, tongue and gallbladder
- Salivary, liver and pancreas
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What are the six essential activites of the digestive system?
- Ingestion
- Propulsion
- Mechanical digestion
- Chemical digestion
- Absorption
- Defecation
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Adjacent segments of alimentary tract alternately contract and relax, which moves food along the tract distally describes
peristalsis
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What are the 4 things saliva does?
- Cleanses the mouth
- Moistens and dissolves food chemicals
- Aids in bolus formation
- Contains enzymes that begin the breakdown of starch
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Saliva is secreted by
serous and mucous cells
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Saliva contains
- electrolytes
- Enzymes (that break down starch)
- mucin
- Metabolic wastes (urea and uric acid)
- Lysozome, lgA, defensins, and a cyanide compound protect against microorganisms
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_______________ (_______, _______) ______________ keep the mouth moist
Intrinsic (small, scattered) glands
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_______________________ (__________, ________________) produce secretions when ingested food stimulates chemoreceptors and mechanoreceptors in the mouth
Extrinsic salivary glands (Large, outside of oral cavity)
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What digestive processes happen in the mouth?
- Ingestion
- Mechanical digestion
- Chemical digestion
- Propulsion (deglutition)
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Deglutition involves
the tongue, soft palate, pharynx, esophagus, and 22 mucle groups
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What is the buccal phase?
Voluntary contraction of the tongue
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The pharyngeal-esophageal phase is ________. It is part of what digestive process?
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What is the stomach's job
Digest proteins
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The ____________ of the stomach allows it to churn, mix, move and physically break down food
inner oblique layer
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Mucosa layer of the stomach is made of
simple columnar epithelium composed of mucous cells
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What types of cells are in gastric glands?
- Mucous neck cell (secrete thin, acidic mucus)
- Parietal cells
- Chief cells
- Enteroendocrine
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Glands in the fundis and body produce ____________
most of the gastric juice
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Parietal cells secrete (2)
- HCI (pH denatures protein in food, activates pepsin and kills bacteria)
- Intrinsic factor (glycoprotein required for absorption of vit B12 in small instestine)
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Chief cells secrete
- Inactive enzyme pepsinogen
- Activated to pepsin by HCI and by pepsin itself (a positive feedback mechanism)
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Enteroendocrine cells secrete _________ into the lamina propria
chemical messengers
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What are the chemical messengers secreted into the lamina propria?
- Paracrines (local hormones)
- Hormones
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Which paracrines are secreted by the gastric glands?
- Serotonine (stomach contraction)
- histamine (activates release of HCI)
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What hormones are secreted by gastric glands?
Somatostatin (inhibits gastric) and gastrin (stimulates gastric)
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What are the 3 things that protect the lining of the stomach?
- Layer of bicarbonate-rich mucus
- Tight junctions between epithelial cells
- Damaged epithelial cells are quickly replaced by division of stem cells
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Errosion of the stomach wall leads to
peptic or gastric ulcers
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Gastritis is
inflammation caused by anything that breaches the mucosal barrier
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Most peptic and gastric ulcers are caused by
Helicobacter pylori bacteria
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What digestive processes occur in the stomach?
- Physical digestion (churning)
- Denaturation of proteins (acid)
- Enzymatic digestion of proteins by pepsin
- Delivers chyme to the small intestine
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The stomach secretes ___________required for absorption of vitamin B12
intrinsic factor
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A lack of intrinsic factor leads to
percutanious anemia
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Gastric secretions are regulated by
neural and hormonal mechanisms
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What are the stimulatory and inhibitory phases that occur in the stomach?
- Cephalic (reflex) phase: few minutes prior to food entry
- Gastric phase: 3-4 hours after food enters the stomach
- Intestinal phase: brief stimulatory effect as partially digested food enters the duodenum, folowed by inhibitory effects
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What are the 3 chemicals that stimulate parietal cells through second-messenger systems in the stomach?
ACh, histamine and gastrin
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_______, ____________ and ________ are necessary for maximum HCI secretion
ACh, histamine and gastrin
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____________ block H2 receptors and decrease HCI release
Antihistamines
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what is the stomach's response to filling? What cooderinates this?
- Reflex-mediated receptive relaxation
- Coordinated by the swallowing center of the brain stem. Gastric accomodation by the placticity of smooth muscle
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__________________ move toward the pylorus at the rate of 3 per minute
peristaltic waves
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__________- and _____________ increase force of contraction in stomach
Distension and gastrin
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Gastric contractile activity is most vigorus near
the pylorus
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Chyme is either delivered _____________ or _____________
- in about 3 ml spurts into the duodenum
- forced backward into the stomach
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As chyme enters the duodenum receptors _____________________ and ____________________
respond to stretch and chemical signals and enterogastric reflex and enterogastrones inhibit secretion and duodenal filling
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_____________ moves quickly though the duodenum. ________________ remains in the duodenum 6 hours or more
- Carbohydrate-rich chyme
- Fatty chyme
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What are the 3 jobs of the small intestine?
- Absorb nutrients into the bloodstream
- Allow for chemical digestion as food passes through it
- Collects several chemicals from external organs of digestive system
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What are the subdivision of the small intestine?
- Duodenum (retroperitoneal)
- jejumum
- ileum
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duodenum collects from
stomach and external organs
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The jejunum finalizes
food digestion process
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the ilium maximizes
food absorption process
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the bile duct and main panceatic duct join ______________ enter _____________ are controlled by ______________
- at the hepatopancreatic duct
- the duodenum at the major duodenal papilla
- the hepatopancreatic sphincter
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What are the structural modifications of the small intestine that increase the surface area of proximal part for nutrient absorption?
- Circular folds (plicae circulares)
- Villi
- Microvilli
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Circular folds are ____________ and force ____________
- permanent
- chyme to slowly spiral through lumen
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Villi are _________________________ and are made up of ____________-
- motile fingerlike extension of the mucosa
- Villus epithelium
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Villus epithelium is made of
Simple columnar Absorptive cells (enterocytes) and Goblet cells (make mucous)
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Microvilli are ___________________ and bear
- projections (brush border) of absorptive cells
- Brush border enzymes
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Submucosa of small intestine is made up of
- Peyer's patches
- Duodenal (Brunner's) glands
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Peyer's patches protect
distal part of small intestine against bacteria
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Duodenal glands of the duodenum secrete
alkaline mucus (post-stomach chyme is acidic - this neutralizes it)
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Intestinal juice is secreted in response to
distension or irritation of the mucosa
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Intestinal juice is slightly _________ and _____________
- alkaline (basic)
- isontonic tithe blood plasma (even concentration of water
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Intestinal juice is largely _____________ but contains _____________
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Intestinal fuild facilitates
transport and absorption of nutrients
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The ____________ is the largest gland in the body
liver
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What are the 3 bile ducts?
- Common hepatic duct leaves the liver
- Cystic ducts connects to gallbladder
- Bile duct formed by the union of the other ducts
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What are the four hepatocyte functions?
- Process bloodborne nutrients
- Store fat-soluble vitamins
- Perform detoxification
- Produce about 900 ml of bile per day
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Bile is a yellow-green, alkaline solution containing
- Bile salts
- Bilirubin
- Cholesterol
- Neutral fats
- phospholipids
- electrolytes
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Bile salts are
cholesterol derivitives that function in fat emulsification (makes fat droplet out of fat) and absorption
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Bilirubin is a pigment formed from
heme
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The recycling of bile salts is called
enterohepatic circulation
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What are the steps of enterohepatic circulation?
Bile salts -> duodenum ->reabsorbed from ileum -> hepatic portal blood -> liver -> secreted into bile
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Bile salts are recirculated ____ or more times for one meal
5
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What is the endocrine function of the pancreas?
Pancreatic islets secrete insulin and glucagon
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What the exocrine functions of the pancreas?
- Acini (clusters of secretory cells) secrete pancreatic juice
- Zymogen granules of secretory cells contain digestive enzymes
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A watery alkaline solution that neutralizes chyme describes
pancreatic juice
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Pancreatic juice is made up of
electrolytes and enzymes
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Bile secretion is stimulated by
- bile salts in enterohepatic circulation
- secretin from intestinal cells exposed to HCI and fatty chyme
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Gallbladder contraction is stimulated by
- cholecystokinin (CCK)
- Vagal stimulation
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Cholecystokinin comes from
intestinal cells exposed to proteins and fat in chyme
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CCK also causes
the hepatopancreatic sphincter to relax (dilate and open)
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CCK induces
the secretion of enzyme-rich pancreatic juice by acini
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Secretin causes
secretion of bicarbonate-rich pancreatic juice by duct cells
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Chyme from stomach contains
- partially digeted carbohydrates and proteins
- undigested fats
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What are the requirements for digestion and absorption in the small intestine?
- Slow delivery of hypertonic chyme
- Delivery of bile, enzymes, and bicarbonate from the liver and pancreas
- Mixing
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How does chyme move through the small intestine?
peristalsis
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Peristalsis in the small intestine is iniciated in __________________
the late intestinal phase
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What are the regions of the large intestine?
- Cecum (pouch with attached vermiform appendix)
- Colon
- Rectum
- Anal canal
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The rectum has three
rectal valves that stop feces from being passed with gas
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What are the two types of anal sphincters and what are they made of?
- Internal anal sphincter-smooth muscle (involuntary)
- External anal phincter-skeletal muscle (voluntary)
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Bacterial flora (E Coli) colonize the ________, ferment ______________, release _______________ and synthesize ________________
- colon
- indigestible carbohydrates
- irritating acids and gases
- B complex vitamins and vitamin K (blood clotting)
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what are the functions of the large intestine?
- Reclaims vitamins, water, and electrolytes
- Major function is propulsion of feces toward the anus
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How does the large intestine move stuff?
Haustral contractions: Slow segmenting movements - haustra sequentially contract in response to distension
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_____________ is initiated by presence of food in the stomach
Gastrocolic reflex
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The gastrocolic reflex activates
three to four slow powerful peristaltic waves per day in the colon (mass movements)
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Parasympathetic signals stimulate _______________________ and relax the ________________
- contraction of the sigmoid colon
- internal anal sphincter
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Distension initiates
spinal defecation reflex
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What are the three processes of chemical digestion?
- Catabolic (breaking down)
- Enzymatic
- Hydrolysis
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