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