Ch. 9 Gastrointestinal Function Flashcards
what are the accessory organs?
salivary glands, liver, gallbladder, bile ducts, and pancreas
what is the alimentary canal?
the canal through which food is passed. consists of the oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, and anus
what is the liver, gallbladder, and pancreas collectively referred to? why is this?
they are collectively referred to as the hepatobiliary system because of their close proximity to each other and their complementary functions
what are the four layers of the GI tract walls from inner to outer?
mucosa, submucosa, muscle, and serosa
what is the purpose of the mucosa layer of the GI tract walls?
it secretes mucus which facilitates the movement of GI contents and protects the GI tissue from the extreme pH conditions of the GI tract
why do the epithelial mucosa cells have a high turnover rate?
because of erosion associated with food passage and the highly acidic environment
what does the submucosa layer of the GI tract walls consist of?
connective tissue. includes blood vessels, nerves, lymphatics, and secretory glands.
what does the muscle layer of the GI tract consist of?
circular and longitudinal smooth muscle layers that function in peristalsis
what is peristalsis?
the wavelike motion of muscle contractions that propels food through the GI tract
large serous membrane that lines the abdominal cavity
peritoneum
are the two layers of the peritoneum and what is the difference?
the outer parietal peritoneum layer overs the abdominal wall and the top of the bladder and uterus. the inner visceral peritoneum layer encases the abdominal organs.
what is the peritoneal cavity?
the space between the parietal and visceral layers of the peritoneum.
what does the peritoneal cavity contain serous fluid?
to decrease friction and facilitate movement
what is the mesentery?
a double layer peritoneum that supplies the intestinal wall. it supports the intestines while allowing flexibility to accommodate peristalsis and varying content volumes
what structures make up the upper GI tract?
the oral cavity, pharynx, esophagus, and stomach
what does mastication do?
(chewing) it pulverizes the food into small pieces so that saliva can break down the food further
what is the function of saliva?
it is secreted from the salivary glands to moisten and further break down food. it contains enzymes and antibodies that can kill or neutralize bacteria
what is the function of the tongue in digestion?
it pushes the semisolid food mass to the back of the throat where it is swallowed.
what cranial nerves initiate the swallowing reflex?
food passing over the trigeminal and glossopharyngeal nerves initiate it
how do the trigeminal and glossopharyngeal nerves initiate the swallowing reflex?
they relay info to the swallowing center in the medulla and then the swallowing center coordinates the movement of food from the mouth through the esophagus to the stomach with cranial nerves V, IX, X, and XII
what is the purpose of the lower esophageal sphincter?
it relaxes to allow food from the esophagus to enter the stomach and then prevents the contents in the stomach from refluxing back into the esophagus
what are rugae?
wrinkles formed by the stomach wall when it is empty and shrinks. when it fills, they unfold and the wall stretches
how much content can the rugae stretch and accommodate for in the stomach?
2-4 L
what digestion occurs in the stomach?
in the stomach, hydrochloric acid and enzymes further chemically digest food and the peristaltic churning mechanically digests the food
what is the food mixture in the stomach called
chyme
what does the highly acidic nature of chyme do?
it aids in digestion and the destruction of bacteria
how does the stomach’s inner lining protect itself from its acidity?
epithelial cells are densely packed to prevent tissue damage and there are numerous glands located in the stomach that coat the inner lining with a thick layer of mucus
are nutrients absorbed in the stomach?
no, they are just prepared for absorption
what can be absorbed in the stomach?
alcohol
how does chyme leave the stomach?
through the pyloric sphincter in small (1-3mL), intermittent amounts
as chyme passes through the pyloric sphincter, into the duodenum, what things are added to the mixture?
liver and pancreatic secretions to continue the digestion process
what are some of the liver’s primary functions that are vital for homeostasis?
metabolize carbs, proteins, and fats; synthesize glucose, protein, cholesterol, triglycherites, and clotting factors; store glucose, fats, and micronutrients and release them when needed; detoxify the blood of potentially harmful chemicals; maintain intravascular fluid volume through the production of circulating proteins; metabilize medications and prepare them for excretion; produce bile; inactivate and prepare hormones for excretion; remove damaged or old erythrocytes from blood to recycle iron and protein; serve as a blood resevoir; convert fatty acids to ketones
about how much blood does the liver store?
approximately 450 mL
what is the tough membrane that protects the liver called?
Glisson’s capsule
where does the liver get its blood supply from?
the hepatic artery and the portal vein
what does the hepatic artery do?
carries oxygenated blood from general circulation to the liver at a rate of approximately 300 mL per minute to nourish the liver
what does the portal vein do?
carries partially deoxygenated blood from the stomach, pancreas, and spleen, as well as from the small and large intestines to the liver at an approximate rate of 1000 mL per minute so that the liver can process nutrients and digestion by-products
as much as ….% of the liver’s tissue can be lost or removed and the liver can still regenerate its tissue
75%
why can the liver regenerate?
primarily due to certain liver cells (hepatocytes) that act as stem cells
what do hepatocytes do in addition to providing the liver with regeneration capabilities?
they produce bile and perform most of the liver’s activities
what is the rate at which hepatocytes produce bile?
600-1200 mL per day
what is bile?
a green or yellowish liquid that contains water, bile salts, conjugated bilirubin, cholesterol, and electrolytes.
what are bile salts necessary for?
emulsifying fats and fat-soluble vitamins so that they can be absorbed by the small intestine
what does the distal ileum do?
it reabsorbs most of the bile and returns it to the liver through the portal vein for recycling
what component of the bile helps to neutralize the acidic gastric contents so that the intestinal and pancreatic enzymes can function?
bicarbonate ions
what are the two places bile can go after it leaves the liver?
straight to the duodenum or to the gallbladder for storage
in addition to storing bile, what does the gallbladder do?
it concentrates it by removing water
what triggers the gallbladder to contract and release bile?
the presence of chyme in the small intestine
where is the pancreas located?
it is nestled under the small intestine and the liver?
what two functions does the pancreas have?
endocrine and exocrine
what is the exocrine function of the pancreas?
it produces enzymes, electrolytes, and water necessary for digestion and secretes these into a duct that delivers them to the duodenum to join chyme
what is the endocrine function of the pancreas?
includes producing hormones to help regulate blood glucose and thereby maintaining homeostasis
what are the structures of the lower GI tract?
the small intestine, large intestine, and anus
what is the longest section of the GI tract?
the small intestine
what is the importance of the length of the small intestine?
it allows for adequate absorption
what digestion occurs in the small intestine?
enzymes that were excreted into the small intestine break the large food molecules into smaller molecules which are then absorbed and transported to the circulatory and lymphatic system
what is the purpose of the villi and microvilli in the small intestine?
they increase the surface area for absorption of nutrients
about how long is the large intestine?
about 5 feet
does the large intestine have villi?
no
cecum
the pouch in which the small intestine ends. this is where the appendix is attached
what makes up most of the large intestine?
the colon
what are the three sections of the colon?
the ascending, transverse, and descending
what does the mixture entering the large intestine contain?
water, unabsorbed food molecules, indigestible food remnants, and electrolytes
how does the colon further participate in digestion?
it absorbs 90% of the water and electrolytes, and E. coli feeds off the undigested or unabsorbed food remains
when does chyme become feces?
when if move through the colon
what is feces comprised of?
the remaining undigested or unabsorbed remnants along with bacteria
why does feces introduce approximately 300 mL of mucus?
to aid in bowel movements, even in times of decreased dietary intake
a resevoir to store feces
rectum
how does the rectum elicit the defecation reflex?
it expands when feces enters the area, stimulating the stretch receptors in the rectal wall which send an impulse through the spinal cord to elicit it
why does feces become more difficult to expel as it stays in the large intestine for longer periods of time?
more water is absorbed from it the longer it remains in the large intestine
how do the sympathetic and parasympathetic nervous systems affect digestive activity?
stimulation of the sympathetic nervous system slows digestive activity while stimulation of the parasympathetic speeds it up
what are age related changes to the stomach?
stomach lining may shrink and become inflammed leading to atrophic gastritis. achlorhydria occasionally because of atrophic gastritis, and achlorhydria can cause b12 deficiency and slow digestion
achlorhydria
decreased stomach acid production
what are liver changes associated with age?
decreased blood flow, delayed drug clearance, and a diminished capacity to regenerate damaged liver cells
changes in the metabolism and absorption of what nutrients can occur with age?
lactose, calcim, and iron
decreased calcium absorption can lead to what in the older adult?
bone mineral loss and osteoporosis
why is the older person at risk for constipation?
decreased peristalsis
what are the two underlying pathological issues that affect the GI tract?
altered nutrition and impaired elimination
what are conditions that alter nutrition?
issues with consuming, digesting, and absorbing food
regardless of the cause of altered nutrition what is the similar end result for almost all cases?
inadequate nutritional states in which individuals may be underweight and vitamin deficient
what are conditions impairing elimination?
constipation and diarrhea
can conditions that cause altered nutrition cause problems with elimination?
yes
what are congenital defects of the upper GI tract?
cleft lip and palate and pyloric stenosis
relatively common congenital defects of the mouth and face that are apparent at birth
cleft lip/cleft palate
when do cleft lip/palate conditions usually develop?
between the 4th and 9th week (2nd and 3rd month) of gestation
what things have cleft lip/palate been linked to?
genetic mutations, maternal diabetes, drugs, toxins, viruses, vitamin deficiencies, and cigarette smoking
who are most likely to be affected by cleft palate/lip?
children of Native American, Hispanic and Asian descent. African Americans are the least likely to have it.
what gender is most likely to have cleft palate? cleft lip?
women are 2x as likely to have cleft palate, men are 2x as likely to have cleft lip
what problems can a cleft lip/palate lead to?
feeding issues - decreased sucking ability and increased risk for aspiration, speech problems, ear infections, and hearing problems
what other malformations may be present with cleft lip/palate?
teeth and nose malformations
what does cleft lip result from?
failure of the maxillary processes and nasal elevations or uppper lip to fuse during development. can be unilateral or bilateral
what does cleft palate result from?
failure of the hard and soft palates to fuse in development, creating an opening between the oral and nasal cavities
by what age is cleft lip repair recommended? when is cleft palate?
by 3 months for cleft lip and by 1 year for cleft palate
what is pyloric stenosis?
a narrowing and obstruction of the pyloric sphincter because muscle fibers become thick and stiff, making it difficult for the stomach to empty food into the small intestine
when does pyloric stenosis usually present itself?
may be present at birth, or may develop later in life, but development after 6 months is rare
what is the cause of pyloric stenosis?
the exact cause is unknown, but genetics are thought to play a role
who is pyloric stenosis most likely to effect?
caucasians and men
when do the clinical manifestations of pyloric stenosis usually appear?
within several weeks after birth
in this form of pyloric stenosis, the hypertrophied pyloric muscle can be palpated as a hard, olive shaped mass in the abdomen and vomiting is usually the first symptom.
the congenital form
what are manifestations of pyloric stenosis?
regurgitation, vomiting - usually after every feeding and it’s usually projectile, belching, wavelike stomach contractions, small infrequent stools, abdominal pain, failure to gain weight, dehydration, irritability
why do wavelike stomach contractions present theirselves with pyloric stenosis?
because there is an increased peristaltic effort to pass food through the narrowed areas
why does irritability occur with pyloric stenosis?
because of persistent hunger
difficulty swallowing
dysphagia
how does dysphagia usually develop?
secondary to a condition that causes mechanical obstruction of the esophagus or impaired esophageal motility
what are some conditions that may lead to dysphagia?
mechanical obstructions, neurologic disorders, muscular disorders
what are some mechanical obstructions that can cause dysphagia?
congenital atresia (separation of the upper and lower esophagus), esophageal stenosis or stricture, esophageal diverticula (outpouching of the esophageal wall), tumors (esophageal or of nearby structures)
what are some neurological disorders that can cause dysphagia?
stroke, cerebral damage, achalasia (failure of the LES to relax because of loss of innervations), Parkinson’s disease, Alzheimer’s disease
what are clinical manifestations of dysphagia?
sensation of food being stuck in the throat, choking, coughing, ‘pocketing’ of food in the cheeks, difficulty forming bolus, delayed swallowing, painful swallowing (odynophagia)
what is there an increased risk of with dysphagia?
aspiration
what is a muscular disorder than can cause dysphagia?
muscular dystrophy
voluntary or involuntary forceful ejection of chyme from the stomach up through the esophagus and out the mouth
vomiting or emesis
what are causes of vomiting?
protection from infection, drug or alcohol overdose, food poisoning, etc; reverse peristalsis from an intestinal obstruction; increased intracranial pressure - projectile; severe pain
what area of the brain coordinates vomiting, and what things can stimulate this center?
the medulla; drugs, toxins, and chemicals can stimulate it
what is the sequence of involuntary vomiting?
a deep breath is taken, the glottis closes and the soft palate rises, respirations cease in order to minimize the risk for aspiration, the gastro esophageal sphincter relaxes, abdominal muscles contract, squeezing the stomach against the diaphragm and forcing the chyme upward toward the esophagus, reverse peristaltic waves eject chyme out the mouth
vomiting may be preceded by what two things?
nausea - the subjective urge to vomit
retching - strong unproductive effort to vomit
what can recurrent vomiting lead to?
fluid, electrolyte, and pH imbalances. also exhaustion due to the strong muscle contractions needed
when is an individual at risk for aspiration while vomiting?
when supine or unconscious, when the vomiting or cough reflex is suppressed
what is the name for the contents vomitted?
vomitus
what can aspiration of vomitus cause?
serious damage and inflammation to lung tissue