Quiz 3 Flashcards
packet 5a and until slide 62 on 5b
what takes place inside the gastrointestinal tract (GIT)?
ingestion: intake of food
digestion: physical and chemical breakdown of food in the GI tract
absorption: movement of nutrients from within the digestive tract into circulation
elimination: the removal of undigested food (solid waste) from the body in the form of feces
what are primary organs of the GIT?
- structures associated with the oral cavity (teeth, tongue, hard and soft
palate), pharynx: the shared region between the oral and nasal cavities towards the back of the mouth - esophagus
- stomach
- small intestine
- large intestine
what are accessory organs of the GIT?
accessory organs participate in digestion by producing and releasing digestive secretions, are not part of the GI tract (part of the digestive
system)
1. salivary glands
2. biliary system (liver, gallbladder,
and bile ducts)
3. pancreas
accessory organs release secretions into ducts that empty into the lumen of the GI tract
what are the two types of digestion?
- physical digestion accomplished by GI movement (GI motility), muscular movements that mix food with
digestive secretions and moves food through the GI tract - chemical digestion of food accomplished by digestive secretions
released from exocrine glands
where do digestive secretions originate from?
digestive secretions come exocrine glands embedded in the lining of the GI tract and from accessory organs
accessory organs:
1. salivary glands: saliva
2. biliary system (liver and gallbladder): bile
3. pancreas: pancreatic Juice
GI tract:
stomach: gastric Juice
goblet cells embedded in the lining of the GI tract: mucus
exocrine glands vs. endocrine glands
endocrine glands release hormones into the blood that regulate the process of digestion
exocrine glands release secretions into ducts that empty into the lumen of the GI tract and facilitate chemical digestion
what are the sources of digestive enzymes?
saliva, pancreatic juice. gastric juice, and lining of the small intestine
what do digestive enzymes do?
facilitate a specific chemical reaction called
hydrolysis (breaking chemical bonds by the addition of water)
proteins, triglycerides, and carbohydrates undergo chemical digestion by hydrolysis, forming small, simple molecules that can
be absorbed
proteins -> amino acids
triglycerides -> fatty acids
carbohydrates –> sugar molecules (glucose)
what are the four tissue layers of the GIT?
mucosa: inner lining
submucosa: layer between mucosa and muscularis
muscularis: smooth muscle
serosa: outer covering
what does the mucosa of the GIT do?
the mucosa is in direct contact with ingested food and exocrine glands release secretions needed for chemical digestion
goblet cells that produce mucus (thick, sticky, viscous material) that protects the
mucosal lining
endocrine glands that release hormones
what is the function of the mucosal lining?
mucosal lining consists of epithelial cells, forms a barrier that regulates the movement of substances from the GIT into the bloodstream, allow nutrients to be absorbed and can block harmful substances from
entering the blood, depending on location GIT, mucosal lining can be highly permeable or highly restrictive, disruption of tight junctions can lead to disease states (celiac disease, inflammatory bowel disease, food
allergies)
what does the submucosa of the GIT do?
submucosa is a highly vascularized layer
that lies between the mucosa and
muscularis, here blood vessels circulate
nutrients to and away from GI tract, lymphatic vessels circulate fat-soluble
nutrients away from the GI tract and an embedded network of nerves that regulate
digestion
what does the muscularis of the GIT do?
muscularis consists of two layers of muscle with an embedded network of nerves, muscularis promotes physical digestion by mixing food with digestion secretions and keeps food moving through the entire
length of the GI tract
what is peristalsis?
rhythmic wave-like series of muscular contractions followed by muscular relaxation that propels food forward in the GI tract
what is segmentation?
process of mixing food contents in the
digestive tract with secretions to create a more uniform mixture, in the process, food is slowly propelled forward
what does the serosa of the GIT do?
serosa is the outer layer of connective
tissue that encloses the GIT and anchors it in the abdominal cavity, it secretes fluid that lubricates and prevents friction between the
digestive organs (protection)
what hormones regulate digestion?
GI hormones are produced by endocrine cells embedded in the mucosal lining of the stomach and small intestine, GI hormones are released into the blood that regulate digestion by:
- ↑↓GI motility
- ↑↓ release of GI secretions
- some GI hormones ↑↓ hunger/satiety
what is the enteric nervous system?
embedded in the lining of the GI tract (submucosa and muscularis) are millions of nerves, signals play a critical role in maintaining optimal digestive functions, gathers information from sensors within the
lining of the GI tract
- ↑↓GI motility
- ↑↓ the release of GI secretions
what are the types of receptors in the ENS?
mechanoreceptors: detect stretching caused by the presence of food in the GI tract
chemoreceptors: detect the chemical composition of food
osmoreceptors: detect how much liquid is present in the GI tract
these send signals to other regions of the GI tract and by sending signals to the CNS via the vagus nerve (brain-gut axis)
what is the cephalic response?
in response to sensory stimuli the brain sends neural signals to GIT which trigger the release of GI secretions and increases gastric motility, prepares the GIT to begin receiving food
what neurotransmitters does the ENS release?
serotonin is a neurotransmitter that regulates both GI and CNS
functions, ~90% of the body’s serotonin is
in the GIT, where it influences GI motility, secretion, and pain sensation
altered levels of serotonin may be a contributing factor in IBS, affecting
stool consistency, elimination frequency, and increased pain sensitivity in the colon
what is a functional disorder?
disorders that affect physiological functions but cannot be explained by structural or biochemical abnormalities (no one identifiable cause)
what are the 3 major functions of the digestive system?
digestion, nutrient absorption, the formation and elimination of unabsorbed food residue
what triggers the release of saliva?
- presence of objects (food) in the mouth (mechanoreceptors)
- acidic beverages/foods (lemons, coffee, soft drinks)
that damage tooth enamel particularly strong trigger
saliva release - thought, sight, smell of food trigger release of saliva
(cephalic response)
what are the functions of saliva?
moistens food making it easier to swallow, dissolves food
components, which enables taste, enzymatic digestion
protects teeth by neutralizing acids produced by bacteria and acidic food/beverages
what is xerostomia?
the (feeling of dry mouth) often (but not always) associated with insufficient saliva production, caused by parkinson’s, some drugs, and aging
what is flavor?
the combined sensory signals of taste (gustation) and smell (olfaction) perceived by the brain
how is taste detected?
the surface of the tongue is covered with protuberances called papillae, embedded within papillae are hundreds of taste buds (taste cells) that contain gustatory (taste)
receptors, saliva dissolves food, which releases molecules, referred to as tastants, that stimulate gustatory receptors that trigger neural signals that are sent to the brain where they are identified as sweet, sour, bitter, salt or savory
what are the 5 tastants that stimulate gustatory receptors?
- monosodium glutamate: umami (savory)
- hydroxyl groups (-OH): sweet
- hydrogen ions (H+): sour
- alkaloids: bitter
- sodium, potassium, chloride ions (Na+, K+, Cl-): salty
how is smell detected?
olfactory receptors are embedded in the lining of
the nasal cavity, aroma molecules in food (referred to as odorants) are detected by olfactory receptors, stimulation of olfactory receptors send signals the
brain, the brain (frontal cortex) interprets gustatory and
olfactory signals to create the true flavor of food, majority of flavor determined by olfaction
what is mastification?
chewing, the process whereby teeth grind food into
smaller pieces, begins the process of physical digestion
how does swallowing work?
soft mass of chewed food is called a bolus, tongue pushes bolus against the hard palate and eventually towards the back of oral cavity, initiate swallowing, soft
palate and uvula rise, blocking the nasal passage, this prevents food from entering nasal cavity
what is dysphagia?
conditions that weaken or damage the muscles and
nerves used for swallowing, caused by neurodegenerative diseases (cerebral palsy, Parkinson’s disease, Alzheimer’s disease), conditions such as stroke and head trauma, anatomical such as scarring, tumors, cleft palate
what is a cleft palate?
when the hard palate fails to fuse properly during embryonic development, resulting in an opening, often includes a split upper lip (cleft lip), food can enter the nasal cavity, making feeding difficult, requires
surgical correction
what prevents food from entering the lungs?
swallow, food passes through the pharynx (shared region
between oral and nasal cavities) and into the esophagus, air passes through the pharynx but enters the lungs via the trachea, to prevent the bolus from entering the trachea, a flap-like structure called the epiglottis,
covers the trachea and directs the bolus into the esophagus
how is the gastroesophageal sphincter regulated?
peristalsis moves the bolus down the esophagus, causes the esophageal wall to stretch detected by mechanoreceptors, the stretching of the esophagus signals the gastroesophageal sphincter to relax, allowing the bolus to enter the stomach, once bolus enters the stomach, gastroesophageal sphincter closes, preventing the contents of the stomach from reentering the esophagus
what are the three digestive events in the stomach?
- chemical digestion: gastric juice
- physical digestion: gastric motility
- storage: temporary holding chamber
what hormone is released when the stomach is empty?
when the stomach is empty, endocrine cells embedded in the mucosal lining of the stomach release the hormone ghrelin, ghrelin signals the brain, which in turn
stimulates hunger and gastric motility (churning)
what hormone is released when food enters the stomach?
the arrival of food into the stomach stimulates release of a hormone called gastrin, food causes stomach
walls to stretch (mechanoreceptors), which triggers the release of gastrin (hormone from endocrine cells in the
mucosal lining of the stomach)
gastrin: ↑ release of gastric juice,↑ gastric motility
what are gastric pits?
invaginations in the mucosal lining of the stomach that release components of gastric juice (digestive enzyme, HCl, intrinsic factor, goblet cells: mucous producing cells)
what are goblet cells?
mucus producing cells located at the surface of gastric pits, secrete mucus that creates the gastric mucosal
barrier that protects the gastric mucosal lining
from the acidic gastric juice, if gastric mucosal
barrier compromised, cause gastritis, ulcers, and increase risk stomach cancer
what are stomach ulcers?
lesion in the mucosal lining of the GIT (typically in
stomach, duodenum, and/or esophagus), can lead to complications such as bleeding and increase risk of
cancer, majority of ulcers not caused by stress, diet, or lifestyle, majority ulcers caused by a bacterium (Helicobacter pylori) that degrades the protective gastric
mucosal barrier, causing inflammation and localized damage
what is intrinsic factor?
intrinsic Factor (IF) is needed for absorption of vitamin B 12 (vitamin B 12 assists in formation of red blood cells and formation of myelin sheath on nerves (neurons)
what is megalobastic anemia vs pernicious anemia?
megalobastic: vitamin B12 deficiency characterized by large (macrocytic) nucleated (immature) red blood cells, which impairs ability to deliver oxygen to tissues, can cause neurological problems since B12 is needed for the formation of myelin sheath
pernicious: autoimmune disorder that attacks the cells that make IF which interferes with B12 absorption
how does the stomach contribute to digestion?
instead of 2 layers, the muscularis in the stomach has a third muscle layer that helps mix food with gastric juice, as a result of vigorous mixing of
food with gastric secretions, food physically/chemically transformed into an acidic, paste-like substance called chyme
how is food stored?
rugae: ridges produced by folds in tissue
as the stomach fills with food, the rugae unfold
and flatten, this allows the stomach to hold large
volumes of food (capacity of 1-2 liters), stretching (mechanoreceptors) of stomach walls signal satiety to the brain
how does gastric emptying work?
peristalsis pushes chyme towards the base of the
stomach (pylorus), the pyloric sphincter regulates the flow of chyme from the stomach into the small intestine, only small amounts of chyme exit the
stomach at any one time, large volume increases the rate of gastric emptying (more distention), liquids have a faster rate of emptying than solids (solids must be liquefied), high fat foods decrease
gastric emptying rate compared to low fat foods
what is pyloric stenosis?
a thickening of the pyloric sphincter, typical age of onset between 2 – 8 weeks when milk is unable to pass through the pyloric sphincter which prevents milk from leaving the stomach and entering
the small intestine (symptoms: projectile vomiting, weight loss, hungry after feeding, and dehydration)
what are the three sections of the small intestine?
duodenum: chyme mixes with secretions from the pancreas and gallbladder, where the majority of chemical digestion takes place
jejunum: where majority of nutrient and water absorption takes place
ileum: absorption of remaining nutrients, mostly vitamin B12
how do hormones regulate gastric emptying?
cholecytokinin (CCK): communicates satiety to the brain and decreases gastric motility and the release of gastric secretions
gastric inhibitory peptide: decreases gastric motility and the release of gastric secretions
what does GLP-1 do?
the presence of food in the stomach (gastric stretching) and nutrients in the SI stimulates
the release of GLP-1 which acts on the hypothalamus to:
- increases feelings of fullness
- reduces overall food intake
- helps regulate body weight
- GLP-1 acts on the stomach to decrease gastric emptying
what is the enterogastric reflex?
the presence of chyme in the duodenum causes the duodenum wall to stretch (mechanoreceptors), in response, a neural signal is sent to the brain, the brain responds by sending a neural signal to the stomach that slows gastric motility and release of gastric juice, slows gastric emptying, giving
the SI time to carry out its digestive functions
what does pancreatic juice do?
aid in chemical digestion in the small intestine, pancreatic juice is alkaline (bicarbonate), which
neutralizes chyme as it enters the duodenum, pancreatic juice contains enzymes needed for the
digestion of CHO, protein, and lipids, pancreatitis (inflammation of the pancreas) can impact digestive enzymes from reaching the duodenum leading to nutrient malabsorption
what does bile do?
bile is produced by the liver, transported through bile ducts to the gallbladder, where bile is stored, in response to the presence of fat in chyme, the hormone CCK causes the gallbladder to contract
and release bile, bile aids in fat digestion by breaking large fat globules into small droplets
(emulsification)
what is enterohepatic circulation?
the liver is unable to synthesize enough bile acids to replenish bile, therefore it depends on the return of bile acids via enterohepatic circulation, enterohepatic circulation is the route where
components of bile (bile bile acids) are recycled
and reused
bile flows liver ⇉ gallbladder ⇉ SI
(emulsification)
bile components flows SI ⇉ liver ⇉ (bile synthesized)
what are gallstones?
pieces of solid material (cholesterol and bile
pigments) that can lodge in bile ducts and block the release of bile, often results in the surgical
removal of gallbladder, liver assumes role of
gallbladder post-surgery, initial low-fat diet
recommended
what happens to undigested food?
undigested food residue passes from the SI into the large intestine where:
1. excess fluids are removed
2. microbial breakdown of undigested food residue
3. formation and elimination of solid waste
the ileocecal sphincter regulates the movement of undigested food residue from the ileum into the cecum
what are the three sections of the large intestine?
extends from the ileocecal sphincter (between ileum and cecum) to the anus
1. cecum
2. colon
3. rectum
what are haustra and haustral contractions?
bands of connective tissue run along the wall of the LI, cause puckers (haustra) to form along the
colon wall, when a haustrum (singular) fills with feces, it stimulates muscles to contract, pushes the feces to the next haustrum, referred to as haustral contractions (a specific type of motility that takes place in the colon), haustral contractions allow maximum absorption of water and electrolytes
what are mass movements stimulated by?
- stretching of the colon wall by feces (why high fiber diet, increases fecal bulk, promotes regular bowel movements)
- gastrocolic reflex: a neural reflex that stimulates mass movements in the colon in response to eating
what is diverticular disease?
when stool is too hard or too little fecal material,
muscles strain to move feces, increased straining can cause weak spots in the colon to bulge outwards (diverticula), if fecal matter becomes
trapped and inflamed then it turns into diverticulitis
