Digestive System Flashcards
what is another name of the digestive tract?
gastrointestinal tract
where does the GI tract extend from?
oral cavity to anus
what does the GI tract pass through?
passes through pharynx, esophagus, stomach and small and large intestines
what are the two surfaces of the GI tract?
mucosal - faces the lumen
serosal- faces the blood
what are mesentery?
double sheets of peritoneal membrane, continous collection of tissue
what are the functions of the mesentery?
- suspend portions of small and large intestine from the posterior abdominal wall
- digestive organs connected to it
- contains blood vessels, nerves, and lymphatic vessels that go
- stabilizes portions of attached organs
- prevent intestines from entangling
what epithelial tissue is the oral cavity lined with?
stratified squamous epithelium
what does the tongue secrete that aids in digestion?
mucins and lingual lipase
what are the three pairs of salivary glands?
- parotid glands
- sublingual glands
- submandibular glands
what do parotid salivary glands produce?
serous secretion, enzyme salivary amylase
what two categories of foods begin digestion in the oral cavity?
starches and lipids
what do sublingual salivary glands produce?
mucous secretion that acts as a buffer and lubricant
what do submandibular salivary glands produce?
secretes buggers, glycoproteins, and salivary amylase
what salivary gland produces the majority of saliva?
submandibular glands
what are the components of saliva?
99.4% water, 0.6% electrolytes, buggers, glycoproteins/mucins, antibodies, enzymes, waste products
what are the functions of saliva?
- lubrication
- dissolving chemicals that stimulate taste buds
- initiating digestion of complex carbohydrates through salivary amylase
what are the three regions of the pharynx?
nasopharynx, oropharynx, laryngopharynx
what is another word for swallowing?
deglutition
what are the three phases of swallowing?
- buccal phase
- pharyngeal phase
- esophageal phase
what is the buccal phase of swallowing?
tongue pushed bolus against soft palate and back of mouth, triggering swallowing reflex
what is the pharyngeal phase of swallowing?
breathing is inhibited as the bolus passes through the closed airway
what is the esophageal phase of swallowing?
food moves downward into esophagus, propelled by peristaltic waves and aided by gravity
where does the esophagus bring food?
to the stomach
where does the esophagus enter the abdominopelvic cavity?
esophageal hiatus
what innervates the esophagus?
esophageal plexus
what are the 4 histological layers of the esophagus?
- mucosal
- submucosal
- muscularis externa
- adventitia
what epithelial cell makes up the mucosal layer of the esophagus?
non-keratinized stratified squamous
what is found in the submucosal layer of the esophagus?
esophageal glands which produce mucous secretions that reduce friction between bolus and esophageal lining
what is the outermost epithelial layer of the esophagus?
adventitia
what is narrowing/tightening of the esophagus called?
strictures
what are strictures often caused by?
stomach acids/ reflux that damages tissue over time; most common gastroesophageal reflux disease (GERD)
what is a common treatment for strictures?
balloon dilators
what are the 4 regions of the stomach?
- cardia
- fundus
- body
- pylorus
what is the function of the cardia?
contains mucous glands; secretions coat connection with esophagus protecting it from acids and enzymes
what is the function of the fundus?
secretes most of the acids and enzyme for gastric digestion
what is the function of the body?
mixer
what is the function of the pylorus?
secretes mucus and digestive hormones
what is the function of the mucosal barrier of the stomach?
prevents enzymes/acids from digesting stomach itself
what are the components of the mucosal barrier that make it impermeable?
- goblet cells produce coast of alkaline mucus
- mucus traps a thick coat of bicarbonate rich fluid
- epithelial cells that are joined by tight junctions
- gastric glands that have cells impermeable to HCL
how quickly do damaged epithelial cells/mucosal cells turnover?
3-7 days
where are gastric glands found?
in the fundus and body of the stomach
what are found at the surface of gastric surfaces?
gastric pits
what are the two cells of gastric glands that secrete the majority of gastric juice into the stomach?
parietal cells and chief cells
what do parietal cells secrete?
intrinsic factor and hydrochloric acid
what do chief cells secrete?
pepsinogen
what happens to pepsinogen in the gastric lumen?
converted to pepsin (active proteloytic enzyme) by HCL
how is HCL secreted from parietal cells?
- hydrogen ions generated inside parietal cell and carbonic anhydrase converts Co2 and H2o into carbonic acid
- Cl- is brought into the parietal cells and bicarbonate ions are ejected into the interstitial fluid by a countertransport mechanism
- chloride ions diffuse across the cell and exit through open chloride channels into the lumen of the gastric gland
- the hydrogen ions are actively transported into the lumen of the gastric gland
what is the pH of the stomach kept at due to parietal cell excretions?
1.5-2 (very acidic)
what are the 4 functions of the acidic environment?
- kills microorganisms
- denatures proteins and inactivates enzymes in food
- helps break down plant cell walls and connective meat tissue
- activates pepsin
what do mucous neck cells secrete?
acid mucus
what do enteroendocrine cells secrete?
gastrin, histamine, endorphins, serotonin, cholecystokinin (CCK), and somatostatin
where are pyloric glands?
located in the pylorus
what is the function of the pyloric glands?
produce mucous secretions
what is commonly found in pyloric glands?
enteroendocrine cells
what are the two important enteroendocrine cells?
G cells and D cells
what do G cells produce?
gastrin
what is the function of gastrin?
stimulates secretion of parietal and chief cells
what do D cells produce?
somatostatin
what is the function of somatostatin?
a hormone that inhibits release of gastrin
what hormone rises before meals to initiate hunger?
ghrelin
what is the role of pepsin in the stomach?
preliminary digestion of proetins
what does salivary amylase digest?
carbohydrates
what is responsible for the digestion of lipids in the stomach?
lingual lipase and gastric lipase
what is the makeup of intestinal juice?
mainly water but some mucous
why is intestinal juice slightly alkaline?
assists in buffering acids, moistens chyme, keeps digestive enzymes and products of digestion in solution
where does chyme arrive in small intestine?
duodenum
what moves chyme to jejunum?
weak peristaltic contractions
what controls peristaltic contractions?
myenteric reflexes and submucosal motor neurons
are peristaltic contractions under CNS control?
no
how long does it take for material to pass from duodenum to end of illeum?
~5 hours
what two reflexes speed up movement along small intestine?
gastroenteric reflex and gastroileal reflex
what does the gastroenteric reflex do?
stimulates motility and secretion along the entire small intestine