Biology Digestive System Flashcards
The oral cavity (mouth) is where ___ and chemical digestion begins
mechanical
___ is the breakdown of large food particles into smaller particles through physical actions, such as the biting and chewing action of teeth (mastication ) or the churning motion of the stomach
mechanical digestion
___ refers to the enzymatic breakdown of macromolecules into smaller molecules and begins in the mouth when the salivary glands secrete saliva
chemical digestion
Saliva contains ___ amylase (ptyalin), which hydrolyzes starch to maltose
salivary
Once food has been swallowed, it is referred to as ___
bolus
The esophagus is the muscular tube responsible for transporting the ___ from the oral cavity to the stomach
bolus
The bolus is moved down the esophagus by rhythmic waves of involuntary ___ contractions called peristalsis
muscular
Peristalsis is not ___
voluntary
The ___ is closed off from the stomach by contraction of a muscular structure called the lower esophageal (cardiac) sphincter
esophagus
The lower ___ sphincter (LES) protects the esophagus from the acidic gastric contents
esophageal
The esophagus lies within the ___ cavity, which regularly is exposed to negative pressure as the person inhales
thoracic
Contrastingly, the stomach is located in the ___ cavity, which has a relative positive pressure
abdominal
Therefore, without the actions of the lower esophageal ___, the pressure gradients favor a continual reflux of gastric content into the esophagus, resulting in a condition known as gastroesophageal reflux disease (GERD)
sphincter
___ digestion relies on the gastric mucosa, which lines the walls of the stomach and contains the gastric pits and gastric glands
chemical
Various cell types in the gastric mucosa produce the chemicals responsible for chemical digestion:
Mucous cells, in gastric pits, secrete mucus to protect the stomach lining from the harshly acidic juices (pH =2) present in the stomach
Chief cells, in the gastric glands, synthesize pepsinogen, which is converted to pepsin upon contact with stomach acid and breaks down proteins
___ cells, also present within gastric glands, synthesize and release hydrochloric acid (HCl), which alters the pH of the stomach, kills bacteria, and produces intrinsic factor (IF), which is necessary for the absorption of vitamin B12
parietal
The churning of the stomach, combined with enzymatic activity (chemical digestion) produces an acidic, semifluid mixture of partially digested food known as ___
chyme
The chyme passes into the first segment of the small intestine, the ____, through the pyloric sphincter
duodenum
Digestion in the small intestine is exclusively chemical and is facilitated by ___ secretions from the pancreas, liver, and local intestinal glands
enzymatic
Enzymes utilized in small intestine chemical digestion include lipases, ___, disaccharidases
aminopeptidases
Pancreatic secretions create a ___ (high pH) environment in the small intestine
basic
Segments of the small intestine: Dow Jones Industrial
Duodenum
___
Ileum
jejunum
The ___ is an accessory digestive organ, meaning it is not part of the digestive tract, but instead secretes compounds into it
liver
The liver produces ___ that is stored in the gallbladder before being released into the small intestine
bile
___ functions to emulsify fats, breaking down large globules into small droplets
bile
Emulsification increases the ___ area of the fat, increasing the digestive actions of pancreatic enzymes
surface
In the absence of ___, fats cannot be digested
bile
The first pass effect: blood from the small intestine containing newly ___ compounds is directly sent to the liver for detoxification before entrance into general circulation
absorbed
The first pass effect serves to protect the body from ___ toxins
ingested
Non-digestive functions of the liver include storage of glycogen, conversion of ___ to urea, protein synthesis, and cholesterol metabolism
ammonia
The pancreas is an accessory digestive ___
organ
Upon stimulation, the ___ releases amylase, lipase and trypsinogen
pancreas
___ is the precursor of trypsin, a powerful proteolytic enzyme, and is activated by enterokinase, which is produced in the small intestine
trypsinogen
Trypsin is only activated once it enters the ___
small intestine
Upon trypsin entering the small intestine, trypsin then cleaves and activates the other ___ (enzyme precursors)
zymogens
The pancreas also secretes a bicarbonate-rich juice that neutralizes the acidic ___ arriving from the stomach in the duodenum
chyme
The ___ enzymes operate optimally at a higher pH
pancreatic
The large intestine is approximately 1.5 m long and absorbs ___ and any water not already absorbed by the small intestine
salts
Digestive Hormones
Gastrin: produced in the ___ of the duodenum, gastrin primarily functions to stimulate histamine and pepsinogen secretion, as well as increase gastric blood flow. Gastrin also stimulates the parietal cells to produce HCl, which denatures proteins and activates digestive enzymes.
Intrinsic factor: a secretion of the parietal cells that facilitates absorption of vitamin b12 across the intestinal lining
Cholecystokinin (CCK): produced and stored in the I cells of the duodenal and jejunal mucosa. it is involved in stimulation of pancreatic enzyme and somatostatin secretion as well as gallbladder contraction. CCK also acts as a hunger suppressant.
Secretin: synthesized and stored in the S cells of the upper intestine. It stimulates the secretion of bicarbonate-containing substances from the pancreas and inhibits gastric emptying and gastric acid production
Ghrelin: synthesized both in the brain and the gut serves as the “hunger hormone.” Increased levels of ghrelin in central circulation cause increased appetite and feeding behavior.
Leptin: synthesized primarily in adipose tissue 9fat cells) serves as an antagonist to ghrelin. Leptin acts on the brain to reduce hunger and provide a satiated state
G cells
