Biology 9: The Digestive System Flashcards
what are the two types of digestion?
intracellular digestion: oxidation glucose and fatty acids for energy
extracellular digestion: obtainment of nutrients from food in the alimentary canal (from mouth to anus)
what is the difference between absorption and digestion?
digestion: the breakdown of food into its constituent organic molecules
absorption: the transport of product for digestion from the digestive tract into the circulatory system for distribution to the body’s tissues and cells
what are the two types of digestion?
mechanical digestion: the physical breakdown of large food particles
chemical digestion: the enzymatic cleavage of chemical bonds
pathway of the digestive tract
oral cavity -> pharnyx -> esophagus -> stomach -> small intestine -> large intestine -> rectum
enteric nervous system
a collection of one hundred million neurons that govern the function of the the gastrointestinal system
present in the walls
trigger peristalsis
can function independent of the brain and spinal cord, but is also regulated by parasympathetic inputs rest and digest
which hormones stimulate feelings of hunger
glucagon and ghrelin
which hormones stimulate feelings of satiety?
leptin and cholecystokinin
which hormones trigger the sensation of thirst?
ADH and aldosterone
salivary amylase
enzyme present in saliva
capable of hydrolyzing starch into smaller sugars
lipase
enzyme present in saliva
catalyzes the hydrolysis of lipids
pharynx
cavity which leads from the mouth and posterior cavity to the esophagus and larynx
the epiglottis covers the larynx during swallowing
what are the three divisions of the pharynx
nasopharynx (behind nasal cavity)
oropharynx (back of mouth)
laryngopharynx (above vocal cords)
esophagus
a muscular tube that connects the pharynx to the stomach
top third skeletal muscle - somatic control
middle third is a mix of skeletal and smooth
bottom third smooth muscle - automatic control
emesis
fancy word for vomiting
upper esophageal sphincter
present in the oropharynx at the back of the mouth
initiates the process of swallowing
lower esophageal sphincter / cardiac sphincter
present at the top of the stomach
relaxes to allow the passage of food into the stomach
stomach
highly muscular organ in upper left quadrant of the abdominal cavity under the diaphragm
uses HCl acid and enzymes to digest food
has thick mucosa to prevent autodigestion
what are the four main divisions of the stomach?
fundus
body
antrum
pylorus
rugae
folds of the internal lining of the stomach
gastric glands
glands in the mucosa of the fundus and body of the stomach
respond to signals from the vagus nerve of parasympathetic (activated by sight, smell, taste of food)
what are the three different cell types of gastric glands?
mucous cells
chief cells
parietal cells
mucous cells
gastric glands which produce the bicarbonate-rich mucous that protects the muscular wall from the acidic and proteolytic environment of the stomach
chief cells
gastric glands which secrete pepsinogen (inactive zymogen form of pepsin)
parietal cells
secrete HCl, producing hydrogen ions which cleave pepsinogen -> pepsin
secrete intrinsic factor - glycoprotein involved in absorption of b12
pepsin
proteolytic enzyme
cleaves peptide bonds near aromatic amino acids
most active at a low pH
pyloric glands
glands in the antrum and pylorus of the stomach
contain G-cells that secrete gastrin
gastrin
secreted by G cells
induces parietal cells to secrete more HCl, signals stomach to contract and mix contents
chyme
acidic, semifluid mixture resulting from the digestion of solid food in the stomach
has a very high surface area for optimal absorption in the small intestine
what are the three segments of the small intestine?
duodenum (chemical digestion)
jejunum (absorption)
ileum (absorption)
how does food leave the stomach to enter the small intestine
through the pyloric sphincter into the duodenum
brush-border enzymes
enzymes present on the luminal surface of cells lining the duodenum
triggered to release by the presence of chyme in the duodenum
ex. disaccharidases, peptidases
breaks down dimers and trimers into absorbable monomers
duodenum
first segment of the small intestine
secretes brush-border enzymes, enteropeptidase (activates other digestive enzymes from accessory organs)
secretes hormones secretin and cholecystokinin into bloodstream
aminopeptidase
peptidase secreted by glands in the duodenum that removes the N-terminal amino acid from a peptide
enteropeptidase
enzyme critical for the activation of trypsinogen (pancreatic protease) to trypsin, which activates a cascade
also activates procarboxypeptidases A and B to their active forms, which removed the C-terminal amino acid from a peptide
cholecystokinin (CCK)
secreted into the duodenum as a response to the presence of chyme
stimulates the release of bile, pancreatic juices
promotes satiety in the brain
bile
complex fluid of bile salts, pigments, and cholesterol
involved in the mechanical digestion of fats and lipids
are amphipathic, can bridge aqueous and lipid enviornments
emulsify fats and cholesterol into micelles to make them accessible to pancreatic lipase (chemical digestion)
pancreatic juices
complex mixtures of enzymes in a bicarbonate-rich alkaline solution
helps to neutralize acidic chyme
provides an ideal working environment for each digestive enzyme (about 8.5)
enzymes can digest carbs, fats, and proteins
secretin
hormone that signals the release of pancreatic enzymes into duodenum
regulates pH by reducing HCl secretion from pancreatic cells and increasing bicarbonate secretion from pancreas
enterogastrone - functions to slow motility through the digestive tract
acinar cells
exocrine cells in the pancreas that produce pancreatic juices
what are three enzymes present in pancreatic juice?
pancreatic amylase - breaks down polysaccharides (carb digestion)
pancreatic peptidases (trypsinogen, chymotrypsinogen, procarboxypeptidases A and B activated by enteropeptidase made in duodenum)
pancreatic lipase breaks down fat into free fatty acids and glycerol
liver
organ in the upper right quadrant of the abdomen
makes bile, which can be stored in gallbladder or secreted into duodenum directly
detoxifies endogenous and exogenous compounds
detoxifies and metabolizes substances
converts ammonia into urea
synthesizes albumin and clotting factors
what are the two unique structures in the liver for communication with the digestive system?
bile ducts: connect liver with gallbladder and duodenum
hepatic portal vein: allows liver to receives all blood draining from the abdominal portion of the abdominal tract for processing before reaching the IVC
bilirubin
a major pigment in bile
byproduct of the breakdown of hemoglobin
conjugates (attached to a protein) in the liver and secreted into bile for secretion
gallbladder
organ located beneath the liver
stores and concentrates bile
contracts and pushes bile out into the biliary tree in response to CCK release
lacteal
located in the middle of each villus in the small intestinal jejunum and ileum
lymphatic channel that takes up fats for transport into the lymphatic system
form the beginning of the lymphatic system
converge and enter the venous circulation directly through thoracic duct, drains into subclavian vein
how are water-soluble compounds absorbed into the small intestines?
water-soluble compounds such as monosaccharides, amino acids, some vitamins, small fatty acids, enter the capillary bed
unlike the others, small fatty acids are nonpolar and thus do not require transporters to cross the membrane
capillaries come together to form portal vein, which drains to the liver
chylomicrons
packages of triglycerides and esterified cholesterol molecules formed from larger fats
don’t enter the bloodstream following absorption but instead enter the lymphatic circulation through lacteals
what are the major sections of the large intestine?
cecum
colon
rectum
cecum
outpocketing in the large intestine that accepts fluid exiting the small intestine through the ileocecal valve
the site of attachment of the appendix
ileocecal valve
valve between the ileum and the cecum connecting the small and large intestines
colon
part of the large intestine which absorbs remaining water and salts from undigested material from the small intestine
concentrates remaining material to form feces
rectum
part of the large intestine that stores feces
what two sphincters control the anus?
external sphincter under voluntary control (somatic)
internal sphincter under autonomic control
what are the two circulatory vessels in a villus?
capillaries, which absorb water-soluble nutrients
lacteals, which absorb fat-soluble nutrients
what are the fat-soluble vitamins?
vitamins A, D, E, and K
