Digestive System Flashcards
What are the four basic processes performed by the digestive system?
1.) motility
2.) secretion
3.) digestion
4.) absorption
What are the two types of motility movements? Which type of muscle produces them?
1.) mixing movements
2.) propulsive movements
accomplished by smooth muscle lining digestive tract
What is the difference between exocrine and endocrine secretions?
exocrine = secretions into digestive tract (mix of H20, electrolytes, enzymes)
endocrine = secretions of GI hormones and GI peptides that enter blood and have targets inside and outside of digestive system
Where does absorption mostly occur?
small intestine
What is hydolysis?
adding H2O to bond site to break bond
What are the three main categories of energy-rich food components?
Carbs, proteins, and fats
What are the absorbable units of carbohydrates?
monosaccharides, disaccharides, polusaccharides
What are the absorbable units of proteins?
small peptides, amino acids
What are the absorbable units of fats?
monoglycerides, fatty acids
What do starch and glycogen consist of? What are soluble and insoluble fibers?
starch: amylase and amylopectin
glycogen: storage form of glucose in muscle
dietary polysaccharides that either can or cannot be digested
What are the four layers of the digestive tract?
1.) serosa
2.) mucosa externa
3.) mucosa
4.) submucosa
In what layer(s) are cells that secrete found? Which layer mainly contains smooth
muscle?
mucous membrane: contains exocrine and endocrine gland cells as well as absorptive epithelial cells
muscularis externa: contains smooth muscle
Where are the two plexuses?
submucosal plexus and myenteric plexus
What is function of serous fluid?
prevents friction between digestive organs and surrounding viscera
What are the four means by which digestive activity can be regulated?
1.) autonomous smooth muscle function
2.) intrinsic nerve plexuses
3.) extrinsic nerves
4.) GI hormones
What do the interstitial cells of Cajal do? How does electrical activity pass between
smooth muscle cells in the digestive tract? Does the slow-wave potential always lead to
contraction?
pacemaker cells throughout muscularis externa, generate spontaneous, rhythmic, slow-wave membrane potentials
propagates to adjacent smooth muscle cells via gap junctions
if depolarization peak crosses threshold (not a given), multiple action potentials fire = contraction of smooth muscle
What is enteric nervous system comprised of?
submucosal plexus and myenteric plexus
How does sympathetic activity generally change digestive processes?
inhibits digestive motility and secretion
How does parasympathetic activity generally change digestive processes?
promotes digestive motility and secretion
Where are GI hormones secreted and what do they act on?
secreted in digestive tract and alte activity of smooth muscle and exocrine cells
What are the functions of mastication?
1.) breaks down food into smaller peaches (increases surface area for salivary enzymes to act on)
2.) mixes food with saliva
3.) exposes food to taste buds
What are the functions of saliva? What secretes it?
1.) begins digestion of dietary starch through enzyme salivary amylase
2.) facilitates swallowing by lubricating with mucus
3.) inhibits bacteria via lysozyme (lyses bacteria) and lactoferrin (sequesters iron), antibodies, rinsing away leftover food material
4.) acts as solvent for tastants
5.) aids speech by allow surfaces of tongue, lips, and cheeks to glide over eachother
6.) neutralizes acids in food and bacteria via bicarbonate buffer
What are the two reflexes by which salivary secretion increases?
1.) simple salivary reflex (pressure receptors and chemoreceptors in brain)
2.) conditioned salivary reflex (thinking, seeing, smelling food
-> cerebral cortex)
What brain structure controls swallowing?
pharyngeal mechanoreceptors send signals to swallowing centers in medulla
What are the three functional sections of the stomach?
1.) fundus
2.) body
3.) antrum
What are the main functions of the stomach?
1.) stores food until it can be emptied into small intestine
2.) secrete HCl and enzymes that begin protein absorption
3.) pulverizes ingested food and mixes with gastric secretions to produce this liquid called chyme
What is receptive relaxation of the stomach?
occurs when stomach is being filled, vagus nerve activity relaxes smooth muscle
allows stomach folds to unfold, volume expands
Which area of the stomach has thicker smooth muscle? What function does it provide?
antrum, greater force for propulsion and mixing (retropulsion)
Does chyme simply dump straight into the duodenum from the stomach?
no, rate of gastric emptying depends on strength of antral contractions
If given a list, could you identify the factors the influence gastric emptying?
Increase
1.) volume of chyme
2.) degree of fluidity of chyme
Decrease
3.) enterogastric reflex (neural response regulated thru intrinsic plexuses and autonomic nerves)
4.) release of enterogastrones (GI hormones that act on the smooth muscle in the stomach
5.) fat, acid, hypertonicity
6.) intense pain
7.) emotion (through autonomic nerves, can promote or inhibit motility)
What factors in the duodenum affect gastric emptying? What mechanisms do they
elicit? Which hormones are secreted by the duodenum by these factors?
enterogastric reflex (neural response regulated thru intrinsic plexuses and autonomic nerves)
release of enterogastrones (GI hormones that act on the smooth muscle in the stomach)
release secretin and CCK
Where are the oxyntic mucosa and pyloric gland area? What component of these areas secretes gastric juices?
located in the fundus and body
1.) mucous cells (lubricant)
2.) chief cells (pepsinogen)
3.) parietal (oxyntic) cells (secrete HCl and intrinsic factor)
What do mucous cells secrete? How about chief cells? How about parietal cells?
1.) mucous cells = mucus (lubricant)
2.) chief cells = pepsinogen
3.) parietal = HCl and intrinsic factor (Vitamin B absorption)
Why does the stomach secrete HCl? Why does it secrete pepsinogen?
HCl = activates pepsin, aids in breakdown of connective tissue and muscle fibers, kills microorganisms, denatures proteins (unwinds it so pepsin can break it down)
Pepsinogen = inactive form of pepsin (breakdowns proteins)
If a stomach epithelial cell dies, is it replaced?
yes, by stem cells
:inside gastric pits continually divide and replace worn-out cells -> entire gastric mucosa replaced every 3 days.
What do G cells secrete? How about ECL cells? How about D cells?
1.) G cells = gastrin
2.) ECL cells = histamine
3.) D cells = somatostatin
What does gastrin do?
- stimulates secretion of gastric juice (HCL, pepsinogen)
- stimulate ECL cells
What are the three phases of gastric secretion? In which phases is secretion increased
and which reduced?
1.) cephalic (increases secretion) (vagus nerve stimulate intrinsic plexuses and G cells)
2.) gastric (increases secretion) (protein stimulates intrinsic plexuses and G cells)
3.) intestinal (decreases secretion) (absence of protein to turn on G cells, high acidity triggers D cells)
How is the stomach lining protected from HCl?
1.) luminal membrane of gastric mucosal cells impermeable to H+
2.) tight junctions between gastric mucosal cells
3.) thick mucus acting as a physical barrier
4.) alkalinity of mucus neutralized acid
In the pancreas, what do acinar cells secrete? How about duct cells?
1.) acinar cells = pancreatic enzymes
2.) duct cells = alkaline solution
What are the three main types of pancreatic enzymes, and what do they do?
1.) proteolytic enzymes = digest proteins
2.) pancreatic amylase = digest carbs
3.) pancreatic lipase = digest fats
What causes the pancreas to secrete its juices? Where does it secrete them into?
pancreatic secretion regulated by enterogastrones secreted by duodenal mucosa– secretin and CCK
secreted into duodenal lumen
How is blood flow to the liver unique? What is the name of the circulation from the digestive tract to liver?
liver receives oxygenated blood from the hepatic artery and deoxygenated blood from hepatic portal vein
hepatic portal system: (digestive tract->liver) carries products absorbed in digestive system thru liver before entering general circulation
What are the functional units that make up the liver?
lobules
What is the function of Kupffer cells?
line sinusoids- resident macrophages that engulf old red blood cells and bacteria
How are hepatocytes organized in the lobules?
organized into plates with bile canaliculi running in between
What does bile contain? Where is it stored? Is it all excreted into the large intestine?
bile contains: bile salts (derivatice of cholesterol), lecithin (phospholipid), bilirubin (waste product from red blood cell breakdown)
What causes the secretion of bile into the duodenum?
presence of fat in duodenum causes release of CCK, sphincter of Oddi relaxes and gallbladder contracts, secretion of bile into duodenum
How do bile salts end up breaking big fat droplets into a lipid emulsion? Why is this important?
detergent action: increases surface area for attack by pancreatic lipase)
What are micelles? What are they made of? What role do they play in absorption?
micelles: lecithin and bile salts aggregate to form these..
lecithin and bile salts each have hydrophobic and hydrophilic ends, monoglycerides and free fatty acids hide inside hydrophobic core, micelles are water soluble and are able to diffuse to the luminal membrane
What is bilirubin and how is it produced?
bilirubin: waste product in the breakdown of heme from hemoglobin in worn out red blood cells
produced by kupffer cells (macrophages) and removed from blood by liver (major constituent of bile)
What is jaundice due to?
due do accumulation of bilirubin in body
could occur with excessive breakdown of red blood cells, diseased liver, or obstruction of bile duct
What are the three segments of the small intestine?
1.) duodenum
2.) jejunum
3.) ileum
What is segmentation motion and what does it do?
alternating ring like contraction of small intestines…
1.) mix chyme together with digestive juices
2.) expose chyme to absorptive surfaces of interstitial lining
(established by pacemaker cells in smooth muscle)
What mechanisms prevent the contents of the large intestine from leaking back into the
small intestine?
ileocecal valve and sphincter prevent small intestine from being contaminated by bacteria in large intestine
What is succus entericus and what does it do?
succus entericus: salt and mucus solution that provides H2O and lubrication of contents (secreted by exocrine glands in mucosa of small intestine)
What structural features increase the surface area of the small intestine mucosa? Why
is this important?
1.) circular folds
2.) villi (microscopic finger like projections lined with epithelial cells and interspersed mucous cells)
3.) microvilli (brush border): extending from each epithelial cell; visible only with electron microscope
Where are the Crypts of Lieberkühn located? What important cells do they contain?
located between villi; contain stem cells that constantly produce new epithelial cells
contain paneth cells: produce lysozyme and defensins that thwart intestinal bacteria
What enzymes are embedded in the brush border? What do they do?
1.) enteropeptidase: activate trypsinogen (pancreatic proteolytic enzyme)
2.) disaccharidases: hydrolyzes disaccharides into monosaccharides
3.) aminopeptidases: hydrolyzes small peptide fragments into amino acids
Does the body regulate absorption of carbohydrates, proteins and fats?
No (usually only calcium and iron absorption is regulated)
Where does the energy come from to power transport of carbohydrates and proteins?
ultimately depend on energy expended by the Na+/K+ pump
Do we excrete digestive enzymes, or proteins from sloughed off intestinal epithelial
cells?
proteins within epithelial cells that are sloughed off of villi become digested and absorbed
What is a chylomicron?
lipid droplets coated with a lipoprotein that makes them water-soluble (exit cell via exocytosis and enter central lacteal, can’t enter capillaries due to structural reasons)
Do absorbed carbohydrates, proteins and fats all enter the blood capillaries?
absorbed carbs and proteins are immediately passed thru the liver before entering general blood circulation
absorbed fats pass directly into general circulation- processed by liver later in diluted form
What are the main functions of the large intestine? What does it receive from the small
intestine?
primary function is a drying and storage organ
cecum receives chyme consisting of: indigestible food residues (ex: cellulose), bilirubin, H2O
Where are the cecum, colon, and rectum?
the large intestine
Does the colon contain a little or a lot of bacteria? What do the bacteria do that is beneficial?
contains 4 lbs of beneficial bacteria… bacteria digest additional plant fiber primarily into fatty acids (some diffuse thru wall of colon)
What do feces contain?
mostly water, plus undigested cellulose, bilirubin, bacteria and small amounts of salt
What do haustral contractions do?
mixing contraction (about every 3o minutes) that shuffle contents to maximize absorption - not a propulsive movement
What are the contractions that propel feces thru the
colon?
mass movement (massive contraction of colon that drive colon contents forward quickly)
What is the gastrocolic reflex?
food enters the stomach -> stomach release of gastrin -> gastrocolic reflex (triggering of propulsive movements (mass movements))
