Unit 4: Digestive Physio Flashcards
2 types of digestion are
mechanical- breaking food down into smaller parts
chemical- breaking covalent bonds
_______________ create stabilization of protein folds
hydrogen bonds
Salivary amylase is produced by ________1______
secreted into _________2___________
It acts on __________3_________
1- salivary glands
2- the oral cavity
3- starch or glycogen
Pepsin is produced by
chief / peptic cells
Hydrochloric acid is secreted by
parietal cells
salivary amylase is most active in which environment?
body temperature
99% of the molecular strucutre of the human body is composed of 4 atonms:
hydrogen
carbon
oxygen
nitrogen
organic molecules are divided into 4 categories:
carbohydrates
proteins
lipids
nucleic acids
Define “digestion”.
the process of breaking food down to the point it is absorbable (reduced down to its basic molecular fundamentals)
Compare and contrast mechanical digestion and chemical digestion
Mechanical-
reducing food from a large to a tiny size [not involving changing molecular structure]
-chewing / mastication: reducing food
[easier to swallow, increases surface area to enhance exposure of food to enzymes for chemical digest.]
Chemical-
always enzymatically catalyzed chemical reactions
-breaking covalent bonds
Define “absorption”.
movement of substances from lumen of GI tract to extracellular fluid
Describe all the structures that form the alimentary canal (digestive tract) from mouth to anus and briefly describe the function of each
mouth
esophagus
stomach
small intestine
large intestine
rectum
anus
Identify all of the accessory organs of the digestive system and briefly describe the function of each
Salivary glands
Pancreas
-provides secretions for chemica digestion & hormones
Liver
-secretions; mechanical & chemical digestion
Gall bladder
-reservoir; regulator of timing of secretion into small intestine
Describe the four layers of the alimentary canal.
Describe the location, structure, regional variations, and function of each layer.
- mucosa
-simple epithelium
-lamina propria (CT layer) - submucosa [CT layer; blood vessels here]
- muscularis externa
-circular layer [faces submucosa] -[constriction/dilation movement]
-longitudinal layer [lengthening/shortening] - serosa
Describe the enteric nervous system.
Identify the divisions, location and general function of the enteric nervous system.
“nervous system of the gut”
- submucosal plexus (Meissner’s) - regulates glandular secretion
- myenteric plexus (auerbach) - regulates motility & mixing actions (contraction/relaxation of muscularis externa)
Describe the types of movement characteristic of the alimentary canal.
Propulsive [peristalsis] - wave-like contraction; causes bolus to be squeezed down
Mixing [segmentation] - circular muscle contracts & squeezes around the bolus back and forth, breaking it up & blending it
Describe the role of the mouth in digestion.
What are the functions of the teeth, tongue, and saliva?
Teeth and tongue: mastication [mechanical digestion associated with chewing]
Salivary glands secrete saliva
~moisturizes food
~provides water base for enzymatic activity
~salivary amylase enzyme initiates chemical digestion of carbs
Describe the process of swallowing.
What prevents food from entering the airways?
~epiglottis: prevents food and drink from entering the windpipe (airways) and into digestive tract
~swallowed bolus > peristalsis > down esophagus > stomach
Describe the structure of the gastric pits.
Identify all of the gastric pit cell types and the produce they secrete.
~they are glands made of a variety of secretory cell types
~narrow, tubular invaginations
1) mucous cells: produce thick mucous, lining stomach contents (barrier)
2) chief / peptic cells: produce a proteolytic enzyme > pepsinogen [inactive; can be converted to active once it reaches acidified stomach contents]»_space;> activated as pepsin; Pepsin will catalyze chemical reactions to break down protein
3) parietal cells: hydrogen ions > hydrochloric acid
4) endocrine cells > secrete into interstitial fluid instead of lumen
~enterochromaffin, G, &D cells
Explain how proteolytic enzymes are prevented from digesting the cells that produce them.
Think of proteolytic enzymes as tiny cell scissors.
To stop them from accidentally cutting up the cell they come from:
They stay in specific, small parts of the cell,
Only activated when needed
They are picky with their function
Cell can turn them “off” when not needed
they are put in the right spots, so they cut only where it’s needed, without harming the cell.
Describe the mechanism of acid secretion.
While eating, stomach lining releases a hormone called gastrin, which activates parietal cells to pump out stomach acid (hydrochloric acid).
HCL helps break down food and protects against harmful bacteria, creating the right conditions for digestion.
Describe the structures of the intestines that are responsible for the large surface area of the intestinal mucosa.
What is the significance of this large surface area?
structures like folds (plicae circulares)
finger-like projections (villi)
tiny extensions (microvilli)
~ together create a large surface area in the intestines.
This large surface area is important because it helps in absorbing nutrients from the food we eat. When we digest food, the intestines need a lot of surface area to absorb nutrients effectively. The folds and projections increase the space available for this absorption
Describe the function of the crypts of Lieberkuhn (aka intestinal crypts or glands).
the epithelial cells at the base of the villi are actively dividing > escalator of epithelial cells against villi walls > old cells die and release their contents
Describe the function of Brunner’s glands (aka duodenal glands).
respond to stimuli associated with the contents of the small intestine, stimuli associated with hormones produces, and stimuli from the submucosal plexus > they will secrete their products into lumen of small intestine
produce bicarbonate > pH regulation
Describe the location and function of the brush border enzymes.
embedded in the microvilli membrane
~Fx: aid with final parts of digestion turning peptides/fats/carbs into small molcules that can be absorbed
Describe the mechanism of digestion and absorption for each of the major macronutrients (carbohydrates, proteins and fats).
Carbohydrates
secondary active transport to absorb against luminal border > into epithelial cell > moves across basil membrane into interstitial fluid > blood by facilitated diffusion
Proteins
follow a similar / more elaborate mode of absorption
~must be mechanically (Hcl denatures [uncoils] protein) and chemically digested (by way of proteases like pepsin) > amino acids move across membrane w/ sodium [secondary active transport] > bloodstream
Fats/lipids
additional challenge- not water soluble
~mechanical step: add emulsifier agent [bile salt] > mixing action reduces fat to smaller droplets > salts and fats released in 2 forms: fatty acids & monoglycerides freely diffuse into cytoplasm of epithelial mucosa cell [diffusion]
Fat is put back together & combined with proteins > released into lymphatic vessels > through lymph nodes > blood stream [bypasses liver processing]
Where does the majority of chemical digestion take place?
Small intestine
Where does the majority of nutrient absorption take place?
small intestine
What are the primary functions of the large intestine (aka colon)?
water absorption
Where are the enzymes necessary for chemical digestion in the small intestine produced?
brush border enzymes - (small intestine)
Pancreas
saliva (amylase)
Describe the structure and hormones associated with the endocrine portion of the pancreas.
property of pancreatic islets
Variety of cell types produce hormones like insulin & glucagon : these regulate glucose / blood sugar levels
Describe the structure and secretory products associated with the exocrine portion of the pancreas.
role where pancreatic acini secrete products into ducts > ducts merge to run down center of pancreas and drain contents in small intestine
Bicarbonate- neutralizes acid in chyme from stomach
Brunner’s glands- also secrete bicarbonate
enzymes associated with lipid digestion- lipases
enzymes associated with carb digestion- amylases
enzymes associated with protein digestion- proteases [3]
Where is bile produced? Where is it stored? What does it do?
~secreted by the liver
~stored/released by gallbladder
~nonenzymatic solution that facilitates digestion of fats
What are the major functions of the liver?
metabolic processing [carb, lipid, processing]
storage [vitamins, glycogen, iron]
detoxification
RBC destruction
blood reservoir
bile production
ingestion is
the process of taking food in
digestion is the process of
breaking foods down
Absorption is the process of:
moving foods into the bloodstream for distribution throughout the body
elimination is AKA
defecation - eliminating materials that could not effectively be digested or absorbed
Absorption is mainly the domain of:
small intestine
[more jejenum and ileum then duodenum]
What does the oral cavity secrete?
saliva from salivary glands
Stomach functions
~can accumulate large quantities of swallowed food
~acts as a reservoir; metering of food movement from stomach to small intestine
Does hydrochloric acid contribute to chemical or mechanical digestion?
NOT chemical bc it is not breaking covalent bonds
mechanical- increasing protein’s surface area
Intrinsic factor is needed for:
vitamin B12 absorption in the small intestine
The type of digestion that does not break chemical (aka covalent) bonds:
mechanical digestion
Secretions added to the alimentary canal can come from:
directly from epithelial cells of the mucosal layer
glands formed from cells of the mucosal epithelium
glands within the submucosal layer of the alimentary canal
glands located outside of the alimentary canal
Which of the following is an accessory organ of digestion?
stomach
duodenum
spleen
pancreas
colon
pancreas
Chief cells (aka peptic cells) secrete:
Be specific
pepsinogen
the enteric nervous system is part of the ______________ nervous system
autonomic
the enteric nervous system is responsible for regulation of :
GI tract motility and secretion
what is made up of two parts - the submucosal plexus and myenteric plexis?
the enteric nervous system
intrinsic factor is secreted by:
parietal cells in the gastric pits:
the enteric nervous system is made of approximately the same number of neurons as:
the spinal cord
Regulation of gastric motility and secretions~
what are the 3 phases?
Cephalic phase
gastric phase
intestinal phase
Cephalic phase
[Regulation of gastric motility and secretions]
phase 1
~sight, smell, and taste of food can initiate GI activity
mediated by way of the vagus nerve [CNS]
regulates the secretion of mucous/chief/parietal cells & G cells (endocrine cell)
+ some motility within alimentary canal
The endocrine cell type G cell produces:
gastrin
[hormone]
Gastric phase
[Regulation of gastric motility and secretions]
Phase 2
regional activation due to exposure to food
[stomach walls are stretched - stretch receptors; chemoreceptors stimulate submucosal & myenteric plexus > increased motility]
Same cells from cephalic phase are stimulated > mucus production > increased pepsinogen»_space;pepsin
~increased Hydrochloric acid; denatures proteins in food consumed, turns pepsinogen to pepsin & denatures proteins associated with any microorganisms swallowed
~G cells producer gastrin > further boost other secretion production
Intestinal phase
[Regulation of gastric motility and secretions]
phase 3
stomach feeding info forward to the small intestine to prep it & small intestine feeds info back to stomach to alter stomach behavior
i. distension
ii. secretin
iii. CCK
iv. GIP- gastric inhibitory peptide
^^^ these hormones decrease cell/secretion production & inhibits peristaltic activity
CCK cholecystokinin stimulates the:
gall bladder
it contracts and squeezes any bile > common bile duct > small intestine
What factors help the small intestine be able to do majority of chemical digestion and nutrient absorption?
~its length [time for processing]
~modification of its lining increases surface area [plica circulares]
Plica circulares
component of submucosa, folds inward to form ridges > takes more mucosa to cover ridges > creates spiraling ridge-like patterns
What are the 3 structures associated with the small intestine?
- Plica circulares- component of submucosa, folds inward to form ridges > takes more mucosa to cover ridges > creates spiraling ridge-like patterns
- Villi
- microvilli
^ increasing surface area ^ so alimentary canal can better absorb
all of the epithelial cells lining the entire small intestine are replaced in about
12-14 days
Name the 3 intestinal secretions
brunners glands
crypts of lieberkuhn (intestinal glands)
brush border enzymes
???
Gastric juice- Hcl, pepsin…
Pancreatic juice- amylase, protease, lipase
Bile - emulsifies fat
what are zymogens?
inactive precursors of functional enzyme
What are the 3 secretions of the exocrine pancreas?
Trypsinogen > trypsin
Chymotrypsinogen > chymotrypsin
Procarboxypeptidate > carboxypeptidase
These all add to proteolytic digestion [protein digestion]
Rugae, plicae, and villi are all features of the alimentary canal that are primarily responsible for:
an increase in surface area
Regulation of digestive processing in the stomach:
Select all that apply—
Is controlled by the enteric nervous system
Responds to stretch and chemical stimuli in the small intestine
is controlled by the central nervous system
responds to stretch and chemical stimuli in the stomach
all of the above
The acinar cells in the pancreas produce and secrete:
trypsinogen, chymotrypsinogen & procarboxypeptidase
During the cephalic phase of gastric secretion, there is an increased :
flow of action potentials along the vagus nerve to the stomach
Almost all chemical digestion takes place in the:
duodenum
In the digestive system, HCl is secreted by:
parietal cells of the stomach
The primary function of the stomach:
storage of ingested food (reservoir)
Brush border enzymes are:
enzymes produced by : 1
membrane-bound enzymes in the : 2
1- the intestinal glands
2- microvilli of mucosal epithelial cells
The acid (HCl) secreted into the stomach lumen is responsible for:
mechanical digestion of protein
conversion of pepsinogen into pepsin
immune protection (chemical barrier to pathogen entry)
Pancreas functions
-provides secretions (major source of enzymes for catalyzing chemical reactions for digestion) [pre-absorbative role]
-produces hormones responsible for regulating distribution absorbed nutrients in the bloodstream [primarily, glucose] — post-absorptive role
the liver always produces:
secretions added to the alimentary canal > mechanical & chemical digestion
Gall bladder
-reservoir;holds bile
-regulator of timing of secretion into small intestine
Identify the target and effect of the major GI tract hormones - gastrin
Target: Stomach (specifically parietal cells and chief cells)
Effect: Stimulates the secretion of gastric acid (HCl) and pepsinogen, promoting digestion. It also enhances gastric motility.
Identify the target and effect of the major GI tract hormones - secretin
Target: Pancreas and stomach
Effect: Stimulates the pancreas to release bicarbonate-rich pancreatic juice, which neutralizes acidic chyme entering the small intestine. It also inhibits gastric acid secretion and slows down gastric emptying.
Identify the target and effect of the major GI tract hormone - cholecystokinin
Target: Gallbladder, pancreas, and stomach
Effect: Stimulates the gallbladder to release bile into the small intestine, promoting the emulsification and digestion of fats. It also stimulates the pancreas to release digestive enzymes and inhibits gastric emptying.
Identify the target and effect of the major GI tract hormones - GIP
Glucose-dependent insulinotropic polypeptide (GIP) / Gastric inhibitory polypeptide (GIP)
Glucose-dependent insulinotropic polypeptide (GIP) / Gastric inhibitory polypeptide (GIP)
Target: Pancreas and stomach
Effect: Inhibits gastric acid secretion and slows down gastric emptying. It also stimulates the release of insulin from the pancreas in response to nutrient intake, promoting glucose uptake and storage.
