Exam 2: Digestive System Part 2 Flashcards
mastication
chewing of food
functions:
1. mixes food with saliva
2. reduces size which facilitates swallowing (mechanical digestion)
3. mixes ingested carbs with salivary amylase to begin chemical digestion
catabolism
digestion of food
types: physical and chemical
saliva
produced by salivary glands
three major salivary glands
parotid, submaxillary, sublingual
acinar vs ductal cells in saliva
acinar cells- initial saliva (isotonic)
ductal cells- modifies the initial saliva to produce the final saliva by altering conc. of electrolytes (hypotonic - water impermeable)
a-amylase
secreted by acinar cells
- begins initial digestion of carbohydrates
lingual lipase
secreted by acinar cells
- begins initial digestion of lipids
ductal cells absorption and secretion
absorption of Na and CL causes conc. of those in saliva to become lower than their conc. in plasma
secretion of K and HCO3 causes conc. of those in saliva to become higher than those in plasma
three phases of swallowing
- oral
- pharyngeal
- esophageal
oral phase of swallowing
voluntary
- initiated when tongue forces a bolus of food back toward the pharynx
pharyngeal phase of swallowing
involuntary
- propel the food bolus from the mouth through the pharynx to the esophagus
esophageal phase of swallowing
involuntary
- controlled by the swallowing reflex and the enteric nervous system
- peristalsis drives food downwards and relaxation of the lower esophageal sphincter admits it into the stomach
mucosa cells in the stomach
mucous cells mucous neck cells parietal cells chief cells enteroendocrine cells
what does enlargement of stomach mucosa show
shows gastric pits and glands
- those secrete gastric fluids
parietal cells in stomach mucosa
synthesizes and secretes gastric acid to maintain an acidic environment
canaliculi in parietal cells
present on surface of lumen
- play a role in secreting gastric acid
intrinsic factor in parietal cells
produced by parietal cells
- absorb B12
HCL formation by parietal cells
is stimulated by ACh, gastrin, histamine
- HCL acidifies gastric contents between a ph of 1-2
chief cells in stomach mucosa produce:
- pepsinogen- inactivated protease for protein chemical digestion
- lipase- aid in lipid digestion
what does pepsinogen do when gastric pH is low
pepsinogen is converted to its active form, pepsin
mucus and mucus neck cells in stomach mucosa
produce protective mucus to protect epithelium of the stomach
enteroendocrine cells in stomach mucosa
located in gastric glands, cells produce hormones types: 1. enterochromaffin (EC) cells 2. enterochromaffin-like (ECL) cells 3. delta cells 4. G cells
enterochromaffin (EC) cell in the stomach (enteroendocrine cell)
produce serotonin
- causes contraction of stomach muscle
enterochromaffin-like (ECL) cell in the stomach (enteroendocrine cell)
produce histamine
- activates parietal cells to release HCL and increase acid levels
delta cell in the stomach (enteroendocrine cell)
produce somatostatin
- inhibits gastric secretin (blocks parietal cells)
G cells in the stomach (enteroendocrine cell)
produce gastrin
- increase parietal cell HCL secretion
gastrin
hormone produced by the stomach to produce gastric acid which is secreted by parietal cells
regulations of HCL
atropine, cimetidine, omeprazole
- all used to block and stop the process of HCL production
HCL in the stomach
helps body break down, digest, and absorb nutrients such as protein.
- eliminates bacteria and viruses in the stomach
- protects body from infection
phases of regulation secretions
- cephalic phase
- gastric phase
- intestinal phase
cephalic phase
- reflex that stimulates the PNS to release acetylcholine
- vagus N stimulates gastric secretion before food is swallowed
- roughly 30% of HCL is secreted in response to a meal
gastric phase
food stretches stomach and myenteric and vagovagal reflexes are activated
- gastic secretion is stimulated, 60% of total HCL is produced
- histamine and gastrin also stimulate acid and enzyme sectretion
intestinal phase
INHIBITION of gastric secretion by CCK, secretin, and reflexes when intestine encounters acid and chyme
- acid production is slowed wayyyy down, do not want to much acid in the SI
- breakdown of food is slowed so all nutrients can be absorbed
three phases of gastric motility
- relaxation of stomach to receive food from the esophagus
- contractions that reduce size of food and mix it with gastric secretions to start digestion
- gastric emptying that propels chyme into the small intestine
chyme
highly acidic material that results from your digestive juices chemically breaking down food.
- product of mechanical chemical digestion
- prerequisite for the process of nutrient absorption
- slows from stomach to small intestine
PNS in digestion
hormones gastrin and moltilin INCREASE action potential frequency and force gastric contractions
SNS in digestion
hormones secretin and GIP DECREASE action potential frequency and the force of contractions
PNS and SNS digestive hormones
PNS- gastrin and motilin, increase contractions
SNS- secretin and GIP, decrease contractions
3 gastric contractions
- propulsion- peristaltic waves
- grinding- vigorous peristalsis and mixing by the pylorus, valve is open slightly
- retropulsion- pyloric valve closes, squishes contents back up into stomach
pyloric end of stomach
acts as a pump that delivers small amounts of chyme to the duodenum
factors that slow/inhibit gastric emptying
- presence of fat
- presence of H+ ions (low pH) in the duodenum
- if pH is to low, SI STOPS
tissue types in the pancreas
- exocrine tissue
2. endocrine cells
pancreatic islet a cells
glucagon producing cells
glucagon function (catabolic)
INCREASES blood sugar
- pulls sugar out of the cells
pancreatic islet B cells
insulin-producing cells
insulin function (anabolic)
DECREASES blood sugar
- sugar is draw into the cells
example of homeostatic imbalance in the pancreas
diabetes
- blood sugar is too high due to lack of insulin production (type 1)
- or improper response to insulin, acquired (type 2)
endocrine cells in the pancreas
hormones that are produced by a and b cells in pancreatic islets
- important for glucose homeostasis
- islets of langerhans (islands of cells that go onto the bloodstream to indicate digestion is occurring)
exocrine tissues in the pancreas
produce alkaline fluid with digestive enzymes in the SI for food digestion
-alkaline counters acidity levels
acinar cells in the exocrine pancreas
found in the acinus
- secrete the enzymatic portion of the pancreatic secretion
ductal cells in the exocrine pancreas
lined on ducts of the pancreas
- centroacinar and ductal cells secrete aqueous HCO3- containing components of the pancreatic secretion
- make area more alkaline
two functions of pancreatic secretion
- aqueous secretion- HCO3- is stimulated by H+ in the duodenum
- enzymatic secretion- stimulated by digestion products
- digests small peptides, amino acids, fatty acids, carbs into absorbable molecules
why are pancreatic enzymes to important
these enzymes are required for digestion
pancreatic enyzmes:
- amylase- active enzyme
- lipase- active enzyme
- protease- secreted in inactive forms but then converted to active form in duodenum
pancreatic proteases conversion
trypsinogen to trypsin in the duodenum
pancreatic acinar cell have receptors for
CCK and ACh
what stimulates CCK secretion
I cells from the presence of amino acids, peptides, and fatty acids in the intestinal lumen
PNS stimulates:
enzyme secretion and increases the action of CCK
pancreatic ductal cell have receptors for
CCK, ACh, and secretin
secretin
secreted by S cells of the duodenum in response to H+ in the lumen
- major stimulant fo aqueous HCO3- rich secretion
- secretin increases action of CCK and ACh
what does secretin signal
signals the arrival of acidic chyme from the stomach into the small intestines
Bile
necessary for digestion and absorption of lipids in the SI
- stored in the gallbladder
- produced in the liver
- secreted continuously by hepatocytes
functions of bile
- absorption- mixture of bile and lipids creates a hydrophobic solution allowing for absorption
- bile emulsifiers lipids to prepare them for digestion and then puts lipid digestion into micelle packets for absorption
- bile surrounds fats/lipids to make them smaller and break them down
bile salts
conserved and recycled through entero-hepatic circulation
bile acids
cholesterol is converted into bile acids (bile acids are amphipathic which allows for two functions to occur)
- emulsification of lipid clusters
- transport of lipids in an aqueous environment
bile acids are important for
transport and absorption of fat-soluble vitamins
- bile acids are lipid carries
micelles in bile acid `
when bile acids solubilize many lipids, micelles are created
- fat center, hydrophobic side touching center, hydrophilic side phasing the outside creating emulsified droplets
what happens when chyme enters the small intestine
acids, partically digested fats, and proteins stimulate the secretion off CCK and secretin
cholecystokinin
a hormone that is secreted by cells in the duodenum
- stimulates the release of bile into the intestine
- secretion of enzymes by the pancreas
secretin
stimulates biliary duct cells to secrete bicarbonate and water
- this expands the bile and increases the flow into the intestine
biliary duct cells
secrete bicarbonate (HCO3-) and water which expand volume of bile and increases the flow
gallstones
composed of insoluble cholesterol
- too much cholesterol
liver
processes, filters, and manages material in the blood
- lobules comprised of hepatocytes (liver cells) that process the blood
- VERY permeable for blood processing
portal triad of the liver
- hepatic portal vein
- hepatic arteriole
- hepatic duct (bile)
function of hepatocytes in the liver
- line cytosiods
- process absorbs substances
- synthesize and secrete bile acids
- bilirubin production and excretion
- metabolism and storage of key nutrients
- excrete and detoxify waste
3 metabolic functions of the liver
- carbohydrate metabolism
- protein metabolism
- lipid metabolism
carbohydrate metabolism
stores glucose as glycogen (gluconeogenesis)
releases stores glucose into bloodstream
protein metabolism
synthesizes and modifys amino acids
- converts amonia to urea which is excreted into the urine
lipid metabolism
fatty acid oxidation
synthesizes lipoproteins, cholesterol, and phsopholipids
liver detoxification
protects body from toxic substances that are absorbed in the GI tract
“first pass metabolism”
- phases modify the harmful substances by adding a salt to make it soluble so it can be excreted
phase 1 reaction of detoxification
P-450 enzymes modfy compounds
phase 2 reaction of detoxification
conjugate the substances
- make them soluble for excretion in bile of urine
hepatitis
inflammation of the liver
- over time scar tissue forms and destroys hepatocytes
cirrhosis in the liver
connective tissue regenerates faster than damaged hepatocytes
- leads to dimished liver activity
- transplant is required
hepatopancreatic ampulla
where the bile duct and pancreatic duct join
- provide digestive components
- empty into the duodenum
- these allow the duodenum to do its job
GI enzymes
carbs, proteins, lipids
small intestine mucosa
water and nutrient absorption
- duodenum- recieves secretion from pancreas and liver from the pancreatic and common bile ducts (get acid out)
- jejunum
- illeum- large end that emties into the large intestine
intestinal mucosa
villi are longest inn the duodenum (most absorption occurs here) and shortest in the ileum
- villi are covered with enterocytes bound by mucus-secreting cells (goblet cells)
- villi and microvilli increase SA of the small intestine creating a large absorptive surface
goblet cells
in the mucosa bound to enterocytes
- mucus secreting cells that help move food through the intestines
five SI mucosal cell types
- enterocytes (absorb)
- goblet cells (mucus)
- enteroendocrine cells
- panth cells (defense)
- stem cells
types of enteroendocrine cells
I cells- produce CCK
S cells- produce secretin
duodenal glands
- located in duodenum submucosa
- produce alkaline mucus to neutralize acidic chyme from stomach
alkaline mucus
neutralize acidic chyme from stomach that has entered the SI
peyer’s patch
aggregated lymphoid follicales that are found in the SI walls
- help protect against bacterial breaches
- increase in amount farther down you go in the body
- most prevalent in the iluem
small intestine motility
peristalsis- faciltate propulsion between meals
segmentation- mix and breakdown in response to meals. NOT about progression, just mixing
- increases contact with absorptive cells
SI digestion
microvilli enzymes complete digestion
- not secreted, always present
- perform final hydrolysis to break down food to monomers
SI secretion
crypts secrete fluid and electrolytes
- creates a watery environment for mixing and absorbing
when does water diffuse into the lumen
when secretion of NaCl occurs
- balances osmotic gradient
- high soluble level draws water in for better movement
SI absorption
transcellular route- across the plasma membrane
paracellular route- across tight junctions between cells
absorption routes
small molecules are transported by both the transcellular and paracelluar route but tight junctions are impermeable to large molecules
- large molecules are ONLY transported through the transcellular route where transport molecules are present
carbohydrate absorption in SI
transporter proteins (symports) form a secondary active transport for monosaccharides ex. glucose
protein absorption in SI
transporter proteins (symports) form a secondary active transport for monosaccharides
- same as carbs
- Na is secreted tp facilitate water movement
lipids absorption in SI
different than carbs and protein
- fats are breakdown products from lipids and are absorbed into micelles
- lipids repackaged into chylomicrons (protein covered lipids)
- secreted into ECF and taken into lymph
large intestine anatomy
- cecum
- appendix
- colon
- rectum
- anal canal
large intestine function
last portion of the alimentary canal and terminal digestion
- recovery of water and electrolytes from ingesta
- formation of storage of feces
- microbial fermentation
movement of salt…
moves water!
large intestine motility
haustral contractions - slow segmentation
mass movements- POWERFUL peristalsis
- LI is more for mixing, not breaking down
gastrocolic reflex
stimulated by foo din stomach
- triggers a mass movement in the LI
large intestine secretions
- mucus- provides protection
- parasympathetic stimulation increases rate of goblet cell secretion - pumps - exchange of ions
pumps in LI secretion
- exchange of bicarbonate ions for chloride ions
- sodium ions for hydrogen ions
defecation reflex
occurs when feces enter the rectum (mass movement)
anal canal sphincters
- external anal canal - skeletal muscle
- volunatry, you control it - internal anal canal- smooth muscle
- involuntary, no control
