PSIO202 Exam 3 - Digestive Organs Flashcards
What are the 4 stages of food processing, and how are they connected (pathways between)?
ingestion - eating
digestion - breakdown
absorption - uptake of nutrients
elimination - passage of undigested materials out of the body as feces
ingestion —> digestion or elimination
digestion —> absorption or elimination
absorption —> elimination
What is the alimentary canal?
the continuous tube that stretches from mouth to anus
What are the parts of the digestive tract, and what do they each do (basics)?
mouth - mechanical and chemical breakdown, deglutition
pharynx/esophagus - swallowing and avoiding airway
stomach - mechanical and chemical breakdown, some absorption
small intestine - chemical and mechanical breakdown, absorption of macro and micro nutrients, vitamins, and 90% of the water
large intestine - absorption of electrolytes, 10% water, and a little of the vitamins
rectm/anus - defecation
Do the plexus in the GI tract need nervous input to function?
No
Where are the submucosal plexus and the myenteric plexus?
submucosal: under the mucosa, above the submucosa
myenteric: between the muscle layers, so above the longitudinal muscle and below the circular muscle
In the glands which lie in the submucosa, the epithelial cells are continuous with the…
mucosa
What branch of the nervous system can control the plexus of the GI tract?
enteric, which branches off the the PNS
What type of cells make up the epithelium of the mucosa and what are its functions?
stratified squamous in the mouth, esophagus, and anus
simple columnar in the rest of the GI tract
secrete enzymes, absorb nutrients, secrete mucous, secrete hormones
What type of cells make up the lamina propria of the mucosa and what are its functions?
thin layers of loose connective tissue
contains blood vessels and lymphatic tissue
What type of cells make up the muscularis mucosae of the mucosa and what are its functions?
thin layer of smooth muscle that forms folds in the mucosal layer
drives local movements to increase absorption by exposing ingested material to absorptive surfaces
What type of cells make up the submucosa and what are it’s functions?
loose connective (contains blood vessels, glands, and lymphatic tissue) and the submucosal plexus (which receives SNS and PNS input but does not need it to regular blood vessel diameter, secretion from glands and neurosecretory neurons, and local motility aka contraction of the muscularis mucosae
What type of cells make up the muscularis external layer of the GI tract? What do these different areas with different cells do?
mouth, pharynx, upper esophagus and anus - skeletal muscle under voluntary control for deglutition and defecation
inner circular fibers and outer longitudinal fibers - smooth muscle under involuntary control for motility of mixing and propulsion
myenteric plexus - nervous, receives PNS and SNS input to regulate motility of the circular and longitudinal muscle
What determines if the muscles of the GI tract do mixing or propulsion?
their rhythm and syncronicity
What is the difference between the serosa and the adventitia?
serosa - stomach and intestines, serious membrane that is the visceral peritoneum which secretes serous fluid and is made of areolar connective tissue/simple squamous epithelium
adventitia - esophagus, areolar connective tissue without any epithelium
Regarding layers of the GI tract, the visceral peritoneum is the same as the ———- in the stomach and intestines.
epithelial cell layer of the serosa
How does the mouth mechanically digest food?
breaks it into pieces, and mixes it with saliva to form a moist bolus
How does the mouth chemically digest food? What are the two things used, and what do they each do?
enzymatic digestion
salivary amylase (starch digestions in the mouth, stops at the stomach because pH is too low for it) and lingual lipase (triglyceride breakdown into fatty acids and glycerol, starts working more int he stomach because that is the appropriate pH)
What is the “map” of teeth in the mouth?
4 quadrants, each 2123 from medial to lateral
What composes saliva?
water, mucus, bicarbonate, enzymes, haptocorrin, lactoferrin, and lysozymes
What are the functions of saliva/the things in saliva?
moisten and lubricate food (water and mucus)
dissolve food (water, mucus, enzymes)
bicarbonate buffers acidic foods
protect mouth from infection (lysozymes and lactoferrin are antimicrobial)
haptocorrin protects vitamin B12
What structures empty saliva into the oral cavity?
salivary glands
How do the SNS and PNS play a role in saliva production?
PNS (sight, smell, sound, memory, and tongue stimulation) will increase saliva excretion, SNS (fear and anxiety) decrease salivation
What type of salivary glands produce the most saliva?
extrinsic (parotid, sublingual, and submandibular)
Describe the ducts that come from the 3 different extrinsic salivary glands
parotid duct - one on each side near the second molar
submandibular duct- one on each side
lesser sublingual ducts- many under the tongue
What are the three stages of swallowing? Are they voluntary or involuntary? Where is food transferred in each stage of swallowing?
oral stage - voluntary, oral cavity to oropharynx
pharyngeal stage - involuntary, pharynx to esophagus
esophageal stage - involuntary, esophagus to stomach
What triggers the pharyngeal stage of swallowing?
What are the effects?
sensory nerves in the pharynx signal the deglutition center in the brainstem
breathing stops, soft palate/uvula rise to cover the nasopharynx, vocal cords adduct, larynx rises, epiglottis covers the larynx
What occurs during the esophageal stage of swallowing?
upper esophageal sphincter (skeletal muscle) relaxes
peristalsis pushes the food down (circular fibers contract behind the bolus to push the food forward, and longitudinal fibers contract in front of the bolus to shorten the distance traveled)
lower esophageal sphincter (smooth muscle) relaxes as food approaches
What is the travel time during the esophageal stage of swallowing for solids and liquids?
solids: 4-8 seconds
liquids: 1 second
What happens if the lower sphincter fails to open during swallowing?
esophagus distends and feels like chest pain or a heart attach
What happens if the lower esophageal sphincter fails to close after swallowing? What can exacerbate the symptoms?
stomach acids can enter the esophagus and cause heartburn (GERD)
weak sphincter
laying down after a large meal
smoking and alcohol use
The stomach is made up of ——- muscle which modulates lumenal ——- and ———-.
smooth muscle
pressure and tension
Smooth muscle is present in 3 ways:
sheets, bundles, and sheaths
Smooth muscle is primarily controlled by the ——- nervous system and two neurotransmitters:
autonomic
ACh and NE
What is the normal resting membrane potential for smooth muscle?
-50 to -60 mV
Smooth muscle cells are put into two categories based on excitation. What are the two categories? What does this mean? What are these types also called, and how are they stimulated?
single/unitary - 1 nerve for a bundle of cells, also called myogenic, auto-excitatory and have spontaneous electrical activity
multi-unit - 1 nerve for each cell (so multiple for a unit), also called neurogenic, stimulated by nerves
Where are unitary SM cells located?
digestive tract, gall bladder, urinary bladder
Describe how unitary SM cells function (how they are stimulated, how the cells respond, etc.)
do not have to contact a motor neuron
auto-rhythmic, adjacent cells have gap junctions that transmit action potentials
cell membrane adhere and help transmit force
produce a slow, synchronized contraction where the entire sheet of muscle contracts in a “functional syncytium”
Smooth muscle has ——– that release neurotransmitters into —— junctions which affect the general area of a SM fiber.
varicosities
diffuse junctions
Compared to skeletal muscle, the sarcoplasmic reticulum of smooth muscle is ——– ———–.
poorly developed
Describe the filament structure of smooth muscle?
thick filaments have actin gripping heads
thick and thin filaments are diagonal, which results in a twisting motion upon contraction
Smooth muscle always maintains some ———, even in the absence of —— ——–.
tone
action potentials
Can smooth muscle have sustained contractions? Why?
Yes
it can sustain contraction without fatigue and at very low energy cost
Describe the stress-relaxation response in smooth muscle. What does it allow smooth muscle to do?
stretch causes increase tension, which decreases in a couple minutes
allows change in length while still maintaining ability to contract (important for storage organs)
Describe the length-tension relationship for SM.
wider range of resting lengths, but still has an optimal length for tension
Stomach filling triggers —— and —— controlled by the —— nervous system.
secretions and motility
enteric NS
What are the 5 types of cells in the gastric pits?
surface mucous cells, mucous neck cells, parietal cells, chief cells, and G cells
What do surface mucous and mucous neck cells produce?
mucous
What do parietal cells produce?
hydrochloric acid and intrinsic factor
What do chief cells produce?
pepsinogen and gastric lipase
What do G cells produce?
gastrin
How do parietal cells function?
Inside the parietal cells, water and CO2 turn into H2CO3 with carbonic anhydrase, which then breaks down into a proton and HCO3-.
The HCO3- (bicarbonate) goes into the blood and creates an alkaline tide. Cl- moves into the parietal cell to balance the charge, then out into the lumen.
The proton also moves out into the lumen via an ATP pump. Potassium gets brought into the cell with this pump but the diffuses back out again.
The Proton and Cl- that moved out into the lumen join to become HCl.
What do the three type of waves do in the stomach?
gentle mixing waves - mix bolus with gastric juice (enzymes, acid, water) and turn it into chyme
more vigorous waves - travel from body of stomach to pyloric sphincter, moving the chyme along
intense waves near the pylorus - lead to opening of the pyloric sphincter and release 1-2 teaspoons of chyme into the duodenum with each wave
What type of chemical digestion occurs in the stomach? What special roles do HCl and mucous have in the stomach?
protein digestion begins, fat digestion continues, HCl kills microbes, and mucous is secreted to protect the stomach walls
What chemical digestion happens to proteins in the stomach?
HCl denatures them (unfolds) and activates pepsinogen into pepsin, which breaks peptide bonds between certain amino acids
What chemical digestion happens to fats in the stomach?
gastric lipase splits triglycerides in milk fat (most effective at pH 5-6 in the infant stomach)
What can be absorbed in the stomach?
water, electrolytes, some drugs (aspirin, NSAIDS, and alcohol)
What is important to note about the absorption of drugs/specifically alcohol in the stomach?
fat content in the stomach sows the passage of alcohol to the intestine, where it would be absorbed much more rapidly.
What is released when amino acids synthesize, or when carbohydrates synthesize, or when fatty acids synthesize to a glycerol backbone?
water
What is the length and diameter of the small intestine? What is different in a cadaver?
3 m (10 ft) in length, 2.5 cm (1 in) in diameter
cadaver length increases to 6.5 m (21 ft) due to loss of smooth muscle tone
What are the starting and ending points of the small intestine?
What are the sections fo the small intestine and how long are they?
starts at the pyloric sphincter and ends at the ileocecal sphincter
duodenum - 25 cm/10 in
jejunum - 1 m/3 ft
ileum - 2 m/6 ft
Where are brush border enzymes found?
on the surfaces of the microvilli, on the villus
What do brush border enzymes do?
breakdown carbohydrates, proteins, and nucleosides (no lipids)
What are the main brush border enzymes of the SI?
maltase, sucrase, and lactase for carbohydrates, aminopeptidase and dipeptidase for proteins and nucleosides, and enterokinase/enteropeptidase to activate other enzymes
How much pancreatic juice is secreted per day, and where does it go? What are some features and the composition of it?
1200-1500 mL per day into the lumen of the SI
clear, colorless, pH 7.1-8.2
consists of water, salts, sodium bicarbonate, and enzymes
What enzymes are secreted by the pancreas?
pancreatic amylase - breaks down starches (maltose and dextrose)
proteases (like trypsin, chymotrypsin, carboxypeptidase, and elastase)
pancreatic lipase-breaks down triglycerides
robinuclease and deoxyribonuclease (nucleases)
In the pancreas, proteases are secreted as…
inactive precursors
What does enteropeptidase on the brush border cells do?
activates trypsinogen to trypsin
What does trypsin activate?
more trypsin, chymotrypsinogen, procarboxypeptidase, and proelastase
What are the two most important functions of the liver?
metabolize/store carbohydrates, proteins, and lipids
release bile salts to help digest lipids
What are the less important functions of the liver?
detox blood by removing drugs/hormones, remove bilirubin, store fat soluble vitamins, store iron/copper/B12, phagocytose blood cells and bacteria, play a role in vitamin D activation
What are Kupffer cells?
cells in the liver which phagocytose microbes and foreign matter
Describe the flow of blood through the liver.
blood from hepatic arteries and hepatic portal veins mix, then flows through the sinusoidal capillaries of the liver before returning to venous circulation (central veins of the lobules, then hepatic vein, etc.)
Components of bile are more concentrated in the ——- than the ——-.
gallbladder than the liver
What feature of bile salts allows them to emulsify lipid droplets?
they are amphipathic - hydrophilic side and hydrophobic side which can bind to a lipid
Describe the pathway of bile secretion.
Bile canaliculi form bile ducts which form the hepatic ducts (left and right)
The left and right hepatic ducts merge into the common hepatic duct.
The cystic duct joins the common hepatic duct to form the common bile duct
The pancreatic duct joins the common bile duct to empty into the duodenum.
In what situation does the bile concentrate in the gallbladder instead of being released?
when the sphincter of Oddi (the hepatopancreatic sphincter) is closed
What regulates pH in the small intestine?
bicarbonate release from the pancreas
Where/what digests carbohydrates?
mouth - salivary amylase breaks starch down to maltose and dextrose
stomach- mechanical only
SI - pancreatic amylase from the pancrease breaks starch down to maltose and dextrose
SI - brush border enzymes (maltase, sucrase, and lactase) from villus breaks disaccharides into monosaccharides fructose, glucose, and galactose
What is the gist of lactose intolerance?
those without lactase have bacteria ferment lactose, which results in gas and diarrhea
Where/what digests proteins?
mouth - mechanical only
stomach - HCl denatures and pepsin breaks proteins into smaller polypeptides
SI - pancreatic enzymes (proteases like trypsin, chymotrypsin, carboxypeptidase, elastase) from the pancreas split peptide bonds
SI - brush border enzymes aminopeptidase and dipeptidase split off amino acids or split apart chains of amino acids
Where/what digests lipids?
mouth - lingual lipase
stomach - gastric lipase
SI - pancreatic lipase split triglycerides into glycerol and FAs
SI - bile from liver emulsifies lipids to form micelles
Does the brush border of the SI break down lipids?
No
What are the three ways that surface area is increased in the small intestine?
plicae circulares, villi, and microvilli
Other than surface area, what else do the villi and microvilli do for the SI?
- produces brush border enzymes (surface of microvilli, participate in chemical breakdown)
- cell division within the intestinal glands produces new cells that move up to produce the cells that have been lost
How are monosaccharides absorbed?
absorbed into epithelial cells
- glucose and galactose are transported by a sodium symporter (secondary active transport)
- fructose moves by facilitated diffusion
out of epithelial cell into bloodstream by facilitated diffusion
How are amino acids and dipeptides absorbed?
absorbed into epithelial cells of the duodenum and jejunum by Na+ or H+ ion symporters
out of epithelial cells into blood by facilitated diffusion
How are lipids absorbed?
short chain FAs and glycerol can be absorbed by simple diffusion
- longer FAs and monoglycerides are emulsified by bile, then make micelles which can enter the cell by simple diffusion
- in the cell, they are combined with protein to form chylomicrons
- chylomicrons are too big for capillaries, so they leave into the ISF where they are taken in by lacteals
travel through the lymphatic system until they get to the subclavian vein - removed from blood by liver and fat
What happens to bile salts?
They do not enter the microvilli with the lipids, but rather they are later reabsorbed and recycled into more bile by the liver
What else can enter the cells via micelles with the lipids?
fat soluble vitamins - A, K, D3, and E
Where do electrolytes come from?
GI secretions, ingested food and liquids
How are electrolytes absorbed?
enter epithelial cells by diffusion and secondary active transport:
sodium and potassium move by active transport
chloride, iodide, and nitrate follow passively
iron, magnesium, and phosphate ions use active transport
intestinal Ca++ absorption requires vitamin D and PTH
How are vitamins absorbed?
fat soluble (A, K, D3, and E) travel in micelles and absorb by simple diffusion with lipids
water soluble are absorbed by diffusion
How is B12 absorbed specifically?
B12 is protected in the stomach by haptocorrin from the saliva
Combines with intrinsic factor from the parietal cells
Transported into cells of the ileum by receptor mediated endocytosis
Describe absorption of water in the GI tract.
6-9 L enters the GI tract each day
small intestine absorbs about 90%
large intestine absorbs 90% of the last 10%
absorption is accomplished by osmosis - trough cell membranes into cells and then into capillaries from the intestinal villi
What are the two most important cells from the large intestine, and what do they do?
absorptive cell - absorb water
goblet cell - secrete mucous
What are the functions of the large intestine?
smooth muscle does mechanical digestion (peristaltic waves, 3-12 per minute)
absorption of water and some nutrients
haustral churning
bacteria ferment undigested carbs into CO2 and methane, and undigested proteins into simpler substances
What is haustral churning?
relaxed pouches are filled from below by muscular contraction, when full they contract and move the contents to the next pouch
What causes diarrhea?
chyme passes too quickly through the intestine, and not enough water is absorbed
What causes constipation, and what are remedies?
decreased intestinal motility and too much water absorbed
fiber, exercise, and water
What is fiber?
complex carb which we can not fully digest
What is insoluble fiber?
the woody parts of plants
speeds up transit time and reduces colon cancer
What is soluble fiber?
gel like consistency - beans, oats, citrus white parts, apples
lowers blood cholesterol by preventing reabsorption of bile salts so the liver has to use cholesterol to make more bile
