Digestive System Flashcards
What is the digestive tract?
the tube from the mouth to the anus
The digestive system is composed of what?
1) digestive tract
2) accessory organs
What are these accessory organs?
teeth, salivary glands, liver, pancreas etc.
What are the four basic processes of the digestive system?
1) digestion
2) absorption
3) motility
4) secretion
What is digestion?
the breaking down of large food pieces into small molecules
What are the different types of digestion?
mechanical and chemical
What is mechanical digestion?
- involves muscle movement (motility)
What is chemical digestion?
involves enzyme with acid
What is absorption?
the passing of the broken down molecules from the lumen to the enterocytes (small intestines cells) in the villi to the blood or lymph
What is motility?
smooth muscle contraction
What are the two kind of motility?
- mixed (segmentation and churning
- move (peristalsis)
What is secretion?
digestive juice into the lumen
What accessory organ is present in the mouth?
salivary gland
What does the salivary gland do in the mouth?
- the saliva it produces moistens (taste, speech, food manipulation) and prevents caries aka decay and crumbling because it has lysozyme and antibodies
How does the PSNS affect the salivary glands in digestion?
it stimulates secretion of thin enzyme rich saliva
How does the SNS affect the salivary glands in digestion?
it stimulates the secretion of mucus rich saliva
in the mouth, what is the mechanical digestion that’s occurring?
chewing
In the mouth, what is the chemical digestion that’s taking place?
1) carbohydrates are turned to disaccharides and oligosaccharides with the help of salivary amylase at the pH level of 7sh
2) triglycerides are turned into fatty acids and monoglycerides with the help of lingual lipase
What enzyme is present in the chemical digestion of carbohydrates?
salivary amylase
What enzyme is present in the chemical digestion of triglycerides?
lingual lipase
is food absorbed in the mouth?
no
whats being absorbed in the mouth?
some drugs such as nitroglycerin for angina to promote vasolidator?
Where does swallowing occur in the digestive system?
Pharynx and Esophagus
Swallowing occurs in three phases. What are they?
1) Buccal phase
2) Pharyngeal phase
3) Esophageal phase
What happens in the buccal phase?
food is compacted into a “bolus” by the tongue and gets sent to the pharynx by the tongue pressing on hard palate
What happens in the pharyngeal phase?
swallowing reflex initiated by the swallowing centre in the medulla
What happens in the esophageal phase?
- food moves down esophagus (peristalsis )
Peristalsis happens because of the nervous system. What do the SNS and PSNS innervate and where are they found in the esophagus?
SNS innervates skel muscle on the upper 1/3
PSNS innervates smooth muscle on the lower 1/3
and the middle 1/3 is a mix of both
Is the buccal phase a voluntary or involuntary action?
voluntary
Is the esophageal phase a voluntary or involuntary action?
involuntary
Is the pharyngeal phase a voluntary or involuntary action?
involuntary
Why cant food reenter while swallowing?
because the tongue is pressing on the hard plate
- the uvula and smooth plate of the nasopharynx are elevated
- the the glottis and epiglottis in the trachea are closed which temporary stops breathing
What is closed in the trachea during swallowing?
glottis and epiglottis
In the mouth, what prevents food from re-entering during swallowing?
tongue pressing on the hard palate
In the nasopharynx, what prevents food from re-entering when swallowing?
the uvula and soft palate are elevated
What is the mechanical digestion happening in the stomach?
motility –> churning
What is the chemical digestion happening in the stomach
1) carbohydrates being digested by salivary amylase until ph is below is 7
2) lipids being broken down by lingual lipase and gastric lipase until pH is less than 5-6
3) proteins are broken down by pepsin
How is pepsin (enzyme that breaks down protein) formed in the stomach?
- it starts of as pepsinogen (inactive form) secreted by the chief cells,
- HCl released by parietal cells converts the pepsinogen to pepsin
What prevents the stomach from self digestion?
by alkaline mucous or mucous cells
Is there absorption happening in the stomach? If so what’s being absorbed?
- food but very little
- alcohol and aspirin which penetrates the mucous
What is the mechanical digestion happening in the small intestines?
segmentation and peristalsis
Does chemical digestion take place in the small intestine?
yes
What are the three things involved in chemical digestion in the small intestines?
1) pancreas
2) gall bladder
3) intestinal wall
In general what are the three steps to intestinal chemical digestion?
1) Acid Neutralization
2) Pancreatic Enzymes
3) Intestinal Wall Enzymes
What happens in the acid neutralization step in intestinal chemical digestion? It this mechanism negative or positive
the acid (from the stomach) that enters the duodenum of the small intestine stimulates the secretion of the hormone “secretin” which increases the production of alkaline fluid HCO3- from the duct cells of the pancreas and gall bladder and the same time, it decreases gastric acid of the parietal cells
- negative
why is it important to neutralize acid first?
so pancreatic enzymes can work
In step 2 of intestinal chemical digestion, how are carbohydrates digested
through the help of pancreatic amylase, carbohydrates are converted into disaccharides(maltose) and oligosaccharides
In step 2 of intestinal chemical digestion,how do pancreatic enzymes digest proteins?
1) trypsinogen (an inactivated form of trypsin) gets converted to trypsin by the help of enteropeptidase from the intestinal wall?
2) the trypsin then activates other protease which aids in chemical digestion
- trypsin helps trypsinogen turn to trypsin (therefore positive feedback)
- trypsin converts chymotrypsinogen to chymotrypsin
- trypsin converts procarboxypeptidase to carboxypeptidase
3) Finally, the proteins from the diet, with the help of these activated protease, get converted to amino acids and peptides
In step 2 of intestinal chemical digestion how do do pancreatic enzymes digest lipids?
triglycerides are broken down to fatty acids and monoglycerides with the help of lipase and bile salt (not an enzyme, a catalyst = speeds up process)
How are pancreatic enzymes that come from pancreatic acinar cells and travel to the lumen regulated?
the increased fatty acids and amino acids in the duodenum increase cholecystokinin (CCK) which is a hormone
- cholecystokinin increases pancreatic enzyme secretion
- it decreases gastric motility (slows emptying) and gastric acid secretions
- it stimulates gall bladder contractions to release bile
Step 3 of intestinal chemical digestion happens is a further _________
breaking down/digestion on microvilli of enterocytes (intestine walls)
How do intestinal wall enzymes, step of 3 of intestinal chemical digestion further break down carbohydrates?
well the disaccharides and oligosaccharides are broken down to monosaccharides with the aid of disaccharidases and oligosaccharidases
For example how is sucrose which is already a broken down disaccharide (by the pancreatic enzyme) broken down even more?
sucrose is converted to glucose and fructose by the aid of surase
How is maltose(disaccharide) a broken down carbohydrate by the pancreatic enzyme broken down even more by the intestinal wall enzyme?
maltose is broken down to glucose and glucose by the enzyme maltase
How is lactose(disaccharide) a broken down carbohydrate by the pancreatic enzyme, further broken down by the intestinal wall enzyme?
lactose is broken down to glucose and galactose with the aid of lactase
deficiency in lactase cause what?
lactose intolerance = lactose remains undigested so the bacteria in the large intestines ferment them which causes diarrhea and gas
How are peptides (broken down protein - by the pancreatic enzyme) further broken down by the intestinal wall enzyme?
peptides are converted to smaller peptides and amino acids with the aide of aminopeptidase and dipeptidase
How are lipids digested on intestinal walls?
they don’t get digested because there are no lipase on the wall
Does absorption happen in the small intestine?
yes
Where in the digestive system is absorption significant? Why?
The small intestine due to:
- large surface area caused by folds, villi and microvilli
- nutrients = small molecules
How are glucose and galactose absorbed?
they enter the enterocytes via secondary active transport and leave them to enter blood via facilitated transport
How are fructose absorbed?
they enter the enterocytes via facilitated transport and leave them to go to blood via facilitated transport as well
Do monosaccharides, finished digested products, go to the blood or lymph in absorption?
blood
How are amino acids absorbed?
1) they enter the enterocytes via secondary active transport
2) then they leave the enterocytes to go the blood via facilitated transport
How are dipeptides and tripeptides absorbed?
they enter the enterocytes via secondary active transport where they get broken down into amino acids via cytosolic enzyme and then they leave the enterocytes to go to the blood via facilitated transport
where do proteins go when being absorbed? Lymph or blood or both?
blood
how are monoglycerides and long fatty acid chains (longer than 12 chains) absorbed?
they enter the enterocytes via diffusion and leave through exocytosis to go the lymph lacteal via diffusion
How are short chained fatty acids (shorter than 12C) absorbed?
they enter the enterocytes via diffusion and leave via diffusion to go to the blood
How is water absorbed?
they enter the enterocytes and leave to go to the blood and lymph via osmosis
where do short chained fatty acids go when being absorbed?
blood
Where to long chained fatty acids and monoglycerides go when being absorbed?
lacteal lymph
where is water absorbed? blood, lymph or both?
both
How much water per day is taken in the body? Where do they come from???
about 9000 ml
- about 7000 ml/day from water secretions
- about 2000 ml/day from ingested food and drink
How much water per day is actually absorbed in the small intestines?
about 8500ml/day
How much water per day is lost to large intestines?
about 500ml
where do absorbed nutrients go? and how do they get there?
1) liver via hepatic portal vein (blood)
2) lacteal lymph —> thoracic duct –> left subclavian vein
What does fat digestion and absorption require?
bile
Where are these bile (required for fat absorption and digestion) from?
- liver where they are produced or synthesized
- gall bladder where they are stored
What does bile consist of?
1) water
2) bile salt (derived from cholesterol)
3) bile pigments (bilirubin from RBC breakdown)
4) ions (bicarbonate aka HCO3-)
5) detoxified/inactivated drugs, toxins, hormones etc.
What is the purpose of bile salt?
1) emulsification = breaks up larger globules of fat into many small droplets
2) formation of micelle = keeps fat digested products in solution
what does micelle consist of?
phospholipids and bile salts
Is the interior of micelle hydrophobic or hydrophyllic?
hydrophobic
Is a micelle’s exterior, hydrophobic or hydrophillic?
hydrophillic
What happens with lipid globules in the lumen?
lipid globule emulsifies and breaks down into fatty acids and monoglycerides with the aid of lipase.
- they then diffuse in the enterocytes and diffuse from micelle into enterocytes
once fatty acids and monoglycerides are in the enterocytes, what happens?
- in the smooth endoplasmic reticulum, they become diglycerides and fatty acids with the aid of an enzyme
- another enzyme turns them into triglycerides
- cholesterols, proteins and phospholipids are then added into the golgi apparatus to create chylomicron (fat + protein package) which is water soluble
- they then travel into the ISF via exocytosis and diffuse into lacteal lymph
What are three regulatory phases of gastric motility/secretion?
1) Cephalic phase
2) Gastric phase
3) Intestinal phase
Generally, what happens in the cephalic phase?
- it prepares the stomach for food
- it triggers thought, sight, smell, taste of food
- basically it sends signals to the brain that food might be eaten
How is the NS (enteric + PSNS) function during the cephalic phase?
It stimulates smooth muscle motility, production of enzymes (pepsinogen, lipase), increases acid secretion and production of gastrin (hormone) which aids in production of enzymes and acid secretion
In details, what happens in gastric phase?
- the food in the stomach causes distension which activates stretch receptors
- which send signals to the NS (enteric + PSNS)
- which stimulates smooth muscle motility, production of enzyme (pepsinogen), increase of acid stimulation, production of gastrin (hormone) that aids in production of enzyme and increase of acid stimulation
- Ca2+, amino acids, alcohol and caffeine also aids in production of gastrin
is food a buffer in gastric phase? What does this mean in terms of pH level
Yes
- it takes awhile to lower pH
When pH level hits 3, what does this mean
stomach is nearly empty
When pH level is BELOW 3, what happens?
Enteric nervous system shuts down which causes decrease in gastrin and acid.
Why is being regulated in the intestinal phase?
- gastric emptying
- rate of chyme (food + gastric) entry into the duodenum
Why is it important to control gastric emptying?
1) so that acid can be neutralized in the small intestine
2) so that tonicity does not overwhelm small intestine
3) time for digestion and absorption in small intestine
Initially, for a short time, what happens in the intestinal phase?
there’s an increase in gastrin secretion (duodenal gastrin release) because of duodenal stretch
After that short period of increased gastrin secretion, what happens in the intestinal phase?
inhibitory signals cause:
1) decrease in gastric motility
2) decreased gastric secretions (enzymes and acid)
What causes the decrease of gastric motility (gastric emptying) in the intestinal phase?
1) CCK or cholecystokinin (from presence of FA and AA)
2) enterogastric reflex (Enteric NS) which is triggered directly by aa/peptides, acid, duodenal stretch, hypertonicity
- it causes CNS to activate SNS ?
How is cholecystokinin formed?
by the presence of FA and AA
enterogastric reflex (enteric NS) is triggered by?
amino acids/peptides, duodenal stretch, acid, hypertonicity
What causes the decreases of gastric secretion in the intestinal phase?
1) release of secretin (hormone) due to acid
2) CCK or cholecystokinin from the presence of FA and aa
What kind of motility is happening in the large intestine?
1) Haustral contractions
2) Mass movements
What are haustral contractions that take place in the large intestines? What do they do?
- they’re slow weak movements that move material down the tube
- they allow mixing, and absorption of salts and H2O
What are mass movements? What causes this?
- they are powerful waves of contractions from the transverse colon to rectum
- due to food in stomach via gastrocolic reflex
What do mass movement allow to do?
movement of fecal mass to the rectum which initiates urge to defecate
Where does rectal (defecation) reflex take place?
Large Intestines
What is the stimuli, receptor, CNS, and effector acting up in a rectal reflex?
- stimuli = feces in rectum
- receptor = stretch receptors in the rectal wall
- CNS = sacral segment of spinal cord (PSNS)
- effector = smooth muscles of rectum contract and internal anal sphincter relaxes
So what is the overall process of a rectal (Defecation) reflex?
- the presence of feces in the rectum stimulates the stretch receptor reflex in the rectal wall.
- this sends signal to the sacral segment of the spinal cord (PSNS)
- which causes the contraction of the smooth muscle in the rectum and the relaxation of the internal anal sphincter
Is the external anal sphincter part of the rectal reflex? Why or why not?
no because it’s a voluntary control
Is there digestion that take place in the large intestines?
no
If digestion doesn’t occur in the large intestines, what does?
bacterial fermentation of undigested nutrients
The presence of bacteria in the large intestines do what?
- fermentation of undigested nutrients
- synthesize some vitamins such as B6, B5, folate, biotin, K)
Does absorption happen in the large intestines? If yes, what’s being absorbed?
- yes
- about 400ml of water per day is absorbed here via osmosis and about 100 ml/day of water is lost in feces
- fermentation products such as gases and vitamins
- some drugs (rectally) like anaesthetics
Does secretion occur in the large intestines, if so what are they?
K+ and HCO3-
When glucose is absorbed in the small intestines and travel to the blood. what happens to it?
it moves to body cells via facilitated transport where it increases insulin uptake in the skel muscle. liver and fat
In a cell after moving from the blood via facilitated transport, what happens with glucose?
it is used for catabolism to create ATP & anabolism to create glyocen
Glycogen is used for anabolism to create glycogen in the cell, percentage wise, where does it go to?
75% in skel. muscle
25% in liver
and 1% of body’s energy stores
Where does cholesterol go after being absorbed?
they are used to create steroid hormones, bile salts and cell membrane
After lipid is digested and absorbed the final product is a triglyceride which can be found in the blood, what happens to it?
with the aid of lipase on endothelial cells of organs, triglycerides becomes 3 fatty acids + glycerol which are sent to tissue cells for numerous purposes such as:
- oxidation to create ATP (except in neurones)
- stored as triglycerides in adipose tissues which is 99% of the body’s energy stores
- used to synthesize membrane and myelin.
what happens to amino acids after being absorbed?
enter cell by secondary active transport OR facilitated transport where they:
1) increase entry of Growth hormone in most cells
2) increase uptake of insulin in skel. muscle
3) used for protein synthesis
4) used for energy when glucose is low eg. starvation.
are amino acids stored? If not, what happens to excess?
no, excess are converted to fat
what is metabolic rate?
the body’s rate of energy use which is the sum of all chemical reactions and mechanical work
what factors affect metabolic rate?
1) SNS
2) hormones eg. epinephrine and thyroid hormone
3) body temperature
4) exercise
5) sleep
How does the SNS influence Metabolic rate?
increases it
how do hormones such epinephrine and thyroid hormone influence Metabolic rate?
increases it
how does exercise affect Metabolic rate?
increases it
how does food ingestion affect Metabolic rate?
increases it
how does body temp Metabolic rate?
increases by 1 degree celcius aka 10%
how does sleep Metabolic rate?
increases it
from the stomach to duodenum, what does the gastrin hormone do?
-increases acid, gastric enzyme secretion such as lipase and pepsinogen
From the duodenum, what does the hormone secretin do?
- increases alkaline fluid secretion from the duct cells of pancreas and gallbladder
- decreases gastric secretion
what does CCK or cholecystokinin hormone do in the duodenum?
- increases pancreatic enzyme secretion
- increases contraction of gallbladder
- decreases gastric motility and secretion
