Module 3: Digestion and Absorption Flashcards
where does digestion occur
gastrointestinal (GI) tract
what does the GI tract consist of
- series of organs
- outer layers of muscles
- inner mucosal layer of glands and absorptive cells
are things in the GI tract (mouth, stomach, intestines) inside or outside the body
- in the GI tract is outside the body
- inside the body would be things in cells, vascular systems, etc
what are the primary organs of the GI tract
- mouth
- esophagus
- stomach
- small intestine
- large intestine
- rectum
what are the accessory organs of the GI tract
- salivary glands
- liver
- pancreas
- gallbladder
why are accessory organs important
although they never come into contact with food, accessory organs are imperative for digestion and absorption
what are the two main functions of the GI tract
- digestion
- absorption
define digestion
- moving food through the GI tract
- breakdown of food into smaller components
- primary site in small intestine
define absorption
crossing the lining of the intestines to enter the body
define transit time
period of time it takes food to travel through the length of the digestive tract
what nutrient can decrease food transit time
fiber
what is the most abundant biopolymer in earth
fiber
define mechanical digestion
- physical break down of food
- chewing, mixing, peristalsis
define paristalsis
wavelike muscular movements that move food through the GI tract
what nerve controls peristalsis
vagus nerve
define chemical digestion
- chemical breakdown of large compounds into smaller units for absorption
- secretions and enzymes
define sphincters
- circular muscles that separate organs of the GI tract
- one-way doors that prevent food from flowing backwards
are sphincters usually contracted or relaxed
always contracting unless food is coming through
how do sphincters relate to surgery
you can’t eat before surgery because the anesthesia may relax your sphincters
what are the 3 main sphincters in the GI tract
- lower esophageal sphincter
- pyloric sphincter
- ileocecal valve
what complications are associated with improper function of sphincters
- heartburn
- vomiting
what nutrients must be digested/broken down before it can be absorbed
- carbohydrates
- proteins
- fats
what form of carbohydrates, proteins, and fats can we absorb
- carbs: monosaccharides
- proteins: amino acids (some dipeptides and tripeptides)
- fats: monoglycerides or free fatty acids
how much of flavor perception is smell
80%
what are the 5 primary tastes
- sweet
- salty
- sour
- bitter
- umami
what is the taste umami
- savory
- from fats and proteins
where do you have taste receptors
- mouth
- nose
- stomach
- small intestine
where does the digestive process begin
mouth
what are two enzymes in saliva and what do they do
- salivary amylase: breaks down carbs
- lingual lipase: breaks down triglycerides into a diglyceride and a free fatty acid
where is food liquified into chyme
stomach
what is chyme
- bolus
- HCL
what is the capacity of the stomach
1 to 4 liters
what is in the stomach’s gastric juices
- HCL
- mucus
- pepsinogen enzyme
- gastrin hormone
which cells make HCL and intrinsic factor (IF)
parietal cells in the stomach
which cells make pepsinogen
chief cells in the stomach
which cells make mucus
goblet cells
explain how is mucus expelled from goblet cells
- as food enters the stomach, blood goes to the GI tract
- the arteries expand and cause pressure to form on the walls on the stomach
- this pressure pushed mucus out of goblet cells
why might you feel cold after eating
blood moves towards your GI tract and away from other areas of the body
what is another name for mucus
mucin
what is mucus composed of
- water
- glycated proteins
what is the purpose of mucus in the stomach
protects the lining of the stomach from HCL
what is the purpose of HCL in the stomach
- denatures proteins
- liquifies foods
- activates enzymes pepsin and lingual lipase
- prepares iron for absorption
what is the purpose of intrinsic factor (IF)
- essential for absorption of vitamin B12
explain how intrinsic factor (IF) works
- IF binds to B12 to protect it from HCL in the stomach
- carries to the ileum and enterocytes on the surface
- binds to receptors on enterocytes
- enterocytes envelop the B12 to absorb it
what is pepsinogen
inactive/deactivated form of pepsin
how is pepsinogen activated to make pepsin
HCL
what is the purpose of pepsin in the stomach
digestion of proteins
what is the purpose of the gastrin hormone in the stomach
controls the movement of the stomach and the secretion of HCL
define rugae in the stomach and their purpose
- folds of tissue in the stomach
- can fold to conserve space or flatten to increase space
how often does the pyloric sphincter open
every 1-3 minutes
how much chyme is deposited from the stomach through the pyloric sphincter and into the small intestine at one time
3 mL of chyme
why does the pyloric sphincter deposit small amounts of chyme into the small intestine at one time
- the chyme is very acidic and the small intestine is more basic
- the small amount allows the chyme to neutralize in the duodenum
what is the primary site of digestion and absroption
small intestine
what are the 3 sections of the small intestine
- duodenum
- jejunum
- ileum
which section of the small intestine is the site of most digestion and absorption
jejunum
what structures assist nutrient absorption in the small intestines
- villi
- microvilli
what is the folded interior of the small intestine called
plicae circulares
how much do plicae circulares increase the surface area of the small intestine
increase 3x
how much do villi increase the surface area of the small intestine
increase 10x
are villi tissue or cell projections
tissue
describe the inside of villi (what might be in a cross section image)
- vascular structures where blood is sent to absorb nutrients (carbs and amino acids)
- lymphatic vessels (lacteals) which also absorb nutrients (fats)
which nutrients are absorbed through the blood
- carbs
- proteins
which nutrients are absorbed through the lymphatic vessels called lacteals
fats
what type of cells are on the surface of villi
enterocytes
what are the cellular projections on enterocytes on villi
microvilli
explain how lactase and the absorption spot of lactose monosaccharides is efficient
- lactase sits on the tip of a microvilli projection and breaks down lactose
- the absorption spot for the monosaccharides is at the adjacent microvilli so the monosaccharides don’t have to be transported anywhere else
how much do microvilli increase the surface area of the small intestine
increase 60x
how big is the surface area of the small intestine
size of a tennis court
what is the function of the pancreas
- secretes alkaline bicarbonate (basic) which raises pH of chyme to neutralize it
- provides many digestive enzymes
what is the function of the liver
produces bile to digest fats
what is bile composed of
- 97% water
- 3% salts made of cholesterol
what is the biliary tree
connects the liver, gallbladder, and pancreas to the duodenum
what is the function of the gallbladder
stores and releases bile
where are water-soluble nutrients absorbed
through intestinal wall and into capillaries
where do water-soluble nutrients in capillaries travel to
liver
where are fat-soluble nutrients absorbed
through intestinal wall and into lacteals of the lymphatic system
what nutrients are absorbed in the duodenum and upper part of jejunum
most minerals except electrolytes
what are the 3 primary electrolytes
- sodium
- potassium
- chloride
what nutrients are absorbed in the jejunum and upper ileum
- carbs
- amino acids
- water-soluble vitamins
what nutrients are absorbed in the terminal segment of the ileum
- lipids
- fat-soluble vitamins (ADEK)
- vitamin B12
where do undigested food components move
to the large intestine
how long is the long intestine
5 to 6 feet
what is the transit time of the long intestine
12 to 24 hours
what are the functions of the large intestine
- propulsion
- absorption of water and sodium
- preparation of waste for defecation
how much bacteria is in the large intestine
100 trillion bacteria
which vitamins do bacteria in the large intestine produce
- vitamin K
- some B vitamins
how much of the vitamin K you have is produced by E. coli in the large intestine
80%
what are the functions of bacteria in the large intestine
- produce vitamin K and some B vitamins
- ferment plant fibers to short chain fatty acids
- metabolize any remaining nutrients
describe the digestion and absorption of carbohydrates
- broken down in the mouth by salivary amylase
- broken down in the duodenum by pancreatic amylase
- enzymes on microvilli break down into monosaccharides
- monosaccharides absorbed from small intestine into the blood
which enzymes break down maltose, sucrose, and lactose
- maltase breaks down maltose
- sucrase breaks down sucrose
- lactase breaks down lactose
what are the monosaccharides in maltose
- glucose
- glucose
what are the monosaccharides in sucrose
- glucose
- fructose
what are the monosaccharides in lactose
- glucose
- galactose
describe the digestion and absorption of proteins
- proteins denatured by HCL in stomach
- proteins broken down by pepsin in the stomach
- enzymes from pancreas break down into amino acids
- amino acids absorbed into the blood
where does protein digestion begin
stomach
describe the digestion and absorption of fats
- broken down in the mouth by lingual lipase
- bile salts enter duodenum from gallbladder and begin to emulsify fats into smaller particles
- lipase from the pancreas breaks down fats into monoglycerides and fatty acids
- monoglycerides and fatty acids are absorbed through the villi and then reform into triglycerides which become chylomicron
- fats enter the lymphatic system
how much bile is made by the liver per day
12 to 14 oz
what does bile being an emulsifier mean
helps mix fats in water
what is chylomicron
- reformed triglycerides after absorption into the small intestines
- acts as an emulsifier
how are fat soluble vitamins absorbed
- facilitated by dietary fat
- transported in chylomicron
how are water soluble vitamins absorbed
into the blood
what is required for absorption of vitamin B12 and where is it absorbed
- requires intrinsic factor
- absorbed in distal ileum
where is alcohol absorbed
- some absorbed in stomach
- most absorbed in small intestine
- travels to liver for detoxification
where are minerals absorbed
along the small intestine
what should be absorbed along with sodium
- glucose
- amino acids
what are two examples of nutrients that are only absorbed based on the body’s need
- iron
- calcium
where is water absorbed
- most in small intestine
- some in large intestine
define ulcer and peptic ulcer
- any removal of epithelial cells
- peptic ulcer is erosion in the lining of the stomach or upper part of small intestine
what is the primary cause of peptic ulcers
Helicobacter pylori
what is the route of transmission for H. pylori
- oral-oral
- fecal-oral
what are causes of ulcers that aren’t H. pylori
- regular use of aspirin
- excessive use of alcohol
- smoking
define constipation
- makes having a bowel movement difficult
- fewer than 3 times per week
what causes constipation
- low fiber
- not enough exercise
- medication
- dehydration
- ignoring the urge to defecate
how to treat constipation
- eat 30g of fiber per day
- drink fluids
- exercise
define diarrhea
- loose and watery stools
- more than 3 times per day
what causes diarrhea
- infections
- food intolerance
- medication
what should you do if you have diarrhea
hydrate
define heartburn/GERD
pain in chest when stomach acid refluxes into esophagus
what causes heartburn/GERD
- overweight
- pregnancy
- hiatal hernia
how to treat heartburn/GERD
- lose weight
- limit foods that increase symptoms
define lactose intolerance
inability to break down lactose because of a lack of the enzyme lactase
define irritable bowel syndrome
- affects large intestine
- leads to cramping, diarrhea, and constipation
what causes irritable bowel syndrome
- overly sensitive muscles and nerves of large intestine
- may react more to stress or certain foods
how to treat irritable bowel syndrome
- increase fiber intake
- eat small and frequent meals
- avoid foods that aggravate condition
define ulcerative colitis
- chronically inflamed large intestine
- surface of small intestine flattens and absorption surface area decreases
what causes ulcerative colitis
autoimmune condition
how to treat ulcerative colitis
- eat omega 3 fatty acids
- decrease consumption of foods that aggravate flare-ups
define probiotics
foods containing live bacteria that have undergone fermentation
examples of sources of probiotics
- yogurt
- kefir
- sauerkraut
- miso soup
- kombucha
define prebiotics
- fiber sources used to support microbes in large intestine
- snacks for the bacteria
examples of sources of prebiotics
- asparagus
- artichokes
- oatmeal
define symbiotics
combinations of probiotics and prebiotics