Midterm 2: Digestion Flashcards
Digestion is a form of ___________
catabolism
A hydrolytic process
breaks down large food molecules (carbohydrates, proteins, lipids) into smaller ones (monosaccharides, amino acids, fatty acids)
Path of the digestive tract:
mouth–> esophagus–> stomach–> small intestine–> large intestine (colon)–> rectum
What other organs are involved in digestion?
pancreas, gallbladder, liver
True/False: Most of our supply of carbohydrates (i.e., glucose) is obtained through our diet.
True
Can our body synthesize glucose? If so, how?
gluconeogenesis; amino acids, pyruvate, and lactate can be used to synthesize glucose
What are the building blocks of carbohydrates?
Monosaccharides (simple carbs)
What type of bonds join monosaccharides together?
glycosidic bonds (covalent bonds) form disaccharides and polysaccharides (complex carbs)
Monosaccharides include:
glucose, galactose, and fructose
Disaccharides include:
lactose, maltose, sucrose
Polysaccharides include:
glycogen, starch, cellulose, and GAGs
Where does carbohydrate digestion begin?
mouth
What enzyme is contained in saliva? What does it break down? How?
salivary amylase (Enzyme) that hydrolyzes 5% of starch in the mouth
Amylase breaks down starch into what two components?
maltose and a polysaccharide
Salivary amylase is inactivated by what?
the acidity of the stomach
(Minimal/maximum) carbohydrate digestion occurs in the stomach?
Minimal
After digestion occurs in the stomach, carbohydrate digestion continues where?
in the lumen of the small intestine
What two components are secreted from the pancreas into the small intestine for carb digestion?
Bicarbonate (HCO3-) and amylase
What is bicarbonate?
It is a buffer that neutralizes acidic stomach contents in the small intestine (secreted by the pancreas)
Pancreatic amylase has what function?
It hydrolyzes disaccharides and complex carbs into monosaccharides in the small intestine (secreted by the pancreas)
What enzymes are secreted by the small intestine, aiding in carb digestion?
Disaccharidases (lactase, sucrase, maltase) are secreted from the small intestines
Hydrolyze disaccharides into monosaccharides
At the end of carbohydrate digestion in the small intestine, what have the carbs become?
~80% of monosaccharides are glucose
After carb digestion occurs in the small intestine, the monosaccharides go where?
they are absorbed into enterocytes (small intestine cells) of the intestinal mucosa to reach blood capillaries
How do the monosaccharides enter enterocytes?
Substances cannot pass between epithelial cells because these cells are bound by tight junctions, so they enter enterocytes by co-transport and facilitated diffusion
What uses movement of 1 molecule through the cell membrane from higher to lower concentration to power the movement of another from lower to higher concentration?
Co-transport
What uses the movement of substances from an area of higher to an area of lower concentration using a carrier protein in the cell membrane?
facilitated diffusion
After entering blood capillaries, monosaccharides are transported to where? Pathway?
the liver via the hepatic portal vein
What 3 things occur here (in the liver with carb digestion)?
Galactose is primarily converted to glucose
Fructose is primarily converted to glucose and lactate
Glucose is stored as glycogen or transported to peripheral tissues
How is glucose stored in the liver?
glucose is stored as glycogen or transported to peripheral tissues
Glycogen is used to maintain blood glucose levels at _________________ mg/dL.
70-100 mg/dL
In the peripheral tissues of the liver, glucose is used for
energy production or stored as glycogen
When liver cells and peripheral tissue are saturated with glycogen, what happens?
excess glucose is converted into fatty acids
Where are undigested carbohydrates (fiber) eliminated?
by the colon
What cannot be digested by humans?
Dietary fiber is from plant cell walls (i.e., cellulose) and is resistant to human digestive enzymes; Unable to be digested and absorbed
How are undigested carbs classified?
insoluble or soluble
Insoluble fiber passes through the digestive tract relatively untouched, why?
Speeds up digestion; Adds bulk to stool so it can pass easier
Soluble fiber forms a gel when mixed with water in the digestive tract, what does this do?
Slows down digestion and absorption of glucose, thereby preventing blood glucose spikes
Fermented by colon bacteria into short-chain fatty acids and gases
Why do some amino acids have to be obtained from our diet?
Because our body cannot synthesize them
Essential amino acids include the following:
histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine
PLT HI LMTV (lets move to Venice)
What are the building blocks of proteins?
Amino acids
• Amino acids are joined together by what type of bond? Forming?
in a peptide bond to form peptides and polypeptides (proteins)
Peptides and polypeptides take on a 3-D shape through various bonds:
Hydrogen bonds Ionic bonds van der Waals interactions Hydrophobic interactions Disulfide bridges
Where does digestion begin for proteins?
Digestion begins in the stomach
What denatures proteins in the stomach?
Stomach acid
What hydrolyzes peptide bonds?
Pepsin
After leaving the stomach, where does protein digestion continue?
in the lumen of the small intestine
Bicarbonate (HCO3-), trypsin, chymotrypsin, and carboxypeptidase are secreted from where? To help digest what?
the pancreas into the small intestine; protein
What is the role of bicarbonate in protein digestion?
it is a buffer that neutralizes acidic stomach contents
What is the role of Trypsin, chymotrypsin, carboxypeptidase in protein digestion?
hydrolyze peptide bond
What are secreted from the small intestine in protein digestion? What is their role?
Peptidases; Hydrolyze peptides into amino acids
Amino acids are then absorbed into enterocytes of the intestinal mucosa to reach blood capillaries, Is this the same thing that occurs with carb digestion?
YES!
Substances cannot pass between epithelial cells because of??
tight junctions
How do amino acids enter enterocytes?
by co-transport
Once in the blood capillaries, monosaccharides are transported to the liver via the _____________
Used for protein synthesis, converted into _________, converted into __________, or transported to peripheral tissues for protein synthesis
hepatic portal vein; glucose; fatty acids
Small amount of protein is eliminated by _______.
the colon
Are lipids synthesized or obtained through our diet?
BOTH: they can either be synthesized or obtained through our diet
How are lipids classified?
due to their hydrophobicity
What does hydrophobicity mean?
Do not dissolve in water; Cluster together away from water (form fat globules)
Lipids are which three?
triacylglycerol (triglyceride, TAG), cholesterol, phospholipids
TAG is composed of __________.
3 fatty acids + glycerol (a sugar) and comprises 90% of dietary lipids
Phospholipids are composed of ___________.
2 fatty acids + Glycerol + Phosphate + 1 of 4 polar groups
Cholesterol is composed of ___________.
a steroid core of 4 fused rings + side chains
Does any digestion for lipids occur in the mouth or stomach?
Limited digestion occurs in the mouth and stomach
Lingual lipases and gastric lipases hydrolyze fatty acids with ≤12 carbons
Fat globules leave the stomach and enter the ___________.
small intestine
__________ are secreted from the gallbladder (synthesized in the liver from cholesterol) into the small intestine. (lipid digestion)
Bile salts
Amphipathic molecules that emulsify fat globules (surround pieces of fat globules and break them into smaller droplets)
Bile Salts
What is the function of bile salts?
Increases the surface area of lipids and makes them more accessible to digestive enzymes
_____________ are secreted from the pancreas into the small intestine (lipid digestion)
Bicarbonate (HCO3-) and lipases
___________ is a buffer that neutralizes acidic stomach contents
Bicarbonate
Pancreatic lipase hydrolyzes triglycerides into ___________.
monoglyceride and (2) free fatty acids
Bile salts continue to surround fat droplets forming ____________ ?
micelles
What are micelles?
They are a core of lipids (hydrophobic regions inside and hydrophilic regions outside) surrounded by bile salts
Transport lipids through the intestinal lumen to the epithelial lining
Bile salts that surround fat droplets forming micelles
Once micelles reach the epithelial lining of the small intestine, where are they are then absorbed?
into enterocytes
How do Micelles enter enterocytes?
by simple diffusion
movement of substances from an area of higher concentration to an area of lower concentration,
Simple diffusion
Where are Bile salts are absorbed?
in the more distal small intestine and transported back to the liver through the portal vein
Once inside the enterocyte, _______ is reformed and packaged into ____________, along with other lipids
TAG; chylomicrons
__________ are a core of lipids (hydrophobic regions inside and hydrophilic regions outside) surrounded by lipoproteins
Chylomicrons
Transport lipids through the bloodstream from the __________ to the ____________.
intestine to the liver
Chylomicrons enter____________, bypassing blood capillaries. Why?
lymph capillaries; Chylomicrons are too LARGE to enter blood capillaries directly
Lipid process through blood?
Lymph → Veins → Arteries → Blood capillaries
Within blood capillaries, _________ are digested.
__________ hydrolyzes triglycerides into fatty acids and glycerol.
Glycerol returns to the __________ to be reused.
Fatty acids enter cells to be used as an energy source or stored as __________ (if entering adipose tissue).
Chylomicron remnants are transported to the liver.
chylomicrons
Lipoprotein lipase
liver
TAG
In the liver, chylomicron remnants are recycled and TAG is reformed
TAG, along with other lipids (mainly ___________), is packaged into _______ for transport through the bloodstream to tissues
The structure of ________is similar to chylomicrons and allows transport of lipids between tissues in an ________ environment
cholesterol
VLDL
VLDL
aqueous
Within blood capillaries, what is digested? (lipid)
VLDL is digested
Loss of triglycerides and some apoproteins
converts _________ to __________
VLDL into LDL (low density lipoprotein)
LDL is an important carrier of __________ to tissues
cholesterol
Cholesterol can be deposited in the cell membrane, used to make what?
Vitamin D, bile acid or steroid hormones
_______________ carries excess cholesterol away from tissues to the liver
HDL (high density lipoprotein)
