Digestion and Absorption Lab
Describe propulsion, grinding, and retropulsion.
1. Propulsion = food pushed against an almost closed pyloric sphincter 2. Grinding = muscle contractions trap food in the antrum and churn it through segmentation 3. Retropulsion = large particles are forced back into the body of the stomach
What does the intestinal lumen contain after carbohydrate digestion? What are they converted to before they enter epithelial cells via transport proteins?
1. a pool of disaccharides 2. monosaccharides
What is the order of events in which lipid digestion ordinarily occurs?
1. delay of stomach emptying 2. bile salt secretion 3. formation of micelles 4. micelle and enzyme interaction 5. digestion of lipids
What is one function of lipids, carbohydrates, and proteins?
1. lipid = cell membranes 2. carbohydrate = rapid energy source 3. protein = growth and repair
What digests the tetramer into smaller peptides? What absorbs it?
1. protease 2. endothelial cells
What are the products of each of the following carbohydrates: starch, maltose, sucrose?
1. starch = many molecules of glucose 2. maltose = two molecules of glucose 3. sucrose = one molecule of fructose, one molecule of glucose
How many different amino acids are there?
20
How many essential amino acids are there?
9
What is catabolism? What is anabolism?
Catabolism is the breakdown of molecules to generate energy. Anabolism is the building up of molecules.
Describe the rate of digestion for lipids.
Chemical receptors in the small intestine detect the lipids and slow gastric emptying. Lipids enter the small intestine slowly, in small amounts, and at the same time as bile salts.
Describe the rate of digestion of proteins.
Chemical receptors in the small intestine detect the protein and delay gastric emptying to the small intestine
How are the products of protein digestion absorbed from the gut lumen to the capillaries?
Cotransporters are utilized to move tripeptides, dipeptides, and amino acids across the cell membrane and into the epithelial cells. The protease pepsin helps break down molecules into amino acids, which move out of the gut lumen via unitransporters to the capillaries.
The cycling of what creates a constant gradient for the entry of dipeptides and tripeptides into the epithelial cells?
H+
How does the cell maintain the electrochemical gradient for H+?
H+ are removed through the Na+/H+ antiporter
What is the electrochemical gradient?
It is the diffusion gradient of an ion, which is affected by both the concentration difference of an ion across a membrane (a chemical force) and the ion's tendency to move relative to the membrane potential (an electrical force).
The SGLT1 cotransporter brings glucose and Na+ into the cell. How does the cell maintain the electrochemical gradient for Na+?
The cells maintains the electrochemical gradient for Na+ by utilizing the Na+/K+ ATPase (counter transport protein, uses primary active transport) to take three sodium out and bring two K+ across the basolateral membrane.
What is denaturing?
The process where the complex three-dimensional structure of a protein is lost and the protein unfolds. This process gives digestive enzymes better access to the peptide bonds.
What are lipids digested by?
a class of enzymes called lipases
What are phospholipids?
a lipid containing a phosphate group in its molecule
What is chyme?
a mixture of partially digested food, water, and gastric juices
What does the stomach act as?
a reservoir that controls the rate at which food enters the small intestine
What are chylomicrons?
a type of lipoprotein (a transport vesicle that contains lipids)
What products can be absorbed without further digestion?
amino acids, tripeptides, dipeptides
What kinds of foods contain more fiber?
apples, peas, beans
Which molecules are required for the formation of micelles?
bile salts and phospholipids
What does pepsin do?
breaks peptide bonds to produce a series of polypeptides and smaller oligopeptides
Describe the rate of digestion for carbohydrates.
carbohydrates are rapidly broken down and absorbed into the blood stream
What are the three classes of macronutrients?
carbohydrates, lipids, proteins
Which of the following cannot be broken down by the human body?
cellulose
What length of fatty acids can dissolve in water?
chain length small (<5) and medium (6-12)
What do proteins consist of?
chains of amino acids which are bound together by peptide bonds
When you consume a high-fat meal, what do chemical receptors in the small intestine trigger the release of?
cholecystokinin (CCK)
How do chylomicron and micelle structures vary?
chylomicrons have the same phospholipid structure as a micelle but with proteins on the surface instead of bile salts
What are micelles?
clusters of bile salts that transport lipids across the cell membrane of the villi; hydrophilic heads interact with water and the hydrophobic tails hide together in spherical droplets
Which process is dependent on cotransport with H+?
dipeptide absorption from the intestinal lumen
What must happen before carbohydrates can be absorbed?
disaccharides, oligosaccharides, and polysaccharides must be digested into monosaccharides
When can denaturing occur?
during cooking and in the acidic environment of the stomach
What slows gastric emptying more than any other macronutrient?
fat
What happens when micelles come into contact with the epithelial cell membrane?
fat-soluble lipids within the micelle diffuse into the cell
What does the digestion of proteins result in?
free amino acids, dipeptides, and tripeptides
After lipids have been digested, what molecules can be found inside a micelle?
free fatty acids and sterols (what is found outside are bile salts)
What does the smooth endoplasmic reticulum do?
free fatty acids are reassembled into triglycerides before they are transported to the Golgi apparatus and packaged for export as chylomicrons
What structures are affected by CCK?
gallbladder, sphincter of oddi, pancreas, and stomach
What are examples of monosaccharides?
glucose, galactose, fructose
What are disaccharides bound by?
glycosidic bonds (covalent bond between two sugar molecules)
What does SGLT1 cotransporter do?
it uses the electrochemical gradient of sodium ions to move glucose through the cell membrane
What are examples of disaccharides?
lactose, maltose, sucrose
What is chemical digestion?
large molecules are broken down into smaller molecules through chemical reactions
What is mechanical digestion?
large particles are broken down into smaller particles by physical force
What role do transport proteins play in helping monosaccharides?
monosaccharides cannot cross cell membranes, so transport proteins allow the monosaccharides to be absorbed from the lumen and move into capillaries
Can chylomicrons enter intestinal capillaries?
no
What is not part of the GI tract?
pancreas, liver, gall bladder, salivary glands (all are accessory organs except salivary glands)
What kinds of foods contain less fiber?
pasta, rice, steak
What kind of lipases are active in the acidic environment of the stomach?
salivary and gastric lipases
How are carbohydrates classified?
simple sugars (monosaccharides and disaccharides) and complex sugars (oligosaccharides and polysaccharides)
What is the main site of monosaccharide absorption?
small intestine
Where does most carbohydrate digestion occur?
small intestine
Where does most lipid digestion occur?
small intestine
What are examples of polysaccharides?
starch, glycogen, cellulose
Where does the process of carbohydrate digestion start?
starts in the mouth, where an enzyme in saliva is mixed into food
Into which of the following vessels does lymphatic fluid enter the blood stream?
subclavian vein
What starts the process of mechanical digestion?
teeth; they grind large food particles into smaller particles
What products cannot be absorbed without further digestion?
tetramers, polypeptides
When SGLT1 moves glucose into the cell, what force does glucose move against?
the chemical gradient of glucose
What is metabolism?
the chemical processes that occur within a living organism in order to maintain life
What determines how quickly the food moves from the stomach into the small intestine (gastric emptying)?
the composition of the meal
What organs form part of the GI tract?
the oral cavity, esophagus, stomach, small intestine, and large intestine
The acidic environment of the stomach activates what?
the protease pepsin
Why is the formation of micelles an advantage for lipid digestion?
the rate of lipid digestion is increased
What happens to the tetramer?
the tetramer will stay in the lumen of the small intestine until it is broken down into smaller fragments by a protease
What happens as lipids enter the small intestine?
they are emulsified by bile salts and phospholipids to form micelles
What happens when digestive enzymes are activated outside of the small intestine?
they will start to digest the pancreatic tissue (ex. if trypsin is activated before it leaves the pancreas, it will activate other digestive enzymes)
How are triglycerides formed?
three different free fatty acids are bound to a glycerol molecule
What do lipid-rich meals do?
trigger a delay in stomach emptying so the stomach contents reach the small intestine at the same time as the bile salts are released from the gall bladder
What kind of fat accounts for the most dietary lipid we consume?
triglycerides
What three factors affect gastric empyting?
volume, liquidity, osmolarity