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