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2. Denatures proteins
3. Releases nutrients from organic complexes
4. Acts as a bactericide (killing bacteria ingested with food)
Location: the submucosa (mostly in the intestines)
Function: controls secretions, local blood flow
serosa- protective outer layer connective tissue
muscularis externa (longitudinal and circular muscles) responsible for GI motility
submucosa- connective tissue that contains blood and lymphatic vessels, nerves, and lymphoid tissues.
mucosa- innermost mucus layer, that produces and releases digestive secretions
lumen- has mucosal epithelium that is in direct contact with the food/nutrients we consume
Describe the structural features of an enterocyte?
golgiAlso tight junction and desmosome which serve to prevent leakage of the SI. The microvilli sit atop the enterocyte and make up the brush border
Paneth cells (excrete antimicrobial pepsins called defensins)
mast cells (endocrine functions)
goblet cells (secretes both cystein-rich proteins that act as antifungals and mucus)
slender, long between the stomach and the duodenum
have ductless endocrine cells (islet of Langerhans) that secrete (insulin and glucagon) hormones into the blood
digestive enzymes produced by acinar exocrine cells
regulation of pancreatic secretions
Alpha cells (A cells)
Beta cells (B cells) - most abundant
Delta cells (D cells)
have channels in their plasma membrane that serve as glucose detectors; secrete insulin in response to a rising level of circulating glucose (“blood sugar”)
What are the components and their functions of pancreatic juice?
1. Bicarbonate is important for neutralizing the acid chyme passing into the duodenum from the stomach and for maximizing enzyme activity within the duodenum.
2. Electrolytes include the cations sodium, potassium, and calcium and the anion chloride.
3. There are a various of pancreatic digestive enzymes in a watery solution e.g pancreatic alpha amylase for carb digestion.
Folds of Kerckring: large circular folds of mucosa that protrude into lumen of SI
Villi: finger-like projections that consist of hundreds of cells
Microvilli: hair-like extensions of the cells’ plasma membranes that pose a surface coat
Crypts of Lieberkuhn
Duodenum receives secretions from the gallbladder via the common bile duct which leads to the sphincter of Oddi which will regulate secretion into the duodenum
because they are detergents (breakdown large fat globules into small fat droplets)
The digestive system works similarly to a washing machine and with the bile acids being laundry detergent, exposing the fats to a lipid-water interface which allow the fats to be broken down
Location: the muscularis externa between longitudinal and circular muscles of muscularis proria
Function: controls peristalsis, motility
Stomach and Small Intestine
stimulates motility and gastric acid release
Inhibits gastric motility and/or secretions
stimulates pancreas and/or gallbladder secretions
Pancreas and Small Intestine
Inhibits gastric secretion and motility
pancreatic (exocrine) and gall bladder secretions
What are the secondary bile acids? Where are they produced?
Deoxycholic acid and Lithocholic acid
They are conjugated by bacteria in the colon and possible the terminal ileum.
What are probiotics and prebiotics? What is the difference between them and what is the common result of them?
Probiotics: foods containing live bacterial cultures
Prebiotics: food ingredients that promote bacterial growth
Both pro and pre biotics function in:
Fermentation in large intestine: breakdown of CHO and protein anaerobically
Products: Lactate, short chain fatty acids, gases
Functions: Probiotics and Prebiotics
What is lactose intolerance?
Cause of it: Reducing sugar (How does this make sense as the cause?)
Which molecule contains α-1,6-glycosidic bond?
maltose is hydrolyzed by maltase, forming free glucose
maltotriose, and isomaltose are further hydrolyzed by maltase or isomaltase (alpha-dextrinase)
Alpha-dextrinase is the only carbohydrase capable of hydrolyzing alpha(1-6) glycosidic bonds
● In the mouth, Salivary a-amylase works to digest everything but amylopectin starch (contains beta-1,4 bonds that are resistant to a-amylase); produces few monosaccharides
● Salivary amylase action continues in the stomach until the gastric acid penetrates the food and lowers the pH sufficiently the inactivate the enzyme
● By now, starches have been partially hydrolyzed, yielding dextrins and maltose
lactose to glucose + galactose
hydrolyzes the alpha(1-6) bond of isomaltose to 2 glucose molecules
Sodium-glucose transporter 1 (SGLT1): transports 2 substances in the same direction; has two binding sites; Na+/K+ ATPase located on the apical side of intestinal lumen
SGLT1 combines with ATP in the presence of Na+ on inner surface of membrane
Transport is considered active in that the carriers are dependent on concentration gradients
GLUT2: located on the basolateral membrane
High affinity for glucose and fructose
energy is not needed with facilitated transport
GLUT5: specific facilitative transporter for transport into the mucosal cells
an integral protein, penetrating and spanning the lipid bilayer of the plasma membrane
Contains 12 transmembrane alpha-helix segments
has a specific combining site for the molecule being transported
undergoes a conformational change upon binding the molecule, allowing the molecule to be translocated to the other side of the membrane released
a low-affinity, high-capacity transporter with predominant expression on B-cells of the pancreas, liver, small intestine, and kidney
Sensitive indicator of blood glucose levels and is involved in the release of insulin from B-cells
How does insulin increase the glucose uptake in muscle and adipose tissue?
In the basal, unstimulated state of the adipocyte and skeletal muscle cells, GLUT4 resides in these structures. When blood glucose levels are elevated, insulin is released by the B-cells of the pancreas
Tetramer composed of 2 alpha and 2 Beta chains; alpha chain is extracellular and contains insulin binding site; Beta chain has an extracellular region, transmembrane region, and an intracellular region
Alpha and Beta chains are bound together by disulfide bonds
GI x g of CHO in 1 serving of food
Considers both the quantity and the quality of the CHO in a meal. The GL equals the GI times the grams of the CHO in a serving of food
Glycemic load considers both the quantity and the quality of the carbohydrate in a meal. The glycemic load equals the glycemic index times the grams of carbohydrate in a serving of the food.
How is pepsin activated?
Lymphoid tissue can be found within and contains a number of white blood cells (especially macrophages and lymphocytes) which provide protection against ingested microorganisms.
Pepcid(famotidine) is an H2 blocker. How does it work to prevent the gastric ulcer?
● If amylose (unbranched) is the dietary starch, a-amylase hydrolysis produces maltose and maltotriose (which is further hydrolyzed to maltose and glucose)
● If amylopectin (branched) is the dietary starch, glucose and maltose is produced
● Alpha-1,6 bonds linking glucose residues at the branch points cannot be hydrolyzed by a-amylase so isomaltose is released (which possesses a-1,6 bonds)
● Digestion ONLY occurs in the upper SI
● Occurs in the brush border (unlike w/ polysaccharides)
● Lactase, sucrase, maltase, isomaltase
o Fructose units in chains of various lengths
o Homopolymers of glucopyranose units
o Highly branched
o Composed of sugars and sugar derivatives
o Highly branched
o Galacturonic acid makes up backbone
Backbone is unbranched chain of a(1-4)-linked D galacturonic acid units
o Carboxyl groups exist as methyl esters
o CHO linked to galacturonic chain
o Additional sugars can be found attached as side chains
o A number of sugars in their backbone and sidechain
Xylose, mannose, galactose = backbone
§ Arabinose, glucuronic acid, galactose = side chain
o Linear and branched
What are the enzymes involved in digestion of cholesterol esters (CE) in small intestine lumen?
What are the enzymes involved in digestion of phospholipid (PL) in small intestine lumen?
What are the enzymes involved in digestion of triacylglycerol (TG) in small intestine lumen?
What are the enzymes responsible for digestion of TG in stomach?
Why are lingual and gastric lipase important for infants?
An infants pancreatic function is not fully developed
so this helps them digest milk fat globules
without substrate stabilization by bile salts
What are the properties of lingual and gastric lipase enzymes that make them special for infants?
a fatty acid and
milk’s medium- and short-chain fatty acids are usually esterified at the sn-3 position
How do medium-chain fatty acid enter the body after being absorbed?
Which part of the digestive tract does the pancreatic lipase work?
What is a lipoprotein?
lipid-protein complexes that play a role in the transport and distribution of lipids
What is apolipoprotein?
How many copies of each apolipoprotein molecule are there in one lipoprotein particle?
Please list from the highest to the lowest percentage contents of TG, PL, Cholesterol and apolipoproteins in chylomicrons
after 80% of chylomicrons is delivered to the muscle and adipose tissue
VLDL of liver origin is stripped of TG by lipoprotein lipase
resulting in the formation of transient IDL particle
The removal of TG then continues until a cholesterol-rich LDL particle remains
LCAT forms cholesteryl esters from free cholesterol and lecithin
by catalyzing the transfer of FA from the C-2 position to free cholesterol
LCAT thus promotes the net transfer of cholesterol out of non-hepatic cells and other lipoproteins
What is the difference between apoB-100 and apoB-48?
contains lipoproteins LDL, VLDL, and IDL
It is synthesized in the liver
is composed of lipoproteins, chylomicrons, and chylomicron remnants
is synthesized in the intestines.
In which lipoproteins can you find ApopB-100 and ApopB-48?
Which enzyme is responsible for the uptake of TG from lipoproteins to muscle and adipose tissue?
What is the reason that chylomicrons are only taken up in muscle and adipose tissue?
Which organ takes the chylomicron remnants?
Dietary lipid is delivered to the liver via chylomicron remnants and MCFA found in the blood
The apo E on surface of the chylomicron remnants binds with specific receptors on the membranes of the endothelial cells.
The chylomicron remnant enters into the hepatocyte and can be used for energy or resynthesis of other lipids.
Newly TAG is combined with PLs, cholesterol, and proteins to form VLDL and HDL, which are released into general circulation.
What are the roles of the liver in lipid metabolism?
Hepatic synthesis of the bile salts
digesting and absorbing dietary lipids
How are chylomicron remnants handled by hepatocyte?
The lipid portion of the chylomicron remnant
is hydrolyzed and absorbed into hepatocytes as
What is the fate of cholesterol and cholesteryl ester in chylomicron remnant?
convert to bile salts and secreted into bile
converted to neutral sterol and secreted into the bile
How is the activity of lipoprotein lipase regulated in muscle and adipose tissue during feeding and fasting?
Feeding: Insulin stimulates LPL,increasing the availability and uptake of FA.
Which apolipoprotein can activate lipoprotein lipase?
Why can you use apoB-100 and apoA-I to represent LDL-Cholesterol to HDL-Cholesterol ratio in a clinic setting?
apoB-100 indicates the number of VLDL, IDL, and LDL
while apoA-1 is the major apolipoprotein in HDL
What are the dietary lipids that have hypercholesterolemic (increasing cholesterol level) effects (High LDL-C:HDL-C ratio)?
What are the dietary lipids that have hypocholesterolemic (lowing cholesterol level) effects (Low LDL-C:HDL-C ratio)?
Polyunsaturated fatty acids
(1) Interference with platelet aggregation, in part by inhibiting thromboxane (TXA2) production. Inhibition is caused by FAs displacement of the TXA2 precursor, arachidonic acid.
(2) Reduction on release of proinflammatory cytokines from cells in fatty plaque formation.
(3) reduction in plasma TG concentration.
When the fatty acid enters the cell, it is activated by Coenzyme A to acyl-CoA, in an energy-requiring reaction catalyzed by fatty acyl-CoA synthetase.
The reaction consumes two high-energy phosphate bonds to yield AMP. This is equivalent to using 2 ATP’s.
What is the material that stimulates the release of secretin and CCK from small intestine?
What is the name of the precursor to pepsin?
What is an endopeptidase?
What is the precursor of trypsin?
How is trypsin activated?
Where is trypsin activated?
1. Na binds to the AA transporter.
2. Binding increases the carrier's affinity for AA
3. Na AA cotransporter forms.
4. Conformational change in complex and results in delivery of Na and AA to cytosol of enterocyte.
5. Na is pumped out by Na/K pump
1. competition between amino acids
2. induced de novo synthesis of specific AA carrier and decreased carrier synthesis
3. affinity of a carrier for an Amino acid is influenced by the hydrocarbon mass of the amino acid side chain
4. neutral amino acids tend to be absorbed at higher rates than basic or acidic
5. absorption of peptides is more rapid than absorption of an equivalent mixture of free AA
What happens to the peptide when it is transported into a cell?
What is the physiological significance that peptides can be administrated directly into blood?
What are the ways that enterocytes use the amino acids absorbed?
a. Structural proteins for new intestinal cells
c. Apoproteins necessary for lipoprotein formation
d. New digestive enzymes
f. Nitrogen-ccontaining compounds
What are the amino acids used by enterocytes?
Please describe the reaction catalyzed by carbamoyl phosphate synthetase II, including substrates, products and high energy bonds consumed.
In what sub-cellular location does CPSII reaction occur?
What is a transamination reaction?
transfer of amino group
Amino acid1 + a-keto acid2 = a-keto acid1 + amino acid2
What are the α-keto-acid (alpha carbon skeleton) of alanine?
What are the α-keto-acid (alpha carbon skeleton) of aspartate?
What are the α-keto-acid (alpha carbon skeleton) of glutamate?
What is deamination?
What is the substrate and products catalyzed by glutamate dehydrogenase?
Substrates: Ammonia and a-ketoglutarate
Products = Glutamate
+NH4 + a-ketoglutarate + NADPH = Glutamate + NADP+ + H2O