Lecture 32 - Carbohydrate Digestion & Absorption Flashcards
Enteroendocrine cells are derived from crypt cells and migrate up
The crypt-villus axis
Digestion:
Process of breaking dietary compounds into simple molecules that can be absorbed
Absorption:
Simple molecules generated from digestion are transferred into blood or lymph
From lumen to capillary blood, nutrient molecules need to cross
Apical membrane: between lumen and intracellular space and extracellular fluid
Basolateral membrane: between intracellular space and extracellular fluid
Cell membranes are composed of
A bilateral membrane of phospholipids: a hydrophilic head extending into the aqueous fluid on the outside and inside of the cell and hydrophobic tails between hydrophilic surfaces
Interspersed among the phospholipids are various types of proteins:
Transporters, pumps, and channels are important for material to cross the lipid bilayer
Lipid-soluble hydrophobic compounds can easily cross the
Lipid bilayer of cell membranes
Water hydrophilic materials cannot easily cross the
Lipid bilayer on their own
Particles will also move from one compartment of high concentration to another compartment of low concentration, if
The barrier between the two compartments is permeable to the substance
The chemical driving force is proportional to
The concentration gradient
If there is more than one molecule crossing a cell membrane, does each kind have its own concentration gradient or chemical gradient
Yes
In electrical driving force, same charges _______ & opposite charges _______
Repel, attract
In the resting cell, cations are attracted to the __________ of the cell and anions are attracted to the ___________ of the cell
Interior, exterior
The magnitude of the electrical force depends upon the
Size of the membrane potential and the charge of the ion
The greater the membrane potential or the charge of the ion the greater the
Electrical driving force
The more lipid soluble a substance is the greater the _____
Permeability to that substance in phospholipid bilayers
When going through a phospholipid bilayer, the membrane permeability is lesser if
The molecule is larger and more irregular in shape
Can fatty acids and triglycerides freely cross the lipid bilayer down their concentration gradient?
Yes, even though they are very large and can be charged, they are very lipid soluble
What is passive transport?
Molecules moving down their electro/chemical gradient to the other side of the membrane. No energy used
All epithelial cells lining the GI tract have an
Apical and basolateral membrane
Adjacent epithelial cells in the GI tract are linked to another on all sides by
Tight junctions
Tight junctions form a seal between cells that is relatively impermeable to
bacteria, viruses, and large molecules that have been ingested
The tight junctions also provide resistance to the passage of
Small ions and water, but can be overcome if electrochemical forces are great enough
Paracellular transport is
Movement of solute across the tight junctions between enterocytes
Accumulation of negatively-charged chloride anions creates an electric potential that attracts
Sodium, pulling it across tight junctions into the lumen. The net result is secretion of NaCl
Secretion of NaCl creates an osmotic gradient across the tight junction and
Water is drawn into the lumen
What is transcellular absorption?
Most of the nutrients of the body are too large to cross the tight junctions and must be moved across the absorptive enterocytes. Think endocytosis or exocytosis
The mechanism used to transport a solute across the apical membrane is often different from that used to transport the same solute across the….
Basolateral membrane
Exocytosis
Vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell
Endocytosis
Engulfing substance from outside the cell with the cell membrane, and bringing it into the cell
LOOK AT SLIDE 33 TO GET DIAGRAM ABOUT TRANSCELLULAR / PARACELLULAR PROCESSES. Did u do it ???????
yes <3 i am gonna slay this midterm
Paracellular transport is ________ driven and only functions when _______________
Concentration, when solute concentration in the lumen is very different than the concentration in the extracellular fluid
The most important enzymatic reaction in digestion is
Hydrolysis - the breaking of a chemical bond by the addition of a water molecule
The diet of any animal contains hundreds of if not thousands of of different molecules but the bulk of the ingested nutrients are in the form of huge macromolecules that cannot be absorbed into the blood without first being reduced to
Much simpler and smaller forms of the molecule
Monosaccharides
Either 6 carbon sugars like glucose and galactose or 5 carbon like fructose
_________ are the breakdown products of more complex carbohydrates and can be efficiently absorbed across the wall of the digestive tube and transported into the blood
Monosaccharides
Disaccharides
Two monosaccharides linked together
Most important disaccharides in nutrition and digestion are
Lactose and sucrose
Oligosaccharides
Relatively short chains of monosaccharides
What are intermediates in the breakdown of polysaccharides to monosaccharides
Oligosaccharides
What are the most abundant dietary carbohydrates for all animals except very young ones?
Polysaccharides
Name 3 large polymers of glucose
Starch, cellulose, glycogen
Starch
A major plant storage form of glucose. Glucose molecules are linked by alpha (1-4) glycosidic bonds
Cellulose
The other major plant carbohydrate. It’s the major constituent of plant cell walls
Cellulose - glucose molecules are linked by
Beta (1-4) glycosidic bonds.
Can vertebrates enzymatically digest beta (1-4) glycosidic bonds
No
Glycogen
Major animal storage form of carbohydrate. It is multi-branched
Glycogen - what links glucose molecules
Alpha (1,4) glycosidic bonds.
Where does fructose come from
Fructose is a naturally occurring sugar found primarily in fruits (such as apples, dates, figs, pears, and prunes)
Vegetables (such as sugar beets, sugar cane, artichokes, asparagus, mushrooms, onions, and red peppers
Honey
What begins the digestion of starch and glycogen and reduces them to disaccharides or oligosaccharides
Salivary and pancreatic amylase
Do stomach acids and proteolytic enzymes have any effects on starches
Nope
If u have 1M of glucose monomers and 1M of maltose (a disaccharide), do they have the same osmolarity?
Yes, as it depends on osmolarity
What is the brush border
The microvillus border of intestinal epithelial cells
What are brush border enzymes
Enzymes present on the apical membrane of absorptive cells lining the small intestines, complete digestion to monosaccharides
Transporter proteins located near brush border enzymes facilitate
Absorption of monomers
Example of development changes according to food intake
Lactase, which digests milk lactose, is found on the enterocyte brush border of all mammalian neonates. It often disappears after the animal is weaned.
OR
Sucrase, which digests sucrose, is often lacking in neonates and is expressed only after the animal is several weeks old
Carbohydrate intolerance is the
Inability to digest certain carbohydrates due to a lack of one or more intestinal enzymes
CHO intolerance - undigested disaccharides cause an osmotic load that attracts water and electrolytes into the bowel, causing
Water diarrhea. Bacterial fermentation of CHO in the colon produces gases (hydrogen, CO2, and methane), resulting in excessive flatulence, bloating and distension, and abdominal pain
Treatment of CHO intolerance
Removal of the causative disaccharides from the diet
Lactose intolerance (shoutout steph) is a digestive disorder caused by the
The inability to digest lactose, the main CHO in dairy products
Lactose intolerance can cause
Various symptoms, including bloating, diarrhea, and stomach cramps
People with lactose intolerance (steph its ur moment to shine) dont make enough of
The enzyme lactase
Does lactose intolerance happen in dogs
Yes & it can cause diarrhea, vomiting, lack of appetite, bloating, flatulence
Absorption of monosaccharides entails transport from
The intestinal lumen, across the epithelium and into the blood
Monosaccharides liberated by the brush border enzymes are too large to cross the
Apical membrane easily
Monosaccharides concentration over the apical membrane rises following a meal so there is a concentration gradient that can help them cross into
The cytoplasm, which the help of transporters (both active and passive)
Once inside cytosol, the sugars exit the cells across the basolateral membrane by
Facilitated diffusion
Why doesn’t the intestine digest all dietary starch and disaccharides to monosaccharides in the lumen?
The reason digestion is completed at the brush border is to prevent the osmolarity of the lumen contents from rising too high and drawing excessive amounts of water into the lumen. By liberating monomers in the brush border they can be absorbed almost as soon as they are liberated, preventing a rise in the osmolarity of the lumen contents
Excess glucose gets stored in the
Liver and skeletal muscles as glycogen or, with the help of insulin, converted into fatty acids, circulated to other parts of the body and stored as fat in adipose tissue.
Glucose can be converted to fatty acids and cholesterol through
De novo lipid biosynthesis pathways
Diabetes is more common in __________ but can also occur in younger or pregnant pets
Older pets
Diabetes is more manageable if
It’s detected early and managed with the help of a veterinarian
Can diabetic pets have long and happy lives
Yes! With proper monitoring, treatment, diet, and exercise
