PSIO 303 Exam 2
What are the 5 physiological functions of a membrane?
1. Barrier 2. Localization & Organization 3. Transport 4. Detection of Signals 5. Cell-to-Cell Communication
How does a membrane function as a barrier?
1. Barrier - The lipid bilayer prevents free-diffusive movement of hydrophilic (water-soluble) compounds between the compartments that are separated from one another by the membrane.
What does the stomach do?
1. Continue mechanical disruption 2. Begin protein digestion (via secretion of ~2 liters/day of gastric juice rich in acid and pepsinogen/pepsin)
What does the large intestine do?
1. Final absorption of salt and water (about 0.4 - 0.5 liters/day) 2. Modest role in regulation of K+ homeostasis 3. Compacting and storage of stool before expulsion
What do the salivary (& lingual: tongue) glands do?
1. Initiate digestion of carbohydrates (alpha-amylase) and fats (lingual lipase) 2. Lubrication: via mucus (protein) and serous (watery) secretions
What are the hollow organs of the GI system?
1. Mouth 2. Esophagus 3. Stomach 4. Small Intestine 5. Large Intestine
What are the two pathways available for flow of material?
1. Paracellular - between adjacent cells; Flow through the paracellular pathway requires movement across/through the tight junction - a structure that attaches adjacent cells to one another 2. Transcellular - across individual cells; involves sequential flux (flow) across basolateral and apical membranes. The movement of most molecules of biological interest involves the transcellular pathway, and therefore 'transporters,' simply because the paracellular pathway is unavailable.
What are the acessory organs of the GI system?
1. Salivary Glands 2. Liver (gall bladder) 3. Pancreas
What does the pancreas do?
1. Secretion of pancreatic juice (~1.5 liters/day, rich in HCO3- and enzymes)
Region 1 of an exocrine gland represents what?
Acinus Principle site of secretion
Why is swear produced at all in CF
CF patients produce normal volumes of salty sweat because the acing cells use ca 2+ activated Cl channel (from CLCA channel family) rather than CFTR to form the primary, isosmotic secreted salt solution
downregulation
ENaC & CFTR interact with one another when expressed together in airway cells, the presence of CFTR results in _______ of ENaC activity CFTR keeps ENaC's ability to mediate apical influx of Na+ in check that works well within the integrated set of solute fluxes that maintains the thin layer of water above the surface of airway cells (airway surface liquid)
distinguishes an 'exocrine' gland from an 'endocrine' gland?
Exocrine glands release materials directly to the external environment (outside the body), whereas endocrine glands release materials into the blood stream.
Integral membrane proteins are distinguished from peripheral membrane proteins in that:
Integral MPs have an amphiphilic/amphipathic structure, whereas peripheral MPs generally don't
What is the general mechanism for zygomen granule release?
It is energetically unfavorable for vesicle membrane and plasma membrane to get close to one another because both tend to have a net negative surface charge (and like charges repel!). The SNAREs (under the regulatory influence of Rabs, and augmented by synaptotagmins) couple vesicles to the cytoplasmic face of the plasma membrane and draw the vesicles close to the membrane, thereby increasing the rate of fusion of vesicle membrane with plasma membrane. Without functional SNAREs the efficiency of vesicle fusion is greatly decreased. And increased vesicle fusion results in increased secretion!
How are membranes involved in cell function?
Membranes play a central role in establishing cell function Membranes serve as scaffolds for localizing membrane proteins. These proteins are the molecular machines that carry out much of the "work" of different organelles and, through the concerted activity of these subcellular units, the work of different types of cells.
How do membranes play a role in cell structure?
Membranes play a central role in establishing cell structure In addition to establishing the structural limits of a cell (via the plasma membrane), membranes "define" the dimensions of the class of organelles that can be referred to as "membranous" (e.g., mitochondria, endoplasmic reticulum, lysosomes).
What are the most important secretagogues and why?
Of these, CCK and ACh are the most important for stimulation of zymogen secretion. They work by binding to the G protein-coupled CCK receptor or to the muscurinic ACh receptor, thereby activating protein kinase C (PKC) and producing an associated rise in intracellular Ca2+ VIP and Secretin can also stimulate (modest) zymogen secretion through activation of protein kinase A (PKA) via interaction with distinct G protein-coupled receptors.
What makes water a polar molecule?
The oxygen-hydrogen bonds in H2O are polar covalent bonds; electrons are shared unequally between the oxygen atom and the two hydrogen atoms, spending 'more time' associated with the oxygen nucleus than with the hydrogen nuclei. Thus, despite the fact that a water molecule is electrically neutral (i.e., has no net electrical charge), there is a 'partial' negative charge around the oxygen atom, and partial positive charges around the two hydrogen atoms (with the sum of the partial charges = 0). The six electrons in oxygen's outer orbital shell results in near-tetrahedral bond angles with the two hydrogen atoms; in other words, the two hydrogen atoms are angled off to one side of the oxygen atom. Taken all together, the result is a molecule with a slightly negative side and a slightly positive side: a molecular dipole. These two oppositely charged ends (or 'poles') are why water is considered to be a 'polar' molecule
What happens in the duct of an exocrine gland?
The duct of an exocrine gland is a site for 'modification' of the primary secretory product of the acinar cells.
How do aquaporins play a role in Isosmotic Salt & Water Secretion by Acinar Cells?
The increase in solute (i.e., Na+ ions and Cl- ions) in the acinar lumen increases the osmotic concentration of this fluid, which supports an osmotically-driven flux of water across the epithelial cells (via "aquaporin" water channels).
How do aquaporins play a role in Isosmotic Salt & bicarbonate secretion of ductal cells?
The net flux of NaHCO3 (i.e., Na+ plus HCO3-) results in an osmotically-obligated flux of water into the ductal lumen. This flow of fluid then serves to hydraulically "push" the secreted zymogens out into the small intestine.
How does Na,K- ATPase play a role in Isosmotic Salt & bicarbonate secretion of ductal cells?
The process is ultimately driven by activity of the Na,K-ATPase (in the basolateral membrane), which maintains (i) an inwardly-directed Na+ gradient; and (ii) an outwardly-directed K+ gradient. As in all cells, the outwardly-directed K+ gradient results in an inside-negative membrane potential.
How does Na,K- ATPase play a role in Isosmotic Salt & Water Secretion by Acinar Cells?
Ultimately driven by activity of the Na,K- ATPase (located in the basolateral membrane), which maintains (i) an inwardly- directed Na+ gradient; and (ii) an outwardly- directed K+ gradient. Importantly, the outwardly-directed K+ gradient results in an inside-negative membrane potential.
Dysfunctional CFTR in airway epithelial cells results in ______________________ (an increase, a decrease, no change) in the thickness of the airway surface film that reflects ______________________ (an increase, a decrease, no change) in the net absorption of Na+ and Cl-.
a decrease; an increase
Which of the following secretagogues can stimulate zymogen release (more than one may be correct)
acetylcholine (ACh) secretin cholecystokinin (CCK) vasoactive intestinal peptide (VIP)
Respiratory problems arise because
airways become plugged with thick secretions resulting in chronic bacterial infections that are often associated with the presence of a mucoid form of the bacterium, Pseudomonas aeruginosa (among others). The chronic loss of lung function due to continual infections is the factor that leads to death in over 95% of CF patients.
Men with CF
almost always sterile (about 98% of the time)
failure of ENaC
also produces salty sweat
Digestion of nucleic acids involves nucleases; digestion of carbohydrates involves _____________ ; digestion of lipids involves ____________ , and digestion of proteins involves _____________ .
amylases : lipases : proteases
duct cells do not express aquaporins in the ______ membrane but do in the _____ membrane.
apical membrane basolateral membrane
Synaptotagmin proteins:
are activated when bound to Ca2+ and then stimulate exocytosis (through the fusion of vesicles with the plasma membrane).
CFTR
autosomal recessive gene (not a sex-linked trait) Being recessive, individuals with cystic fibrosis must have two abnormal copies of CFTR gene, that is, they must be homozygous with respect to the presence of abnormal CFTR.
Chronic pulmonary disease poses a serious threat for the CF patient
beginning at an early age (several years), CF patients develop chronic lung infections that lead to scarring of the lung and irreversible reduction of access to airway surface CF generally affects the bronchial epithelium (upper airway)
According to the fluid mosaic model of membrane structure, integral membrane proteins:
can diffuse laterally in the plane of the membrane
women with CF
can generally become pregnant, but frequently have difficulty carrying the child to term
Physiologically, the most important secretagogue(s) for stimulation of pancreatic zymogens is(are) (more than one answer may be correct):
cholecystokinin (CCK) acetylcholine (ACh)
innate immunity
chronic bacterial colonization of the airways trigger this
The principal cause of the "morbidity and mortality" associated with cystic fibrosis reflects:
chronic pulmonary disease due to bacterial infections
The hydrophobic effect (more than one answer may be correct):
contributes to the stability of membrane structure drives the self-association of non-polar molecules when placed in water
The ability of water molecules to 'solvate' hydrophilic solute particles and thereby hold them in solution is, in large part, due to
dipole moment of water
In a duct of a sweat gland from a CF patient, the apical membrane is ___.
effectivley impermeant to Cl-, owing to the dysfunctional CFTR chloride channel the failure to reabsorb Cl- leads to a failure to reabsorb Na+ result: swear with a high Cl- [ ] & high Na+ [ ]
The duct cells of sweat glands have to restrict water reabsorption (so that the reabsorption of salt does not wind up eliminating the production of sweat!). They do this by simply restricting the expression of aquaporin water channels. Which of the following 'restriction' strategies makes most physiological sense?
express no aquaporin water channels in the apical membrane, but do express them in the basolateral membrane
Dysfunctional CFTR (in CF)
fails to keep ENaC activity in check with the result being a large increase in ENaC activity increases apical Na+ entry (via hyperactive ENaC) is matched by an increase in basolateral Na+ efflux (via the Na, K-ATPase) result: large increase in Na+ flux across the epithelium, which makes the blood side electrically positive relative to airway side
treatment strategies for chronic inflammation and subsequent destruction of the upper airways
gene therapy inhibition of ENaC Pharmacological "repair" of mutant CFTR
Clinical presentation of CF
high Cl- concentration ( > 60 met/l) in sweat chronic pulmonary disease
Carbohydrate and lipid digestion starts in the mouth in the stomach in the intestine in the pancreas in the colon
in the mouth
The abnormal flux of Cl- across airway epithelial in cystic fibrosis reflects
increased net apical-to-basolateral paracellular Cl- flux
In a sweat gland, acinar cells secrete a fluid that is _____________________ (hypoosmotic, isoosmotic) with respect to blood. The duct cells of the sweat gland then normally _____________________ (secrete, reabsorb) Na+ and Cl-, thereby making the sweat that is ultimately excreted onto the surface of the body __________________ (hypoosmotic, hyperosmotic) with respect to the blood.
isoosmotic; reabsorb; hypoosmotic
In a patient with cystic fibrosis the CFTR channels in the apical membrane of duct cells in sweat glands is dysfunctional: it fails to pass Cl-. However, the apical ENaC Na+ channels are fully operable (and generally open). Normally, the membrane potential of sweat duct cells is inside negative (surprise, surprise), about -30 mV. If you could measure the membrane potential of a sweat gland duct cell from a patient with CF, you would expect it to be:
less negative than -30 mV
dds of a couple both being carriers of a bad copy of CFTR
0.035 x 0.035 = 0.00123, or 1 in ~815
What is the difference between the endocrine and exocrine pancreas?
1. "Endocrine" pancreas - Endocrine glands secrete their products, hormones, directly into the blood. The 0.5 to 2 million Islets of Langerhans are the source of insulin (from -cells) and glucagon (from beta- cells), which are secreted directly into the blood (that's why they represent "endocrine" function). 2. "Exocrine" pancreas - Exocrine glands secrete their products (including digestive enzymes, and some hormone chemical messengers) into ducts that lead to the external environment. The exocrine pancreas is a collection of "lobules" (the secretory unit of the pancreas); each lobule is a collection of "ducts" each of which begins at an "acinus." The watery secretion (rich in bicarbonate and enzymes) is delivered to "outside" of the body (i.e., into the lumen of ducts that communicate directly with the lumen of the intestine - which is "topologically" outside of your body!); that is why this is considered an "exocrine" function
What does the tight junction do?
1. Serves as a barrier to reduce free diffusive movement of molecules via the paracellular pathway. Molecules larger than about 4 Å (glucose is a bit larger than 4 Å) have a tough time getting through the 'pores' within the tight junction 2. Provides a barrier to prevent the intermixing of molecules (e.g., proteins) between the apical vs. basolateral membranes. Tight junction proteins form the 'chicken wire' that separates the lateral (i.e., basolateral) and microvilli (i.e., apical) domains of the plasma membrane. The tight junction forms a physical barrier (a fence, if you will) that prevents the movement of proteins between the two membrane domains 3. Generally is in located near the apical "pole" (side) of epithelial cells. 4. The claudin family of proteins (with 20+ members) plays a critical role in establishing the 'permselective' character of tight junctions and, therefore, of the paracellular pathway
What does the small intestine do?
1.Absorbs and secretes salt and water; the NET result is absorption of 9-10 liters/day! 2. Finish digestion of proteins, carbohydrates & lipids a. pancreatic enzymes b. hepatic bile c. luminal disaccharidases and peptidases for final digestion
Describe how a membrane helps with organization.
2. Localization & Organization - Many macromolecules (typically proteins) are "kept in place" by being inserted into, or attached onto, membranes. By providing a way to organize many separate proteins into functional units, the efficiency of metabolism or signaling pathways can be markedly increased.
How does a membrane participate in transport? lect 1
3. Transport - It's not enough to simply separate two compartments from one another (e.g., inside vs. outside of a cell). Maintenance of living systems requires the regulated exchange of materials between compartments, i.e., transport of materials across the membrane.
How does a membrane detect signals?
4. Detection of Signals - The plasma membrane is the interface between a cell and the surrounding environment (the "rest of the universe"). When the surrounding environment changes, the cell frequently has to "respond" to that change (to maintain homeostasis). Typically, a change in the surrounding environment is detected by a change in the chemical composition of the extracellular solution, e.g., an increase or decrease in the concentration of a molecule released by other cells. Some of the (many) proteins in the plasma membrane are "receptors" that interact (bind) with these chemicals; when bound to these "signaling molecules," the membrane receptor takes on a (slightly) different shape, and this is detected by one or more other proteins that result in changes in cell processes that (generally) modify cell activity in a way that facilitates maintenance of homeostasis.
How does a membrane participate in cell to cell communication?
5. Cell-to-Cell Communication - Direct interactions of proteins in the membranes of neighboring cells (including "adhesion" proteins and selected classes of "channel" proteins) play a critical role in coordinating the activity of cells in tissues.
What is secreted by the exocrine pancreas?
A. 1.2 - 1.5 liters/day of isotonic pancreatic juice Water, salts, (incl. sodium bicarbonate: NaHCO3 B. 15-100 grams of protein (20 distinct enzymes) Zymogens inactive zymogens: trypsinogen (when activated is trypsin), chymotrypsinogen (when activated is chymotrypsin), procarboxypeptidase (when activated is carboxypeptidase) proelastase (when activated is elastase) active enzymes pancreatic alpha-amylase pancreatic lipase ribonuclease/deoxyribonuclease
How is bicarbonate secreted by ductal cells?
Basically, ductal cells exchange luminal Cl- for blood HCO3-. That requires pathways to move HCO3- across the basolateral membrane, and an apical Cl/HCO3 exchanger. What makes this process so effective in producing a large volume of HCO3-—rich fluid is the clever way the system "recycles" Cl-, i.e., using the modest amount of Cl- secreted by acinar cells over and over again, with each cycle resulting in the movement of more HCO3-
How does Na-HCO3 cotransporter play a role in Isosmotic Salt & bicarbonate secretion of ductal cells?
Basolateral HCO3- entry involves a Na-HCO3 cotransporter (using the energy in the inward directed Na+ gradient to support "uphill" bicarbonate transport).
Diagnosis for CF
Cl- [ ] in sweat of 60 mM or more
How does apical Cl- channel play a role in Isosmotic Salt & Water Secretion by Acinar Cells?
Cl- moves from acinar cells into the lumen of the acinus through an apical Cl- channel (which opens in response to activation of PKC via CCK or ACh). Cl- is "pushed" out of the cell, through the channel, because of the inside-negative membrane potential ('like charges repel...').
The principal 'barrier epithelia,' i.e., cell layers that line organs that have large surfaces exposed (albeit in a rather controlled fashion) to the exterior of the body, include:
GI tract, Kidney (Renal) nephron, Liver
How does Cl-/HCO3- exchanger play a role in Isosmotic Salt & bicarbonate secretion of ductal cells?
HCO3- is secreted into the ductal lumen via a Cl-/HCO3- exchanger. The Cl- that enters the cell via the Cl-/HCO3- exchanger then exits the cell, back into the lumen of the duct via one of two distinct Cl- channels. The "Cystic Fibrosis Transmembrane-conductance Regulator (CFTR) is quantitatively the more significant one (the other is the 'outwardly rectifying Cl- channel,' ORCC) The result of this shuttling of Cl- into and then back out of the cell permits the Cl ions to be used over and over again, with each cycle in resulting in the secretion of HCO3-. The electrogenic, channel-mediated efflux of Cl- keeps the inside of the ductal lumen electrically negative (with respect to the blood), and that supports the paracellular diffusive movement of Na+ into the lumen to serve as a "counter ion" for the continued movement of the anionic HCO3-
How many genes are in a human and what portion of them is used to code for membranes and transport proteins?
Human: ~20,000 genes (100,000+ transcripts) 'proteome' w/ >1,000,000 members... Of these genes, ~30% (~6,000) code for 'membrane' proteins Of these, ~1/2 are suspected to code for 'transporters' (carriers & channels) 3,000!
Liddle's Syndrome
Hyper activity of ENaC associated with abnormally high retention of Na+ and severe hypertension bc if you retain more osmolytes in the blood, you'll retain more water; increasing plasma volume & increasing pressure
What are secretagogues?
Zymogens are released from the acinar cells into the lumen of the acinus in response to stimulation by several endocrine signal molecules: "secretagogues." Cholecystokinin (CCK), Acetylcholine (ACh), Vasoactive Intestinal Peptide (VIP), Secretin
How is salt and water secreted by acinar cells
Na,K- ATPase Na,K,2Cl cotransporter apical Cl- channel paracellular pathway aquaporins
So, what is it about CFTR that gives it so much physiological "influence"
Quantitative impact on flux of Cl- (the major anion in extracellular fluid) That gives CFTR an impact on many processes that involve + absorption or secretion of Na (the major cation in extracellular fluid) That gives CFTR direct influence on the absorption/secretion of water in many (but not all) tissues And CFTR regulates many additional processes (e.g., ENaC)
What is the purpose of bicarbonate in digestion?
The bicarbonate (HCO3-) neutralizes the acid in gastric (stomach) juice, which facilitates that action of pancreatic enzymes
What are SNARE proteins?
SNARE proteins - SNARE is an acronym derived from "SNAP (Soluble NSF Attachment Protein) REceptor." SNAP proteins play a critical role in releasing the SNARE complex after the fusion event. But let's focus on SNAREs. There are 'v-SNAREs' (vesicle-SNAREs) and 't-SNAREs' (target-SNAREs). There are more than 60 SNARE proteins expressed in different cells types, assisting in getting the right vesicles to fuse in the right place.
What does the liver do?
Secretion of bile ( emulsifies fat; stored in gallbladder, releasing ~0.5 liters/day into duodenum)
What is the primary observation used to secure a clinical diagnosis of CF?
Sweat [Cl-] in excess of 60 milliequivalents/liter
What are synaptotagmins?
Synaptotagmins are integral membrane proteins in vesicle membranes. They bind Ca2+ and play a key role in stimulating the fusion event in exocytosis. There are some 15 synaptotagmins
How does Na,K,2Cl cotransporter play a role in Isosmotic Salt & Water Secretion by Acinar Cells?
The Na+ gradient drives the "uphill" accumulation of Cl- from the blood into acinar cells via a Na,K,2Cl cotransporter (located in the basolateral membrane). This transport is "electrically neutral" because it involves parallel movement of 2 cations (1 Na+ and 1 K+) and 2 anions (2 Cl-), which facilitates the entry of anionic Cl- into the electrically negative "inside of the cell."
What are the two sides of the plasma membrane?
The basolateral side of an epithelium always (really) sits on an extracellular matrix secreted by the epithelial cells (called the basal lamina) that faces the 'blood side' of the cell layer and is directly exposed to the 'interstitial fluid;' the apical side, in most cases, is exposed to the 'outside' of the body (e.g., the lumen of the intestine is, topologically speaking, outside of the body...). Interesting exceptions (interesting to 'epitheliologists') include tissues like the 'choroid plexus' in which the apical side is exposed to the cerebrospinal fluid, which is an 'internal compartment.' The two membrane 'domains' (i.e., apical and basolateral) are distinct, not only 'anatomically' but also in their biochemical and physiological characteristics
How does the paracellular pathway play a role in Isosmotic Salt & Water Secretion by Acinar Cells?
The transepithelial movement of Na+, interestingly, relies on the paracellular pathway. The movement of Cl- into the lumen of the acinus makes the luminal side of the acinar epithelium electrically negative with respect to the basolateral (blood) side. This provides an electrical force which supports net paracellular diffusive movement of positively charged Na+ through a "cation-selective" tight junction pathway. The result of these several distinct transport processes is, then, the net transepithelial transport of Na+ and Cl- ("salt").
What is a RAB protien?
These are small G-proteins (i.e., they bind and hydrolyze GTP) that serve as 'molecular switches' that help assemble the SNARE fusion complex. There are about 70 different Rabs, which aids in targeting specificity
What is a zymogen and how are they activated?
Zymogens are a type of 'proenzyme,' i.e., an inactive form of an enzyme. The pancreas secretes several digestive enzymes as zymogens principally to prevent the enzymes from digesting proteins in the cells in which they are synthesized Enteropeptidase (also called enterokinase), an enzyme in the brush border of small intestine, cleaves a peptide from trypsinogen, thereby forming the active digestive enzyme, trypsin. Trypsin then activates the other pancreatic zymogens Additional strategy to reduce 'early' (intracellular) activation of trypsin: • zymogen granules include protein that is a specific inhibitor of trypsin
The duct of an exocrine gland is a site for
modification of the primary secretion
CFTR is the 'cystic fibrosis transmembrane conductance regulator.' That turns out to be a more accurate name than its discoverers may have guessed because, in addition to its well-characterized function as a chloride channel, CFTR also exerts a regulatory influence on a number of other cellular processes. Which one of the following is known to be an example of this 'regulatory function of CFTR:
normal CFTR downregulates ENac activity in airway cells
Airway surface volume (ASF)
normally, there is a balance between ENaC-mediated Na influx and CFTR-mediated Cl efflux resulting in finely regulated ___.
gastrointestinal problems are typically due to
pancreatic insufficiency
The acinar cell epithelium
secretes Na+ and Cl- secretes water secretes zymogens relies on the paracellular pathway for the net transepithelial flux of Na+
typical clinical presentation of CF include the simultaneous presentation of
some form of malnourishment chronic pulmonary disease and a high concentration of NaCl in sweat
The organ responsible for generation of the digestive enzyme pepsinogen/pepsin is salivary gland stomach liver pancreas small intestine
stomach
hyper absorption of salt
substantial increase in trans epithelial Na+ flux is matched by a large paracellular Cl- flux increases the osmotic absorption of water net result: reduction in the thickness of the airway surface liquid and a concomitant drying out of the airway that traps mucus and provides a great place for bacteria to colonize and infections to catch hold
The basolateral side of the epithelial cell layer that comprises (for example) the renal proximal tubule is exposed to:
the blood
What does a claudin do?
the claudin complex within the tight junction forms aqueous pores of about 4 Å in diameter (schematically shown as the light blue protein strands in the figure to the left). The sequence of amino acids within the portion of claudin proteins that forms these pores includes some charged amino acids, e.g., the anionic amino acids, glutamate and/or aspartate; and the cationic amino acids lysine and/or arginine (the 'colored beads' in the claudin pores in the figure). The precise combination and location of these amino acids is different in different claudin isoforms. But here's a key observation: claudins that form pores that contain a surplus of cationic residues in the postulated pore forming region (e.g., Claudin 10) have been found to favor the paracellular movement of anions (e.g., Cl-), whereas the homologous region of claudins that favor the paracellular flux of cations (e.g., Na+) contain a surplus of anionic residues (e.g., Claudin 2).
The physiological activation of zymogens typically requires
the conversion of trypsinogen to trypsin by enteropeptidase
Cystic fibrosis (CF)
the most common fatal inherited disease in America carried as an autosomal recessive gene by approximately 3.5% of the white population in the United States, so the disease occurs in about one live birth in 3,300
what is typically used in clinical sweat tests?
the muscarinic agonist, pilocarpine
Phospholipids are considered to be amphiphilic because
their structure includes both hydrophobic, hydrocarbon (alkyl) chains and a hydrophilic phosphate residue bonded to a polar 'head group.'
The paracellular pathway for transepithelial transport is not freely available to all molecules. This is primarily due to the influence of:
tight junction proteins that connect adjacent epithelial cells
Which of following generally occurs at rates so low that ATP-requiring enzymes are involved in supporting that associated movement?
translational diffusion
Failure of CFTR in airway
up regulation of ENaC increased NaCl reabsorption reduction of ASF stagnant mucus (permissive of bacterial colonization)
The ionic 'permselectivity' of tight junctions (TJs) is primarily influenced by
which claudin(s) are associated with the TJ complex
how many American children are born with cystic fibrosis?
~ 1 in 4,000
What does the pancreas secrete each day on average?
• about 1.5 L of pancreatic fluid per day • containing between 15-100 g of protein • consisting of more than 20 distinct proteins required for digestion of: carbohydrates (via amylases), proteins (via proteases), lipids (via lipases), nucleic acids (via nucleases)