7356927
Descripción
Fichas por Francisco Sacadura, actualizado hace más de 1 año
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Creado por Francisco Sacadura
hace casi 8 años
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| Pregunta | Respuesta |
| A patient with a body w of 65kg was injected with 10ml of a 1% (w/v) solution of Evans blue. After 10min, the blood was sampled and found to contain 0.037 mg/ml of the dye. (a) What is the plasma V? (b) If the hematocrit is 45%, what is the blood V? (c) Are these values within the normal range? | a. 2.70L b. 4.91L c. Yes |
| A patient was given an intravenous infusion of 10g 14C-labeled inulin and 10 ml of 3H2O. After 90min, the plasma c of inulin was 0.3mg/ml and of 3H2O was 0.18 μl/ml. Over the same period, 5.2g of inulin and 2.26ml of 3H2O were excreted in the urine. Calculate (a) the total body water, (b) the excell V, and (c) the incell V. (d) Assuming the patient is a normal adult male, what is his approx body w? | a. 43L b. 16L c. 27L d. 72kg |
| A miner with body w of 75kg loses 4L of sweat during the day. (a) If the sweat contained 50mmol/L of NaCl, what would be the osmolality of the body fluids after he finished work? (b) If he replaces the lost fluid by drinking pure water, what would be the osmolality of the tissue fluid? (The initial osmolality of the body fluids is 290 mOsm/kg of NaCl and initially total body water accounted for 60% of his body w) | a. 308mOsm/kg b. 281mOsm/kg |
| What % of body w does water account for? | ~60% (2/3) |
| How is the body water distributed between compartments? | Intracellular water (28L, 2/3) Plasma (2.8L, 7%) Intersticial water (11.2L or 10.4L*, 27%) Transcellular water (*0.8L, part of intersticial water in spaces like ventricles, peritoneal cavity, joints and eyes) |
| Which molecules can freely cross the cell membrane? | Lipid soluble molecules like O2, CO2, urea... |
| What does the rate of diffusion depend on? | • directly proportional to c gradient • directly proportional to A • increases with T • decreases with M of solute • directly proportional to diffusion coefficient (physical const that reflects molecular characteristics of both solute and solvent - decreases with M; also increases with T) |
| What is the osmotic pressure? What does it depend on? | Osmotic p (π) is an hydrostatic p sufficient to stop the flow of water (osmosis). Since π=MRT, π depends on c of solution (all particles) and NOT their chemical makeup. (physiological T is const so doesn't affect π) |
| Calculate the osmolarity of the following: a. 58.4g NaCl(Mr=58.4) in 1L water b. 8.77g NaCl in 1L water c. 18.03g urea(Mr=60.1) 1L water d. 1mg/ml of glucose(Mr=180.2) in water e. 45g of albumin(Mr=69000) in 1L water | a. 2 Osmolar (NaCl dissociates into 2 ions) b. 0.3 Osmolar c. 0.3 Osmolar d. 5.55 mOsmolar e. 0.67 mOsmolar |
| If 29.2g NaCl(Mr=58.4) were dissolved in 1L of water what would be the osmolarity? b) Calculate the osmolality of the same quantity of NaCl present in 1kg of NaCl solution (specific gravity of solid NaCl is approx 2.2) | a) 1 Osmolar b) 1.01 Osmolal (difference between Osmolar - Osmol/L of solution - and osmolal - Osmol/kg of solvent: osmolarity is slightly less than osmolality because total solvent weight excludes weight of solutes, whereas total solution V includes solute content) (at low c, <~500 mM, m of solute is negligible and osmolarity and osmolality are very similar) |
| If, in a sample of blood, there are approx 6.15g NaCl/L of plasma and solids make up 5.5% of plasma by w, what is the osmolality contributed by the NaCl(Mr=58.4)? | 6.15g NaCl in a L of plasma is equivalent to 6.15g in 945ml of water or 6.50g/kg of water. This is 223 mOsmolal. This accounts for ~2/3 of the N in plasma; the rest is mainly NaHCO3. |
| Why is it convenient to use osmolality as opposed to osmolarity? | Osmolarity is affected by changes in water content, as well as T and p. In contrast, osmolality is independent of T and p. |
| What is the osmotic pressure (in kPa) exerted by a solution of 9g NaCl in 1L of water at body T (310K)? (R=8.314Jmol-1K-1) | 793 kPa |
| What is the osmotic p of a solution of 50g albumin in 1L water at body T (310K)? | 1.87 kPa |
| If red cells were isolated from the blood and placed in solutions of the follwoing compositions, would they swell, shrink, or stay approx the same size? a) 0.9g NaCl/100ml (0.9% saline solution) b) 7.5g NaCl/L c) 10.5g NaCl/L d) 18g urea/L | a. osmolarity is 308 mOsM, approx isotonic with blood so cells neither swell nor shrink b. osmolarity is 256 mOsM, hypotonic to blood so cells swell and may burst (lyse) c. osmolarity is 360 mOsM, hypertonic to blood so the cells shrink d. osmolarity is 299 mOsM, approx iso-osmotic with blood, but solution is not isotonic and cells will swell and burst |
| What are the main contributors to the plasma osmolality? | Plasma has an osmolality of ~300mOsM. The principal ions (Na+, K+, Cl-, HCO3-) contribute most of this (~290 mOsM). Glucose and other small molecules contribute <10mOsM Proteins contribute only ~1mOsM (<0.5%) |
| What is the difference between iso-osmotic and isotonic? | Iso-osmotic: same osmolality (same π) Isotonic: const cell V (no water flow) Isotonic fluids are also iso-osmotic BUT not all iso-osmotic solutions are isotonic with cells (e.g. urea) |
| What determines direction of solute transport across membrane? | Electrochemical gradient: 1. c gradient 2. charge of molecule/ion 3. Vm |
| How does the diffusion rate changes as c gradient increases in facilitated diffusion? | Diffusion rate first increases with c gradient and then rise slows down until stabilizes (saturation due to limited carrier proteins) |
| How can you distinguish between ion channels and carrier proteins mediated transport? | Saturation (in carrier proteins) and diffusion rate (much higher for channels) |
| what are the 3 different types of carrier protein? | Uniport (1 ion/molecule transported) Symport (2 ions/molecules cotransported in same direction, e.g. glucose symport) Antiport (2 counter-transported in opposite directions, e.g. Na+/Ca2+ exchanger) |
| What is the difference between primary and secondary active transport? Give examples of both and their importance. | Primary: E from ATP (important to establish ion gradients, e.g. Na+ pump) Secondary: E from ion gradients (important to transport aa & glucose across epithelia, e.g. lining of intestine and kidney tubules) |
| Which transport mechanisms depend on Na+ gradient? | Secondary active transport: Co-transport (solutes move in same direction as Na+ across membrane) Counter-transport (solutes move in opposite direction as Na across membrane |
| What is the difference between constitutive and regulated exocytosis? | Constitutive: performed continuously by all cells to deliver new membrane proteins Regulated: triggered by chemical/electrical signal turned to rise in intracellular Ca2+ (e.g. hormone or NT release) |
| What are the 3 types of endocytosis and their differences? | Phagocytosis ("cell-eating"): absorption of solids, like bacteria, viruses, or cell debris (forming phagosomes) Pinocytosis ("cell-drinking"): how cells take in fluids/dissolved molecules (forming endosomes) Receptor-mediated transport: specific active event where membrane folds inward forming coated pits |
| Which important adaptation prevents the free flow of fluid to the lower regions of the body due to gravity? | The space between cells (interstitium) consists of connective tissue, chiefly collagen, and proteoglycan filaments together with an ultrafiltrate of plasma. The water of the interstitial fluid hydrates the proteoglycan filaments to form a gel which prevents free flow of fluid |
| How is the ultrafiltrate of interstitial fluid formed? Where is the filtration essential? | Capillaries' walls aren't normally permeable to plasma proteins but are to small solutes (ultrafiltration). The pumping action of the heart causes p gradient across capillaries forcing fluid into interstitial space (very important in glomerular capillaries of kidney) |
| How are extracellular signals translated into intracellular signals that regulate vesicle secretion in regulated excocytosis? | The universal trigger for regulated exocytosis is an increase in intracellular c of free Ca2+ . This occurs via 2 processes: 1. entry through membrane Ca2+ channels 2. Ca2+ release from incell stores (ER) |
| Gases such as oxygen and carbon dioxide cross the plasma membrane by: | Gases are very lipid soluble and readily pass through the lipid bilayer. They diffuse down their concentration gradient by passive transport. |
| Ions can cross the plasma membrane by: | Ions and other polar molecules cannot diffuse through the lipid bilayer but cross the membrane via channel proteins or are transported from one side of the membrane to the other by carrier proteins. |
| A substance can be accumulated against its electrochemical gradient by: | For any substance to be accumulated against its electrochemical gradient E must be expended. In active transport this is provided either by ATP hydrolysis (e.g.Na+ pump) or by coupling mov of 1 substance against electrochemical gradient to that of another down electrochemical gradient. This is secondary active transport (e.g. Na+-dependent glucose uptake in small intestine) |
| The principal intracellular cation is: | Na+ is the principal extracellular cation and K+ is the principal intracellular cation. Cl- is the principal extracellular anion. |
| The following are examples of active transport: a. Na+ pump b. Cl--HCO3- exchange c. Na+-Ca2+ exchange d. Na+-linked glucose uptake by enterocytes e. Na+-H+ exchange | Only b is F. The Na+ pump is an example of ATP driven active transport. Na+-Ca2+ exchange and Na+-H+ exchange are examples of secondary active transport. In these cases the E is provided by the Na+ gradient generated by the Na+ pump. |
| The Na+ pump: a. Exchanges intracellular Na+ for extracellular K+ b. Requires ATP c. Directly links Na+ efflux with K+ influx. d. Is an ion channel e. Can be inhibited by metabolic poisons. f. Is important in maintaining const cell V | All true except d. The sodium pump is a carrier protein not an ion channel. |
| Secretion: a. Always involves membrane vesicles b. May be triggered by rise in incell Ca2+ c. Provides means of inserting proteins into plasma membrane | b (regulated exocytosis) and c (constitutive exocytosis) are T. Lipid-soluble molecules like steroids and prostaglandins are secreted (they are synthesized and pass directly across lipid bilayer). Vesicle-mediated secretion is exocytosis. |
| 10. Endocytosis is used by cells to: a. Ingest bacteria and cell debris b. Retrieve elements of the plasma membrane after exocytosis c. Take up large molecules from the extracellular space | All T except a. Cells take up large proteins from the ECF by receptor mediated endocytosis. Bacteria and cell debris are taken up by phagocytosis. |
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