What is the function of electrolytes?
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Run maintenance of water homeostasis, maintenance in acid-base balance and muscle functions as well as serves as cofactors for enzymes.
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What is the major cation of extracellular fluid?
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Sodium (Na+)
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What does Sodium determine in the extracellular fluid?
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The osmolality.
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When is sodium excreted in the urine?
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When serum sodium exceeds 110-130 mmol/L
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What happens when serum levels are below 110 mmol/L?
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All the sodium in the glomerular filtrate is virtually reabsorbed in the proximal and distal tubules, a process that is influenced by aldosterone.
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Sodium specimens consist of…?
And should be stored at…?
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Serum, plasma and urine specimens and may be stored at 4°C or may be frozen. Lipemic samples need to be ultracentrifuged.
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What are the methods of measuring sodium?
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Atomic Absorption Spectrophotometry (AAS),
Sodium Ion selective electrode (ISE), and Spectrophotometry.
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What is the major intercellular cation?
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Potassium (K+)
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How are high concentrations of potassium maintained?
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Na+K+ adenosine triphosphate (ATP) pump which is fueled by oxidative energy and continually transports K+ into the cell against a concentration gradient.
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Does potassium exhibit a renal threshold?
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No, however it is excreted into the urine even in K-depleted states.
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What are some of the functions of potassium?
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Regulation of neuromuscular excitability (both hypo- and hyperkalemia can cause muscle weakness) and contraction of the heat and cardiac rhythm (decrease K+ increases cardiac excitability and often leads to arrhythmia. High K+ slows the heart rate).
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How does potassium affect acid-base status?
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In hypokalemic states, sodium and H+ ions move into the cell to replace K+. The H+ concentration is therefore decreased in the ECF=alkalemia (reverse is true of hyperkalemia).
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What should the concentration of K+ be?
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In plasma and whole blood the concentration is 0.1-0.7 mmol/L lower than those in serum.
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How does the release of K+ affect values?
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As few as 0.5% K+ of RBCs will increase K+ values by 0.5 mmol/L. An increase of K+ of 0.6% has been estimated for every 10 mg/L of plasma hemoglobin (Hb) caused by hemolysis.
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What causes glycolysis to be inhibited and the energy-dependent Na+, K+-ATPase will not maintain the Na+/K+ gradient?
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When a whole blood specimen is maintained at 4°C versus 25°C before separation.
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What does a K+ leakage from erythrocytes and other cells cause?
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It causes an increase in plasma K+.
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What causes falsely decreased K+ value?
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When an un-separated sample is stored at 37°C because glycolysis occurs and K+ shifts intracellularly. Leukocytosis will initially cause falsely decreased K+ concentration at room temp.
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What are reliable determinations recommended for K+?
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Collect blood with heparin, maintain near 25°C and separate the plasma within minutes by high-speed centrifugation without cooling.
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What can falsely increase K+ concentration?
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Skeletal muscle activity as a result of repeated clenching of fist and application of the tourniquet.
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What are methods for the determination of sodium and potassium?
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Ion selective electrodes (ISE) and spectrophotometric methods.
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What is the major anion of the extracellular fluid?
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Chloride (CI-)
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What is the function of chloride?
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Maintains the water distribution, osmotic pressure, and anion-cation balance in the ECF.
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Where is chloride absorbed?
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In the intestinal tract and is excreted by kidneys.
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What specimens contain chloride?
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Serum, plasma, urine and sweat.
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How is chloride affected by hemolysis, change in posture or stasis, and tourniquet use?
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It is not affected.
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Methods for chloride determination?
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Coulometric-amperometric titration of chloride (cotlove chloridometer technique) and ion selective electrode methods.
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Measurement of sweat chloride (sweat testing)?
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Cystic fibrosis, the most common lethal genetic disorder of Caucasian population characterized by increased sweat chloride concentration.
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Sweat testing and newborn screening…
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Are performed in conjunction, with a positive screening test are referred to as a quantitative sweat chloride test.
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What phases are done for sweat testing?
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Sweat stimulation by pilocarpine electrophoresis, collection of sweat, qualitative or quantitative analysis of sweat, sodium or conductivity.
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What is an abnormal infant sweat testing result?
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≥60 mmol/L = indicative of CF
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Bicarbonate is another name for:
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Total carbon dioxide
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True or False: Plasma or serum can be used to measure bicarb?
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True
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True or False: Sample must be centrifuged in an open tube?
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False, be must be unopened
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True or False: Ambient air contains far more CO2 than plasma?
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False
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If CO2 is allowed to escape from the sample into air, ___to___ mmol/L will be lost per hour.
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4 - 5
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Two ways of measuring total CO2 are acidification and ____
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Alkalinization
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Acidification is a(n) ___ electrode based method?
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Indirect
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Define osmometry:
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a technique for measuring the concentration of solute particles that contribute to the osmotic pressure of a solution.
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Define osmotic pressure:
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the pressure required to stop osmosis through a semipermeable membrane between a solution and pure solvent.
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Define osmosis:
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process by which molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one.
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Name 4 colligative properties of solutions:
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1. Increased osmotic pressure
2. Lowered vapor pressure
3. Increased boiling point
4. Decreased freezing point
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Colligative properties of solutions are all directly related to:
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total number of solute particles per mass of solvent.
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The term osmolality expresses:
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concentrations relative to mass of the solvent.
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The term osmolarity expresses:
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concentrations per volume of solution.
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Plasma and urine osmolality is useful in the assessment of:
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Electrolyte and acid-base disorders
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The 4 major osmotic substances in normal plasma are:
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Na+ / Cl- / glucose / urea
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The Henderson-Hasselbalch equation defines pH as:
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The negative log of the H+ activity
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The Henderson-Hasselbalch equation is widely used to calculate the ___ point of proteins.
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isoelectric
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Total O2 content (cdO2) is:
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the sum of the concentrations of hemoglobin-bound O2 (oxyhemoglobin) and of dissolved O2 (cdO2).
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Oxyhemoglobin (O2Hb) is defined as:
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erythrocyte hemoglobin with O2 reversibly bound to Fe2+ of its heme group.
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Define the following terms:
pO2 =
pCO2 =
ctCO2 =
HCO3 =
cdCO2 =
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pO2=partial oxygen pressure.
pCO2=partial carbon dioxide pressure.
ctCO2=total concentration of carbon dioxide.
HCO3=bicarbonate.
cdCO2=concentration of dissolved carbon dioxide.
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What specimen is used for blood gas analysis?
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Whole blood.
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What is the only clinical reason for an arterial draw?
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PO2 value
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PO2 is generally 60 mm Hg ___ in venous blood.
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Lower
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PCO2 is 2-8 mm Hg ___ in venous blood.
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Higher
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Arterial and venous specimens for blood gas analysis are best collected:
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anaerobically with lyophilized heparin using glass syringes
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Lyophilized heparin is preferred to liquid heparin because:
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liquid heparin dilutes the sample, and the effect is greatest when the syringe is not completely filled
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3 effects of exposing blood gas samples to the air:
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Increase in pO2, increase in pH, decrease in pCO2
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The pCO2 in blood is much ___ than the pCO2 in the air.
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greater
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On exposure of blood to the air, the total CO2 and the pCO2 both ___
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decrease
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On exposure of blood to the air pO2 __
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increases
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In blood gas samples, clots are ___
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unacceptable
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In blood gas samples, air bubbles cause (increase or decrease) in total CO2, pCO2, pH, pO2.
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Decrease, decrease, increase, increase.
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What are the reasons for the following changes in pCO2, pH and pO2 in a sealed specimen left at room temperature for 2 hours:
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Increase in pCO2 as a result of continued metabolism, decrease in pH due to increased production of carbonic acid and lactic acid during glycolysis, decrease in pO2 because O2 is consumed during prolonged standing.
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Arterialized capillary blood is an acceptable alternative to arterial blood but it has to be:
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freely flowing cutaneous blood.
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The first drop is discarded and the subsequent free forming drops should be taken up in a:
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capillary collection tube containing lyophilized heparin
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Transport and analysis of specimen should be within ___ of collection.
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30
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Because electrodes are not stable over long periods of time, frequent calibration of ___, ___ and ___ is required:
Proper maintenance includes:
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pH, PCO2, and PO2
-meticulous care.
-adherence to the manufacturer's procedures.
-control of the equipment.
-proper collection and handling of specimens.
-the frequency with which maintenance should be maintenance = volume of analysis performed.
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Good quality assurance includes:
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-proper maintenance of the instrument.
-use of control materials.
-verification of electrode linearity.
-checking of barometer accuracy.
-accurate measurement of temperature.
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External quality assurance (proficiency testing) mandated by:
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CLIA'88
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A hormone is:
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a chemical substance produced in the body by an organ, cells of an organ, or scattered cells that has a specific regulatory effect on the activity of an organ or organs.
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Hormones are produced at one site in the body and exert their action(s):
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at distant sites through what is called the endocrine system.
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Paracine action is:
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action of certain hormones that exert their effect locally on nearby cells.
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Autocrine action is:
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action of certain hormones that exert their effects on the cells of origin.
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Adrenocorticotropic hormone (ACTH), insulin, parathyroid hormone (PTH) are examples of ___ or ___ hormones
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Polypeptide or Protein
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This class of hormone is soluble in:
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Water/blood
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This class of hormone has a half-life of ___ to ___.
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≤10 to 30 minutes
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This class of hormone initiates response by:
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Binding to cell membrane receptors and exciting the second messenger system.
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Cortisol and estrogen are 2 examples of _____ hormones.
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Steroid
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Steroid hormones are hydrophobic and water insoluble.
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True
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Steroid hormones circulate in plasma, reversibly bound to transport proteins with only a small fraction free or unbound and available to exert physiological action.
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True
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What is the half-life of steroid hormones?
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30-90 minutes
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How do steroid hormones enter the cell?
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Passive diffusion
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What are 2 examples of amino acid-related hormones?
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Thyroxine and catecholamines
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Amino acid-related hormones are water soluble.
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True
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Amino acid-related hormones interact with membrane associated receptors and use a second messenger system.
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True
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Amino acid-related hormones circulate in plasma bound to ______ or _______
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Proteins, free
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Estrogen and androgen are examples of ______ hormones.
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Gonadal
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What is the ability or tendency of an organism or cell to maintain internal equilibrium by adjusting its physiological processes?
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Homeostasis
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In response to a glucose load, _____ is released from the ______.
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Insulin, pancreas
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What is responsible for regulating the dispersal of glucose into cells for the metabolism necessary to produce energy?
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Insulin
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What are the counter regulatory hormones that regulate glucose concentration?
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Glucagon, cortisol, epinephrine, growth hotmone and incretins
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What are some examples of incretins?
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GLP-1 and GIP
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What is GLP-1?
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Glucagon-like peptide 1
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What is GIP?
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Gastic inhibitory pepide
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What is CaSR?
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Calcium-sensing receptor
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The CaSR on the parathyroid gland recognizes the circulating level of ionized calcium and regulates the synthesis and secretion of ____.
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PTH
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What is PTH?
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Parathyroid hormone
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PTH enhances renal tubular reabsorption of ?
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Calcium
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PTH catalyzes the synthesis of renal hormone _____ to increase intestinal absorption of calcium.
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Calcitrol
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The metabolism of water and electrolytes is regulated by _____, _______, and ______.
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Aldosterone, renin, vasopressin
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