Because of the presence of tight junctions, passage of materials across an epithelial barrier must take place between the cells, not through them
Indicate whether the statement is true or false
F
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In the autorhythmic cells, the ________ channels open when the cell membrane potential is -60 mV. These channels are permeable to ________ and ________.
Fill in the blank(s) with the appropriate word(s).
Some athletes, in order to gain an advantage over their competitors, participate in blood doping. This process increases the number of red blood cells in their cardiovascular systems and in turn delivers more oxygen to their metabolically active tissues. Which statement best describes how athletes' blood dope and the dangers associated with blood doping?
A) Athletes receive blood transfusions to increase the number of red blood cells and by doing so increase their chances of developing aids or hepatitis C. B) Hemoglobin is injected, increasing the oxygen carrying capacity of red blood cells. However, too much hemoglobin can cause hemolysis. C) Colony-stimulating factors are injected to increase the number of red blood cells. Too many, however, can clog arteries, causing a heart attack. D) Leukocytes are injected because they are larger than red blood cells. However, they make the body more susceptible to infection. E) Erythropoietin is injected stimulating more red blood cell production. An increase in red blood cells increases the hematocrit which can increase blood pressure and weaken vessels making the chances of stroke increase.
Binding of hydrophilic hormones to their receptors often results in the formation of one or more second messengers that lead to alterations of the cell's activity.
Answer the following statement true (T) or false (F)
Gas exchange at the respiratory membrane is efficient because
A. the difference in partial pressures is substantial. B. the distances involved in exchange are small. C. the total surface area of the membrane is large. D. blood flow and air flow are coordinated (blood flow is highest around alveoli with highest Po2). E. All of these are correct.