the percentage of red blood cells in a sample of human blood is normally about nearly half.
the percentage of red blood cells in a sample of human blood is normally about nearly half.
he percentage of red blood cells in a sample of human blood is normally about?
nearly half
in humans, mature red blood cells are flexible and oval biconcave disks. they lack a cell nucleus and most organelles, in order to accommodate maximum space for hemoglobin; they can be viewed as sacks of hemoglobin, with a plasma membrane as the sack. approximately 2.4 million new erythrocytes are produced per second in human adults. the cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages. each circulation takes about 60 seconds (one minute). approximately a quarter of the cells in the human body are red blood cells. nearly half of the blood's volume (40% to 45%) is red blood cells.
red blood cell
the mechanism by which topical progesterone in cream and water-based gel produces very high salivary and capillary blood levels in spite of low circulating levels is not well-understood. however, at least two hypotheses have been proposed. steroid hormones including progesterone have been found to be transported by red blood cells in addition to serum carrier proteins like albumin, sex hormone-binding globulin, and corticosteroid-binding globulin, and as much as 15 to 35% of total steroid hormone content in whole blood may be confined to red blood cells. according to the hypothesis, very high local concentrations of progesterone occur in skin capillaries after topical application and are taken up by red blood cells. the transit time of red blood cells from capillaries and the release of steroid hormones from red blood cells are both very rapid, so it is suggested that progesterone is delivered through circulation to tissues via red blood cells without having time to equilibrate with systemic blood. this could potentially explain the low levels of progesterone in venous blood in spite of very high levels in capillary blood and saliva. however, one study assessed progesterone levels in red blood cells with topical progesterone and found that they were significantly increased but still very low. nonetheless, according to other authors, "[a]lthough the investigators of that study concluded that the progesterone levels in red blood cells were too low to be important in the delivery of progesterone to target tissues, it should be realized that even small amounts of progesterone taken up by red blood cells might be important because the transit time of red blood cells from capillaries is very rapid. [...] however, the role of red blood cells in steroid hormone transport has not been studied thoroughly, and such studies are warranted."
pharmacokinetics of progesterone