Vertebrates There is an immense size variation in vertebrate<unk> s, as well as a correlation between<unk>  and nucleus size. Mammalian<unk> s, which do not contain nuclei, are considerably smaller than those of most other vertebrates. Pygoscelis papua enucleated<unk> s (B) have been observed, but with very low frequency.222x222px The vast majority of vertebrates, including mammals and humans, have<unk> s.<unk> s are<unk> s present in blood to transport oxygen. The only known vertebrates without<unk> s are the crocodile icefish (family Channichthyidae); they live in very oxygen-rich cold water and transport oxygen freely dissolved in their blood. While they no longer use hemoglobin, remnants of hemoglobin genes can be found in their genome. Vertebrate<unk> s consist mainly of hemoglobin, a complex metalloprotein containing heme groups whose iron atoms temporarily bind to oxygen molecules (O2) in the lungs or gills and release them throughout the body. Oxygen can easily diffuse through the<unk> 's<unk>  membrane. Hemoglobin in the<unk> s also carries some of the waste product carbon dioxide back from the tissues; most waste carbon dioxide, however, is transported back to the pulmonary capillaries of the lungs as bicarbonate (HCO3−) dissolved in the blood plasma. Myoglobin, a compound related to hemoglobin, acts to store oxygen in muscle<unk> s. The color of<unk> s is due to the heme group of hemoglobin. The blood plasma alone is straw-colored, but the<unk> s change color depending on the state of the hemoglobin: when combined with oxygen the resulting oxyhemoglobin is scarlet, and when oxygen has been released the resulting deoxyhemoglobin is of a dark<unk>  burgundy color. However, blood can appear bluish when seen through the vessel wall and skin. Pulse oximetry takes advantage of the hemoglobin color change to directly measure the arterial blood oxygen saturation using colorimetric techniques. Hemoglobin also has a very high affinity for carbon monoxide, forming carboxyhemoglobin which is a very bright<unk>  in color. Flushed, confused patients with a saturation reading of 100% on pulse oximetry are sometimes found to be suffering from carbon monoxide poisoning. Having oxygen-carrying proteins inside specialized<unk> s (as opposed to oxygen carriers being dissolved in body fluid) was an important step in the evolution of vertebrates as it allows for less viscous blood, higher concentrations of oxygen, and better diffusion of oxygen from the blood to the tissues. The size of<unk> s varies widely among vertebrate species;<unk>  width is on average about 25% larger than capillary diameter, and it has been hypothesized that this improves the oxygen transfer from<unk> s to tissues. Mammals Typical mammalian<unk> s: (a) seen from surface; (b) in profile, forming rouleaux; (c) rendered spherical by water; (d) rendered crenate (shrunken and spiky) by salt. (c) and (d) do not normally occur in the body. The last two shapes are due to water being transported into, and out of, the<unk> s, by osmosis. The<unk> s of mammals are typically shaped as biconcave disks: flattened and depressed in the center, with a dumbbell-shaped cross section, and a torus-shaped rim on the edge of the disk. This shape allows for a high surface-area-to-volume (SA/V) ratio to facilitate diffusion of gases. However, there are some exceptions concerning shape in the artiodactyl order (even-toed ungulates including cattle, deer, and their relatives), which displays a wide variety of bizarre<unk>  morphologies: small and highly ovaloid<unk> s in llamas and camels (family Camelidae), tiny spherical<unk> s in mouse deer (family Tragulidae), and<unk> s which assume fusiform, lanceolate, crescentic, and irregularly polygonal and other angular forms in<unk>  deer and wapiti (family Cervidae). Members of this order have clearly evolved a mode of<unk>  development substantially different from the mammalian norm. Overall, mammalian<unk> s are remarkably flexible and deformable so as to squeeze through tiny capillaries, as well as to maximize their apposing surface by assuming a cigar shape, where they efficiently release their oxygen load.<unk> s in mammals are unique amongst vertebrates as they do not have nuclei when mature. They do have nuclei during early phases of erythropoiesis, but extrude them during development as they mature; this provides more space for hemoglobin. The<unk> s without nuclei, called reticulocytes, subsequently lose all other<unk> ular organelles such as their mitochondria, Golgi apparatus and endoplasmic reticulum. The spleen acts as a reservoir of<unk> s, but this effect is somewhat limited in humans. In some other mammals such as dogs and horses, the spleen sequesters large numbers of<unk> s, which are dumped into the blood during times of exertion stress, yielding a higher oxygen transport capacity. thrombocyte (platelet), leukocyte. Human Two drops of blood are shown with a bright<unk>  oxygenated drop on the left and a deoxygenated drop on the right. Animation of a typical human<unk>  cycle in the circulatory system. This animation occurs at a faster rate (~20 seconds of the average 60-second cycle) and shows the<unk>  deforming as it enters capillaries, as well as the bars changing color as the<unk>  alternates in states of oxygenation along the circulatory system. A typical human<unk>  has a disk diameter of approximately 6.2–8.2 µm and a thickness at the thickest point of 2–2.5 µm and a minimum thickness in the centre of 0.8–1 µm, being much smaller than most other human<unk> s. These<unk> s have an average volume of about 90 fL with a surface area of about 136 μm2, and can swell up to a sphere shape containing 150 fL, without membrane distension. Adult humans have roughly 20–30 trillion<unk> s at any given time, constituting approximately 70% of all<unk> s by number. Women have about 4–5 million<unk> s per microliter (cubic millimeter) of blood and men about 5–6 million; people living at high altitudes with low oxygen tension will have more.<unk> s are thus much more common than the other blood particles: there are about 4,000–11,000 white blood<unk> s and about 150,000–400,000 platelets per microliter. Human<unk> s take on average 60 seconds to complete one cycle of circulation. The blood's<unk>  color is due to the spectral properties of the hemic iron ions in hemoglobin. Each hemoglobin molecule carries four heme groups; hemoglobin constitutes about a third of the total<unk>  volume. Hemoglobin is responsible for the transport of more than 98% of the oxygen in the body (the remaining oxygen is carried dissolved in the blood plasma). The<unk> s of an average adult human male store collectively about 2.5 grams of iron, representing about 65% of the total iron contained in the body.
Red blood cell
Agranulocyte
Blood cell
Monocyte
White blood cell
Thymocyte
Podocyte
Lymphoblast