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[[Blood]] is a specialized bodily [[fluid]] that delivers [[necessary]] substances to the [[body]]'s [[cells]] (in animals) – such as nutrients and oxygen – and transports waste products away from those same cells.

[[Blood]] is a specialized bodily [[fluid]] that delivers [[necessary]] substances to the [[body]]'s [[cells]] (in animals) – such as nutrients and oxygen – and transports waste products away from those same cells.

In vertebrates, it is composed of [http://en.wikipedia.org/wiki/Blood_cells blood cells] suspended in a liquid called [http://en.wikipedia.org/wiki/Blood_plasma blood plasma]. Plasma, which constitutes 55% of blood fluid, is mostly [[water]] (92% by volume), and contains dissipated [[proteins]], glucose, mineral ions, [[hormones]], carbon dioxide (plasma being the main [[medium]] for excretory product transportation), [http://en.wikipedia.org/wiki/Platelets platelets] and blood cells themselves. The blood cells present in blood are mainly [http://en.wikipedia.org/wiki/Red_blood_cell red blood cells] (also called RBCs or erythrocytes) and [http://en.wikipedia.org/wiki/White_blood_cell white blood cells], including leukocytes and platelets. The most abundant cells in vertebrate blood are red blood cells. These contain [http://en.wikipedia.org/wiki/Hemoglobin hemoglobin], an iron-containing protein, which [[facilitates]] [[transportation]] of [[oxygen]] by reversibly binding to this [[respiratory]] gas and greatly increasing its solubility in blood. In [[contrast]], carbon dioxide is almost entirely transported extracellularly dissolved in plasma as [http://en.wikipedia.org/wiki/Bicarbonate bicarbonate ion].

In vertebrates, it is composed of [https://en.wikipedia.org/wiki/Blood_cells blood cells] suspended in a liquid called [https://en.wikipedia.org/wiki/Blood_plasma blood plasma]. Plasma, which constitutes 55% of blood fluid, is mostly [[water]] (92% by volume), and contains dissipated [[proteins]], glucose, mineral ions, [[hormones]], carbon dioxide (plasma being the main [[medium]] for excretory product transportation), [https://en.wikipedia.org/wiki/Platelets platelets] and blood cells themselves. The blood cells present in blood are mainly [https://en.wikipedia.org/wiki/Red_blood_cell red blood cells] (also called RBCs or erythrocytes) and [https://en.wikipedia.org/wiki/White_blood_cell white blood cells], including leukocytes and platelets. The most abundant cells in vertebrate blood are red blood cells. These contain [https://en.wikipedia.org/wiki/Hemoglobin hemoglobin], an iron-containing protein, which [[facilitates]] [[transportation]] of [[oxygen]] by reversibly binding to this [[respiratory]] gas and greatly increasing its solubility in blood. In [[contrast]], carbon dioxide is almost entirely transported extracellularly dissolved in plasma as [https://en.wikipedia.org/wiki/Bicarbonate bicarbonate ion].

Vertebrate blood is bright red when its hemoglobin is oxygenated. Some animals, such as [http://en.wikipedia.org/wiki/Crustacean crustaceans] and [http://en.wikipedia.org/wiki/Mollusk mollusks], use [http://en.wikipedia.org/wiki/Hemocyanin hemocyanin] to carry oxygen, instead of hemoglobin. [http://en.wikipedia.org/wiki/Insect Insects] and some molluscs use a fluid called hemolymph instead of blood, the difference being that [http://en.wikipedia.org/wiki/Hemolymph hemolymph] is not contained in a closed [http://en.wikipedia.org/wiki/Circulatory_system circulatory system]. In most insects, this "blood" does not contain [[oxygen]]-carrying [[molecules]] such as hemoglobin because their bodies are small enough for their[http://en.wikipedia.org/wiki/Invertebrate_trachea  tracheal system] to suffice for supplying oxygen.

Vertebrate blood is bright red when its hemoglobin is oxygenated. Some animals, such as [https://en.wikipedia.org/wiki/Crustacean crustaceans] and [https://en.wikipedia.org/wiki/Mollusk mollusks], use [https://en.wikipedia.org/wiki/Hemocyanin hemocyanin] to carry oxygen, instead of hemoglobin. [https://en.wikipedia.org/wiki/Insect Insects] and some molluscs use a fluid called hemolymph instead of blood, the difference being that [https://en.wikipedia.org/wiki/Hemolymph hemolymph] is not contained in a closed [https://en.wikipedia.org/wiki/Circulatory_system circulatory system]. In most insects, this "blood" does not contain [[oxygen]]-carrying [[molecules]] such as hemoglobin because their bodies are small enough for their[https://en.wikipedia.org/wiki/Invertebrate_trachea  tracheal system] to suffice for supplying oxygen.

[http://en.wikipedia.org/wiki/Gnathostomata Jawed vertebrates] have an [http://en.wikipedia.org/wiki/Adaptive_immune_system adaptive immune system], based largely on [http://en.wikipedia.org/wiki/White_blood_cell white blood cells]. White blood cells help to resist infections and parasites. Platelets are important in the [http://en.wikipedia.org/wiki/Coagulation clotting of blood]. [http://en.wikipedia.org/wiki/Arthropod Arthropods], using hemolymph, have [http://en.wikipedia.org/wiki/Hemocyte hemocytes] as part of their immune system.

[https://en.wikipedia.org/wiki/Gnathostomata Jawed vertebrates] have an [https://en.wikipedia.org/wiki/Adaptive_immune_system adaptive immune system], based largely on [https://en.wikipedia.org/wiki/White_blood_cell white blood cells]. White blood cells help to resist infections and parasites. Platelets are important in the [https://en.wikipedia.org/wiki/Coagulation clotting of blood]. [https://en.wikipedia.org/wiki/Arthropod Arthropods], using hemolymph, have [https://en.wikipedia.org/wiki/Hemocyte hemocytes] as part of their immune system.

Blood is circulated around the body through [http://en.wikipedia.org/wiki/Blood_vessel blood vessels] by the pumping action of the [[heart]]. In animals with [http://en.wikipedia.org/wiki/Lung lungs], [http://en.wikipedia.org/wiki/Artery arterial] blood carries oxygen from inhaled air to the tissues of the body, and [http://en.wikipedia.org/wiki/Vein venous] blood carries carbon dioxide, a waste product of [http://en.wikipedia.org/wiki/Metabolism metabolism] produced by [[cells]], from the tissues to the lungs to be exhaled.

Blood is circulated around the body through [https://en.wikipedia.org/wiki/Blood_vessel blood vessels] by the pumping action of the [[heart]]. In animals with [https://en.wikipedia.org/wiki/Lung lungs], [https://en.wikipedia.org/wiki/Artery arterial] blood carries oxygen from inhaled air to the tissues of the body, and [https://en.wikipedia.org/wiki/Vein venous] blood carries carbon dioxide, a waste product of [https://en.wikipedia.org/wiki/Metabolism metabolism] produced by [[cells]], from the tissues to the lungs to be exhaled.

Medical terms related to blood often begin with hemo- or hemato- (also spelled haemo- and haemato-) from the [http://en.wikipedia.org/wiki/Ancient_Greek Ancient Greek] word αἷμα (haima) for "blood". In terms of [http://en.wikipedia.org/wiki/Anatomy anatomy] and [http://en.wikipedia.org/wiki/Histology histology], blood is considered a specialized form of connective tissue, given its origin in the bones and the presence of potential molecular fibers in the form of [http://en.wikipedia.org/wiki/Fibrinogen fibrinogen].[http://en.wikipedia.org/wiki/]

Medical terms related to blood often begin with hemo- or hemato- (also spelled haemo- and haemato-) from the [https://en.wikipedia.org/wiki/Ancient_Greek Ancient Greek] word αἷμα (haima) for "blood". In terms of [https://en.wikipedia.org/wiki/Anatomy anatomy] and [https://en.wikipedia.org/wiki/Histology histology], blood is considered a specialized form of connective tissue, given its origin in the bones and the presence of potential molecular fibers in the form of [https://en.wikipedia.org/wiki/Fibrinogen fibrinogen].[https://en.wikipedia.org/wiki/]

[[Category: Biology]]

[[Category: Biology]]