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Blood


For other uses, see Blood (disambiguation).

Blood
Venous (darker) and arterial (brighter) blood
Identifiers
MeSHD001769
TA98A12.0.00.009
TA23892
FMA9670
Anatomical terminology

Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells.[1] Blood in the circulatory system is also known as peripheral blood, and the blood cells it carries, peripheral blood cells.[2]

Blood is composed of blood cells suspended in blood plasma. Plasma, which constitutes 55% of blood fluid, is mostly water (92% by volume),[3] and contains proteins, glucose, mineral ions, hormones, carbon dioxide (plasma being the main medium for excretory product transportation), and blood cells themselves. Albumin is the main protein in plasma, and it functions to regulate the colloidal osmotic pressure of blood.[citation needed] The blood cells are mainly red blood cells (also called RBCs or erythrocytes), white blood cells (also called WBCs or leukocytes), and in mammals platelets (also called thrombocytes).[4] The most abundant cells in vertebrate blood are red blood cells.[5] These contain hemoglobin, an iron-containing protein, which facilitates oxygen transport by reversibly binding to this respiratory gas thereby increasing its solubility in blood.[6] In contrast, carbon dioxide is mostly transported extracellularly as bicarbonate ion transported in plasma.

Vertebrate blood is bright red when its hemoglobin is oxygenated and dark red when it is deoxygenated.[7][8]

Some animals, such as crustaceans and mollusks, use hemocyanin to carry oxygen, instead of hemoglobin.[9] Insects and some mollusks use a fluid called hemolymph instead of blood, the difference being that hemolymph is not contained in a closed circulatory system. In most insects, this "blood" does not contain oxygen-carrying molecules such as hemoglobin because their bodies are small enough for their tracheal system to suffice for supplying oxygen.

Jawed vertebrates have an adaptive immune system, based largely on white blood cells. White blood cells help to resist infections and parasites. Platelets are important in the clotting of blood. Arthropods, using hemolymph, have hemocytes as part of their immune system.

Blood is circulated around the body through blood vessels by the pumping action of the heart. In animals with lungs, arterial blood carries oxygen from inhaled air to the tissues of the body, and venous blood carries carbon dioxide, a waste product of metabolism produced by cells, from the tissues to the lungs to be exhaled.

Medical terms related to blood often begin with hemo-, hemato-, haemo- or haemato- from the Greek word αἷμα (haima) for "blood". In terms of anatomy and histology, blood is considered a specialized form of connective tissue,[10] given its origin in the bones and the presence of potential molecular fibers in the form of fibrinogen.[citation needed]

  1. ^ "Definition of BLOOD". Merriam-Webster. Archived from the original on 23 March 2017. Retrieved 4 March 2017.
  2. ^ "def/peripheral-blood". www.cancer.gov. 2 February 2011. Archived from the original on 13 September 2022. Retrieved 13 September 2022.
  3. ^ The Franklin Institute Inc. "Blood – The Human Heart". Archived from the original on 5 March 2009. Retrieved 19 March 2009.
  4. ^ "Definition of red blood cell". National Cancer Institute. 2 February 2011. Archived from the original on 25 April 2022. Retrieved 28 April 2022.
  5. ^ Aryal, Sagar (3 January 2017). "Blood cells and its types with functions". Microbiology Info.com. Archived from the original on 12 April 2022. Retrieved 28 April 2022.
  6. ^ "Low Hemoglobin: Causes & Symptoms". Cleveland Clinic. Archived from the original on 28 April 2022. Retrieved 28 April 2022.
  7. ^ Séguin, Chantal (8 January 2022). "Did You Know That Not All Blood is Red? • The Blood Project". The Blood Project. Archived from the original on 2 July 2022. Retrieved 2 July 2022.
  8. ^ "Is blood blue? 7 facts about blood". www.medicalnewstoday.com. 10 April 2018. Archived from the original on 29 March 2023. Retrieved 29 March 2023.
  9. ^ Kato, Sanae; Matsui, Takashi; Gatsogiannis, Christos; Tanaka, Yoshikazu (April 2018). "Molluscan hemocyanin: structure, evolution, and physiology". Biophysical Reviews. 10 (2): 191–202. doi:10.1007/s12551-017-0349-4. ISSN 1867-2450. PMC 5899709. PMID 29235083.
  10. ^ Krause, William J. (2005). Krause's Essential Human Histology for Medical Students (3rd ed.). Universal-Publishers. p. 67. ISBN 978-1-58112-468-2. Archived from the original on 26 April 2023. Retrieved 21 June 2022.

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