Table of contents
Blood of different speciesThere are differences in blood between species.
HumansHuman blood is a liquid tissue; its major function is to transport oxygen necessary to life throughout the body. It also supplies the tissues with nutrients, removes waste products, and contains various components of the immune system defending the body against infection. Endocrine hormones also travel in the blood. (see List of human blood components)
Blood moves in blood vessels and is circulated by the heart, a muscular pump. It passes to the lungs to be oxygenated, and then is circulated throughout the body by the arteries. It diffuses its oxygen by passing through tiny blood vessels called capillaries. It then returns to the heart through the veins. See circulatory system for a more detailed description of this circulation.
InsectsIn insects, the blood (more properly called hemolymph) is not involved in the transport of oxygen. (Openings called tracheae allow oxygen from the air to diffuse directly to the tissues). Insect blood moves nutrients to the tissues and removes waste products.
Small invertebratesIn some small invertebrates, oxygen is simply dissolved in the plasma. All other animals use respiratory proteins to increase the oxygen carrying capacity. Hemoglobin is the most efficient respiratory protein found in nature. Hemocyanin (blue) contains copper and is used in crustaceans. Sea squirts, among others marine life, use a vanadium chromagen (bright green, blue, or orange) for its respiratory pigment.
In many invertebrates, these oxygen-carrying proteins are freely soluble in the blood; in vertebrates they are contained in specialized red blood cells, allowing for a higher concentration of respiratory pigments without increasing viscosity.
Anatomy of bloodBlood is composed of several kinds of corpuscles; these formed elements of the blood constitute about 45% of whole blood. The other 55% is blood plasma, a yellowish fluid that is the blood's liquid medium.
The corpuscles are:
- Red blood cells or erythrocytes (about 99%). These corpuscles lack a nucleus and organelles, so are not cells strictly speaking. They contain the blood's hemoglobin and distribute oxygen. The red blood cells also give rise to the system of blood types.
- Platelets or thrombocytes (0.6 - 1.0%) are responsible for blood clotting or coagulation.
- White blood cells or leukocytes (0.2%), are part of the immune system; they destroy infectious agents.
- blood clotting factors
- immunoglobulins (antibodies)
- various other proteins
- various salts
The normal pH of arterial blood is approximately 7.40.
Health and diseaseBlood is different in health and disease.
Wounds can cause major blood loss. The thrombocytes cause the blood to coagulate, blocking relatively minor wounds, but larger ones must be repaired at speed to prevent exsanguination. Damage to the internal organs can cause severe internal bleeding, or hemorrhage.
Hemophilia is a genetic illness that causes dysfunction in one of the blood's clotting mechanismss. This can allow otherwise inconsequential wounds to be life-threatening, but more commonly results in hemarthrosis, or bleeding into joint spaces, which can be crippling.
Major blood loss, whether traumatic or not (e.g. during surgery), as well as certain blood diseases like anemia and thalassemia, can require blood transfusion. Several countries have blood banks to fill the demand for transfusable blood. A person receiving a blood transfusion must have a blood type compatible with that of the donor.
Blood is an important vector of infection. One well-known example of a blood-borne illness is AIDS, whose virus, HIV, is transmitted through contact between blood, semen, or the bodily secretions of an infected person. Owing to blood-borne infections, bloodstained objects are treated as a biohazard.
Blood pressure is an important diagnostic tool.
Blood in mythology and religionDue to its importance to life, blood is associated with a number of beliefs. One of the most basic is the use of blood as a symbol for family relationships; to be "related by blood" is to be related by ancestry or descendance, rather than marriage.
JudaismIn Judaism, blood cannot be consumed in the smallest quantity (Leviticus 3:17 and elsewhere); this is reflected in the dietary laws. Blood is purged from meat by salting (food) and pickling.
Other rituals involving blood are the covering of the blood of fowl and game after slaughtering (Leviticus 17:13); the reason given by the Torah is: "Because the soul of every animal is [in] his blood" (ibid 17:14), although from its context in Leviticus 3:17 it would appear that blood cannot be consumed because it is to be used in the sacrificial service in the Temple in Jerusalem.
ChristianityChristians believe that the Eucharist wine either is or represents the blood of Jesus Christ shed for their salvation.
Vampire legendsVampires are fictional beings thought to cheat death by drinking the blood of the living.
Blood in ancient medicineIn the Greek theory of the four bodily humours, which dominated medicine until the 19th century, blood was associated with fire and with a merry and gluttonous (sanguine) personality. An excess was removed by blood letting or leeching.
Physiology of bloodBlood has diverse physiological roles.
Transport of oxygen in bloodThe amount of oxygen dissolved in blood is directly proportional to the PO2 of the blood.
Transport of carbon dioxide in bloodWhen systemic arterial blood flows through capillaries, carbon dioxide diffuses from the tissues into the blood. Some carbon dioxide is dissolved in the blood. Some carbon dioxide reacts with hemoglobin to form carbamino hemoglobin. The remaining carbon dioxide is converted to bicarbonate and hydrogen ions.
Transport of hydrogen ions in bloodSome oxyhemoglobin loses oxygen and becomes deoxyhemoglobin. Deoxyhemoglobin has a much greater affinity for H+ than does oxyhemoglobin so it binds most of the hydrogen ions.
- blood cells
- blood plasma
- Blood Types
- Landsteiner & blood groups
- Blood diseases
- decreased numbers of cells
- increased numbers of cells
- cancers of blood and immune cells
- Hodgkin's disease
- Burkitts lymphoma
- Blood-borne diseases
- blood transfusion
- Blood pressure
- Blood gas monitor
- Artificial blood
- List of human blood components