•  Blood 

 

  Travel with the red blood cell as it transports oxygen and carbon dioxide through the heart, lungs and body tissues.

  In a circuit through the cardiovascular system, red blood cells carry oxygen from the lungs to the body's tissues and carry carbon dioxide from the body's tissues back to the lungs.

 

  Blood, the fluid that carries oxygen and nutrients to the cells and carries carbon dioxide and other waste products.  Technically, blood is a transport fluid that is pumped through the heart (or its equivalent structure) to all parts of the body, then returned to the heart to repeat this process.  Blood is both a tissue and a fluid.  It is a tissue because it is a collection of similar specialized cells that perform specific functions.  These cells are suspended in the liquid matrix (plasma), which makes the blood fluid.  If the blood flow stops, highly sensitive cells will die within minutes due to the effects of the unfavorable environment.

•    Blood

 

  Observe how a red blood cell travels from the heart to the lungs and other body tissues to exchange oxygen and carbon dioxide.

  In a circuit through the cardiovascular system, red blood cells carry oxygen from the lungs to body tissues and carry carbon dioxide from body tissues to the lungs.

 

  The consistency of the blood structure is made possible by the circulation, which carries the blood through the organs that regulate the concentration of its components.  In the lungs, the blood receives oxygen and releases carbon dioxide from the tissues.  The kidneys remove excess water and dissolved waste products.  Nutrients from food reach the bloodstream after being absorbed by the stomach.  The glands in the endocrine system secrete fluids into the bloodstream, which carry these hormones to the tissues where they work.  Many substances are recycled through the blood.  For example, iron released during the destruction of old red blood cells is transported by plasma to new red blood cell production sites where it is reused.  Each of the various components of the blood is kept within the appropriate concentration limits by an effective regulatory mechanism.  In many cases, feedback control systems are operative.  Thus, falling blood sugar (glucose) levels cause rapid blood glucose release so that potentially dangerous glucose depletion does not occur.

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  Unicellular organisms, ancient multicellular animals, and early life embryos have no circulatory system.  Due to their small size, these organisms can absorb oxygen and nutrients and expel the waste directly through the middle of their surroundings.  Sponges and coliforms (e.g., jellyfish and hydrangeas) also lack the blood system.  The source of food and oxygen to all the cells of these large multicellular animals is pumped through water, sea or fresh, spaces inside the organism.  In larger and more complex animals, blood circulation is needed to transport adequate amounts of oxygen and other substances.  In most of these animals, the blood passes through the respiratory tract, which is in the throat, lungs, or even the skin.  There the blood picks up oxygen and wastes carbon dioxide.

  In the animal kingdom, the cellular structure of blood varies from group to group.  Most invertebrates contain various large blood cells that are capable of moving amygdala.  Some of them help in the transportation of goods;  Other foreign particles or debris (phagocytosis) have the ability to surround and digest.  The blood of invertebrates, however, has relatively fewer cells than the blood of the phrase.  In vertebrates, there are many classes of amygdala cells (white blood cells, or leukocytes) and cells that help stop the blood (platelets, or thrombocytes).

  Oxygen requirements play an important role in determining both the structure of the blood and the structure of the circulatory system.  In some simple animals, including small insects and mollusks, the oxygen carried is simply dissolved in the plasma.  Larger and more complex animals, which require more oxygen, contain pigments that are capable of carrying relatively large amounts of oxygen.  Red hemoglobin, which contains iron, is found in all vertebrates and some invertebrates.  In almost all vertebrates, including humans, hemoglobin is present exclusively inside red cells (erythrocytes).  Red cells in the lower extremities (e.g., birds) have a nucleus, whereas red mammals lack a nucleus.  In mammals, red blood cells are significantly different.  Goats are much smaller than humans, but goats compensate for having too many red cells per unit amount of blood.  The concentration of hemoglobin in red blood cells varies slightly between species.  Hemocyanin, a copper-containing protein chemically unlike hemoglobin, is found in some crustaceans.  Hemocyanin is blue when released from oxygen and colorless when oxygen is removed.  In some annulus the green oil containing the iron is hemosethrin, in others the red oil containing the iron is hemotherm.  In many invertebrates respiratory pigments are transported to a solution in plasma, but in higher animals, including all vertebrates, the pigments are trapped in the cells.  If the oils were in the solution freely, the concentration of the required oils would make the blood so sticky that it would impede circulation.

    For information about the organ system that carries blood to all parts of the body, the cardiovascular system.  For additional information on blood in general and to compare blood and lymph from diverse organisms, see Circulation.

  Blood components

  In humans, blood is a vague red fluid that flows freely but is thicker and more viscous than water.  The characteristic color is given by hemoglobin, a unique protein containing iron.  When saturated with oxygen (oxygen hemoglobin), hemoglobin glows in color and turns black when oxygen is removed (deoxy hemoglobin).  Because of this, partially deoxygenated blood from a vein is darker than oxygenated blood from an artery.  Red blood cells (erythrocytes) make up about 45% of the blood volume, and the remaining cells (white blood cells, or leukocytes, and platelets, or thrombocytes) are less than 1%.  The liquid part, plasma, is a clear, slightly viscous, yellow liquid.  After a greasy meal, the plasma looks temporarily dirty.  The blood is constantly flowing inside the body, and the turbulent flow ensures that the cells and plasma are fairly evenly mixed.

  The total amount of blood in humans varies depending on age, sex, weight, body type, and other factors, but for adults the average body weight is 60 milliliters per kilogram.  The average young man has a plasma volume of about 35 milliliters and a red cell volume of about 30 milliliters per kilogram of body weight.  The blood volume of a healthy person varies slightly over a long period of time, although each component of the blood is in a state of constant flow.  In particular, water moves rapidly in and out of the bloodstream, balancing with extracellular fluids (which are outside the blood vessels) within minutes.  Normal blood volume provides adequate storage so that commendable anemia is well tolerated.  Withdrawing 500 ml (approximately one pint) of blood from ordinary blood donors is a harmless procedure.  Blood volume changes rapidly after anemia.  Within hours, the volume of plasma is restored by the movement of extravascular fluid in the bloodstream.  The red blood cell transplant is completed in several weeks.  The large area of ​​the capillary membrane through which water flows freely will allow immediate loss of plasma from blood circulation if these plasma proteins - in particular, are not for serum albumin.  Capillary membranes are invincible for serum albumin, the smallest in weight and the highest in plasma protein concentration.  The osmotic effect of serum albumin retains fluid within circulation, as opposed to the hydrostatic forces that tend to carry fluid outward into the tissues.