Red blood cell
Red blood cells known as RBCs, red cells, red blood corpuscles, erythroid cells or erythrocytes, are the most common type of blood cell and the vertebrate's principal means of delivering oxygen to the body tissues—via blood flow through the circulatory system. RBCs take up oxygen in the lungs, or gills of fish, release it into tissues while squeezing through the body's capillaries; the cytoplasm of erythrocytes is rich in hemoglobin, an iron-containing biomolecule that can bind oxygen and is responsible for the red color of the cells and the blood. The cell membrane is composed of proteins and lipids, this structure provides properties essential for physiological cell function such as deformability and stability while traversing the circulatory system and the capillary network. In humans, mature red blood cells are oval biconcave disks, they lack most organelles, in order to accommodate maximum space for hemoglobin. 2.4 million new erythrocytes are produced per second in human adults. The cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages.
Each circulation takes about 60 seconds. A quarter of the cells in the human body are red blood cells. Nearly half of the blood's volume is red blood cells. Packed red blood cells are red blood cells that have been donated and stored in a blood bank for blood transfusion. All vertebrates, including all mammals and humans, have red blood cells. Red blood cells are cells present in blood; the only known vertebrates without red blood cells are the crocodile icefish. While they no longer use hemoglobin, remnants of hemoglobin genes can be found in their genome. Vertebrate red blood cells consist of hemoglobin, a complex metalloprotein containing heme groups whose iron atoms temporarily bind to oxygen molecules in the lungs or gills and release them throughout the body. Oxygen can diffuse through the red blood cell's cell membrane. Hemoglobin in the red blood cells carries some of the waste product carbon dioxide back from the tissues. Myoglobin, a compound related to hemoglobin, acts to store oxygen in muscle cells.
The color of red blood cells is due to the heme group of hemoglobin. The blood plasma alone is straw-colored, but the red blood cells change color depending on the state of the hemoglobin: when combined with oxygen the resulting oxyhemoglobin is scarlet, when oxygen has been released the resulting deoxyhemoglobin is of a dark red burgundy color. However, blood can appear bluish when seen through skin. Pulse oximetry takes advantage of the hemoglobin color change to directly measure the arterial blood oxygen saturation using colorimetric techniques. Hemoglobin has a high affinity for carbon monoxide, forming carboxyhemoglobin, a bright red 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 cells was an important step in the evolution of vertebrates as it allows for less viscous blood, higher concentrations of oxygen, better diffusion of oxygen from the blood to the tissues.
The size of red blood cells varies among vertebrate species. The red blood cells of mammals are shaped as biconcave disks: flattened and depressed in the center, with a dumbbell-shaped cross section, a torus-shaped rim on the edge of the disk; this shape allows for a high surface-area-to-volume ratio to facilitate diffusion of gases. However, there are some exceptions concerning shape in the artiodactyl order, which displays a wide variety of bizarre red blood cell morphologies: small and ovaloid cells in llamas and camels, tiny spherical cells in mouse deer, cells which assume fusiform, lanceolate and irregularly polygonal and other angular forms in red deer and wapiti. Members of this order have evolved a mode of red blood cell development different from the mammalian norm. Overall, mammalian red blood cells 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.
Red blood cells in mammals are unique amongst vertebrates. Red blood cells of mammals cells have nuclei during early phases of erythropoiesis, but extrude them during development as they mature; the red blood cells without nuclei, called reticulocytes, subsequently lose all other cellular organelles such as their mitochondria, Golgi apparatus and endoplasmic reticulum. The spleen acts as a reservoir of red blood cells. In some other mammals such as dogs and horses, the spl
Hemorheology spelled haemorheology, or blood rheology, is the study of flow properties of blood and its elements of plasma and cells. Proper tissue perfusion can occur only when blood's rheological properties are within certain levels. Alterations of these properties play significant roles in disease processes. Blood viscosity is determined by plasma viscosity and mechanical properties of red blood cells. Red blood cells have unique mechanical behavior, which can be discussed under the terms erythrocyte deformability and erythrocyte aggregation; because of that, blood behaves as a non-Newtonian fluid. As such, the viscosity of blood varies with shear rate. Blood becomes less viscous at high shear rates like those experienced with increased flow such as during exercise or in peak-systole. Therefore, blood is a shear-thinning fluid. Contrarily, blood viscosity increases when shear rate goes down with increased vessel diameters or with low flow, such as downstream from an obstruction or in diastole.
Blood viscosity increases with increases in red cell aggregability. Blood viscosity is a measure of the resistance of blood to flow, it can be described as the thickness and stickiness of blood. This biophysical property makes it a critical determinant of friction against the vessel walls, the rate of venous return, the work required for the heart to pump blood, how much oxygen is transported to tissues and organs; these functions of the cardiovascular system are directly related to vascular resistance, preload and perfusion, respectively. The primary determinants of blood viscosity are hematocrit, red blood cell deformability, red blood cell aggregation, plasma viscosity. Plasma's viscosity is determined by water-content and macromolecular components, so these factors that affect blood viscosity are the plasma protein concentration and types of proteins in the plasma. Hematocrit has the strongest impact on whole blood viscosity. One unit increase in hematocrit can cause up to a 4% increase in blood viscosity.
This relationship becomes sensitive as hematocrit increases. When the hematocrit rises to 60 or 70%, which it does in polycythemia, the blood viscosity can become as great as 10 times that of water, its flow through blood vessels is retarded because of increased resistance to flow; this will lead to decreased oxygen delivery. Other factors influencing blood viscosity include temperature, where an increase in temperature results in a decrease in viscosity; this is important in hypothermia, where an increase in blood viscosity will cause problems with blood circulation. Many conventional cardiovascular risk factors have been independently linked to whole blood viscosity. Anemia can reduce blood viscosity. Furthermore, elevation of plasma viscosity correlates to the progression of coronary and peripheral artery diseases. In pascal-seconds, the viscosity of blood at 37 °C is 3 × 10−3 to 4 × 10−3 3 - 4 centipoise in the centimetre gram second system of units. Μ = ⋅ 10 − 3 P a ⋅ s ν = μ ρ = ⋅ 10 − 3 1.06 ⋅ 10 3 = ⋅ 10 − 6 m 2 s Blood viscosity can be measured by viscometers capable of measurements at various shear rates, such as a rotational viscometer.
Viscoelasticity is a property of human blood, due to the elastic energy, stored in the deformation of red blood cells as the heart pumps the blood through the body. The energy transferred to the blood by the heart is stored in the elastic structure, another part is dissipated by viscosity, the remaining energy is stored in the kinetic motion of the blood; when the pulsation of the heart is taken into account, an elastic regime becomes evident. It has been shown that the previous concept of blood as a purely viscous fluid was inadequate since blood is not an ordinary fluid. Blood can more be described as a fluidized suspension of elastic cells; the red blood cells possess elastic properties. This elastic property is the largest contributing factor to the viscoelastic behavior of blood; the large volume percentage of red blood cells at a normal hematocrit level leaves little room for cell motion and deformation without interacting with a neighboring cell. Calculations have shown that the maximum volume percentage of red blood cells without deformation is 58%, in the range of occurring levels.
Due to the limited space between red blood cells, it is obvious that in order for blood to flow, significant cell to cell interaction will play a key role. This interaction and tendency for cells to aggregate is a major contributor to the viscoelastic behavior of blood. Red blood cell deformation and aggregation is coupled with flow induced changes in the arrangement and orientation as a third major factor in its vi
Phlebotomy is the process of making an incision in a vein with a needle. The procedure itself is known as a venipuncture. A person who performs phlebotomy is called a "phlebotomist", although doctors, medical laboratory scientists and others do portions of phlebotomy procedures in many countries. Phlebotomists are people trained to draw blood from a patient for clinical or medical testing, donations, or research. Phlebotomists collect blood by performing venipunctures. Blood may be collected from infants by means of a heel stick; the duties of a phlebotomist may include properly identifying the patient, interpreting the tests requested on the requisition, drawing blood into the correct tubes with the proper additives explaining the procedure to the patients, preparing patients accordingly, practising the required forms of asepsis, practising standard and universal precautions, performing the skin/vein puncture, withdrawing blood into containers or tubes, restoring hemostasis of the puncture site, instructing patients on post-puncture care, ordering tests per the doctor's requisition, affixing tubes with electronically printed labels, delivering specimens to a laboratory.
Some countries, states, or districts require that phlebotomy personnel be registered. In Australia, there are a number of courses in phlebotomy offered by educational institutions, but training is provided on the job; the minimum primary qualification for phlebotomists in Australia is a Certificate III in Pathology Collection from an approved educational institution. In the UK there is no requirement for holding a formal qualification or certification prior to becoming a phlebotomist as training is provided on the job; the NHS offers training with formal certification upon completion. Special state certification in the United States is required only in four states: California, Washington and Louisiana. A phlebotomist can become nationally certified through many different organizations. However, California only accepts national certificates from six agencies; these include: American Certification Agency, American Medical Technologists, American Society for Clinical Pathology, National Center for Competency Testing/Multi-skilled Medical Certification Institute, National Credentialing Agency, National Healthcareer Association, National Phlebotomy Certification Examination.
These and other agencies certify phlebotomists outside the state of California. To qualify to sit for an examination, candidates must complete a full phlebotomy course and provide documentation of clinical or laboratory experience. Early "phlebotomists" used techniques such as leeches and incision to extract blood from the body. Bloodletting was used as a therapeutic as well as a prophylactic process, thought to remove toxins from the body and to balance the humours. While physicians did perform bloodletting, it was a specialty of barber surgeons, the primary provider of health care to most people in the medieval and early modern eras. Cytotechnologist Injection Medical technologist Venipuncture List of surgeries by type
Rouleaux are stacks or aggregations of red blood cells which form because of the unique discoid shape of the cells in vertebrates. The flat surface of the discoid RBCs gives them a large surface area to make contact with and stick to each other, they occur when the plasma protein concentration is high, because of them the ESR is increased. This is a non-specific indicator of the presence of disease. Conversely the presence of Rouleaux is a cause of disease because it will restrict the flow of blood throughout the body because capillaries can only accept free flowing singular and independent red blood cells; the aggregations known as "clumping" form as an allergic reaction to certain antibiotics and not because of disease. Conditions which cause rouleaux formation include infections, multiple myeloma, Waldenstrom's macroglobulinemia and connective tissue disorders, cancers, it occurs in diabetes mellitus and is one of the causative factors for microvascular occlusion in diabetic retinopathy. Acute-phase proteins fibrinogen, interact with sialic acid on the surface of RBCs to facilitate the formation of rouleaux.
An increase in the ratio of RBCs to plasma volume, as seen in the setting of polycythemia and hypovolemia, increases rouleaux formation and accelerates sedimentation. Rouleaux formation is retarded by albumin proteins. Rouleaux formations are adopted by spermatozoa as a means of cooperation between genetically similar gametocytes so as to improve reproductive success through enhanced motility and, fertilization capacity—e.g. The guinea pig. According to Smoluchowski aggregation, the kinetics of colloids is based on the assumption that each particle is surrounded by a "sphere influence". Single spherical particles which undergo Brownian motion collide and sticking of particles happens; as aggregation proceeds, the average diffusion constant of the aggregate population decreases. The aggregation of red blood cells progresses in the same manner except that cells are biconcave rather than spherical. Hemorheology Stoltz, J. F. et al.: Experimental approach to rouleau formation. Comparison of three methods.
Biorheology Suppl. 1: 221-6 Huang CR in: Biorheology. 1987. Thixotropic properties of whole blood from healthy human subjects. Samsel RW, Perelson AS.: Biophys J. 1982 Feb. Kinetics of rouleau formation. I. A mass action approach with geometric features. Samsel RW, Perelson AS in: Biophys J. 1984 Apr. Kinetics of rouleau formation. II. Reversible reactions. Stoltz JF, Gaillard S, Paulus F, Henri O, Dixneuf P.: Biorheology Suppl. 1984. Experimental approach to rouleau formation. Comparison of three methods. Fabry TL.: Blood. 1987 Nov. Mechanism of erythrocyte aggregation and sedimentation. Http://bloodjournal.hematologylibrary.org/cgi/content/full/107/11/4205 http://www.biophysj.org/cgi/content/full/78/5/2470 Rouleaux: Presented by the University of Virginia
Retinopathy is any damage to the retina of the eyes, which may cause vision impairment. Retinopathy refers to retinal vascular disease, or damage to the retina caused by abnormal blood flow. Age-related macular degeneration is technically included under the umbrella term retinopathy but is discussed as a separate entity. Retinopathy, or retinal vascular disease, can be broadly categorized into proliferative and non-proliferative types. Retinopathy is an ocular manifestation of systemic disease as seen in diabetes or hypertension. Diabetes is the most common cause of retinopathy in the U. S. as of 2008. Diabetic retinopathy is the leading cause of blindness in working-aged people, it accounts for about 5% of blindness worldwide and is designated a priority eye disease by the World Health Organization. Many people do not have symptoms until late in their disease course. Patients become symptomatic when there is irreversible damage. Symptoms are not painful and can include: Vitreous hemorrhage Floaters, or small objects that drift through the field of vision Decreased visual acuity "Curtain falling" over eyes The development of retinopathy can be broken down into proliferative and non-proliferative types.
Both types cause disease by altering the normal blood flow to the retina through different mechanisms. The retina is supplied by small vessel branches from the central retinal artery. Proliferative retinopathy refers to damaged caused by abnormal blood vessel growth. Angiogenesis is a natural part of tissue growth and formation; when there is an unusually high or fast rate of angiogenesis, there is an overgrowth of blood vessels called neovascularization. In the non-proliferative type, abnormal blood flow to the retina occurs due to direct damage or compromise of the blood vessels themselves. Many causes of retinopathy may cause both proliferative and non-proliferative types, though some causes are more associated one type. Non-proliferative retinopathy is caused by direct damage or remodeling of the small blood vessels supplying the retina. Many common causes of non-proliferative damage include hypertensive retinopathy, retinopathy of prematurity, radiation retinopathy, solar retinopathy, retinopathy associated with sickle cell disease.
There are three main mechanisms of damage in non-proliferative retinopathy: blood vessel damage or remodeling, direct retinal damage, or occlusion of the blood vessels. The first mechanism is indirect damage by altering the blood vessels. In the case of hypertension, high pressures in the system causes the walls of the artery to thicken, which reduces the amount of blood flow to the retina; this reduction in flow causes tissue ischemia leading to damage. Atherosclerosis, or hardening and narrowing of blood vessels reduces flow to the retina; the second mechanism is direct damage to the retina caused by free radicals that causes oxidative damage to the retina itself. Radiation, solar retinopathy, retinopathy of prematurity fall under this category; the third common mechanism is occlusion of blood flow. This can be caused by either physically blocking the vessels of the retinal artery branches or causing the arteries to narrow. Again, the end result is reduced blood flow to the retina causing tissue damage.
Sickle cell disease compromises blood flow by causing blood to sludge, or thicken and flow through the retinal arteries. Other disorders that cause hyperviscosity syndrome may cause blood sludging. Lastly, clots or central artery thrombosis directly blocks flow to the retina causing the cells to die. Proliferative retinopathy is the result of aberrant blood flow to the retina due to blood vessel overgrowth, or neovascularization; these pathologically overgrown blood vessels are fragile and ineffective at perfusing the retinal tissues. These weak, fragile vessels are often leaky, allowing fluids and other debris to leech out into the retina, they are prone to hemorrhage due to their poor strength. This makes proliferative types of retinopathy more risky since vessel hemorrhaging leads to vision loss and blindness. Many of the causes mentioned in non-proliferative retinopathy may cause proliferative retinopathy at stages. Angiogenesis and neovascularization tend to be a manifestation of non-proliferative retinopathy.
Many types of non-proliferative retinopathies result in direct retinal damage. The body responds by trying to increase blood flow to damaged retinal tissues. Diabetes mellitus, which causes diabetic retinopathy, is the most common cause of proliferative retinopathy in the world. Genetic mutations are rare causes of certain retinopathies and are X-linked including NDP family of genes causing Norrie Disease, FEVR, Coats disease among others. There is emerging evidence that there may be a genetic predisposition in patients who develop retinopathy of prematurity and diabetic retinopathy. Trauma to the head, several diseases may cause Purtscher's retinopathy. Retinopathy is diagnosed by an optometrist during eye examination. Stereoscopic fundus photography is the gold standard for the diagnosis of retinopathy. Dilated fundoscopy, or direct visualization of the fundus, has been shown to be effective as well. Telemedicine programs are available that allow primary care clinics to take images using specially designed retinal imaging equipment which can be shared electronically with specialists at other locations for review.
In 2009, Community Health Center, Inc. implemented a telemedicine retinal screening program for low-income patients with diabetes as part of those patients annual visits at the Federally Qualified Health Center. Treatment is based on the cause of the retinopathy and may in
In blood, the serum is the component, neither a blood cell, nor a clotting factor. Serum includes all proteins not used in blood clotting and all the electrolytes, antigens and any exogenous substances; the study of serum is serology. Serum is used in numerous diagnostic tests, as well as blood typing. Measurements of serum concentrations has proved useful in many fields including clinical trials of therapeutic vs toxic response. Blood is centrifuged to remove cellular components. Anti-coagulated blood yields plasma containing clotting factors. Coagulated blood yields serum without fibrinogen. Serum is an essential factor for the self-renewal of embryonic stem cells in combination with the cytokine leukemia inhibitory factor; the serum of convalescent patients recovering from an infectious disease can be used as a biopharmaceutical in the treatment of other people with that disease, because the antibodies generated by the successful recovery are potent fighters of the pathogen. Such convalescent serum is a form of immunotherapy.
Blood serum and plasma are some of the largest sources of biomarkers, whether for diagnostics or therapeutics. Its vast dynamic range, further complicated by the presence of lipids and post-translational modifications, as well multiple mechanisms of degradation, presents challenges in analytical reproducibility, sensitivity and potential efficacy. For analysis of biomarkers in blood serum samples, it is possible to do a pre-separation by free-flow electrophoresis that consists of a depletion of serum albumin protein; this method enables greater penetration of the proteome via separation of a wide variety of charged or chargeable analytes, ranging from small molecules to cells. Like many other mass nouns, the word serum can be pluralized. To speak of multiple serum specimens from multiple people, physicians sometimes speak of sera. Blood
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity can be conceptualized as quantifying the frictional force that arises between adjacent layers of fluid that are in relative motion. For instance, when a fluid is forced through a tube, it flows more near the tube's axis than near its walls. In such a case, experiments show; this is because a force is required to overcome the friction between the layers of the fluid which are in relative motion: the strength of this force is proportional to the viscosity. A fluid that has no resistance to shear stress is known as an inviscid fluid. Zero viscosity is observed only at low temperatures in superfluids. Otherwise, the second law of thermodynamics requires all fluids to have positive viscosity. A fluid with a high viscosity, such as pitch, may appear to be a solid; the word "viscosity" is derived from the Latin "viscum", meaning mistletoe and a viscous glue made from mistletoe berries.
In materials science and engineering, one is interested in understanding the forces, or stresses, involved in the deformation of a material. For instance, if the material were a simple spring, the answer would be given by Hooke's law, which says that the force experienced by a spring is proportional to the distance displaced from equilibrium. Stresses which can be attributed to the deformation of a material from some rest state are called elastic stresses. In other materials, stresses are present which can be attributed to the rate of change of the deformation over time; these are called. For instance, in a fluid such as water the stresses which arise from shearing the fluid do not depend on the distance the fluid has been sheared. Viscosity is the material property which relates the viscous stresses in a material to the rate of change of a deformation. Although it applies to general flows, it is easy to visualize and define in a simple shearing flow, such as a planar Couette flow. In the Couette flow, a fluid is trapped between two infinitely large plates, one fixed and one in parallel motion at constant speed u.
If the speed of the top plate is low enough in steady state the fluid particles move parallel to it, their speed varies from 0 at the bottom to u at the top. Each layer of fluid moves faster than the one just below it, friction between them gives rise to a force resisting their relative motion. In particular, the fluid applies on the top plate a force in the direction opposite to its motion, an equal but opposite force on the bottom plate. An external force is therefore required in order to keep the top plate moving at constant speed. In many fluids, the flow velocity is observed to vary linearly from zero at the bottom to u at the top. Moreover, the magnitude F of the force acting on the top plate is found to be proportional to the speed u and the area A of each plate, inversely proportional to their separation y: F = μ A u y; the proportionality factor μ is the viscosity of the fluid, with units of Pa ⋅ s. The ratio u / y is called the rate of shear deformation or shear velocity, is the derivative of the fluid speed in the direction perpendicular to the plates.
If the velocity does not vary linearly with y the appropriate generalization is τ = μ ∂ u ∂ y, where τ = F / A, ∂ u / ∂ y is the local shear velocity. This expression is referred to as Newton's law of viscosity. In shearing flows with planar symmetry, it is what defines μ, it is a special case of the general definition of viscosity, which can be expressed in coordinate-free form. Use of the Greek letter mu for the viscosity is common among mechanical and chemical engineers, as well as physicists. However, the Greek letter eta is used by chemists and the IUPAC; the viscosity μ is sometimes referred to as the shear viscosity. However, at least one author discourages the use of this terminology, noting that μ can appear in nonshearing flows in addition to shearing flows. In general terms, the viscous stresses in a fluid are defined as those resulting from the relative velocity of different fluid particles; as such, the viscous stresses. If the velocity gradients are small to a first approximation the v