5th Lecture dentistry (31st -3rd Nov. 2016)
Blood (Hematology)Medical terms related to blood often begin with hemo- or hemato from the Greek word (haima) for "blood". In terms of anatomy and 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 fibrinogen.
It is a bodily fluid in animals and human that delivers necessary substances i.e. nutrients and oxygen to the cells and transports metabolic waste products away from those same cells. When it reaches the lungs, gas exchange occurs as carbon dioxide (CO2) is diffused out of the blood into the alveoli and oxygen (O2) is diffused into the blood. This oxygenated blood is pumped to the left hand side of the heart in the pulmonary vein and enters the left atrium. From here it passes through the bicuspid valve, through the ventricle and taken all around the body by the dorsal aorta. Blood contains antibodies, nutrients, oxygen and lots more to help the body work.
In vertebrates, it is composed of blood cells suspended in 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), as well as blood cells themselves. Albumin is the main protein in plasma, and it functions to regulate the colloidal osmotic pressure of blood. The blood cells are mainly red blood cells (also called RBCs or erythrocytes) and white blood cells, including leukocytes and platelets. The most abundant cells in vertebrate blood are red blood cells (corpuscles). These contain hemoglobin, an iron-containing protein, which facilitates transportation of O2 by reversibly binding to this respiratory gas and greatly increasing its solubility in blood. In contrast, CO2 is almost entirely transported extra-cellularly dissolved in plasma as bicarbonate ion.
Vertebrate blood is bright red when its hemoglobin is oxygenated. 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 O2 from inhaled air to the tissues of the body, and venous blood carries CO2, a waste product of metabolism produced by cells, from the tissues to the lungs to be exhaled.
Functions:
Blood performs many important functions within the body including:
Supply of O2 to tissues (bound to hemoglobin, which is carried in red cells)
Supply of nutrients such as glucose, amino acids, and fatty acids (dissolved in the blood or bound to plasma proteins e.g., blood lipids).
Removal of waste such as CO2, urea, and lactic acid.
Immunological functions, including circulation of white blood cells, and detection of foreign material by antibodies
Coagulation, the response to a broken blood vessel, the conversion of blood from a liquid to a semi-solid gel to stop bleeding.
Messenger functions, including the transport of hormones and the signaling of tissue damage
Regulation of body pH.
Regulation of core body temperature.
Hydraulic functions.
Blood accounts for 7% of the human body weight. In human, the average adult has a blood volume of roughly 5 liters (1.3 gal), which is composed of plasma and several kinds of cells. These blood cells (which are also called corpuscles or "formed elements") consist of erythrocytes (red blood cells, RBCs), leukocytes (white blood cells), and thrombocytes (platelets). By volume, the red blood cells constitute about 45% of whole blood, the plasma about 54.3%, and white cells about 0.7%. Blood amount does vary among other animals.
Whole blood (plasma and cells) exhibits non-Newtonian fluid dynamics; its flow properties are adapted to flow effectively through tiny capillary blood vessels with less resistance than plasma by itself. In addition, if all human hemoglobin were free in the plasma rather than being contained in RBCs, the circulatory fluid would be too viscous for the cardiovascular system to function effectively.
Cells:
One microliter (1.0 mL) of human blood contains:
4.7-6.1 million (male), 4.2-5.4 million (female) erythrocytes: They contain the blood's hemoglobin and distribute O2. Mature RBC lack a nucleus and organelles in mammals. The proportion of blood occupied by RBC is referred to as the hematocrit, and is normally about 45%. The combined surface area of all RBC of the human body would be roughly 2,000 times as great as the body's exterior surface.
4,000-11,000 leukocytes (WBC)s are part of the body's immune system; they destroy and remove old or aberrant cells and cellular debris, as well as attack infectious agents (pathogens) and foreign substances. The cancer of leukocytes is called leukemia.
200,000-500,000 thrombocytes (platelets): Take part in blood clotting (coagulation). Fibrin from the coagulation cascade creates a mesh over the platelet plug.
Hemoglobin, a globular protein; green = hem groups; red & blue = protein subunits
Narrow range of pH valuesBlood pH is regulated to stay within the narrow range of 7.35 to 7.45, making it slightly basic. Blood that has a pH below 7.35 is too acidic, whereas blood pH above 7.45 is too basic. Blood pH, partial pressure of oxygen (pO2), partial pressure of carbon dioxide (pCO2), and HCO3− are carefully regulated by a number of homeostatic mechanisms, which exert their influence principally through the respiratory system and the urinary system in order to control the acid-base balance and respiration. An arterial blood gas test will measure these. Plasma also circulates hormones transmitting their messages to various tissues. The list of normal reference ranges for various blood electrolytes is extensive.
Plasma:
Makes about 55% of blood which is a fluid of the blood's liquid medium, which by itself is straw-yellow in color. It is essentially an aqueous solution containing 92% water, 8% blood plasma proteins, and trace amounts of other materials. Plasma is the liquid component of blood, in which the RBC, WBC and platelets are suspended. Plasma circulates dissolved nutrients, such as glucose, amino acids, and fatty acids (dissolved in the blood or bound to plasma proteins), and removes waste products, i.e. CO2, urea, and lactic acid. Other proteins in plasma include antibodies (immunoglobulins), which actively defend the body against viruses, bacteria, fungi, and cancer cells, and clotting factors, which control bleeding.
Other important components include:
Serum albumin
Blood-clotting factors (to facilitate coagulation)
Immunoglobulins (antibodies)
lipoprotein particles
Various other proteins
Various electrolytes (mainly sodium and chloride).
The term serum refers to plasma from which the clotting proteins have been removed. Most of the proteins remaining are albumin and immunoglobulins.
Red Blood Cells (RBC):
Red blood cells (erythrocytes) make about 40% of the blood's volume. RBC contain hemoglobin, a protein that gives blood its red color and enables it to carry oxygen from the lungs and deliver it to all body tissues. O2 is used by cells to produce energy that the body needs, leaving carbon dioxide as a waste product. RBC carry CO2 away from the tissues and back to the lungs. When the number of RBC is too low (anemia), blood carries less oxygen, fatigue and weakness develop. When the number of red blood cells is too high (polycythemia), blood can become too thick, which may cause the blood to clot more easily and increase the risk of heart attacks and strokes.
White Blood Cells (WBC):
White blood cells (Leukocytes) are fewer in number than RBC, with a ratio of about 1:600-700 RBC. WBCs are responsible primarily for defending the body against infection. There are 5 main types of white blood cells.
Neutrophils: The most numerous type, help protect the body against infections by killing and ingesting bacteria and fungi and by ingesting foreign debris.
Lymphocytes: Consist of three main types: T-cells (T lymphocytes) and natural killer cells, which both help protect against viral infections and can detect and destroy some cancer cells, and B-cells (B lymphocytes), which develop into cells that produce antibodies.
Monocytes: Ingest dead or damaged cells and help defend against many infectious organisms.
Eosinophils: kill parasites, destroy cancer cells, and are involved in allergic responses.
Basophils:(participate in allergic responses): Some WBC flow smoothly through the bloodstream, but many adhere to blood vessel walls or even penetrate the vessel walls to enter other tissues. When WBC reaches the site of an infection they release substances that attract more WBC. The WBC function like an army, dispersed throughout the body but ready at a moment's notice to gather and fight off an invading organism and they accomplish this by engulfing and digesting organisms and by producing antibodies that attach to organisms so that they can be more easily destroyed.The high number of cells can be an indication of a disease such as an infection or leukemia
Platelets: Platelets (thrombocytes) are cell-like particles that are smaller than red or white blood cells and are fewer in number than red blood cells, with a ratio of about 1:20 RBC. Platelets help in the clotting process by gathering at a bleeding site and clumping together to form a plug that helps seal the blood vessel. At the same time, they release substances that help promote further clotting.
