Learning Objectives - Blood
Describe the composition and physical characteristics of whole blood. Explain why it is classified as a connective tissue.
Blood is a sticky, opaque fluid with a characteristic metallic taste. Depending on the amount of oxygen it is carrying, the color of blood varies from scarlet (oxygen rich) to dark red (oxygen poor). Blood is more dense than water and about five times more viscous, largely because of its formed elements. Blood is slightly alkaline, with a pH between 7.35 and 7.45, and its temperature (38C or 100.4F) is always slightly higher than body temperature. Blood accounts for approximately 8% of body weight.
Blood is the only fluid tissue in the body. The microscope reveals that blood has both cellular and liquid components. Blood is a specialized type of connective tissue in which living blood cells, called the formed elements, are suspended in a nonliving fluid matrix called plasma (plaz mah). The collagen and elastic fibers typical of other connective tissues are absent from blood, but dissolved fibrous proteins
List eight functions of blood.
1.Delivering oxygen from the lungs and nutrients from the digestive tract to all body cells.
2.Transporting metabolic waste products from cells to elimination sites
3.Transporting hormones from the endocrine organs to their target organs.
4.Maintaining appropriate body temperature by absorbing and distributing heat throughout the body and to the skin surface to encourage heat loss.
5.Maintaining normal pH in body tissues. Many blood proteins and other blood-borne solutes act as buffers to prevent excessive or abrupt changes in blood pH
6.Maintaining adequate fluid volume in the circulatory system. Salts (sodium chloride and others) and blood proteins act to prevent excessive fluid loss from the bloodstream into the tissue spaces.
7.Preventing blood loss. When a blood vessel is damaged, platelets and plasma proteins initiate clot formation, halting blood loss.
8.Preventing infection. Drifting along in blood are antibodies, complement proteins, and white blood cells, all of which help defend the body against foreign invaders such as bacteria and viruses.
Discuss the composition and functions of plasma.
straw-colored, sticky fluid Although it is mostly water (about 90%), plasma contains over 100 different dissolved solutes, including nutrients, gases, hormones, wastes and products of cell activity, ions, and proteins.
Function of Plasma
1.Carries nutrients including glucose which is the primary source of energy for cell metabolism.
2.Hormones are transported around the body in plasma attached to plasma proteins.
3.Contains inorganic ions which are important in regulating cell function and maintaining homeostasis.
4.Contains clotting agents and on exposure to air it will form a clot. Aids healing and stops bleeding.
5.Contains antibodies (gammaglobulins) to help resist/fight off infections.
Describe the structure, function, and production of erythrocytes.
•small cells, about 7.5 μm in diameter. Shaped like biconcave discs—flattened discs with depressed centers—they appear lighter in color at their thin centers than at their edges. Bound by a plasma membrane but lack a nucleus (are anucleate) and have essentially no organelles.
•RBC function is to transport respiratory gases (oxygen and carbon dioxide).
•Blood cell formation is referred to as hematopoiesis (hem ahto-poi-e sis), or hemopoiesis (hemo, hemato = blood; poiesis = to make). This process occurs in the red bone marrow On average, the marrow turns out an ounce of new blood containing some 100 billion new cells each and every day.
Describe the chemical composition of hemoglobin.
made up of the protein globin bound to the red heme pigment. Globin consists of four polypeptide chains—two alpha and two beta —each binding a ringlike heme group. Each heme group bears an atom of iron set like a jewel in its center . A hemoglobin molecule can transport four molecules of oxygen because each iron atom can combine reversibly with one molecule of oxygen. A single red blood cell contains about 250 million hemoglobin molecules, so each of these tiny cells can scoop up about 1 billion molecules of oxygen!
Give examples of disorders caused by abnormalities of erythrocytes. Explain what goes wrong in each disorder.
Anemia “lacking blood” is a condition in which the blood has abnormally low oxygen-carrying capacity. It is a sign of some disorder rather than a disease in and of itself. Its hallmark is blood oxygen levels that are inadequate to support normal metabolism. Anemic individuals are fatigued, often pale, short of breath, and chilly. Caused by
Blood loss – hemorrhagic anemia
Not enough blood cells produced –
Pernicious anemia is due to a deficiency of vitamin B12. An autoimmune disease in which the stomach mucosa atrophies, and it most often affects the elderly
Too many RBC destroyed
Thalassemias “sea blood” are typically seen in people ofMediterranean ancestry, such as Greeks and Italians. One of the globin chains is absent or faulty, and the erythrocytes are thin, delicate, and deficient in hemoglobin.
Sickle-cell anemia, the havoc caused by the abnormal hemoglobin, hemoglobin S (HbS), results from a change in just one of the 146 amino acids in a beta chain of the globin molecule.This alteration causes the beta chains to link together under low-oxygen conditions, forming stiff rods so that hemoglobin S becomes spiky and sharp. This, in turn, causes the red blood cells to become crescent shaped when they unload oxygen molecules
Polycythemia “many blood cells”) is an abnormal excess of erythrocytes that increases blood viscosity, causing it to sludge, or flow sluggishly.
Secondary polycythemias result when less oxygen is available or EPO production increases. The secondary polycythemia that appears in individuals living at high altitudes is a normal physiological response to the reduced atmospheric pressure and lower oxygen content of the air in such areas.
Blood doping, practiced by some athletes competing in aerobic events, is artificially induced polycythemia. Some of the athlete’s red blood cells are drawn off and then reinjected a few days before the event. The erythrocytes are quickly replaced because the erythropoietin mechanism is triggered shortly after blood removal. Then,when the stored blood is reinfused, a temporary polycythemia results. risk of stroke and heart failure due to high hematocrit and high blood viscosity
List the classes, structural characteristics, and functions of leukocytes.
Granulocyte - Are all roughly spherical in shape. They are larger and much shorter lived (in most cases) than erythrocytes. They characteristically have lobed nuclei (rounded nuclear masses connected by thinner strands of nuclear material). Functionally, all granulocytes are phagocytes to a greater or lesser degree.
Neutrophil – 50-70%, multilobed nucleus, Acute infection
Eosinophil – 2-4%, bilobed nucleus, red cytoplasmic granules, Parasites
Basophil – 0.05 – 1%, bilobed nucleus, purplish-black cytoplasmic granules, Inflammatory Infections
Agranulocyte - lack visible cytoplasmic granules. Although they are similar structurally, they are functionally distinct and unrelated cell types. Their nuclei are typically spherical or kidney shaped.
Lymphocyte – 25-45%, large spherical nucleus, Immunity
Monocyte – 3-8%, kidney-shaped nucleus, Chronic Infection
Describe how leukocytes are produced.
The production of white blood cells, is stimulated by chemical messengers. These messengers, which can act either as paracrines or hormones, are glycoproteins that fall into two families of hematopoietic factors, interleukins and colony-stimulating factors, or CSFs. are named for the leukocyte population they stimulate
Give examples of leukocyte disorders, and explain what goes wrong in each disorder.
•Leukopenia (loo_ko-pe_ne-ah) is an abnormally low white blood cell count commonly induced by drugs, particularly glucocorticoids and anticancer agents.
•Leukemia, literally “white blood,” refers to a group of cancerous conditions involving white blood cells. the renegade leukocytes are members of a single clone (descendants of a single cell) that remain unspecialized and proliferate out of control, impairing normal red bone marrow function. the red bone marrow becomes almost totally occupied by cancerous leukocytes and immature WBCs flood into the bloodstream. The other blood cell lines are crowded out, so severe anemia and bleeding problems also result. Other symptoms include fever, weight loss, and bone pain. Although tremendous numbers of leukocytes are produced, they are nonfunctional and cannot defend the body in the usual way.
•Infectious Mononucleosis Once called the kissing disease, infectious mononucleosis is a highly contagious viral disease most often seen in young adults. Caused by the Epstein-Barr virus, its hallmark is excessive numbers of agranulocytes, many of which are atypical. The affected individual complains of being tired and achy, and has a chronic sore throat and a low-grade fever. There is no cure, but with rest the condition typically runs its course to recovery in a few weeks.
Describe the structure and function of platelets.
•Platelets are not cells in the strict sense. About one-fourth the diameter of a lymphocyte, they are cytoplasmic fragments of extraordinarily large cells (up to 60 μm in diameter) called megakaryocytes
•Platelets are essential for the clotting process that occurs in plasma when blood vessels are ruptured or their lining is injured. By sticking to the damaged site, platelets form a temporary plug that helps seal the break.
Describe the process of hemostasis. List factors that limit clot formation and prevent
1. vascular spasm - In the first step of blood vessel repair, the damaged blood vessels respond to injury by constricting (vasoconstriction), triggers include direct injury to vascular smooth muscle, chemicals released by endothelial cells and platelets, and reflexes initiated by local pain receptors.
2. Platelet Plug Formation - the second step of blood vessel repair, platelets play a key role in hemostasis by aggregating (sticking together), forming a plug that temporarily seals the break in the vessel wall
3. Coagulation - The third step in blood vessel repair, blood clotting, reinforces the platelet plug with fibrin threads that act as a “molecular glue” for the aggregated platelets
Give examples of hemostatic disorders. Indicate the cause of each condition.
•Thromboembolic disorders-conditions that cause undesirable clot formation
•Bleeding disorders-arise from abnormalities that prevent normal clot formation
•Disseminated Intravascular Coagulation (DIC)- involves both wide spread clotting and severe bleeding.
Describe the ABO and Rh blood groups. Explain the basis of transfusion reactions.
•Blood types has a classification which is based on two things:
ABO group - depends on two antigens; antigen A and antigen B. which lie on the surface of the red blood cell (RBC)
A person having an A antigen on his RBC cells will show a blood type of A
A person having a B antigen on his RBC cells will show a blood type of B
A person having both A & B antigens on his RBC cells will show a blood type of AB
A person having neither of those antigens will show a blood type of O
Rhesus factor - the rhesus factor, which depends on a single antigen; antigen D, which also lies on the surface of the RBC
A person having a D antigen is called an Rh positive, e.g. A, B and D antigens’ presence exhibit a blood type of AB+ (universal acceptor)
A person without the D antigen is called an Rh negative, e.g. Neither A, nor B, nor D antigens’ presence exhibit a blood type of O- (universal donor).
Both factors combine to form the blood types as we know them today
•if you transfuse type B blood cells into a type A person then that persons immune system won’t recognise the type B antigens as part of the body and will attack them just as it would invading bacteria. Transfusion reactions can range from the mild such as a fever too the more serious such as lung injury and acute heamolytic reaction where donor red cell are rapidly destroyed which is bad. (life threatening medical emergency bad).
Describe fluids used to replace blood volume and the circumstances for their use.
When a patient’s blood volume is so low that death from shock is imminent, there may not be time to type blood, or appropriate whole blood may be unavailable. Such emergencies demand that blood volume be replaced immediately to restore adequate circulation. Fundamentally, blood consists of proteins and cells suspended in a salt solution. Replacing lost blood volume essentially consists of replacing that isotonic salt solution. Normal saline or a multiple electrolyte solution that mimics the electrolyte composition of plasma (for example, Ringer’s solution) are the preferred choices.
Explain the diagnostic importance of blood testing.
A laboratory examination of blood yields information that can be used to evaluate a person’s current state of health.
Name some blood disorders that become more common with age
The most common blood diseases that appear during aging are chronic leukemias, anemias, and clotting disorders.