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CHAPTER 13: BLOOD VESSELS AND
CIRCULATION
13.1 FUNCTIONS OF THE CIRCULATORY SYSTEM
- Carries blood.
- Exchanges nutrients, waste products, and gases with tissues.
- Transports substances
- Helps regulate blood pressure.
- Directs blood flow to the tissues.
13.2 GENERAL FEATURES OF BLOOD VESSEL STRUCTURE
Pulmonary vessels - transport blood from the right ventricle of the heart through the lungs and back to the left atrium. Systemic vessels - transport blood from the left ventricle of the heart through all parts of the body and back to the right atrium. Arteries - carry blood away from the heart; usually, the blood is oxygenated ( oxygen-rich ). As they become smaller , the artery walls undergo a gradual transition from having more elastic tissue than smooth muscle to having more smooth muscle than elastic tissue. Normally classified as elastic arteries, muscular arteries, or arterioles Capillaries - where exchange of substances such as O2, CO2, nutrients, and other waste products occurs between the blood and the tissue fluid. have thinner walls than do arteries Blood flows more slowly and there are far more of them than of any other blood vessel type. Veins - carry blood toward the heart; usually, the blood is deoxygenated ( oxygen-poor ). Walls of veins are thinner than arteries and contain less elastic tissue and fewer smooth muscle cells. May be classified as venules, small veins, medium-sized veins, or large veins. Tunics - Blood vessel walls consist of three layers (tunics) except in capillaries and venules.
From the inner to the outer wall, the tunics : (1) Tunica intima Innermost layer Consists of an endothelium composed of simple squamous epithelial cells , a basement membrane, and a small amount of connective tissue. In muscular arteries , it also contains a layer of thin elastic connective tissue. (2) Tunica media Middle layer Consists of smooth muscle cells arranged circularly around the blood vessel. It also contains variable amounts of elastic and collagen fibers , depending on the size and type of the vessel. In muscular arteries , a layer of elastic connective tissue forms the outer margin of the tunica media (3) Tunica adventitia or tunica externa Composed of dense connective tissue adjacent to the tunica media ; the tissue becomes loose connective tissue toward the outer portion of the blood vessel wall.
Arteries
Elastic arteries Largest-diameter arteries and have the thickest walls Compared to other arteries, a greater proportion of their walls is composed of elastic tissue , and a smaller proportion is smooth muscle. Aorta and pulmonary Muscular arteries Medium-sized The walls of medium-sized arteries are relatively thick compared to their diameter. Most of wall’s thickness results from smooth muscle cells of the tunica media Medium-sized arteries are called distributing arteries because the smooth muscle tissue enables these vessels to control blood flow to different body regions. Vasoconstriction - contraction of the smooth muscle in blood vessels. Decreases blood vessel diameter and blood flow. Vasodilation - Relaxation of the smooth muscle in blood vessels. Increases blood vessel diameter and blood flow. Supply blood to small arteries. Small arteries Have about the same structure as the medium-sized arteries, except for a smaller diameter and thinner walls. The smallest of the small arteries have only three or four layers of smooth muscle in their walls Arterioles Transport blood from small arteries to capillaries.
Smallest arteries in which the three tunics can be identified The tunica media of arterioles consists of only one or two layers of circular smooth muscle cells. Small arteries and arterioles are adapted for vasodilation and vasoconstriction.
Capillaries
From arterioles into capillaries Precapillary sphincters Blood flow through capillary networks is regulated by this smooth muscle cells. Located at the origin of the branches of the capillaries By contracting and relaxing , regulate the amount of blood flow through the various sections of the network. Consist of endothelium , which is a layer of simple squamous epithelium surrounded by delicate loose connective tissue.
When compressed , the valves prevent backward movement of lymph. Consequently, compression of the lymphatic vessels causes lymph to move forward through them. Three factors cause compression of the lymphatic vessels : (1) Contraction of surrounding skeletal muscle during activity (2) Periodic contraction of smooth muscle in the lymphatic vessel wall, and (3) Pressure changes in the thorax during breathing. Right lymphatic duct Formed by lymphatic vessels from the right upper limb and the right half of the head, neck, and chest. Empties into the right subclavian vein Thoracic duct Lymphatic vessels from the rest of the body enter this duct Empties into the left subclavian vein
Lymphatic Organs
Include the tonsils, the lymph nodes, the spleen, and the thymus. Lymphatic tissue Characterized by housing many lymphocytes and other defense cells, such as macrophages. Found within lymphatic organs as well as other organs. Lymphocytes Originate from red bone marrow and are carried by the blood to lymphatic organs. These divide and increase in number when the body is exposed to pathogens. Reticular fibers Form an interlaced network that holds the lymphocytes and other cells in place. When lymph or blood filters through lymphatic organs, this also traps
microorganisms and other items in the fluid.
Tonsils
There are three groups of tonsils : (1) The palatine (palate) tonsils are located on each side of the posterior opening of the oral cavity; these are the ones usually referred to as “ the tonsils .” (2) The pharyngeal tonsil is located near the internal opening of the nasal cavity. When the pharyngeal tonsil is enlarged, it is commonly called the adenoid or adenoids. An enlarged pharyngeal tonsil can interfere with normal breathing. (3) The lingual (tongue) tonsil is on the posterior surface of the tongue. Form a protective ring of lymphatic tissue around the openings between the nasal and oral cavities and the pharynx. Protect against pathogens and other potentially harmful material entering from the nose and mouth. Tonsillectomy – removal of the palatine tonsils Adenoidectomy – removal of the pharyngeal tonsil Lingual tonsil – becomes less infected than other tonsils and is more difficult to remove.
Lymph Nodes
Are rounded structures, varying from the size of a small seed to that of a shelled almond. Distributed along the various lymphatic vessels. classified as superficial or deep Filter lymph and are sites where lymphocytes respond to infections. Three superficial aggregations of lymph nodes on each side of the body: ( IAC ) (1) Inguinal nodes in the groin (2) The axillary nodes in the axilla (armpit) (3) The cervical nodes in the neck. Capsule – A dense connective tissue surrounds each lymph node
Trabeculae – Extensions of the capsule that subdivide a lymph node into compartments containing lymphatic tissue and lymphatic sinuses. Lymphatic tissue – consists of lymphocytes and other cells that can form dense aggregations of tissue called lymphatic nodules. Lymphatic nodules – are areas of tissue within lymph nodes and other organs as well. ( not the same as lymph nodes ) Lymphatic sinuses – are spaces between the lymphatic tissues that contain macrophages on a network of fibers. As lymph moves through the lymph nodes, two functions are performed.
- To activate the immune system. Pathogens in the lymph can stimulate lymphocytes in the lymphatic tissue to divide. Germinal centers – lymphatic nodules containing the rapidly dividing lymphocytes. The newly produced lymphocytes are released into the lymph and eventually reach the blood, where they circulate and enter other lymphatic tissues.
- To remove pathogens from the lymph through the action of macrophages.
Spleen
Roughly the size of a clenched fist and is located in the left, superior corner of the abdominal cavity. Have an outer capsule of dense connective tissue and a small amount of smooth muscle. Trabeculae from the capsule divide the spleen into small, interconnected compartments containing two specialized types of lymphatic tissue: white pulp and red pulp. White pulp
- Is lymphatic tissue surrounding the arteries within the spleen
- Lymphocytes in the white pulp can be stimulated in the same manner as in lymph nodes
Red pulp
- Is associated with the veins.
- Consists of a fibrous network, filled with macrophages and red blood cells , and enlarged capillaries that connect to the veins.
- Macrophages in the red pulp remove foreign substances and worn-out red blood cells through phagocytosis. The spleen filters blood instead of lymph. Cells within the spleen detect and respond to foreign substances in the blood and destroy old and damaged red blood cells. Spleen also functions as a blood reservoir , holding a small volume of blood. In emergency situations, such as hemorrhage , smooth muscle in splenic blood vessels and in the splenic capsule can contract, allowing a small amount of blood to move out of the spleen into the general circulation. Splenectomy – removal of the spleen may be necessary if these techniques (mesh and blood- clotting agent) do not stop the bleeding. Other lymphatic organs and the liver then compensate for the loss of the spleen’s functions.
Thymus
A bilobed gland roughly triangular in shape Located in the superior mediastinum, the partition dividing the thoracic cavity into left and right parts Each lobe of the thymus is surrounded by a thin connective tissue capsule. Trabeculae from the capsule divide each lobe into lobules. Cortex – Dark-staining areas formed by numerous lymphocytes near the capsule and trabeculae. Medulla – A lighter-staining, central portion of the lobules; has fewer lymphocytes. Thymus is the site for the maturation of a class of lymphocytes called T cells
(1) The skin and mucous membranes form barriers that prevent their entry (2) Tears, saliva, and urine wash these substances from body surfaces. Pathogens cannot cause a disease if they cannot get into the body.
Chemical Mediators
Molecules responsible for many aspects of innate immunity. Some chemicals on the surface of cells destroy pathogens or prevent their entry into the cells. For example, lysozyme in tears and saliva kills certain bacteria, and mucus on the mucous membranes prevents the entry of some pathogens. Other chemical mediators, such as histamine , complement , prostaglandins , and leukotrienes , promote inflammation by causing vasodilation, increasing vascular permeability, and stimulating phagocytosis. In addition, interferons protect cells against viral infections. Complement proteins A group of more than 20 proteins found in plasma. The operation of complement proteins is similar to that of clotting proteins Once activated , certain complement proteins promote inflammation and phagocytosis and can directly lyse (rupture) bacterial cells Interferons Are proteins that protect the body against viral infections Released by infected cells like a “ Save yourself !” signal from an infected cell to its neighbors. Some play a role in activating immune cells, such as macrophages and natural killer cells Infected cell produces viral nucleic acids and proteins , which are assembled into new viruses.
White Blood Cells
White blood cells and the cells derived from them are the most important cellular components of immunity. Produced in red bone marrow and lymphatic tissue and released into the blood. Chemicals that attract WBC include:
- Complement
- Leukotrienes
- Kinins
- Histamine Chemotaxis - the movement of white blood cells toward these chemicals Phagocytic Cells
- Phagocytosis is the ingestion and destruction of particles by cells called phagocytes
- The most important phagocytes are neutrophils and macrophages , although other white blood cells also have limited phagocytic ability.
- Neutrophils - are small phagocytic white blood cells. Usually the first white blood cells to enter infected tissues from the blood in large numbers. Often die after phagocytizing a single microorganism.
- Pus - an accumulation of fluid, dead neutrophils, and other cells at a site of infection.
- Macrophages are monocytes that leave the blood, enter tissues, and enlarge about fivefold.
- Monocytes and macrophages form the mononuclear phagocytic system because they are phagocytes with a single (mono), unlobed nucleus.
- Macrophages are given specific names, such as dust cells in the lungs , Kupffer cells in the liver , and microglia in the central nervous system. Cells of Inflammation
- Basophils , which are derived from red bone marrow, are motile white blood
cells that can leave the blood and enter infected tissues.
- Mast cells , which are also derived from red bone marrow, are nonmotile cells in connective tissue, especially near capillaries. Like macrophages, they are located at points where pathogens may enter the body, such as the skin, lungs, gastrointestinal tract, and urogenital tract.
- Basophils and mast cells can be activated through innate immunity or through adaptive immunity
- When activated, these cells release chemicals, such as histamine and leukotrienes that produce an inflammatory response or activate other mechanisms, such as smooth muscle contraction in the lungs.
- Eosinophils also participate in inflammation associated with allergies and asthma.
- Inflammation beneficial in the fight against pathogens, but too much can be harmful, destroying healthy tissues as well as the microorganisms. Natural Killer Cells
- Natural killer (NK) cells are a type of lymphocyte produced in red bone marrow, and they account for up to 15% of lymphocytes.
- Do not exhibit a memory response
- Classified as part of innate immunity.
- Use a variety of methods to kill their target cells, including releasing chemicals that damage cell membranes and cause the cells to lyse.
Inflammatory Response
Local inflammation is an inflammatory response confined to a specific area of the body Systemic inflammation is an inflammatory response that is generally distributed throughout the body.
- Pyrogens (fever-producing), chemicals released by microorganisms,
neutrophils, and other cells, stimulate fever production.
- Affect the body’s temperature regulating mechanism in the hypothalamus in the brain
- Fever it promotes the activities of the immune system, such as phagocytosis, and inhibits the growth of some microorganism
14.5 ADAPTIVE IMMUNITY
Two defining characteristics :
- Specificity
- Memory Antigens (anti (body) + - gen , producing)
Lymphocyte Proliferation
- An important process that generates the needed defense cells to protect the body
- Interleukin-2 - binds to the receptors and stimulates the helper T cell to divide
- The “ daughter ” helper T cells – presented with the antigen by macrophages and again be stimulated to divide.
Antibody-Mediated Immunity
Structure of Antibodies
- Antibodies - are proteins produced in response to an antigen. They are Y-shaped molecules consisting of four polypeptide chains: Two identical heavy chains. Two identical light chains.
- Variable region - The end of each “arm” of the antibody
- Constant region - The rest of the antibody; can activate complement, or it can attach the antibody to cells, such as macrophages, basophils, and mast cells.
- Gamma globulins - when antibodies are found mostly in the gamma globulin part of plasma.
- Immunoglobulins – when antibodies are globulin proteins involved in immunity.
- The five general classes of antibodies are denoted 1. IgG 2. IgM 3. IgA 4. IgE 5. IgD
Effects of Antibodies
- Antibodies can affect antigens either directly or indirectly.
- Direct effects - occur when a single antibody binds to an antigen and inactivates the antigen, or when many antigens are bound together and are inactivated by many antibodies.
- Indirect effects - Most of the effectiveness of antibodies results from this
Inhibiting and Stimulating Immunity
Decreasing the production or activity of cytokines can suppress the immune system. Cyclosporine - a drug used to prevent the rejection of transplanted organs , inhibits the production of interleukin-.
Antibody Production
- The production of antibodies after the first exposure to an antigen is different from that following a second or subsequent exposure.
- Primary response results from the first exposure of a B cell
- Secondary response or memory response ; Memory B cells are responsible for this; occurs when the immune system is exposed to an antigen against which it has already produced a primary response
Cell-Mediated Immunity
Is a function of cytotoxic T cells and Most effective against microorganisms that live inside body cells. Cytotoxic T cells - responsible for the immediate cell-mediated immune response Memory T cells - provide a secondary response and long-lasting immunity in the same fashion as memory B cells.
14.6 ACQUIRED IMMUNITY
Four ways to acquire adaptive immunity :
- Active natural
- Active artificial
- Passive natural
- Passive artificial Active immunity - results when an individual is exposed to an antigen (either naturally or artificially) and the response of the individual’s own immune system is the cause of the immunity; Immunity is provided by the individual’s own immune system Passive immunity - occurs when another person or an animal develops immunity and the immunity is transferred to a nonimmune
individual; Immunity is transferred from another person or an animal. Natural and artificial refer to the method of exposure or antibody transfer. Natural - implies that contact with the antigen or transfer of antibodies occurs as part of everyday living and is not deliberate. Artificial - implies that deliberate introduction of an antigen or antibody into the body has occurred.
Active Natural Immunity
Active natural immunity – results from natural exposure to an antigen, such as a disease- causing microorganism, that stimulates the immune system to respond against the antigen.
Active Artificial Immunity
Active artificial immunity – When an antigen is deliberately introduced into an individual to stimulate the immune system. This process is called vaccination and the introduced antigen is a vaccine.
Passive Natural Immunity
Passive natural immunity – results when antibodies are transferred from a mother to her child across the placenta before birth.
Passive Artificial Immunity
Passive artificial immunity – involves the collecting of antibodies from one source and introducing them to an infected individual, usually through injection. Achieving passive artificial immunity begins with vaccinating an animal , such as a horse. Antiserum – general term for antibodies that provide passive artificial immunity.
14.7 OVERVIEW OF IMMUNE INTERACTIONS
Systemic Lupus Erythematosus
A disease in which tissues and cells are damaged by the immune system Lupus – literally means “wolf” and originally referred to eroded (as if gnawed by a wolf) lesions of the skin. Erythematosus – refers to redness of the skin resulting from inflammation. Systemic – implies the disorder is not confined to the skin but can affect tissues and cells throughout the body. Symptoms of SLE (Highly variable) o Skin lesions, particularly on face o Fever o Fatigue o Arthritis o Anemia
Lymphedema
Abnormal accumulation of lymph in tissues, often the limbs; 70%–90% cases in women ; can be caused by developmental defects, disease, or damage to the lymphatic system
Lymphoma
Cancer of lymphocytes that often begins in lymph nodes; immune system becomes depressed, with increased susceptibility to infections
Immediate Allergic Reactions
Symptoms occur within a few minutes of exposure to an antigen because antibodies are already present from prior exposure.
Asthma
Antigen combines with antibodies on mast cells or basophils in the lungs, which then release inflammatory chemicals that cause constriction of the air tubes, so that the patient has trouble breathing
Anaphylaxis
