Chapter 13 Notes
Chapter 13 Notes BIOL 3160
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This 9 page Class Notes was uploaded by MBattito on Thursday March 24, 2016. The Class Notes belongs to BIOL 3160 at Clemson University taught by Dr. Tamara McNutt-Scott in Fall 2015. Since its upload, it has received 43 views. For similar materials see Human Physiology in Biological Sciences at Clemson University.
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Date Created: 03/24/16
Chapter 13: Blood, Heart and Circulation • Circulatory System o Functional term o Prefer the use of cardiovascular system • Blood o Function divided into 3 broad areas: § Transportation – moving oxygen and wastes, hormones, clotting factors, etc. § Regulation – body temperature for example § Protection – antibodies Composition of Blood: • Blood is the only fluid tissue of the human body • Arterial Blood: blood leaving the heart o Bright red because of high oxyhemoglobin concentration • Venous Blood: blood returning to the heart o Darker red because of less oxygen • Plasma: fluid portion o Liquid of water and dissolved solutes, plus varied organic molecules à sodium makes up the largest percentage o 55% of blood composition • Cellular component: (Table 13.2) o Suspended in plasma o 45% of blood composition o Platelets: also called thrombocytes § Smallest of formed elements that are actually fragments of large cells found in bone marrow § Lack nuclei but are capable of movement through the capillaries § Survive for 5-‐9 days before being destroyed by liver and spleen § Important in blood clotting § Release serotonin (causes vasoconstriction) and growth factors (maintain integrity of blood vessel) o Erythrocyte § Function to transport oxygen and carbon dioxide § Lack nuclei and mitochondria § Circulating life span of about 120 days § Contain 280 million hemoglobin à give blood its red color • Hemoglobin molecule = 4 globin protein chains bound to one heme molecule – the iron group in heme is able to combine with oxygen in the lungs an release it in the tissues § Transferrin: protein that carries iron in the blood tot the bone marrow § The iron is recycled from old red blood cells by phagocytes in the liver and spleen o Leukocyte: § Different from erythrocytes because they have nuclei and mitochondria and can move through capillary walls • Diapedesis or Extravasation: movement of leukocytes through capillary walls to reach sites of infection • Aids in defense against infections by microorganisms § Granulocytes: survive 12 hours-‐3 days • Neutrophils: o 2-‐5 lobes o 54-‐62% of WBC o Phagocytic • Eosinophil: o Bilobed o 1-‐3% of WBC o Detoxify foreign substances, secrete enzymes that dissolve clots, fight parasitic infection • Basophil: o >1% of WBC o Release anticoagulant heparin § Agranulocytes: Survive 100-‐300 days • Monocytes: o 3-‐9% of WBC o phagocytic • Lymphocytes: o Nucleus nearly fits cell o 25-‐33% of WBC o provides specific immune response (includes antibodies) Hematopoiesis • Occurs in red bone barrow • Influence by cytokines and other regulatory molecules o Thrombopoietin and erythropoietin regulate the pathway of what the stem cells produce • Hemacytoblast: pluripotent hematopoietic stem cell o Forms lymphoid stem cell à produces lymphocyte o Forms myeloid stem cellà forms erythropoietin and interleukins, CSFs § Erythropoietin produces erythrocytes, neutrophil and monocyte § Interleukins produce eosinophil, basophil and megakaryocyte Erythrocytes: Red Blood Cells • Supply of iron, vitamin B12 and folic acid needed for proper red blood cell production • Regulated by EPO o Produced by kidney o Looks at oxygen carrying capacity (oxygen level) – if oxygen level is too low à makes more erythrocytes • Lover, spleen and bone marrow remove aged cells, recycle iron and globin • Erythropoiesis is a very active process – requires iron and myoglobin • Ferroportin channels in enterocytes – regulate iron concentration levels • Transferrin (plasma protein) in plasma • Role of HEPCIDIN (poly peptide hormone produced by the liver) o Promotes cellular storage of iron and lower blood iron concentration, does so by working through Ferroportin channels • Blood type result of distinguishing antigens displayed on cell surface o Genetically determined o Immune system exhibits tolerance to body’s red blood cells • Longevity ~ 120 days Blood Clotting: • Homeostasis: cessation of bleeding • Effective in dealing with injury to small vessels but little help for middle to large vessels • Observe 3 separate but overlapping homeostatic mechanisms o Vascular spasm o Formation of platelet plug o Clot forming Vascular Phase: • Function: close off vessels, reduce blood loss and allow time for other processes to stop bleeding in larger vessels • Vasocontrictive event: immediate response to injury o Occurs in smooth muscle of vessel walls – inherent in smooth muscle itself • Vascular spasm: occurs in vascular wall o Makes the lumen smaller by contracting to reduce blood flow/loss and gives time for other process Platelet Phase: • Platelet Plug: o Positive feedback event o Organizes for blood clot formation o Platelets activate clotting factors o Temporary fix – must be stabilized • Platelets repelled from each other and endothelium • Prostacyclins/Prostaglandins and NO – vasodilators and inhibit platelet aggregation • CD39: enzyme that breaks down ADP à promotes platelet aggregation • Degranulate • Platelet release reaction o Exposure of collagen and VWF activate platelets o More platelets activated and recruited Coagulation Phase: • Blood Clot – initiating the process of transforming blood from a liquid to a gel • Represents the transformation of blood from a liquid to a gel that results in the formation of a clot • Conversion of fibrinogen (soluble plasma protein) into fibrin (insoluble fibrous protein) o Fibrin stabilizes the clot Clotting Pathways • Extrinsic Pathway: o Chemical released by damaged tissue – tissue thromboplastin o Activator tissue factor activates VII à activates X à activates common pathway § VII complex: VII, tissue factor, calcium, phospholipids à require calcium and phospholipids from platelets • Intrinsic Pathway o Contact pathway: initiated by negatively charged structures – collagen, phosphates and NETS o Initial activation factors activate XII à activates XI à activates IX (forms VIII complex)à activates X à activates common pathway § VIII complex: VII, activated IX, calcium and phospholipids from platelets) • Common Pathway o Activate factor 10: Stewart Brower factor o Activated X forms V complex § V complex: V, X activated, calcium and phospholipids (from platelets) o Activate factor 10 activates thrombin from prothrombin à thrombin activates fibrinogen into fibrin which is polymerized by factor XIII à blood clot is formed • Intrinsic is slower than Extrinsic • Many clotting factors are synthesized in the liver o Deficiency of vitamin K can lead to clotting problems and dysfunction in the liver • Clot retraction: contraction within platelet mass to form more compact and effective plug – serum (plasma-‐lacking clotting factor) • Vitamin K: important in the synthesis of the clotting factor produced in the liver o Problems in people that take a lot of antibiotics because it kills the bacteria hat provides vitamin K à leads to problems in clotting Clot Dissolution • Plasminogen activators turns plasminogen into plasmin à produces soluble fibrin fragments from fibrin (breaks down some of the clot) o Kallikrein: main plasminogen activator in humans – tears down the clot • 3 mechanisms that oppose clot formation: o Tissue factor pathway inhibitor – TFPI § From endothelium; blocks clotting o Thrombomodulin: § Receptor for thrombin – becomes inactive upon binding protein C (natural anticoagulant) activator o Antithrombin III: § Inactivates thrombin and other clotting factors • Function: limit clot formation so that the clot does not get too large – does not completely inhibit • Balance between clot formation and elements that are depressing the clotting process Circulation Circuits and the Heart: • Pulmonary: out of the right side of the heart à lungs à drop CO2 and add O2 à back to the left side of the heart through the aorta • Systematic: pick up CO2 out of the left side of the heart and brings oxygen to the tissues • Equal blood flow in circuits – prevents fluid accumulation in lungs and oxygenated blood delivery to the body • Side-‐by-‐side pumps: right and left side feed different circulatory circuit o Right side serves pulmonary circuit o Left side serves systematic circuit o In general: blood flows from right side of heart à lungs à left side à body tissue à back to right side (constant cycle) o More resistance in the systematic circuit so the wall of the left ventricle is thicker than the right • Valves: direct blood flow in the heart o Atrioventricular valves: direct blood from the atria to the ventricles § Valves between atria and ventricles • Tricuspid valve: has 3 flaps on the right side of the heart • Bicuspid valve: has 2 flaps on the left side o Semilunar valves: direct flow from atria to aorta or pulmonary trunk but do not allow backflow from the ventricles to the atria § Allow blood from the heart out to the circulation circuits – oppose blood back into the heart from circuits § Located at the origin of the pulmonary artery and aorta • Fibrous Skeleton: layer of dense connective tissue found between the atria and the ventricles o Serves as an attachment site for the myocardium of the ventricles o Structurally and functionally separates the atria from the ventricles o Provides support for the valves Cardiac Cycle • Repeating pattern of the contraction and relaxation of the heart o Systole: contraction phase § Isovolumetric contraction phase and ejection phase o Diastole: relaxation phase § Isovolumetric relaxation phase, rapid filling phase and atrial contraction phase o Diastole and systole partitioned differently – diastole is longer • Occurs in both the atria and the ventricles • Ventricles are power pumps – generate force to push blood through circuits • Atria primary job is to fill up ventricles • Isovolumetric contraction: all valves are closed o Closed compartment with the ventricle contracting à pressure building up but volume stays the same o Atria relaxed, ventricles contract • Ventricular ejection: pressure in left ventricle > pressure in aorta à blood is pushed out of the ventricles of the heart à semilunar valves open o Atria relaxed, ventricles contract • Isovolumetric ventricular relaxation: all valves closed with entering diastole o Pressure in the atria > pressure in the ventricle à Atrioventricular valves open and the heart begins to fill – rapid ventricular filling o Atria and ventricles relaxed, Semilunar valves closed • Atrial contraction (atrial systole): delivers final amount of blood into the ventricles o Atria contract, ventricles relaxed • Atria are primer pumps but serve an important purpose the textbook overlooks • During systole there is a spike in pressure to eject the blood out o EDV (End Diastolic Volume): volume of the blood in the heart before it ejects o Stroke Volume: ejected out Electrical Activity of the Heart • Atria and ventricles are “electrically isolated” from each other by the fibrous skeleton of the heart o They can contract separately • Functional syncytium: o Gap junctions of intercalated discs electrically couple cardiac mycocytes o Automaticity § Automatic nature of the heartbeat § Due to autorhythmic cells that comprise the heart’s conduction system • Autorhythmic cells: non-‐contractile cardiac muscle cells o Pacemaker: right atrium, where the autorhythmic cells are found § Region where spontaneous electrical signal originates • Location of autorhythmic cells § Sinoatrial or SA node • Right atrium Pacemaker Potential: • Cells of SA node exhibit slow, spontaneous depolarization—called pacemaker potential • Result due to channels opening because of membrane events (hyperpolarization from previous AP) • Channel permits Na to flow into the cell, causes a depolarization event à funny current • Channels open because of the hyperpolarization of the previous action potential – not because of depolarizationà sodium channels • Diastolic depolarization: o At threshold, voltage-‐gated calcium channels open for depolarization with repolarization resulting from opening of voltage-‐gated potassium channels • Autonomic nervous system influences the rate: o Everything starts in the right atria – the SA node is under influence of parasympathetic and sympathetic o Parasympathetic decreases heart rate because receptors open up separate potassium channels à elongate pacemaker potential o Sympathetic releases epinephrine and norepinephrine which increases heart rate – causes an increase in cAMP in the cell § Pacemaker potential cells are called HCN channels § cAMP influences the HCN channels and shortens the pacemaker potential Myocardial Action Potential • In adjacent cardiac muscle cells in the myocardium, initiated by pacemaker cells to produce action potentials • Different from skeletal muscle: o Open up fast sodium channels which causes a spike o Open slow calcium channels and slow potassium channels à produces elongation aka plateau Conducting Tissue of the Heart • Action potentials from SA node spread at 0.8-‐1m/sec across atria • Conduction slows with AV node-‐delay • Conduction speeds increase with fastest in purkinje fibers – 5m/sec • Ventricular contraction begins ~ 0.1-‐0.2 seconds after atrial contraction Excitation-‐Contraction Coupling • Note, a calcium-‐induced calcium release is observed from the SR as seen in skeletal muscle, however excitation-‐contraction coupling is slower due to system not as efficient as in skeletal muscle • Calcium is lowered by calcium-‐ATPase pumps of SR and Na-‐Ca exchanger in plasma membrane • Unlike skeletal muscle and smooth muscle, cardiac muscle cannot sustain a contraction – contractions lasting about 300msec • Long absolute refractory period prevents summation of contraction, ensures rhythmic pumping of heart • Is summation important to the heart? o No, it is electrically coupled – the cardiac muscle cells are activated anyway by gap junctions o We don’t need summation because we have functional syncytium Blood Vessels • Conduits that form a network throughout body permitting distribution of blood to body tissues • Diverging: big vessels going to smaller ones • Converging: vessels coming together to get larger and larger • Muscular: deliver and control blood flow to organs o Large tunica media • Layers – TIME o Layers of a vessel deepest to the most superficial § Tunica interna § Tunica media § Tunica externa • Elastic: internal elastic lamina o Can enlarge and recoil back à smoothing effect • Capillaries: site of exchange o Endothelium with a basement membrane wrapping around them • Arterioles: adapted for vasoconstriction and vasodilation o Used for regulation o Respond to minute-‐to-‐minute changes o Regulation within the organ • Pressure within the venial side is less than on the arterial side Capillaries • Functional unit of cardiovascular system • Smallest blood vessels • Endothelium with basal membrane o Endothelium: simple squamous cells • Branch extensively o Metarteriole (arterial capillary): shunt between these branches • Well suited for function – exchange • Do not function independently but together as a group à referred to as a capillary bed o Allow blood to flow through it then close the blood supply off if it is not needed • Flow into capillary bed controlled by pre-‐capillary sphincter – contracts/relaxes in response to tissue needs o Observed to follow a cycle, contracting/relaxing at a rate of ~5-‐10 cycles/min – vasomotion Basic types of capillaries: • Continuous: (Least leaky) o Most common o Located in all vascularized tissue o All organs have these • Fenestrated: o Similar to continuous but contain pores or fenestrations covered by membrane (diaphragm) o Allows exchange and usually found where active absorption or filtration occur o Intestine, kidney, and endocrine organs • Sinusoids (discontinuous): most leaky o Highly modified, leaky capillaries restricted to certain organs o Suited for passage of large molecules and blood cells o Discontinuous basement membranes o Restricted to the liver, spleen and bone marrow Veins • Large lumens and thin walls • Accommodate large blood volume, thus referred to as capacitance vessels • Low pressure, so structural adaptations arose to ensure blood returns to heart: o Large diameter, low resistance o Venous valves – ensures unidirectional flow o Skeletal muscle pumps
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