Circulatory System Chapter 13 Chapter 13 Outline Functions and Components of the Circulatory System Composition of Blood Structure of the Heart Cardiac Cycle and Heart Sounds Electrical Activity of the Heart and the ECG Blood Vessels Atherosclerosis and Cardiac Arrhythmias Lymphatic System Functions and Components of the Circulatory System 1
Functions of Circulatory System Transportation of respiratory gases Delivery of nutrients and hormones Waste removal Temperature regulation Clotting Immune function Components of Circulatory System Include cardiovascular and lymphatic systems Heart pumps blood thru cardiovascular system Blood vessels carry blood from heart to cells and back Includes arteries, arterioles, capillaries, venules, veins Lymphatic system picks up excess fluid filtered out in capillary beds and returns it to veins Its lymph nodes are part of immune system Composition of the Blood 2
Composition of Blood Consists of formed elements (cells) suspended and carried in plasma (fluid part) When centrifuged, blood separates into heavier formed elements on bottom and plasma on top Composition of Blood Total blood volume is about 5L Plasma is straw-colored liquid consisting of H 2 O and dissolved solutes Includes ions, metabolites, hormones, antibodies Red blood cells (RBCs) comprise most of formed elements % of RBCs in centrifuged blood sample = hematocrit Hematocrit is 36-46% in women; 41-53% in men RBC Antigens and Blood Typing Antigens present on RBC surface specify blood type Major antigen group is ABO system Type A blood has only A antigens Type B has only B antigens Type AB has both A and B antigens Type AB has both A and B antigens Type O has neither A or B antigens 3
Transfusion Reactions People with Type A blood make antibodies to Type B RBCs, but not to Type A Type B blood has antibodies to Type A RBCs but not to Type B Type AB blood doesn t have antibodies to A or B Type O has antibodies to both Type A and B If incompatible blood types are mixed, antibodies will cause mixture to agglutinate If blood types incompatible, recipient s antibodies agglutinate donor s RBCs Type O is universal donor because lacks A and B antigens Recipient s p antibodies won t agglutinate donor s Type O RBCs Type AB is universal recipient because doesn t make anti-a or anti-b antibodies Won t agglutinate donor s RBCs Transfusion Reactions Rh Factor Is another type of antigen found on RBCs Rh+ has Rho(D) antigens; Rh- does not Can cause problems when Rh- mother has Rh+ babies At birth, mother may be exposed to Rh+ blood of fetus In later pregnancies mom produces Rh antibodies In Erythroblastosis fetalis, Rh antibodies from mom cross placenta and combine with Rh+antigens on fetal blood cells causing hemolysis of fetal RBCs 4
Structure of the Heart Structure of Heart Heart has 4 chambers 2 atria receive blood from venous system 2 ventricles pump blood to arteries 2 sides of heart are 2 pumps separated by muscular septum Cardiac Cycle and Heart Sounds 5
Heart Valves Cardiac Cycle Cardiac Cycle Is repeating pattern of contraction and relaxation of heart Systole refers to contraction phase Diastole refers to relaxation phase Both atria contract simultaneously; ventricles follow 0.1-0.2 sec later 6
Cardiac Cycle End-diastolic volume is volume of blood in ventricles at end of diastole Stroke volume is amount of blood ejected from ventricles during systole End-systolic volume is amount of blood left in ventricles at end of systole 7
Electrical Activity of Heart and the ECG SA Node Pacemaker In normal heart, SA node functions as pacemaker Depolarizes spontaneously to threshold (= pacemaker potential) Membrane voltage begins at -60mV and gradually depolarizes to -40 threshold Spontaneous depolarization is caused by Na + flowing through channel that opens when hyperpolarized (HCN channel) At threshold V-gated Ca 2+ channels open, creating upstroke and contraction Repolarization is via opening of V-gated K + channels SA Node Pacemaker 8
Myocardial Action Potentials Myocardial cells have RMP of 90 mv Depolarized to threshold by action potentials originating in SA node Upstroke occurs as V-gated Na + channels open MP rapidly declines to 15mV and stays there for 200-300 msec (plateau phase) Plateau results from balance between slow Ca 2+ influx and K + efflux Repolarization due to opening of extra K + channels Myocardial APs Refractory Periods Heart s Act. Pot. lasts about 250 msec Has refractory periods almost as long as Act. Pot. Cannot be stimulated to contract again until has relaxed 9
Electrocardiogram (ECG/EKG) Is a recording of electrical activity of heart conducted thru ions in body to surface Types of ECG Recordings Bipolar leads record voltage between electrodes placed on wrists and legs (right leg is ground) Lead I records between right arm and left arm Lead II: right arm and left leg Lead III: left arm and left leg Types of ECG Recordings Unipolar leads record voltage between a single electrode placed on body and ground built into ECG machine Limb leads go on right arm (AVR), left arm (AVL), and left leg (AVF) The 6 chest leads, placed as shown, allow certain abnormalities to be detected 10
ECG Correlation of ECG with Heart Sounds 1st heart sound (lub) comes immediately after QRS wave as AV valves close 2nd heart sound (dub) comes as T wave begins and semilunar valves close Blood Vessels 11
Arteries Small arteries and arterioles are muscular Provide most resistance in circulatory system Arterioles cause greatest pressure drop Mostly connect to capillary beds Some connect directly to veins to form arteriovenous anastomoses Capillaries Provide extensive surface area for exchange Blood flow through a capillary bed is determined by state of precapillary sphincters of arteriole supplying it Types of Capillaries In continuous capillaries, endothelial cells are tightly joined together Have narrow intercellular channels that permit exchange of molecules smaller than proteins Present in muscle, lungs, adipose tissue Fenestrated capillaries have wide intercellular pores Very permeable Present in kidneys, endocrine glands, intestines. Discontinuous capillaries have large gaps in endothelium Are large and leaky Present in liver, spleen, bone marrow 12
Veins Contain majority of blood in circulatory system Very compliant (expand readily) Contain very low pressure (about 2mm Hg) Insufficient to return blood to heart Blood is moved toward heart by contraction of surrounding skeletal muscles (skeletal muscle pump) And pressure drops in chest during breathing 1-way venous valves ensure blood moves only toward heart Veins Lymphatic System 13
Lymphatic System Has 3 basic functions: Transports interstitial fluid (lymph) back to blood Transports absorbed fat from small intestine to blood Helps provide immunological defenses against pathogens Lymphatic System Lymphatic capillaries are closed-end tubes that form vast networks in intercellular spaces Very porous, absorb proteins, microorganisms, fat Lymphatic System Lymph is carried from lymph capillaries to lymph ducts to lymph nodes 14
Lymph nodes filter lymph before returning it to R. & L. subclavian veins via thoracic duct or right lymphatic duct Nodes make lymphocytes and contain phagocytic cells that remove pathogens Lymphocytes also made in tonsils, spleen, thymus Lymphatic System 15