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Chapter 13. Blood, Heart and Circulation. 13-1. Chapter 13 Outline Overview Blood Pulmonary and Systemic Circulations Heart Valves Cardiac Cycle Electrical Activity of the Heart Structure of Blood Vessels Heart Disease Lymphatic System. 13-2. Overview. 13-3.

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Chapter 13

Blood, Heart

and Circulation


Chapter 13 Outline

  • Overview

  • Blood

  • Pulmonary and Systemic Circulations

  • Heart Valves

  • Cardiac Cycle

  • Electrical Activity of the Heart

  • Structure of Blood Vessels

  • Heart Disease

  • Lymphatic System


Functions of circulatory system
Functions of Circulatory System

  • Plays roles in transportation of respiratory gases, delivery of nutrients and hormones, and waste removal

    • And in temperature regulation, clotting, and immune function


Components of circulatory system
Components of Circulatory System

  • Include cardiovascular and lymphaticsystems

    • 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 blood
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 blood1
Composition of Blood

  • Total blood volume is about 5L

  • Plasma is straw-colored liquid consisting of H2O 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


Plasma proteins
Plasma Proteins

  • Constitute 7-9% of plasma

  • 3 types of plasma proteins: albumins, globulins, and fibrinogen

    • Albumin accounts for 60-80%

      • Creates colloid osmotic pressure that draws H2O from interstitial fluid into capillaries to maintain blood volume and pressure

  • Globulins carry lipids

    • Gamma globulins are antibodies

  • Fibrinogen serves as clotting factor

    • Converted to fibrin

    • Serum is fluid left when blood clots


Formed elements
Formed Elements

  • Are erythrocytes (RBCs) and leukocytes (WBCs)

  • RBCs are flattened biconcave discs

    • Shape provides increased surface area for diffusion

    • Lack nuclei and mitochondria

    • Each RBC contains 280 million hemoglobins

    • About 300 billion RBCs are produced each day



  • Have a nucleus, mitochondria, and amoeboid ability

  • Can squeeze through capillary walls (diapedesis)

    • Granular leukocytes help detoxify foreign substances and release heparin

      • Include eosinophils, basophils, and neutrophils


Leukocytes continued
Leukocytes continued

  • Agranular leukocytes are phagocytic and produce antibodies

    • Include lymphocytes and monocytes


Platelets thrombocytes
Platelets (thrombocytes)

  • Are smallest of formed elements, lack nucleus

  • Are amoeboid fragments of megakaryocytes from bone marrow

  • Constitute most of mass of blood clots

  • Release serotonin to vasoconstrict and reduce blood flow to clot area

  • Secrete growth factors to maintain integrity of blood vessel wall

  • Survive 5-9 days



  • Is formation of blood cells from stem cells in bone marrow (myeloid tissue) and lymphoid tissue

    • Marrow produces about 500 billion blood cells/day

    • In fetus occurs in liver


Hematopoiesis continued
Hematopoiesis continued

  • Erythropoiesis is formation of RBCs

    • Stimulated by erythropoietin (EPO) from kidney

  • Leukopoiesis is formation of WBCs

    • Stimulated by variety of cytokines

      • = autocrine regulators secreted by immune system



  • 2.5 million RBCs are produced/sec

  • Lifespan of 120 days

  • Old RBCs removed from blood by phagocytic cells in liver, spleen, and bone marrow

    • Iron recycled back into hemoglobin production


Rbc antigens and blood typing
RBC Antigens and Blood Typing

  • Antigens present on RBC surface specify blood type

  • Major antigen group is ABOsystem

    • Type A blood has only A antigens

    • Type B has only B antigens

    • Type AB has both A and B antigens

    • Type O has neither A or B antigens


Transfusion reactions
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 different blood types are mixed, antibodies will cause mixture to agglutinate


Transfusion reactions continued
Transfusion Reactions continued

  • If blood types don't match, recipient’s antibodies agglutinate donor’s RBCs

  • Type O is “universal donor” because lacks A and B antigens

    • Recipient’s 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


Rh factor
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 may produce Rh antibodies

      • In Erythroblastosis fetalis, this happens and antibodies cross placenta causing hemolysis of fetal RBCs



  • Is cessation of bleeding

  • Promoted by reactions initiated by vessel injury:

    • Vasoconstriction restricts blood flow to area

    • Platelet plug forms

      • Plug and surroundings are infiltrated by web of fibrin, forming clot


Role of platelets
Role of Platelets

  • Platelets don't stick to intact endothelium because of presence of prostacyclin (PGI2--a prostaglandin) and NO

    • Keep clots from forming and are vasodilators


Role of platelets1
Role of Platelets

  • Damage to endothelium allows platelets to bind to exposed collagen

    • von Willebrand factor increases bond by binding to both collagen and platelets

    • Platelets stick to collagen and release ADP, serotonin, and thromboxane A2

      • = platelet release reaction


Role of platelets continued
Role of Platelets continued

  • Serotonin and thromboxane A2 stimulate vasoconstriction, reducing blood flow to wound

  • ADP and thromboxane A2 cause other platelets to become sticky and attach and undergo platelet release reaction

    • This continues until platelet plug is formed


Role of fibrin
Role of Fibrin

  • Platelet plug becomes infiltrated by meshwork of fibrin

  • Clot now contains platelets, fibrin and trapped RBCs

    • Platelet plug undergoes plug contraction to form more compact plug


Conversion of fibrinogen to fibrin
Conversion of Fibrinogen to Fibrin

  • Can occur via 2 pathways:

    • Intrinsic pathway clots damaged vessels and blood left in test tube

      • Initiated by exposure of blood to negatively charged surface of glass or blood vessel collagen

        • This activates factor XII (a protease) which initiates a series of clotting factors

        • Ca2+ and phospholipids convert prothrombin to thrombin

          • Thrombin converts fibrinogen to fibrin which polymerizes to form a mesh

    • Damage outside blood vessels releases tissuethromboplastin that triggers a clotting shortcut (= extrinsic pathway)


Dissolution of clots
Dissolution of Clots

  • When damage is repaired, activated factor XII causes activation of kallikrein

    • Kallikrein converts plasminogen to plasmin

      • Plasmin digests fibrin, dissolving clot



  • Clotting can be prevented by Ca+2 chelators (e.g. sodium citrate or EDTA)

    • or heparin which activates antithrombin III (blocks thrombin)

  • Coumarin blocks clotting by inhibiting activation of Vit K

    • Vit K works indirectly by reducing Ca+2 availability


Structure of 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


Structure of heart continued
Structure of Heart continued

  • Between atria and ventricles is layer of dense connective tissue called fibrous skeleton

    • Which structurally and functionally separates the two

      • Myocardial cells of atria attach to top of fibrous skeleton and form 1 unit (or myocardium)

      • Cells from ventricles attach to bottom and form another unit

    • Fibrous skeleton also forms rings, the annuli fibrosi, to hold heart valves


Pulmonary and systemic circulations1
Pulmonary and Systemic Circulations

  • Blood coming from tissues enters superior and inferior vena cavae which empties into right atrium, then goes to right ventricle which pumps it through pulmonary arteries to lungs


Pulmonary and systemic circulations continued
Pulmonary and Systemic Circulations continued

  • Oxygenated blood from lungs passes thru pulmonary veins to left atrium, then to left ventricle which pumps it through aorta to body


Pulmonary and systemic circulations continued1
Pulmonary and Systemic Circulations continued

  • Pulmonary circulation is path of blood from right ventricle through lungs and back to heart

  • Systemic circulation is path of blood from left ventricle to body and back to heart

  • Rate of flow through systemic circulation = flow rate thru pulmonary circuit


Pulmonary and systemic circulations continued2
Pulmonary and Systemic Circulations continued

  • Resistance in systemic circuit > pulmonary

    • Work done by left ventricle pumping to systemic is 5-7X greater

      • Makes left ventricle more muscular (and 3-4X thicker)


Atrioventricular valves
Atrioventricular Valves

  • Blood flows from atria into ventricles thru 1-way atrioventricular (AV) valves

    • Between right atrium and ventricle is tricuspid valve

    • Between left atrium and ventricle is bicuspid or mitral valve


Atrioventricular valves continued
Atrioventricular Valves continued

  • Opening and closing of valves results from pressure differences

    • High pressure of ventricular contraction is prevented from everting AV valves by contraction of papillary muscles which are connected to AVs by chorda tendinea


Semilunar valves
Semilunar Valves

  • During ventricular contraction blood is pumped through aortic and pulmonary semilunar valves

    • Close during relaxation


Cardiac cycle1
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


Cardiac cycle2
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


Cardiac cycle continued
Cardiac Cycle continued

  • As ventricles contract, pressure rises, closing AV valves

    • Called isovolumetric contraction because all valves are closed

  • When pressure in ventricles exceeds that in aorta, semilunar valves open and ejection begins

  • As pressure in ventricle falls below that in aorta, back pressure closes semilunars

  • All valves are closed and ventricles undergo isovolumetricrelaxation

  • When pressure in ventricles falls below atria, AVs open and ventricles fill

  • Atrial systole sends its blood into ventricles


Heart sounds
Heart Sounds

  • Closing of AV and semilunar valves produces sounds that can be heard thru stethoscope

    • Lub (1st sound) produced by closing of AV valves

    • Dub (2nd sound) produced by closing of semilunars


Heart murmurs
Heart Murmurs

  • Are abnormal sounds produced by abnormal patterns of blood flow in heart

  • Many caused by defective heart valves

    • Can be of congenital origin

    • In rheumatic fever, damage can be from antibodies made in response to strep infection


Heart murmurs continued
Heart Murmurs continued

  • In mitral stenosis, mitral valve becomes thickened and calcified, impairing blood flow from left atrium to left ventricle

    • Accumulation of blood in left ventricle can cause pulmonary hypertension

  • Valves are incompetent when don't close properly

    • Can be from damage to papillary muscles


Heart murmurs continued1
Heart Murmurs continued

  • Murmurs caused by septal defects are usually congenital

    • Due to holes in septum between left and right sides of heart

    • Pressure causes blood to pass from left to right


Electrical activity of heart1
Electrical Activity of Heart

  • Myocardial cells are short, branched, and interconnected by gap junctions

  • Entire muscle that forms a chamber is called a myocardium or functional syncytium

    • Because APs originating in any cell are transmitted to all others

    • Chambers separated by nonconductive tissue


Sa node pacemaker
SA Node Pacemaker

  • In normal heart, SA node functions as pacemaker

    • Depolarizes spontaneously to threshold (= pacemaker potential)


Sa node pacemaker continued
SA Node Pacemaker continued

  • 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 Ca2+ channels open, creating upstroke and contraction

  • Repolarization is via opening of V-gated K+ channels


Ectopic pacemakers
Ectopic Pacemakers

  • Other tissues in heart are spontaneously active

    • But are slower than SA node

    • Are stimulated to produce APs by SA node before spontaneously depolarize to threshold

    • If APs from SA node are prevented from reaching these, they will generate pacemaker potentials


Myocardial aps
Myocardial APs

  • Myocardial cells have RMP of –90 mV

  • Depolarized to threshold by APs originating in SA node


Myocardial aps continued
Myocardial APs continued

  • 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 Ca2+ influx and K+ efflux

  • Repolarization due to opening of extra K+ channels


Conducting tissues of heart
Conducting Tissues of Heart

  • APs from SA node spread through atrial myocardium via gap junctions

  • But need special pathway to ventricles because of non-conducting fibrous tissue

    • AV node at base of right atrium and bundle of His conduct APs to ventricles

Insert Fig 13.20


Conducting tissues of heart continued
Conducting Tissues of Heart continued

  • In septum of ventricles, His divides into right and left bundle branches

    • Which give rise to Purkinje fibers in walls of ventricles

      • These stimulate contraction of ventricles


Conduction of aps
Conduction of APs

  • APs from SA node spread at rate of 0.8 -1 m/sec

  • Time delay occurs as APs pass through AV node

    • Has slow conduction of 0.03– 0.05 m/sec

  • AP speed increases in Purkinje fibers to 5 m/sec

    • Ventricular contraction begins 0.1–0.2 sec after contraction of atria


Excitation contraction coupling
Excitation-Contraction Coupling

  • Depolarization of myocardial cells opens V-gated Ca2+ channels in sarcolemma

    • This depolarization opens V-gated and Ca2+ release channels in SR (calcium-induced-calcium-release)

    • Ca2+ binds to troponin and stimulates contraction (as in skeletal muscle)

    • During repolarization Ca2+ pumped out of cell and into SR


Refractory periods
Refractory Periods

  • Heart contracts as syncytium and thus cannot sustain force

  • Its AP lasts about 250 msec

  • Has a refractory period almost as long as AP

  • Cannot be stimulated to contract again until has relaxed


Electrocardiogram ecg ekg
Electrocardiogram (ECG/EKG)

  • Is a recording of electrical activity of heart conducted thru ions in body to surface


Types of ecg recordings
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 continued
Types of ECG Recordings continued

  • 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



  • 3 distinct waves are produced during cardiac cycle

  • P wave caused by atrial depolarization



  • QRS complex is caused by ventricular depolarization

  • T wave results from ventricular repolarization


Correlation of ecg with heart sounds
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


Structure of blood vessels1
Structure of Blood Vessels

  • Innermost layer of all vessels is the endothelium

  • Capillaries are made of only endothelial cells

  • Arteries and veins have 3 layers called tunicaexterna, media, and interna

    • Externa is connective tissue

    • Media is mostly smooth muscle

    • Interna is made of endothelium, basement membrane, and elastin

  • Although have same basic elements, arteries and veins are quite different



  • Large arteries are muscular and elastic

    • Contain lots of elastin

    • Expand during systole and recoil during diastole

      • Helps maintain smooth blood flow during diastole



  • 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



  • 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
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



  • 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



  • Is most common form of arteriosclerosis (hardening of arteries)

    • Accounts for 50% of deaths in US

  • Localized plaques (atheromas) reduce flow in an artery

    • And act as sites for thrombus (blood clots)



  • Plaques begin at sites of damage to endothelium

    • E.g. from hypertension, smoking, high cholesterol, or diabetes



  • Plaques begin at sites of damage to endothelium

    • E.g. from hypertension, smoking, high cholesterol, or diabetes


Cholesterol and plasma lipoproteins
Cholesterol and Plasma Lipoproteins

  • High blood cholesterol is associated with risk of atherosclerosis

  • Lipids, including cholesterol, are carried in blood attached to LDLs (low-density lipoproteins) and HDLs (high-density lipoproteins)


Cholesterol and plasma lipoproteins1
Cholesterol and Plasma Lipoproteins

  • LDLs and HDLs are produced in liver and taken into cells by receptor-mediated endocytosis

    • In cells LDL is oxidized

      • Oxidized LDL can injure endothelial cells facilitating plaque formation

    • Arteries have receptors for LDL but not HDL

      • Which is why HDL isn't atherosclerotic


Ischemic heart disease
Ischemic Heart Disease

  • Is most commonly due to atherosclerosis in coronary arteries

  • Ischemia occurs when blood supply to tissue is deficient

    • Causes increased lactic acid from anaerobic metabolism

  • Often accompanied by angina pectoris (chest pain)


Ischemic heart disease continued
Ischemic Heart Disease continued

  • Detectable by changes in S-T segment of ECG


Ischemic heart disease continued1
Ischemic Heart Disease continued

  • Myocardial infarction (MI) is a heart attack

    • Usually caused by occlusion of a coronary artery

      • Causing heart muscle to die

      • Diagnosed by high levels of creatine phosphokinase (CPK) and lactate dehydrogenase (LDH)

        • And presence of plasma troponin T and I from damaged muscle

      • Dead cells are replaced by noncontractile scar tissue


Arrhythmias detected on ecg
Arrhythmias Detected on ECG

  • Arrhythmias are abnormal heart rhythms

  • Heart rate <60/min is bradycardia; >100/min is tachycardia


Arrhythmias detected on ecg continued
Arrhythmias Detected on ECG continued

  • In flutter, contraction rates can be 200-300/min

  • In fibrillation, contraction of myocardial cells is uncoordinated and pumping ineffective

    • Ventricular fibrillation is life-threatening

      • Electrical defibrillation resynchronizes heart by depolarizing all cells at same time


Arrhythmias detected on ecg continued1
Arrhythmias Detected on ECG continued

  • AV node block occurs when node is damaged

  • First–degree AV node block is when conduction through AV node > 0.2 sec

    • Causes long P-R interval

  • Second-degree AV node block is when only 1 out of 2-4 atrial APs can pass to ventricles

    • Causes P waves with no QRS

  • In third-degree or complete AV node block no atrial activity passes to ventricles

    • Ventricles are driven slowly by bundle of His or Purkinjes


Arrhythmias detected on ecg continued2
Arrhythmias Detected on ECG continued

  • In third-degree or complete AV node block, no atrial activity passes to ventricles

    • Ventricles are driven slowly by bundle of His or Purkinjes


Lymphatic system1
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 continued
Lymphatic System continued

  • Lymphatic capillaries are closed-end tubes that form vast networks in intercellular spaces

    • Very porous, absorb proteins, microorganisms, fat


Lymphatic system continued1
Lymphatic System continued

  • Lymph is carried from lymph capillaries to lymph ducts to lymph nodes


Lymphatic system continued2
Lymphatic System continued

  • Lymph nodes filter lymph before returning it to 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