Lecture 20, The Heart

MC

AT Prep. ExamLecture 20, The Heart

Lecturer: Dr. BarjisRoom P313Phone: (718) 260-5285E-Mail: [email protected]

Learning Objectives

• Describe the organization of the cardiovascular system.

• Describe the location and general features of the heart, including the pericardium.

• Discuss the differences between nodal cells and conducting cells and describe the components and functions of the conducting system of the heart.

• Identify the electrical events associated with a normal electrocardiogram.

Learning Objectives

• Explain the events of the cardiac cycle including atrial and ventricular systole and diastole, and relate the heart sounds to specific events in the cycle.

• Define cardiac output, heart rate and stroke volume and describe the factors that influence these variables.

• Explain how adjustments in stroke volume and cardiac output are coordinated at different levels of activity.

The cardiovascular system is divided into two circuits

• Pulmonary circuit • Delivers blood from the right ventricle of

the heart to the lungs and from the lungs to the left atrium of the heart

• System circuit • Delivers blood from the left ventricle of

the heart to the rest of the body and collects blood from the rest of the body and delivers it to the right atrium of the heart.

An Overview of the Cardiovascular System

• Pulmonary circuit:• Right ventricle Pulmonary Artery

Muscular Arteries Lungs (Arterioles Capillaries Venules) Medium Size Veins Pulmonary veins Left Atrium

• System circuit • Left Ventricle Aorta Muscular

Arteries Arterioles Capillaries Venules Medium Size Veins Superior and Inferior Vena Cava

Right Atrium

An Overview of the Cardiovascular System

• Blood flows through the blood vessels from the heart and back to the heart in the following order:• Elastic Arteries e.g. Aorta, pulmonary

artery• Muscular Arteries• Arterioles• Capillaries – the only vessels that allow

exchange• Venules• Medium Veins• Large Veins e.g. vena cava, pulmonary

vein

Blood Flow Through the Blood Vessels

• Visceral pericardium or epicardium • Parietal pericardium

• Pericardial fluid

Anatomy of the Heart

The pericardia

The Location of the Heart in the Thoracic Cavity

• The heart consists of four chambers• Two upper chamber called atria • Two lower chambers called ventricles

• The two upper and two lower chambers are separated by atrioventricular valve

Superficial Anatomy of the Heart

The Superficial Anatomy of the Heart

• The heart wall is composed of three layers:• Epicardium is primarily composed of

Areolar Tissue and epithelium • Myocardium is primarily composed of

cardiac muscle tissue• Endocardium is primarily composed of

Areolar Tissue and endothelium

The Heart Wall

• Right Atrium• Thin walled chambers that receive blood from

superior and inferior vena cava and pumps blood to the right ventricle

• Left Atrium• Thin walled chambers that receive blood from

pulmonary veins and pumps blood to left ventricle

• Right Ventricle• Thick walled chamber that receives blood from

right atrium and pumps blood to pulmonary artery.

• Left Ventricle • Thick walled chamber that receives blood from

left atrium and pumps blood to the Aorta.

Internal Anatomy and Organization

Internal Anatomy and Organization

• The two ventricles are separated from the atria by atrioventricular (AV) valves• Tricuspid valve separates right atrium from right

ventricle• Bicuspid valve separates left atrium from left

ventricle• Chordae tendineae

• Tendinous fibers attached to the cusps of AV valves

• It attaches the cusps of atrioventricular valves to papillary muscles

• It prevents the AV valve from reversing into the atria as papillary muscles contract

• Right atria –receives blood from superior and inferior vena cava and pumps it to the right ventricle through the tricuspid valve

• Right ventricle –receives blood from right atrium and pumps it toto the pulmonary artery through the pulmonary semilunar valve

• Pulmonary artery -delivers the blood to the lungs• At the lungs gas exchange occur

Blood flow through the heart

• Oxygen diffuses from the alveoli to the capillary and carbon dioxide diffuses from the capillary to the alveoli.


• Pulmonary Vein - after the gas exchange at the lungs pulmonary veins collect the blood and delivers them to the left atrium.

• Left atria – receives blood from pulmonary veins and pumps it to the left ventricle through the bicuspid valve

• Left ventricle- receives blood from the left atria and pumps it to the aorta through the aortic semilunar valve


• Aorta branches into smaller arteries and delivers the blood to the cells throughout the body.

• Gas exchange occur between the cell and the capillaries

• Oxygen diffuses from the capillaries to the cell and carbon dioxide diffuses from the cell to the capillaries.

• After the gas exchange the blood is delivered back to the heart by superior and inferior vena cava.

• Compared to the right ventricle the left ventricle is:• More muscular and has thicker wall• Develops higher pressure during contraction• Produces about 6 times more force during

contraction• Round in cross section

• Functions of valves• AV valves prevent backflow of blood from the

ventricles to the atria• Semilunar valves prevent backflow of blood from

the pulmonary trunk and aorta to the ventricles.

Structural Differences in heart chambers and valves

• Coronary arteries are the first blood vessels to branch from the aorta

• Coronary arteries supply blood to the heart and coronary veins collect the blood from the heart• Arteries include the right and left

coronary arteries, marginal arteries, anterior and posterior interventricular arteries, and the circumflex artery

• Veins include the great cardiac vein, anterior and posterior cardiac veins, the middle cardiac vein, and the small cardiac vein

Blood Supply to the Heart

Coronary Circulation

• Two classes of cardiac muscle cells• Specialized muscle cells of the

conducting system• Contractile cells

The Heartbeat

Cardiac Physiology

• The conducting system includes:• Sinoatrial (SA) node - Pacemaker cells

are located in the SA node• Atrioventricular (AV) node• AV bundle, • bundle branches, and • Purkinje fibers

The Conducting System

Animation: Heart flythrough (see tutorial)

• SA node begins the action potential• Stimulus spreads to the AV node• Impulse is delayed at AV node• Impulse then travels through ventricular

conducting cells• Then distributed by Purkinje fibers

Impulse Conduction through the heart

Impulse Conduction through the Heart

Animation: Cardiac Activity (see tutorial)

• ECG is a recording of the electrical events occurring during the cardiac cycle• The P wave of ECG indicates the depolarization of

the atriums• The QRS complex of ECG indicates the

depolarization of the ventricles• The T wave of ECG indicates ventricular

repolarization

• Analysis of ECG can reveal• Condition of conducting system• Effect of altered ion concentration• Size of ventricles• Position of the heart

The electrocardiogram (ECG)

An Electrocardiogram

• Resting membrane potential of approximately –90mV

• Action potential • Rapid depolarization• A plateau phase unique to cardiac

muscle• Calcium channels remain open longer than the sodium channels

• Repolarization• Refractory period follows the action

potential

Contractile Cells

The Action Potential in Skeletal and Cardiac Muscle

• The period between the start of one heartbeat and the beginning of the next

• During a cardiac cycle• Each heart chamber goes through

systole and diastole• Correct pressure relationships are

dependent on careful timing of contractions

The cardiac cycle

Animation: Intrinsic Conduction System (see tutorial)

• Auscultation – listening to heart sound via stethoscope

• Four heart sounds• S1 – “lubb” caused by the closing of the

AV valves• S2 – “dupp” caused by the closing of the

semilunar valves• S3 – a faint sound associated with blood

flowing into the ventricles• S4 – another faint sound associated with

atrial contraction

Heart sounds

Heart Sounds

• Stroke volume - is the volume of blood ejected with each ventricle contraction

• Cardiac output – is the amount of blood pumped by each ventricle in one minute• Cardiac output equals heart rate times

stroke volume

Cardiodynamics

Stroke Volume and Cardiac Output

Medulla Oblongata centers affect autonomic innervation

• Cardioacceleratory center activates sympathetic neurons

• Cardioinhibitory center controls parasympathetic neurons

• Medulla Oblongata centers receives input from higher centers, monitoring blood pressure and dissolved gas concentrations

Autonomic Innervation of the Heart

• Heart is innervated by sympathetic and parasympathetic nerves.• Sympathetic stimulation

• Positive inotropic effect• Releases NE

• Parasympathetic stimulation• Negative inotropic effect• Releases ACh

Autonomic Activity

Summary: Regulation of Heart Rate and Stroke Volume

• Sympathetic stimulation increases heart rate• Parasympathetic stimulation decreases heart rate• Circulating hormones, specifically E, NE, and T3,

accelerate heart rate• Increased venous return increases heart rate• EDV is determined by available filling time and

rate of venous return• ESV is determined by preload, degree of

contractility, and afterload

• Fluid connective tissue• Functions include

• Transporting dissolved gases, nutrients, hormones, and metabolic wastes

• Regulating pH and ion composition of interstitial fluids

• Restricting fluid loss at injury sites• Defending the body against toxins and

pathogens• Regulating body temperature by

absorbing and redistributing heat

Functions and Composition of Blood

Blood Composition

Blood

Plasma 46-63% Formed Elements 37-54%

Plasma Protein 7% Water 92% Other Solutes 1% Platelets RBC 99.9% WBC

Albumin

Fibrinogen

Globulin

Regulatory Proteins

Eg. Electrolytes

Monocytes

Basophils

Eosinophils

Neatrophils

Lymphocytes

The Composition of Whole Blood

The chief difference between plasma and interstitial fluid involves the concentration of dissolved oxygen and proteins.

The Composition of Whole Blood

• Process of blood cell formation• Hemocytoblasts are circulating stem cells

that divide to form all types of blood cells• Whole blood from anywhere in the body

has roughly the same temperature (38ºC), pH (7.4) and viscosity.• Bright red color if taken from artery• Dull red color if taken from vein

Hemopoiesis

• Accounts for 46-63% of blood volume• 92% of plasma is water• Higher concentration of dissolved

oxygen and dissolved proteins than interstitial fluid

Plasma

• more than 90% are synthesized in the liver• Albumins are the most abundant plasma

proteins• 60% of plasma proteins• Responsible for viscosity and osmotic

pressure of blood

Plasma proteins

• Globulins• ~35% of plasma proteins• Include immunoglobins which attack

foreign proteins and pathogens • Include transport globulins which bind

ions, hormones and other compounds• Fibrinogen

• Converted to fibrin during clotting• Are necessary for blood clotting

• Removal of fibrinogen leaves serum

Additional Plasma Proteins

• Erythrocytes (RBC) account for slightly less than half the blood volume, and 99.9% of the formed elements.

• Hematocrit measures the percentage of whole blood occupied by formed elements• Commonly referred to as the volume of

packed red cells

Red Blood Cells

Abundance of RBCs

• Molecules of hemoglobin account for 95% of the proteins in RBCs

• Hemoglobin is a globular protein, formed from two pairs of polypeptide subunits• Each subunit contains a molecule of

heme which reversibly binds an oxygen molecule

• Damaged or dead RBCs are recycled by phagocytes

Hemoglobin

The Structure of Hemoglobin

• Replaced at a rate of approximately 3 million new blood cells entering the circulation per second.

• Replaced before they hemolyze• Components of hemoglobin individually

recycled• Heme stripped of iron and converted to

biliverdin, then bilirubin• Iron is recycled by being stored in

phagocytes, or transported throughout the blood stream bound to transferrin

RBC life span and circulation

Red Blood Cell Turnover

• Erythropoeisis = the formation of new red blood cells

• Occurs in red bone marrow• Process speeds up with in the presence of

EPO (Erythropoeisis stimulating hormone)• RBCs pass through reticulocyte and

erythroblast stages

RBC Production

• Determined by the presence or absence of surface antigens (agglutinogens) • Antigens A, B and Rh (D)

• Rh factor was first described in Rhesus monkeys

• Antibodies in the plasma (agglutinins)• Cross-reactions occur when antigens meet

antibodies

Blood types

Blood Typing and Cross-Reactions

Blood Type Testing

Rh Factors and Pregnancy

Carbon Dioxide Transport in Blood

A Summary of the Primary Gas Transport Mechanisms

• Have nuclei and other organelles• Defend the body against pathogens • Remove toxins, wastes, and abnormal or

damaged cells• Are capable of amoeboid movement

(margination) and positive chemotaxis• Some are capable of phagocytosis

The White Blood Cells

Leukocytes

Granular and agranular

• Granular leukocytes• Neutrophils – 50 to 70 % total WBC

population• Eosinophils – phagocytes attracted

to foreign compounds that have reacted with antibodies

• Basophils – migrate to damaged tissue and release histamine and heparin

Types of WBC

• Agranular leukocytes• Agranular leukocytes are formed inred

bone marrow. • Agranular leukocytes include:

• Monocytes - become macrophage• Lymphocytes – includes T cells, B cells, and NK cells

Types of WBC

Figure 19.12

The Origins and Differentiation of Formed Elements

Animation: The origins and differentiation of blood cells (see tutorial)

• Flattened discs• Circulate for 9-12 days before being

removed by phagocytes

Platelets

• Transporting chemicals important to clotting

• Forming temporary patch in walls of damaged blood vessels• When platelets come into contact with

exposed collagen, they sense this as evidence of injury

• In response to injury they begin to aggregate. Or clump together

• Contracting after a clot has formed

Platelet functions

• Megakaryocytes release platelets into circulating blood

• Rate of platelet formation is stimulated by thrombopoietin, thrombocyte-stimulating factor, interleukin-6, and Multi-CSF

Platelet production (thrombocytopoiesis)

Blood Clotting

• As blood flows from the aorta toward the capillaries and from capillaries toward the vena cava:• Pressure decreases• Flow decreases• Resistance increases

Blood Flow Through the Blood Vessels

• Undergo changes in diameter in order to increase or decrease the size of the artery:• Vasoconstriction – decreases the size of

the lumen• Vasodilation – increases the size of the

lumen• Arteries include:

• Elastic -conducting• Muscular – distributes the blood• Arteriole - small arteries

Arteries

Histological Structure of Blood Vessels

• Capillaries form networks called capillary bed

• Blood flow through the capillary is regulated by pre-capillary sphincter.

• Capillaries allow exchange between interstitial fluid and blood by• Active transport• Passive transport

• Osmosis, • Diffusion, • Filtration,• Facilitated Transportation

Capillaries

• Capillaries have two basic structures• Continuous capillaries

• Have complete lining• Supply most region of body • Can be found in all tissues except epithelial and cartilage

• Fenestrated capilaries• Contain windows (pores) that span endothelial lining

• Permit rapid exchange of large solutes as large as peptide

• Flattened fenestrated capillaries = sinusoids

Capillaries

• Collect blood from all tissues and organs and return it to the heart

• Vein are classified according to their size into:• Venules• Medium-sized veins• Large veins

Veins

• Venules and medium-sized veins contain valves • Valves prevent backflow of blood

Venous Valves

• Circulatory pressure is divided into three components• Blood pressure (BP)• Capillary hydrostatic pressure (CHP)• Venous pressure

• Blood pressure is influenced by:• Weight of the person• Age of the person• Gender of the person• Time of the day

Cardiovascular Physiology

Circulatory Pressure

• Arterial blood pressure• Maintains blood flow through capillary

beds• Rises during ventricular systole and falls

during ventricular diastole• Pulse is a rhythmic pressure oscillation

that accompanies each heartbeat

Arterial blood pressure

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Lecture 20, The Heart