Lecturer: Dr. Barjis
Room P313
Phone: (718) 260-5285
E-Mail: ibarjis@citytech.cuny.edu
MCAT Prep. Exam
Lecture 20, The Heart
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 Flow Through the Blood Vessels
• 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
Anatomy of the Heart
The pericardia
• Visceral pericardium or epicardium
• Parietal pericardium
• Pericardial fluid
The Location of the Heart in the Thoracic Cavity
Superficial Anatomy of the Heart
• 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
The Superficial Anatomy of the Heart
The Heart Wall
• 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
Internal Anatomy and Organization
• 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
• 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
Blood flow through the heart
• 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
• Oxygen diffuses from the alveoli
to the capillary and carbon
dioxide diffuses from the
capillary to the alveoli.
Blood flow through the heart
• 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
Blood flow through the heart
• 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.
Structural Differences in heart chambers and valves
• 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.
Blood Supply to the Heart
• 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
Coronary Circulation
The Heartbeat
Cardiac Physiology
• Two classes of cardiac muscle cells
• Specialized muscle cells of the conducting
system
• Contractile cells
The Conducting System
• 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
Animation: Heart flythrough (see tutorial)
Impulse Conduction through the heart
• 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
Animation: Cardiac Activity (see tutorial)
The electrocardiogram (ECG)
• 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
An Electrocardiogram
Contractile Cells
• 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
The Action Potential in Skeletal and Cardiac
Muscle
The cardiac cycle
• 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
Animation: Intrinsic Conduction System (see tutorial)
Heart sounds
• 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
Cardiodynamics
Stroke Volume and Cardiac Output
• 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
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
Autonomic Activity
• Heart is innervated by sympathetic and
parasympathetic nerves.
• Sympathetic stimulation
• Positive inotropic effect
• Releases NE
• Parasympathetic stimulation
• Negative inotropic effect
• Releases ACh
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
Functions and Composition of Blood
• 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
Blood Composition
Blood
Plasma 46-63%
Plasma Protein 7%
Water 92%
Formed Elements 37-54%
Other Solutes 1%
Albumin
Globulin
Fibrinogen
Regulatory Proteins
Platelets
WBC
RBC 99.9%
Monocytes
Eg. Electrolytes
Neatrophils
Basophils
Lymphocytes
Eosinophils
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
Hemopoiesis
• 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
Plasma
• Accounts for 46-63% of blood volume
• 92% of plasma is water
• Higher concentration of dissolved oxygen and
dissolved proteins than interstitial fluid
Plasma proteins
• 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
Additional 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
Red Blood Cells
Abundance of RBCs
• 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
Hemoglobin
• 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
The Structure of Hemoglobin
RBC life span and circulation
• 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
Red Blood Cell Turnover
RBC Production
• 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
Blood types
• 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 Typing and Cross-Reactions
Blood Type Testing
Rh Factors and Pregnancy
Carbon Dioxide Transport in Blood
A Summary of the Primary Gas Transport
Mechanisms
The White Blood Cells
Leukocytes
• 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
Types of WBC
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
The Origins and Differentiation of Formed
Elements
Animation: The origins and differentiation of blood cells (see tutorial)
Figure 19.12
Platelets
• Flattened discs
• Circulate for 9-12 days before being removed by
phagocytes
Platelet functions
• 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 production (thrombocytopoiesis)
• Megakaryocytes release platelets into circulating
blood
• Rate of platelet formation is stimulated by
thrombopoietin, thrombocyte-stimulating factor,
interleukin-6, and Multi-CSF
Blood Clotting
Blood Flow Through the Blood Vessels
• As blood flows from the aorta toward the
capillaries and from capillaries toward the vena
cava:
• Pressure decreases
• Flow decreases
• Resistance increases
Arteries
• 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
Histological Structure of Blood Vessels
Capillaries
• 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
Veins
• 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
Venous Valves
• Venules and medium-sized veins contain valves
• Valves prevent backflow of blood
Cardiovascular Physiology
Circulatory Pressure
• 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
Arterial blood 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