Chapter 20
The Cardiovascular System: The Heart
Heart pumps over 1 million gallons per year
Over 60,000 miles of blood vessels
Heart Location
Heart is located in the mediastinum
area from the sternum to the
vertebral column and between the lungs
Heart Orientation
Apex - directed anteriorly,
inferiorly and to the left
Base - directed posteriorly,
superiorly and to the right
Anterior surface - deep to the sternum and ribs
Inferior surface - rests on the diaphragm
Right border - faces right lung
Left border (pulmonary border) - faces left lung
Heart Orientation
Heart has 2 surfaces: anterior and inferior, and 2 borders: right and left
Surface Projection of the Heart
Superior right point at the superior border of the 3rd
right costal cartilage
Inferior left point at the 5th intercostal space, 9 cm from the midline
Inferior right point at superior border of the 6th
right costal cartilage, 3 cm from the midline
Pericardium
Fibrous pericardium
dense irregular CT
protects and anchors the heart,
prevents overstretching
Serous pericardium
thin delicate membrane
contains
parietal layer-outer layer
pericardial cavity with pericardial
fluid
visceral layer (epicardium)
Layers of Heart Wall
Epicardium
visceral layer of serous
pericardium
Myocardium
cardiac
muscle layer is the bulk of the heart
Endocardium
chamber lining & valves
Muscle Bundles of the Myocardium
Cardiac muscle fibers swirl diagonally around the heart in
interlacing bundles
Chambers and Sulci of the Heart
Four chambers
2 upper atria
2 lower ventricles
Sulci - grooves on surface of
heart containing coronary blood vessels and fat
coronary sulcus
encircles
heart and marks the boundary between the atria and the ventricles
anterior interventricular
sulcus
marks the boundary between the
ventricles anteriorly
posterior interventricular
sulcus
marks the boundary between the
ventricles posteriorly
Chambers and Sulci
Chambers and Sulci
Right Atrium
Receives blood from 3 sources
superior vena cava, inferior vena
cava and coronary sinus
Interatrial septum partitions the
atria
Fossa ovalis
is a remnant of the fetal foramen ovale
Tricuspid valve
Blood flows through into right ventricle
has three cusps composed of dense
CT covered by endocardium
Right Ventricle
Forms most of anterior surface of heart
Papillary muscles are cone shaped trabeculae
carneae (raised bundles of cardiac muscle)
Chordae tendineae:
cords between valve cusps and papillary muscles
Interventricular septum:
partitions ventricles
Pulmonary semilunar valve: blood
flows into pulmonary trunk
Left Atrium
Forms most of the base of the heart
Receives blood from lungs - 4 pulmonary veins (2 right + 2
left)
Bicuspid valve: blood passes through into left ventricle
has
two cusps
to remember names of this valve,
try the pneumonic LAMB
Left Atrioventricular, Mitral, or Bicuspid valve
Left Ventricle
Forms the apex of heart
Chordae tendineae
anchor bicuspid valve to papillary muscles (also has trabeculae
carneae like right ventricle)
Aortic semilunar valve:
blood passes through valve into the
ascending aorta
just above valve are the openings
to the coronary arteries
Myocardial Thickness and Function
Thickness of myocardium varies according to the function of
the chamber
Atria are thin walled, deliver blood to adjacent ventricles
Thickness of Cardiac Walls
Fibrous Skeleton of Heart
Support structure for heart valves
Insertion point for cardiac muscle bundles
Electrical insulator between atria and ventricles
prevents direct propagation of AP’s
to ventricles
Atrioventricular Valves Open
A-V valves open and allow blood to flow from atria into
ventricles when ventricular pressure is lower than atrial
pressure
occurs when ventricles are relaxed,
chordae tendineae are slack
and papillary muscles are relaxed
Atrioventricular Valves Close
A-V valves close preventing backflow of blood into atria
occurs when ventricles contract,
pushing valve cusps closed, chordae tendinae are pulled taut and papillary muscles contract to
pull cords and prevent cusps from everting
Semilunar Valves
SL valves open with ventricular contraction
allow blood to flow into pulmonary
trunk and aorta
SL valves close with ventricular relaxation
prevents blood from returning to
ventricles, blood fills valve cusps, tightly closing the SL valves
Valve Function Review
Valve Function Review
Blood Circulation
Two closed circuits, the systemic and pulmonic
Systemic circulation
left side of heart pumps blood
through body
left ventricle pumps oxygenated
blood into aorta
aorta branches into many arteries
that travel to organs
arteries branch into many
arterioles in tissue
arterioles branch into thin-walled
capillaries for exchange of gases and nutrients
deoxygenated blood begins its
return in venules
venules
merge into veins and return to right atrium
Blood Circulation (cont.)
Pulmonary circulation
right
side of heart pumps deoxygenated blood to lungs
right ventricle pumps blood to
pulmonary trunk
pulmonary trunk branches into
pulmonary arteries
pulmonary
arteries carry blood to lungs for exchange of gases
oxygenated blood returns to heart
in pulmonary veins
Blood Circulation
Blood flow
blue = deoxygenated
red = oxygenated
Coronary Circulation
Coronary circulation is blood supply to the heart
Heart as a very active muscle needs lots of O2
When the heart relaxes high pressure of blood in aorta
pushes blood into coronary vessels
Many anastomoses
connections between arteries
supplying blood to the same region, provide alternate routes if one artery
becomes occluded
Coronary Arteries
Branches off aorta above aortic semilunar
valve
Left coronary artery
circumflex branch
in coronary sulcus,
supplies left atrium and left ventricle
anterior interventricular
art.
supplies both ventricles
Right coronary artery
marginal branch
in coronary sulcus,
supplies right ventricle
posterior interventricular
art.
supplies both ventricles
Coronary Veins
Collects wastes from cardiac muscle
Drains into a large sinus on posterior surface of heart
called the coronary sinus
Coronary sinus empties into right atrium
Cardiac Muscle Histology
Branching, intercalated discs with gap junctions,
involuntary, striated, single central nucleus per cell
Cardiac Myofibril
Conduction System of Heart
Conduction System of Heart
Autorhythmic Cells
Cells fire spontaneously, act as pacemaker and form
conduction system for the heart
SA node
cluster of cells in wall of Rt.
Atria
begins heart activity that spreads
to both atria
excitation spreads to AV node
AV node
in atrial
septum, transmits signal to bundle of His
AV bundle of His
the connection between atria and
ventricles
divides into bundle branches & purkinje fibers, large diameter fibers that conduct signals
quickly
Rhythm of Conduction System
SA node fires spontaneously 90-100 times per minute
AV node fires at 40-50 times per minute
If both nodes are suppressed fibers in ventricles by
themselves fire only 20-40 times per minute
Artificial pacemaker needed if pace is too slow
Extra beats forming at other sites are called ectopic pacemakers
caffeine & nicotine increase
activity
Timing of Atrial &
Ventricular Excitation
SA node setting pace since is the fastest
In 50 msec excitation spreads
through both atria and down to AV node
100 msec delay
at AV node due to smaller diameter fibers- allows atria to fully contract
filling ventricles before ventricles contract
In 50 msec excitation spreads
through both ventricles simultaneously
Electrocardiogram---ECG or EKG
EKG
Action potentials of all active cells can be detected and
recorded
P wave
atrial depolarization
P to Q interval
conduction
time from atrial to ventricular excitation
QRS complex
ventricular depolarization
T wave
ventricular
repolarization
One Cardiac Cycle
At
75 beats/min, one cycle requires 0.8 sec.
systole
(contraction) and diastole (relaxation) of both atria, plus the systole and
diastole of both ventricles
End diastolic volume
(EDV)
volume
in ventricle at end of diastole, about 130ml
End systolic volume
(ESV)
volume
in ventricle at end of systole, about 60ml
Stroke volume (SV)
the
volume ejected per beat from each ventricle, about 70ml
SV = EDV - ESV
Phases of Cardiac
Cycle
Isovolumetric
relaxation
brief
period when volume in ventricles does not change--as ventricles relax, pressure
drops and AV valves open
Ventricular filling
rapid
ventricular filling:as blood flows from full atria
diastasis: as blood flows from atria in smaller
volume
atrial systole pushes final 20-25 ml blood into
ventricle
Ventricular systole
ventricular
systole
isovolumetric contraction
brief
period, AV valves close before SL valves
open
ventricular
ejection: as SL valves open and blood is ejected
Ventricular Pressures
Blood pressure in aorta is 120mm Hg
Blood pressure in pulmonary trunk is 30mm Hg
Differences in ventricle wall thickness allows heart to push
the same amount of blood with more force from the left ventricle
The volume of blood ejected from each ventricle is 70ml
(stroke volume)
Why do both stroke volumes need to be same?
Auscultation
Stethoscope
Sounds of heartbeat
are from turbulence in blood flow caused by valve closure
first
heart sound (lubb) is created with the closing of the
atrioventricular valves
second
heart sound (dupp) is created with the closing of semilunar valves
Heart Sounds
Cardiac Output
Amount of blood
pushed into aorta or pulmonary trunk by ventricle
Determined by stroke
volume and heart rate
CO = SV x HR
at
70ml stroke volume & 75 beat/min----5 and 1/4 liters/min
entire
blood supply passes through circulatory system every minute
Cardiac reserve is
maximum output/output at rest
average
is 4-5 while athlete is 7-8
Influences on Stroke Volume
Preload (affect of
stretching)
Frank-Starling Law of
Heart
more
muscle is stretched, greater force of contraction
more
blood more force of contraction results
Contractility
autonomic
nerves, hormones, Ca+2 or K+ levels
Afterload
amount
of pressure created by the blood in the way
high
blood pressure creates high afterload
Congestive Heart
Failure
Causes of CHF
coronary
artery disease, hypertension, MI, valve disorders, congenital defects
Left side heart
failure
less
effective pump so more blood remains in ventricle
heart
is overstretched & even more blood remains
blood
backs up into lungs as pulmonary edema
suffocation
& lack of oxygen to the tissues
Right side failure
fluid
builds up in tissues as peripheral edema
Risk Factors for Heart Disease
Risk factors in heart
disease:
high
blood cholesterol level
high
blood pressure
cigarette
smoking
obesity
& lack of regular exercise.
Other factors
include:
diabetes
mellitus
genetic
predisposition
male
gender
high
blood levels of fibrinogen
left
ventricular hypertrophy
Plasma Lipids and Heart Disease
Risk factor for
developing heart disease is high blood cholesterol level.
promotes
growth of fatty plaques
Most lipids are
transported as lipoproteins
low-density
lipoproteins (LDLs)
high-density
lipoproteins (HDLs)
very
low-density lipoproteins (VLDLs)
HDLs
remove excess cholesterol from circulation
LDLs
are associated with the formation of fatty plaques
VLDLs
contribute to increased fatty plaque formation
There are two sources
of cholesterol in the body:
in
foods we ingest & formed by liver
Desirable Levels of
Blood Cholesterol for Adults
TC (total cholesterol) under 200 mg/dl
LDL under 130 mg/dl
HDL over 40 mg/dl
Normally,
triglycerides are in the range of 10-190 mg/dl.
Among the therapies
used to reduce blood cholesterol level are exercise, diet, and drugs.
Exercise and the Heart
Sustained exercise
increases oxygen demand in muscles.
Benefits of aerobic
exercise (any activity that works large body muscles for at least 20 minutes,
preferably 3-5 times per week) are;
increased
cardiac output
increased
HDL and decreased triglycerides
improved
lung function
decreased
blood pressure
weight
control.
Coronary Artery
Disease
Heart muscle receiving insufficient blood supply
narrowing of
vessels---atherosclerosis, artery spasm or clot
atherosclerosis--smooth muscle
& fatty deposits in walls of arteries
Treatment
drugs, bypass graft, angioplasty, stent
Clinical Problems
MI = myocardial infarction
death of area of heart muscle from
lack of O2
replaced with scar tissue
results depend on size &
location of damage
Blood clot
use clot dissolving drugs
streptokinase or t-PA & heparin
balloon angioplasty
Angina pectoris----heart pain from ischemia of cardiac
muscle
By-pass Graft
Percutaneous Transluminal
Coronary Angioplasty
Stent in an Artery
Maintains patency of blood vessel