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Biology and Anatomy & Physiology Helps:
The Heart
By Carolyn Miller
All Rights Reserved
© 2013 Carolyn Miller
Outside of fair use, no part of this book may be reproduced or transmitted in any way without
express permission of the author.
Cover art
Heart by Leonardo da Vinci
public domain image
Dedication:
For EVERYONE who has ever loved
Preface:
Please note this text is designed to act as a lesson supplement. This text is not intended to
provide a comprehensive review of the materials covered without a full Biology or Anatomy
& Physiology curriculum to back it up. The Biology and Anatomy & Physiology Helps series
is designed to provide a limited review of the objectives and vocabulary covered by many
instructors. This series is in note-like format to supplement any student study guide on the
topic, and provides a self test at the end of each text to help with material review.
The Biology and Anatomy & Physiology Helps series also provides note taking tips to further
develop classroom and study skills.
Table of Contents:
Preface
Note Taking Helps
Heart
Heart Anatomy
Coverings of the Heart
The Four Chambers
Coronary Circulation
Heart Valves
Cardiac Muscle
Electrocardiogram
The Cardiac Cycle
Cardiac Output
Regulation of Cardiac Output
Self Test
Answers
Resources and References
About the Author
Note Taking Helps:
Note taking helps are provided to aid the student in further development of study and
classroom skills. The following abbreviations can help you increase your note taking speed in
class and increase readability of notes at a later time.
~ = approximately
∴
= therefore
w/ = with
w/o = without
b/c = because
# = number or pounds
↑
= increase
↓
= decrease
+ = positive
- = negative
= = equals
> = greater than
< = less than
ex = example
excp = exception
⇒ or ➝
= yields
Biology:
NZ = enzyme
NG = energy
O₂ = oxygen
CO₂ = carbon dioxide
C = carbon
AA = amino acid
H₂O = water
CT = connective tissue
RBC = red blood cell
WBC = white blood cell
Hb = hemoglobin
♀
= female
♂
= male
1˚ = primary
2˚ = secondary
3˚ = tertiary
4˚ = quaternary
temp = temperature
A&P = anatomy and physiology
SA = sinoatrial
Heart
heart
the circulatory system's pump
continuously propels oxygen, nutrients and wastes to the body's tissues
consists of 2 pumps side by side
right side -receives oxygen-depleted blood from the body and pumps this blood to the lungs
to pick up oxygen
pulmonary circuit
carries blood to and from the lungs
short
low pressure
left side -receives oxygenated blood form the lungs and pumps it throughout the body to
supply oxygen and nutrients to the body's tissues
systemic circuit
carries blood to and from all the body tissues
blood encounters much more resistance in the long pathways
equal volumes of blood are pumped to the pulmonary and systemic circuits
has 2 receiving chambers that receive blood returning from the lungs and body
right atrium (from body)
left atrium (from lungs)
has 2 pumping chambers that pump blood around the 2 circuits
right ventricle (to lungs)
left ventricle (to body)
Heart Anatomy
size
~the size of a fist
~5 inches long
shape
cone shaped
hollow
position
enclosed in the mediastinum
mediastinum -the medial cavity of the thorax
enclosed in the pericardium
extends from second rib to fifth intercostal space
rests on the superior surface of diaphragm
left of the midsternal line
anterior to the vertebral column
posterior to the sternum
the lungs flank the heart laterally
Coverings of the Heart
pericardium -a double membraned sac that surrounds the heart
fibrous pericardium
loose fitting superficial part of the pericardium
tough, dense connective tissues
protects the heart
anchors heart to surrounding structures
prevents over filling of the heart with blood
serous pericardium
deep, thin, slippery
two layered pericardium
membranes separated by fluid filled pericardial cavity
pericardial cavity
contains lubricating serous fluid
allows heart to pump in a relatively friction free environment
has parietal and visceral layers
parietal layer -lines internal surface to fibrous pericardium
visceral layer or epicardium
lines external surface of heart
smooth outer surface of the heart
integral part of the heart wall
The Heart Wall
heart wall
richly supplied with blood
three layers
1. epicardium -visceral layer of pericardium
2. myocardium
composed mostly of cardiac muscle
this layer of the heart contracts
muscle cells arranged in spiral or circular bundles
contains cardiac skeleton -a fibrous network of connective tissue that anchors the
cardiac muscle, supports the great vessels and valves and limits the spread of action
potentials
1. endocardium
lines the heart chambers
covers fibrous skeleton of the valves
continuous with endothelial linings of the blood vessels that enter and leave the
heart
The Four Chambers
heart chambers
2 superior atria
atria -the right and left atria located at the top of the heart receive blood returning
from the veins
interatrial septum or atrial septum -divides the heart longitudinally, where it
divides the atria
coronary sulcus or atrioventricular groove
wraps the junction of the atria and ventricles
contains the right coronary artery, the small cardiac vein, the coronary
sinus and the circumflex branch of the left coronary artery
2 inferior ventricles
ventricles -the right and left ventricles are located at the bottom of the heart and act
as the body's main pumps
right ventricles form most of the anterior surface
left ventricles form most of the posterior surface
interventricular septum or ventricular septum -divides the heart longitudinally,
where it divides the ventricles
interventricular sulci -separate the two ventricles of the heart
the anterior interventricular sulcus contains the anterior interventricular
artery and great cardiac vein
the posterior interventricular sulcus contains the posterior interventricular
artery and middle cardiac vein
atria
the receiving chambers for blood returning to the heart from circulation.
Push blood down to the ventricles
small, thin walled chambers
walls ridged with pectinate muscles
blood enters right atrium via 3 veins
1. superior vena cava -returns blood from areas of the body above the diaphragm
2. inferior vena cava -returns blood from areas of the body below the diaphragm
3. coronary sinus -collects blood leaving the muscle of the heart or myocardium
blood enters the left atrium via 4 pulmonary veins
these veins transport blood from the lungs back to the heart after oxygenation
ventricles
discharging chambers, actual pumps of the heart, propelling blood into circulation
make up the majority of the hearts volume
much more massive walls than the atria
walls ridged with irregular trabeculae carneae muscle
papillary muscles project into the ventricular cavities, and play a role in valve function
right ventricle pumps blood to the lungs, where gas exchange occurs
the left ventricle pumps blood into the aorta, the largest artery of the body
route of blood through the heart and associated vessels
body➝right atrium➝right ventricle➝pulmonary artery➝lungs➝left atrium➝left
ventricle➝aorta➝body
Coronary Circulation
coronary circulation
provides the functional blood supply to the heart
shortest circulation of the body
coronary arteries
provide the oxygenated blood supply to the heart
left coronary artery -runs toward the left side of the heart and divides
anterior interventricular artery -supplies blood to the interventricular septum
and anterior walls of both ventricles
circumflex artery -supplies left atrium and posterior walls of left ventricle
right coronary artery -runs toward the right side of the heart and divides
right marginal artery -supplies the myocardium of the lateral side of the heart
posterior interventricular artery -runs to the apex of the heart and supplies
the posterior ventricular walls
coronary veins
collect blood from the capillary beds after emerging from the myocardium
coronary sinus -where the coronary veins join and empty, made up of 3 large veins
great cardiac vein -located in the anterior interventricular sulcus
middle cardiac vein – located in the posterior interventricular sulcus
small cardiac vein -located running along the heart's inferior right margin
anterior cardiac veins -empty directly into the right atrium
Heart Valves
heart valves
ensure unidirectional flow through the heart
the heart has 4 valves
2 atrioventricular (AV) valves -located at each atrial-ventricular junction
tricuspid valve -the right AV valve
mitral valve or bicuspid valve -the left AV valve
2 semilunar (SL) valves -guard the bases of the large arteries leaving the ventricles,
preventing back-flow when ventricles relax
aortic semilunar valve -protects the aorta from back-flow
pulmonary semilunar valve -protects the pulmonary trunk from back-flow
chordae tendineae
tiny white collagen cords attached to each atrioventricular valve flap
function with papillary muscles as stabilizing structures that anchor the valve
flaps
“heart strings”
heart sounds
are associated with the heart valves closing
2 sounds are normally heard during a heartbeat
basic sound: lub-dub-pause, lub-dub-pause, etc...
lub
atrioventricular valves closing
ventricular pressure rises above atrial pressure
longer and more resonant
dub
semilunar valves closing
short, sharp sound
murmurs
result when blood strikes obstructions in the heart
common in the young and some elderly with healthy hearts, likely due to thinner
heart walls that vibrate from rushing blood
can indicate valve problems
insufficient or incomplete valve closure, resulting in a swishing sound as blood
back flows through the heart
stenotic valve - valve that fails to open fully, resulting in a high pitched sound
or click when the valve should be open
Cardiac Muscle
microscopic anatomy
striated
short
fat
branched
interlocking junctions with neighboring cardiac cells called intercalated disks
contains loose connective tissue matrix called the endomysium that connects to fibrous
skeleton of the heart
simpler sarcoplasmic reticulum than skeletal muscle
wide T tubules but less numerous than skeletal muscle
large numbers of mitochondria present
functional syncytium -a characteristic of the heart to resemble a single enormous muscle cell
allowing all the cells to react mechanically, chemically and electrically as one unit (a
characteristic also found in smooth muscle)
cardiac muscle excitation
action potential is dependent upon noncontractile autorhythmic cells or pacemaker
cells
initiate and distribute impulses to coordinate depolarization and contraction of the
heart
make up the intrinsic cardiac conduction system
have an unstable resting potential due to open, slow, sodium (Na+) channels
influx of calcium (Ca2+) produces the resting phase of the action potential
inactivation of calcium (Ca2+) channels results in repolarization and the opening of
voltage-gated potassium (K+) channels
there are 5 steps in the sequence of electric excitation of the heart muscle
1. the sinoatrial node also know as the pacemaker generates impulses
sinoatrial node -impulse generating tissue located in the right atria of the heart
impulses generated ~75 times a minute, this is the sinus rhythm or normal beating of the
heart
depolarizes faster than any other part of the heart muscle
2. the impulses pause at the atrioventricular (AV) node
contains fibers of smaller diameter than the sinoatrial node with fewer gap junctions
delays impulse
in the absence of sinoatrial node input, depolarizes ~50 times per minute
3. the atrioventricular (AV) bundle, also know as the bundle of His, connects the atria to
the ventricles
the only electrical connection between the atria and the ventricles
4. right and left atrioventricular (AV) bundle branches conduct impulses through the
interventricular septum
these 2 branches carry impulses toward the apex of the heart
5. the subendocardial conducting network or Purkinje fibers continue the pathway into
the apex and ventricular walls, depolarizing the contractile cells of both ventricles
atrioventricular (AV) bundle and Purkinje fibers depolarize ~30 times a minute in the
absence of atrioventricular (AV) node input
cardiac muscle contraction
depolarization is rhythmic and spontaneous
gap junctions ensure the heart contracts as a unit (all or nothing contraction)
long absolute refractory period or inexcitable period that prevents the occurrence of
tetanic contractions
Electrocardiogram (ECG or EKG)
ECG
measures the normal beating of the heart
composite of a the action potentials generated by nodal and contractile cells of the heart
at a given time
has general features that serve as characteristics for comparison with normal ECGs
typically has 3 distinct waves in a single beat of the heart
1. P wave -precedes the QRS complex, results from the depolarization of the sinoatrial
(SA) node through the atria
2. QRS complex -results from ventricular depolarization
3. T wave -results from ventricular repolarization
PQ interval or PR interval -period of atrial excitation to the beginning of ventricular
excitation
QT interval – period of ventricular depolarization through ventricular repolarization
Abnormalities that can be detected from an ECG
changes in ECG patterns may indicate disease or heart damage
arrhythmia -abnormal heat rhythm
heart block -inability of the ventricles to receive pacing impulses, can be a full or partial
block
atrial fibrillation
the most common cardiac arrhythmia
a condition where blood pools in the upper 2 chambers of the heart.
ventricular fibrillation -the uncoordinated contraction of the ventricles making them
quiver rather than contract properly
bradycardia
a heart rate below 60 beats/min
may result from low temperature, drugs or parasympathetic nervous activation
asymptomatic until rate is below 50 beats/min
tachycardia
an abnormally fast heart rate above 100 beats/min
yields less efficient blood flow
may result from elevated body temperature, stress, certain drugs, or heart disease
if persistent may become pathological and promote fibrillation
The Cardiac Cycle
cardiac cycle -events associated with blood flow through the heart during one complete
heartbeat
mechanical events
systole -contraction
diastole -relaxation
phases of the cardiac cycle
1. ventricular filling
takes place mid to late diastole
atrioventricular (AV) valves are open
aortic and pulmonary valves closed
80% of blood passively flows into ventricles
atrial systole occurs (P wave of the ECG)
remaining 20%of blood enters ventricles
end diastolic volume (EDV) -volume blood in each ventricle at the end of diastole
atria relax and ventricles depolarize (QRS complex of the ECG)
2. ventricular systole/atria in diastole
atria relax and ventricles begin to contract
increasing ventricular pressure yields closure of atrioventricular (AV) valves
isovolumetric contraction phase (all valves are closed)
ejection phase, ventricular pressure exceeds pressure in large arteries and aortic and
pulmonary valves are opened
end systolic volume (ESV) -volume of blood remaining in each ventricle at the end of
systole
3. isovolumetric relaxation/early diastole
ventricles relax
atrioventricular (AV) valve open
back-flow of blood into the aorta and pulmonary trunk closes the aortic and pulmonary
valves causing a brief rise in aortic blood pressure or dicrotic notch