The Heart Flashcards
The Heart
a muscular double pump
Pulmonary circuit—takes blood to and from the lungs • Systemic circuit—vessels transport blood to and from body tissues • Atria—receive blood from the pulmonary and systemic circuits • Ventricles—the pumping chambers of the heart that propels blood toward the pulmonary and systemic circuits
Heart Location within Thorax
• Heart—typically weighs 250–350 grams (healthy heart) • Largest organ of the mediastinum • Located between the lungs • Apex lies to the left of the midline • Base is the broad posterior surface
Four “Corners” of the Heart
Superior right: at costal cartilage of
third rib and sternum
• Inferior right: at costal cartilage of sixth
rib lateral to the sternum
• Superior left: at costal cartilage of
second rib lateral to the sternum
• Inferior left: lies in the fifth intercostal
space at the midclavicular line
Heart Sulci
Coronary sulcus forms a “crown” by circling
boundary between atria and ventricles and
contains left and right coronary arteries and
coronary sinus (vein)
• Anterior interventricular sulcus marks
anterior position over interventricular septum and contains anterior interventricular artery and great cardiac vein
• Posterior interventricular sulcus marks
posterior position over interventricular septum and contains posterior
interventricular artery and middle cardiac vein
Serous cavities in body:
slit-like space lined by a
serous membranes
- pericardium (heart)
- pleura (lung)
- peritoneum (abdominal)
Serous cavities
Parietal serosa: outer wall of the cavity
• Visceral serosa: covers the visceral organs
• Serous cavities do not contain air, but rather
a thin layer of serous fluid that is produced
by both the parietal and visceral serous
membranes
• The slippery serous fluid allows the visceral
organs to slide with minimal friction across
the cavity wall as they carry out their routine
functions
Pericardium: two primary layers
• Fibrous pericardium is strong layer of
dense connective tissue
• Serous pericardium formed from two layers
– Parietal layer of the serous pericardium
– Visceral layer of the serous pericardium =
epicardium
Layers of the Heart Wall
Epicardium
– Visceral layer of the serous pericardium
• Myocardium
– Consists of cardiac muscle and forms bulk of heart
– Surrounding the cardiac muscle cells in the myocardium
are connective tissues that form the “fibrous skeleton of
the heart” which binds these muscle cells together
arranged in elongated circular and spiral patterns
– These bundles of muscle cells enable blood to be
appropriately squeezed through the heart
• Endocardium
– Endothelium (sheet of simple squamous epithelium) on a
layer of connective tissue
– Lines the internal walls of the heart chambers & valves
Heart Chambers
- Right and left atria: superior chambers
- Interatrial septa
- Right and left ventricles: inferior chambers
- Interventricular septa
Right Atrium
Forms right border of heart
• Receives de-oxygenated blood from systemic circuit
via the superior and inferior vena cava and via the
coronary sinus (large vein) in posterior part of
coronary sulcus which receives blood from cardiac
veins (great, middle, and small cardiac veins)
• Pectinate muscles: ridges inside anterior of right
atrium
• Fossa ovalis: depression in interatrial septum;
remnant of foramen ovale
• Crista terminalis: C-shaped ridge landmark used to
locate veins entering right atrium
Right Ventricle
• Receives blood from right atrium through the
atrioventricular (tricuspid) valve
• Pumps blood through pulmonary semilunar valve
into pulmonary trunk which branches into the right
and left pulmonary arteries
• Internal walls of right ventricle
– Trabeculae carneae: irregular ridges of muscles
along inner surface of ventricle
– Papillary muscles: cone shaped muscle
projections
– Chordae tendineae: strong thin bands which
project superiorly from the papillary muscles to
the cusps of the tricuspid AV valve
Left Atrium
Makes up heart’s posterior surface
• Receives oxygen-rich blood from lungs
through two right and two left pulmonary
veins
• Opens into the left ventricle through mitral
valve (left atrioventricular valve)
Left Ventricle
• Pumps blood through systemic circuit via
aortic semilunar valve (aortic valve)
• Forms apex of the heart
• Internal walls of left ventricle
– Trabeculae carneae: irregular ridges of muscle
on inner ventricular wall
– Papillary muscles: cone shaped
– Chordae tendineae: bands which project from
papillary muscles to flaps (cusps) of left
atrioventricular valve
Heart Valves—Valve Structure
Each valve composed of two to three cusps
made of endocardium with connective tissue
core
• Right atrioventricular (tricuspid/3 cusps)
valve and left atrioventricular/mitral
(bicuspid/2 cusps) valve between atria and
ventricles
• Aortic and pulmonary valves each have 3
cusps and are at junction of ventricles and
great arteries; these valves are called semilunar
because each of the 3 cusps look like a
crescent moon
Fibrous Skeleton
• Lies in the plane between the atria and ventricles
and surrounds and reinforces all four valves
• Composed of dense connective tissue
• Anchors valve cusps
• Prevents overdilation of valve openings
• Main point of insertion for bundles of cardiac
muscle in the atria and ventricles
• Supports proper coordination of atrial and
ventricular contractions by blocking direct spread
of electrical impulses from atria to ventricles
As blood returns to heart and
fills atria, AV valves open
Blood returning to the heart fills atria
causing atria pressure to be greater than
the ventricular pressure, putting pressure
against AV valves which forces AV valves
to open into ventricles
• As ventricles fill, AV valve flaps hang limply
into ventricles as atria contract, forcing
additional blood into ventricles
When atrial pressure < ventricular pressure
AV valve closes
• Ventricles contract forcing blood against
AV valve cusps causing the AV valves
to close.
• Papillary muscles contract and chordae
tendinae tighten which prevents valve
flaps from everting into atria
Semilunar valves open & close
• As ventricles contract, the intraventricular pressure rises and blood is pushed up against semilunar (aortic and pulmonic) valves, forcing them open. • As venticles relax and intraventricular pressure falls, blood flows back from aorta and pulmonary trunk arteries, filling the cusps of semilunar valves which causes them to close
1st & 2nd Heart Sounds
• “Lub-dup”—sound of valves closing
• 1st sound “lub”: closure of AV valves
• 2nd sound “dup”: closure of semilunar
valves
Heart Sounds
• Each valve sound is best heard near a different heart corner – Pulmonary valve—superior left corner – Aortic valve—superior right corner – Mitral (bicuspid) valve—at the apex – Tricuspid valve—inferior right corner
Heartbeat
• 60–80 beats per minute at rest
– Systole—contraction of a heart chamber
which pushes blood out through aorta and
pulmonary trunk arteries
– Diastole—expansion of a heart chamber
volume as atria and ventricles fill up with
blood
• Systole and diastole may be referred to as
stages of heartbeat when ventricles contract
(systole) and when ventricles relax with
expansion of chamber volume and fill with blood
(diastole)
Pathway of Blood Through Heart
• Beginning with oxygen-poor blood in the
superior and inferior vena cava
• through right atrium, right ventricle, and
pulmonary circuit
• through left atrium, left ventricle, and
systemic circuits
• as blood passes through all structures
sequentially
• Atria contract together
• Ventricles contract together
Blood flow
Superior/Inferior Vena Cava -> Coronary Sinus -> Right Atrium -> Tricuspid valve -> Right Ventricle -> Pulmonary Semilunar valve -> Pulmonary Trunk -> To lungs -> Pulmonary arteries -> To Left Atrium -> Mitral Valve -> Left Ventricle -> Aortic semilunar valve -> Aorta -> Rest of Body -> Heart
Heart valve abnormalities
• Valve insufficiency or incompetence: valves leak
because they fail to close properly
• Mitral valve prolapse: weakness of the collagen in
the valve and the chordae tendinae allow one or
both cusps to flop into the left atrium during
ventricular systole causing some blood to flow back
from left ventrical into left atrium; this is most
common heart valve disorder
• Valve stenosis (e.g. aortic valve stenosis): valves
with narrow openings due to fused or stiffened
cusps; the constricted opening does not open
maximally causing less blood to flow through the
valve
Structure of Heart Wall
• Atria—thin walls • Ventricles—thick walls – Systemic circuit is longer than pulmonary circuit and offers greater resistance to blood flow, hence left ventricular walls are thicker than right ventricular walls
Structure of Heart Wall
• Left ventricle— circular wall is three times thicker than right ventricle wall – Exerts more pumping force – Flattens right ventricle into a crescent shape
Myocardium
Thick layer of cardiac muscle tissue
• Contains cardiac muscle cells and the
connective tissue that surrounds these cells
• Contractions pump blood through the heart
and into blood vessels
• Contracts by sliding filament mechanism
Cardiac Muscle Cells
Short compared to skeletal muscle fibers
• Branching
• Have one or two nuclei
• Contain myofibrils with sarcomeres composed
of A bands, I bands, H zones, titin, Z discs, and
M lines
• Striations are less apparent in cardiac muscle
compared to skeletal muscle
• Mechanism for contraction of cardiac muscle is
similar to that of skeletal muscle
Endomysium
• Loose fibrous connective tissue
• In intercellular space around each cardiac
fiber
• Contains blood vessels and nerves that
serve muscle cells
• Binds adjacent cardiac fibers
• Merges with the fibrous skeleton of the
heart and thus functions to anchor the
muscle cells and facilitate the transmission
of contractile forces by muscle cells
Cardiac Muscle Tissue
Intercalated discs—complex junctions
• At these junctions, adjacent sarcolemmas
interlock through meshing “fingers” and
specialized types of cell junctions:
• Fasciae adherans are contained in transverse
regions and are long desmosome-like junctions
which bind adjacent cells together, transmitting
the contractile signal to adjacent cells
• Gap junctions are contained in longitudinal
regions and allow ions to pass between cells,
transmitting the contractile signal to adjacent
cells
Cardiac muscle contraction triggered by
Ca2+ entering the
sarcoplasm (muscle cell cytoplasm)
Small amount of Ca2+ ions from extracellular fluid
enter cardiac muscle sarcoplasm through the
sarcolemma (muscle cell plasma membrane)
• Signals sarcoplasmic reticulum to release stored
Ca2+ ions
• Ca2+ ions diffuse into sarcomeres (part of
myofibril between two Z discs) which triggers a
sliding filament mechanism
Conducting System
Cardiac muscle tissue has intrinsic ability to
generate and conduct electrical impulses to signal
these same cells to contract rhythmically
• Even if all the extrinsic nerve connections to the
heart are severed, the heart continues to beat
rhythmically
• Intrinsic conducting system consists of:
– a series of specialized cardiac muscle cells (not
nervous tissue) that transmit impulses throughout
the cardiac musculature
– sinoatrial (SA) node sets the inherent rate of
contraction
Cardiac conducting system
SA (sinoatrial) node • AV (atrioventricular) node • AV bundle • Bundle branches • Subendocardial branches (Purkinje fibers)
Conducting system in atria
• Sino-atrial (SA) node in wall of right
atrium generates impulses and is the
heart’s pacemaker
• Impulses from SA node spread in wave
through atrial muscle fibers signaling the
atria to contract
• Impulses from SA node are also
transmitted to the atrial-ventricular (AV)
node in inferior part of the interatrial
septum and pause for 0.1 second
Conducting system in ventricles
• Impulses from AV node are rapidly transmitted
through the atrioventricular (AV) bundle
which connects atria to ventricles
• AV bundle enters the interventricular septum
and divides into right and left bundle
branches which conduct impulses through the
interventricular septum
• Halfway down the septum the bundle branches
become subendocardial branches (Purkinje
fibers) which extend down to the heart wall
apex and up into the ventricular walls
Innervation
Heart rate is altered
by external controls
• Visceral sensory fibers can perceive cardiac muscle stress in person with ischemic
heart disease
• Parasympathetic motor branches of the
vagus nerve decreases heart rate
• Sympathetic motor fibers—from cervical and upper thoracic chain ganglia increases heart rate
Autonomic nervous system
input into heart rate
Autonomic input into the heart is controlled by cardiac centers in the reticular formation of the medulla oblongata of the brainstem • Cardioinhibitory center influences parasympathetic • Cardioacceleratory center influences sympathetic
Blood Supply to the Heart
• Functional blood supply from coronary arteries
• Coronary arteries arise from the base of the aorta
– Run in the coronary sulcus
– Main branches: left coronary artery and right
coronary artery
– Left coronary artery branches into circumflex
artery and anterior interventricular artery
– Right coronary artery branches into marginal
artery and posterior interventricular artery
Coronary artery disease
• Atherosclerosis—fatty deposits inside coronary
arteries
• Angina pectoris—chest pain from cardiac muscle
ischemia from decreased blood supply to cardiac
muscle due to coronary artery disease; this chest
pain is perceived by the visceral sensory fibers
• Myocardial infarction (heart attack)—diseased
coronary artery becomes blocked which results in
interruption of blood supply to cardiac muscle
causing cell death (infarction) to muscle tissue
Treatments of atherosclerosis of coronary arteries:
(a) Angioplasty and placement of stent
(b) Coronary bypass graft (CABG) performed on two
vessels; double bypass surgery
Disorders of the Heart
• Heart failure including CHF (congestive
heart disease)
– Progressive weakening of the heart
muscle
– Cannot meet the body’s demands for
oxygenated blood
• Pulmonary arterial hypertension
– Enlargement and potential failure of right
ventricle from the elevated pressure in the
pulmonary circuit
Disorders of the Conduction System
Arrythmias = variation from normal heart
rate and/or rhythm e.g., fibrillation
- Ventricular fibrillation
* Atrial fibrillation
Atrial fibrillation
Impulses circle within atrial myocardium,
randomly stimulating AV node, which
signals the ventricles to contract irregularly
and quickly which causes blood to move
irregularly and sluggishly through the heart
• Occur in episodes characterized by heart
palpitations, shortness of breath, fatigue,
and anxiety
• Sluggish movement of blood can promote
formation of clots which lead to a stroke
and/or myocardial infaction
Ventricular fibrillation
Rapid, random firing of electrical impulses
in the ventricle prevents coordinated
contraction of the ventricle
• Results from damaged conducting system
• Common cause of cardiac arrest
