The Heart

Question 1

The Heart

a muscular double pump

Answer 1

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

Question 2

Heart Location within Thorax

Answer 2

•  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

Question 3

Four “Corners” of the Heart

Answer 3

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

Question 4

Heart Sulci

Answer 4

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

Question 5

Serous cavities in body:
slit-like space lined by a
serous membranes

Answer 5

•   pericardium (heart)
•   pleura (lung)
•   peritoneum (abdominal)

Question 6

Serous cavities

Answer 6

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

Question 7

Pericardium: two primary layers

Answer 7

•  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

Question 8

Layers of the Heart Wall

Answer 8

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

Question 9

Heart Chambers

Answer 9

•   Right and left atria: superior chambers
•   Interatrial septa
•   Right and left ventricles: inferior chambers
•   Interventricular septa

Question 10

Right Atrium

Answer 10

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

Question 11

Right Ventricle

Answer 11

•  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

Question 12

Left Atrium

Answer 12

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)

Question 13

Left Ventricle

Answer 13

•  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

Question 14

Heart Valves—Valve Structure

Answer 14

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

Question 15

Fibrous Skeleton

Answer 15

•  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

Question 16

As blood returns to heart and

fills atria, AV valves open

Answer 16

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

Question 17

When atrial pressure < ventricular pressure

AV valve closes

Answer 17

•  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

Question 18

Semilunar valves open & close

Answer 18

•  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

Question 19

1st & 2nd Heart Sounds

Answer 19

•  “Lub-dup”—sound of valves closing
•  1st sound “lub”: closure of AV valves
•  2nd sound “dup”: closure of semilunar
valves

Question 20

Heart Sounds

Answer 20

•  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

Question 21

Heartbeat

Answer 21

•  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)

Question 22

Pathway of Blood Through Heart

Answer 22

•  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

Question 23

Blood flow

Answer 23

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

Question 24

Heart valve abnormalities

Answer 24

•  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

Question 25

Structure of Heart Wall

Answer 25

``` •  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 ```

Question 26

Structure of Heart Wall

Answer 26

``` •  Left ventricle— circular wall is three times thicker than right ventricle wall – Exerts more pumping force – Flattens right ventricle into a crescent shape ```

Question 27

Myocardium

Answer 27

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

Question 28

Cardiac Muscle Cells

Answer 28

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

Question 29

Endomysium

Answer 29

•  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

Question 30

Cardiac Muscle Tissue | Intercalated discs—complex junctions

Answer 30

•  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

Question 31

Cardiac muscle contraction triggered by Ca2+ entering the sarcoplasm (muscle cell cytoplasm)

Answer 31

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

Question 32

Conducting System

Answer 32

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

Question 33

Cardiac conducting system

Answer 33

``` SA (sinoatrial) node •  AV (atrioventricular) node •  AV bundle •  Bundle branches •  Subendocardial branches (Purkinje fibers) ```

Question 34

Conducting system in atria

Answer 34

•  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

Question 35

Conducting system in ventricles

Answer 35

•  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

Question 36

Innervation

Answer 36

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

Question 37

Autonomic nervous system | input into heart rate

Answer 37

``` 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 ```

Question 38

Blood Supply to the Heart

Answer 38

•  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

Question 39

Coronary artery disease

Answer 39

•  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

Question 40

Treatments of atherosclerosis of coronary arteries:

Answer 40

(a) Angioplasty and placement of stent (b) Coronary bypass graft (CABG) performed on two vessels; double bypass surgery

Question 41

Disorders of the Heart

Answer 41

•  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

Question 42

Disorders of the Conduction System Arrythmias = variation from normal heart rate and/or rhythm e.g., fibrillation

Answer 42

*   Ventricular fibrillation | *   Atrial fibrillation

Question 43

Atrial fibrillation

Answer 43

  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

Question 44

Ventricular fibrillation

Answer 44

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