Heart - Key concepts
- Define the functions of the heart
- It generates blood pressure: Contractions of the heart generates blood pressure,
which provides the force necessary to propel blood through your blood vessels
- It directs blood: The right side of your heart directs the blood to your lungs
(pulmonary circulation), whilst the left side of the heart moves blood throughout the
entire body (systemic circulation).
- It regulates blood supply: The rate and force of heart contractions can quickly
change depending on how much blood your tissues need. For example, heart rate
and force increase to send more blood to muscle tissues.
- State the location, shape and size of the heart
- Location: The heart is located in the thoracic cavity between the lungs and behind
(posterior to) the sternum. It specifically lies within an anatomical region called the
mediastinum, a central compartment of the thoracic cavity that also contains the
trachea and oesophagus. About two-thirds of the mass of the heart lies to the left of
the body’s midline
- Shape: The rounded point of the cone is the apex and rests on the diaphragm. The
larger flat pointed part at the opposite end is the base. In addition, the heart has an
anterior and posterior surface, as well as a left and right border.
- Size: It’s roughly the same size, but not shape as a clenched fist
- Describe the structure and function of the pericardium
- The heart is surrounded, protected and held by a membrane called the pericardium.
- The pericardium consists of two layers:
- Fibrous pericardium - An outer tough layer made of dense irregular
connective tissue. It anchors the heart in place, protects the heart, and
prevents the heart from overstretching
- Serous pericardium - An inner delicate layer composed of simple squamous
epithelium overlying loose connective tissue
- The serous pericardium forms a double layer around the heart consisting of a
parietal (outer) layer of the serous pericardium,
which is fused to the fibrous pericardium and a
visceral (inner) layer of the serous pericardium,
also called the epicardium, which adheres to the
surface of the heart.
- Between the parietal (outer) and visceral (inner)
layers of the serous pericardium is a space called
the pericardial cavity that is filled with a thin layer
of pericardial fluid produced by both the parietal
and visceral layers of the serous pericardium.
Pericardial fluid is slipper and reduces friction as
the heart moves within the pericardial sac.
- Describe the three layers of the heart wall
,- The wall of the heart is made of three distinct layers: the epicardium (external layer),
the myocardium (middle layer) and the endocardium (inner layer)
- Epicardium
- Also known as the visceral layer
of the serous pericardium. It
consists of simple squamous
epithelium overlying a thin layer of
loose connective tissue. In some
places, the epicardium also
includes a thick layer of adipose
(fat) tissue. The largest branches
of the coronary blood vessels
travel through the epicardium
- Myocardium
- Consists of cardiac muscle tissue
and is the thickest layer. It is
responsible for the pumping action of the heart.
- Endocardium
- Lines the inside of the heart and covers the valves. It is continuous with the
endothelium of blood vessels and serves as a protective lining.
- Identify and describe the heart chambers and valves
- Heart chambers
- These are the upper right and left atria and the lower left and right ventricles.
- The atria receive blood from veins (into the heart), whilst the ventricles pump
blood into the lungs (right) and the
body (left).
- The right ventricle only has
to pump blood a short
distance to the lungs, so not
much force is required and
the wall is relatively thin.
- The left ventricle has to
pump blood great distances
throughout the entire body,
so more force and muscle
tissue is required, thus the
wall is much thicker
- Heart valves
, - There are four valves that regulate blood flow through the heart, keeping
blood moving efficiently, smoothly and in the right direction.
- These are the:
- Two atrioventricular (AV) valves - termed tricuspid and mitral valves
- that control blood flow from the atria to the ventricles
- Two semilunar (SL) valves - termed aortic and pulmonary valves -
that control blood flow out of the ventricles
- A heart stops the blood from exiting until it is needed, a defective valve that is
will cause the heart to work much harder than it should as blood tries to flow
in the wrong direction
- Trace the flow of blood throughout the heart and coronary circulation
- Coronary Circulation
- To maintain its pumping activity, the heart requires continuous, abundant
supply of oxygen and nutrients. The heart has its own supply of blood vessels
that deliver blood to every cell of the myocardium. The blood vessels of the
heart wall constitute the coronary circulation. At rest, coronary vessels
supply the myocardium with about 250 mL of blood.
- Coronary Arteries
- Two major arteries that supply oxygenated blood to the heart are the right
coronary artery and the left coronary artery.
- Both of these arteries arise from the base of the aorta just above the aortic
(semilunar) valve. The right coronary artery supplies the right atrium and SA
node. It branches into the:
- Right marginal artery - Runs towards the apex of the heart and
supplies the right atrium and ventricle
- Posterior interventricular branch - Supplies the posterior walls of
both ventricles
- The left coronary artery has two major branches:
- Anterior interventricular branch - Supplies blood to the anterior
surface of both ventricles and most of the interventricular system
- Circumflex artery - Supplies the left atrium and posterior wall of the
left ventricle
- Coronary Veins
- The coronary veins drain blood from the heart. Their pathways are near
identical to those of the coronary arteries. Approximately 5-10% of the
coronary blood empties directly into the heart chambers particularly the right
ventricle. The rest of this blood returns to the right atrium via the following
route:
- Great cardiac vein - Collects blood from the anterior aspect of the
heart
- Anterior cardiac veins - Collects blood from the posterior aspects of
the heart
- Coronary sinus - A large vein located on the posterior aspect of the
heart. It collects blood from all of the above veins and empties blood
into the right atrium
, - Describe the histology of cardiac muscle
- Heart Muscle Tissue:
- The thickest layer of the heart, the myocardium, is composed of cardiac
muscle cells. The dark bands characterised by the dark striations on cardiac
muscle cells are called ‘A’ bands and the light bands characterised by the
light striations are called ‘I’ bands. The ends of adjacent cardiac muscle cells
connect to one another by irregular thickenings of the sarcolemma called
intercalated discs.
- These discs contain two junctions:
- Desmosomes - Hold the cardiac muscle cells together, preventing
them from pulling apart when the heart contracts
- Gap junctions - Allow action potentials to quickly spread from one
muscle cell to another. Gap junctions allow the entire myocardium of
the atria or the ventricles to contract as a single, coordinated unit
when the heart beats. This is essential for the effective pumping of a
heart chamber.
- Fibrous skeleton of the heart:
- In addition to cardiac muscle tissue, the heart also contains dense connective
tissue that forms the fibrous skeleton of the heart. The fibrous skeleton
consists of four dense connective tissue rings that surround the valves of the
heart, fuse with one another, and merge with the interventricular septum.
- The functions of the fibrous skeleton are to:
- Support the heart valves and prevent them from overstretching
- Serve as an attachment point for cardiac muscle cells
- Act as an electrical insulator between the atria and ventricles
- Describe the electrical conduction system of the heart
- Cardiac conduction system
- A heart beat is a two-part pumping action ensuring that oxygenated blood is
pumped through the body to provide oxygen and nutrients to cells and tissues
that deoxygenated blood returning from capillary beds is pumped to the lungs
for gas exchange. The heart contains a network of cells constituting a
conducting system, ensuring regularity and consistency of the heartbeat in
response to oxygen demands within the body. These are specialised,
autorhythmic cells, otherwise known as the pacemaker, with an ability to
initiate electrical impulses and contraction of cardiac muscle without neural or
hormonal stimulus
- List the phases of the cardiac cycle
- The cardiac cycle represents a sequence of contraction and relaxation events of
cardiac muscle to move the blood received by the heart to the lungs or the body.
Contraction of cardiomyocytes, lining the heart chambers is initiated and propagated
by the conduction system of the heart. Further to this, movement of blood across the
- Define the functions of the heart
- It generates blood pressure: Contractions of the heart generates blood pressure,
which provides the force necessary to propel blood through your blood vessels
- It directs blood: The right side of your heart directs the blood to your lungs
(pulmonary circulation), whilst the left side of the heart moves blood throughout the
entire body (systemic circulation).
- It regulates blood supply: The rate and force of heart contractions can quickly
change depending on how much blood your tissues need. For example, heart rate
and force increase to send more blood to muscle tissues.
- State the location, shape and size of the heart
- Location: The heart is located in the thoracic cavity between the lungs and behind
(posterior to) the sternum. It specifically lies within an anatomical region called the
mediastinum, a central compartment of the thoracic cavity that also contains the
trachea and oesophagus. About two-thirds of the mass of the heart lies to the left of
the body’s midline
- Shape: The rounded point of the cone is the apex and rests on the diaphragm. The
larger flat pointed part at the opposite end is the base. In addition, the heart has an
anterior and posterior surface, as well as a left and right border.
- Size: It’s roughly the same size, but not shape as a clenched fist
- Describe the structure and function of the pericardium
- The heart is surrounded, protected and held by a membrane called the pericardium.
- The pericardium consists of two layers:
- Fibrous pericardium - An outer tough layer made of dense irregular
connective tissue. It anchors the heart in place, protects the heart, and
prevents the heart from overstretching
- Serous pericardium - An inner delicate layer composed of simple squamous
epithelium overlying loose connective tissue
- The serous pericardium forms a double layer around the heart consisting of a
parietal (outer) layer of the serous pericardium,
which is fused to the fibrous pericardium and a
visceral (inner) layer of the serous pericardium,
also called the epicardium, which adheres to the
surface of the heart.
- Between the parietal (outer) and visceral (inner)
layers of the serous pericardium is a space called
the pericardial cavity that is filled with a thin layer
of pericardial fluid produced by both the parietal
and visceral layers of the serous pericardium.
Pericardial fluid is slipper and reduces friction as
the heart moves within the pericardial sac.
- Describe the three layers of the heart wall
,- The wall of the heart is made of three distinct layers: the epicardium (external layer),
the myocardium (middle layer) and the endocardium (inner layer)
- Epicardium
- Also known as the visceral layer
of the serous pericardium. It
consists of simple squamous
epithelium overlying a thin layer of
loose connective tissue. In some
places, the epicardium also
includes a thick layer of adipose
(fat) tissue. The largest branches
of the coronary blood vessels
travel through the epicardium
- Myocardium
- Consists of cardiac muscle tissue
and is the thickest layer. It is
responsible for the pumping action of the heart.
- Endocardium
- Lines the inside of the heart and covers the valves. It is continuous with the
endothelium of blood vessels and serves as a protective lining.
- Identify and describe the heart chambers and valves
- Heart chambers
- These are the upper right and left atria and the lower left and right ventricles.
- The atria receive blood from veins (into the heart), whilst the ventricles pump
blood into the lungs (right) and the
body (left).
- The right ventricle only has
to pump blood a short
distance to the lungs, so not
much force is required and
the wall is relatively thin.
- The left ventricle has to
pump blood great distances
throughout the entire body,
so more force and muscle
tissue is required, thus the
wall is much thicker
- Heart valves
, - There are four valves that regulate blood flow through the heart, keeping
blood moving efficiently, smoothly and in the right direction.
- These are the:
- Two atrioventricular (AV) valves - termed tricuspid and mitral valves
- that control blood flow from the atria to the ventricles
- Two semilunar (SL) valves - termed aortic and pulmonary valves -
that control blood flow out of the ventricles
- A heart stops the blood from exiting until it is needed, a defective valve that is
will cause the heart to work much harder than it should as blood tries to flow
in the wrong direction
- Trace the flow of blood throughout the heart and coronary circulation
- Coronary Circulation
- To maintain its pumping activity, the heart requires continuous, abundant
supply of oxygen and nutrients. The heart has its own supply of blood vessels
that deliver blood to every cell of the myocardium. The blood vessels of the
heart wall constitute the coronary circulation. At rest, coronary vessels
supply the myocardium with about 250 mL of blood.
- Coronary Arteries
- Two major arteries that supply oxygenated blood to the heart are the right
coronary artery and the left coronary artery.
- Both of these arteries arise from the base of the aorta just above the aortic
(semilunar) valve. The right coronary artery supplies the right atrium and SA
node. It branches into the:
- Right marginal artery - Runs towards the apex of the heart and
supplies the right atrium and ventricle
- Posterior interventricular branch - Supplies the posterior walls of
both ventricles
- The left coronary artery has two major branches:
- Anterior interventricular branch - Supplies blood to the anterior
surface of both ventricles and most of the interventricular system
- Circumflex artery - Supplies the left atrium and posterior wall of the
left ventricle
- Coronary Veins
- The coronary veins drain blood from the heart. Their pathways are near
identical to those of the coronary arteries. Approximately 5-10% of the
coronary blood empties directly into the heart chambers particularly the right
ventricle. The rest of this blood returns to the right atrium via the following
route:
- Great cardiac vein - Collects blood from the anterior aspect of the
heart
- Anterior cardiac veins - Collects blood from the posterior aspects of
the heart
- Coronary sinus - A large vein located on the posterior aspect of the
heart. It collects blood from all of the above veins and empties blood
into the right atrium
, - Describe the histology of cardiac muscle
- Heart Muscle Tissue:
- The thickest layer of the heart, the myocardium, is composed of cardiac
muscle cells. The dark bands characterised by the dark striations on cardiac
muscle cells are called ‘A’ bands and the light bands characterised by the
light striations are called ‘I’ bands. The ends of adjacent cardiac muscle cells
connect to one another by irregular thickenings of the sarcolemma called
intercalated discs.
- These discs contain two junctions:
- Desmosomes - Hold the cardiac muscle cells together, preventing
them from pulling apart when the heart contracts
- Gap junctions - Allow action potentials to quickly spread from one
muscle cell to another. Gap junctions allow the entire myocardium of
the atria or the ventricles to contract as a single, coordinated unit
when the heart beats. This is essential for the effective pumping of a
heart chamber.
- Fibrous skeleton of the heart:
- In addition to cardiac muscle tissue, the heart also contains dense connective
tissue that forms the fibrous skeleton of the heart. The fibrous skeleton
consists of four dense connective tissue rings that surround the valves of the
heart, fuse with one another, and merge with the interventricular septum.
- The functions of the fibrous skeleton are to:
- Support the heart valves and prevent them from overstretching
- Serve as an attachment point for cardiac muscle cells
- Act as an electrical insulator between the atria and ventricles
- Describe the electrical conduction system of the heart
- Cardiac conduction system
- A heart beat is a two-part pumping action ensuring that oxygenated blood is
pumped through the body to provide oxygen and nutrients to cells and tissues
that deoxygenated blood returning from capillary beds is pumped to the lungs
for gas exchange. The heart contains a network of cells constituting a
conducting system, ensuring regularity and consistency of the heartbeat in
response to oxygen demands within the body. These are specialised,
autorhythmic cells, otherwise known as the pacemaker, with an ability to
initiate electrical impulses and contraction of cardiac muscle without neural or
hormonal stimulus
- List the phases of the cardiac cycle
- The cardiac cycle represents a sequence of contraction and relaxation events of
cardiac muscle to move the blood received by the heart to the lungs or the body.
Contraction of cardiomyocytes, lining the heart chambers is initiated and propagated
by the conduction system of the heart. Further to this, movement of blood across the
