Transcript The Structure of The Mammalian Heart

The Structure of The Mammalian
Heart
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A muscular pump
Divided into two sides
Right side - deoxygenated
Left side – oxygenated
Both sides of the heart squeeze putting
blood under pressure
• Pressure forces blood along the arteries
Tips
• If you are asked how the pressure in the arteries
is produced, you need to explain that it is due to
the contraction of the left ventricle walls
• When memorising the parts of the heart,
remember veins take blood towards the heart,
arteries take blood from the heart- pulmonary
means lung and vena cava means ‘main vein’
• So… pulmonary artery takes blood away from
the heart to the lung…. Easy!
External Features of the Heart
• Sits slightly off centre to
left of chest cavity
• Lies at an angle with the
atria in the middle
• Consists of dark red
muscle that feels firm
• The muscle surrounds
the two ventricles
• Atria are much smaller
than the ventricles
External Features of the Heart
• Coronary arteries lie over the
heart’s surface
• They carry oxygenated blood to the
heart itself
• These arteries are important and if
constricted at all can have serious
consequences
• Restricted blood flow to the heart
can cause angina (pain) or a heart
attack (myocardial infarction)
• At the top of the heart are tubesveins carrying blood to the heart
and arteries carrying blood away
from the heart
Internal Structure of the Heart
• Divided into 4 chambers
• Two atria, receiving blood
from the major veins
• Vena Cava:
deoxygenated blood from
the body into the right
atrium
• Pulmonary Vein:
oxygenated blood from
the lungs to the left atrium
Internal Structure of the Heart
• From the atria, blood flows through the atrioventricular
valves into the ventricles.
• The valves are thin flaps of tissue arranged in a cup
shape
• When the ventricles contract, the valves fill with blood
and remain closed
• This ensures blood flows upwards into the major arteries
leading away from the heart, and not back into the atria
• Tendinous cords inside the ventricles attach the valves to
the walls of the ventricle and prevent flimsy valves from
turning inside out and allowing backflow of blood
Check out the next 2 slides for diagrams that go with this description
A damaged valve and
healthy valve showing
tendinous cords
The Septum
• A wall of muscle
separating the
ventricles from each
other
• Ensures that
oxygenated blood
does not mix with
deoxygenated blood
The diagram shows a defect in the
septum often referred to as a ‘hole in
the heart’
Leaving the Heart
• Deoxygenated blood leaving the right ventricle
flows into the pulmonary artery leading to the
lungs
• Oxygenated blood leaving the right ventricle
flows into the aorta
• The aorta carries blood to a number of arteries
supplying all parts of the body.
• Semi-lunar (half-moon) valves at the base of the
arteries leading from the heart prevent blood
flowing back into the heart as the ventricles relax
Blood Pressure
• The muscles of each
chamber contract to
create increased
pressure in the blood
• The higher the
pressure, the further
the blood can go
Blood Pressure
• Atria: the muscle is thin, as not much pressure is needed
to make blood flow into the ventricles
• Right ventricle: thicker walls than the atria, but as the
blood is only pumped to the lungs, the pressure is not as
great as that created by the left ventricle. Also, the lungs
have fine capillaries and the alveoli are thin. The
pressure cannot be too high or damage to the capillaries
around the alveoli could result
• Left ventricle: 2-3 times thicker than the right ventriclesufficient pressure is needed to pump blood through the
aorta and overcome the resistance of systemic
circulation
Units of Pressure
• The SI unit of pressure is
the Pascal, but because
blood pressure used to be
measured with a tube of
mercury whose chemical
symbol is Hg, we still use
mmHg (millimetres of
mercury) as a pressure
measurement