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The Heart and blood vessels
Clinical Science Team
School of Nursing and Midwifery
The Heart and blood vessels
Learning outcomes:
The learner should be able to..
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State the function of the heart and blood vessels
Label a diagram of the heart, indicating its gross
anatomical features
State the function of the right and left sides of the heart
State the function of the valves within the heart
Describe the blood flow through the heart
Outline the hearts electrical conduction pathway
Describe the pressure changes that occur in the
ventricles during the cardiac cycle
Outline the neural and hormonal control of the heart
The circulatory system
List the components of the circulatory
system:
1.
2.
3.
4.
What are its main functions?
a)
b)
c)
The circulatory system
The circulatory system
consists of the
following
components:
The Heart
The blood vessels
The blood
The lymphatic system
Functions of the Circulatory System
• The circulatory system has the
following main functions:
• Transportation
• Regulation
• Protection
Functions of the Circulatory System
•
Transportation:
1. Respiratory: transports oxygen to the tissues and
carbon dioxide back to the lungs
2. Nutritive: Absorbed digested products are
transported to the liver and to tissues
3. Excretory: Waste products from metabolism are
transported to the kidneys for excretion in urine
Functions of the Circulatory System
• Regulation:
–Hormonal: Hormones are
carried from the endocrine
glands to their target tissues
–Temperature: The blood can be
diverted to warm or cool the
body
Functions of the Circulatory System
• Protection:
• Clotting: Blood contains clotting factors
and platelets- when activated prevent
blood loss through clot formation
• Immune: Blood contains leucocytes
(white blood cells), cytokines, and
complement which protects against
infective pathogens
The Heart
Describe the Heart
What is its function?
The Heart
The Heart
The Heart
The Heart
• Slightly larger than the size
of a fist
• Contains four chambers
• Right side supplies the
pulmonary circulation
• Left side supplies the
systemic circulation
• Two sides are separated by
a muscular wall called the
septum
• Atria and ventricles are
separated by a dense layer
of fibrous tissue- the
fibrous skeleton
The Heart wall
Myocardial tissue
The Heart: Valves
• The Heart contains four
valves
• The Tricuspid valve
opens from the R atrium
into the R ventricle
• The Pulmonary
(semilunar) valve opens
from the R ventricle into
the pulmonary artery
• The Mitral valve opens
from the L atrium into the
L ventricle
• The Aortic (semilunar)
valve opens from the L
ventricle into the Aorta
The Heart: Valves
Function of the valves
• Situated at the entrance and exit of
the ventricles
• Ensure that blood moves only in one
direction…Forward
• Blood flows though the valves as a
result of pressure changes
Roche
The Cardiac Cycle
• Refers to the repeated pattern of
contraction and relaxation of the heart.
–Phase of contraction is called systole,
–Phase of relaxation is called diastole
• The heart has a two step pumping
action: the atria contract simultaneously,
followed approx 0.1-0.2 seconds later
by the ventricles.
cycle
5. Ventricles contract, about two thirds of the
volume they contain is ejected, leaving one third
called the end systolic volume
1. Atria fill with blood
4. Atria contract
Contributing approx 20%
To end diastolic volume
2.AV valve opens when
pressure in atria
exceeds ventricle
The Cardiac cycle
3. Blood flows from atria
to ventricles through
open AV valve. This
contributes approx 80% of
end diastolic volume
The Hearts conduction pathway
conduct
Nerve supply to the heart
• The heart is influenced by autonomic nerves
originating in the cardiovascular centre in the
medulla oblongata
– Consisting of sympathetic and parasympathetic
nerves with antagonistic effects
– The vagus nerves (parasympathetic) supply the
SA node, AV node and atrial muscle.
Parasympathetic stimulation decreases HR and
force of contraction
– Sympathetic nerves supply the SA node, AV node
and the myocardium of the atria and ventricles.
Sympathetic stimulation increases HR and force
of contraction
Factors affecting Heart Rate
•
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Gender
Autonomic nerve activity
Age
Circulating hormones e.g adrenaline,
thyroxine
Activity and exercise
Temperature
The baroreceptor reflex
Emotional states
Waugh and Grant (2006)
Cardiac blood supply
• The heart receives its blood supply via the
coronary arteries.
• These arteries supply a huge network of
capillaries
• Ensures that myocardial cells are close to
their blood supply
• Diffusion of gases between the myocardial
cells and capillaries occurs very quickly
Cardiac blood flow
• Cardiac blood flow is different from blood
flow in other organs.
• Blood flows around coronary vessels
during diastole.
• Myoglobin in myocardial cells stores
oxygen.
• This ensures that the heart muscle has a
constant supply.
Summary
• The heart is a four chambered pump, which is
effectively two pumps working together
• The heart contains valves which function to ensure
no backflow of blood
• The wall of the heart is made up of the following
layers: epicardium, pericardium, myocardium,
endocardium
• The heart has ‘autorhythmicity’ it will beat without
outside nervous input
• The heart has a specialist conduction pathwayensuring a smooth coordinated contraction,
• Cardiac muscle contains large numbers of
mitochondria, and the heart has an excellent blood
supply
Blood vessels
Learning outcomes:
1. Compare the structure of an artery and a
vein
2. Explain how the structure of an artery
and a vein relates to its function
3. Describe the structure of a capillary and
explain the physiological significance of
this structure
Blood vessel structure
•
Walls of arteries and veins are composed
of three coats or tunics:
1. Tunica externa (composed of
connective tissue)
2. Tunica media (composed of primarily of
smooth muscle)
3. Tunica intima or interna (composed of
three distinct layers, a) endothelium, b)
basement membrane, c) internal elastic
lamina)
Blood vessels
“ a tubular network throughout the body that permits
blood to flow from the heart to all living cells of the
body and then back to the heart. Blood leaving the
heart passes through vessels of progressively smaller
diameters, referred to as arteries, arterioles, and
capillaries. Capillaries are microscopic vessels that
join the arterial flow to the venous flow. Blood
returning to the heart passes through vessels of
progressively larger diameters, called venules and
veins”
Fox (2004) p 390
Blood vessel structure
Differences between arteries and
veins
Why do we have different types
of blood vessel?
• Large arteries e.g. aorta are elastic
arteries
• Smaller arteries and arterioles are
resistance arteries
• Capillaries can be continuous, fenestrated
or discontinuous, exchange takes place in
these vessels
• Veins are the capacity vessels, approx
64% of blood is here
Distribution of blood in the vascular
system
Blood flow through the vessels
Blood flow through
vessels is directly
proportional to the
difference in pressure
between the ends
of the tube
Blood flow through the vessels
• Is inversely proportional to the resistance in the
vessels.
• Resistance- determined by blood viscosity,
vessel length & vessel radius.
• Blood viscosity & vessel length rarely change,
radius can be changed by vasoconstriction
(reducing radius) or vasodilation (increasing
radius)
Blood flow through the vessels
Blood flow through vessels
• Normally laminar, with the blood components arranged
in layers
• The plasma forms the outer layer & slides smoothly
along the endothelium
• Blood cells form the ‘axial’ layer in the centre of the
blood stream
• This allows the blood to flow smoothly, layers slide over
each other, axial part moves fastest.
Blood flow through vessels
• When we take a blood pressure the sounds we
here are caused by turbulent flow of blood
• Turbulent flow -caused by change in vessel
diameter, increase in velocity, & low blood
viscosity