Cardiovascular System
Vascular System
Blood & blood vessels
What are the components of blood?
Plasma – Pale yellow, 90% Water, 8% Protein, 2% Salts
Red Blood Cells – Iron rich Haemoglobin combines with
oxygen & transported in blood
White Blood Cells – Fight infection and disease
Platelets – Assist in clotting blood
Functions of blood
What are the functions of blood?
•Transport nutrients such as Glucose and Oxygen whilst
removing waste such as Carbon dioxide & Lactic Acid
•Protect and fight disease through lymphatic system
•Maintain Homeostasis including temperature
regulation, and acid base pH balance
Blood Viscosity
• A term used to describe the relative thickness
of the blood. If the blood is very viscous, it has
a high amount of blood cells to plasma and
consequently does not flow very quickly
• Training brings about an increase in total
blood volume but the increase in plasma
levels is proportionally higher therefore blood
viscosity decreases, so faster oxygen delivery
to working muscles
The Circulatory System
This system is referred as a double circulatory
•Pulmonary system – blood between heart
and lungs
•Systemic system – blood between heart
and rest of the body
Blood Vessels
• The vascular network through which blood flows to all
parts of the body comprises of arteries, arterioles,
capillaries, venules and veins.
Arteries and Arterioles
• Arteries are high pressure vessels which carry blood
from the heart to the tissues.
• The largest artery in the body is the aorta which is the
main artery leaving the heart.
• The aorta constantly subdivides and gets smaller.
• The constant subdivision decreases the diameter of
the vessel arteries, which now become arterioles.
Arteries are composed of three layers of tissue:
• 1 an outer fibrous layer — the tunica
adventitia or tunica externa
• 2 a thick middle layer — the tunica media
• 3 a thin lining of cells to the inside — the
endothelium or tunica interna.
• The tunica media is comprised of smooth
muscle and elastic tissue, which enables the
arteries and arterioles to alter their diameter.
• Arteries tend to have more elastic tissue,
while arterioles have greater amounts of
smooth muscle; this allows the vessels to
increase the diameter through vasodilation or
• It is through vasoconstriction and vasodilation
that the vessels can regulate blood pressure
and ensure the tissues are receiving sufficient
blood — particularly during exercise.
Arteries and arterioles have
three basic functions:
• to act as conduits carrying and controlling
blood flow to the tissues
• to cushion and smooth out the pulsate flow of
blood from the heart
• to help control blood pressure.
Veins and venules
• Veins are low pressure vessels which return blood to
the heart. The structure is similar to arteries,
although they possess less smooth muscle and
elastic tissue.
• Venules are the smallest veins and transport blood
away from the capillary bed into the veins.
• Veins gradually increase in thickness the nearer to
the heart they get, until they reach the largest vein in
the body, the venae cavae, which enters the right
atrium of the heart.
Veins and Venules
• The thinner walls of the veins often distend
and allow blood to pool in them. This is also
allowed to happen as the veins contain pocket
valves which close intermittently to prevent
back flow of blood.
• This explains why up to 70% of total blood
volume is found in the venous system at any
one time.
• Capillaries are the functional units or the
vascular system.
• Composed of a single layer of endothelial
cells, they are just thin enough to allow red
blood cells to squeeze through their wall.
• The capillary network is very well developed
as they are so small; large quantities are able
to cover the muscle, which ensures efficient
exchange of gases.
• If the cross-sectional area of all the capillaries
in a muscle cell were to be added together,
the total area would be much greater than
that of the aorta.
• Distribution of blood through the capillary
network is regulated by special structures
known as pre-capillary sphincters, the
structure of which will be dealt with later in
this chapter.
• Before looking at venous return it is important to
look at the structure of veins.
• Veins have thinner walls than arteries.
• Veins also have valves.
Venous return mechanism’s
• The pressure of blood in the veins is too low to push
blood back to the heart.
• This problem is overcome in a number of ways.
• Hydrostatic Pressure
• Gravity
• Action of the Heart
• Inspiration
• Pocket Valves
• Adjacent Arteries
• Skeletal Pump
Skeletal Pump
• The muscles
surrounding the veins
expand and contract,
pressing on veins and
causing a pumping
• This muscle action is
particularly important
in maintaining venous
return during exercise.
• It is referred to as the
skeletal pump.
Adjacent Arteries
• The surges of pressure in the adjacent arteries
cause them to push against the veins, creating
a regular pumping effect.
Pocket Valves
• The blood in the veins
can only move towards
the heart; It cannot fall
back to where it came
• This is because at
regular intervals there
are semi lunar pocket
valves situated in large
Pocket Valves
• These allow the free
flow of blood towards
the heart, but they
close to prevent blood
towards the heart, but
they close to prevent
blood flowing away
from the heart.
• Increases thoracic
volume, and so
decreases thoracic
• The vein in this region
expand, causing blood
to be ‘sucked’ through
• Gravity assists the flow of venous blood from
body parts above the heart.
• However, it also hinders the flow from parts
below the heart.
Action of the Heart
• The pumping action of
the heart causes blood
to flow in to replace the
blood pumped out.
• This creates a sucking
action in the veins close
to the heart.
Hydrostatic Pressure
• There is an attraction between the molecules
in any fluid moving in a particular direction,
and this attraction helps maintain the
constant flow.
• This is called hydrostatic pressure.
• This is important in blood, particularly as the
fluid column moves back, against gravity, to
the heart.
• The pressure of blood in the veins is too low push
blood back to the heart.
• This problem is overcome in a number of ways.
• Hydrostatic Pressure
• Gravity
• Action of the Heart
• Inspiration
• Pocket Valves
• Adjacent Arteries
• Skeletal Pump
Blood Pressure
Learning Objective
• To understand how you take blood pressure
• To identify what an average pressure reading
is and the units its displayed in
• To understand how blood pressure is
controlled and how exercise effects it
Success Criteria
• You can define blood pressure giving an
average reading with the correct units
• You can take someone's blood pressure
• You can explain how the body controls blood
pressure and how exercise effects it
Home Learning
What is a sphygmomanometer used for?
What is the average reading of a
What part of the body controls this reading?
What two factors influence the reading?
Cardiac output & Blood viscosity
Blood Pressure
Controlled by the Vasomotor Centre (medulla
oblongata in brain)
• Blood pressure is the force exerted by the blood
against the walls of the blood vessels.
• It is necessary to maintain blood flow though the
circulatory system
• It is determined by two main factors –
1) Cardiac Output – the volume of blood flowing into
the system from the left ventricle.
2) Resistance to flow – the impedance offered by the
blood vessels to the blood flow.
Blood Pressure
• Blood pressure = cardiac output x resistance
• Therefore, blood pressure increases when either
cardiac output or resistance increases.
• Blood pressure in the arteries also increases and
decrease in a pattern which corresponds to the
cardiac cycle during ventricular systole, when blood
is pumped into the aorta and lowest during
ventricular diastole.
Blood Pressure Measurement
• BP is usually measured a the brachial artery using a
sphygmomanometer, and is recorded as mmHg of
systolic pressure over diastolic pressure:
• SYSTOLE pressure is experienced when the heart
pumps blood into the system
• DIASTOLIC pressure is recorded when the heart is
relaxing and filling with blood.
• Typical Reading = 120mmHg
Blood Pressure and Exercise
• BP Changes during exercise.
• During Aerobic exercise, the systolic pressure
increases as a result of increased cardiac output,
while diastolic pressure remains constant, or in well
trained athletes may even drop as blood feeds into
the working muscles.
• During isometric or anaerobic exercise both systolic
and diastolic pressure rise significantly due to
increased resistance of the blood vessels.
In pairs you are going to take each others blood
pressure using a more current
These are digital and are almost as accurate as
the original but are easier to use as you do not
have to listen for the pulse.

Cardiovascular System - Vascular System