Download The Vascular System Handout

THE VASCULAR SYSTEM
*Comprised of circulatory vessels and blood
*Responsible for the transportation of nutrients and waste products, to and
from different parts of the body e.g. O2 from lungs -> muscles or Lactic acid
from muscles -> liver.
BLOOD
Temperature of about 38˚C
8% of total body weight
5-6 litres in an average male, 4-5 litres in an average female.
Blood’s Functions
1.
Transports 02 from lungs -> all cells
2.
Transports CO2 from cells -> lungs
3.
Transports nutrients from digestive organs -> cells
4.
Transports waste products from cells -> kidneys, lungs and sweat
glands
5.
Transports hormones from glands -> cells
6.
Transports enzymes -> various cells
7.
Regulates body pH through buffers and amino acids
8.
Regulates body temperature (water -> heat absorber -> coolant)
9.
Prevents body fluid loss through the process of clotting
10.
Protects against toxins and foreign bodies
Components of Blood
4 basic elements:
1. Red Blood Cells (Erythrocytes)
2. White Blood Cells (Leucocytes)
3. Platelets (Thrombocytes)
4. Plasma (55% volume of blood)
Red Blood Cells
 These contain haemoglobin which is responsible for the red colour.
 O2 combines with haemoglobin to create oxyhaemoglobin.
 CO2 combines with haemoglobin to create carbaminohaemoglobin and it
is in the plasma.
25% CO2 -> carbaminohaemoglobin
75% CO2 -> plasma
Key words:
Hypoxia – lack of O2
Anaemia – lack of O2 carrying capacity
Life span – 120 days. Produced 2-3 million per second
White Blood Cells
Produced in red bone marrow and lymphoid tissue
Destroy foreign bodies
Life Span is very short particularly in an infected body.
Ratio RBC: WBC
700:1
Platelets
Prevent fluid loss – initiate a chain of reactions that results in blood clotting.
Life Span – 5-9 days
Produced in red bone marrow
Plasma
When the above are removed a straw coloured liquid remains and is known as
plasma.
It contains dissolved substances such as electrolytes.
CONTROL OF BLOOD SUPPLY
Recap on the Circulatory Networks:
The heart consists of two separate pumps which pump blood to two
different locations via two circulatory networks of blood vessels.
1. Pulmonary Circulation – All blood flow to and from the heart and
lungs i.e. deoxygenated blood from the right ventricle of the heart to
the lungs and oxygenated blood back to the left atrium.
2. Systematic Circulation – All blood flow to and from the heart and
body i.e. oxygenated blood from the left ventricle to the body and
deoxygenated blood back to the right atrium.
BLOOD VESSELS
Blood Vessels of the Systemic Circulation:
*Arteries are the largest blood vessels, as they spread away from the heart
they reduce in size to become arterioles and finally the narrowest blood
vessels, capillaries. Capillaries flow into venules and then even larger veins
before entering the right atrium from either the inferior vena cava from
the body or the superior vena cava from the upper body.
Blood Vessels of the Pulmonary Circulation
Pulmonary artery - only artery to carry deoxygenated blood
Pulmonary vein – only vein to carry oxygenated blood
Blood Vessel Structure
Structure/Function Arteries
e.g. Size
Arterioles
Capillaries Venules
Veins
VENOUS RETURN (VR)
VR is the transport of blood from the capillaries through venules, veins and
then either the superior or inferior vena cava back to the right atrium of
the heart.
Simple definition: - return of deoxygenated blood to the Right atrium of the
heart, this helps maintain cardiac output.
Starlings Law of the Heart
Starlings Law states that “stroke volume is dependant upon venous return”.
Hence, if VR increases, SV increases; if VR decreases, SV decreases.
At rest VR is sufficient to maintain SV and Q to supply the demand for
oxygen. During exercise the pressure of blood in the veins is too low to
maintain VR and so SV and Q therefore decrease. Additional mechanisms
are used to help push the blood against gravity through the veins back to the
heart.
Factors/Mechanisms that Aid Venous Return:
1. Pocket valves – one way valves in the veins prevent backflow of blood
and direct it towards the heart.
2. Muscle pump – Veins are situated between skeletal muscles, which
when contracting and relaxing help squeeze blood back towards the
heart.
3. Respiratory Pump – During exercise, breathing becomes deeper and/or
faster, which causes pressure changes in the thorax and abdomen.
This increases the pressure in the abdomen, squeezing the large veins
in that area and forcing the blood back to the heart.
4. Smooth Muscle – Contraction and relaxation of smooth muscle in the
middle layer of the vein also helps push blood.
5. Gravity – Blood from the upper body is aided by gravity as it descends.
Blood Pooling
VR requires a force to push the blood back towards the heart, if there is
insufficient pressure blood can pool in lower limbs.
Pocket valves, gravity and smooth muscle during rest are enough to maintain
VR. Skeletal and respiratory pumps are needed during and immediately after
exercise.
An active cool down is essential to help keep these two important
mechanisms working, ensuring that VR is maintained and it prevents blood
pooling.
VASCULAR SHUNT MECHANISM
This is the redistribution of blood to the working muscles during exercise
(being most concerned of the bloods distribution to working muscles).
 At Rest
- Only 15-20% resting Q is supplied to muscles.
- Remainder (80-85%) is supplied to the body organs.

-
During Exercise
Increased Q to working muscles – 80-85% as exercise intensity
increases.
Decreasing percentage of Q is supplied to body organs.
Blood supply to the brain in maintained.
Increased blood supply to the skin during lighter work, but decreased
as exercise intensity increases.
How is this Redistribution Achieved?
Key Words
Vasodilation – Increase in the size of the lumen of a blood vessel.
Vasoconstriction – Decrease in the size of the lumen of the blood vessel.
The vascular shunt involves the following mechanisms:
1. The vasodilation of arterioles supplying the skeletal muscles
consequently increasing the blood flow.
2. The vasoconstriction of arterioles supplying the other non essential
organs (NEO)
3. The opening of the pre-capillary sphincters in the capillary networks
supplying the working muscles
4. The closing the pre-capillary sphincters in the capillary networks
supplying the NEO.
IT ALSO…
If you are involved in long periods of exercise you get hot, the vascular
shunt mechanism also ensures that the blood vessels near the skin vasodilate
allowing heat to escape from the body.
VASOMOTOR CONTROL CENTRE (VCC)
*Located in the Medulla oblongata
*Stimulates the sympathetic system to either vasodialte or vasoconstrict
the pre-capillary sphincters and arterioles supplying the muscles and organs.
*Works very similarly to the CCC.
Why do the Veins Vasodilate/Vasoconstrict?
REMEMBER: Chemoreceptors pick up the following changes:
 Increase in Lactic Acid
 Increase in CO2
 Increase in Temperature
 Increase in Metabolic Activity
 Decrease in pH (thus an increase in Acidity)
1. Receives information from chemoreceptors (detect increases in lactic
acid, CO2 levels and decreases in O2 and pH levels) and baroreceptors
(systolic blood pressure indicators).
2. Sends messages via the sympathetic nervous system.
3. This is transmitted via the Vasomotor Nerve and Venomotor Nerve to
the Arterial and Venous blood vessel walls. (Sometimes referred to as
Venomotor Tone and Vasomotor Tone).
4. Vascular shunt occurs – either vasodilation or vasoconstriction occurs.
OXYGEN AND CARBON DIOXIDE TRANSPORT
Oxygen transport is achieved

(97%) transported within the protein, haemoglobin, packed with red
blood cells.

(3%) within blood plasma
Carbon dioxide transport is achieved



(70%) combined with water within red blood cells as carbonic acid
(23%) combined with haemoglobin as carbaminohaemoglobin (HbCO2)
(7%) dissolved in plasma
WARM UP AND COOL DOWN EFFECTS ON THE VASCULAR SYSTEM
Warm Up – effects on the vascular system
1. Gradual increase in blood flow/Q due to the vascular shunt mechanism via:
- Vasoconstriction of arterioles/pre-capillary sphincters to organs
decreasing blood flow to organs and therefore increasing blood flow to
working muscles.
- Vasodilation of muscle arterioles/pre-capillary sphincters increasing blood
flow delivery to working muscles.
2. Increased body/muscle temperature causing a more rapid increase in
transport of the enzymes required for energy systems and muscle
contraction.
3. Increase in body/muscle temperature which
- decreases blood viscosity, improving blood flow to working muscles
- increases the dissociation of oxygen from haemoglobin in muscle tissues
4. Decrease OBLA (onset of blood lactic acid) due to the early onset of
anaerobic work when a warm up is not carried out.
Cool Down – Effects on vascular System




Keeps metabolic activity elevated which gradually decreases HR and
respiration.
Maintains respiratory/muscle pump which
Prevents blood pooling in veins
Maintains venous return
Maintains blood flow to supply O2 maintaining blood pressure.
Keeps capillaries dilated to flush muscles with oxygenated blood,
which increases the removal of blood and muscle lactic acid and
carbon dioxide.
Simple Version of Warm Up and Cool Down
Warm Up
 Your vasomotor centre is making sure that more blood is being
distributed to the working muscle, therefore there will be more
oxygen being delivered to the muscle cells, which will help reduce the
oxygen deficit when you start your activity for real.
 Oxygen dissociates more readily from haemoglobin as muscle
temperature increases.
 Blood vessels within the muscles dilate further increasing blood flow.
Cool Down
 Your body returns to its pre exercise state more quickly if you
perform light exercise during the recovery period.
 Increased blood flow helps to flush out waste products, i.e. lactic acid
and CO2 – reducing your overall recovery time.
 Prevents blood pooling – maintaining skeletal pump mechanism.
 If you stop suddenly, the amount of blood returning to the heart
suddenly which reduces SV and causes a drop in blood pressure making
the athlete feel dizzy and light-headed.