Download ECG and blood vessels File

Heart and circulation
ECG and Blood vessels
The ECG Trace
R
P wave
T wave
Q
S
The ECG trace for each heartbeat displays a P wave, a QRS wave
or complex and a T wave
R
P wave
T wave
Q
S
The P wave is the result of depolarisation spreading across the atria
from the SA node; it coincides with atrial contraction or systole
The QRS wave or complex is the result of depolarisation of the
ventricles and coincides with ventricular systole
The T wave is the result of repolarisation of the ventricles as the
ventricles begin to relax; repolarisation of the atria is not detected as
the small voltage changes involved are masked by the QRS wave
Blood vessels
• Arteries carry blood away from the heart,
each organ has a main artery supplying blood
e.g. renal artery to the kidneys, hepatic artery
to the liver.
• The arteries branch into smaller vessels called
arterioles
• These branch into tiny vessels called
capillaries
Structure of arteries
• A tough outer layer of collagen
for strength.
• Elastic fibres which recoil after
each pulse of blood. This evens
out the blood flow and maintains
blood pressure. Elastic recoil is
particularly important in the
major arteries like the aorta.
• Smooth muscle which contracts
to narrow(constrict) the artery,
reducing blood flow.
• Endothelium a single layer of
squamous epithelial cells which
provide a smooth surface for
blood to flow over. (smooth
surface =less friction)
Arterioles
•
•
•
•
•
Smooth muscle in the arteriole walls
enables different quantities of blood to
be directed to different organs.
During exercise the arterioles in the
muscles dilate to increase the blood
flow bringing more oxygen to muscle
cells for respiration to release energy.
In a cold environment, smooth muscle
in the walls of the arterioles bringing
blood to the skin contracts.
This narrows(constricts) the arterioles in
the skin so less blood flows through the
capillary networks in the skin and less
heat is lost from the body
Muscle in the artery walls DOES NOT
PUSH THE BLOOD ALONG!!!
Capillaries
• Capillaries are about 810µm in diameter (about
0.01mm)
• Capillaries have walls which
are one cell thick, made of
squamous epithelial cells
that have small gaps or
pores between them.
• There is no smooth muscle
or elastic tissue.
• Blood plasma escapes from
the capillaries and forms
tissue fluid which bathes all
the body tissues
Blood cells in a capillary
Veins
• Have a wider lumen
• Thin layers of elastic
tissue and smooth
muscle –veins do not
need to constrict to
reduce blood flow.
Blood pressure in veins
is lower
Veins continued
• Valves in veins prevent
back flow of blood
Pressure changes in blood vessels
• In the aorta blood flows in
surges.
• Pressure is high as the
ventricles in the heart
contract (systole)
• Pressure falls when the
ventricles relax (diastole)
Changes in blood flow across
capillaries
• Although individual capillaries
have a tiny diameter, adding
the diameter of all the
capillaries together provides a
total wide diameter in a
capillary network.
• The wide diameter leads to a
drop in blood pressure and a
slowing of blood flow, allowing
time for the exchange of gases
and nutrients between the
tissues and the blood
Constituents of blood
Formation of tissue fluid