Transcript File

Structure of the
Cardiovascular System
What you Should Know
• The structure and function of arteries,
capillaries and veins including the
endothelium, central lumen, connective
tissue, elastic fibres, smooth muscle and
valves.
• The role of vasoconstriction and
vasodilation in controlling blood flow.
What is the Cardiovascular
system?
• The cardiovascular system, also
known as the circulatory system,
is composed of blood, blood
vessels and the heart.
• The heart functions as a pump to
move blood through the blood
vessels of the body.
• A circulatory system is essential
for large, multi-cellular
organisms, such as humans and
animals, and provide at least five
major functions that are
necessary for life.
The five major functions of the
cardiovascular system are:
• Transporting oxygen and
removing carbon dioxide
• Transporting nutrients and
removing wastes
• Fighting disease
• Transporting hormones
• Regulating body temperature
Cardiovascular system
• http://www.youtube.com/watch?v=CjNKbL
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Components of the CVS
• The CVS consists of
a double pump (the
heart) and a complex
system of blood
vessels.
• Blood circulates from the heart through the
arteries to the capillaries to the veins and
back to the heart.
• There is a decrease in blood pressure as
the blood moves away from the heart.
Blood Vessels
There are 3 types of blood vessel:
• Arteries (and arterioles)
• Capillaries
• Veins (and venules)
Central lumen of blood vessels
• The endothelium lining the central lumen
of the blood vessels is surrounded by
layers of tissue.
• These surroundings layer differ in each
type of blood vessel
ARTERIES
• Carry blood away from
the heart
• Endothelium
– One cell thick
• Elastic tissues & smooth
muscles
– Rebounds
– Evens flow
• Fibrous tissue
– Tough
– Resists stretch
Arteries
•Arteries carry blood away from the heart.
•The largest arteries e.g. the Aorta, have thick elastic walls
which can stretch to accommodate the surge of blood after each
contraction of the heart.
•Arteries branch many times, forming smaller and smaller
vessels, the smallest of which are arterioles.
• Contraction of the smooth muscle lining the walls of the
arterioles allows them to open or close to varying degrees to
adjust blood flow to different parts of the body e.g. during
vasodilation and vasoconstriction
VEINS
• Carry blood towards
the heart
• Endothelium
• Larger lumen than
arteries
• Thinner muscle layer
& few elastic fibres
– Blood at lower
pressure
• Fibrous tissue
VEINS
• Contain valves
– Prevents backflow of
blood
• Situated between
skeletal muscles
– Muscle compresses
vein when contracted
– Blood “squirted”
towards heart
CAPILLARIES
• Transport blood between
arteries and veins
• Form large networks
(capillary beds)
• Exchange of materials
between blood and cells
• Their walls are only one
cell thick, allowing
nutrients and waste to
diffuse through with
ease.
Capillaries
Arteriole
Capillaries
(capillary bed)
Venule
Blood vessels
Tissue Fluid and the Lymphatic
system
What you Should Know
• Tissue fluid supplies cells with glucose, oxygen and
other substances.
• Carbon dioxide and other metabolic wastes diffuse out of
the cells and into the tissue fluid to be excreted.
• Much of the tissue fluid returns to the blood.
• Lymphatic vessels absorb excess tissue fluid and return
the lymph fluid to the circulatory system.
• Similarity of tissue fluid and blood plasma
• Pressure filtration of fluids through capillary walls.
Tissue Fluid
• Blood consists of red and white blood
cells, platelets and plasma
• Plasma is a watery yellow liquid containing
dissolved substances such as glucose,
amino acids, respiratory gases, plasma
proteins and useful ions
• The blood plasma fluid which leaks into
•
the tissues is called tissue fluid
Some of the tissue fluid returns to the
blood at the venous end of the capillary
Cells
Lymphatic system
tissue
organs
Blood plasma to tissue fluid
• Blood pressure forces the fluid part of the blood
•
•
•
along with small soluble molecules out of the
capillaries into the tissue fluid.
Blood cells and large protein molecules are left
behind
The cells exchange molecules with the tissue
fluid by diffusion down a concentration gradient
Useful molecules such as food and oxygen
diffuse into the cells whilst carbon dioxide and
wastes diffuse out of them
Lymph
• The fluid that does not return to the blood is now
referred to as lymph and is collected by the
lymphatic system.
• Lymph travels under low pressure to enter the
main circulation near the heart
• The lymphatic system has no pump
• The contraction of skeletal muscles squeezes
lymph along the vessels
• Lymph travels through vessels in one direction
only due to the presence of valves
Comparison of contents of plasma and tissue fluid
Plasma
Tissue fluid
More protein
Less protein
Red blood cells & white
blood cells
White blood cells
Less fat
More fat
Summary Tissue Fluid and
Lymphatic System
Lymph passes
into lymphatic
system
Lymph
vessel
Blood
leaving in
venule
low
pressure
Some tissue
fluid enters
capillary by
osmosis
Some tissue
fluid enters
lymphatic
system
Blood
arriving in
the
arteriole
high
pressure
capillary
Some plasma
forced out of
capillary
Respiring cell
Tissue fluid
Structure and Function of the Heart
Cardiac Function and Cardiac
Output
What You Should Know
• Definition of cardiac output and its
calculation.
• Description of the cardiac cycle to include
the functions of atrial systole, ventricular
systole, diastole.
• Effect of pressure changes on atrioventricular (AV) and semi lunar (SL)
valves.
Heart Rate (HR)
• Number of times heart beats in one minute
• Normal values around 72bpm
• Normal range is between 60-90
Cardiac Output
Cardiac Output is the volume of blood pumped
by each ventricle per minute and is the
function of two factors:
• Heart rate (beats per minute)
• Stroke volume (the volume of blood ejected by
each ventricle during each contraction)
• The left and right ventricles pump the same
volume of blood through the aorta and
pulmonary artery.
CO = HR x SV
Cardiac Output (CO)
• The volume of blood pumped by each
ventricle per minute, measured in litres
• Calculated as follows
• CO = HR x SV
• Normal values are around 5 litres/min
Stroke Volume (SV)
• Volume of blood ejected by each ventricle
during contraction
• Normal values are around 70ml
At rest: HR = 72bpm
SV = 70ml
i.e. CO = 72 x 70
= 5040 ml/min
= 5 litres/min
• Cardiac Output varies between individuals and
depends on their physical fitness and level of
activity.
• For example, the heart of a highly trained athlete
can pump 30-35 l/min
• Most non-athletes can only achieve a max of 20
litres.
Some typical values for cardiac output at varying levels of
activity
Activity
Level
Heart rate
(bpm)
Stroke
Volume (ml)
Cardiac
Output
(l/min)
Rest
72
70
5
Mild
100
110
11
Moderate
120
112
13.4
Heavy
(athlete)
200
150
30
Structure of the Heart
Revision on Circulatory System
• Double system
• The pulmonary circuit carries deoxygenated
blood from the right ventricle to the lungs and
returns oxygenated blood to heart
• The systemic circuit carries oxygenated blood
from the left ventricle to the aorta and then the
rest of the body and returns deoxygenated from
the body to the heart
The cardiac cycle
• Each heartbeat is called a cardiac cycle
and consists of the following
• Atria contract simultaneously
• Ventricles contract simultaneously
• All chambers relax
• Lasts about 0.8 secs (0.3systole,0.5
diastole)
Two phases of the cardiac
cycle
• Systole: contraction of the heart
(Atrial first, the ventricular), blood
forced out of chambers
• Diastole: relaxation of the heart,
chambers fill with blood
• The opening and closing of the AV and SL
valves are responsible for the heart
sounds heard with a stethoscope.
THE CARDIAC CYCLE
1. Atrial & ventricular
diastole
2. Atrial systole,
ventricular diastole
3. Ventricular systole,
atrial diastole
ATRIAL & VENTRICULAR
DIASTOLE
• Blood enters atria
from vena cava &
pulmonary vein
• AV valves open
ATRIAL SYSTOLE &
VENTRICULAR DIASTOLE
• Both atria contract
• Blood forced into
relaxed ventricles
• AV valves still open
• Ring of muscle
around entrance to
each atrium closed
• Prevents backflow of
blood into veins
ATRIAL DIASTOLE &
VENTRICULAR SYSTOLE
• About 0.1 secs after
atrial systole
• Ventricles contract
• Blood forced into
arteries through the
open semi-lunar
valves
• AV valves close
• Prevents backflow of
blood to atria
ATRIAL DIASTOLE &
VENTRICULAR SYSTOLE
• Semi-lunar valves
close when pressure
in arteries exceeds
pressure in ventricles
• Cardiac cycle begins
again!
PRESSURE CHANGES
THE CONDUCTING SYSTEM
OF THE HEART
What You Should Know
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•
•
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•
•
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The structure and function of cardiac conducting system including nervous
and hormonal control.
Control of contraction and timing by cells of the sino-atrial node (SAN) and
atrio-ventricular node (AVN).
Interpretation of electrocardiograms (ECG).
The medulla regulates the rate of the SAN through the antagonistic action of
the autonomic nervous system (ANS).
Sympathetic accelerator nerves release adrenaline (epinephrine) and
slowing parasympathetic nerves release acetylcholine.
Blood pressure changes, in response to cardiac cycle, and its
measurement.
Blood pressure changes in the aorta during the cardiac cycle.
Measurement of blood pressure using a sphygmomanometer.
A typical reading for a young adult is 120/70 mmHg.
Hypertension is a major risk factor for many diseases including coronary
heart disease.
The Conducting System of the
Heart
• The heart beat starts in the heart itself
• It is regulated by the nervous system and
hormones
1. Sino-atrial (SA) node
2. Atrio-ventricular (AV)
node
3. Bundle of His
4. Right & left bundle
branches
5. Purkinje fibres
• The muscle cells of the heart are myogenic as
they contract spontaneously
• The sinoatrial node (SAN) also known as the
pacemaker is situated in the wall of the right
atrium
• It ensures that both atria contract simultaneously
• It sends out a wave of excitation (electrical
impulses) which is carried through the muscular
walls of both atria
• Results in atrial systole
THE AV NODE
• (2)The AVN then picks up
the impulse from SAN
• (3)Passes to Bundle of
His
• Travels down the septum
• (4)Passes to the bundle
branches (right & left)
• (5)Passes to Purkinje
fibres
• Ventricles contract from
bottom up
SAN
Bundle
of His
AVN
septum
Regulation of the Heart
Autonomic Nervous System and
the Heart
• The autonomic nervous system regulates the
functions of our internal organs such as the heart,
stomach and intestines.
• The autonomic nervous system functions
involuntary. For example, we do not notice when
blood vessels change size or when our heart
beats faster.
• The control centre for regulation of heart rate is
located in the medulla of the brain
• The autonomic nervous system consists of
2 opposing (antagonistic) branches
– Sympathetic pathway
– Parasympathetic pathway
Sympathetic Nerve
• An increase in the
number of nerve
impulses at the SAN
via the sympathetic
nerve increases heart
rate
• Sympathetic
accelerator nerves
release
norepinephrine
(noradrenaline)
Parasympathetic Nerve
• An increase in the
number of nerve
impulses at the SAN
via the
parasympathetic
nerve decreases
heart rate
• parasympathetic
nerves release
acetylcholine.
Hormonal Regulation of the Heart
• Under certain
circumstances e.g. stress
or exercise the
sympathetic nervous
system causes the
adrenal glands to produce
adrenaline which travels in
the blood to act on the
SAN, which generates
impulses at a higher rate,
increasing heart rate
ELECTROCARDIOGRAM
• ECG (electrocardiogram) is a test that measures the
electrical activity of the heart.
• The signals that make the heart's muscle fibres contract
come from the sinoatrial node.
• In an ECG test, the electrical impulses made while the
heart is beating are recorded and shown on a piece of
paper.
• This is known as an electrocardiogram, and records any
problems with the heart's rhythm, and the conduction of
the heart beat through the heart which may be affected
by underlying heart disease.
• Electrodes placed on body
• Three waves
ELECTROCARDIOGRAM
• P wave
– Electrical excitation
from SA node
spreading across atria
• QRS wave
– Wave of excitation
passing over the
ventricles
• T wave
– Electrical recovery of
the ventricles
ABNORMAL ECG’S
• Atrial flutter
• Rapid contraction of
the atria
• Atria contract 3 times
for every ventricular
contraction
ABNORMAL ECG
• Ventricular
tachycardia
• Ventricles beat rapidly
and independently of
the atria
ABNORMAL ECG’S
• Ventricular fibrillation
• Unco-ordinated
electrical activity
• Pumping cannot take
place
• Fatal if not corrected
• Defibrillation
Blood Pressure
• Force exerted by blood against walls of
blood vessels
• Measure 2 values – systolic BP (pressure
during ventricular contraction) and
diastolic BP (pressure during ventricular
relaxation)
• Measured using sphygmomanometer in
mm Hg
• Normal values are around 120/70
Hypertension
• Hypertension is a
major risk factor for
many diseases
including coronary
heart disease.
Measurement of BP
Both systolic and diastolic BP can
be measured by an inflatable
instrument called a
sphygmomanometer which is
wrapped around the upper arm.