Download The Cardiovascular System

The Cardiovascular System
Chapter 11
The Cardiovascular System
• Cardiovascular system is a closed system
• Consists of
• Heart: The heart pumps blood
• Blood vessels : Blood vessels allow blood to circulate to
all parts of the body
• Function:
• To deliver oxygen and nutrients and to remove carbon
dioxide and other waste products
Heart
• Heart is transport system pump for
the blood
• Heart is two pumps in one
• Pulmonary Circulation:
• R side of heart receives blood
from body, pumps blood to lungs
and returns to L heart
• Systemic Circulation:
• L side of heart pumps blood to
tissues of the body & return to
R heart
• Heart of healthy person pumps
approx. 7200 L of blood each day
at the rate of 5L/min.
Anatomy of the Heart
• Location, size and shape of Heart
• Size: size of a closed fist
• Shape
– Apex: Blunt rounded cone
– Base: larger flat part
• Location:
– Located in thoracic cavity in left
of mediastinum (midline)
between the two lungs
– Superior surface of diaphragm
– Important clinically when using
a stethoscope, performing an
ECG, or performing CPR
Anatomy of the Heart
• Heart is enclosed by a double-walled
sac called Pericardium
• Composed of:
– A superficial fibrous pericardium
– A deep two-layer serous
pericardium
• Parietal pericardium lines the
internal surface of the fibrous
pericardium
• The visceral pericardium or
epicardium lines the surface of
the heart
• & separated by fluid-filled
pericardial cavity
• Helps in reducing friction as
heart moves within the
pericardial sac
Anatomy of the Heart
• Heart Wall: composed of 3
layers of tissues:
• Epicardium – visceral layer of
the serous pericardium, lines
the surface of the heart
• Myocardium – Middle layer,
cardiac muscle layer forming
the bulk of the heart,
responsible for heart
contraction
• Endocardium – Lines inner
surface of heart chambers
Heart Chambers and Vessels
• Heart consists of 4 chambers:
• Two atria, two ventricle
• Atria: Thin walled, forms the superior
part of heart
• Ventricle: Thick-walled, forms the
inferior part of heart
• Large veins: carry blood to the heart:
– Superior and inferior venae cavae
– carry blood from body to R atrium
– 4 pulmonary veins carry blood
from lungs to L. atrium
• Arteries: conveying blood away from
heart:
– Aorta carries blood from L.
ventricle to the body
– Pulmonary trunk carries blood
from R. ventricle to lungs
Heart Chambers and Valves
• Atria
– Right atrium: three major
openings to receive blood
returning from the body
(superior vena cava,
inferior vena cava,
coronary sinus)
– Left atrium: four openings
that receive blood from 4
pulmonary veins from lungs
– Two atria are separated
from each other by
Interatrial septum
Heart Chambers and Valves
• Ventricles
– Atrioventricular valves:
openings between atria
and ventricles
– Right ventricle opens to
pulmonary trunk
– Left ventricle opens to
aorta
– Interventricular septum
between the two ventricle
Heart Valves
• Heart valves ensure
unidirectional blood flow
through the heart
• Atrioventricular (AV)
valves: lie between the atria
and the ventricles
• AV valves allow blood flow
from atria to ventricle
• But prevent backflow into
the atria when ventricles
contract
• AV valve between L atrium
& L ventricle has 2 cusps –
Bicuspid Valve
• AV valve between R atrium
& R ventricle has 3 cusps –
Tricuspid Valve
Heart Valves
• Semilunar Valves:
• Aortic semilunar valve:
lies between the left
ventricle and the aorta
• Pulmonary semilunar
valve: lies between the
right ventricle and
pulmonary trunk
• Semilunar valves prevent
backflow of blood into the
ventricles
Blood Flow Through the Heart
• Superior and inferior vena
cava dump blood into the
right atrium
• From right atrium, through
the tricuspid valve, blood
travels to the right ventricle
• From the right ventricle,
blood leaves the heart as it
passes through the
pulmonary semilunar valve
into the pulmonary trunk
• Pulmonary trunk splits into
right and left pulmonary
arteries that carry blood to
the lungs
Blood Flow Through the Heart
• Oxygen is picked up and
carbon dioxide is dropped off
by blood in the lungs
• Oxygen-rich blood returns to
the heart through the four
pulmonary veins from lungs
• Blood enters the left atrium
and travels through the
bicuspid valve into the left
ventricle
• From the left ventricle, blood
leaves the heart via the aortic
semilunar valve and aorta
• From aorta, supply blood to all
body parts
Blood Flow Through the Heart
Cardiac Circulation
• Blood in the heart chambers does not
nourish the heart muscles
• Coronary arteries in heart supply
blood to heart muscles
• Coronary arteries branch from the
aorta to supply the heart muscle with
oxygenated blood
• Cardiac veins from heart drain
blood into a large venous cavity
called Coronary sinus
• Coronary sinus then empties into
the right atrium
Physiology of Heart
• Heart muscle cells contract,
without nerve impulses, in
a regular, continuous way
• Heart is autorhythmic
• Initiate, conduct and
impulse
• Heart contains special
tissue that produces &
sends electrical impulses to
the heart muscle to
contract
Physiology of Heart
• The heart's conducting
system consists of:
• Sinoatrial (SA) node
• Atrioventricular
(AV)node
• Bundle of His
• Bundle branches
• Purkinje fibers
Physiology of Heart
– Sinoatrial (SA) Node
• Mass of autorhythmic cells
• Electrical impulse that causes
rhythmic contraction of heart
muscles arises in the SA node
• Pacemaker of the heart
• Located in R. atrium
• Send impulse 70 to 80 times a
minute
Physiology of Heart
•
AV Node:
• The electrical impulse
from the SA node
spreads over the right
and left atria
• causes atrial contraction
• Then impulses are
conducted to the
atrioventicular (AV) node
Physiology of Heart
•
Bundle of His (AV bundle)
• Then electrical impulse is relayed
down to Bundle of HIS
•
Conducts impulse to right and left
bundle branches
•
•
•
Bundle Branches
Right and left branches
Branch into purkinje fibers
•
Purkinje Fibers
• Enter myocardium of ventricle walls
• Carry impulse to ventricles
• Ventricular contraction
CARDIAC CONDUCTION SYSTEM SUMMARY
Sinoatrial Node
AV Node
AV Bundle
Bundle Branches
Purkinje Fibers
Cardiac Cycle
• Cardiac cycle: Is the
sequence of events in one
heartbeat
• It is the repetitive pumping
process that begins with
onset of cardiac muscle
contraction and ends with
beginning of next contraction
• Cardiac muscle contraction is
responsible for pressure and
blood movement. How?
• Blood moves from high
pressure to low pressure
Cardiac Cycle
• The length of cardiac cycle is about 0.8 sec
• Interval from end of one contraction to the following
contraction
• Consists of Two Phases:
– Systole phase
– Diastole phase
CARDIAC CYCLE
• Systole Phase
– Contraction phase
– Atrial Systole (0.1 sec.)
• After passive filling with blood
• Atrial pressure rises above
ventricular pressure
• And AV valves open
• Blood is ejected from atria to
ventricle
• semilunar valves closed
• Ventricles fill with blood
CARDIAC CYCLE
• Ventricular Systole (0.3
sec.)
• AV and semilunar valves
closed until Ventricle
pressure rises above aorta
and pulmonary trunk
pressure
• opens semilunar valves
• Blood pushed into pulmonary
trunk and Aorta
• 120 mm Hg pressure
• Atria in diastole
CARDIAC CYCLE
• Diastole Phase
– Relaxation phase
– Ventricular Diastole
• Follows ventricular
systole
• AV valves reopen
and filling begins
• 80 mm Hg pressure
Electrocardiogram: ECG
• When impulse pass through the
heart, electric currents are generated
• Electric current that can be
measured at the surface of the
body - ECG
•P
wave: Atrial
depolarization
• QRS complex: Ventricular
depolarization
• T wave: Ventricular
repolarization
Heart Contractions
• Tachycardia—rapid heart rate over 100
beats per minute
• Bradycardia—slow heart rate less than 60
beats per minutes
Heart Sounds
• First heart sound or “lubb”
– Atrioventricular valves vibrations as valves close
at beginning of ventricular systole
• Second heart sound or “dupp”
– Results from closure of aortic and pulmonary
semilunar valves at beginning of ventricular
diastole, lasts longer
Cardiac Output
• Cardiac output (CO)
– Amount of blood pumped by heart in one minute
• Stroke volume (SV)
– Volume of blood pumped by each heartbeat
– Usually remains relatively constant
– About 70 mL of blood is pumped out of the left
ventricle with each heartbeat
• Heart rate (HR)
– Typically 75 beats per minute
Cardiac Output
CO = HR  SV
CO = HR (75 beats/min)  SV (70 mL/beat)
CO = 5250 mL/min
Starling’s law of the heart— the more the cardiac muscle
is stretched, the stronger the contraction
• Important factor for stretching the heart muscle is
venous return
• The greater the volume of blood returned to the heart by
the veins, the greater the volume of blood the heart will
pump
•
•
•
•
Regulation of the Heart
• To maintain homeostasis, amount of blood pumped
by heart must vary:
•
Eg. Cardiac output increases more during exercise
than resting
• Intrinsic regulation: Results from normal functional
characteristics of heart, not depend on neural or
hormonal regulation
Regulation of the Heart
• Extrinsic regulation: Involves neural
and hormonal control
• Neural Control
– Parasympathetic stimulation
• Supplied by vagus nerve,
acetylcholine is secreted,
decreases heart rate, maintain
heart beat average of 70
beats/min.
– Sympathetic stimulation
– Supplied by cardiac nerves
– Increases heart rate and force of
contraction.
– Epinephrine and norepinephrine released.
– Increased heart beat causes increased
cardiac output
Regulation of the Heart
– Hormonal Control
– Epinephrine and
norepinephrine from
the adrenal medulla
– Increases rate and
force of heart
contraction
– Occurs in response to
increased physical
activity, emotional
excitement, stress
Blood Vessels: The Vascular System
• Transport blood to the
tissues and back
– Carry blood away from
the heart
• Arteries
• Arterioles
– Exchanges between
tissues and blood
• Capillary beds
– Return blood toward the
heart
• Venules
• Veins
• Arteries and veins are
composed of three tunics
(layers) – tunica intima, tunica
media, and tunica externa
• Lumen – central bloodcontaining space surrounded
by tunics
• Capillaries are composed of
endothelium
Blood Vessels: Microscopic Anatomy
• Three layers (tunics)
– Tunic intima
• Endothelium
• Basement membrane
– Tunic media
• Smooth muscle
• Blood flow is regulated by
smooth muscle of Tunica Media
– Vasoconstriction: smooth muscles
contract, decrease in blood flow
– Vasodilation: smooth muscles
relax, increase in blood flow
• Controlled by sympathetic
nervous system
– Tunic externa
• Mostly fibrous connective tissue
• Thickness of each layer varies
with type and diameter of blood
vessel
Differences Between Blood
Vessels
• Walls of arteries are the thicker than veins
• Lumens of veins are larger than arteries
• Because BP is low in veins and work
against gravity
• Larger veins have valves to prevent
backflow
•
More valves in veins of lower extremities
than in veins of upper extremities
• Walls of capillaries are only one cell layer
thick to allow for exchanges between
blood and tissue
Movement of Blood Through
Vessels
• Most arterial blood is
pumped by the heart
• Veins use the milking
action of muscles to
help move blood
Capillary Beds
• Capillary beds consist
of two types of vessels
– Vascular shunt— vessel
directly connecting an
arteriole to a venule
– True capillaries—
exchange vessels
• Oxygen and nutrients
cross to cells
• Carbon dioxide and
metabolic waste products
cross into blood
• The vascular system has two
distinct circulations
– Pulmonary circulation –
short loop that runs from the
heart to the lungs and back to
the heart
– Systemic circulation –
routes blood through a long
loop to all parts of the body
and returns to the heart
• Heart pumps blood from
right ventricle into
pulmonary trunk
• Pulmonary trunk divides
into left and right
pulmonary arteries,
Transport blood to each
lung
• Two pulmonary veins
exit each lung and enter
left atrium
• Oxygenated blood enter the
heart from pulmonary veins
through L. atrium
• From L. atrium to L. ventricle
• From L. ventricle to aorta
• From aorta blood flows to all
body parts
 Aorta





All arteries are derived from aorta
Aorta is divided into 3 parts:
Ascending aorta
Aortic arch
Descending aorta
– Ascending aorta: Passes superiorly
to heart, has 2 branches
– right and left coronary arteries, supply
blood to cardiac muscles
– Aortic arch: arching posteriorly and to
the left and has 3 branches, carry
blood to head and neck
• Brachiocephalic artery
• Left common carotid
• Left subclavian artery
Systemic Circulation: Arteies
 Aorta
 Descending aorta: Longest part
 Consists of:
Thoracic aorta: portion in thorax
 Abdominal aorta: inferior to
diaphragm: branches supply blood
to abdominal wall and organs
 Ends as two common iliac arteries:
supply blood to pelvis & lower limbs
 Coronary Arteries:
- Only branches of ascending
arteries, supply blood to heart
Major veins of the Systemic Circulation
• Return blood from body to right atrium
• Major veins
– Coronary sinus : returning blood from heart walls
– Superior vena cava: Returning blood from head,
neck, thorax, upper limbs
– Inferior vena cava: Returning blood from abdomen,
pelvis, lower limbs
• Types of veins
– Superficial, deep, sinuses (cranium & heart)
Special Circulations
• Arterial Supply of Brain
• Supply of blood to brain is crucial
• Lack of O2 kills the brain cells that
cannot be revived
• The main arteries that supply blood to
brain include
– Internal carotid artery
– Vertebral artery
• Internal carotid arteries divide into
– Anterior and middle cerebral arteries
– These arteries supply most of the
cerebrum
• Vertebral arteries join once within the
skull to form the basilar artery
– Basilar artery serves the brain stem
and cerebellum
Special Circulations
• Arterial Supply of the
Brain:
• Basilar artery divides to form Posterior
cerebral arteries
– These arteries supply the posterior
cerebrum
• Anterior and posterior blood supplies
are united by small communicating
arterial branches
• Result—complete circle of connecting
blood vessels called cerebral arterial
circle or circle of Willis around the
pituitary gland
Hepatic Portal System
 Nutrients and other substances
absorbed by stomach and intestine are
transported to liver by hepatic portal
system
 Hepatic portal system carries blood
through veins from capillaries of
stomach, intestine, spleen to liver
 Largest vein of the system
 From liver Hepatic veins join the
Inferior vena cava
Pulse
• Pulse
– Pressure wave of blood
• Monitored at “pressure
points” in arteries
where pulse is easily
palpated
• Pulse averages 70–76
beats per minute at rest
BLOOD PRESSURE
• Pressure exerted on vessel walls
• Blood pressure measured in mm Hg
• Measured with sphygmomanometer
– Pressure in cuff compresses artery until no pulse heard
– Systolic pressure: taken at first pulse as pressure in cuff
released (ave. 120) = pressure while heart ventricles contracting,
1st Korotkoff sound
– Diastolic pressure: taken when cuff released to point where
sound no longer audible (ave. 80) = pressure when ventricles not
contracting
– Pulse pressure = systolic - diastolic (measure of stress exerted
on small arteries)
Blood Pressure: Effects of Factors
• Blood Pressure varies directly with the following:
Cardiac Output
• Stroke volume X heart rate
• Normal is 5.5 liters/min.
Peripheral Resistance
• Opposition to blood flow
–  with blood viscosity
–  with length of vessel
–  with  in vessel diameter (has the greatest influence
on B.P.)
INFLUENCES ON B.P.
• Blood Pressure varies directly with the
following:
Blood Volume
• Mainly regulated by kidneys
•  in blood volume =  in B.P.
•  in blood vol. =  decrease in B.P.
REGULATION OF B.P.
• Neural Factors:
– Sympathetic nerve fibers cause
• Vasoconstriction of blood vessels
–  diameter,  resistance   B.P.
REGULATION OF B.P.
• Renal Factors:
• Renin (Enzyme)
– Renin enzyme released from kidneys in response to
low B.P.
– Stimulates angiotensin II, vasoconstrictor chemical
– Which stimulates hormone aldosterone
– Which enhances sodium and water reabsorption
–  blood volume and B.P.
REGULATION OF B.P.
• Temperature
– Heat has a vasodilating effect
– Cold has a vasoconstricting effect
• Chemicals
– Various substances can cause increase or
decrease in B.P.
• Diet
Variations in Blood Pressure
• Normal human range is variable
– Normal
• 140–110 mm Hg systolic
• 80–75 mm Hg diastolic
– Hypotension
• Low systolic (below 110 mm HG)
• Often associated with illness
– Hypertension
• High systolic (above 140 mm HG)
• Can be dangerous if it is chronic