Transcript Cardiovascular System

Cardiovascular System
Northwest Rankin High School
Human A&P
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Introduction
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The cardiovascular system consists of the heart and
vessels (arteries, capillaries and veins.)
A functional cardiovascular system is vital for
supplying oxygen and nutrients to tissues and
removing wastes from them.
Deoxygenated blood is carried by the pulmonary
circuit to the lungs, while the systemic circuit sends
oxygenated blood to all body cells.
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Size of Heart
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The heart is about the
size of a person’s fist.
It is hollow, cone
shaped and weighs less
than one pound.
Location of Heart
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Behind the sternum and is flanked on either
side by the lungs.
The heart rests on the diaphragm and the
pointed apex of the heart is directed toward
the left hip.
The superior part of the heart is pointing
towards the right shoulder.
Walls of the Heart
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The heart is enclosed by a double sac called
pericardium.
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The visceral pericardium, or epicardium tightly
hugs the heart.
The parietal pericardium is the outside layer that
anchors the heart to the surrounding structures
(diaphragm and sternum).
Between the pericardial layers is a fluid to reduce
friction.
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Layer of the Heart Wall
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Epicardium – outside layer
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Myocardium – middle layer
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Made of connective and epithelial tissue
Houses blood and lymph capillaries as well as the
coronary arteries
thick layers of cardiac muscle
Endocardium –the inside layer
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Very smooth
Made of connective and epithelial tissue
Contains Purkinje fibers
Chambers of the heart
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The heart has 4 chambers
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2 atria
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2 ventricles
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Superior chambers
Receive blood returning to the heart
Thin walls
Inferior chambers
Pump blood to the body and to the lungs
Thick walls
A septum divides the atrium and ventricles on each side.
Valves of the heart
 Valves
prevent backflow of
blood in the heart.
 The valves open and close in
response to pressure changes
in the heart
Atrioventricular (AV) Valves
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Each side of the heart has an AV valve to ensure
one way flow of blood
There are two AV valves:
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Biscuspid (mitral) valve – LEFT AV valve with 2
cusps, between the left atria and ventricle
Tricuspid valve – RIGHT AV valve with three cusps
located between the right atria and ventricle
Each AV valve cusps attach to chordae tendinae
which are attached to papillary muscles.
AV Valves
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The AV valves open during heart relaxing and
close when the heart contracts to prevent blood
from returning to the atria.
When the heart is relaxed and blood is passively
filling its chambers, the AV- valve flaps hang
limply into the ventricles. As the ventricles
contract, the pressure begins to rise and forces the
valves closed. This prevents backflow into the
atria when the ventricles are contracting.
Semilunar Valves
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Each side of the heart also has a semilunar
valve to further ensure one way flow of blood
There are also two semilunar valves
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Pulmonary – in the pulmonary artery leaving the
heart to the lungs.
Aortic – in the aortic arch leaving the heart to the
body.
Semilunar Valves
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The semilunar valves open during heart contraction
and close to prevent backflow into the ventricles
when relaxing.
When the ventricles are contracting and forcing
blood out of the heart, the cusps are forced open
and flattened against the wall of the arteries by the
tremendous force of rushing blood. Then when the
ventricles relax the blood begins to flow backward
toward the heart, and the cusps fill with blood,
closing the valves.
Heart functions as a double pump
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Pulmonary circulation – right side of heart to
the lungs and back to the left side of the heart.
It’s only function is to carry blood to the lungs
for gas exchange and then to return it to the
heart.
Systemic circulation – left side of the heart
through the body tissues and back to the right
side of the heart. It supplies oxygen and
nutrient rich blood to all body organs.
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Path of Blood through the Heart
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Blood low in oxygen returns to the right atrium via
the venae cavae and coronary sinus.
The right atrium contracts, forcing blood through the
tricuspid valve into the right ventricle.
The right ventricle contracts, closing the tricuspid
valve, and forcing blood through the pulmonary
valve into the pulmonary trunk and arteries.
The pulmonary arteries carry blood to the lungs
where it can rid itself of excess carbon dioxide and
pick up a new supply of oxygen.
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Path of Blood through the Heart
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Freshly oxygenated blood is returned to the left
atrium of the heart through the pulmonary veins.
The left atrium contracts, forcing blood through the
left bicuspid valve into the left ventricle.
The left ventricle contracts, closing the bicuspid
valve and forcing open the aortic valve as blood
enters the aorta for distribution to the body.
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Blood Supply to the Heart
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The first branches off of the
aorta, which carry freshly
oxygenated blood, are the right
and left coronary arteries that
feed the heart muscle itself.
Branches of the coronary
arteries feed many capillaries of
the myocardium.
Cardiac veins drain blood from
the heart muscle and carry it to
the coronary sinus, which
empties into the right atrium.
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Heart Actions
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The cardiac cycle consists of the atria beating in
unison (atrial systole) followed by the contraction
of both ventricles, (ventricular systole) then the
entire heart relaxes for a brief moment (diastole).
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It includes events of one complete heartbeat, during
which both atria and ventricles contract and then
relax.
(0.8 seconds) or 75 times a minute
Common terms: Systole-Ventricle contraction;
Diastole- Ventricle relaxation
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Cardiac Cycle
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During the cardiac cycle, pressure within the
heart chambers rises and falls with the contraction
and relaxation of atria and ventricles.
When the atria fill, pressure in the atria is greater
than that of the ventricles, which forces the A-V
valves open.
Pressure inside atria rises further as they contract,
forcing the remaining blood into the ventricles
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Cardiac Cycle
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When ventricles contract, pressure inside
them increases sharply, causing A-V valves to
close and the aortic and pulmonary valves to
open.
As the ventricles contract, papillary muscles
contract, pulling on chordae tendinae and
preventing the backflow of blood through the
A-V valves.
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Heart Sounds
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Heart sounds are due to vibrations in heart
tissues as blood rapidly changes velocity
within the heart.
Heart sounds can be described as a "lubbdupp" sound.
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The first sound (lubb) occurs as ventricles contract
and A-V valves are closing.
The second sound (dupp) occurs as ventricles relax
and aortic and pulmonary valves are closing
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Controlling systems of the heart
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Without a controlling system, the heart would
be an inefficient pump
There are two controlling systems
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Intrinsic Conduction System
Autonomic nervous system
Intrinsic Conduction System
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Specialized cardiac muscle tissue conducts
impulses throughout the myocardium and
comprises the intrinsic conduction system.
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It is not found anywhere else in the body
It causes heart muscle depolarization in only one
direction from the atria to the ventricles
The Intrinsic Conduction System consists of an SA
node (pacemaker), an AV node , the AV bundle
(bundle of His) and bundle branches, and the
Purkinje fibers
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SA Node
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A self-exciting mass of specialized cardiac
muscle called the sinoatrial node (S-A node or
pacemaker), located on the posterior right
atrium, generates the impulses for the
heartbeat.
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AV Node
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Impulses spread next to next grouping of
cells, it contracts, and impulses then travel to
the junctional fibers leading to the
atrioventricular node (A-V node) located in
the septum.
Junctional fibers are small, allowing the atria
to contract before the impulse spreads rapidly
over the ventricles.
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Bundle of His and Purkinje fibers
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From the AV Node signals spread to the AV
bundle (Bundle of His)
And then the branches of the A-V bundle give
rise to Purkinje fibers leading to papillary
muscles
These fibers stimulate contraction of the
papillary muscles at the same time the
ventricles contract.
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Electrocardiography: ECG
All the activity of the heart produces electrical
waves we can measure. The measurement is
typically represented as a graph called an
electrocardiogram (ECG)
The typical ECG has three recognizable waves
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P wave: small and signals the depolarization of the atria
immediately before they contract
QRS complex: results from the depolarization of the
ventricles, complicated shape; precedes the contraction
of the ventricles
T wave: results from currents flowing during the
repolarization of the ventricles
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Regulation of the Cardiac Cycle
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The amount of blood pumped at any one time
must adjust to the current needs of the body
The SA node is innervated by branches of the
sympathetic and parasympathetic divisions, so
basically the autonomic system of the CNS
controls heart rate.
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Sympathetic impulses increase the speed of heart
rate.
Heart rate is decreased by parasympathetic impulses
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Cardiac control center
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The cardiac control center of the medulla oblongata
maintains a balance between the sympathetic and
parasympathetic divisions of the nervous system in
response to messages from baroreceptors which
detect changes in blood pressure.
Impulses from the cerebrum or hypothalamus may
also influence heart rate, as do body temperature
and the concentrations of certain ions.
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Heart Sounds
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Lub-dup- pause
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Lub: closing of the AV valves, longer and
louder sound
Dub: closing of the semilunar valves at the end
of systole, shorter and sharper sound
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Blood Vessels
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The blood vessels (arteries, arterioles,
capillaries, venules, and veins) form a closed
tube that carries blood away from the heart, to
the cells, and back again.
Large arteries leave heart (aorta) THEN to
smaller arteries THEN to arterioles THEN to
capillary beds THEN to venules THEN to
veins THEN to larger veins (inferior and
superior vena cavae) that dump blood back
into heart.
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Anatomy of Blood Vessels
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Arteries and veins have 3 layers
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Tunica intima – forms slick surface to decrease
friction of blood flow
Tunica media – smooth muscle and elastic tissue.
Tunica media is thick in arteries and relatively
thin in veins
Tunica externa – the outermost tunic basically
supports and protects the vessels
Capillaries have only one layer: tunica intima
Anatomy of Arteries
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Arteries are strong, elastic vessels adapted for
carrying high-pressure blood.
All the major arteries of the systemic circulation are
branches of the aorta, which leaves the left ventricle
Arteries are capable of vasoconstriction as directed
by the sympathetic impulses; when impulses are
inhibited, vasodilation results.
Arteries become smaller as they divide and give rise
to arterioles.
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Anatomy of Capillaries
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Capillaries are the smallest vessels, consisting only of a layer
of endothelium through which substances are exchanged with
tissue cells.
Capillary permeability varies from one tissue to the next,
generally with more permeability in the liver, intestines, and
certain glands, and less in muscle and considerably less in the
brain (blood-brain barrier).
Precapillary sphincters can regulate the amount of blood
entering a capillary bed and are controlled by oxygen
concentration in the area.
 If blood is needed elsewhere in the body, the capillary beds
in less important areas are shut down
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Exchanges in the Capillaries
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Blood entering capillaries contains high concentrations of
oxygen and nutrients that diffuse out of the capillary wall
and into the tissues.
Plasma proteins remain in the blood due to their large size.
Hydrostatic pressure drives the passage of fluids and very
small molecules out of the capillary at this point.
At the venule end, osmosis, due to the osmotic pressure of
the blood, causes much of the tissue fluid to return to the
bloodstream.
Lymphatic vessels collect excess tissue fluid and return it
to circulation.
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Anatomy of Veins
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Veins have the same three layers as arteries but the walls are
thinner, their lumens are larger, and they are equipped with
valves. These modifications reflect low-pressure nature of
veins. The valves prevent the backflow of blood.
The major veins of the systemic circulation ultimately
converge on one of the venae cavae. All veins above the
diaphragm drain into the superior vena cava, and those below
the diaphragm drain into the inferior vena cava. Both venae
cavae enter the right atrium of the heart
Varicose veins are caused by incompetent valves in the veins.
It is common in the obese and people who stand for long
hours
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Blood Pressure
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Blood pressure is the force of blood against
the inner walls of blood vessels anywhere in
the cardiovascular system, although the term
"blood pressure" usually refers to arterial
pressure.
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Arterial Blood Pressure
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Arterial blood pressure rises and falls following a
pattern established by the cardiac cycle.
During ventricular contraction, arterial pressure is
at its highest (systolic pressure).
When ventricles are relaxing, arterial pressure is at
its lowest (diastolic pressure).
The surge of blood that occurs with ventricular
contraction can be felt at certain points in the body
as a pulse
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Factors that Affect Arterial
Pressure
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Arterial pressure depends on heart action, blood
volume, resistance to flow, and blood viscosity.
Heart Action
 Heart action is dependent upon stroke volume and
heart rate (together called cardiac output); if
cardiac output increases, so does blood pressure.
Blood Volume
 Blood pressure is normally directly proportional
to the volume of blood within the cardiovascular
system.
 Blood volume varies with age, body size, and
gender.
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Factors that Influence Arterial Pressure
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Peripheral Resistance
 Friction between blood and the walls of blood
vessels is a force called peripheral resistance.
 As peripheral resistance increases, such as
during sympathetic constriction of blood
vessels, blood pressure increases.
Blood Viscosity
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The greater the viscosity (ease of flow) of
blood, the greater its resistance to flowing, and
the greater the blood pressure.
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Control of Blood Pressure
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Blood pressure is determined by cardiac output and peripheral
resistance. The body maintains normal blood pressure by
adjusting cardiac output and peripheral resistance.
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Cardiac output depends on stroke volume and heart
rate, and a number of factors can affect these
actions.
Other factors, such as emotional upset, exercise,
and a rise in temperature can result in increased
cardiac output and increased blood pressure.
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Control of Blood Pressure
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The volume of blood that enters the right atrium is
normally equal to the volume leaving the left
ventricle.
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If arterial pressure increases, the cardiac center of the
medulla oblongata sends parasympathetic impulses to
slow heart rate.
If arterial pressure drops, the medulla oblongata sends
sympathetic impulses to increase heart rate to adjust
blood pressure.
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