cardiovascularsystem 110221045748-phpapp02
TRANSCRIPT
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Cardiovascular System:Heart & Circulation
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I. Anatomy of the Heart
A. Coverings
1. Pericardium
• fibrous pericardium
• serous pericardium• parietal pericardium• visceral pericardium
B. Heart wall layers 1. Epicardium – (visceral pericardium)
• protects heart 2. Myocardium – cardiac muscle
3. Endocardium – epithelial/ connective/ fibers
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C. Chambers, Vessels, and Valves
1. Four chambers
• upper chambers – rt and left atria
Collects blood
• lower chambers – rt and left ventricle
pumps blood from heart
2. Arteries
• carry blood away from heart
3. Veins
• blood toward heart
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4. Valves
• AV valves
Tricuspid – rt atrium
Bicuspid or mitral - lt atrium
• Semilunar valves
Pulmonary semilunar (pulmonary trunk)
Aortic semilunar (aortic arch)
II. Pulmonary and Systemic Circulation
A. Pulmonary pathway
oxygenated blood –rt ventricle from rt atrium
myocardium (rt ventricle) contracts
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low oxygen blood through pulmonary semilunar
pulmonary trunk -> arteries -> lungs
oxygenated blood -> rt & lt pulmonary veins ->
left atrium
B. Systemic pathway
Oxygenated blood -> Lt atrium to Lt ventricle
Left ventricle contracts ->aortic semilunar
Aortic arch -> arteries to tissues
oxygen depleted blood from tissues ->
veins to heart -> rt atrium (vena cava)
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Passage of Blood Through the Heart
Blood follows this sequence through the heart: superior and inferior vena cava → right atrium → tricuspid valve → right ventricle → pulmonary semilunar valve → pulmonary trunk and arteries to the lungs → pulmonary veins leaving the lungs → left atrium → bicuspid valve → left ventricle → aortic semilunar valve → aorta → to the body.
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Direction of blood flow through the heart
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The relationship between the systemic and pulmonary circulations
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Blood supply to the heart orcoronary circulation
The coronary arteries
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Blood supply to the heartArterial supply
The heart is supplied with arterial blood by the right and left coronary arteries, which branch from the aorta immediately distal to the aortic valve
The coronary arteries receive about 5% of the blood pumped from the heart, although the heart comprises a small proportion of body weight
This large blood supply, especially to the left ventricle, highlights the importance of the heart to body function
The coronary arteries traverse the heart, eventually forming a vast network of capillaries
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Blood supply to the heart –
Venous drainage
Most of venous blood is collected into several small veins that join to form coronary sinus, which opens into right atrium
The remainder passes directly into the heart chambers through little venous channels
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THE CARDIAC CYCLE
What is the cardiac cycle
The cardiac cycle is the sequence of events that occur when the heart beats There are two phases of this cycle:
Diastole - Ventricles are relaxedSystole - Ventricles contract
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The cardiac cycle
Exercise increases blood flow through the heart so that the cardiac cycle accelerates to accommodate the increased demand for oxygen
The normal cycle is around 0.8 seconds. This accelerates with faster and more powerful atrial and ventricular contraction, which is stimulated by the cardiac centre in the brain
Heart rate:- is defined as the number of heart contractions in each minute
# There are two distinct periods in the cardiac cycle- one of the heart muscle relaxation (cardiac diastole), the other of contraction (cardiac systole)
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Cardiac diastole
During cardiac diastole
• The bicuspid and tricuspid valves are closed and the atrium is full
• Once full with blood, the atria forces the bicuspid and tricuspid valves to open and fill the ventricles
• This lasts for around 0.4 seconds at rest
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Cardiac systoleCardiac systole
• The atria contract and send blood via the bicuspid and tricuspid valves into the ventricles
• When full, these contract causing blood to be expelled from the heart via the semi-lunar valves
• (the bicuspid and tricuspid valves are closed at this time)
• This lasts around 0.4 seconds at rest
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The Cardiac CycleHeart at rest– Blood flows from large veins into atria– Passive flow from atria into ventricles
Atria (R & L) contract simultaneously– Blood forced into ventricles
Ventricles (R & L) contract simultaneously– Atrioventricular valves close “lubb” sound– Blood forced into large arteries
Ventricles relax– Semilunar valves close “dub” sound
Heart at rest
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Heart valves• Valves are flap-like structures that allow blood to flow in
one direction
• The heart has two kinds of valves, atrioventricular and semilunar valves
Heart sounds
• The audible sounds that can be heard from the heart are made by the closing of the heart valves
• These sounds are referred to as the “lub-dupp” sounds
• The “lub” sound is made by the contraction of the ventricles and the closing of the atria-ventricular valves
• The “dupp” sound is made by the semi-lunar valves closing
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Conducting system of Heart
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Stimulation of the heart originates in the cardiac centre, in the “medulla oblongata.”
The “sympathetic and parasympathetic nervous systems” work antagonistically and provide the stimulation for acceleration and deceleration of the heart rate
Cardiac systole (contraction) is initiated by the electrical cardiac impulse from the “sinu-atrial node” (the pace-maker found in the right atria wall)
This distributes electrical stimulus through the “myocardial” (heart muscle) wall between the heart chambers
where the “atrio-ventricular node” (between the right atrium and right ventricle) continues distribution of the electrical signal across the ventricles
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• In the upper part of the right atrium of the heart is a specialized bundle of neurons known as the sino-atrial node (SA node)
• Acting as the heart's natural pacemaker, the SA node "fires" at regular intervals to cause the heart of beat with a rhythm of about 60 to 70 beats per minute for a healthy, resting heart
• The electrical impulse from the SA node triggers a sequence of electrical events in the heart to control the orderly sequence of muscle contractions that pump the blood out of the heart
The SA node
The AV node
• The AV node (AV stands for atrioventricular) is an electrical relay station between the atria (the upper) and the ventricles (the lower chambers of the heart)
• Electrical signals from the atria must pass through the AV node to reach the ventricles
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AV node (bundle of his)
The bundle of His is located in the proximal interventicular septum
It emerges from the AV node to begin the conduction of the impulse from the AV node to the ventricles
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Purkinje fibersPurkinje fibers
Purkinje fibers are heart muscle tissues that are specialized to conduct electrical impulses to ventricular cells, which induce the lower chambers of the heart to contractImpulses from the upper chambers of the heart are relayed by this node to large bundles of Purkinje fibers referred to as the Bundle of HisThese bundles branch into smaller elements and eventually form terminal ends that burrow into left and right ventricular chamber musclesAs the impulse is passed to the ventricles, the muscles contract and pump bloodThe contraction caused by the specialized fibers begins from the bottom of the ventricles and move upwards so that the blood leaves the lower chambers through the pulmonary arteries and the aorta
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Signal Conduction Pathway
• SA action potentials -> contraction in atrium
• AV action potentials (slower) -> bundle of HIS->
through septum -> Purkinje fibers -> contraction
C. Electrocardiography
• electrical events corresponding to mechanical
• P wave: atrial fibers depolarize
• QRS complex: ventricles depolarize
• T wave: ventricles repolarize
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Electrocardiography
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Cardiac Output (CO) CO is the amount of blood pumped by each
ventricle in one minute CO is the product of heart rate (HR) and
stroke volume (SV) HR is the number of heart beats per minute SV is the amount of blood pumped out by a
ventricle with each beat
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Cardiac Output: Example CO (ml/min) = HR (75 beats/min) x SV
(70 ml/beat) CO = 5250 ml/min (5.25 L/min)
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Regulation of Stroke Volume SV = end diastolic volume (EDV) minus
end systolic volume (ESV) EDV = amount of blood collected in a
ventricle during diastole ESV = amount of blood remaining in a
ventricle after contraction
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Factors Affecting Stroke Volume Preload – amount ventricles are stretched
by contained blood Contractility – cardiac cell contractile force
due to factors other than EDV Afterload – back pressure exerted by blood
in the large arteries leaving the heart
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Preload and Afterload
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Regulation of Heart Rate Positive chronotropic factors increase heart
rate Negative chronotropic factors decrease
heart rate Autonomic nervous system Hormones
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Blood Pressure & its regulation Blood pressure is the force or pressure that the
blood exerts on the walls of the blood vessels BP = CO x TPR CO= SV x HR BP = Blood Pressure CO = Cardiac Output TPR = Total Peripheral Resistance SV = Stroke Volume HR = Heart rate
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Control of Arterial Blood Pressure
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Control of Blood Pressure Short term control :
Baroreceptors Chemoreceptors Higher centres in the brain
Long term control:
RAAS system
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Summary of the main mechanisms in blood pressure control
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Baroreceptors
Located in walls of aortic arch and left and right carotid sinus
Mechanical stretch receptors Neuronal circuits in brainstem compare
actual value of BP provided by the baroreceptors with the set point or optimal value
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The baroreceptor reflex
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Chemoreceptor Nerve ending situated in the carotid and aortic bodies
control of respiration
Sensitive to changes in the levels of Co2 , O2 and acidity of the blood
The relationship between stimulation of chemoreceptors and arterial blood pressure
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Higher centres in the brain
Fear
Anxiety
Pain
Anger
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Long term Blood pressure regulation
Renin-angiotensin-aldosterone system (RAAS)
Anti-diuretic harmone (ADH) Atrial natriuretic peptide (ANP)
harmone released by heart
sodium and water loss from the kidney
reduces blood pressure
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RAAS System
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Disorder of CVS• Hypertension
• Hypotension
• Congestive heart failure
• Cardiac Arrhythmia
• Angina Pectoris
• Arteriosclerosis
• Myocardial Infarction
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Hypertension
Essential hypertension
Benign (chronic ) hypertension
Malignant ( accelerated) hypertension
Secondary hypertension
Kidney disease
Endocrinal disorders
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Heart failure
Acute heart failure
Chronic heart failure
Right-sided (congestive) heart failure
Left-sided (left ventricular) heart failure
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Cardiac arrhythmia
Sinus bradycardia
Sinus tachycardia
Asystole
Fibrillation
Atrial fibrillation
Ventricular fibrillation
Heart block
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Blood VesselsFunctions: Distribution of blood Exchange of materials with tissues Return of blood to the heart
Structure: Most have the same basic structure:
– 3 layers surrounding a hollow lumen
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General Structure of Blood Vessels
Arteries and veins are composed of three tunics:
tunica interna tunica media tunica externa
Capillaries are composed of endothelium
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General Structure
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The Vessels1. Tunica Intima innermost smooth layer simple squamous epithelium continuous with the endocardium present in all vessels
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The Vessels2. Tunica Media layer of smooth muscle - circular arrangement –
contains elastin
supplied by sympathetic division of the ANS
depending on body’s needs – lumen is narrowed (vasoconstriction) or widened (vasodilation)
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The Vessels3. Tunica Externa (Adventitia) thin layer of CT elastic & collagen fibres
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The VesselsTypes of Vessels:
Arteries – carry blood away from the heart Veins – carry blood towards the heart Capillaries – the most important part of
the vascular system; site of exchange of materials
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Types of Blood vessels: Arteries
Elastic Arteries: Thick-walled arteries near the heart; the aorta and its
major branches
Large lumen allows low-resistance conduction of blood
Contain lots of elastin in all three tunics
walls stretch and recoil to propel blood
Withstand and regulate large blood pressure fluctuations
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Types of Blood vessels: Arteries
Muscular (distributing) arteries medium sized vessels tunica media more smooth muscle;
less elastin major area of vaso-constriction &
dilation to regulate blood flow
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The VesselsArterioles (diameter of 0.3 mm or less)
- smallest arteries; lead to capillary beds
- close to capillaries - single layer of muscle spiralling around the endothelial
lining
- regulates blood flow to capillary
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The VesselsCapillaries Smallest vessels – diameter just large
enough for a red blood cell walls consist of tunica intima only
(i.e. layer of endothelium) thinness facilitates exchange of
materials