Transcript ANPS 020 Black 01-31

Overview of the Cardiovascular System
Topics to be addressed:
Blood
Anatomy of Blood Vessels
Anatomy of the Heart
The Conduction System
The Cardiac Cycle
Cardiodynamics
Blood Flow and its Regulation
Adaptation and Disorders of the Cardiovascular System
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Cardiovascular Adaptation
Blood, heart, and cardiovascular system work
together as unit
Allows for both short- and long-term responses to physical and
physiological changes (eg. exercise or blood loss)
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Cardiovascular Adaptation : Standing Up
In rising from a lying to a standing position, the effect of gravity is to
cause blood to accumulate in capacitance veins of the legs and feet.
Less blood returns to heart (decreased EDV)
Stroke Volume decreases (SV is a function of EDV)
Cardiac Output decreases (CO = SV X HR)
Blood Pressure decreases
Decreased blood flow to brain
What prevents us
from fainting?
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Cardiovascular Adaptation : Standing Up
A rapid response by the cardiovascular system raises
blood pressure and restores blood flow to brain within a
few beats.
1. Carotid and aortic baroreceptors detect low BP
2. Cardiovascular center in medulla of brainstem activates
sympathetic branch of ANS, decreases parasympathetic
3. Sympathetic nerves to blood vessels cause
vasoconstriction in arteries and veins (increasing EDV)
4. Sympathetic nerves to heart increase heart rate and
force of ventricular contraction, increasing stroke volume
and restoring cardiac output and blood pressure
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Cardiovascular Adaptation : Response to Exercise
1.
2.
Light exercise
•
Driven by metabolite buildup, extensive vasodilation occurs, increasing
circulation to active muscles
•
Skeletal muscle activity enhances venous return via “muscular pump”
•
Venous return increases and increases stretch on ventricular wall
(Frank–Starling principle); increased stretch increases contractility to
increase stroke volume and cardiac output
Heavy exercise
Induces same changes as light exercise, but also activates sympathetic
nervous system
• Sympathetic stimulation increases heart rate and contractility,
increasing cardiac output to about four times resting level
• Selective vasoconstriction restricts blood flow to “nonessential” organs
(e.g., digestive system) and redirects blood flow to skeletal muscles,
lungs, and heart. Blood supply to brain is unaffected
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Cardiovascular Adaptation: Changes in
Blood Distribution during Exercise
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Exercise, Cardiovascular Fitness, and Health
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Hemorrhage
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The Cardiovascular Response to Hemorrhaging
Entire cardiovascular system adjusts to maintain blood pressure
and restore blood volume
Short-Term Elevation of Blood Pressure (seconds)
Carotid and aortic reflexes stimulate cardiovascular center in medulla
• Increase cardiac output by increasing heart rate & contractility
• Peripheral vasoconstriction improves venous return (increasing preload, SV, CO)
Hormonal effects (minutes)
• Increase cardiac output by increasing heart rate and contractility
• Increase peripheral vasoconstriction (E, NE, ADH, angiotensin II)
Long-Term Restoration of Blood Volume (hours to weeks)
Recall of fluids from interstitial spaces
Aldosterone and ADH promote fluid retention and reabsorption
Thirst increases to replace fluid volume
Erythropoietin stimulates red blood cell production to replace RBC loss
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Circulatory Shock
Short-term responses compensate for blood losses of up to 20% of total
blood volume
Failure to restore blood pressure results in circulatory shock
Intense vasoconstriction shunts blood away from organs and into bloodstream to
maintain blood pressure
Prolonged vasoconstriction causes cells in organs to die and organ damage results
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Disorders of the Cardiovascular System
Hypertension : high blood pressure
Risk Factors:
• genetics
• gender (males more at risk)
• high cholesterol levels
• obesity
• chronic stress
• cigarette smoking
• often no known cause
Strain on the system:
• increased work for heart, leading to heart enlargement
• greater oxygen demands lead to ischemia
• stress on blood vessel walls promotes arteriosclerosis
Clinical Intervention:
• lifestyle, diet and exercise changes
• drugs: calcium channel blockers, beta blockers, diuretics, ACE inhibitors
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Disorders of the Cardiovascular System
Atherosclerosis
Atherosclerosis is an
Inflammatory Disease
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The link between
cholesterol and cardiovascular disease
Cholesterol is a necessary component of cell membranes and a building block
for steroid hormones. However, high levels of blood cholesterol are associated
with an increased risk of cardiovascular disease.
LDL (low density lipoprotein) is one form of cholesterol in
the blood. It is thought to carry cholesterol toward tissues
and high levels are associated with atherosclerosis,
which is why it is considered the “bad cholesterol”
HDL (high density lipoprotein) is another form of
cholesterol in the blood. It is thought to carry cholesterol
away from tissues to the liver, and is considered the
“good cholesterol”
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Disorders of the Cardiovascular System :
The model for atherosclerosis
Step 1: High levels of LDL in blood lead to
accumulation of LDL in tunica intima
LDL
Step 2: Chemical reaction of LDL in intima
leads to lymphocyte and monocyte attraction
from blood; LDL recognized as foreign
WBC
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Disorders of the Cardiovascular System :
The model for atherosclerosis
Step 3: Chemicals
released from
lymphocytes and
macrophages induce
inflammation, causing
thickening in wall of
artery
Plaque
Plaques contain:
Lipids
Connective tissue
Calcium deposits
“hardening of arteries”
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Disorders of the Cardiovascular System :
Atherosclerosis
Result:
Narrowing of opening : Decreased blood flow to tissues
Decreased blood flow : Heart works harder to overcome resistance
Calcification over time : Loss of ability to dilate/constrict
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Disorders of the Cardiovascular System :
Coronary Artery Disease
When atherosclerosis affects coronary arteries, the function
of the heart is compromised
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Disorders of the Cardiovascular System :
Coronary Artery Disease
Decreased coronary blood flow can lead to angina pain and
eventually to a heart attack
Symptoms of Heart Attack:
Chest discomfort. Most heart attacks involve discomfort in
the center of the chest that lasts more than a few minutes, or
that goes away and comes back. It can feel like
uncomfortable pressure, squeezing, fullness or pain.
Discomfort in other areas of the upper body. Symptoms
can include pain or discomfort in one or both arms, the
back, neck, jaw or stomach.
Shortness of breath with or without chest discomfort.
Other signs may include breaking out in a cold sweat,
nausea or lightheadedness
As with men, women's most common heart attack symptom
is chest pain or discomfort. But women are somewhat more
likely than men to experience some of the other common
symptoms, particularly shortness of breath,
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nausea/vomiting, and back or jaw pain.
A stress test is often used to assess
heart problems
Patient is asked to walk on a treadmill while heart is being monitored
A medical team is present to watch for changes in ECG, shortness of
breath, chest pain, or other signs of heart problems
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Disorders of the Cardiovascular System :
Coronary Artery Disease
Coronary bypass surgery is one technique to restore blood
flow to the heart wall
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Disorders of the Cardiovascular System :
Coronary Artery Disease
Less invasive options include
balloon angiography
and/or
the insertion of a stent
to open the blocked artery
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Disorders of the Cardiovascular System:
Arrhythmias
• Atrial fibrillation:
– Atria can depolarize at rate of 500 beats per minute without
driving ventricle beyond normal limits
– Atrial wall “quivers”
– Blood clots may form near the atrial walls, creating emboli and
leading to stroke
• Ventricular fibrillation:
– Purkinje cells fire abnormally; muscle overly sensitive to
stimulation
– Ventricle wall “quivers” and fails to pump blood out of heart
– Leads to cardiac arrest
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Disorders of the Cardiovascular System:
Congestive Heart Failure
• Heart cannot pump enough blood to body organs
Causes:
• damage to heart: infection, heart attack, congenital defects
• coronary artery disease
• heart valve disease or defects leads to backward flow in
system
• As heart pumps inadequately, blood backs up on venous side
– Edema in tissues, including visible swelling in limbs
– Back up into lungs interferes with breathing
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Aging and the Cardiovascular System
•
Changes in Blood
– Decreased hematocrit impacts oxygen delivery
– Changes to clotting factors increase clot likelihood
– Pooling of blood in legs due to venous valve deterioration
•
Changes in Blood Vessels
– Arteries become less elastic leading to wall rupture or
aneurysm
– Plaque deposits and calcification of vessel walls
reduce blood flow and may trigger clot formation
leading to stroke
•
Changes within the Heart impact Cardiac Output
– Changes in nodal and conducting cells
– Reduced elasticity of cardiac (fibrous) skeleton
– Progressive atherosclerosis and valve stiffening
– Replacement of damaged cardiac muscle cells by scar tissue
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