NURS 2550H Study Guide - Final Guide: Insulin Resistance, Microalbuminuria, Peripheral Artery Disease
28 Jun 2018
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WEEK 4-DISORDERS OF THE CARDIOVASCULAR SYSTEM
Structures and Functions of the Cardiovascular System (p.842-847)
Heart
Structure
- Heart is comprised of three layers: endocardium (thin inner lining), myocardium (layer
of muscle), and the epicardium (fibrous outer layer)
- Heart is surrounded by the pericardium
- Small amount of pericardial fluid lubricates the space between the pericardial layers and
prevents friction between the surfaces as the heart beats
- The thickness of each chamber wall is different; atrial myocardium is thinner than the
ventricles, left ventricular wall is three times thicker than the right ventricular wall
- The thickness of the ventricle provides the force needed to pump the blood into the
systemic circulation
Blood Flow
- Right atrium receives venous blood from, the inferior and superior venae cavae and the
coronary sinus
- Blood passes through the tricuspid valve into the right ventricle
- With each contraction, the right ventricle pumps blood through the pulmonic valve into
the pulmonary artery
- Blood flows to the left atrium by way of the pulmonary veins
- Passes through the mitral valve and into the left ventricle
- As the heart contracts, blood is ejected through the aortic valve into the aorta and thus
enter the high pressure systemic circulation
Blood Supply to the Myocardium
- Myocardium has its own blood supply called the coronary circulation blood flow into the
coronary arteries
- Obstruction of the right coronary artery often causes serious defects in cardiac
conduction (it supplies to AV node and bundle of His)
Conduction System
- Specialized nerve tissue responsible for creating and transporting the electrical impulse
or action potential
- The electrical impulse is initiated by the SA node
Electrocardiogram
- Electrical activity of the heart can be detected on the surface of the body and recorded
using an ECG
- PQRSTU are used to identify the separate waveforms
- P wave begins with the firing of the SA node and represents depolarization of the fibres
of the atria
- QRS wave represents depolarization from the AV node throughout the ventricles
- There is a delay of impulse transmission through the AV node that accounts for the time
sequence between the end of the P wave and the beginning of the QRS wave
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- T wave represents repolarization of the ventricles
- U wave, if seen, represents delayed ventricular repolarization and may be associated
with electrolyte imbalance (typically seen in bradycardias)
- Intervals between these waves reflect the length of time for the impulse to travel from
one area of the heart to another
- Time intervals can be measured and deviations from these time references often
indicate pathological conditions
Mechanical System
- Cardiac output is the measurement of mechanical efficiency, it is the amount of blood
pumped by each ventricle in one minute
- CO=SV x HR
Factors Affecting Cardiac Output
- HR is regulated primarily by the autonomic nervous system
- Factors affecting the SV are preload, contractility, and afterload
- Increasing preload, contractility, and afterload increases workload o the myocardium
resulting in increased oxygen demand
- Volume of blood in the ventricles at the end of diastole, before the next contraction is
called preload
- Preload determines the amount of stretch on the myocardial fibres (starlings law; more
fibres are stretched, greater their force of contraction/contractility)
- Contractility can be increased by administering norepinephrine or epinephrine,
increasing contractility raises the SV by increasing ventricular emptying
- Afterload is the peripheral resistance against which the left ventricle must pump (it is
affected by size of ventricle, wall tension, and the arterial BP)
- If arterial BP is elevated, the ventricles will meet increased resistance to ejection of
blood, increasing the work demand (eventually resulting in ventricular hypertrophy)
Cardiac Reserve
- Ability to respond to these demands by increasing CO (results from an increase in HR or
SV)
Vascular System
Blood Vessels
- Three major types of blood vessels; arteries, veins, and capillaries
- Arteries carry oxygenated blood away (except pulmonary artery)
- Veins carry deoxygenated blood towards the heart (except pulmonary vein)
- Blood circulates from heart into arteries, arterioles, capillaries, venules, and veins and
back to the heart
Arteries and Arterioles
- Differs from venous system by amount and type of tissue that makes up the arterial wall
- Large arteries have thick walls that are composed mainly of elastic tissue, the elastic
property cushions impact of pressure created by ventricular contraction and provides
recoil that propels blood forward into the circulation
- Large arteries also contain some smooth muscle
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- Arterioles have little elastic tissue and more smooth muscle; their major role is control
of arterial BP & distribution of blood flow
Capillaries
- Thin capillary wall is made of endothelial cells, no elastic or muscle tissue
- Exchange of cellular nutrients and metabolic end products takes place through those
thin-walled vessels
Veins and Venules
- Large-diameter, thin-walled vessels that return blood to the right atrium
- Amount of blood in the venous system is affected by arterial flow, compression of veins
by skeletal muscles, alterations in thoracic and abdominal pressures, and right atrial
pressure
Regulation of the Cardiovascular System
Autonomic Nervous System
- Consists of sympathetic and parasympathetic
Effect on the Heart
- Stimulation of the sympathetic nervous system increases HR, the speed of impulse
through AV node, and the force of atrial and ventricular contractions
- Effect is mediated by sites in the heart called B-adrenergic receptors that are receptors
fir norepinephrine and epinephrine
- Stimulation of the parasympathetic system causes a decrease in HR by action on the SA
node and slows conduction through the AV node
Effect on the Blood Vessels
- Source of neural control of blood vessels is the sympathetic nervous system
- a-adrenergic receptors are located in vascular smooth muscles, when stimulated results
in vasoconstriction but when there is decreased stimulation it causes vasodilation
- parasympathetic nerves have selective distribution in blood vessels and skeletal muscle
blood vessels do not receive parasympathetic input
Baroreceptors
- in aortic arch and carotid sinus are sensitive to stretch or pressure within the arterial
system
- stimulation of the receptors sends info to the vasomotor centre in the brainstem
- results in temporary inhibition of the sympathetic NS and enhancement of the
parasympathetic NS, causing decreased HR and peripheral vasodilation Baroreceptors
have important role in maintaining BP stability during normal activities, therefore
longstanding hypertension baroreceptors becomes adjusted to elevated levels of BP and
recognize this as “normal”
Chemoreceptors
- located in the aortic arch and carotid body
- capable of initiating changes in the HR and arterial BP in response to decreased arterial
oxygen pressure, increased arterial carbon dioxide pressure, and decreased plasma pH
- when chemoreceptor reflexes are stimulated, they stimulate the vasomotor centre
which increases cardiac activity
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find more resources at oneclass.com
Document Summary
Structures and functions of the cardiovascular system (p. 842-847) Heart is comprised of three layers: endocardium (thin inner lining), myocardium (layer of muscle), and the epicardium (fibrous outer layer) Small amount of pericardial fluid lubricates the space between the pericardial layers and prevents friction between the surfaces as the heart beats. The thickness of each chamber wall is different; atrial myocardium is thinner than the ventricles, left ventricular wall is three times thicker than the right ventricular wall. The thickness of the ventricle provides the force needed to pump the blood into the systemic circulation. Right atrium receives venous blood from, the inferior and superior venae cavae and the coronary sinus. Blood passes through the tricuspid valve into the right ventricle. With each contraction, the right ventricle pumps blood through the pulmonic valve into the pulmonary artery. Blood flows to the left atrium by way of the pulmonary veins. Passes through the mitral valve and into the left ventricle.
