CARDIOVASCULAR Flashcards
Cardiovascular function is based on
1. Cardiac pumping ability
Pace-making electrical signals
Force of contraction
Height of ventricle discharge pressure
2. Integrity of vasculature
Presence of blockage
Muscular tone/structural integrity
Pressure drop needed to move blood to and through capillary beds
3. Blood volume/composition
Water
Electrolyte
Iron balances
Lipid and protein composition
Functional components of the heart
1. Myocardium
Cardiac muscle fibers are arranged into four chambers
2 atria
2 ventricles
2. Conduction system
Specialized tissue that conducts nerve impulses throughout the heart
SA and AV node
Bundle of His
Bundle branches, and
Purkinje fibers
3. Nerve supply
Include nerve branches from autonomic nervous system
-Sympathetic
-Parasympathetic
Regulates
-Heart rate
-Force of contraction
AP superhighway
Electrical System of the Heart
Action potential superhighway
Sinoatrial (SA) node
Atrioventricular (AV) node
Bundle of His
Bundle Branches
Purkinje Network
Regulation of Heart Rate
Primarily accomplished by SA node
Located on right atrium
Receives autonomic input
When stimulated, SA signals atrial contractile fibers
Causes atrial depolarization and contraction
Primes ventricles with blood
Depolarization picked up by atrioventricular (AV) node
Ventricular depolarization and contraction
Blood discharged to
-Pulmonary artery and dorsal aorta
-Eventually rest of the body
Normal Electrocardiogram at Rest
P wave: Atrial depolarization
QRS complex: Ventricular depolarization
T wave: Ventricular repolarization
Cardiac Function dependent on
1. Adequate amounts of ATP
Derived primarily from fatty acids as glycogen reserves are limited
Needed to:
-Maintain electrochemical gradients
-Propagate action potentials
-Power muscle contraction
2. Adequate amounts of Ca++
Calcium is the link between electrical and mechanical events
Required for cardiac muscle contraction
3. Coordinated electrical stimulus
Heart capable of automaticity
Two types of myocardial tissue
-Contractile
-Conductive
Impulses travel through ‘action potential superhighway’
Electrophysiology
Two types of action potentials
Fast potentials
Found in contractile tissue
Slow potentials
Found in SA and AV node tissues
Fast potentials
Phase 0: Na+ influx “fast sodium channels”
Phase 1: K+ efflux
Phase 2: (Plateau) K+ efflux and Ca+ + influx
Phase 3: K+ efflux
Phase 4: Resting membrane potential
Slow potentials
Self-depolarizing: Responsible for automaticity
Phase 4 depolarization: slow sodium-calcium channels
Phase 3 repolarization: K+ efflux
Maintenance of Normal Heart Function
Normal cardiac output (CO) is needed to adequately perfuse peripheral organs
-Provide O2, nutrients, etc.
-Remove CO2, metabolic wastes, etc.
-Maintain fluid flow from capillaries into interstitium and back into venous system
If flow reduced or pressure increased in venous system -> build up of interstitial fluid = Oedema
CO,HR, SV, Venous tone, Vascular vol, TPR, quantification of TPR
Regulation of Blood Pressure
Arterial blood pressure is maintained by combination of
-Cardiac output
-Total peripheral resistance
Cardiac Output (CO)
Regulated by
-Heart rate (HR)
-Stroke volume (SV)
Atrial/ventricular/valvular coordination
CO = HR x SV
- Heart rate:
Determined by pacemaker cells in SA node
Function of
Sympathetic, vagal nervous activity
Neuro-hormonal substances
-Norepinephrine (NE) and epinephrine (Adrenaline)
-Acetylcholine (ACh) - Stroke volume
Determined by fill rate and contractile force
Function of
-Venous tone
-Vascular volume
Venous tone is function of
Sympathetic activity (α1 and α2 receptors)
Vascular volume depends on
-Intake of fluids (thirst)
-Output of fluids (urine, sweat, etc.)
-Distribution of fluids (Starling’s law)
-Myocardial contractility
**
Total peripheral resistance (TPR)**
TPR is a function of
-Viscosity of blood (hematocrit)
-Length of blood vessels
-Blood vessel luminal diameter (especially precapillary arterioles)
- Quantification of TPR
TPR proportional to (Lη)/r^4 for sum of all blood vessels (Poiseuille’s eqn.)
r = radius of blood vessel
L = length of blood vessel
η = viscosity of blood (function of hematocrit)
Therefore, change in blood vessel radius has greatest effect on TPR
Autonomic regulation of blood pressure
-Coordinates and integrates all regulators of cardiovascular function
-Can regulate both cardiac output and blood vessel size
-Coordinates via sympathetic and parasympathetic innervation of cardiovascular end-organs
Heart, vasculature, kidneys, adrenal glands, etc
Beat-to-beat modulation of blood pressure
-Controlled by baroreceptor reflex arch
-Baroreceptors located in
Aortic arch
Carotid sinus
-Fast acting
Aortic arch baroreceptors
inc stretching due to higher aortic arch pressure
inc vagus nerve (cranial nerve X) activity
dec heart rate
dec cardiac output
dec blood pressure
Carotid sinus baroreceptors
-Via glossopharyngeal nerve (cranial nerve IX) activity
-Respond to both inc and dec in blood pressure
Heart Rate
-Parasympathetic input via vagus nerve dec HR (dominates)
-Sympathetic input to SA node inc HR (usually minor)
Heart contractility
inc by sympathetic activity causing release of epinephrine and norepinephrine from adrenal gland
Increased sympathetic activity on heart:
Increased activity of sympathetic cardiac nerves
Decreased activity of vagus (parasympathetic) nerve
Increased heart rate and contractility
Higher cardiac output
Increased blood pressure
Increased sympathetic activity on arteries
Increased activity of vasomotor fibers
Constriction of vascular smooth muscle
Decreased arterial diameter
Increased blood pressure
Humoral regulation of blood pressure
Renin-Angiotensin-Aldosterone System
Renin is secreted by kidney in response to reduced blood pressure or blood volume
Renin converts angiotensinogen -> angiotensin I
Angiotensin converting enzyme (ACE) converts angiotensin I -> angiotensin II in lungs
Angiotensin II causes:
Intense vasoconstriction
-Increase TPR
Release of aldosterone from adrenal gland
-> Promotes Na+ and water reabsorption in kidney
-> Increases blood volume
Regulatory negative feedback on the release of renin
CNS: Stimulate thirst in hypothalamus and sympathetic outflow
The above system is designed to bring arterial blood pressure back to normal
Hypertension - causes
Most people have essential hypertension with no known secondary cause
Increased sympathetic activity and sodium overload
Renal disease and increased renin-angiotensin-aldosterone activity -> Sodium and fluid retention
Smoking, body overweight, and increased sodium consumption
Diuretics
Sympatholytic drugs
Vasodilators
Calcium channel blockers
Angi
Antihypertensive Drugs
Diuretics
Sympatholytic drugs
Vasodilators
Calcium channel blockers
Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers
- Diuretics
Diuretics increase sodium excretion and relax arteries (vasodilation)
Thiazides are preferred in patients with adequate renal function
Organic acid diuretics (loop diuretics) are used in patients with reduced renal function
Act on the loop of Henle
Diuretics can be used alone or in combination with other antihypertensive drugs
Common side effects: excessive loss of fluid and Na+
Types:
Thiazide diuretic: E.g., Chlorothiazide,
Loop diuretic: E.g., Furosemide
Potassium-sparing diuretics: E.g., Amiloride,
