6 - Cardiovascular Control 2 Flashcards
What is TPR?
- total peripheral resistance
- resistance of all vessels in your body
What are the 3 assumptions for the flow equation?
- blood flow is steady
- vessels are rigid
- negligible right atrial pressure
What are the equations for stroke volume, cardiac output, and mean arterial pressure?
- SV = end-diastolic volume - end-systolic volume
- CO = SV x HR
- MAP = CO X TPR
What is the venous volume distribution affected by?
- peripheral venous tone
- gravity
- skeletal pump
- breathing
What is flow control?
- BP constant so vessel resistance changes to regulate flow (vasodilation and vasoconstriction)
- difference in pressures drives flow of blood through bodies where it encounters resistance
What is Poisseuile’s equation?
- resistance is inversely proportional to r^4
- describes resistance to blood flow in vessels
What does resistance reduce in veins?
- compliance
- venous return
What does constriction determine in arterioles?
- blood flow to downstream organs
- MAP
- pattern of blood flow to organs
What are the two mechanisms for regulating blood flow?
- local mechanisms intrinsic to smooth muscle
- systemic mechanisms extrinsic to smooth muscle
What are the features of the local, intrinsic mechanism for regulating blood flow?
- auto-regulation (intrinsic capacity to compensate for changes in perfusion pressure by changing vascular resistance)
- myogenic theory: smooth muscle fibres respond to tension in vessel wall
- metabolic theory: as blood flow decreases, metabolites accumulate and vessels dilate
What are the features of the systemic, extrinsic mechanism for regulating blood flow?
- circulating hormones for vasodilation and vasoconstriction
- autonomic nervous system (PNS controls HR; SNS controls circulation and vessel radius)
Which circulating hormones are vasodilators and which are vasoconstrictors?
- vasodilator: kinins, atrial natriuretic peptide, NO and prostacyclin
- vasoconstrictor: vasopressin, adrenaline, AGTii, thromboxane A2 and endothelins
What 3 features is Poiseuille’s equation dependent on?
- length of tube
- fluid viscosity (not fixed but usually constant)
- radius of tube (variable - main way to measure resistance)
What is the mode of action of noradrenaline on blood vessels?
- binds to α1 adrenoreceptors to cause smooth muscle contraction and vasoconstriction
Which organs are heavily or poorly SNS innervated?
- heavily: kidney, gut, spleen, skin
- poorly: skeletal muscle, brain
What is the vasomotor centre?
- located bilaterally in reticular substance of medulla and lower third of pons
- vasoconstrictor (pressor) area, vasodilator (depressor) area and cardioregulatory inhibitory area
- transmits impulses through spinal cord to blood vessels
- high brain centres can exert powerful excitatory or inhibitory effects on VMC
- lateral portions of VMC influences heart rate and contractility
- medial portions of VMC transmits signals via vagus nerve to heart to decrease heart rate
What is the nervous control of vessel diameter?
- increased tonic activity = vasoconstriction
- decreased tonic activity = vasodilation
- no PNS innervation to vasculature
- blood vessels receive SNS post-ganglionic innervation
What effects strength of cardiac muscle contraction?
- sympathetic nerves increase strength of contraction and HR
- NA released which binds to adrenoreceptors on myocytes
- increases cAMP, activating PKA
- PKA phosphorylates L-type Ca2+ channels, SR Ca2+ release channels and SERCA
- Ca2+ influx increases and Ca2+ taken up by intracellular store
What is SERCA?
sarco/endoplasmic reticulum Ca2+ ATPase
What is the circulation and its features?
- transports blood around body
- delivers O2 and nutrients and removes CO2 and metabolites
- heart generates pressure gradient
- BP drives flow of blood within body
What are some features of the blood vessels?
- arteries: large and elastic
- veins: highly compliant, act as reservoir for blood volume
- capillaries: numerous and thin (10μm diffusion distance)
What controls increase stroke volume?
- increased SNS efferents to heart (extrinsic)
- increased plasma adrenaline (extrinsic)
- increased EDV (intrinsic)
What controls blood vessel diameter?
- sympathetic vasoconstrictor nerves (extrinsic)
- circulating hormones (extrinsic)
- local controls (intrinsic)
What is the reciprocal innervation with the heart?
increased afferent input from increased baroreceptor activity stimulates parasympathetic nerves to heart and inhibits sympathetic innervation to heart, arterioles and veins
What are baroreceptors and their mode of action?
- mechanoreceptors in carotid sinus and aortic arch change firing rate in response to changes in pressure
- respond to stretch (greater stretch = greater fire)
- respond to changes in pressure (greater pressure = greater fire)
- increase PNS and decrease SNS when fire
