6 - Cardiovascular Control 2

Question 1

What is TPR?

Answer 1

• total peripheral resistance

- resistance of all vessels in your body

Question 2

What are the 3 assumptions for the flow equation?

Answer 2

• blood flow is steady
• vessels are rigid
• negligible right atrial pressure

Question 3

What are the equations for stroke volume, cardiac output, and mean arterial pressure?

Answer 3

• SV = end-diastolic volume - end-systolic volume
• CO = SV x HR
• MAP = CO X TPR

Question 4

What is the venous volume distribution affected by?

Answer 4

• peripheral venous tone
• gravity
• skeletal pump
• breathing

Question 5

What is flow control?

Answer 5

• 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

Question 6

What is Poisseuile’s equation?

Answer 6

• resistance is inversely proportional to r^4

- describes resistance to blood flow in vessels

Question 7

What does resistance reduce in veins?

Answer 7

• compliance

- venous return

Question 8

What does constriction determine in arterioles?

Answer 8

• blood flow to downstream organs
• MAP
• pattern of blood flow to organs

Question 9

What are the two mechanisms for regulating blood flow?

Answer 9

• local mechanisms intrinsic to smooth muscle

- systemic mechanisms extrinsic to smooth muscle

Question 10

What are the features of the local, intrinsic mechanism for regulating blood flow?

Answer 10

• 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

Question 11

What are the features of the systemic, extrinsic mechanism for regulating blood flow?

Answer 11

• circulating hormones for vasodilation and vasoconstriction

- autonomic nervous system (PNS controls HR; SNS controls circulation and vessel radius)

Question 12

Which circulating hormones are vasodilators and which are vasoconstrictors?

Answer 12

• vasodilator: kinins, atrial natriuretic peptide, NO and prostacyclin
• vasoconstrictor: vasopressin, adrenaline, AGTii, thromboxane A2 and endothelins

Question 13

What 3 features is Poiseuille’s equation dependent on?

Answer 13

• length of tube
• fluid viscosity (not fixed but usually constant)
• radius of tube (variable - main way to measure resistance)

Question 14

What is the mode of action of noradrenaline on blood vessels?

Answer 14

• binds to α1 adrenoreceptors to cause smooth muscle contraction and vasoconstriction

Question 15

Which organs are heavily or poorly SNS innervated?

Answer 15

• heavily: kidney, gut, spleen, skin

- poorly: skeletal muscle, brain

Question 16

What is the vasomotor centre?

Answer 16

• 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

Question 17

What is the nervous control of vessel diameter?

Answer 17

• increased tonic activity = vasoconstriction
• decreased tonic activity = vasodilation
• no PNS innervation to vasculature
• blood vessels receive SNS post-ganglionic innervation

Question 18

What effects strength of cardiac muscle contraction?

Answer 18

• 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

Question 19

What is SERCA?

Answer 19

sarco/endoplasmic reticulum Ca2+ ATPase

Question 20

What is the circulation and its features?

Answer 20

• transports blood around body
• delivers O2 and nutrients and removes CO2 and metabolites
• heart generates pressure gradient
• BP drives flow of blood within body

Question 21

What are some features of the blood vessels?

Answer 21

• arteries: large and elastic
• veins: highly compliant, act as reservoir for blood volume
• capillaries: numerous and thin (10μm diffusion distance)

Question 22

What controls increase stroke volume?

Answer 22

• increased SNS efferents to heart (extrinsic)
• increased plasma adrenaline (extrinsic)
• increased EDV (intrinsic)

Question 23

What controls blood vessel diameter?

Answer 23

• sympathetic vasoconstrictor nerves (extrinsic)
• circulating hormones (extrinsic)
• local controls (intrinsic)

Question 24

What is the reciprocal innervation with the heart?

Answer 24

increased afferent input from increased baroreceptor activity stimulates parasympathetic nerves to heart and inhibits sympathetic innervation to heart, arterioles and veins

Question 25

What are baroreceptors and their mode of action?

Answer 25

• 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