9- Regulation Of The Cvs

Question 1

How do you calculate SV, CO and MSBP

Answer 1

Stroke Volume = End diastolic volume – End systolic volume (SV = EDV – ESV)
Cardiac Output = Heart Rate x Stroke Volume (CO = HR x SV) (
MSBP = CO x TPR)

Question 2

Which 4 factors influence venous volume distribution

Answer 2

o peripheral venous “tone”
o gravity
o skeletal muscle pump
o breathing (decreased pressure in thoracic cavity)

Question 3

What is auto regulation

Answer 3

the intrinsic capacity to compensate for changes in perfusion pressure by changing vascular resistance

Question 4

What are the 2 theories for autoregulation

Answer 4

o MYOGENIC THEORY - smooth muscle fibres respond to tension in the vessel wall; e.g. as pressure rises muscle fibres contract; stretch-sensitive Ca2+ channels probably involved
o METABOLIC THEORY - as blood flow decreases “metabolites” accumulate and vessels dilate; when flow increases “metabolites” are washed away. Involves e.g. CO2, H+, adenosine, K+

Question 5

Name some substances released from the endothelium

Answer 5

• NITRIC OXIDE – endothelium-derived relaxing factor synthesised from arginine
  o Plays a key role in vasodilation
• PROSTACYCLIN & THROMBOXANE A2 – relative amounts for clotting
  o Vasodilator and vasoconstrictor respectively - ENDOTHELINS – potent vasoconstrictors

Question 6

Which hormones are involved in systemic regulation

Answer 6

 Kinins
o e.g. bradykinin, have complex interactions with renin-angiotensin system; relax vascular smooth muscle
 ANP
o Atrial natriuretic peptide - secreted from the cardiac atria, vasodilator o Circulating vasoconstrictors
 ADH – antidiuretic hormone (also known as vasopressin) secreted from posterior pituitary, o noradrenaline released from adrenal medulla,
o angiotensin II formed by increased renin secretion from kidney

Question 7

Which vessels do sympathetic nerves innervate

Answer 7

Sympathetic nerve fibres innervate ALL VESSELS EXCEPT CAPILLARIES (and
precapillary sphincters and some metarterioles)

Question 8

Which receptors does adrenaline bind to?

Answer 8

Circulating adrenaline binds with high affinity to smooth muscle beta-2- adrenoreceptors to cause vasodilation in some organs, however the effect is very concentration-dependent
• At high concentrations, adrenaline can bind to ALPHA adrenoreceptors which can override the vasodilatory effects of the beta-2-adrenoreceptor stimulation and produce vasoconstriction
• The constriction you see in blood vessels is an alpha-1-adrenoreceptor effect

Question 9

Where is the VMC located and what 3 areas does it consist of

Answer 9

VMC is located bilaterally in the reticular
substance of the medulla and the lower third
of the pons
• The VMC consists of a:
Vasoconstrictor Area (Pressor) Vasodilator Area (Depressor) Cardioregulatory Inhibitory Area

Question 10

What do the lateral and medial portions of the VMC do?

Answer 10

Lateral Portions of the VMC controls heart activity by influencing heart rate and contractility
• Medial Portions of the VMC transmits signals via the vagus nerve to the heart that tends to decrease heart rate

Question 11

Give an example of a Higher centre in the brain that can exert excitatory and inhibitory effects on the VMC

Answer 11

Hypothalamus

Question 12

What are the 3 ways to control blood vessel radius

Answer 12

Local Controls (Autoregulation) 
Circulating Hormones
Sympathetic Vasoconstrictor Nerves

Question 13

How can force of contraction be controlled

Answer 13

Increase NA release from intracellular stores

And