L1 CVS Homeostasis

Question 1

Outline the role of the sensor, central integrator and effector organ in a biological control system.

Answer 1

1. Sensor senses output/state of a process in the body and compares it with a desired state/set point.
2. Central integrator receives sensory information and sends an error signal to the effector
3. Effector then undergoes a process which adjusts the output to match set point/desired state

Question 2

Compare the variables and relationship of the cardiac function curve and the vascular function curve

Answer 2

1. Cardiac function= Cardiac output (L/min) will Increase if
   Mean right atrial pressure= reflection of heart filling INCREASES
2. Vascular function= Venous return to the heart (L/min) will Increase if
   Mean right atrial pressure DECREASES.

Question 3

Explain how cardiac output is established by the equilibrium between the cardiac and vascular function curves at rest and under the following conditions; venoconstriction, blood loss, and exercise.

Answer 3

Because the heart and vascular system is closed, Venous return = Cardiac Output.

Mean Right Atrial pressure has to be kept at a small range of values where these two function curves intersect because venous return will stop if the MRAP is equal to pressure driving blood back to the heart and the veins will collapse if MRAP = extravascular pressure (0). (not too high or too low)

1. Venoconstriction/ increase in venous return pressure increases mean systemic filling pressure, shifting vascular function curve up and right, leading to an intersection at a higher cardiac output.
2. Blood loss/decrease in venous return pressure will cause a decrease in MRAP to maintain the same CO, because it will decrease mean systemic filling pressure, leading to intersection at lower cardiac output.
3. In exercise, there is a shift of vascular function curve up and right due to increased venoconstriction, increased venous return
   AND a shift of cardiac function curve up and left due to reduction in total peripheral resistance, increased HR etc.

Question 4

Compare the distribution of cardiac output at rest vs. exercise with a large muscle mass.

Answer 4

At rest CO is distributed relatively uniformly across organ systems in relation to resistance to blood flow across its vascular network.

In exercise there is preferential blood flow to muscle (skeletal, cardiac) - highest metabolic support) and skin and decrease to liver, spleen, GI tract and kidney while brain remains the same. The distribution within the organs themselves may also differ even if the CO overall has increased.

Question 5

Provide an overview of the neural control of blood pressure by the arterial baroreflex

Answer 5

1. Blood pressure sensed by arterial baro-receptors in the aortic arch and carotid bifurcation.
2. Stretch on vessels is relayed to medulla which instigates a change in autonomic activity:
   3a) either increased tonic inhibition of sympathetic system/ increase in PS if Bp is high

or
3b) Increase sympathetic: vasoconstriction, positive inotropy, tachycardia. / decrease in PS

4. This acts on heart, kidneys. (+ symp on the GI, Bv)

Question 6

Summarize the structure and function of the autonomic nervous system as it relates to the control of the cardiovascular system (heart)

Answer 6

PS: via Vagus nerve -> visceral ganglion –> short PoG axon

Innervates SA node on right, AV node on the left + atrial muscle.

Symp: via T1-T12 symp afferents –> sympathetic chain –> long PoG nerves from cervical ganglion.

Innervates atria (SA node), ventricles + conduction system

Question 7

Outline the main endocrine mechanisms of cardiovascular control

Answer 7

RAAS to increase BP + ADH.

Natriuetic peptides ANP and BNP to decrease BP

Question 8

Describe the triggers and effects of Renin-Angiotensin- Aldosterone system

Answer 8

1. Renin released by JG cells due to
   a) symp stim
   b) decrease bp (Gfr)
   c) decrease nacl at JGA
2. Converts angiotensinogen –> Angiotensin 1 –> (via ACE in lungs) to Angiotensin 2.
3. Angiotensin 2
   a) Increases Symp activity of CVS and adrenal medulla by acting on postrema in hypothalamus to helping symp ganglia transmission/ NA synthesis

b) Promotes water and salt retention in kidneys via stimulating production of Aldosterone, ADH
c) Directly causes vasoconstriction
d) causes release of ANP

Question 9

Where is adrenaline/noradrenaline made and stored in the body to be released by sympathetic activation

Answer 9

Adrenal medulla.

Question 10

Describe the triggers and effects of Natriuretic peptides

Answer 10

1. Cardiac distension, symp stim, Angiotensin 2 and endothelin cause release of
   ANP and B (ventricular)NP
2. BNP directly inhibits, and ANP increases GFR which inhibits: renin, Ang 2, Aldo secretion.
3. This leads to increased loss of salt and water.
4. BNP also causes systemic vasodilation
5. Overall leading to Reduced
   a) blood volume,
   b) arterial, pulmonary capillary wedge & central venous pressure
   c) and reduced CO.

Question 11

How is BNP used clinically

Answer 11

BNP and Nt-pro-BNP are sensitive, diagnostic markers elevated in HF,

• Has prognostic value as proportional to the severity of cardiac loading.
• Can be used to differentiate between HF and COPD