3008 Dampney: CV Regulation and Stress (1-5)

Stressor: The cause - An agent or factor that triggers the stress response, usually threatens to overwhelm homeostasis

Stress: The effect, a generalized nonspecific response of the body to a stressor

- Activation of the sympathetic nervous system
- Release of adrenocorticotropic hormone (ACTH) from anterior pituitary (hypothalamic-pituitary-adrenal-axis, HPA)
- The release of ACTH is controlled by corticotropin releasing hormone (CRH), released from nerves originating from the paraventricular nucleus (PVN) in hypothalamus.

See image (needs more detail).

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See Image. Response is very similar to cardiovasculatory responses which are evoked during exercise.
Example of physiological response to psychological stress: Cardiovascular events in Munich during the World Cup (2006).

Study comparing lay women to nuns, showed lay women to have significantly higher blood pressure over a long period of time, blood pressure significantly increased with age. As for Nuns, blood pressure remained relatively stable. This study showed that environmental stress could have long term effects on BP.

The Anterior cingulate cortex (ACC). Studies showed that lesions of the ACC prevent the cardiovascular responses to mental stress.

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- VRG: affects major nerve (phrenic nerve) that controls the diaphragm hence controls the rate and depth of breathing.

- RP: controls HR

- PVN: regulates release of ACTH --> Cortisol, controlling sympathetic outflow.

Study in mice, showed that inhibition of the DMH (using muscimol and agonist of GABA receptors) blocked the CV response to air jet stress, for both BP and HR.

Check book: Sympathetic has short pre and long post

Parasympathetic has long pre and short post - allowing the parasympathetic ganglia to be very close to the target organ.

In both cases change to upright position causes a shift of 500-1000mL of blood from thorax to lower part of th body (from above to below the hydrostatic indifference point)

The marked difference is due to the leg and abdominal muscle contractions involved in standing up which contribute to the muscle pump mechanically aiding in increasing blood flow back to the heart. This mechanism is not involved in passive tilt.

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- Baroreflex and atrial receptors cause an overall increase in HR and TPR.

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Immediately (first 10 seconds): Leg and abdominal muscle contractio - muscle pump

Later effects (after 10 seconds): Baroreceptor and atrial receptor reflexes as in passive tilting.

Meaduring activity of a single nerve fibre to measure the overall level of sympathetic nerve activity.

Compensatory response would still be present, but impaired.