Coordinated response of CVS Flashcards
Orthostasis
On standing up the CVS changes according to the effect of gravity
What occurs when orthostasis occurs
Blood pressure falls at first - postural hypotension, lack of blood flow to brain - faint
Quickly recovers - due to homeostatic mechanisms such as baroreflex
What 3 things does the baroreflex integrate
Increase heart rate
Increase heart contractility
Increase TPR
Bernoulli’s law
Blood flow = pressure energy + potential energy + kinetic energy
Gravity induced high venous blood pressure
High BP in venous system at feet is due to hydrostatic pressure
How does orthostasis cause hypotension when standing
1) Fall in CVP
2) Decreased end diastolic volume
3) Decreased SV
4) Decreased CO
5) Poor perfusion of brain -dizziness and fainting
How does orthostasis cause hypotension when lying down
1) Increased central venous pressure
2) Increased end diastolic volume
3) Increased SV
4) Increased CO
Reflex response to orthostasis
1) Less stimulation (unloading) of baroreceptors
2) Lower afferent fibre activity
3) Switches off inhibitory nerves that go from CVLM to RVLM
4) Results in RVLM being more active sending efferent signals to heart and arterioles
5) Increased sympathetic drive to SA node and Increased HR
Myocardium increased contractility.
Vasoconstriction increases TPR
Less vagal parasympathetic activity to SA node - overall increase in BP
What makes postural hypotension worse
- α-adrenergic blockade, generalized sympathetic blockade or other drugs that reduce vascular tone
- Varicose veins
- Lack of skeletal muscle activity
- Reduced circulating blood volume
- Increased core temperature
The initial effect of microgravity (space) on CVS
- Blood not pooling in feet and returning to the heart easily, increases atria/ventricle volume so increase CO and preload
- Sensed by cardiac mechanoreceptors leading to a reduction in sympathetic activity
- Reduces ADH and RAAS
- Increases ANP and GFR
- Overall reduction in blood volume by 20%
Long term effect of microgravity on CVS
Less BV, reduced stress on heart, heart reduces in muscle mass, genreal drop in BP
Effect of returning to gravity on CVS
Severe postural hypotension due to lower blood volume and smaller heart
Baroreflex can’t compensate
Cardiovascular response to the exercise
Increase sympathetic activity and reduce vagal inhibition Increase lung O2 uptake Control BP Dynamic Static
CVS response to dynamic excercise
Constantly shortening and relaxing with lots of different muscle groups involved - lower BP and sympathetic tone
CVS response to static exercise
1 specific muscle group is being worked without constant movement - Higher BP, local metabolic hyperaemia
What are some small adaptations that will increase pulmonary circulation
Increase HR
Increase SV
Increase atriovenous O2 difference
Exercise induced tachycardia
Maximum HR = 220
Decrease vagal tone
Increase sympathetic activity
Exercise induced stroke volume
- INCREASE END DIASTOLIC VOLUME
- FASTER EJECTION
- DECREASED END SYSTOLIC VOLUME
What does an increase end-diastolic volume mean in exercise induced SV
increase venous return/CVP through veno-constriction
Increase sympathetic activity and calf muscle pump - activates starling law increasing preload
What does a faster ejection mean in exercise induced SV
increase contractility by sympathetic activation of β1 receptor (inotropic increase in Ca2+)
What does a decreased end systolic volume mean in exercise induced SV
Accounts for increase SV. Increase contractility by sympathetic activation of β1 receptors and starling’s law
What does compensatory vasoconstriction of non-essential circulations do
Prevent hypotension due to exercise induced decreased TPR
Prevent BP from falling
What does RVLM control
Specific pre-ganglionic sympathetic nerves in spinal cord which send out post ganglionic nerves to specific tissues
Metaboreceptors
Small diameter sensory fibres in skeletal muscle
Are chemosensitive
What stimulates metaboreceptors
K+, H+, Lactate which increase in exercising muscle
Reflex effects of metaboreceptors
- Tachycardia (via increased sympathetic activity)
- Increased blood pressure
- ‘Pressor response’ to exercise
What do metaboreceptors do
- Important during isometric exercise (increased muscle load). Static exercise raises BP more than dynamic exercise
- Raised BP maintains blood flow to contracted muscle to try force blood into the contracted muscle
- Contracted muscle supplied by dilated resistance vessels due to metabolism – selective metabolic hyperaemia
