Co-ordinated cardiovascular responses: Gravity and Exercise Flashcards
What is Orthostasis?
Why does the CVS change when standing?
What happens directly after standing up and what is in place to correct it?
- Upright position
- Due to effect of gravity
- ↓BP at first, leading to Postural Hypotension - due to lack of blood flow to brain. Homeostatic mechanisms in place to correct BP - includes ↑HR, ↑Contractility, ↑TPR.
What is the effect on arterial and venous gradient when lying down and standing up?
LOOK AT DIAGRAMS!
When lying down, the arterial and venous BP has a very SMALL gradient between heart and feet.
On standing, BP at the feet is much higher than at heart. The potential and kinetic energy at the heart dominates that at the feet, so blood flows towards the feet.
Why does gravity create high BP’s in the venous system?
It causes blood to pool in the lower limbs, and the compliancy (stretchiness) of the venous walls aids this.
How does Orthostasis lead to Postural Hypotension?
LOOK AT PICTURE!
When lying down, blood is evenly distributed in veins. This ↑CVP = ↑EDV = ↑SV.
As you stand up, blood pools in the legs (no longer evenly distributed). This ↓CVP = ↓EDV = ↓SV = ↓BP - poor perfusion to brain causes dizziness and fainting.
What is the role of the reflex response to Postural Hypotension?
Explain what occurs in this response?
LOOK AT DIAGRAM!
- To prevent fainting
- Pressor Response: Low BP will cause ↓Firing of Baroreceptors (Unloading) = ↓Stimulation of NTS-CVLM inhibitory pathway. There will then be no inhibition of the RVLM, therefore allowing for ↑Sympathetic activity - ↑HR, ↑Contractility, Vasoconstriction = ↑TPR, ↓Vagal activity to SAN = ↑BP.
What substances or conditions make postural hypotension worse?
In who can postural hypotension be very serious in? Why?
- • Drugs that ↓Sympathetic activity - is a side-effect of using CCBs
• Varicose veins - impaired venous return
• Lack of skeletal muscle activity due to paralysis or forced inactivity e.g. bed-bound
• ↓Circulating blood volume e.g. haemorrhage - will ↓CVP
• ↑Core temperature - lead to peripheral vasodilation, ↓core blood volume - Elderly - they can fall
What is Microgravity?
What’s the blood distribution when standing and lying down in microgravity?
Where is blood redistributed to?
What occurs Initially when going into microgravity conditions?
What occurs Long-term in microgravity?
What occurs on return to gravity?
- Low gravity, like in space
- It’s the same in both positions
- Thoracic region
- ↑Preload/EDV = ↑Chamber volume - sensed by baroreceptors and cardiac receptors. This leads to ↓Sympathetic activity/RAAS/ADH and ↑GFR/ANP. Overall, there’s a diuretic effect to reduce blood volume (by 20%).
- ↓Blood volume = ↓Stress on heart = Heart loses muscle mass. This will cause a ↓BP - lower BP needed to drive circulation in space.
- Severe postural hypotension due to a much smaller heart - Baroreflex can’t compensate.
What does the CVS achieve during exercise?
What 3 smaller changes massively increase O2 uptake during exercise?
- It works to ↑O2 uptake, transport, and supply, as well as controlling BP while there’s a huge increase in CO - prevent overload of heart.
- • ↑HR
• ↑SV
• ↑Arteriovenous O2 gradient
How is the O2 uptake in the lungs increased?
How is the CO increased during exercise?
Why does SV have a maximum value?
LOOK AT GRAPHS!!
- Pulmonary CO and the arteriovenous O2 gradient increase.
- HR increases the most, and SV increases but has a max value
- Ventricle is at maximum contractility
What is exercise-induced tachycardia?
How is this response brought about?
- ↑HR before exercising
- On initiation of exercise, muscle mechanoreceptors send frequent impulses to brain to ↑HR - this is due to ↓Vagal tone and ↑Sympathetic activity to SAN and AVN.
What occurs in exercise-induced change in SV?
Due to ↑Sympathetic activity:
- ↑EDV - ↑Venous return due to Venoconstriction and calf muscle pump
- Faster Ejection - ↑Contractility by activation of β1-receptors
- ↓ESV - ↑Contractility by activation of β1-receptors - accounts for ↑SV
What are the blood flow changes that increase heart rate during exercise?
What occurs In muscle to decrease local arteriole resistance?
- Vasodilation of arterioles in active muscle, myocardium, and skin
- Metabolic Hyperaemia:
• Metabolic vasodilation - stimulated by K, H, Adenosine etc.
• β2-mediated vasodilation - due to circulating Adr
What happens to blood pressure when CO is increased by a lot?
Why does BP only increase by a small amount?
What’s the reason for this happening?
- A relatively small increase in BP
- Vasodilation in skeletal muscle = ↓TPR - ↑↑↑CO almost cancelled out by ↓TPR.
- Prevent excessive afterload on heart
What is compensatory vasoconstriction? Why does it occur?
Compensatory vasoconstriction in inactive/unrequired tissues (e.g, kidneys, GIT) - prevents ↓↓BP due to ↓TPR during exercise.
What is the difference between static and dynamic exercise?
What is resistive exercise?
- Static exercises e.g. handgrip, is where there’s a constant contraction of a small number of muscles.
Dynamic exercise e.g. running, is where there’s a shortening/lengthening of many muscles.
- Resistive exercise e.g. weightlifting, is a combination of dynamic and static exercise with a high load - leads to very high BP.
