963694
Description
Flashcards by Hannah Tribe, updated more than 1 year ago
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Created by Hannah Tribe
almost 10 years ago
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| Question | Answer |
| What happens immediately upon orthostasis? | Hypotension, due to the effect of gravity on the blood. |
| Why does the venous flow to the heart not change on orthostasis? | The change in arterial pressure is the same as the change in venous pressure (they both increase by the same amount). |
| What factors affect the pressure at the feet? (3) | 1. Length of leg 2. Density of the blood 3. Gravity |
| After prolonged orthostasis, what happens to blood in the legs? | Veins distend as so blood pools in the legs |
| What is the result of this? | CVP decreases (blood returning to the heart), so SV decreases, causing CO to decrease and thus also BP. This can result in decreased brain perfusion and fainting. |
| What homeostatic mechanisms correct postural hypotension, and how is it detected? | Low pressure detected by baroreceptors and ventricular stretch receptors. This leads to decreased stimulation of the NTS in medulla, and increased sympathetic activity from the RVLM (and decreased parasympathetic activity). Results in increased HR, SV and therefore CO, increased TPR and therefore BP, and vasoconstriction. |
| What makes postural hypotension worse? (4) | 1. Sympathetic blockers (e.g. prazosin [alpha blocker], amlodipine [VDCC blocker]) 2. Varicose veins 3. Haemorrhage 4. Long term bed rest (2,3 and 4 due to imparied venous return) |
| What are the 3 main things the body needs to do when we exercise? | 1. Maintain BP 2. Increase uptake and circulation of O2 3. Direct O2 to areas where it is needed, and away from areas where it is unnecessary. |
| What small responses are integrated to provide for the body's needs in exercise? (3) | 1. Increased HR 2. Increased SV (therefore increased CO) 3. Increased difference between arterial and venous O2 (increased delivery of O2 to tissues) |
| What causes the increased HR in exercise? (4) | 1. Increased sympathetic activity commanded by cortex 2. Decreased parasympathetic activity demanded by muscle mechanoreceptors 3. Increased sympathetic activity demanded by muscle metaboreceptors (increased metabolites) 4. Increased circulating NA and adrenaline due to increased sympathetic activity |
| What causes the increased SV? (3) | 1. Slightly increased EDV (due to increased CVP) 2. Faster ejection (due to increased contractility by sympathetic beta 1 activity) 3. Large decrease in ESV (increased ejection fraction) |
| Why does blood flow to exercising muscle and skin increase? | To muscle, due to increased metabolites and circulating adrenaline causing local vasodilation. To skin, due to need for heat loss. |
| If vasodilation in muscle and skin causes a fall in TPR, how is BP maintained during exercise? | Blood flow to non-essential tissues is limited by vasoconstriction (gut, kidneys, inactive muscle etc.) |
| Why does static exercise (e.g. weight lifting) increase BP more than dynamic exercise? | In the exercising muscle, metaboreceptors detect K+ and H+ (produced during the exercise) and cause the reflex effect of increasing sympathetic activity (and therefore BP) in order to maintain perfusion of the contracted muscle. It rises more here as the muscle load is increased. |
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