Cardiovascular System - Lecture 9 Flashcards
What do peripheral chemoreceptors monitor?
pressures of oxygen, carbon dioxide and pH levels in the arterial blood
What are the 2 chemoreceptors located close to baroreceptors?
carotid body and aortic body
What do the peripheral chemoreceptors act on?
breathing
What 2 things do peripheral chemoreceptors increase?
- respiratory frequency
- tidal volume
What do peripheral chemoreceptors do to HR? Why?
increase HR to eliminate CO2 and increase oxygenation faster
What system controls blood volume?
renal
What are the 2 systems used by the renal system to control blood volume?
- urinary loss, water retention via pressure diuresis
- renin angiotensin aldosterone system
What happens when blood volume decreases (5)?
- dec venous pressure
- dec venous return
- dec end-diastolic volume
- dec stroke volume
- dec cardiac output
What happens when arterial pressure increases during pressure diuresis?
- inc urinary loss of sodium and water
- dec plasma volume 60% BV
What expels H2O and waste?
nephrons
What kind of system is pressure diuresis?
negative
What kind of drug is used to control BP?
diuretics
How does the RAA system sense pressure?
kidneys and brain
How does the RAA system sense pressure by the kidneys?
via changes in filtration rates which are sensed as changes in excreted sodium, signalling specialized cells to release renin
How does the RAA system sense pressure change by the brain?
via baroreceptors, resulting in ADH release from neurons in the hypothalamus
What is renin?
an enzyme released by the kidneys
What happens to renin when MAP decreases?
it increases
Why do specialized cells sense a drop in BP using renin?
because of low Na+
What does renin convert when it is increased?
angiotensinogen into angiotensin I
Where is angiotensinogen made?
in the liver
What converts angiotensin I into angiotensin II?
ACE
Where is ACE found?
in the lungs
What produces ACE?
pulmonary endothelium
What is angiotensin II?
vasoconstrictor
What does angiotensin II increase? (2)
TPR and MAP
What happens to renin when MAP is low?
it increases
What happens to renin when MAP is high?
it decreases
What is vasopressin?
antidiuretic hormone
Where is vasopressin synthesized?
hypothalamus
What releases vasopressin?
pituitary gland
What triggers the release of vassopressin?
low output from arterial baroreceptors
What are the 2 mechanisms of vasopressin?
vasoconstriction and antidiuretic
What kind of system is the vasopressin system?
negative feedback
When angiotensin II binds receptors in adrenal gland, what hormone is released?
aldosterone
What does aldosterone bind to?
receptors in the kidney
What retention does aldosterone cause?
Na and H20
What kind of system is the RAA system 3?
negative feedback
Low MAP -> aldosterone ___ -> ___ MAP
increases, increased
High MAP -> aldosterone ___ -> ___ MAP
decreases, decreased
What are the 4 main classes of hypertension drugs?
- aldosterone receptor antagonists
- angiotensin II receptor blockers
- ACE inhibitors
- renin inhibitors
What is the function of aldosterone receptor antagonists?
binds to aldosterone receptors, prevents binding by aldosterone.
What is the function of angiotensin II receptor blockers?
Prevents binding of angiotensin II in i)brain, ii) arterioles, and iii) adrenal glands
What is the function of ACE inhibitors?
prevents conversion of angiotensin I to I
What is the function of renin inhibitors?
prevents conversion of angiotensinogen to angiotensin I
What is orthostasis?
maintenance of an upright standing posture
What is orthostatic hypotension?
BP drop when standing up
What happens to systolic and diastolic pressure when baroreflex is in action?
systolic: drops a little
diastolic: increases a little
What happens to BP immediately after standing up?
it drops from 120/80 to 75/40
What would happen to BP after standing up without baroreflex?
it would continue to drop
What happens to MAP right after standing up?
it doesn’t change
What kind of hydrostatic pressure is found in the veins furthest from the heart?
high pressure
Why is there a large increase in volume of veins when there is a modest increase in hydrostatic pressure?
because veins have a higher compliance
Small change in pressure in venous compartment gives a ___ change in volume.
large
What is central blood volume?
blood in thorax, lungs, heart and great vessels
What happens to the central blood volume when you stand up?
it goes from 1.2L to 0.9L (lost 300 mL)
What happens to the pressure in the veins when the central blood volume decreases?
it falls because there is less blood and there is a drop in venous return
Why does stroke volume decrease?
because there is less blood filling the ventricles
How much does stroke volume decrease?
50%
How much does cardiac output drop?
6 to 4.5
What happens to heart rate when you stand up?
it increases
By how much does heart rate increase when you stand up?
60 to 90 (+50%)
What increases HR to compensate for the drop in SV?
baroreflex
How is MAP preserved when you stand up?
map is the product of the cardiac output x total peripheral resistance (increasing)
What happens to blood flow in many organs when you stand up?
it drops
What happens to blood flow in forearm when you stand up?
it drops
Constriction in arterioles results in an ___ in TPR.
increase
TPR increase is due to…
baroreflex
What 2 things does baroreflex increase?
contractility and venoconstriction
What is the function of the muscle pump after standing up?
contracting your muscles results in higher venous return while standing, resulting in higher SV, and less need to have a high heart rate
What are the 2 reasons why soldiers who stand for long periods of time may faint?
- Blood pooled in leg veins, resulting in lower central blood volume, reducing venous return.
- Loss of plasma volume
What can we do to avoid low central blood volume?
reduce venous return
What happens to plasma volume loss when there is high pressure in legs?
it increases
After 15 minutes of standing, how much plasma volume can be lost?
750 mL
Why is there a drop in MAP while standing for long periods?
due to drop in venous return
High venous pressure in legs = ___ fluid loss = ___ blood plasma = ___ venous return
high, low, low
How much water is lost per day?
4 L
How are the 4L of water lost in a day returned to the body?
through the lymphatic system
In the 2D reentry demo, what is the spiral generated by?
the interaction of an ectopic beat (PVC) with a normal wave of excitation, resulting in a tachycardia
Why are the spirals in the 2D reentry demo hard to get by chance?
because the timing has to be precise (which is why PVCs are often benign)
