Q2-CB11/Cardiac Output 1

Question 1

What is cardiac output?

Answer 1

the volume of blood ejected from a ventricle per minute (L/min)

Question 2

equation of cardiac output

Answer 2

cardiac output = heart rate x number of beats per minute

CO = HR x number of bpm

Question 3

What is a cardiac output of a textbook person?

Answer 3

5 L/min

Question 4

What is cardiac output controlled by?

Answer 4

either heart rate and stroke volume

Question 5

what controls cardiac output?

Answer 5

it is regulated by the automatic nervous system

Question 6

What does the ANS do?

Answer 6

it controls multiple systems that maintains normal homeostasis

Question 7

is the ANS subconscious or involuntary?

Answer 7

it is involuntary

Question 8

The only rigorous definition for these is from the anatomy and where on the spine the fibres emerge. What are these places?

Answer 8

SNS: thoraco-lumbar (segments T1 to L2 )

PNS: cranio-sacral (cranial nerves III, VII, IX & X, sacral segments 2,3,4)

Question 9

The Sympathetic NS primarily acts via __________

Answer 9

catecholamines

Question 10

what are catacholamines?

Answer 10

Catecholamines are a group of similar substances released into the blood in response to physical or emotional stress.

The primary catecholamines are dopamine, epinephrine (adrenaline), and norepinephrine.

Question 11

What is released from nerve endings in the Sympathetic NS?

Answer 11

noradrenaline

Question 12

Sympathetic NS action in the heart is mediated via ______ and _______

Answer 12

alpha and beta adrenoceptors

Question 13

What is the most important adrenoceptor for the heart?

Answer 13

beta1-adrenoceptor

Question 14

Where are beta1-adrenoceptors located?

Answer 14

all throughout the heart (SA node, AV node, atria, and ventricles)

Question 15

What is a beta-adrenoceptor?

Answer 15

a G-protein coupled receptor linked to an adenylate cyclase

Question 16

what does a beta-adrenoceptor do?

Answer 16

it increases cAMP which then turns on protein kinase A

Question 17

Where does the main depolarizing curent in the SA node come from?

Answer 17

it comes from the Na+/K+ channel, current through this channel is increased by the binding of cAMP

Question 18

What causes the increase of Ca2+ into myocytes?

Answer 18

cAMP/PKA, when Ca2+ levels increase, so does the force of contraction

Question 19

What ion is crucial for muscle contraction?

Answer 19

calcium

Question 20

how is calcium crucial to muscle contraction in the heart?

Answer 20

it binds to troponin on the thin filament, allowing the thick filament to interact.

Question 21

explain the SA node action potential.

Answer 21

Question 22

What can be said about sympathetic agonists?

Answer 22

they are both positive chronotropes and positive inotropes

positive chronotropes increase the rate and positive inotropes increase the force

Question 23

What are some types of beta-blockers?

Answer 23

atenolol and propranolol

Question 24

What can be said about beta-blockers?

Answer 24

they are negative chronotropes and negative inotropes

negative chronotopes decrease the rate

negative inotropes decrease the force

Question 25

What is the primary neurotransmitter in the parasympathetic NS?

Answer 25

acetylcholine (ACh)

Question 26

At what receptors does ACh work at?

Answer 26

muscarinic and nicotinic cholinergic receptors

Question 27

What are muscarinic cholinergic receptors?

Answer 27

they are G-protein coupled receptors

Question 28

What are nicotinic cholinergic receptors?

Answer 28

they are ion channels found in nerves and skeletal muscle

Question 29

Parasympathetic innervation of the heart is via the \_\_\_\_\_\_\_\_\_\_\_\_

Answer 29

vagus nerve (cranial nerve X)

Question 30

What is the main cholinergic receptor in the heart?

Answer 30

M2 (muscarinic type 2)

Question 31

what does the vagus nerve innervate specifically?

Answer 31

the SA node, AV node, and parts of the atria (there is little to none innervation in the ventricles)

Question 32

What does the M2 receptor do?

Answer 32

it inhibits adenylate cyclase, which decreases the amt of the cAMP

Question 33

What happens to sodium influx when the amt of cAMP decreases?

Answer 33

Na+ influx is decreased so the rate of depolarization is decreased. since it decreases the rate of SA node firing, heart rate decreases as well

Question 34

what effect does the decrease in cAMP have on atrial and ventricular contraction?

Answer 34

it has a small effect on the force of atrial contraction but no effect on the ventricles (the atrial effect has little if any effect on cardiac output)

Question 35

explain SA node action potential in cholinergic action.

Answer 35

Question 36

what 2 divisions of the nervous system innervate the SA node?

Answer 36

sympathetic and parasympathetic

Question 37

What is controlled by the balance of the sympathetic and parasympathetic nervous systems?

Answer 37

heart rate

Question 38

what is a sign of sympathetic activation?

Answer 38

tachycardia (atropine, the muscurinic antagonist, can cause tachycardia)

Question 39

the natural rate of the SA node is abt 100bpm, but ______ stimulation drops it down to abt 70 bpm

Answer 39

vagal

Question 40

what is equation for mean arterial pressure?

Answer 40

mean arterial pressure = cardiac output x total peripheral resistance

Question 41

Explain the baroreceptor reflex.

Answer 41

it is a negative feedback loop sensory fibers in the aortic arch and carotid sinus detect a stretch in blood vessel walls(the firing is directly proportional to the stretch) these fibers then go to the medulla oblongata on the brain stem the medulla regulates the sympathetic/parasympathetic NS outflow to the heart

Question 42

Explain cardiac changes in exercise.

Answer 42

exercise is related to an increase of sympathetic NS activity. Normal feedback via the baroreceptor would be expected to prevent this, BUT instead this looks to be reset in exercise; the effect is the BP is perceived to be too low!

Question 43

What 2 changes does exercise cause in the heart?

Answer 43

Increases heart rate and stroke volume – heart rate can increase approx. 300% to ~200 bpm – stroke volume can increase approx. 175% to ~125 ml – overall cardiac output can increase by approx. 500% to 25 L

Question 44

heart rate cannot increase over ______ bpm

Answer 44

200

Question 45

why cant heart rate increase over 200 bpm?

Answer 45

due to the length in action potential and high rates also decrease perfusion as this occurs in diastole

Question 46

explain cardiac changes in athletes.

Answer 46

Athletes have low rates but large stroke volumes – \<60 bpm (bradycardia)