chapter 9: cardiac output

Question 1

how does HR increase

Answer 1

influences the SA node through SANS and PANS

• PANS innervated through vagus nerve

Question 2

where is the cardiovascular control center located

Answer 2

medulla oblongata

Question 3

how does the parasympathetic NS influence HR through vagus nerve

Answer 3

fibers connect to SA and AV node and when stimulated release Acetylcholine which decreased activity of SA and AV to decrease HR

Question 4

during low intensity exercise what does the HR get to and why?

Answer 4

100 beat/min from parasympathetic tone withdrawal (intrinsic firing of the SA node is roughly this number)

Question 5

what is the sympathetic NS role in HR

Answer 5

innervate through cardiac accelerator nerves (SA node and ventricles) which release norepinephrine that acts on beta receptors to increase HR and force of myocardial contraction

Question 6

example of SANS and PANS reflex when resting BP is increased

Answer 6

sensor : pressure receptor in carotid arteries and arch of aorta
integration center: medulla oblongata increased parasympathetic activity
effector (heart) : decreased HR and CO which reduced BP back to normal

Question 7

what is the reflex or feedback loop for frank starling

Answer 7

sensor: pressure receptor in right atrium
want to prevent systemic venous system so increase CO
effector: sympathetic accelerator impulses to Heart which increase HR and and CO

Question 8

what is heart rate variability

Answer 8

variation in time between heartbeats
- expressed as the standard deviation between R-R intervals

Question 9

what is the physiological significance of HRV

Answer 9

reflects autonomic nervous system control of the heart

Question 10

what is sympathovagal balance

Answer 10

ability to shift between parasympathetic and sympathetic reflected in beat-to-beat changes of cardiac cycle

Question 11

what are some known diseases that decrease HRV

Answer 11

• depression
• hypertension
• heart disease
• myocardial infarction
• inactivity

Question 12

what are the three factors related to Stroke Volume

Answer 12

1. end diastolic volume (EDV)
2. average aortic blood pressure
3. strength of ventricular contraction

Question 13

what is the mechanism behind frank-starling theory

Answer 13

increase cardiac fiber length optimizes the number of myosin cross bridge with actin that causes and increase in force production

Question 14

what factors regulate venous return during exercise

Answer 14

1. venoconstriction
2. skeletal muscle pump
3. respiratory pump

Question 15

explain venoconstriction

Answer 15

sympathetic reflex control causes constriction of smooth muscle around blood vessels which accelerates return of blood to heart`

Question 16

explain the muscle pump

Answer 16

due to rhythmic skeletal muscle contraction between contractions the blood fills the veins and is prevented from flowing backwards due to one way values
BUT during isometic contraction this can not occur so venous return is decreased

Question 17

explain the respiratory pump

Answer 17

when you inspire you decrease pressure in thoracic cavity and increase in abdominal which helps drive blood up to heart

Question 18

how does aortic pressure influence stroke volume

Answer 18

you want to decrease aortic pressure to increase stroke volume.
- can overcome during exercise through increased SANS & frank-starling
- dilation of major arterioles

Question 19

how do catecholamines influence stroke volume

Answer 19

complements the direct stimulation through (norepinephrine and epinephrine) help to increase entry of extracellular Ca2+ to cardiac muscle fibers which increase cross-bridging and force production