Homeostasis and Pulse Rate

How is heart rate controlled?

• how?

• what does this control exhibit?

HR control mechanism: through negative feedback by the ANS

• sympathetic nerves to the heart increase the rate of the beat

• parasympathetic nerves to the heart decrease the rate of the beat

this control exhibits dynamic equilibrium, as the beat varies minute by minute

Is the heart rate homeostatically regulated? Why?

• then what is homeostatically regulated? How does it relate to HR?

The heart is NOT homeostatically regulated because it has no sensor

• what is homeostatically regulated is blood pressure and HR acts as its effector

Explain the relationship between blood pressure as a homeostatic variable and HR as its effector

Blood pressure is what our body measures and maintains and HR affects the BP

• so HR is adjusted as an effector to help homeostatically regulate BP (mean arterial pressure)

What is an important note to keep about homeostasis and negative feedback

ALL homeostatic mechanisms utilize negative feedback, but not all cases of negative feedback control homeostatic variables

What is the average heart rate?

• how about for athletes?

avg: 60-100bpm

• avg: 25-40 bpm

What factors influence heart rate?

genetics, size, sex, fitness, age, etc.

HR: Genetics

a persons base HR is set by their pacemaker, which is determined genetically

• it may be faster or slower than avg

HR: Size

size matters, large animals (across species) tend to have a lower heart rate while smaller animals tend to have a higher heart rate

HR: Sex

between men and women the same size, women will have a faster heart rate potentially due to hormonal differences and other yet determined factors

HR: fitness

individuals that are physically fit have a stronger heart that pumps more efficiently (higher stroke volume), causing their HR to lower to maintain the same resting cardiac output

Ecological fallacies in HR

you should not assume someone is sick just because their HR is higher or lower than avg, as many individual factor influence the rate

What is cardiac output?

volume of blood pumped per minute

Cardiac output formula

• include units

Cardiac Output (CO) = Stroke Volume (SV) x Heart Rate (HR)

ml/min ml/beat beat/min

What is the CO requirement for everyone at rest?

• how does it change its rates to main the constant CO?

5L/min CO requirement at rest

• Higher Fitness results in a stronger heart that has greater stroke volume. Because of this, the heart does not need to beat as often, resulting in a lower resting heart rate

• Lower fitness results in a weaker heart that has lower stroke volume. Because of this the heart needs to beat more frequently, resulting in a higher resting heart rate

What is the role of CO in BP regulation?

CO is a major component in determining mean arterial pressure (MAP).

the body homeostatically regulates MAP by adjusting the components of CO, using the HR as an effector to either increase or decrease CO as needed to return MAP to its set point