Regulation of Heart Rate

Question 1

What are the methods of counting heart rate?

Answer 1

Arterial Pulse Counting
Stethoscope
ECG

Question 2

What are the causes of physiological variations in heart rate?

Answer 2

Age: Heart rate is infant average 120/min and decrease to 70 /min at 20 years
Sex: Female>male due to less vagal tone
Sleep: Decreases heart rate
Athlete: <60/min because their heart is stronger and more efficient
Emotions & Exercise: Increase heart rate

Question 3

How does sympathetic and parasympathetic stimulation affect the SA node?

Answer 3

Parasympathetic nerves decrease SA nodal discharge and decrease heart rate (bradycardia)
Sympathetic nerves increase the SA nodal discharge and increase the heart rate (tachycardia)

Question 4

What are the three ways in which heart rate is regulated?

Answer 4

Nervous
Chemical
Physical

Question 5

What are the sites of nervous regulation?

Answer 5

Site 1: Impulses from higher centers
Site 2: Impulses from the right side of the heart
Site 3: Impulses from the baroreceptors
Site 4: Impulses from other parts of the body

Question 6

What are the sites of impulses from a higher center?

Answer 6

Cerebral cortex
Hypothalamus
Respiratory center

Question 7

What types of stimuli affect the cerebral cortex?

Answer 7

Conditional reflex (visual, auditory and olfactory)
Emotion
Voluntary control

Question 8

How does stimulation of the hypothalamus affect heart rate?

Answer 8

Anterior hypothalamus: stimulates CIC→ bradycardia
Posterior hypothalamus: stimulates CAC → tachycardia

Question 9

How does the respiratory center affect heart rate?

Answer 9

Deep inspiration increases heart rate while deep expiration decrease HR (Respiratory sinus arrythmia)

Question 10

What reflexes are related to the right side of the heart?

Answer 10

Bainbridge reflex
McDowal’s reflex

Question 11

What is the Bainbridge reflex?

Answer 11

↑ Venous return → ↑ right atrial pressure → stimulation of atrial stretch receptor → ↑ cardiac filling → ↑ Heart rate

Question 12

What is McDowal’s reflex?

Answer 12

↓ Venous return (as in decreased Arterial blood pressure ) → ↑ heart rate

Question 13

Where are impulses from baroreceptors received?

Answer 13

Arterial baroreceptors (stretch receptors in the carotid sinus and aortic arch)

Question 14

Describe the pathway by which the increased arterial blood pressure affects the heart rate

Answer 14

Increase ABP → ↑discharge of baroreceptors → Stimulation of Cardiac inhibitory center (CIC) → ↑ vagal stimulation → decrease heart rate

Question 15

What is the carotid sinus syndrome?

Answer 15

Stimulation of carotid sinus leads to bradycardia

Question 16

What is Marey’s Law?

Answer 16

Heart rate ∝ 𝟏/(𝑨𝒓𝒕𝒆𝒓𝒊𝒂𝒍 𝑩𝒍𝒐𝒐𝒅 𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆)

Question 17

What impulses from other parts of the body influence heart rate?

Answer 17

Oculo-cardiac reflex: Applying pressure on the eyeball → bradycardia
Visceral pain → bradycardia
Alam-Smirk reflex: Voluntary contraction of the of the skeletal muscle → tachycardia

Question 18

What are some methods of chemical regulation of heart rate?

Answer 18

Blood gases
Hormones
Drugs

Question 19

How does blood gas influence heart rate?

Answer 19

Hypoxia:
Mild & Moderate = Tachycardia
Severe = Bradycardia
Hypercapnia:
Moderate = Tachycardia
Severe = Bradycardia

Question 20

Which hormones may influence heart rate?

Answer 20

Adrenaline: Tachycardia
Noradrenaline: Increases ABP → Bradycardia (Mary’s law)
Thyroxine: Tachycardia

Question 21

Which drugs may influence heart rate?

Answer 21

Atropine & sympathomimetic: Tachycardia
Bile salt and morphine: Bradycardia

Question 22

What physical factor influences heart rate?

Answer 22

Increased body temperature causes tachycardia
Decreased body temperature causes bradycardia
In extreme cody, tachycardia occurs because of shivering

1°C increase causes 10-13 bpm increase