Topic 11: Cardiovascular System - Cardiac Output - Control - Extrinsic

Question 1

How is cardiac output controlled? (2)

Answer 1

1. control of HR
2. Stroke Volume

Question 2

How is heart rate controlled? (2)

Answer 2

• basic rate set by SA node that is INTRINSIC (built in)
• MODIFIERS of HR is b EXTRINSIC control

Question 3

How is HR modified?

Answer 3

• change pacemaker potential (AP does not change)
  remember it is extrinsic

Question 4

What are the types of extrinsic control for HR? (3)

Answer 4

1) neural
2) Hormonal
3) other factors

Question 5

Which nerves in SNS and PSNS control neural extrinsic control for HR?

Answer 5

• SNS is thoracic
• PSNS is vagus nerve

Question 6

How does the SNS control extrinsic control of HR? (3)

Answer 6

1) sodium channels open wider to increase sodium permeability at SA node
2) increases slope of pacemaker potential
3) reach threshold potential faster to increase HR

Question 7

How does the PSNS control extrinsic control of HR? (5)

Answer 7

1) keeps resting HR lower than pace set by SA node alone (sends continuous impulses)
2) increases K+ permeability at SA node
3) thus more negative on repolarization
4) further to go to get to threshold so takes longer
5) decreases HR

Question 8

What occurs in hormonal control for HR with epinephrine and NE?

Answer 8

• Epinephrine, NE increase HR with same SNS mechanisms

Question 9

What occurs in hormonal control for HR with thyroid hormone? (2)

Answer 9

• thyroid hormone directly increases HR (but slow, so takes days)
• also increase in number of epinephrine receptors, so more sensitive to epi

Question 10

What are other factors that contribute to extrinsic control of HR? (4)

Answer 10

• ions
• fever
• age
• illness

Question 11

How do ions contribute to HR extrinsic control, if there is high K+ in ISF? (4)

Answer 11

• MP more positive than normal
• pacemaker Na+ channels may not open
• also slow repolarization
• therefore decrease in HR and may lead to cardiac arrest

Question 12

How do ions contribute to HR extrinsic control if there is LOW K+ in ISF? (4)

Answer 12

• evidence that K+ channels in some cells change specificity
• so allows Na+ through instead of K+
• this depolarizes membrane to increase HR
• feeble beats, abnormal rhythms

Question 13

How does fever affect HR extrinsic control?

Answer 13

• increased temp increases HR

Question 14

How does age affect HR extrinsic control?

Answer 14

newborn have high HR

Question 15

How does fitness affect extrinsic control of HR?

Answer 15

• increased fitness decreases HR