Cardiac Output & Blood Pressure

Question 1

What is ‘Cardiac Output’?

Answer 1

The volume of blood that is pumped out by the heart every minute

Question 2

What does cardiac output depend on?

Answer 2

Heart Rate (bpm) x Stroke Volume (volume of blood ejected per beat (ml/l))

Question 3

What controls heart rate?

Answer 3

The Autonomic Nervous System

Question 4

What slows down heart rate?

Answer 4

Parasympathetic nervous system - nerve endings secrete acetylcholine (neurotransmitter) which slows down heart rate. Parasympathetic stimulation is concentrated to the atria at SA and AV nodes. This causes their membranes to become hyperpolarised and depolarising drift to become slower.

Question 5

What speeds up heart rate?

Answer 5

Sympathetic nervous system - cardiac nerve fibres supply SA and AV nodes and increase heart rate by releasing norepinephrine. This causes SA node cell membranes to become more depolarised and depolarising drift to become faster (so SA node rhythm becomes faster and HR increases)

Question 6

What 2 opposing factors is stroke volume regulated by?

Answer 6

1) Force by which muscle cells contract
2) Arterial pressure against which they have to eject the blood

Question 7

What 2 processes is ‘force of contraction’ regulated by?

Answer 7

1) Length-tension properties of cardiac muscle cells
2) Effects of hormonal influence on the contractility of cardiac muscle

Question 8

What is the equation for Mean Arterial Pressure (MAP)?

Answer 8

MAP=diastolic+(systolic-diastolic/3)

Question 9

What are ‘normal’ blood pressure values (systolic, diastolic and MAP)?

Answer 9

Systolic = 120mmHg
Diastolic = 80mmHg
MAP = 93mmHg

These numbers would be commonly presented as 120/80

Question 10

What 3 factors affect blood pressure?

Answer 10

• Arteries become stiffer with age due to loss of elasticity
• On average, women have lower blood pressure than men throughout their lives
• Pressure is higher in the foot and lower in the head due to hydrostatic pressure

Question 11

How does blood pressure differ between static and dynamic exercise?

Answer 11

• In dynamic exercise, mean blood pressure remains relatively steady
• Conversely, in static exercise (weightlifting) means blood pressure rises dramatically

Question 12

What physiological factors determine arterial blood pressure?

Answer 12

Mean arterial blood pressure= Cardiac Output x Total Peripheral Resistance (sum of resistance to blood flow in all tissues of the body)