Cardiac physiology

Question 1

functions of the heart

Answer 1

transportation:

• blood
• nutrients
• oxygen
• waste
• heat
• hormones
• immune cells

Question 2

define the refractory period

Answer 2

Absolute: Cardiac muscle cell completely insensitive to further stimulation
Relative: Cell exhibits reduced sensitivity to additional stimulation
Long refractory period prevents tetanic contractions

Question 3

define electrocardiogram

Answer 3

check heart rhythm. 
Action potentials through myocardium during cardiac cycle produces electric currents than can be measured 
Pattern
P wave 
Atria depolarization
QRS complex
Ventricle depolarization
Atria repolarization
T wave: 
Ventricle repolarizati

Question 4

describe the cardiac cycle

Answer 4

Repetitive contraction (systole) and relaxation (diastole) of heart chambers
Blood moves through circulatory system from areas of higher to lower pressure.
Contraction of heart produces the pressure

Question 5

describe the period of isovolumetric contraction.

Answer 5

Ventricular muscles start to contract, increasing the pressure inside the ventricles. This causes the AV valves to close, which is the beginning of ventricular systole. The semilunar valves were closed in the previous diastole and remain closed during this event.

120-130 mL of blood are in the ventricles, left from the last diastole when the atria emptied into the ventricles. This is referred to as the end diastolic volume (EDV).

Question 6

what is the period of ejection?

Answer 6

when the pressure in the ventricles has increased to the point where it is greater than the pressure in the pulmonary trunk/aorta. this pushes the cusps of the semi lunar valves against the walls of the vessels, opening the valve.

pressure in the two ventricles are different.

after the first initial spurt, pressure starts to drop.
at the end period of ejection, 50-6-ml remain, end-systolic volume.

Question 7

what is ventricular filling

Answer 7

While the ventricles were in systole, the atria were filling with blood.

Atrial pressure rises above ventricular pressure and the AV valves open.

Blood flows into the relaxed ventricles, accounting for most of the ventricular filling (70%).

Question 8

describe active ventricular filling

Answer 8

Depolarization of the SA node generates action potentials that spread over the atria (P wave) and the atria contract. This completes ventricular filling.

At rest, contraction of atria not necessary for heart function.

During exercise, atrial contraction necessary for function as heart pumps 300-400%.

Question 9

what is the mean arterial pressure?

Answer 9

the Average blood pressure in aorta
MAP = CO (cardiac output) x PR (peripheral resistance)
CO is amount of blood pumped by heart/min.
CO = SV x HR
SV: Stroke volume (blood pumped during each heart beat)
HR: Heart rate (number of times heart beats per minute)
Cardiac reserve: Difference between CO at rest and maximum CO
PR is total resistance against which blood must be pumped
CO will be affected by anything that affects SV &/or HR

Question 10

describe the extrinsic regulation of the heart.

Answer 10

involves hormonal control
Hormonal Control. Epinephrine (adrenaline) and norepinephrine (noradrenaline) from the adrenal medulla. Occurs in response to increased physical activity, emotional excitement, stress

Question 11

how is blood pressure monitored within the body?

Answer 11

Baroreceptors monitor blood pressure; located in walls of internal carotids and aorta. This sensory information tracels to centres in the medulla oblongata

Question 12

factors which affect MAP?

Answer 12

Effect of pH, carbon dioxide, oxygen
Receptors that measure pH and carbon dioxide levels found in hypothalamus
: pH & CO2 levels can alter HR, so that CO responds to the metabolic demands of the body
- Acidity & increasing CO2 will increase HR
Chemoreceptors monitoring oxygen levels found in aorta and internal carotids. Prolonged lowered oxygen levels causes increased heart rate, which increases blood pressure and can thus deliver more oxygen to the tissues

Effect of extracellular ion concentration
Increase or decrease in extracellular K+ decreases heart rate

Effect of body temperature
Heart rate increases when body temperature increases, heart rate decreases when body temperature decreases

Question 13

what are the effects of ageing on the heart

Answer 13

• maximum heart rate decreases
• hypertrophy of the left ventricle
• increased tendency for valves to function abnormally and arrhythmias to occur
• increased oxygen consumption required to pump same amount of blood