Week 7: Chp 28: Physiology of the heart: Cardiac Cycle

Question 1

Cardiac Cycle

Answer 1

circular sequence of events that produces the eventual muscular contraction that causes the ejection of blood from the right ventricle into the pulmonary circulation or from the left ventricle into the systemic circulation

Question 2

The Cardiac Cycle works in Coordination with what other system?

Answer 2

electrical cardiac conduction system

Question 3

2 Parts to The Cardiac Cycle

Answer 3

• Systole (contraction)

- Diastole (relaxation)

Question 4

Systole

Answer 4

contraction

-facilitates the ejection of blood from the ventricles and occurs during the last 1/3 of the cycle

Question 5

Diastole

Answer 5

relaxation

• is when filling of the ventricles occurs and accounts for the first 2/3 of the cycle
• myocardial tissue perfusion occurs during diastole
• the ventricles are relaxed, with a lower pressure than that of the atria, allowing the AV valves to open
• as blood flows into the ventricles, pressure drops in the atria and rises in the ventricles
• the final phase of ventricular filling occurs when the atria contract, known as atrial systole, which accounts for the final 30% on ventricular filling; referred to as atrial kick
• the final volume in the ventricle at then end of diastole is the end diastolic volume (preload)

Question 6

Preload

Answer 6

the final volume in the ventricle at the end of diastole
-amount of stretch of the muscle tissue at the end of filling
>increased volume produces increased stretch, which produces an increased contraction (starlings law); this is true up to a point, extreme overfilling decreases effectiveness of the contraction, thus decreasing CO

Question 7

Blood Pressure

Answer 7

is a reflection of the pressure generated during the cardiac cycle
-represents the forced exerted against the vessel wall by blood flow

Question 8

Factors that influence BP

Answer 8

-amount of blood ejected during systole, or CO2, and the resistance to flow in the peripheral vessels, or peripheral vascular resistance

Question 9

Blood Pressure: Systolic Pressure

Answer 9

peak pressure generated when blood is expelled from the left ventricle during ventricular contraction

Question 10

Blood Pressure: Diastolic Pressure

Answer 10

minimal pressure maintained on the vessel walls during relaxation

Question 11

Mean Arterial Pressure

Answer 11

the average pressure maintained throughout the cardiac cycle

Question 12

Changes in flow and resistance are principally controlled by?

Answer 12

the autonomic nervous system (ANS) and hormones

Question 13

The ANS responds to messages sent by various sensory tissues in the body which are?

Answer 13

• baroreceptors

- chemoreceptors

Question 14

Baroreceptors

Answer 14

located in the aortic and carotid arches

• are sensitive to changes in pressure
• an increase in pressure stimulates the parasympathetic nervous system to dilate vessels and reduce the heart rate (HR) to reduce BP
• the decrease in pressure stimulates the sympathetic nervous system to constrict vessels and increase the HR, which increases BP

Question 15

Chemoreceptors

Answer 15

respond to changes in oxygen and CO2 concentrations

• decreased levels of oxygen with increased levels of CO2 produce acidosis
• the chemoreceptors respond to decreased oxygen levels and acidosis by inducing vasoconstriction to increase BP and increase blood flow to the lungs, facilitating oxygen and CO2 exchange
• respiratory rate is also increased

Question 16

What are the hormonal mechanisms that exert control over BP?

Answer 16

-angiotensin II, epinephrine and norepinephrine, aldosterone, and antidiuretic hormone

Question 17

Cardiac Output

Answer 17

the blood ejected from the left heart each minute to facilitate the delivery of oxygen and nutrients to the tissues

Question 18

Normal Cardiac Output in an adult?

Answer 18

4 to 8 L/min

• value does not remain constant
• increased by exercise or activity
• decreased by rest

Question 19

Cardiac Output is calculated by what formula?

Answer 19

HR x Stroke Volume

Question 20

Stroke Volume

Answer 20

the amount of blood ejected with each ventricular contraction

Question 21

Heart Rate

Answer 21

number of cardiac contractions per minute

• can be affected by many variables
• stimulus from ANS does adjust it up or down
• can be increased or decreased depending on pressure
  ex: when BP is low, the HR is increased to maintain adequate CO

Question 22

Stroke Volume is influenced by 3 variables

Answer 22

1. Preload
2. Afterload
3. Contractility

Question 23

Afterload

Answer 23

the resistance to flow the ventricle must overcome to open the semilunar valves and eject its contents

• related to BP, vessel lumen diameter, and/or vessel compliance
• hypertension on the right or left is implicated in the negative effects of increased afterload

Question 24

Contractility

Answer 24

the force of mechanical contraction

• can be increased with sympathetic stimulation or calcium release
• decreased in the face of hypoxia or acidosis

Question 25

Transportation of O2

Answer 25

• 97% is bound to hemoglobin
• 3% is dissolved
• only dissolved can pass through capillary membranes
• hemoglobin is an oxygen reservoir
• at tissue level, O2 leaves hemoglobin, becomes dissolved in the blood, and passes through capillary membrane into the tissues

Question 26

Transportation of CO2

Answer 26

-waste product of normal aerobic tissue metabolism
-carried in blood by 3 ways”
>7% dissolved in plasma
>23% attaches to hemoglobin
>70% converted to bicarbonate ions
-travels dissolved, attached, or as bicarbonate ions
-CO2 bound to hemoglobin eventually detaches and becomes dissolved in the plasma for diffusion into the alveoli of the lungs
-the bicarbonate ions in plasma convert back to CO2 which becomes dissolved, diffuses into alveoli, and is exhaled