Cardiac Cycle Description Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the function of the nodal tissue in the cardiac system?

Generating irregular impulses

Generating regular impulses (correct)

Causing tetanic contractions

Carrying excitation wave from atria to ventricles

During which period does the cardiac muscle fiber not respond to any stimulus?

Systole

Relative refractory period

Diastole

Absolute refractory period (correct)

What defines rhythmicity in the cardiac muscle?

Lack of excitability changes

Presence of specialized conductive fibers

Ability to initiate impulses dependent on nerve supply

Ability to initiate own impulses regularly (correct)

Which part of the Specialized Cardiac Excitatory Conductive System carries the excitation wave from atria to ventricles?

Conductive Tissue Signup and view all the answers

When does the relative refractory period end?

Phase 4 Signup and view all the answers

What coincides with the whole period of systole and the beginning of diastole?

Absolute refractory period Signup and view all the answers

What is the formula for calculating Cardiac Output (CO)?

CO = Heart rate (HR) x Stroke volume (SV) Signup and view all the answers

How does digitalis affect the force of ventricular contraction?

By increasing intracellular Ca2+ Signup and view all the answers

What is the role of the Na+/Ca2+ exchanger in the mechanism of action of digitalis?

It helps pump Ca2+ out of the cell Signup and view all the answers

How does digitalis increase myocardial contractility?

By increasing intracellular Ca2+ levels Signup and view all the answers

What is Stroke Volume (SV) defined as?

The volume of blood pumped by each ventricle per beat. Signup and view all the answers

What happens to the Na+/K+ pump due to digitalis action?

It is inhibited, leading to increased intracellular Na+ levels. Signup and view all the answers

What is the effect of sympathetic stimulation on contractility?

Increases contractility Signup and view all the answers

What is the effect of parasympathetic stimulation on ventricular contraction?

Has no effect on ventricular contraction Signup and view all the answers

What effect does epinephrine hormone have on the force of ventricular contraction?

Increases the force of ventricular contraction Signup and view all the answers

What is the afterload in relation to blood ejection?

Decreases the force of blood ejection Signup and view all the answers

What is the function of elastic fibers in the walls of big arteries during blood ejection?

Expand to prevent excessive rise in blood pressure Signup and view all the answers

What is diastolic blood pressure?

$75$ mmHg Signup and view all the answers

What is the formula for calculating pulse pressure?

Systolic pressure - Diastolic pressure Signup and view all the answers

What is the formula for calculating mean arterial blood pressure?

Systolic pressure + 1/3 pulse pressure Signup and view all the answers

What is the main function of arterial baroreceptors in response to a rise in arterial blood pressure?

Decrease sympathetic activity and increase parasympathetic activity Signup and view all the answers

Which receptors are found in the walls of both atria?

Atrial receptors Signup and view all the answers

What is the role of decreased sympathetic supply in regulating arterial blood pressure?

Decreases total peripheral resistance Signup and view all the answers

In the context of rapid regulation of arterial blood pressure, what is the primary response mechanism to minimize initial changes in ABP?

Alter both cardiac output and total peripheral resistance Signup and view all the answers

What is the primary effect of antidiuretic (vasopressin) hormone?

Increased water reabsorption by the kidney Signup and view all the answers

How does aldosterone hormone affect Na+ reabsorption in the kidney?

Increases Na+ reabsorption followed by water reabsorption Signup and view all the answers

What is the role of the Renin-Angiotensin System in the body?

Increases plasma volume and venous return Signup and view all the answers

How do ACE inhibitors like captopril affect the Renin-Angiotensin System?

Block the conversion of angiotensin I to angiotensin II Signup and view all the answers

What is the consequence of decreased CVP (central venous pressure) on atrial receptors?

Increased rate of discharge of impulses from atrial receptors Signup and view all the answers

What is the role of arterioles in the circulatory system?

Increase total peripheral resistance (TPR) Signup and view all the answers

Study Notes

Control of Cardiac Output (COP)

Sympathetic stimulation increases contractility
Parasympathetic stimulation has no effect on ventricular contraction due to negligible parasympathetic supply to the ventricles
Digitalis increases the force of ventricular contraction
Epinephrine hormone increases the force of ventricular contraction by the same mechanism as norepinephrine

The Afterload

The resistance against which the blood is expelled
Equivalent to the arterial blood pressure
The greater the afterload, the less the cardiac muscle can shorten
Not important in normal range of arterial blood pressure

The Arteries

Transport blood from the heart to all organs of the body
Wall of big arteries contains elastic fibers that expand during systole and recoil during diastole
Arteries have large radii and offer little resistance to the flow of blood
Low resistance vessels

Arterial Blood Pressure (ABP)

The lateral pressure of the blood on the arterial wall
Systolic blood pressure: 125 mmHg, maximum pressure reached during ventricular ejection
Diastolic blood pressure: 75 mmHg, minimum pressure reached just before ventricular ejection begins
Diastole starts at the beginning of late rapid repolarization and repolarization is completed by the end of the first half of diastole

Excitability Changes During Action Potential

Absolute refractory period: cardiac muscle fiber does not respond to any stimulus during phases 0, 1, 2, and about half of phase 3
Mechanically, this period coincides with the whole period of systole and the beginning of diastole
Cardiac muscle cannot be tetanized (sustained contraction)
Relative refractory period: stronger stimulus than normal is needed to produce an action potential during phase 3 until phase 4

Rhythmicity

The ability of the cardiac muscle to initiate its own impulses regularly, independent of any nerve supply
Due to the presence of specialized self-excitable fibers (Nodal Tissue)
The Specialized Cardiac Excitatory-Conductive System consists of:
- Nodal Tissue: self-excitable fibers that generate regular impulses (Sino-Atrial node, Atrio-Ventricular node, and Purkinje fibers)
- Conductive Tissue: fibers that carry the cardiac excitation wave from the atria to the ventricles

Digitalis

Increases the force of ventricular contraction
Inhibits Na+ K+ pump, increasing intracellular Na+ and decreasing Na+ gradient across the cell membrane
Prevents Na+ /Ca2+ exchanger from pumping Ca2+ to the extracellular fluid, leading to increased intracellular Ca2+ and increased force of contraction

The Cardiac Output (COP)

The volume of blood pumped by each ventricle per minute
COP = Heart rate (HR) x Stroke volume (SV) = 72 beats/min x 70 ml = 5 L/min in a resting average-sized adult
Stroke volume: the volume of blood pumped by each ventricle per beat = 70 ml
Pulse pressure: the difference between systolic and diastolic pressure = 50 mmHg
Mean arterial blood pressure: the average pressure throughout the cardiac cycle = 90 mmHg

Regulation of Arterial Blood Pressure (ABP)

Nervous regulation: rapid regulation of ABP through reflexes that act within seconds to hours
Reflexes include receptors, afferent nerves, center, efferent nerves, and response on effector organs
Most important receptors include arterial baroreceptors and atrial receptors

Arterial Baroreceptors

Functions:
- If ABP rises, the rate of discharge of impulses from baroreceptors increases, leading to decreased sympathetic and increased parasympathetic activity
- Decreased sympathetic supply decreases heart rate and stroke volume, thus decreasing COP
- Decreased vasoconstriction (VC) decreases total peripheral resistance (TPR), leading to decreased ABP
- Antidiuretic (Vasopressin) hormone produces both vasoconstriction and increased water reabsorption by the kidney, increasing plasma volume and venous return, thus increasing COP and ABP
- Aldosterone hormone increases Na+ reabsorption by the kidney, followed by water, increasing extracellular fluid volume, blood volume, and ABP

The Renin-Angiotensin System

Causes powerful vasoconstriction of the arterioles, increasing TPR and ABP
Stimulates the release of aldosterone hormone, leading to salt and water retention by the kidney, increasing plasma volume and venous return, thus increasing COP and ABP
ACE inhibitors block the conversion of angiotensin I to angiotensin II, decreasing the arterial blood pressure

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on the different phases of the cardiac cycle including systole, diastole, and excitability changes during action potential. Understand the timing of repolarization, refractory periods, and the mechanical events within the heart.