Cardiovascular System: The Heart as a Pump

Cardiovascular System - The Heart as a Pump

• Curriculum: Phase 1/Semester 2/CVS/Session 2/L 2 (2018/2019)
• Lecturer: Dr. Shahlaa Kh. Chabuk
• Qualifications: MSc, PhD, Physiology
• Institution: Hammurabi Medical College/Babylon University

Cardiac Cycle Valve Function

• Describe when each heart valve opens and closes during the cardiac cycle.
• Explain the flow pattern through each valve.

Heart Sounds

• Explain the origin of the first and second heart sounds.

Pressure Profile and Tasks

• Analyze a diagram illustrating pressure profiles in the left atrium, left ventricle, and aorta during a single cardiac cycle in a healthy adult.
• Label the pressure axes.
• Label the time base (assuming a heart rate of 60 bpm).
• Indicate valve opening and closing points (mitral and aortic valves).
• Mark the position of the first and second heart sounds on the diagram.

The Heart

• The heart is composed of two pumps in series.
• Each side comprises a thin-walled atrium and a muscular ventricle.
• Blood flows into and out of ventricles via valves.
• Atrioventricular valves (mitral and tricuspid) regulate blood flow.
• Outflow valves (aortic and pulmonary) control blood flow.

Heart Muscle

• Heart muscle is a specialized form.
• Heart muscle cells are electrically connected.
• These cells contract when an action potential occurs within the membrane.
• Action potentials cause a rise in intracellular calcium.
• Action potentials are long duration, causing a single contraction (systole), lasting approximately 280 milliseconds.
• Action potentials spread from cell to cell.

Pacemakers

• Action potentials originate in a specialized group of cells (pacemakers).
• These signals spread throughout the heart, coordinating contractions.
• Pacemakers generate one action potential at regular intervals.

Phases of the Cardiac Cycle

• Each action potential triggers one heart beat (systole).
• The interval between beats is called diastole.

Spread of Excitation - 1

• The pacemaker (sino-atrial node) initiates the heartbeat in the right atrium.
• Excitation spreads across the atria, leading to atrial systole.
• The signal reaches the atrioventricular node, where it is delayed for about 120 milliseconds.

Spread of Excitation - 2

• The signal then spreads through the ventricular myocardium, from inner (endocardial) to outer (epicardial) surfaces.
• Ventricular contraction begins at the apex and forces blood towards the outflow valves.

The Cardiac Cycle

• At rest, the sinoatrial (SA) node generates an action potential once per second, producing one heartbeat.
• A short atrial systole follows, then a longer ventricular systole.
• Ventricular systole lasts about 280 milliseconds.
• Ventricular relaxation (diastole) lasts about 700 milliseconds before the next systole.

Ventricular Pumping

• The alternating systole and diastole, together with inflow and outflow valves, creates a reciprocating pumping mechanism for the heart.
• Blood fills the ventricles from the veins during diastole.
• During systole, ventricles pump blood into arteries.

The Left Ventricle

• The aortic valve is the outflow valve.
• It allows blood to flow from the ventricle to the aorta but not vice-versa.
• The valve opens when intraventricular pressure exceeds aortic pressure.
• The valve closes when aortic pressure exceeds ventricular pressure.

Cardiac Cycle, Graphs and Charts

• Diagrams and graphs of pressure/volume dynamics are given and must be analyzed.

Ventricular Filling

• During systole, blood gathers in the atria.
• At the end of systole, high atrial pressure opens the atrioventricular (AV) valves, causing rapid ventricular filling.
• This process lasts approximately 200-300 milliseconds.
• Minimal flow occurs during the middle third of ventricular filling.
• Atrial contraction contributes up to 20% of ventricular filling volume.

Isovolumic Contraction

• At the start of systole, intraventricular pressure rises, closing the AV valves.
• For ~20-30 ms, pressure increases but not enough to open the semilunar valves.
• This is isovolumetric contraction because ventricular volume remains unchanged.

Ejection Period

• Once the semilunar valves open, the ejection phase begins.
• Approximately 70% of blood ejection occurs in the first third of the ejection period.
• The remaining 30% is ejected during the next two-thirds, in the slow ejection period.

Isovolumic Relaxation

• During late systole, ventricular relaxation reduces intraventricular pressure.
• Once this pressure is lower than the aortic pressure, the semilunar valves close.
• The AV valves remain closed, preventing filling, for approximately 30-60 ms.
• This period is called isovolumic relaxation.

Normal Volume of Blood in Ventricles

• After atrial contraction, ventricles hold approximately 110-120 ml of blood (end-diastolic volume).
• Ventricular contraction ejects about 70 ml of blood (stroke volume).
• 40-50 ml of blood remains in each ventricle (end-systolic volume).

Preload and Afterload

• Preload is the tension on the heart muscle at the start of systole, related to end-diastolic volume/pressure.
• Afterload is the tension the heart muscle works against during systole.

Cardiac Output and Venous Return

• Cardiac output is the blood pumped into the aorta per minute (stroke volume x heart rate).
• Venous return is the blood flow from veins to the right atrium.
• Cardiac output typically equals venous return, except during transient periods.

Normal Cardiac Output

• Normal resting cardiac output is about 5 liters/minute.
• Stroke volume is approximately 70 ml.
• Heart rate is around 72 beats per minute.
• Cardiac output during exercise can increase to over 20 liters/minute.

Cardiac Output Calculation

• Stroke Volume (SV) = End Diastolic Volume (EDV) - End Systolic Volume (ESV)
• Cardiac Output (CO) = SV × Heart Rate (HR)

Factors Affecting Stroke Volume

• End-diastolic volume (EDV) is affected by venous return and preload.
• End-systolic volume (ESV) is affected by contractility and afterload.

Heart Sounds

• Two main sounds are associated with valve closures.
• The first sound ("lub") is the closure of the atrioventricular valves.
• The second sound ("dub") is the closure of the semilunar valves.
• These sounds occur at ventricular systole onset and end.
• Normal interval from first to second sound is about 280 milliseconds.
• The interval from the second sound to the next first sound is approximately 700 milliseconds.

Extra Heart Sounds

• Occasionally, extra sounds are heard; a third sound is heard during early diastole, and a fourth sound during atrial systole.

Heart Murmurs

• Turbulent blood flow produces murmurs.
• Murmurs occur due to narrowed valves (stenosis) or valves not closing properly (incompetence)
• Murmurs occur when blood flow is highest, so their presence can pinpoint their origin in the cardiac cycle.

Dive into the mechanics of the cardiovascular system with this quiz focused on the heart as a pump. Explore the cardiac cycle, valve functions, heart sounds, and pressure profiles through detailed analysis and diagram labeling. Perfect for students in the second semester of cardiovascular studies!