Cardiovascular System

Hemodynamics

• Hemodynamics is a collection of mechanisms that influence the active and changing circulation of blood.
• Circulation is a vital function and the only means by which cells can receive materials needed for survival and have their waste removed.
• Different volumes of blood per minute are required for different organs at different times.
• More active cells need more blood per minute than less active cells.

Conduction Mechanisms

• Conduction fibers are specifically adapted for rapid conduction through the syncytium.
• They are high-speed carriers of action potential from pacemakers to more distant areas of the syncytium.

Electrocardiogram

• Impulse conduction generates tiny electrical currents in the heart that spread through surrounding tissues to the surface of the body.
• The atrial systole begins with the P wave of the ECG, which is an electrical wave of depolarization followed by contracting (systole) myocardium of the atria.
• The contracting force creates a pressure gradient that pushes blood out of the atria into the relaxed ventricles.
• The AV (cuspid) valves remain open during this phase.

Cardiac Reflexes

• Cardiac pressoreflexes involve receptors sensitive to changes in pressure located in two places in the heart: aortic baroreceptors and carotid baroreceptors.
• The carotid sinus reflex is located at the beginning of the internal carotid artery and involves sensory fibers running through the carotid sinus nerve and the glossopharyngeal nerve to the cardiac control center.
• Parasympathetic impulses leave the cardiac control center, travel through the Vagus nerve, and reach the SA node.
• The aortic reflex and other reflexes, including emotions, exercise, hormones, blood temperature, pain, and stimulation of various exteroceptors, also influence the heart.

Peripheral Resistance

• Peripheral resistance is the resistance to blood flow imposed by the force of friction between blood and the walls of its vessels.

Heart Structure and Function

• Valves ensure one-way flow, enabling the heart to act as a pump.
• The heart is divided into four chambers: two upper chambers called the Atria (atrium singular) and two lower chambers called the Ventricles.
• The Atria are separated into left and right chambers by a septum (interatrial septum).
• The Atria are called "receiving chambers" as they receive blood from veins.
• Veins pump blood toward the heart from various tissues.

ECG Waves

• The T wave reflects repolarization of the ventricles.
• An inverted T wave is often seen after myocardial muscle damage.
• A U wave can appear as a tiny hump at the end of the T wave, representing late repolarization of subendocardial branches (Purkinje fibers) in the papillary muscle of the ventricular myocardium.

Blood Pressure Regulation

• Arterial blood pressure is proportional to arterial blood volume.
• An increase in arterial blood volume increases arterial pressure, and vice versa.
• Factors that determine arterial pressure include cardiac output (CO) and peripheral resistance.

Cardiac Output and Peripheral Resistance

• Cardiac output affects the blood entering the arteries.
• If cardiac input increases, the amount of blood entering the arteries increases, tending to increase the volume in the arteries.
• Peripheral resistance affects the blood leaving the arteries.
• If peripheral resistance increases, it decreases the amount of blood leaving the arteries, which increases the amount of blood left in them.

Ejection Fraction and Afterload

• Ejection fraction (EF) is the ratio of stroke volume (SV) to end-diastolic volume (EDV).
• EF is usually expressed as a percentage (EF = (SV ÷ EDV) × 100).
• Healthy adults have an EF of at least 55%.
• EF goes down as the myocardium fails.
• Afterload is also influenced by neutral factors.
• Unusually high afterload from flow resistance in arteries can cause heart failure.

Cardiac Pressoreflexes

• Cardiac pressoreflexes have receptors sensitive to changes in pressure located in two places in the heart: aortic baroreceptors and carotid baroreceptors.
• The carotid sinus reflex is located at the beginning of the internal carotid artery.
• Sensory fibers from carotid sinus baroreceptors run through the carotid sinus nerve and the glossopharyngeal nerve to the cardiac control center.

Hemodynamics and Cardiovascular System

• Many controls mechanisms help regulate and integrate each function and component of the cardiovascular system.
• Hemodynamics refers to the collection of mechanisms that influence the active and changing circulation of blood.

Circulation

• Circulation is a vital function and the only means by which cells can receive material needed for survival and have their waste removed.
• Different organs require circulation of different volumes of blood per minute at different times.
• More active cells need more blood per minute than less active cells.

Electrocardiogram (ECG)

• The T wave reflects repolarization of the ventricles.
• An inverted T wave is often seen after myocardial muscle damage.
• Sometimes a U wave can appear as a tiny hump at the end of the T wave, representing late repolarization of subendocardial branches (Purkinje fibers) in the papillary muscle of the ventricular myocardium.

Cardiac Cycle

• One cycle consists of contraction (systole) and relaxation (diastole) of both atria and both ventricles.
• The two atria contract simultaneously, then as they relax, the two ventricles contract and relax, giving the heart a pumping action.
• The cardiac cycle illustrates and integrates changes in pressure gradients in the left atrium, left ventricle, and aorta.

Steps of the Cardiac Cycle

• Step 1: SL valves remain closed as the arterial pressure is higher than the pressure in the relaxed ventricles.
• Step 2: Isovolumic ventricular contraction, where intraventricular pressure begins to increase, closing the AV valves and producing the first heart sound.
• Step 3: End of ventricular ejection, the SL valves close when the ventricular pressure drops, producing the second heart sound.
• Step 4: (Not mentioned in the text)
• Step 5: (Not mentioned in the text)

Heart Failure

• In heart failure, the residual volume remaining in the ventricles may greatly exceed that ejected during systole.
• Diastasis-reduced ventricular filling of the heart occurs in heart failure.

Explore the controls and mechanisms that regulate and integrate the functions and components of the cardiovascular system, including hemodynamics.