Cardiovascular Physiology Basics

Cardiovascular Physiology (Normal)

• Cardiovascular system is a complex network including the heart and vasculature.
• There are approximately 100,000 km of blood vessels in the human body, enough to encircle the Earth twice.
• The heart beats over 100,000 times daily, pumping about 7,500 liters of blood.

The Heart

• The heart is a hollow muscular organ, about the size of a fist (280-300 g in young adults).
• Located between the sternum and vertebrae.
• Functions as a dual-pump, delivering blood, acting as a suction device, and a performance engine.
• The human heart beats more than 2.5 billion times during an average lifetime.
• It's a highly adaptive and incredibly enduring organ.

Heart Structure and Anatomy

• Divided into right and left halves, consisting of four chambers (two for deoxygenated, and two for oxygenated blood).
• Two atria: upper chambers that receive blood returning to the heart and transfer it to the lower chambers.
• Two ventricles: lower chambers that pump blood from the heart - either to the lungs or to the rest of the body.

Heart Circulation

• The heart pumps 4-5 liters of blood per minute at rest.
• The heart performs two types of circulation: pulmonary and systemic.
• Pulmonary Circulation: Blood is pumped from the right ventricle to the lungs for oxygenation.
• Systemic Circulation: Oxygenated blood is pumped from the left ventricle to the rest of the body.

Cardiac Output

• Cardiac output is the amount of blood pumped by the heart per minute.
• In a resting adult, cardiac output is generally 5-6 liters per minute.
• During peak exercise, cardiac output can increase to over 40 liters per minute.

Heart Rate Variability (HRV)

• Heart rate changes constantly, and HRV measures the variability of heart rate changes over time.
• HRV depends on activity levels and stress.
• Low HRV is associated with chronic stress.

The Role of Atria

• Two atria (right and left) with thinner walls compared to ventricles.
• Deliver blood to the ventricles.
• Contains a septum (dividing wall).
• The sinoatrial (SA) node is located in the upper wall of the right atrium (RA) and controls the heart rate and heart rate variability (HRV).

The Role of Ventricles

• The primary pumps of the heart, responsible for oxygenating and delivering blood to the rest of the body and the lungs.
• Right ventricle: sends blood to the lungs for oxygenation.
• Left ventricle: the most powerful chamber, delivers oxygenated blood to the body.
• Thicker walls for greater force of contraction (contractility).
• Can handle larger blood volumes during exercise.

Layers of the Heart

• The heart has three layers:
• Endocardium: the inner lining.
• Myocardium: the middle layer made of muscle tissue.
• Epicardium: the outer layer.
• Cardiac muscle is involuntary and specialized for endurance.

Coronary Circulation

• The coronary vasculature supplies oxygen and nutrients to the heart muscle, removes metabolic waste products, and is crucial for heart function.
• Ischemia, plaque formation, and heart attacks are potential problems in the coronary circulation.

Blood Flow Through The Heart

• Deoxygenated blood enters the right atrium via the superior and inferior vena cava.
• Blood flows from the right atrium to the right ventricle through the tricuspid valve.
• The right ventricle pumps blood to the lungs via the pulmonary arteries.
• Oxygenated blood returns to the heart from the lungs via the pulmonary veins and enters the left atrium.
• Blood flows from the left atrium to the left ventricle through the mitral valve.
• The left ventricle pumps oxygenated blood to the body via the aorta.

The Cardiac Cycle

• The cardiac cycle is a continuous cycle of contraction and relaxation of the heart muscle.
• Systole: Ventricular contraction (ejection of blood).
• Diastole: Ventricular relaxation (filling with blood).
• Valves play a critical role ensuring one-way blood flow.

4 Main Phases of the Cardiac Cycle

• Ventricular filling period (diastole): AV valves open, passive filling, and atrial contraction.
• Isovolumetric contraction period: all valves closed, ventricular pressure rises.
• Ventricular ejection period (systole): semilunar valves open, blood ejected.
• Isovolumetric relaxation period: all valves closed, ventricular pressure falls.

Control of Heart Rate

• Factors influencing heart rate include:
• Autonomic nervous system (sympathetic and parasympathetic).
• Exercise.
• Environmental factors (e.g., temperature, toxins).