Cardiovascular System Overview

Cardiovascular System (CVS) Physics

• The cardiovascular system (CVS) comprises blood, vessels, and the heart
• It functions to deliver energy (fuel from food) and oxygen (O2) to the body, while removing byproducts like carbon dioxide (CO2), water, and heat.
• Blood constitutes 7% of a 64-kg person's body mass, equivalent to approximately 4.5 kg or 4.4 liters.

Heart

• The heart is a hollow organ situated in the chest, positioned between the lungs behind the sternum and above the diaphragm.
• It's enclosed by the pericardium.
• The heart's size is roughly comparable to a human fist, weighing approximately 250-300 grams.
• Its center is positioned approximately 1.5 centimeters to the left of the mid-sagittal plane.
• The great blood vessels, including the superior and inferior venae cavae, the pulmonary artery and vein, and the aorta, are located above the heart, with the aortic arch positioned behind the heart.

Fetal Heart

• Fetal heart function initiates around the eighth week after conception.
• Oxygenated blood is obtained from the mother through the umbilical cord.
• There is an opening between the right and left atria.
• 90% of blood flows from the right atrium (RA) to the left atrium (LA), while 10% goes through fetal lungs.
• After birth, the opening between atria closes.
• Complete closure usually takes several months.

Heart Valves and Artificial Heart Valves

• Valves regulate one-way blood flow within the heart.
• Valve closure or closing action creates turbulence leading to the characteristic heart sounds.
• There are four heart valves:
  • Tricuspid valve
  • Pulmonary valve
  • Mitral valve
  • Aortic valve
• Artificial heart valves are needed in some cases of valve malfunction. Illustrations and types of artificial valves are shown.

How Does the Heart Work?

• Blood enters the left atrium, flows to the left ventricle, exits to enter the right atrium, and then out to the right ventricle, and finally goes to the lungs, after which it returns to the left atrium.
• Each cell requires 1 minute to complete a complete cycle.
• The capillary function is responsible for providing oxygen and removing carbon dioxide.

Blood Components

• Red blood cells (RBCs): Constitute 45% of blood, responsible for oxygen transport.
• White blood cells (WBCs): Crucial for combating diseases; their count varies depending on infections. Several types of WBCs exist, each with specific functions.
• Platelets: Play a critical role in blood clotting.
• Plasma: Contains various substances, including electrolytes, hormones, proteins, and minerals. The fluidity of plasma is impacted by its water content. A critical amount of Calcium (10mg per 100ml is required) ,if reduced, could lead to death.

Blood Volume

• Overall blood volume in a human is approximately 5 liters.
• 80% (4 liters) circulate systemically, and 20% (1 liter) within the lungs.
• In systemic circulation, arteries account for 15%, capillaries for 10%, and veins account for 75% of the total volume.
• In pulmonary circulation, pulmonary arteries account for approximately 46.5%, while pulmonary capillaries and veins together make up 7%.

Heart Valves, Artificial Heart Valve

• One-way valves in the heart are crucial.
• Valves close, creating turbulence and heart sounds.
• Artificial valves may be required for certain malfunctions
• Diagrams and illustrations are included for various types of artificial valves.

Cardiac Muscle

• Cardiac muscle shares characteristics of skeletal and smooth muscle, but has unique properties. -Under autonomic nervous system control.
• Cardiac muscle cells exhibit rhythmic self-excitation.
• There is a long refractory period to prevent tetanic contractions.
• Cardiac output (heart's pumping ability) is a crucial parameter.
• Cardiac output formula: Cardiac output= heart rate x stroke volume.
• Cardiac output affected by : heart rate, contractility and peripheral resistance.
• Typical Cardiac output value for an average male adult is about 5 litres per minute, and 40 litres per minute in trained athletes.

Blood Vessels and Blood Flow Regulation

• Blood vessels come in various types and sizes, each with varying anatomies and functions.
• Heart's combined blood vessels' length approximately earth's circumference.
• Normal mean arterial pressures range from 70-100 mmHg.
• Pressure is also affected by body positioning
• Factors that regulate blood flow and pressure, like autonomic nervous system stimulation,local metabolism response.

Physics of Blood Flow

• Flow rate equals blood volume divided by time( e.g liter/minute)
• Flow rate is continuous under certain assumptions
• Blood is incompressible, Vessels are rigid and there are no sources or sinks
• Flow velocity is inversely proportional to the total cross-sectional area of the vessels.

Flow Resistance

• Laminar flow (below critical velocity) is characterized by silent flow with maximum velocity at the center of the tube resulting in near zero velocity at the tube walls.
• Turbulent flow (above critical velocity) is noisy, with higher flow resistance than laminar flow, typically heard as a heart sound.
• The likelihood of turbulent flow is higher at narrow points or constrictions in the vessel.

Typical Values for Adult Standing

• Typical blood pressure at the heart, is ~ 13.3 kPa.
• Applying Bernoulli's equation to relate the blood pressures at the heart, brain, and feet with the relevant heights results in typical values.

Role of Gravity on Blood Circulation

• Blood pressure in the large arteries in the reclining position is basically uniform, whereas standing results in varying pressure differences between the feet, heart, and the brain, mainly due to gravitational forces.

Measurement of Arterial Blood Pressure

• Sphygmomanometer (inflatable cuff and pressure gauge) is used to measure blood pressure.
• Steps involved in taking a blood pressure: cuff inflation and controlled deflation to measure systole and diastole pressure.

Fluid Flow and the Continuity Equation

• The continuity equation shows that the fluid flow rate everywhere in a closed system must be constant with time
• The mathematical equation of continuity equation: Qin= Q out= (ΔV)/(Δt)=constant.

Bernoulli's Equation

• In a closed system, work done on a liquid is equal to the change in its mechanical energy, and a mathematical formula is applied.

Viscosity

• Viscosity is a measure of a fluid's resistance to flow.
• Different factors including the degree of bodily activity, the altitude, and state of any potential anemia can affect blood viscosity.
• An increase in hematocrit generally increases viscosity, impeding blood flow.

Reynolds Number

• The Reynolds number is a dimensionless quantity that distinguishes between laminar and turbulent fluid flow.
• The formula for calculating the Reynolds number takes into account the fluid's density, viscosity, and velocity, as well as the tube radius.

Cardiovascular Disease

• Congestive Heart Failure (CHF): A condition where the heart becomes weak and enlarged, leading to decreased cardiac output and fluid build-up in the body.
• Risk factors of vessel disease and consequent heart attack includes sex, age, weight, risk factors associated with blood pressure, cholesterol and lifestyle choices (diet and exercise)

Stroke

• Stroke, a cerebrovascular accident, results from either a blockage or rupture of a brain blood vessel.
• Symptoms include numbness, weakness, speech issues, vision problems, and difficulty understanding speech.
• Aneurysms, weakened artery sections increasing in diameter and causing rupture, can cause a stroke.

Heart Attack

• A heart attack occurs due to either complete blockage or partial blockage of coronary arteries.
• Characteristic symptoms include pressure in the chest, pain or tingling/numbness in arm, neck and shoulders/jaw, shortness of breath, and sweating.
• There are various methods to address heart attacks, including drug therapies, angioplasty, or bypass surgery.

Other factors that increase risk of vessel disease and consequent heart attacks

• Smoking: affects blood pressure, and causes stress on the heart.
• Increased platelet aggregation: promotes atherosclerosis.
• Salt: has a potential impact on blood pressure.
• Caffeine: is not directly linked to heart disease, although may increase risk in some individuals
• Chronic stress: can potentially increase heart diseases risk in some individuals

Explore the intricate details of the cardiovascular system (CVS), including its components, functions, and the anatomy of the heart. This quiz covers vital aspects such as blood composition, heart structure, and the differences in fetal heart function. Test your knowledge and understanding of how this essential system supports life.