The Cardiovascular System

• The cardiovascular system transports blood, oxygen, nutrients, and waste products throughout the body.

Components

• The heart, a muscular organ, pumps blood throughout the body.
• Blood vessels include arteries, veins, and capillaries.
• Blood contains red blood cells (oxygen transport), white blood cells (fight infections), platelets (blood clotting), and plasma (liquid component).

The Heart

• The heart is the pump of the circulatory system
• Contraction of the heart pushes blood throughout the body, delivering oxygen and nutrients while removing waste.
• Heart rate increases or decreases depending on the body's needs.
• The shape is like an inverted blunt cone.
• The base is the larger, flat part and the apex tapers to a rounded point.
• The heart is located between the two lungs in the mediastinum, behind the sternum.

Cardiac Muscle

• Cardiac muscle is a specialized involuntary striated muscle in the heart's myocardium, pumping blood.
• Types of cardiac muscle cells include contractile cells and pacemaker cells.
• Contractile cells (myocardial cells) make up 99% of cardiac muscle, in the atria and ventricles, generating the force needed to pump blood.
• These cells contract and relax to push blood through the heart and circulation, requiring electrical signals to contract.
• Pacemaker cells (autorhythmic cells) constitute 1% of cardiac muscle, control the heart's rhythm and location include the sinoatrial (SA) node, atrioventricular (AV) node, bundle of His, and Purkinje fibers.
• The sinoatrial (SA) node, in the right atrium, the heart's pacemaker, generates electrical impulses for each heartbeat.
• The atrioventricular (AV) node receives signals from the SA node and delays them slightly before transmitting them to the ventricles, which delays the electrical impulse for approximately 0.1 seconds.
• Bundle of His and Purkinje fibers, from the AV node, splits into two branches and conduct electrical impulses rapidly to the ventricles for coordinated contractions.
• Purkinje fibers branch off from the left and right bundle branches and spread throughout the inner walls of the ventricles
• The SA node generates the impulse.
• The AV node delays the impulses, allowing the atria to contract first.
• The Bundle of His receives and splits the impulses into left and right bundle branches.
• Purkinje fibers distribute the impulses to all ventricular muscle cells for simultaneous contraction.

Cardiac Cycle

• The cardiac cycle is the sequence of events in one complete heartbeat, involving contraction and relaxation of the atria and ventricles to circulate blood.
• It consists of two main phases: Systole (contraction) and Diastole (relaxation).

Systole

• Systole phase where the heart contracts, pushing blood out and is divided into two stages.
• During atrial systole, the atria contract, forcing blood into the ventricles through the tricuspid and mitral valves.
• The purpose of atrial systole is to fill the ventricles with blood before they contract.
• Ventricular systole is when the ventricles contract, pushing blood into the arteries and the semilunar valves open, allowing blood to flow from the ventricles through the arteries.
• The purpose of ventricular systole is to pump blood from the heart to the lungs and the rest of the body.

Diastole

• During diastole, the heart relaxes, allowing blood to fill the chambers flowing from the veins into the atria and ventricles.

Blood Vessels and Circulation

• Blood vessels are the network of tubes that transport blood throughout the body.
• They deliver oxygen, nutrients, and hormones while removing waste products like carbon dioxide, urea, and lactic acid.
• Major types of blood vessels include arteries, veins, and capillaries.

Arteries

• Arteries are thick-walled blood vessels that carry oxygenated blood away from the heart, except for the pulmonary artery.
• The thick walls withstand high-pressure blood flow and the elastic fibers allow them to stretch and recoil, helping maintain blood pressure.
• Arteries do not have valves because high-pressure flow prevents backflow.
• The small lumen (narrow inner space) in arteries helps maintain high blood pressure.
• The aorta is the largest artery

Veins

• Veins are thin-walled blood vessels that carry deoxygenated blood back to the heart, except for the pulmonary vein.
• Veins experience low pressure, so their walls are thinner and less muscular than the arteries.
• Veins have valves to prevent backflow and ensure blood moves in one direction towards the heart.
• Veins have a wider lumen to accommodate the slow-moving, low-pressure blood flow.
• The vena cava is the largest vein.

Capillaries

• Capillaries are the smallest blood vessels, forming networks that connect arteries to veins.
• Capillaries are one cell thick, with extremely thin walls made of a single layer of endothelial cells, enabling easy exchange of oxygen, nutrients, and waste products.
• Capillaries lack valves, and blood flow is controlled by arterial pressure and osmotic forces.
• Capillaries have a small diameter, ensuring close contact with tissues for efficient exchange

Blood Circulation

• Blood circulation is the continuous movement of blood through the heart, blood vessels, and organs to supply oxygen and nutrients while removing waste.
• It is divided into pulmonary circulation (heart to lungs) and systemic circulation (heart to body).
• In pulmonary circulation, deoxygenated blood from the body enters the right atrium via the superior and inferior vena cava.
• Blood moves into the right ventricle through the tricuspid valve.
• The right ventricle pumps blood through the pulmonary artery to the lungs.
• In the lungs, carbon dioxide is released, and oxygen is absorbed into the blood.
• Oxygenated blood returns to the left atrium via the pulmonary veins.
• In systemic circulation, oxygenated blood from the lungs enters the left atrium via the pulmonary veins.
• Blood moves into the left ventricle through the bicuspid valve.
• The left ventricle pumps oxygenated blood at high pressure into the aorta through the aortic valve.
• The aorta distributes oxygenated blood through arteries to all body parts and organs.
• Cells use the oxygen, and carbon dioxide is collected.
• Deoxygenated blood returns to the right atrium through the superior and inferior vena cava, completing the cycle.

Coronary Circulation

• Coronary circulation is the heart's own blood supply.
• The left and right coronary arteries branch from the aorta and supply blood to the heart muscle (myocardium).
• Coronary veins drain the deoxygenated blood into the right atrium via the coronary sinus.

Blood Pressure

• Blood pressure is the force exerted by circulating blood on the walls of blood vessels.
• It is measured in mmHg and expressed as systolic/diastolic pressure (e.g., 115/75 mmHg).
• Normal blood pressure is systolic: 90-120 mmHg and diastolic: 60-80 mmHg.

Blood Resistance

• Blood resistance is the opposition to blood flow within the vessels.
• Causes of blood resistance include blood vessel diameter and blood viscosity (thicker blood = greater resistance).