Cardiovascular System: Heart Anatomy

• The cardiovascular system transports nutrients, oxygen, hormones, and immune cells.
• It regulates body temperature, pH, and fluid balance.
• Main components: the heart, blood vessels (arteries, veins, capillaries), and blood.

The Heart

• The heart is a muscular organ which pumps blood through the circulatory system.
• It's located in the thoracic cavity, between the lungs, in the mediastinum.
• The heart consists of four chambers: the right atrium, right ventricle, left atrium, and left ventricle.
• Atria receive blood, while ventricles pump blood out of the heart.
• The heart also has valves, which ensure unidirectional blood flow.
• Atrioventricular valves include the tricuspid (right side) and mitral (bicuspid, left side) valves, which prevent backflow from the ventricles into the atria.
• Semilunar valves include the pulmonary (right side) and aortic (left side) valves, preventing backflow from the arteries into the ventricles.
• The heart wall is composed of three layers: the epicardium (outer layer), myocardium (middle, muscular layer), and endocardium (inner layer).
• Cardiac muscle cells are interconnected by intercalated discs, containing gap junctions for rapid electrical conduction and coordinated contraction.
• The heart possesses an intrinsic conduction system to initiate and coordinate heartbeats.
• The sinoatrial (SA) node, located in the right atrium, serves as the primary pacemaker, initiating electrical impulses.
• The atrioventricular (AV) node delays the impulse, allowing atria to contract before ventricles.
• The impulse travels through the bundle of His, bundle branches, and Purkinje fibers, distributing the impulse to the ventricular myocardium.
• The coronary arteries branch off the aorta and supply the heart with blood.
• The right and left coronary arteries provide oxygenated blood to the heart muscle.
• Blockage of these arteries can lead to myocardial infarction (heart attack).

Blood Vessels

• Arteries carry blood away from the heart with thick, elastic walls to withstand high pressure.
• The aorta is the largest artery, receiving blood directly from the left ventricle.
• Arteries branch into smaller arterioles, which regulate blood flow into capillaries.
• Capillaries, the smallest blood vessels, facilitate the exchange of oxygen, carbon dioxide, nutrients, and waste between the blood and tissues, via their thin walls.
• Veins carry blood back to the heart and have thinner walls and lower pressure than arteries.
• Veins contain valves to prevent backflow of blood, especially in the limbs.
• Venules are small veins that collect blood from capillaries, merging into larger veins.
• The superior and inferior vena cava are the largest veins, returning blood to the right atrium.

Blood

• Blood is a connective tissue composed of plasma and formed elements (cells and cell fragments).
• Plasma, the liquid component of blood, consists mostly of water, along with proteins, electrolytes, nutrients, and waste products.
• Red blood cells (erythrocytes) transport oxygen bound to hemoglobin.
• White blood cells (leukocytes) are involved in the immune response, defending the body against infection and foreign invaders.
• Platelets (thrombocytes) are cell fragments involved in blood clotting (hemostasis).
• Blood volume: The average adult has about 5 liters of blood.

Blood Circulation

• Blood circulation is divided into systemic and pulmonary circuits.
• Systemic circulation carries oxygenated blood from the left ventricle to the body tissues and returns deoxygenated blood to the right atrium.
• Pulmonary circulation carries deoxygenated blood from the right ventricle to the lungs for oxygenation and returns oxygenated blood to the left atrium.
• Blood pressure is the force exerted by blood against the walls of blood vessels.
• It is typically measured in arteries and is expressed as systolic pressure (during ventricular contraction) over diastolic pressure (during ventricular relaxation).
• Normal blood pressure: around 120/80 mmHg
• Blood pressure is regulated by several factors, including heart rate, stroke volume, peripheral resistance, blood volume, and hormones.
• Cardiac output is the amount of blood pumped by the heart per minute.
• It is calculated as heart rate multiplied by stroke volume (the amount of blood ejected with each beat).
• Peripheral resistance is the opposition to blood flow in the blood vessels.
• Vasoconstriction (narrowing of blood vessels) increases peripheral resistance, while vasodilation (widening of blood vessels) decreases it.