Circulatory System and Heart Anatomy

• The circulatory system is responsible for transporting oxygen, nutrients, hormones, and cellular waste throughout the body.
• It comprises the heart, blood vessels, and blood.

Heart Anatomy

• The human heart is a muscular organ located in the thoracic cavity.
• It is a dual pump, with two atria and two ventricles.
• The right atrium receives deoxygenated blood from the body via the superior and inferior vena cava.
• The left atrium receives oxygenated blood from the lungs via the pulmonary veins.
• The right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery.
• The left ventricle pumps oxygenated blood to the body via the aorta.
• Valves within the heart ensure unidirectional blood flow, preventing backflow.
• The atrioventricular valves (tricuspid on the right, mitral/bicuspid on the left) are located between the atria and ventricles.
• The semilunar valves (pulmonary and aortic) are located at the exit of the ventricles.
• The heart wall consists of three layers: the epicardium (outer), myocardium (middle muscular layer), and endocardium (inner).

Blood Vessels

• Arteries carry blood away from the heart, typically oxygenated (except for the pulmonary artery).
• Veins carry blood towards the heart, typically deoxygenated (except for the pulmonary veins).
• Capillaries are tiny vessels where exchange of oxygen, carbon dioxide, nutrients, and waste products occurs between blood and tissues.
• Arteries have thicker walls with more elastic fibers and smooth muscle than veins, allowing them to withstand high pressure.
• Veins have thinner walls and contain valves to prevent backflow of blood, especially in the limbs.
• Blood flow is regulated by vasoconstriction (narrowing of blood vessels) and vasodilation (widening of blood vessels).

Blood Components

• Blood consists of plasma and formed elements (cells).
• Plasma is the liquid component, primarily water, containing dissolved proteins, glucose, ions, hormones, and gases.
• Formed elements include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).
• Red blood cells transport oxygen bound to hemoglobin.
• White blood cells are involved in immune responses, defending the body against infection.
• Platelets are involved in blood clotting.

Blood Circulation

• Blood circulation is divided into two main circuits: pulmonary and systemic.
• In pulmonary circulation, deoxygenated blood flows from the right ventricle to the lungs, where it picks up oxygen and releases carbon dioxide. Oxygenated blood returns to the left atrium.
• In systemic circulation, oxygenated blood flows from the left ventricle to the body, delivering oxygen and nutrients to tissues. Deoxygenated blood returns to the right atrium.
• Coronary circulation supplies the heart muscle itself with oxygen and nutrients.

Fetal Circulation

• Fetal circulation differs from adult circulation because the fetal lungs are not functional.
• The fetus receives oxygen and nutrients from the placenta via the umbilical cord.
• There are three shunts in fetal circulation: the ductus venosus, foramen ovale, and ductus arteriosus.
• The ductus venosus bypasses the liver, directing blood from the umbilical vein to the inferior vena cava.
• The foramen ovale is an opening between the right and left atria, allowing blood to bypass the pulmonary circulation.
• The ductus arteriosus connects the pulmonary artery to the aorta, further bypassing the pulmonary circulation.
• After birth, these shunts close, and the fetal circulation converts to the adult circulation pattern.

Blood Pressure

• Blood pressure is the force exerted by blood against the walls of blood vessels.
• It is typically measured in the brachial artery using a sphygmomanometer.
• Systolic pressure is the pressure when the heart contracts (ventricular systole).
• Diastolic pressure is the pressure when the heart relaxes (ventricular diastole).
• Blood pressure is influenced by factors such as cardiac output, blood volume, and peripheral resistance.
• Hypertension (high blood pressure) is a major risk factor for cardiovascular disease.

Heartbeat

• The heartbeat is a coordinated sequence of atrial and ventricular contractions.
• The sinoatrial (SA) node in the right atrium initiates the electrical impulses that trigger the heartbeat.
• The atrioventricular (AV) node delays the impulse, allowing the atria to contract before the ventricles.
• The impulse then travels through the bundle of His and Purkinje fibers, causing ventricular contraction.
• Heart rate is the number of heartbeats per minute.

Electrical Signal Process

• The electrical activity of the heart can be recorded using an electrocardiogram (ECG or EKG).
• The P wave represents atrial depolarization.
• The QRS complex represents ventricular depolarization.
• The T wave represents ventricular repolarization.
• Abnormalities in the ECG can indicate various heart conditions.
• The SA node generates an electrical impulse.
• The impulse spreads through the atria, causing them to contract.
• The AV node delays the impulse slightly.
• The impulse travels down the bundle of His and Purkinje fibers.
• The ventricles contract.
• The heart muscle cells repolarize, preparing for the next cycle.