Cardiovascular System — Study Pack (2025-26) Study Guide

❤️ Overview of the Cardiovascular System

Purpose: The cardiovascular system delivers oxygen and nutrients, removes waste, and dissipates heat. It consists of the heart (pump), blood vessels (piping and exchange beds), capillaries, and blood (transport medium). There are two linked circulations: systemic (left heart → body) and pulmonary (right heart → lungs).

🫀 Heart: Location and Basic Facts

The heart lies in the mediastinum, between the sternum and spinal column and is slightly left of midline. In health it is roughly the size of the owner's fist. Its primary role is to generate the pressure and flow needed to circulate blood through the vascular tree.

🧱 Heart Structure: Layers and Chambers

The heart wall has three layers: the endocardium (inner lining over valves and tendons), myocardium (muscular middle layer), and epicardium (outer lining). There are four chambers: two atria (upper chambers) separated by the interatrial septum and two ventricles (lower chambers) separated by the interventricular septum.

🔁 Heart Valves and Function

There are two pairs of valves that prevent backflow. The atrioventricular valves (tricuspid and mitral) separate atria from ventricles and are anchored by papillary muscles and tendons. The semilunar valves (aortic and pulmonary) sit at the exits of the ventricles and open during ventricular ejection.

🩸 Coronary Blood Supply

The myocardium has high oxygen demand at rest. Oxygen-rich blood reaches the heart muscle via the right and left coronary arteries and their branches. Venous drainage includes the coronary sinus (left ventricle drainage) and anterior cardiac veins (right ventricle drainage).

⚡ Electrical Conduction and the Heart as a Pump

Specialized cardiac muscle fibers form the conduction system: SA node, AV node, bundle of His, left and right bundle branches, and Purkinje fibers. Excitation starts in the SA node, spreads through atria, delays at the AV node, then travels through His/Purkinje system to activate ventricular muscle and generate coordinated contraction.

📈 Electrocardiogram (ECG)

An ECG records the heart's electrical activity and helps detect rhythm problems. Key waveforms: P wave (atrial depolarization/SA node firing), QRS complex (ventricular depolarization and associated atrial repolarization), and T wave (ventricular repolarization).

🔄 The Cardiac Cycle

The cardiac cycle runs from the end of one contraction to the end of the next and has two main phases: diastole (relaxation/filling) and systole (contraction/emptying). Diastole allows ventricular filling via open AV valves; systole generates pressure to open semilunar valves and eject blood.

🔊 Heart Sounds

Heart sounds arise from turbulent flow when valves close. The first sound ("lubb") is closure of the AV valves at systole onset. The second sound ("dupp") is closure of the semilunar valves at systole end and diastole start.

🧭 Vascular System: Vessel Structure

Vessel walls share layers: an endothelium, connective tissue membrane, a middle muscular/elastic layer, and an outer fibrous layer. Arteries are elastic and convert pulsatile cardiac output to steadier flow. Arterioles provide major resistance due to muscular walls. Capillaries have thin walls for exchange and large surface area. Veins are distensible, have valves (endothelial folds), and act as capacitance vessels.

⚙️ Hemodynamics: Flow, Resistance, Pressure

Blood flow depends on pressure differences and resistance. Resistance is influenced by vessel radius, length, and blood viscosity. Systemic blood pressure decreases from the aorta toward the right atrium. Pulmonary pressures are lower than systemic pressures.

🩺 Blood Pressure: Definitions and Determinants

Systolic pressure is peak arterial pressure after ventricular ejection and depends on stroke volume and contractile force. Diastolic pressure is minimum arterial pressure before the next systole and reflects peripheral resistance and arterial elasticity. Arterial pressure is determined primarily by cardiac output and total peripheral resistance.

❤️ Cardiac Output and Stroke Volume

Cardiac output is the volume pumped per minute (typical resting value ≈ 5 L/min). Stroke volume is the volume ejected per beat. Cardiac output = heart rate × stroke volume. During exercise both heart rate and stroke volume increase, markedly raising cardiac output.

🧠 Control of Circulation

Heart rate and contractility are modulated by the autonomic nervous system: sympathetic stimulation increases heart rate and contractility, while parasympathetic (vagal) activity slows heart rate. Hormones (adrenaline, noradrenaline, thyroid hormones) also influence heart rate and vascular tone. Baroreceptors and atrial stretch receptors provide reflex control.

🩸 Blood: Composition and Function

Blood is ~55% plasma and ~45% cellular elements. Cellular components include red cells (oxygen/CO2 transport), white cells (immune defense), and platelets (clotting). Knowledge of blood groups and transfusion compatibility is essential in clinical care.

⚠️ Common Cardiovascular Conditions (Dental Relevance)

Conditions of concern include coronary heart disease, angina, myocardial infarction/cardiac arrest, hypertension, and atrial fibrillation. These can affect dental management via emergency risk, medication interactions (e.g., anticoagulants), and required monitoring.

🦷 Role of Dental Hygienists in Cardiovascular Health

Dental hygienists can contribute to systemic health by delivering diet advice, smoking and alcohol cessation support, education on oral hygiene and links between periodontal and cardiovascular disease, stress awareness, and providing basic life support (CPR) when required. Review patients' medications and medical histories for cardiovascular risk and implications for dental care.