Cardiovascular System: Heart and Blood Vessels – Study Guide for Exam 2

Cardiovascular System Overview

The cardiovascular system consists of the heart and blood vessels, working together to circulate blood throughout the body. This system is essential for delivering oxygen and nutrients to tissues and removing waste products.

Heart Anatomy and Function

• Position of the Heart: The heart is located in the thoracic cavity, between the lungs in the mediastinum, slightly left of the midline.

• Double Pump Function: The heart acts as a double pump, with the right side pumping deoxygenated blood to the lungs (pulmonary circuit) and the left side pumping oxygenated blood to the body (systemic circuit). This separation ensures efficient oxygenation and nutrient delivery.

• Heart Wall Layers:

  • Epicardium: Outer layer (visceral pericardium)

  • Myocardium: Middle, muscular layer responsible for contraction

  • Endocardium: Inner lining of the heart chambers

• Pericardium: A double-walled sac surrounding the heart, consisting of the fibrous and serous pericardium, providing protection and reducing friction.

• Heart Chambers: Four chambers – right atrium, right ventricle, left atrium, left ventricle. The right side handles deoxygenated blood; the left side handles oxygenated blood.

• Valves: Atrioventricular (tricuspid and mitral) and semilunar (pulmonary and aortic) valves ensure unidirectional blood flow and prevent backflow.

Cardiac Muscle Structure and Function

• Cardiac Muscle Cells: Striated, branched, interconnected by intercalated discs, allowing rapid electrical conduction and synchronized contraction.

• Unique Features: Cardiac muscle has automaticity (can generate its own action potentials) and is resistant to fatigue due to abundant mitochondria.

Cardiac Conduction System

The heart's electrical system coordinates contraction:

• Sinoatrial (SA) Node: Pacemaker of the heart, initiates action potentials.

• Atrioventricular (AV) Node: Delays impulse, allowing atrial contraction before ventricles contract.

• Bundle of His, Bundle Branches, Purkinje Fibers: Rapidly conduct impulses through ventricles for coordinated contraction.

Action Potentials

• Pacemaker Cells: Exhibit spontaneous depolarization due to unstable resting membrane potential.

• Contractile Cells: Have a plateau phase due to calcium influx, prolonging contraction.

Electrocardiogram (ECG)

• ECG Segments: P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization).

• Intervals: PR, QT, and ST intervals provide information about conduction and repolarization.

Cardiac Cycle

The cardiac cycle describes the sequence of events in one heartbeat:

• Systole: Contraction phase (ventricular or atrial)

• Diastole: Relaxation phase

• Valve Operation: AV valves open during diastole, close during systole; semilunar valves do the opposite.

• Pressure and Volume Changes: Pressure changes drive blood flow; volume changes correspond to filling and ejection phases.

Coronary Circulation

• Coronary Arteries: Supply oxygenated blood to the heart muscle; main branches include the left and right coronary arteries, with further branches such as the circumflex and anterior interventricular arteries.

• Coronary Veins: Drain deoxygenated blood from the myocardium into the coronary sinus.

Cardiac Output and Regulation

• Cardiac Output (CO): The volume of blood pumped by each ventricle per minute.

  • Formula: $CO = HR \times SV$

  • Where $HR$ = heart rate, $SV$ = stroke volume

• Regulation: Influenced by autonomic nervous system (sympathetic increases HR and contractility; parasympathetic decreases HR), hormones (e.g., epinephrine), and intrinsic factors (preload, afterload, contractility).

Blood Vessels and Circulation

Blood vessels form a closed circuit for blood flow, including arteries, veins, and capillaries.

Types and Structure of Blood Vessels

• Arteries: Thick-walled, elastic vessels that carry blood away from the heart under high pressure.

• Veins: Thinner-walled, less elastic, contain valves to prevent backflow, carry blood toward the heart under lower pressure.

• Capillaries: Microscopic vessels with thin walls for exchange of gases, nutrients, and wastes.

• Arterioles and Venules: Small branches of arteries and veins, respectively, that regulate blood flow into capillary beds.

Blood Vessel Function and Regulation

• Vessel Diameter and Blood Flow: Blood flow is inversely proportional to resistance, which is affected by vessel diameter, length, and blood viscosity.

• Blood Pressure: The force exerted by blood on vessel walls; highest in arteries, lowest in veins.

• Regulation: Neural (baroreceptors, chemoreceptors), hormonal (epinephrine, ADH, angiotensin II), and local factors (metabolites, nitric oxide) regulate vessel diameter and blood pressure.

Anastomoses

• Definition: Connections between blood vessels that provide alternate pathways for blood flow.

• Significance: Important for collateral circulation, especially in the heart and brain.

Capillary Exchange

• Mechanisms: Diffusion, filtration, and osmosis allow exchange of substances between blood and tissues.

• Starling Forces: Balance of hydrostatic and osmotic pressures determines net filtration or absorption.

• Net Filtration Pressure (NFP):

  • Formula: $NFP = (HP_c - HP_i) - (OP_c - OP_i)$

  • Where $HP_c$ = capillary hydrostatic pressure, $HP_i$ = interstitial hydrostatic pressure, $OP_c$ = capillary osmotic pressure, $OP_i$ = interstitial osmotic pressure

• Edema: Accumulation of excess fluid in tissues, can result from increased capillary hydrostatic pressure, decreased plasma proteins, or lymphatic obstruction.

Special Circulatory Routes

• Hepatic Portal System: Blood from digestive organs passes through the liver before returning to the heart, allowing nutrient processing and detoxification.

• Pulmonary Circulation: Right ventricle pumps blood to lungs for oxygenation; left atrium receives oxygenated blood.

Blood Pressure Measurement

• Sphygmomanometer: Device used to measure arterial blood pressure, typically at the brachial artery.

• Pulse Points: Locations where arterial pulse can be palpated (e.g., radial, carotid, femoral arteries).

Regulation and Pathophysiology

Short-Term and Long-Term Blood Pressure Regulation

• Short-Term: Baroreceptor and chemoreceptor reflexes, autonomic nervous system, and circulating hormones.

• Long-Term: Renal mechanisms (regulation of blood volume), hormonal control (aldosterone, ADH).

Hypertension and Shock

• Hypertension: Chronic high blood pressure; risk factors include genetics, diet, obesity, and stress. Can lead to heart disease, stroke, and kidney failure.

• Shock: Inadequate tissue perfusion; types include hypovolemic, cardiogenic, vascular, and obstructive shock.

Key Calculations and Equations

• Cardiac Output: $CO = HR \times SV$

• Net Filtration Pressure (NFP): $NFP = (HP_c - HP_i) - (OP_c - OP_i)$

• Blood Flow (Q): $Q = \frac{\Delta P}{R}$, where $\Delta P$ is pressure difference, $R$ is resistance

• Mean Arterial Pressure (MAP): $MAP = DP + \frac{1}{3}(SP - DP)$, where $SP$ = systolic pressure, $DP$ = diastolic pressure

Table: Comparison of Arteries, Veins, and Capillaries

Feature	Arteries	Veins	Capillaries
Wall Thickness	Thick	Thin	Very thin (one cell layer)
Pressure	High	Low	Low
Valves	Absent	Present (in limbs)	Absent
Function	Carry blood away from heart	Carry blood toward heart	Exchange of substances

Additional info:

• Some content was inferred and expanded for clarity and completeness, such as detailed explanations of the cardiac cycle, conduction system, and regulatory mechanisms.

• Key equations and a comparison table were added for exam preparation.