The Cardiovascular System: The Heart and Blood Vessels

Chapter 12: The Heart

Heart Structure and Layers

The heart is a muscular organ responsible for pumping blood throughout the body. It is composed of several layers and specialized structures that ensure efficient circulation.

• Visceral Pericardium (Epicardium): The outermost layer covering the heart's surface.

• Myocardium: The thick, muscular middle layer responsible for heart contractions.

• Endocardium: The innermost layer lining the heart chambers and valves.

Heart Chambers and Septa

• Interatrial Septum: Wall separating the two atria.

• Interventricular Septum: Wall separating the two ventricles.

Heart Valves

Valves ensure unidirectional blood flow through the heart:

• Atrioventricular (AV) Valves: Allow blood to flow from atria to ventricles.

• Right Side – Tricuspid Valve: Three cusps; between right atrium and ventricle.

• Left Side – Bicuspid (Mitral) Valve: Two cusps; between left atrium and ventricle; withstands higher pressure.

• Pulmonary Semilunar Valve: Located at the opening of the pulmonary trunk; prevents backflow into the right ventricle.

Coronary Sinus

• Coronary Sinus: Collects deoxygenated blood from the myocardium and returns it to the right atrium; contains sensors for pH balance.

Cardiac Conduction System

The heart's rhythm is controlled by specialized cells:

• Nodal Cells: Generate and conduct electrical impulses.

• Sinoatrial (SA) Node: Located in the posterior right atrium; acts as the primary pacemaker.

• Atrioventricular (AV) Node: Receives impulses from the SA node and delays them before passing to the ventricles.

• Purkinje Fibers: Distribute impulses to ventricular muscle cells.

• Ectopic Pacemaker: Abnormal cells that generate irregular signals, potentially disrupting normal rhythm.

Heart Anatomy Orientation

• Base: Superior end of the heart where major vessels attach.

• Apex: Inferior, pointed end of the heart.

Cardiac Cycle and Heart Sounds

• Systole: Contraction phase of the heart.

• Diastole: Relaxation phase of the heart.

• Heart Sounds:

  • Lubb: Caused by closure of AV valves.

  • Dupp: Caused by closure of semilunar valves.

Cardiac Output and Stroke Volume

• Stroke Volume (SV): Volume of blood ejected by a ventricle in one beat.

• Cardiac Output (CO): Volume of blood ejected from a ventricle in one minute.

Formula:

$CO = SV \times HR$

Where $CO$ is cardiac output, $SV$ is stroke volume, and $HR$ is heart rate.

Frank-Starling Principle

• An increase in venous return stretches myocardial cells, causing them to contract more forcefully and increasing cardiac output.

Example: During exercise, increased venous return leads to a stronger heartbeat and greater cardiac output.

Chapter 13: The Cardiovascular System – Blood Vessels and Circulation

Vascular Beds and Vessel Types

Blood circulates through a network of vessels organized into vascular beds:

• Arteries: Carry blood away from the heart.

• Arterioles: Small branches of arteries leading to capillaries.

• Capillaries: Sites of exchange between blood and tissues.

• Venules: Small vessels collecting blood from capillaries.

• Veins: Return blood to the heart.

Layers of Vessel Walls

• Tunica Intima: Endothelial lining with elastic connective tissue.

• Tunica Media: Smooth muscle with collagen and elastic fibers; regulates vessel diameter.

• Tunica Externa: Outer connective tissue sheath; may anchor vessel to surrounding tissues.

Types of Arteries

• Elastic Arteries: First arteries leaving the heart (e.g., aorta, pulmonary trunk); contain more elastic fibers to absorb pressure changes.

Capillaries and Capillary Beds

• Capillaries: Only vessels permitting exchange between blood and interstitial fluid via diffusion, filtration, and osmosis.

• Capillary Beds: Networks of capillaries; entrance regulated by precapillary sphincters (bands of smooth muscle).

Functions of Capillary Beds:

• Maintain communication between plasma and interstitial fluid.

• Speed distribution of nutrients, hormones, and gases.

• Assist movement of insoluble molecules.

• Flush bacterial toxins and chemicals to lymphatic tissues for immune response.

Mechanisms of Capillary Exchange

• Diffusion: Movement of substances from high to low concentration.

• Filtration: Movement of fluid out of capillaries due to hydrostatic pressure.

• Osmosis: Movement of water into capillaries due to osmotic pressure.

Vascular Anastomoses

• Anastomosis: Joining of blood vessels to provide alternate routes for blood flow.

• Arteriovenous Anastomosis: Direct connection between arteriole and venule, bypassing capillary bed.

• Arterial Anastomosis: Fusion of arteries before branching into arterioles; ensures blood delivery to vital organs (e.g., brain, heart).

Veins

• Collect blood from tissues and organs and return it to the heart.

Peripheral Resistance

Peripheral resistance affects the pressure required to move blood through the body.

• Vascular Resistance: Friction between blood and vessel walls.

• Viscosity: Thickness of blood; higher viscosity increases resistance.

• Turbulence: Irregular blood flow increases resistance.

Hormonal Control of Cardiovascular Performance

• Short-term Regulation: Epinephrine and norepinephrine increase heart rate and blood pressure.

• Long-term Regulation:

  • Antidiuretic Hormone (ADH): Increases blood volume and pressure.

  • Angiotensin II: Raises blood pressure via vasoconstriction and increased blood volume.

  • Erythropoietin (EPO): Stimulates red blood cell production, increasing blood volume.

  • Atrial Natriuretic Peptide (ANP): Released in response to high blood pressure; lowers blood pressure by promoting sodium and water excretion.

Portal System

• A circulatory pathway with two capillary beds in series, connected by a portal vessel (e.g., hepatic portal system).

Major Arteries and Veins

• Students should be familiar with the locations and names of major arteries and veins throughout the body (e.g., aorta, pulmonary arteries and veins, superior and inferior vena cava).

Additional info: For detailed diagrams and specific vessel locations, refer to anatomical charts or atlases.