Overview of the Cardiovascular System Functions and Structure

Cardiovascular System

Transports blood throughout the body, delivering oxygen, nutrients, hormones, and removing waste products.

Perfusion

The delivery of blood to tissues, providing oxygen and nutrients while removing waste.

Deoxygenated Blood Flow Through the Heart

Enters the right atrium via the superior and inferior vena cava, flows through the tricuspid valve into the right ventricle, and pumps through the pulmonary valve into the pulmonary arteries to the lungs.

Oxygenated Blood Flow Through the Heart

Returns to the left atrium via the pulmonary veins, passes through the mitral (bicuspid) valve into the left ventricle, and is ejected through the aortic valve into the aorta and systemic circulation.

Arteries

Carry blood away from the heart (usually oxygenated, except for pulmonary arteries).

Veins

Carry blood toward the heart (usually deoxygenated, except for pulmonary veins).

Right Side of the Heart

Receives deoxygenated blood from the body and pumps it to the lungs (pulmonary circulation).

Left Side of the Heart

Receives oxygenated blood from the lungs and pumps it to the body (systemic circulation).

Chambers of the Heart

Right atrium, right ventricle, left atrium, left ventricle.

Valves of the Heart

Tricuspid, pulmonary, mitral (bicuspid), aortic.

Epicardium

Outer layer of the heart wall.

Myocardium

Muscular middle layer of the heart wall, responsible for contraction.

Endocardium

Inner lining of the heart chambers.

Superior/Inferior Vena Cava

Great vessels that lead to the right atrium.

Pulmonary Arteries

Carry blood from the right ventricle to the lungs.

Pulmonary Veins

Carry blood to the left atrium from the lungs.

Aorta

Carries blood from the left ventricle to the body.

Pulmonary Circulation

Right ventricle → Pulmonary arteries → Lungs → Pulmonary veins → Left atrium.

Systemic Circulation

Left ventricle → Aorta → Body tissues → Vena cava → Right atrium.

Papillary Muscles

Contract to prevent valve prolapse during ventricular contraction.

Chordae Tendineae

Anchor valve leaflets to papillary muscles, maintaining valve function.

Heart Valves Opening Mechanism

Valves open in response to pressure changes, preventing backflow of blood.

Left Ventricular Wall Thickness

Thicker due to the need to pump blood to the entire body (systemic circulation).

SA Node

Pacemaker that initiates electrical impulses in the heart.

AV Node

Delays impulse, allowing atrial contraction.

Bundle of His

Transmits impulses to the ventricles.

Purkinje Fibers

Distribute impulse through ventricles, triggering contraction.

Resting Membrane Potential (RMP) of Nodal Cells

Around -60 mV.

Threshold of Nodal Cells

Approximately -40 mV.

Contractile Cell Action Potential RMP

Approximately -90 mV.

Action Potential Trigger

When threshold is reached, Ca²⁺ influx occurs.

RMP

Approximately -90 mV.

Threshold

Around -70 mV.

Channels

Na+ channels for rapid depolarization, Ca²⁺ channels for plateau phase, and K+ channels for repolarization.

Importance of Calcium Channels

Prolong the action potential (plateau phase), preventing tetany (sustained contraction).

Plateau Phase

Ca²⁺ influx balances K+ efflux, extending the refractory period.

Tetany Prevention

Prolonged refractory period ensures the heart relaxes between contractions.

P Wave

Atrial depolarization.

QRS Complex

Ventricular depolarization (and atrial repolarization).

T Wave

Ventricular repolarization.

Systole

Contraction phase, blood is ejected.

Diastole

Relaxation phase, chambers fill with blood.

Primary Driver of Blood Movement

Changes in pressure within heart chambers.

Cardiac Output (CO)

Volume of blood pumped by a ventricle per minute.

CO Formula

CO = Heart Rate (HR) × Stroke Volume (SV).

Factors Affecting CO

Heart Rate: Influenced by autonomic nervous system, hormones. Stroke Volume: Affected by preload, contractility, and afterload.

End-Diastolic Volume (EDV)

Volume of blood in ventricles at the end of diastole.

End-Systolic Volume (ESV)

Volume of blood remaining in ventricles after contraction.

Frank-Starling Law

Greater stretch of the heart muscle (due to increased EDV) results in a stronger contraction.

Tunica Intima

Composed of endothelial cells and a subendothelial layer. Provides a smooth surface for blood flow.

Tunica Media

Contains smooth muscle and elastic fibers. Regulates vessel diameter via vasoconstriction and vasodilation.

Tunica Externa

Made of connective tissue with collagen and elastic fibers. Provides structural support and anchors vessels.

Differences in Tunics Between Arteries, Capillaries, and Veins

Arteries have a present tunica intima, thick tunica media, and moderate thickness tunica externa; capillaries have only an endothelial layer for tunica intima, absent tunica media, and absent tunica externa; veins have a present tunica intima, thin tunica media, and moderate thickness tunica externa.

Tunica Intima

Present in arteries and veins; only endothelial layer in capillaries.

Tunica Media

Thick in arteries with more smooth muscle and elastic fibers; none in capillaries; thin with fewer muscle fibers in veins.

Tunica Externa

Thin in large arteries; none in capillaries; thickest layer in veins.

Arteries

Thick tunica media allows arteries to withstand high pressure.

Capillaries

Only a thin tunica intima to allow efficient gas and nutrient exchange.

Veins

Have thinner walls and large lumens, with valves to prevent backflow.

Large Elastic Arteries

Have more elastic fibers.

Medium-Sized Arteries

Have more smooth muscle.

Large Veins

Have thicker tunica externa.

Small Veins

Have thinner walls and larger lumens.

Continuous Capillaries

Tight junctions, least permeable; found in skin, muscles, and CNS; allow only small molecules to pass.

Fenestrated Capillaries

Pores for moderate permeability; found in kidneys and intestines, allow small proteins to pass.

Sinusoidal Capillaries

Large gaps, most permeable; found in liver, spleen, bone marrow; allow large proteins and cells to pass.

Veins as Blood Reservoir

Veins contain ~60-70% of the body's blood at rest; their large lumen and compliance allow them to hold extra blood.

Portal System

A network of two capillary beds connected by a vein; example: Hepatic portal system (gut-liver circulation).

Anastomoses

Alternative pathways for blood flow that connect arteries or veins, providing collateral circulation.

Cross-Sectional Area and Blood Flow Velocity

As cross-sectional area increases, blood velocity decreases; capillaries have the largest total cross-sectional area.

Bulk Flow

Movement of fluid across capillary walls due to pressure differences.

Filtration

Fluid exits capillaries at the arterial end due to high hydrostatic pressure.

Reabsorption

Fluid re-enters capillaries at the venous end due to osmotic pressure.

Hydrostatic Pressure (HP)

The force exerted by blood pushing against capillary walls (pushes fluid out).

Colloid Osmotic Pressure (COP)

The force exerted by plasma proteins pulling fluid into the capillaries.

Net Filtration Pressure (NFP)

The balance between HP and COP, determining whether fluid moves in or out.

Net Filtration Pressure Formula

NFP=(HP capillary - HP interstitial) - (COP capillary - COP interstitial).

Local Blood Flow

The volume of blood delivered to a specific tissue.

Perfusion

Local blood flow relative to tissue mass (mL/min/g).

Degree of Vascularization

The number of blood vessels supplying a tissue.

Highly Vascularized Tissues

Examples include brain, heart, and muscles.

Low Vascularization

Examples include cartilage and tendons.

Vascularization

More vascularization = Higher blood flow; Less vascularization = Lower blood flow.

Myogenic Response

Smooth muscle constricts or dilates to maintain constant blood flow.

Myogenic response to high blood pressure

Vasoconstriction to reduce excessive blood flow.

Myogenic response to low blood pressure

Vasodilation to increase blood flow.

Local regulatory factors (autoregulation)

Tissues release local signals that adjust blood vessel diameter.

Vasodilation

Widening of blood vessels, increasing blood flow.

Vasoconstriction

Narrowing of blood vessels, decreasing blood flow.

Chemical conditions of actively metabolizing tissue

High CO₂, low O₂, low pH, high temperature.

Autoregulatory response to conditions of actively metabolizing tissue

Vasodilation to increase oxygen delivery and waste removal.

Total Blood Flow

Total blood flow = Cardiac Output (CO); Local blood flow is a fraction of total blood flow directed to specific tissues.

Blood Pressure

The force exerted by blood against vessel walls.

Systolic Pressure

Pressure during ventricular contraction (~120 mmHg).

Diastolic Pressure

Pressure during ventricular relaxation (~80 mmHg).

Pulse Pressure

Difference between systolic and diastolic pressure.

Mean Arterial Pressure (MAP)

MAP = Diastolic pressure + 1/3 Pulse Pressure; Indicates average blood pressure during one cardiac cycle.

Blood Pressure Gradient

The difference in blood pressure between two points in circulation; it drives blood flow from high pressure (arteries) to low pressure (veins).

Venous Return

The flow of blood back to the heart via veins.

Skeletal Muscle Pump

Muscle contractions squeeze veins, pushing blood toward the heart.