Cardiovascular System

The cardiovascular system delivers oxygen and nutrients to tissues and removes waste products. The heart is a muscular pump with four chambers, one-way valves, and major vessels that maintain unidirectional blood flow.

Superior Vena Cava (SVC)

Function: Returns deoxygenated blood from the head, neck, arms, and upper chest
Blood: Deoxygenated
Empties into: Right atrium

Inferior Vena Cava (IVC)

Function: Returns deoxygenated blood from the abdomen, pelvis, and legs
Blood: Deoxygenated
Empties into: Right atrium

Right Atrium

Role: Receives deoxygenated blood from the body and serves as a collecting chamber
Blood flows into: Right ventricle
Blood: Deoxygenated

Tricuspid Valve

Location: Between the right atrium and right ventricle
Function: Prevents backflow into the right atrium during ventricular contraction

Right Ventricle

Role: Pumps deoxygenated blood to the lungs
Blood: Deoxygenated
Pumps into: Pulmonary artery
Key Point: The ventricles are the heart's major pumping chambers

Pulmonary Semilunar Valve

- Function: Prevents blood from flowing back into the right ventricle after it has been pumped into the pulmonary artery

Pulmonary Artery

Role: Carries blood from the heart to the lungs
Blood: Deoxygenated
Key Point: Although arteries usually carry oxygenated blood, the pulmonary artery carries deoxygenated blood because arteries are defined by carrying blood away from the heart

Lungs

Primary function: Gas exchange
Inside the alveoli: Oxygen diffuses into blood and carbon dioxide diffuses into alveoli to be exhaled
Hemoglobin binds oxygen immediately, maintaining diffusion

Pulmonary Veins

Role: Return oxygenated blood to the heart
Blood: Oxygenated
Destination: Left atrium
Key Point: Pulmonary veins carry oxygenated blood even though veins usually carry deoxygenated blood because veins are defined by carrying blood toward the heart

Left Atrium

Role: Receives oxygenated blood from the lungs and sends blood to the left ventricle
Blood: Oxygenated

Mitral (Bicuspid) Valve

Location: Between the left atrium and left ventricle
Function: Prevents backflow into the left atrium

Left Ventricle

Role: Strongest chamber of the heart; pumps oxygenated blood throughout the body
Blood: Oxygenated
Pumps into: Aorta

Aortic Semilunar Valve

Location: Between the left ventricle and the aorta
Function: Prevents blood from flowing backward from the aorta into the left ventricle

Aorta

Description: Largest artery in the body
Role: Delivers oxygenated blood to every organ except the lungs
Blood: Oxygenated

Summary of Blood Flow

SVC + IVC ↓ Right Atrium ↓ Tricuspid Valve ↓ Right Ventricle ↓ Pulmonary Valve ↓ Pulmonary Artery ↓ Lungs ↓ Pulmonary Veins ↓ Left Atrium ↓ Mitral Valve ↓ Left Ventricle ↓ Aortic Valve ↓ Aorta ↓ Body ↓ Repeat

Cardiac Cycle

The cardiac cycle consists of two main phases:

Systole: Contraction phase; blood is ejected
Diastole: Relaxation phase; chambers fill with blood

Blood Pressure and Hemodynamics

Blood Pressure — Blood pressure is the force that circulating blood exerts against the walls of blood vessels. It is primarily determined by cardiac output and total peripheral resistance.
Blood Pressure (BP) = Cardiac Output (CO) × Total Peripheral Resistance (TPR)
Cardiac Output (CO) — Cardiac output is the volume of blood pumped by the heart each minute.
Cardiac Output (CO) = Heart Rate (HR) × Stroke Volume (SV)
Heart Rate (HR): beats per minute
Stroke Volume (SV): blood ejected per beat
Total Peripheral Resistance (TPR) — Total peripheral resistance is the resistance blood encounters as it flows through the systemic circulation. It is created mainly by the arterioles.
Mean Arterial Pressure (MAP) — Mean arterial pressure is the average pressure in the arteries during one complete cardiac cycle. It is the pressure driving blood flow to organs and tissues.
MAP = CO × TPR
Any factor that changes cardiac output or total peripheral resistance will change blood pressure.

Blood Vessel Wall Layers

Arteries and veins have three concentric layers:

Tunica intima — innermost layer; endothelium in direct contact with blood.
Tunica media — middle layer of smooth muscle and elastic tissue; controls vessel diameter through vasoconstriction and vasodilation.
Tunica adventitia — outer connective-tissue layer that anchors the vessel to surrounding tissue.

Blood Volume Distribution

Veins contain the largest percentage of the body's blood volume. Their thin walls and large lumens allow them to act as capacitance vessels that store blood and help regulate venous return to the heart.

Vascular Resistance

Arterioles are the primary resistance vessels of the circulation. Their small radius and thick smooth-muscle wall create the greatest resistance to blood flow, so changes in arteriolar tone are the main determinant of total peripheral resistance and blood pressure.

Anatomy & Physiology