circulatory system

Arteries

Blood vessels that carry blood away from the heart; they have thick elastic walls and the highest blood pressure.

Veins

Vessels that carry blood back to the heart; they have thinner walls, larger lumens, and contain valves to prevent backflow.

Capillaries

Thin-walled, tiny vessels connecting arterioles to venules; the primary site for gas, nutrient, and waste exchange.

Vasoconstriction

The narrowing of blood vessels to reduce blood flow and prevent heat loss.

Vasodilation

The widening of blood vessels to increase blood flow, often used to regulate body temperature.

Sinoatrial (SA) Node

The heart's pacemaker located in the right atrium; it initiates the regular heartbeat.

Atrioventricular (AV) Node

A node that delays ventricle contraction until atrial contraction is complete.

Systolic Blood Pressure

The highest arterial pressure reached during ventricular contraction, ideally 120\ mmHg.

Diastolic Blood Pressure

The lowest arterial pressure reached during ventricular relaxation, ideally 80\ mmHg.

Pulmonary Circuit

The path of blood circulation between the heart and the lungs for gas exchange.

Systemic Circuit

The path of blood circulation throughout the body, excluding the lungs.

Red Blood Cells (RBCs)

Biconcave discs produced in bone marrow that use hemoglobin to transport oxygen; they have a lifespan of approximately 120\ days.

Platelets

Small, colorless blood components that play a key role in blood clotting.

Lymphatic System

A one-way vascular system that recovers tissue fluid, absorbs fats via lacteals, and produces lymphocytes for immunity.

Oval Opening

A fetal heart structure allowing blood to flow from the right atrium to the left atrium, bypassing the lungs.

Arteries

Blood vessels that carry blood away from the heart, characterized by thick elastic walls and high blood pressure.

Veins

Blood vessels that carry blood back to the heart, featuring valves to prevent backflow and thin walls.

Capillaries

The smallest blood vessels where the primary exchange of gases, nutrients, and waste occurs between blood and tissues.

Vasoconstriction

The narrowing of blood vessels to decrease blood flow and reduce heat loss.

Vasodilation

The widening of blood vessels to increase blood flow, often used to regulate body temperature.

Sinoatrial (SA) Node

The heart's natural pacemaker located in the right atrium that triggers atrial contraction.

Atrioventricular (AV) Node

A node that delays the electrical impulse to ensure atria contract fully before the ventricles begin to contract.

Systolic Blood Pressure

The highest pressure in the arteries during ventricular contraction; typically around 120 \text{ mmHg}.

Diastolic Blood Pressure

The lowest pressure in the arteries during ventricular relaxation; typically around 80 \text{ mmHg}.

Pulmonary Circuit

The pathway of blood circulation between the heart and the lungs.

Systemic Circuit

The circulation of blood from the heart to the rest of the body (excluding the lungs) and back.

Plasma

The liquid portion of the blood that contains water, proteins, gases, nutrients, and wastes.

Red Blood Cells / Erythrocytes

Biconcave discs packed with hemoglobin that transport oxygen; they lack a nucleus and live for about 120 days.

White Blood Cells / Leukocytes

Nucleated cells involved in immune defense, either by engulfing pathogens or producing antibodies.

Platelets

Small, colorless cell fragments in the blood that play a vital role in blood clotting.

Lacteals

Specialized lymph vessels in the small intestine that absorb fats and fat-soluble vitamins.

Spleen

A lymphatic organ that filters blood, removes old red blood cells, and stores lymphocytes.

Oval Opening (Fetal)

An opening between the right and left atria in a fetus that allows blood to bypass the non-functional lungs.