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.