Circulatory System

Hemoglobin

An iron-containing molecule specialized for oxygen transport

Hematocrit

The fraction of red blood cells within the blood of vertebrates

Cooperative Binding

The increase in binding affinity of hemoglobin with additional binding of oxygen

Open Circulatory System

A circulatory system found in many invertebrate animals in which most of the circulatory fluid is contained within the animal’s body cavity

Closed Circulatory System

A circulatory system made up of a set of internal vessels and a heart that functions as a pump to move blood to different regions of the body

Heart

The pump of the circulatory system, which moves blood to different regions of the body

Arteries

Large, high-pressure vessels that move blood flow away from the heart and toward the body tissues and organs

Veins

In animals, a large, low-pressure vessel that returns blood to the heart

Arterioles

A small branch of an artery

Capillaries

A very small blood vessel, arranged in finely branched networks connecting arterioles to venules, where gases, nutrients, and waste products are exchanged by diffusion with surrounding tissues

Venules

A blood vessel into which capillaries drain as blood is returned to the heart

Collagen

A strong protein fiber found in bone, artery walls, tendons, and other connective tissues

Elastin

A protein fiber found in artery walls that provides elasticity

Venae Cavae

Two large veins in the vertebrate body that drain blood from the head and body into the heart

Vasoconstriction

The narrowing of a blood vessel by the contraction of smooth muscle, which in turn increases resistance and decreases blood flow

Vasodilation

The widening of a blood vessel by the relaxation of smooth muscle, which in turn decreases resistance and increases blood flow