This program takes a close look at the organs of the human circulatory system and how they work to sustain life. After an introductory overview, the composition of blood—its plasma, erythrocytes, leukocytes, and platelets—is analyzed, blood types and Rh factor are considered, the role of hemoglobin in transporting oxygen is explained, and the anatomy and function of the heart is examined. Factors that affect blood pressure and circulation are also discussed, along with the circulatory demands of exercise. A viewable/printable instructor’s guide is available online. A Films for the Humanities & Sciences Production. A part of the series The Human Body: How It Works. (22 minutes)

The circulatory system functions as a rapid delivery system to bring molecules of oxygen and nutrients close enough to each cell for the diffusion system to work. The heart pumps blood throughout the body.

Blood is a fluid connective tissue that functions to deliver the flow of substances that are critical to life throughout the body. Blood consists of plasma, buffy coat (platelets and leukocytes), and red blood cells. There are 4 blood types: A, B, AB, and O.

Red blood cells are packed with hemoglobin, an iron-containing protein molecule that transports oxygen. Hemoglobin has an affinity for oxygen molecules.

The heart is surrounded by the pericardium. It has four chambers into which blood enters and leaves the heart. Coronary arteries feed the heart itself.

The heart's atria and ventricles contract in coordination with each other. The sinoatrial node sends an electrical pulse that passes to the right and left atria. The atrioventricular bundles stimulate contractions in the ventricles.

Systolic pressure measures pressure of ventricular contraction; diastolic pressure measures pressure of the resting heart. Vocabulary: hypertension, viscosity, plaque, atherosclerosis, and vasodilation.

Blood pressure is lowest in the capillaries to allow for capillary exchange. Filtration occurs when pressure in the capillaries is greater than in the interstitial compartments. Waste products are reabsorbed back into the capillaries.

Exercise demands more oxygen and more blood flow to the coronary arteries and to the exercises muscles and skin. Blood flow must increase during vigorous activity. Venous return is enhanced by an overall increase in blood volume.