Review of Medical Physiology - William F. Ganong 2002

Circulation
Body Fluids
Introduction

The Circulatory system is a transport system that delivers O₂ and substances absorbed from the gastrointestinal tract to the Tissues, returns CO₂ to the Lungs and other Metabolic waste products to the Kidneys, participates in body Temperature regulation, and distributes Hormones and Other Compounds that regulate Cell function. Blood, serving as the carrier of these substances, is pumped through a closed system of Blood Vessels by The Heart, which in mammals consists of two synchronous pumps. From the left ventricle, blood is pumped through Arteries and arterioles to capillaries, where it equilibrates with the interstitial fluid. Blood flows from the capillaries through venules to Veins and returns to the right atrium; this constitutes the systemic Circulation. From the right atrium, blood moves into the right ventricle, which pumps it through the pulmonary vasculature—the Pulmonary Circulation. In the pulmonary capillaries, the levels of O₂ and CO₂ in the blood and alveolar air are equilibrated. Part of the tissue fluid enters another system of closed vessels, The Lymphatic system, from which Lymph returns via the thoracic and right lymphatic ducts to the Venous system (lymphatic circulation). Fluid circulation is controlled by multiple regulatory systems whose overall function is to ensure adequate Blood flow through the capillaries (wherever possible in all Organs, but especially in The Heart and Brain). This chapter examines BLOOD AND LYMPH, as well as the various Functions of the Cells contained within these fluids.