The Circulatory System

Functions of the Circulatory System

• Stabilizes body temperature and pH to maintain homeostasis

• An organ system which distributes blood throughout the entire body– Transports oxygen to body cells– Transports CO2 away from cells– Transportation of hormones– Transportation of immune system components

Contains 3 Major Parts

• The Heart

• Blood Vessels

• Blood

The Heart

The Heart as a Double Pump

• The heart is a double pump, simultaneously pumping blood to and from body cells through the systemic circulation and to and from the lungs in the pulmonary circulation

Parts of the Heart

• The atria– Receiving chambers

• The ventricles– Pumping chambers

• Valves: two atrioventricular and two semilunar valves– Control one-way flow

• The interventricular septum– Separates right and left ventricles

Blood Vessels

Types of Blood Vessels• Arteries

– Carry blood away from the heart– Aorta is the largest artery

• Veins– Carry blood to the heart– Contain valves– Vena cava is the largest vein

• Capillaries– Site of exchange of nutrients, wastes, and gases between

blood and interstitial fluid (fluid surrounding tissue cells)

Walls of Arteries and Veins• Tunica externa

– Outermost layer– Composed of mainly elastic and collagen fibers– Strengthens, Anchors

• Tunica media– Middle layer– Composed of elastic and smooth muscle fibers– Circular Smooth Muscle– Vaso-constriction/dilation

• Tunica interna– Innermost layer– Endothelium– Minimize friction

• Lumen

Blood

Functions of the Blood

• Carries oxygen from the lungs to all of the cells in the body

• Carries carbon dioxide from the body cells to the lungs to be exhaled

• Carries waste to the kidneys to be disposed of • Carries nutrients to body cells• Contains immune system cells and molecules that

help fight infection

Components of Blood

• Plasma– Comprise 55% of

whole blood volume

• Formed Elements– Comprise 45% of

whole blood volume

Plasma

• 91% water

• Contains dissolved proteins, glucose, clotting factors, mineral ions, hormones and carbon dioxide

Formed Elements

• Red Blood Cells (Erythrocytes or RBCs)– Contain a large molecule called hemoglobin used to

transport oxygen and carbon dioxide

• White blood cells (Leukocytes or WBCs)– Cells of the immune system defending the body against

both infectious disease and foreign materials

• Platelets (Thrombocytes)– Special cell fragments that protect the body by forming

a platelet plug to stop bleeding by ruptured vessels– Secrete chemicals that aid in blood clotting