AP Biology Animal Form and function Circulatory System

Circulatory System Transports: Oxygen and nutrients to cells Takes away wastes and CO2 from cells Two kinds: Open and Closed

Open Circulatory Systems Open: pump blood into an internal cavity called a hemocoel (or cavities called sinuses) The tissues are bathed with an oxygen- and nutrient-carrying fluid called hemolymph. Found in insects and most mollusks The hemolymph returns to the heart through holes called ostia.

Closed Circulatory Systems Blood is the nutrient- and oxygen-carrying (and waste-carrying) fluid. It is carried inside vessels called arteries and veins. Found in Annelids (segmented worms), mollusks (octopus and squid) and vertebrates

Arteries and Veins Arteries—carry blood away from the heart to the cells Veins—carry blood back towards the heart from the cells Arteries branch into smaller and smaller arterioles until they reach the cellular level as capillaries Coming from capillaries near the cells, the blood moves into larger blood vessels called venules, which eventually merge into veins.

The Heart The heart is the main blood-pumping mechanism of circulatory systems. Hearts have two types of chambers: atriums and ventricles Ventricles are the pumping, muscular parts of the heart

Types of Hearts in Different Vertebrate Animals Amphibians and Reptiles have 3-chambered hearts (2 atrium, and 1 ventricle) Fish—Have 2-chambered hearts (1 atrium, 1 ventricle) Mammals and Birds have 4-chambered hearts (2 atrium, and 2 ventricles)

4-Chambered Hearts of Mammals and Birds

Flow Of Blood in 4-Chambered Hearts 1. Deoxygenated blood enters the right atrium through the vena cava 2. Blood moves through the AV valve (aka tricuspid valve) to the right ventricle 3. The right ventricle pumps the deoxygenated blood to the lungs through the semilunar valve to the pulmonary artery. 4. Blood goes to the lungs and gets oxygenated.

Flow Of Blood in 4-Chambered Hearts 5. Oxygenated Blood then returns to the heart via the pulmonary veins and enters the left atrium 6. Blood passes through the AV valve (aka bicuspid) to the left ventricle. 7. The left ventricle pumps the oxygenated blood out of the heart to the body via the aorta.

Cardiac Cycle (Heart Cycle) The rhythmic contraction and relaxation of heart muscles Regulated by specialized tissues in the heart called autorhythmic cells These cells are self- excitable and able to initiate contractions without external stimulus by nerve cells.

Cardiac Cycle Steps 1. The Sinoatrial node (pacemaker), located in the upper wall of the right atrium, spontaneously initiates the cycle by simultaneously contracting both atria and sending a signal to the atrioventricular node 2. The AV node sends an impulse through the bundle of His, nodal tissue that branches down between both ventricles and then branches into the ventricles through the Purkinje fibers. This impulse contracts the ventricles.

Cardiac Cycle Steps 3. When the ventricles contract (the systole phase), blood is forced through the pulmonary arteries and the aorta. The AV valves are forced to close. When the ventricles relax (the diastole phase), backflow into the ventricles causes the semilunar valves to close.

Blood Pressure Hydrostatic pressure created by the heart forces blood to move through the arteries. As blood reaches the capillaries, blood pressure drops dramatically and approaches zero in the venules. Blood continues to flow in the veins back to the heart, not because of contractions of the heart, but because of the movements of adjacent muscles which squeeze the blood vessels. Valves in the veins prevent backflow.

The Flow of Blood Throughout the entire Circulatory System

The Lymphatic System Some of the wastes and excess interstitial fluids enter the circulatory system when they diffuse into capillaries. The rest of the interstitial fluids and wastes are returned to the circulatory system by way of the lymphatic system, a second network of capillaries and veins.

Lymphatic System Veins The fluid in the lymphatic veins is called lymph. It moves slowly through lymphatic vessels by the contraction of adjacent muscles. Valves in the lymphatic veins prevent backflow. Lymph returns to the blood circulatory system through 2 ducts located in the shoulder region.

Lymphatic System Functions In addition to returning fluids to the circulatory system, the lymphatic system functions as a filter. Lymph nodes, enlarged bodies throughout the lymphatic system, act as cleaning filters and as immune response centers that defend against infection.

Red Blood Cells 1. Red Blood cells (erythrocytes), transport oxygen and catalyze the conversion of CO2 and H2O to H2CO3. Mature red blood cells lack a nucleus, thereby maximizing hemoglobin content and their ability to transport O2.

White Blood Cells White Blood Cells, or leukocytes, consist of five major groups of disease-fighting cells that defend the body against infection.

Platelets and Plasma Platelets are cell fragments that are involved in blood clotting. Platelets release factors that help convert the major clotting agent, fibrinogen into its active form, fibrin. Threads of fibrin protein form a network that stops blood flow. Plasma is the liquid portion of the blood—it contains various dissolved substances.