Chapter 35 THE CIRCULATORY SYSTEM

Some organisms do not have a circulatory system. Amoeba sea anemone flatworm roundworm

A. Types of Circulatory Systems 1. Open Fluid (hemolymph) is pumped through open-ended vessels, directly bathing body cells. most mollusks arthropods

2. Closed Fluid (blood) is pumped through an extensive network of vessels. annelids some mollusks vertebrates

B. Respiratory Pigments 1. Hemoglobin F iron-containing; red when fully oxygenated F transports 25 times more O 2 than seawater Ex. vertebrates, echinoderms, annelids, some mollusks 2. Hemocyanin F copper-containing; blue when fully oxygenated F transports 3 times more O 2 than seawater Ex. most mollusks & arthropods

C. Vertebrate Circulatory Systems All vertebrate circulatory systems: F are closed F have a highly specialized heart F possess red & white blood cells F use hemoglobin to transport O 2 F are closely associated with respiratory structures (gills, skin, lungs)

1. Fish F 2-chambered heart (1 atrium & 1 ventricle) F blood flows through heart once/circuit

2. Amphibians F 3-chambered heart (2 atria & 1 ventricle) F blood flows through heart twice/circuit F mixing of oxygenated & deoxygenated blood in ventricle Skin / 3. Reptiles F 3-chambered heart [partially divided ventricle] F minimal mixing of oxygenated & deoxygenated blood in ventricle

4. Birds & Mammals F 4-chambered heart (2 atria & 2 ventricles) F blood flows through heart twice/circuit F pulmonary circulation separate from systemic circulation F NO mixing of oxygenated & deoxygenated blood

D. Human Circulatory System Consists of heart, blood vessels & blood. 1. Heart ] Structure Has 4 chambers: F right & left atria (small, thin-walled uppermost chambers) F right & left ventricles (large, thick- walled lowermost chambers)

Right atrium Right ventricle Left atrium Left ventricle Interventricular septum

Has 4 valves: F Tricuspid valve - located between right atrium & right ventricle. F Bicuspid valve - located between left atrium & left ventricle. F Pulmonary semilunar valve - located between right ventricle & pulmonary arteries. F Aortic semilunar valve - located between left ventricle & aorta. Valves ensure a 1-way flow of blood through heart (prevent back-flow).

Right atrium Right ventricle Left atrium Left ventricle Pulmonary arteries Aorta Tricuspid valve Bicuspid valve Pulmonary semilunar valve Aortic semilunar valve Chordae tendinae

] Blood Flow through the Heart Blood enters right atrium via superior vena cava, inferior vena cava & coronary sinus. right atrium  tricuspid valve  right ventricle  pulmonary semilunar valve  pulmonary arteries  LUNGS  pulmonary veins  left atrium  bicuspid valve  left ventricle  aortic semilunar valve  aorta Blood in the aorta is routed to the coronary arteries & body.

] Heartbeat 1 heartbeat [“lub-dup”] = 1 cardiac cycle Each cardiac cycle consists of a synchronized sequence of systole (contraction) & diastole (relaxation). F during atrial systole, blood is forced into the ventricles. F during ventricular systole, blood is forced into the pulmonary arteries & aorta. How is the heart able to generate & coordinate contractions?

Three groups of specialized cardiac muscle cells generate & conduct electrical signals. F SA node - located in upper right atrial wall; sets tempo (pacemaker). F AV node - located in lower right atrial wall; picks up signal from SA node & passes to Purkinje fibers. F Purkinje fibers - located in wall of ventricles. Intercalated disks enable groups of cardiac muscle cells to contract in unison.

2. Blood Vessels ] Arteries - vessels that transport blood away from the heart. ] Veins - vessels that transport blood toward the heart. Artery walls are thicker & more elastic; usually transport oxygenated blood. Veins have valves; usually transport deoxygenated blood.

] Arterioles - tiny arteries that help regulate blood pressure. - if arterioles constrict (vasoconstriction), blood pressure . - if arterioles dilate (vasodilation), blood pressure . ] Venules - tiny veins; do not have valves. ] Capillaries - vessels consisting of a single layer of cells; sites of gas, waste & nutrient exchange.

Direction of blood flow in vessels: Arteries  Arterioles  Capillaries  Venules  Veins

Blood Pressure Force that blood exerts against the wall of a blood vessel. Avg. BP in young adult = 120/80 F upper value (systolic pressure) is force during ventricular systole. F lower value (diastolic pressure) is force during ventricular diastole. Blood pressure is measured using a sphygmomanometer.

Blood pressure continually drops as it travels away from the left ventricle. Which type of vessel carries blood under greatest pressure? Which type of vessel carries blood under least pressure?

Autonomic nervous system regulates blood pressure. F Sympathetic division  BP - constricts arterioles - increases heart rate F Parasympathetic division  BP - slows heart rate

3. Blood Composed of plasma (liquid) & formed elements (RBCs, WBCs & platelets).

] RBCs (erythrocytes) F most numerous formed element F biconcave shape F produced in bone marrow RBC F lose nucleus when enter bloodstream (live ~ 120 days) F packed with hemoglobin F function to transport O 2 Most CO 2 is transported as bicarbonate ion (HCO 3 - ) in plasma.

] WBCs (leukocytes) F least numerous formed element F produced in bone marrow F retain nucleus (live ~ 1 year) F leave bloodstream & travel through tissues F 5 major types F function to defend against infection or injury & to destroy cancer cells

] Platelets F more numerous than WBCs, but less numerous than RBCs F produced in bone marrow from megakaryocytes F cell fragments (live ~ 1 week) F function to initiate blood clotting Vertebrates other than mammal have thrombocytes rather than platelets.

Blood Clotting  Blood vessel is damaged  Vessel constricts  Platelets are activated (adhere to damaged cells & to each other)

 Platelet plug forms  Damaged cells release thromboplastin (protein)  initiates a biochemical cascade

E. Circulatory System Disorders ] Anemia ] Leukemia ] Hemophilia ] Hypertension / Hypotension ] Aneurysm ] Atherosclerosis ] Thrombus / Embolus ] Heart attack / Stroke ] Arrhythmia

F. Lymphatic System One-way transport system consisting of lymph vessels & lymph nodes. Functions to collect, filter & return fluid to the bloodstream. Fluid constantly seeps out of blood capillaries & into surrounding tissues. This interstitial fluid is picked up by dead-end lymphatic capillaries. Lymph

Lymph travels from: lymph capillaries  lymph vessels & nodes  right & left subclavian veins Superior vena cava Lymph vessels ] possess valves Lymph nodes ] structures packed with WBCs Lymph node