Circulatory Systems: Pumps, Vessels, and Blood A circulatory system is composed of a pump (heart), fluid (blood), and conduits (blood vessels). This is also called a cardiovascular system.

Every organism must exchange materials with its environment Overview: Trading Places Every organism must exchange materials with its environment Exchanges ultimately occur at the cellular level In unicellular organisms, these exchanges occur directly with the environment 2

Concept 42.1: Circulatory systems link exchange surfaces with cells throughout the body In small and/or thin animals, cells can exchange materials directly with the surrounding medium In most animals, transport systems connect the organs of exchange with the body cells Most complex animals have internal transport systems that circulate fluid 3

Circulatory Systems: Pumps, Vessels, and Blood Some simple aquatic animals do not have circulatory systems. In small animals, nutrients, gases, and wastes can diffuse between the cells and the environment and a circulatory system is not needed. Some aquatic animals have a flat body shape or a highly-branched gastrovascular cavity (cnidaria) to provide maximum surface area for exchange. Larger animals with many cell layers must rely on extracellular tissue fluids to carry materials to and from cells.

Not very efficient -as hemolymph under low pressure Figure 49.1 Open Circulatory Systems Not very efficient -as hemolymph under low pressure -not able to be directed to tissues that may need more oxygen

Figure 49.2 A Closed Circulatory System

Circulatory Systems: Pumps, Vessels, and Blood Closed systems have advantages over open systems: Blood flow, nutrient delivery and waste removal are more rapid. Closed systems can direct the blood to specific tissues. Cellular elements and large molecules that aid in transport can be kept within the vessels. Closed systems generally support higher levels of metabolic activities. Insects are an exception to this rule, but they do not rely on their circulatory systems for gas exchange.

REPTILES (EXCEPT BIRDS) Pulmocutaneous circuit Vertebrate circulatory systems FISHES AMPHIBIANS REPTILES (EXCEPT BIRDS) MAMMALS AND BIRDS Systemic capillaries Lung capillaries Lung and skin capillaries Gill capillaries Right Left Systemic circuit Pulmocutaneous circuit Pulmonary circuit Systemic circulation Vein Atrium (A) Heart: ventricle (V) Artery Gill circulation A V Systemic aorta Right systemic aorta Figure 42.4

Vertebrate Circulatory Systems The four-chambered hearts of birds and mammals completely separate the pulmonary and systemic circuits. The advantages of separate circuits are: Oxygenated and deoxygenated blood cannot mix. Gas exchange is maximized because the lungs receive only blood with low O2 and high CO2 content. The separate circuits can operate at different pressures.

Figure 49.3 The Human Heart and Circulation (Part 2)

The mammalian cardiovascular system Pulmonary vein Right atrium Right ventricle Posterior vena cava Capillaries of abdominal organs and hind limbs Aorta Left ventricle Left atrium artery Capillaries of left lung head and forelimbs Anterior of right lung Figure 42.5 1 10 11 5 4 6 2 9 3 7 8

The heart contracts and relaxes In a rhythmic cycle called the cardiac cycle The contraction, or pumping, phase of the cycle Is called systole The relaxation, or filling, phase of the cycle Is called diastole

The cardiac cycle Figure 42.7 Semilunar valves closed AV valves open AV valves closed Semilunar valves open Atrial and ventricular diastole 1 Atrial systole; ventricular diastole 2 Ventricular systole; atrial diastole 3 0.1 sec 0.3 sec 0.4 sec

The heart rate, also called the pulse, is the number of beats per minute The stroke volume is the amount of blood pumped in a single contraction The cardiac output is the volume of blood pumped into the systemic circulation per minute and depends on both the heart rate and stroke volume 14

Maintaining the Heart’s Rhythmic Beat Some cardiac muscle cells are self-excitable Meaning they contract without any signal from the nervous system. The electrical impulse is then rapidly conducted due to the branching nature of cardiac muscle and the presence of intercalated discs (which have gap junctions to allow rapid flow of charge) The impulses that travel during the cardiac cycle Can be recorded as an electrocardiogram (ECG or EKG) The pacemaker is influenced by Nerves, hormones, body temperature, and exercise The autonomic nervous system controls heart rate by influencing the rate at which pacemaker cells gradually depolarize. Acetylcholine and norepinephrine from the parasympathetic and sympathetic nerve endings slow and increase the rate, respectively

The control of heart rhythm Figure 42.8 SA node (pacemaker) AV node Bundle branches Heart apex Purkinje fibers 2 Signals are delayed at AV node. 1 Pacemaker generates wave of signals to contract. 3 Signals pass to heart apex. 4 Signals spread Throughout ventricles. ECG

Artery Vein SEM 100 µm Valve Basal lamina Endothelium Endothelium Fig. 42-10 Artery Vein SEM 100 µm Valve Basal lamina Endothelium Endothelium Smooth muscle Smooth muscle Connective tissue Connective tissue Capillary Artery Vein Figure 42.10 The structure of blood vessels Arteriole Venule 15 µm Red blood cell Capillary LM 17

Capillaries have thin walls, the endothelium plus its basement membrane, to facilitate the exchange of materials Arteries and veins have an endothelium, smooth muscle, and connective tissue Structural differences in arteries, veins, and capillaries correlate with their different functions Arteries have thicker walls than veins to accommodate the high pressure of blood pumped from the heart 18

All blood vessels Are built of similar tissues Have three similar layers

Figure 49.14 Atherosclerotic Plaque (Part 1)

Figure 49.14 Atherosclerotic Plaque (Part 2)

The Vascular System: Arteries, Capillaries, and Veins If the coronary arteries are affected, blood supply to the heart decreases. A thrombus here (coronary thrombosis) can block an artery, causing a heart attack (myocardial infarction, or MI). If part of the thrombus breaks away (an embolism), lodges in the brain, and blocks blood flow, stroke may occur. The best approach to reducing heart disease is prevention. Risk factors include high-fat/high-cholesterol diets, smoking, a sedentary life style, and obesity.

Blood tends to accumulate in veins Blood tends to accumulate in veins. Veins are called capacitance vessels because of their high capacity to store blood. Direction of blood flow in vein (toward heart) Valve (open) Skeletal muscle Valve (closed) Pressure in veins is very low, Contraction of skeletal muscles pushes blood toward the heart because one-way valves in veins prevent backflow. If veins become stretched, the valves no longer do their job and varicose veins develop.

The Vascular System: Arteries, Capillaries, and Veins During walking or running, the legs act as auxiliary vascular pumps and return blood to the heart from the veins of the lower body. A greater volume of blood is returned to the heart, which stretches the cardiac muscle cells, and the heart contracts more forcefully. This is known as the Frank-Starling law. Breathing also helps return venous blood by creating negative pressure (suction), which pulls blood and lymph toward the chest area. In large veins near the heart, smooth muscles also contract with exercise, increasing venous return and cardiac output.

Physical laws governing the movement of fluids through pipes Influence blood flow and blood pressure The velocity of blood flow varies in the circulatory system And is slowest in the capillary beds as a result of the high resistance and large total cross-sectional area

Blood pressure Is the hydrostatic pressure that blood exerts against the wall of a vessel Systolic pressure Is the pressure in the arteries during ventricular systole Is the highest pressure in the arteries Diastolic pressure Is the pressure in the arteries during diastole Is lower than systolic pressure

Two mechanisms Regulate the distribution of blood in capillary beds In one mechanism Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel

In a second mechanism Precapillary sphincters control the flow of blood between arterioles and venules

Figure 49.12 Starling’s Forces (Part 1)

Figure 49.12 Starling’s Forces (Part 2)

The Vascular System: Arteries, Capillaries, and Veins The medical phenomenon called edema (tissue swelling) in certain diseases, or the inflammation accompanying injury or an allergic reaction, supports this model. However, edema does not occur during strenuous exercise, for example, or in birds, which have higher arteriole pressure and lower osmotic pressure than mammals.

The Vascular System: Arteries, Capillaries, and Veins CO2 and bicarbonate ions (HCO3–) are major factors that pull water back into the capillaries. As blood flows through the capillary, CO2 diffuses into the plasma and is converted into HCO3–. The increasing bicarbonate concentration causes osmotic pressure to be higher at the venous end, especially during exercise. In fact, CO2 and HCO3– are the major factors that pull water back into the capillaries, not colloidal osmotic pressure.

Figure 49.15 The Composition of Blood

Figure 49.16 Blood Clotting (Part 1)

Blood pressure is determined partly by cardiac output And partly by peripheral resistance due to variable constriction of the arterioles

Figure 49.18 Control of Blood Pressure through Vascular Resistance

Control and Regulation of Circulation When atria are receiving too much venous return they release a hormone called atrial natriuretic factor, which stimulates the kidney to excrete sodium and water, resulting in a reduced blood volume.

Figure 49.19 Regulating Blood Pressure

Control and Regulation of Circulation Several adaptations permit the air-breathing seal to remain under water for long periods of time. Seals have greater blood volume, greater blood O2 carrying capacity, and more myoglobin in their muscles than do humans. The diving reflex is the most important adaptation. During a dive, the heart rate slows, and all major blood vessels are constricted except those critical to survival under water. Metabolic rate slows, and tissues switch to glycolytic (anaerobic) metabolism.

Figure 49.20 The Diving Reflex