44.1 Circulatory systems are the transportation highways of the animal body.
Open and Closed Circulatory Systems
• In an open circulatory system, there is no distinction between the circulating fluid and the extracellular fluid of body tissues. In a closed circulatory system, the circulating fluid is always enclosed within blood vessels that transport it away from, and back to, a pump. (p. 908)
• The three principal functions of the vertebrate circulatory system are transportation, regulation, and protection. (pp. 908-909)
Blood
• The fluid portion of blood is plasma, and it contains metabolites, wastes, and hormones, as well as ions and proteins. (p. 910)
• Red blood cells (erythrocytes) function in oxygen transport, white blood cells (leukocytes) function in immunological defenses, and platelets help in blood clotting. (pp. 910-911)
Characteristics of Blood Vessels
• Blood leaves the heart through arteries and returns to the heart in veins. (p. 912)
• As blood passes through capillaries, gases and metabolites are exchanged with interstitial fluids and body cells. (p. 912)
• The lymphatic system returns interstitial fluid (lymph) to the vascular system in an open system. The lymphatic system is composed of lymphatic capillaries, lymphatic vessels, lymph nodes, and lymphatic organs such as the spleen and thymus. (p. 913-914)
44.2 The circulatory and respiratory systems evolved together in vertebrates.
Increasing Body Size Requires Special Circulatory and Respiratory Adaptations
• As animal body size and physiological complexity increase, so does the need for more efficient mechanisms to deliver nutrients and oxygen to the tissues and to remove wastes and carbon dioxide from the tissues. (p. 915)
• The development of gills by fishes required a more efficient pump, and thus a true chamber-pump heart evolved. (p. 915)
• The advent of lungs in reptiles and amphibians results in two circulations: pulmonary circulation between the heart and the lungs, and systemic circulation between the heart and the rest of the body. (p. 916)
• Amphibians can obtain additional oxygen through cutaneous respiration. (p. 916)
• Mammals, birds, and crocodiles have a four-chambered heart with two separate atria and two separate ventricles, and there is no mixing of oxygenated and deoxygenated blood. (pp. 916-917)
44.3 The cardiac cycle drives the cardiovascular system.
The Cardiac Cycle
• The cardiac cycle is composed of two periods: systole (ventricles contract) and diastole (ventricles relax). (p. 918)
• Systolic pressure is the peak pressure during ventricular systole, while diastolic pressure is the minimum pressure between heartbeats. (p. 918)
• The sinoatrial node acts as a pacemaker for the rest of the heart by producing spontaneous depolarizations (reversal of electrical polarity) at a faster rate than other cardiac cells. (p. 919)
• An electrocardiogram records how the cells of the heart depolarize and repolarize during the cardiac cycle. (p. 919)
Blood Flow and Blood Pressure
• Cardiac output refers to the volume of blood pumped by each ventricle per minute, and is calculated by multiplying the heart rate by the stroke volume. (p. 920)
• Blood flow is regulated by artery constriction, and blood pressure is influenced by blood volume. (p. 920)
• Blood volume regulation involves the effects of four hormones: antidiuretic hormone, aldosterone, atrial natriuretic hormone, and nitric oxide. (pp. 920-921)
• Cardiovascular disease, the leading cause of death in the United States, includes such conditions as angina pectoris, strokes, atherosclerosis, and arteriosclerosis. (p. 921)
44.4 Respiration has evolved to maximize the rate of gas diffusion.
How Animals Maximize the Efficiency of Respiration
• Increasing the concentration gradient and surface area and decreasing the distance diffusing gases must travel maximize the exchange of oxygen and carbon dioxide between an organism and its environment. (pp. 923-924)
• The countercurrent flow of blood and water in bony fish maximizes gas exchange. (pp. 925-926)
• Gills were replaced in terrestrial animals because air is less buoyant than water, and water diffuses into the air through evaporation. (p. 926)
• Terrestrial vertebrates take air into saclike lungs that provide a large surface area for gas exchange. (pp. 927)
• The respiration system in birds is highly efficient because it has unidirectional air flow and cross-current blood flow through the lungs. (p. 928-929)
44.5 Mammalian breathing is a dynamic process.
Structures and Mechanisms of Breathing
• When the pressure within the lungs is lower than the atmospheric pressure, air enters the lungs. (p. 930)
• The maximum amount of air that can be expired after a maximum inspiration is the vital capacity. (p. 931)
• Humans breathe in (inspire) by contracting intercostal muscles between the ribs and contracting the diaphragm. They breathe out (expire) by relaxing the intercostal muscles and the diaphragm. (p. 932)
• A proper rate and depth of breathing is required to maintain the blood oxygen and carbon dioxide levels in normal ranges. (p. 932)
Hemoglobin and Gas Transport
• Hemoglobin takes up oxygen in the lungs, forming oxyhemoglobin, which releases oxygen as blood passes through capillaries in the rest of the body, forming deoxyhemoglobin. (p. 934)
• Carbon dioxide is transported in the blood via three methods: dissolved in plasma, bound to hemoglobin, and diffused into red blood cells where carbonic acid is formed (pp. 935-936)