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UNIT B: Human Body Systems Chapter 8: Human Organization Chapter 9: Digestive System Chapter 10: Circulatory System and Lymphatic System: Section 10.1 Chapter 11: Respiratory System Chapter 12: Nervous System Chapter 13: Urinary System Chapter 14: Reproductive System UNIT B Chapter 10: Circulatory System and Lymphatic System Chapter 10: Circulatory System and Lymphatic System In this chapter, you will learn about the structure and function of the circulatory system and lymphatic system. In 2013, Lance Armstrong confessed to long-term blood doping and the use of banned substances. Blood doping involves artificially boosting the blood’s ability to bring more oxygen to muscles. Aerobic capacity and endurance improve where there are additional red blood cells available to carry oxygen. TO PREVIOUS SLIDE What is the composition of blood, including blood cells? What organs and structures control the flow of blood throughout the body? UNIT B Chapter 10: Circulatory System and Lymphatic System Section 10.1 10.1 The Blood Vessels The circulatory system has three types of blood vessels. • Arteries: carry blood away from the heart to the capillaries • Capillaries: permit exchange of material with the tissues • Veins: return blood from the capillaries to the heart All three blood vessel types have an inner endothelium, a simple squamous epithelium attached to a connective tissue basement membrane that has elastic fibres. TO PREVIOUS SLIDE UNIT B Chapter 10: Circulatory System and Lymphatic System Section 10.1 The Arteries The largest artery in the body is the aorta, which carries O2-rich blood from the heart to other parts of the body. The arterial wall has three layers. • Inner layer: endothelium • Middle layer: smooth muscle that contracts and relaxes to regulate blood flow and pressure • Outer layer: fibrous connective tissue TO PREVIOUS SLIDE Figure 10.1 Blood vessels. The walls of arteries and veins have three layers. The inner layer is composed largely of endothelium, with a basement membrane that has elastic fibres; the middle layer is smooth muscle tissue; the outer layer is connective tissue (largely collagen fibres). a. Arteries have a thicker wall than veins because they have a larger middle layer than veins. UNIT B Chapter 10: Circulatory System and Lymphatic System Arterioles are small arteries that branch off from an artery. Arterioles have three layers. • Inner layer: endothelium • Middle layer: some elastic tissue but mostly smooth muscle o Smooth muscle contracts: blood vessel constricts, resulting in higher blood pressure o Smooth muscle relaxes: blood vessel relaxes, resulting in lower blood pressure • Outer layer: fibrous connective tissue TO PREVIOUS SLIDE Section 10.1 UNIT B Chapter 10: Circulatory System and Lymphatic System The Capillaries Capillaries are narrow blood vessels that join arterioles to venules. • Composed of a single layer of epithelium with a basement membrane • Form vast networks (capillary beds) throughout the body TO PREVIOUS SLIDE Section 10.1 UNIT B Chapter 10: Circulatory System and Lymphatic System Section 10.1 • Only certain capillary beds are open at any given time. o After eating, capillary beds that serve the digestive system are open, and those that serve the muscles are mostly closed o Sphincter muscles relax to open the bed and allow blood flow o Sphincter muscles contract to close the bed and prevent blood flow o When the bed is closed, blood flows through anastomoses (arteriovenous shunts) directly from arterioles to venules, bypassing the bed TO PREVIOUS SLIDE UNIT B TO PREVIOUS SLIDE Chapter 10: Circulatory System and Lymphatic System Section 10.1 Figure 10.2 Anatomy of a capillary bed. A capillary bed forms a maze of capillary vessels that lies between an arteriole and a venule. When precapillary sphincter muscles are relaxed, the capillary bed is open, and blood flows through the capillaries. When sphincter muscles are contracted, blood flows through a shunt (anastomosis) that carries blood directly from an arteriole to a venule. As blood passes through a capillary in the tissues, it gives up its oxygen. Therefore, blood goes from being O2-rich in the arteriole (red colour) to being O2-poor in the vein (blue colour). UNIT B Chapter 10: Circulatory System and Lymphatic System Section 10.1 • Exchange of substances takes place across the thin walls of the capillaries. o Oxygen and nutrients diffuse out of the capillary and into the tissue fluid that surrounds cells o Wastes (carbon dioxide) diffuse into the capillary o Some water leaves the capillaries, and excess is picked up by lymphatic vessels TO PREVIOUS SLIDE UNIT B Chapter 10: Circulatory System and Lymphatic System The Veins Veins and venules (small veins) take blood from the capillary beds to the heart. • Veins and venules have the same three layers as arteries, but there is less smooth muscle and connective tissue • Veins have valves, which allow blood to flow toward the heart when open and prevent blood from flowing backward when closed TO PREVIOUS SLIDE Section 10.1 UNIT B Chapter 10: Circulatory System and Lymphatic System Section 10.1 • Veins act as a blood reservoir o Since their walls are thinner, they can expand to a greater extent o About 70% of blood is in the veins • The largest veins in the body are the venae cavae (superior vena cava, inferior vena cava), which deliver O2-poor blood to the heart TO PREVIOUS SLIDE UNIT B TO PREVIOUS SLIDE Chapter 10: Circulatory System and Lymphatic System Section 10.1 Figure 10.1 Blood vessels. The walls of arteries and veins have three layers. The inner layer is composed largely of endothelium, with a basement membrane that has elastic fibres; the middle layer is smooth muscle tissue; the outer layer is connective tissue (largely collagen fibres). a. Arteries have a thicker wall than veins because they have a larger middle layer than veins. b. Capillary walls are one-cell-thick endothelium. c. Veins are generally larger in diameter than arteries, so collectively, veins have a larger holding capacity than arteries. d. Light micrograph of an artery and a vein. UNIT B Chapter 10: Circulatory System and Lymphatic System Check Your Progress 1. Describe how blood flow is controlled in each of the three major types of blood vessels. 2. List several specific substances that diffuse across capillary walls. TO PREVIOUS SLIDE Section 10.1 UNIT B TO PREVIOUS SLIDE Chapter 10: Circulatory System and Lymphatic System Section 10.1