UNIT B: Human Body Systems

Chapter 8: Human Organization

Chapter 9: Digestive System

Chapter 10: Circulatory System and Lymphatic System: Section 10.4

Chapter 11: Respiratory System

Chapter 12: Nervous System

Chapter 13: Urinary System

Chapter 14: Reproductive 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.

UNIT B Chapter 10: Circulatory System and Lymphatic System

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What is the composition of blood, including blood cells?

What organs and structures control the flow of blood throughout the body?

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.

10.4 The Vascular Pathways

The circulatory system includes two circuits.

•Pulmonary circuit: circulates blood through the lungs

•Systemic circuit: circulates blood to the body tissues

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Section 10.4Chapter 10: Circulatory System and Lymphatic System

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Section 10.4Chapter 10: Circulatory System and Lymphatic System

Figure 10.15 Path of blood. This symbolic and not-to-scale drawing shows the path of blood in the pulmonary and systemic circuits. The pulmonary arteries and veins take blood from the right (blue) to the left (red) side of the heart. Tracing blood from the digestive tract to the right atrium in the systemic circuit involves the hepatic portal vein, the hepatic vein, and the inferior vena cava. The blue-coloured vessels carry O2-poor blood, and the red-coloured vessels carry O2-rich blood; the arrows indicate the direction of blood flow.

The Pulmonary CircuitPulmonary circuit: circulates blood to lungs

•Blood from all regions of the body first collects in the right atrium.

•Blood passes into the right ventricle, which pumps it into the pulmonary trunk.

•Pulmonary trunk divides into right and left pulmonary arteries, which branch into arterioles.

•Arterioles take blood to the pulmonary capillaries, where gas exchange occurs.

•Blood passes through pulmonary venules, which lead to pulmonary veins that enter the left atrium.

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Section 10.4Chapter 10: Circulatory System and Lymphatic System

The Systemic Circuit

Systemic circuit: circulates blood to body tissues.

•The aorta and venae cavae serve as the major pathways for blood in the systemic circuit

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Section 10.4Chapter 10: Circulatory System and Lymphatic System

The path of systemic blood to any organ in the body begins in the left ventricle.

Trace the path of blood to and from the legs:

•left ventricle aorta common iliac artery femoral artery leg capillaries femoral vein common iliac vein inferior vena cava right atrium

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Section 10.4Chapter 10: Circulatory System and Lymphatic System

Figure 10.16 Major arteries (red) and veins (blue) of the systemic circuit. This representation of the major blood vessels of the systemic circuit shows how the systemic arteries and veins are arranged in the body. The superior and inferior venae cavae take their names from their relationship to which organ?

Blood Pressure

As blood passes through the blood vessels in the body, it exerts pressure against the vessel walls (blood pressure).

•Systolic pressure: results from blood being forced into arteries when ventricles contract (ventricular systole)

•Diastolic pressure: results from pressure in the arteries when ventricles fill with blood (ventricular diastole)

o Blood pressure can be measured with a sphygmomanometer, which has a pressure cuff that determines the amount of pressure required to stop the flow of blood through an artery

o Expressed in millimetres of mercury as a fraction of systolic pressure over diastolic pressure (e.g., 120/80 mm Hg)

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Section 10.4Chapter 10: Circulatory System and Lymphatic System

Blood pressure decreases as blood flows from the aorta into the arteries, arterioles, and capillaries.

•Blood is under minimal pressure in capillaries since capillaries have a high total cross-sectional area.

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Section 10.4Chapter 10: Circulatory System and Lymphatic System

Figure 10.17 Blood velocity and blood pressure. In capillaries, blood is under minimal pressure and has the least velocity. Blood pressure and velocity drop off because capillaries have a greater total cross-sectional area than arterioles.

Blood pressure in the veins is low.

•Valves prevent the backward flow of blood in veins, and muscle contraction is sufficient to move blood toward the heart.

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Section 10.4Chapter 10: Circulatory System and Lymphatic System

Figure 10.18 Cross section of a valve in a vein. a. Pressure on the walls of a vein, exerted by skeletal muscles, increases blood pressure within the vein and forces the valve open.

b. When external pressure is no longer applied to the vein, blood pressure decreases, and back pressure forces the valve closed. Closure of the valve prevents the blood from flowing in the opposite direction.

Check Your Progress

1. Identify which arteries carry O2-poor blood.

2. Name the major blood vessels through which blood flows to the lungs and other parts of the body.

3. Describe blood flow in an artery versus a vein.

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Section 10.4Chapter 10: Circulatory System and Lymphatic System

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Section 10.4Chapter 10: Circulatory System and Lymphatic System

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Section 10.4Chapter 10: Circulatory System and Lymphatic System