Download Functions of the Circulatory System

Chapter 33 Summary
Functions of the Circulatory System The circulatory system transports oxygen,
nutrients, and other substances throughout the body, and removes wastes from tissues.
The Heart The muscle layer of the heart is the myocardium. Its powerful contractions pump
blood through the circulatory system. The human heart has four chambers. A wall called the
septum separates the right side of the heart from the left side. On each side of the septum are an
upper and lower chamber.
Each upper chamber, or atrium (plural: atria), receives blood from the body; each lower
chamber, or ventricle, pumps blood out of the heart.
Flaps of connective tissue called valves are located between the atria and the ventricles and
between the ventricles and blood vessels leaving the heart. The valves open and close to keep
blood moving in one direction.
The heart pumps blood through two pathways:
Pulmonary circulation pumps blood from the heart to the lungs and back to the heart again.
Blood picks up oxygen and releases carbon dioxide in the lungs.
Systemic circulation pumps blood from the heart to the rest of the body. Cells absorb much of
the oxygen and load the blood with carbon dioxide.
The heart muscle beats in an orderly and coordinated way. A small group of cardiac muscle fibers,
the sinoatrial node (SA node), is also called the pacemaker. When the pacemaker fires, an electrical
impulse causes the atria to contract. Another group of muscle fibers, the atrioventricular node (AV
node), causes the ventricles to contract. The nervous system influences the SA node, increasing or
decreasing heart rate to meet the body’s needs.
Blood Vessels Blood flows through the circulatory system in blood vessels:
Arteries are large vessels that carry blood away from the heart to the tissues of the body. Except
for the pulmonary arteries, all arteries carry oxygen-rich blood.
Capillaries are the smallest vessels. Their thin walls allow oxygen and nutrients to pass from
blood into tissues and wastes to move from tissues into blood.
Veins return blood to the heart. Many have valves that prevent backflow.
The contractions of the heart produce a wave of fluid pressure in the arteries, known as blood
pressure. Without that pressure, blood would stop flowing through the body. The body regulates
blood pressure through actions of the brain and the kidneys.
Blood Blood has four main components:
Plasma is a straw-colored fluid. It is about 90 percent water and 10 percent dissolved gases, salts,
nutrients, enzymes, hormones, waste products, plasma proteins, cholesterol, and other important
compounds. Parts of plasma help control body temperature, transport substances, and fight
infection. Plasma proteins are involved in blood clotting.
Red blood cells transport oxygen. Blood gets its red color from the iron in hemoglobin, a protein
that binds oxygen in the lungs and releases it in the capillaries.
White blood cells guard against infection, fight parasites, and attack bacteria.
Platelets are cell fragments involved in blood clotting.
The Lymphatic System The lymphatic system is a network of vessels, nodes, and organs that
collects the fluid that leaves the capillaries, “screens” it for microorganisms, and returns it to the
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Chapter 33 Summary
circulatory system.
Lymph is fluid that consists of blood components that have moved through the walls of
capillaries.
Lymph vessels transport materials and lymph nodes act as filters, trapping microorganisms, stray
cancer cells, and debris.
Circulatory System Diseases Three common and serious diseases of the circulatory system
are:
Heart disease: A leading cause of heart disease is atherosclerosis, a condition in which fatty
deposits called plaque build up in artery walls and eventually cause the arteries to stiffen. A heart
attack occurs as heart muscle cells become damaged.
Stroke: A clot that blocks a blood vessel in the brain may cause a stroke, which is the sudden
death of brain cells when their blood supply is interrupted. A stroke can also occur if a weak
vessel breaks and causes bleeding in the brain.
High blood pressure, or hypertension, is usually defined as blood pressure higher than 140/90.
Uncontrolled high blood pressure can damage the heart and blood vessels. It can also lead to
heart attack, stroke, and kidney damage.
Understanding Circulatory Disease Cholesterol is a lipid that is part of animal cell
membranes. It is transported in the blood primarily by two types of lipoproteins: low-density
lipoprotein (LDL) and high-density lipoprotein (HDL). The liver manufactures cholesterol, but it also
comes from animal product foods. High cholesterol levels, along with other risk factors, lead to
atherosclerosis and higher risk of heart attack.
Structures of the Respiratory System For organisms, respiration means the process
of gas exchange between a body and the environment. The human respiratory system picks up
oxygen from the air we inhale and releases carbon dioxide into the air we exhale. The structures of
the respiratory system include the
nose, where air is filtered, moistened, and warmed.
pharynx, or throat, which serves as a passageway for both air and food.
trachea, or windpipe, and the larynx, or vocal cords.
bronchi, two large tubes that lead to the lungs. Each bronchus branches into smaller passageways
called bronchioles that end in tiny air sacs called alveoli within the lungs.
Gas Exchange and Transport Oxygen and carbon dioxide are exchanged across the walls
of alveoli and capillaries. Chemical properties of blood and red blood cells allow for efficient
transport of gases throughout the body.
Carbon dioxide and oxygen are exchanged across capillary and alveolus walls.
Hemoglobin binds with and transports oxygen that diffuses from alveoli to capillaries. It also
increases the efficiency of gas exchange.
Carbon dioxide is transported in the blood in three ways. Most combines with water and forms
carbonic acid. Some dissolves in plasma. Some binds to hemoglobin and proteins in plasma.
Breathing Movements of the diaphragm and rib cage change air pressure in the chest cavity
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Chapter 33 Summary
during inhalation and exhalation.
The dome-shaped muscle at the bottom of the chest cavity is the diaphragm. During inhalation,
contraction of the diaphragm and rib muscles increases chest volume and air rushes in. In
exhalation, these muscles relax and air rushes out.
The nervous system has final control of the breathing muscles. Breathing does not require
conscious control.
Smoking and the Respiratory System Chemicals in tobacco smoke damage structures
throughout the respiratory system and have other negative health effects. Smoking causes a number
of diseases, including chronic bronchitis, emphysema, and lung cancer
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