Circulatory and Respiratory Systems

Circulatory and Respiratory Systems
This scanning electron micrograph shows individual red and white blood cells flowing through a vein (magnification 3850×)

Circulatory and Respiratory Systems

The Circulatory System
Your heartbeat is a sign of life itself Even when you drift off to sleep, your heart continues to beat at a steady rhythm Why is this process so important that it must keep going even when you sleep?

The Circulatory System
Each breath you take brings air into your respiratory system The oxygen in that air is needed by the trillions of cells in your body Your heart is essential in delivering that oxygen Its beating produces the force to move oxygen-rich blood through the circulatory system Interrelationships between the circulatory and respiratory systems supply cells throughout the body with the nutrients and oxygen they need to stay alive

Functions of the Circulatory System
Organisms composed of a small number of cells do not need a circulatory system Most cells in such organisms are in direct contact with the environment Oxygen, nutrients, and waste products can easily diffuse back and forth across cell membranes

Larger organisms, however, cannot rely on diffusion Most of their cells are not in direct contact with the environment, and substances made in one part of the organism may be needed in another part In a way, this same problem is faced by the millions of people living in a large city Cities have transportation systems that move people, goods, and waste material from one place to another The transportation system of a city is its streets, highways, and rail lines The transportation system of a living organism is its circulatory system

CIRCULATORY SYSTEM Consist of the heart, blood vessels, and blood
Transports gases, nutrients, hormones, and waste products throughout the body

Humans and other vertebrates have closed circulatory systems This means that a circulating fluid called blood is contained within a system of vessels The human circulatory system consists of the heart, a series of blood vessels, and the blood that flows through them

HEART Muscular organ that pumps blood throughout the body
Average heart rate is 70 beats per minute The beating noise is the opening and closing of the valves Four chambers (2 atria/2ventricles)

The Heart As you can feel with your hand, your heart is located near the center of your chest The heart, which is composed almost entirely of muscle, is a hollow organ that is about the size of your clenched fist The heart is enclosed in a protective sac of tissue called the pericardium In the walls of the heart, there are two thin layers of epithelial and connective tissue that form a sandwich around a thick layer of muscle called the myocardium The powerful contractions of the myocardium pump blood through the circulatory system

HEART STRUCTURE Pericardium: saclike membrane that surrounds the heart and secretes a fluid that reduces friction as the heart beats Septum: divides the heart lengthwise into two pumps (right pumps deoxygenated blood to the lungs and the left pumps oxygenated blood to the body) Atrium: thin walled upper chamber (receives blood) Ventricle: thick walled lower chamber (pumps blood) (Which side is the thickest ?) Blood moves from the atrium to the ventricle One way valves (a-v valve) separate the atria and ventricles tricuspid valve: right side bicuspid valve: left side pulmonary semilunar valve: exit of right ventricle aortic semilunar valve: exit of left ventricle

The Heart The heart muscle contracts on average 72 times a minute, pumping about 70 milliliters of blood with each contraction This means that during one year, an average person's heart pumps more than enough blood to fill an Olympic-sized swimming pool An Olympic-sized swimming pool is about 2,000,000 liters: 0.07 liters × 4320 beats per hour × 24 hours × 365 days = 2,649,024 liters

The Heart Dividing the right side of the heart from the left side of the heart is the septum The septum prevents the mixing of oxygen-poor and oxygen-rich blood On each side of the septum are two chambers The upper chamber, which receives the blood, is the atrium (plural: atria) The lower chamber, which pumps blood out of the heart, is the ventricle The heart has four chambers—two atria and two ventricles

Circulation Through the Body
The heart functions as two separate pumps The figure shows the circulation of blood through the body The right side of the heart pumps blood from the heart to the lungs This pathway is known as pulmonary circulation In the lungs, carbon dioxide leaves the blood and oxygen is absorbed The oxygen-rich blood then flows into the left side of the heart and is pumped to the rest of the body This pathway is called systemic circulation Blood that returns to the right side of the heart is oxygen-poor because cells have absorbed much of the oxygen and loaded the blood with carbon dioxide At this point, it is ready for another trip to the lungs

Circulatory Pathways The circulatory system is divided into two pathways Pulmonary circulation carries blood between the heart and the lungs Systemic circulation carries blood between the heart and the rest of the body Diagrams use red to show oxygen-rich blood, and blue to show oxygen-poor blood What kind of blood—oxygen-rich or oxygen-poor—leaves the lungs and returns to the heart?

Circulatory Pathways

CIRCULATION PATTERNS Pulmonary Circulation
movement of deoxygenated blood from the heart (right ventricle) to the lungs by means of the pulmonary artery blood will become oxygenated in the lungs oxygenated blood returns to the heart (left atrium) by means of the pulmonary vein

CIRCULATION PATTERNS Systemic Circulation
Movement of oxygenated blood from the heart (left ventricle) to the aorta and all regions of the body by means of the major arteries Deoxygenated blood returns to the heart (right atrium) by means of the superior/inferior vena cava Subsystems: Coronary: penetrates tissues of the heart Renal: penetrates tissues of the kidneys Hepatic portal: penetrates tissues of the liver

Circulation Through the Heart
Blood enters the heart through the right and left atria, as shown in the figure As the heart contracts, blood flows into the ventricles and then out from the ventricles to either the body or the lungs There are flaps of connective tissue called valves between the atria and the ventricles Blood moving from the atria holds the valves open When the ventricles contract, the valves close, which prevents blood from flowing back into the atria

Structures of the Heart
The circulatory system consists of the heart, a series of blood vessels, and the blood Notice the valves between the atria and ventricles and those between the ventricles and the blood vessels leaving the heart The valves prevent blood from flowing backward

Structures of the Heart

Circulation Through the Heart
At the exits from the right and left ventricles, there are valves that prevent blood that flows out of the heart from flowing back in This system of valves keeps blood moving through the heart in one direction, like traffic on a one-way street The one-way flow increases the pumping efficiency of the heart The valves are so important to heart function that surgeons often attempt to repair or replace a valve that has been damaged due to disease

Heartbeat There are two networks of muscle fibers in the heart, one in the atria and one in the ventricles When a single fiber in either network is stimulated, all the fibers are stimulated and the network contracts as a unit Each contraction begins in a small group of cardiac muscle cells—the sinoatrial node—located in the right atrium Because these cells “set the pace” for the heart as a whole by starting the wave of muscle contraction through the heart, they are also called the pacemaker

HEARTBEAT RATE Controlled by the pacemaker (sinoatrial node: s-a node)
Located in the right atrium Generates electrical impulse which is sent to the atrioventricular node (a-v node) located in the septum between the atria which delays the impulse about a millisecond and then sends it into the ventricles Two nerves connect to the pacemaker One increases the rate and the other decreases the rate

Heartbeat As shown in the figure, the impulse spreads from the pacemaker (SA node) to the network of fibers in the atria It is picked up by a bundle of fibers called the atrioventricular node and carried to the network of fibers in the ventricles When the network in the atria contracts, blood in the atria flows into the ventricles When the muscles in the ventricles contract, blood flows out of the heart This two-step pattern of contraction makes the heart a more efficient pump

The Heartbeat The signal to contract spreads from the sinoatrial node to the cardiac muscle cells of the atria, causing the atria to contract The impulse is picked up by the atrioventricular node, which transmits the impulse to muscle fibers in the ventricles, causing the ventricles to contract In times of stress, does the heart beat faster or slower?

The Heartbeat

Heartbeat Your heart can beat faster or more slowly, depending on your body's need for oxygen-rich blood During vigorous exercise, your heart rate may increase to about 200 beats per minute Although the heartbeat is not directly controlled by the nervous system, the autonomic nervous system does influence heart rate Neurotransmitters released by the sympathetic nervous system increase heart rate Those released by the parasympathetic nervous system decrease heart rate

Blood Vessels Blood leaving the left side of the heart is loaded with oxygen from the lungs When it leaves the left ventricle, the blood passes into a large blood vessel known as the aorta The aorta is the first of a series of blood vessels that carry the blood on its round trip through the body and back to the heart As blood flows through the circulatory system, it moves through three types of blood vessels—arteries, capillaries, and veins

BLOOD VESSELS Direction of blood flow: artery to arteriole to capillary to venule to vein Artery: blood vessel that carries blood away from the heart Vein: blood vessel that carries blood to the heart Arterioles: smaller arteries Venules: smaller veins Capillaries: Connect arterioles and venules Thickness: single cell Location of exchange between blood and body tissue

Blood Vessels In the circulatory system, there are three types of blood vessels—arteries, capillaries, and veins The walls of these vessels contain connective tissue, smooth muscle, and endothelium

Blood Vessels

Arteries Large vessels that carry blood from the heart to the tissues of the body are called arteries Arteries are the superhighways of the circulatory system Except for the pulmonary arteries, all arteries carry oxygen-rich blood Arteries have thick walls that help them withstand the powerful pressure produced when the heart contracts and pushes blood into the arteries The figure shows that the walls contain connective tissue, smooth muscle, and endothelium The elastic connective tissue allows an artery to expand under pressure Contractions of the smooth muscle regulate the diameter of an artery

ARTERY Same number of tissue layers as veins but thicker and more elastic Blood under high pressure since it is coming from the heart Tend to be deeper in the body Arteriosclerosis: disease in which the artery walls become less elastic (blood pressure increases)

Capillaries The smallest of the blood vessels are the capillaries
Capillaries are the side streets and alleys of the circulatory system The walls of capillaries are only one cell thick, and most are so narrow that blood cells must pass through them in single file The real work of the circulatory system—bringing nutrients and oxygen to the tissues and absorbing carbon dioxide and other waste products from them—is done in the capillaries

CAPILLARY Wall consists of only a single layer of cells
Small molecules easily diffuse through this thin wall Location of the exchange between blood and body tissues

Veins Once blood has passed through the capillary system, it must be returned to the heart This is the job of the veins As with arteries, the walls of veins contain connective tissue and smooth muscle Large veins, such as those shown in the leg in the figure below, contain valves that keep blood moving toward the heart Many veins are located near and between skeletal muscles When you exercise, contracting these muscles helps force blood through the veins Blood flow through the veins of the arms and legs often occurs against the force of gravity Exercise helps to keep blood from accumulating in the limbs and stretching the veins out of shape If the walls around the veins weaken from lack of activity, the valves can weaken This causes blood to pool in the veins, producing a condition known as varicose veins

VEIN Under very low pressure
Contain valves that regulate the direction of blood flow (every few cm) toward the heart Close if blood moves backwards Separation of valves can result in varicose veins

Blood Vessels Veins: Contraction of skeletal muscles helps move blood in veins toward the heart.

Blood Vessels

ARTERY BLOOD PRESSURE Pressure results from the force the heart applies to the blood at any given time Pressure is the highest in arteries when the ventricles contract (Systole) Pressure is the lowest in arteries when the ventricles relax (Diastole) Expressed as a fraction (120/80) Systole/diastole phases create the characteristic “lubb dup” we call a heartbeat (opening/closing of valves)

HYPERTENSION High blood pressure
Many different causes (e.g. arteriosclerosis) Blood vessels can burst (e.g. capillaries) Can result in kidney damage, heart attack, and even death

Blood Pressure Like any pump, the heart produces pressure
When the heart contracts, it produces a wave of fluid pressure in the arteries The force of the blood on the arteries' walls is known as blood pressure Blood pressure decreases when the heart relaxes, but the system still remains under pressure It's a good thing, too Without that pressure, blood would stop flowing through the body

Blood Pressure Medical workers can measure blood pressure with a device called a sphygmomanometer A cuff is wrapped around the upper arm Air is pumped into the cuff until blood flow through an artery is blocked As the pressure is released, the worker listens to the pulse with a stethoscope and records two numbers from a pressure gauge The first number is the systolic pressure—the force felt in the arteries when the ventricles contract The second number is the diastolic pressure—the force of the blood felt in the arteries when the ventricles relax A typical blood pressure reading for a healthy person is 120/80

Blood Pressure The body normally regulates blood pressure in two ways
1.Sensory receptors at several places in the body detect the level of blood pressure, sending impulses to the medulla oblongata region of the brain stem When blood pressure is too high, the autonomic nervous system releases neurotransmitters that cause the smooth muscles in blood vessel walls to relax, lowering blood pressure When blood pressure is too low, neurotransmitters are released that elevate blood pressure by causing these smooth muscles to contract

Blood Pressure 2.The kidneys, which remove water from the blood, also help to regulate blood pressure Hormones produced by the heart and other organs cause the kidneys to remove more water from the blood when blood pressure is high This action reduces blood volume, thereby lowering the blood pressure

Diseases of the Circulatory System
Unfortunately, diseases of the circulatory system are all too common Cardiovascular diseases—especially heart disease and stroke—are among the leading causes of death and disability in the United States High blood pressure and a condition known as atherosclerosis are two of the main causes of cardiovascular disease Atherosclerosis is a condition in which fatty deposits called plaque build up on the inner walls of the arteries

High Blood Pressure If blood pressure is too high, medical problems may result High blood pressure, or hypertension, forces the heart to work harder, which may weaken or damage the heart muscle and blood vessels People with high blood pressure are more likely to develop coronary heart disease and to suffer from other diseases of the circulatory system Hypertension increases the risk of heart attack and stroke

Consequences of Atherosclerosis
Atherosclerosis is particularly dangerous in the coronary arteries, which bring oxygen and nutrients to the heart muscle itself If one of these arteries becomes blocked, part of the heart muscle may begin to die from a lack of oxygen If enough heart muscle is damaged, a condition known as a heart attack occurs

The symptoms of a heart attack include nausea, shortness of breath, and severe, crushing chest pain People who show these symptoms need immediate medical attention New drugs are available that can increase blood flow enough to save the heart, but they must be given in the early stages of a heart attack to save the heart muscle and prevent death

Blood clots that can form as a result of atherosclerosis may break free and get stuck in one of the blood vessels leading to a part of the brain This condition is known as a stroke Brain cells served by the particular blood vessel gradually die from a lack of oxygen, and brain function in that region may be lost Depending on what part of the brain they affect, strokes may cause paralysis, loss of the ability to speak, and death

Circulatory System Health
Like other diseases, cardiovascular diseases are easier to prevent than to cure Some of the ways of avoiding cardiovascular disease include getting regular exercise, eating a balanced diet, and avoiding smoking Exercise makes your heart muscle stronger and more efficient It also helps control your weight, reduces body fat, and reduces stress

Circulatory System Health
A diet low in saturated fat and cholesterol can reduce your risk of developing heart disease as well High levels of fat and cholesterol in the blood increase the likelihood that it will be deposited onto the artery walls This process begins in childhood and worsens as you get older For this reason, you should limit your intake of foods with saturated fat A low-fat diet will also help control your weight Being overweight enlarges the circulatory system, causing the heart to pump harder to force blood through it The cardiovascular system is also damaged by smoking You will learn more about the effects of smoking later in this chapter A timeline of some advances in cardiovascular medicine is shown in the chart

Cardiovascular Advances

BLOOD Liquid connective tissue
Transport medium of the circulatory system Composed of a liquid called plasma (55%) and blood solids (45%) Erythrocytes: red blood cells (RBC) Leukocytes: white blood cells (WBC) Platelets: blood clotting

Blood and the Lymphatic System
Just as a plumbing system carries water through a series of pipes to different parts of a house, the circulatory system carries blood through a series of blood vessels to different parts of the body Blood is a type of connective tissue containing both dissolved substances and specialized cells Blood collects oxygen from the lungs, nutrients from the digestive tract, and waste products from tissues Blood helps to regulate factors in the body's internal environment, such as body temperature In addition, components in blood help to fight infections Blood can even form clots to repair damaged blood vessels

Blood Plasma The human body contains 4 to 6 liters of blood, which is about 8 percent of the total mass of the body As the figure shows, about 45 percent of the volume of blood consists of cells, which are suspended in the other 55 percent—a straw-colored fluid called plasma Plasma is about 90 percent water and 10 percent dissolved gases, salts, nutrients, enzymes, hormones, waste products, and proteins called plasma proteins

PLASMA Clear golden fluid
90% water Cells receive nourishment from dissolved substances carried in the plasma Vitamins Minerals Amino acids Glucose Additional substances transported Hormones Waste (urea) Proteins (antibodies/fibrinogen)

Blood Plasma Plasma proteins, which perform a variety of functions, are divided into three groups: Albumins: Transports substances such as fatty acids, hormones, and vitamins Helps to regulate osmotic pressure and blood volume Globulins: Transport substances such as fatty acids, hormones, and vitamins Some globulins fight viral and bacterial infections Fibrinogen: Fibrinogen is the protein responsible for the ability of blood to clot

Blood Composition Blood consists of plasma, blood cells, nutrients, hormones, waste products, and plasma proteins When a whole blood sample is placed in a centrifuge, as shown, what is the result?

Blood Composition

Blood Cells The cellular portion of blood consists of red blood cells, white blood cells, and platelets Red blood cells transport oxygen White blood cells perform a variety of protective functions Platelets: Help in the clotting process Are actually fragments of cells derived from larger cells in bone marrow

ERYTHROCYTES Red blood corpuscles Formed in the red marrow of bones
Contains hemoglobin (iron containing protein) in the cytoplasm which combines readily with oxygen which it transports to the body cells 4.5 to 5.5 million per cubic millimeter of blood During formation nuclei and organelles disintegrate Life expectancy is usually 120 to 130 days 2 million disintegrate every second Remains removed by liver and spleen

Red Blood Cells The most numerous cells in the blood are the red blood cells, or erythrocytes One milliliter of blood contains about 5 million red blood cells Red blood cells transport oxygen They get their color from hemoglobin Hemoglobin is the iron-containing protein that binds to oxygen in the lungs and transports it to tissues throughout the body where the oxygen is released

Red Blood Cells Red blood cells are shaped like disks that are thinner in the center than along the edges These cells are produced from cells in red bone marrow As these cells gradually become filled with hemoglobin, their nuclei and other organelles are forced out Thus, mature red blood cells do not have nuclei Red blood cells circulate for an average of 120 days before they are worn out from squeezing through narrow capillaries Old red blood cells are destroyed in the liver and spleen

BLOOD TYPES Protein (antigen) on surface of RBC Two types: A and B
Results in four different blood types Type A: RBC has antigen A Type B: RBC has antigen B Type AB: RBC has antigen A and B Type 0: RBC has no antigen

Rh FACTOR An additional antigen can be associated with the membrane of the RBC Antigen present (Rh+) Antigen lacking (Rh-) Can be a problem in a pregnant female

LEUKOCYTES White blood cells
5,000 to 9,000 per cubic millimeter of blood Produced in red bone marrow, lymph nodes, and the spleen Larger than RBC Function for years (live longer than RBC) Can leave the blood through capillaries Protect the body against infection (increase in numbers during infections) Different types: Phagocytes: engulf microorganisms Lymphocytes: produce antibodies

White Blood Cells White blood cells, or leukocytes, do not contain hemoglobin They are much less common than red cells, which outnumber them almost 1000 to 1 Both white and red blood cells are produced from the same population of blood-forming stem cells found in the bone marrow Unlike red blood cells, however, white blood cells contain nuclei They may live for days, months, or even years

White Blood Cells White blood cells are the “army” of the circulatory system—they guard against infection, fight parasites, and attack bacteria There are many types of white blood cells, and they perform a wide variety of important functions Some protect the body by acting as phagocyte, or “eating cells,” that engulf and digest bacteria and other disease-causing microorganisms Some white blood cells react to foreign substances by releasing chemicals known as histamines These chemicals increase blood flow into the affected area, producing redness and swelling that are often associated with allergies A special class of white blood cells, known as lymphocytes, produce antibodies that are proteins that help destroy pathogens Antibodies are essential to fighting infection and help to produce immunity to many diseases

White Blood Cells White blood cells are not confined to the circulatory system. Many white blood cells are able to slip out of capillary walls, travel through the lymphatic system, and attack invading organisms in the tissues of the body. In many ways, white blood cells are the first lines of defense when the body is invaded by disease-causing organisms, making them part of the immune system as well

White Blood Cells Like an army with units in reserve, the body is able to increase the number of white blood cells dramatically when a “battle” is underway A sudden increase in the white blood cell count is one of the ways in which physicians can tell that the body is fighting a serious infection

PLATELETS Also called Thrombocytes
Are not whole cells but merely fragments of very large cells with several nuclei that were formed in the marrow Lack a nucleus and have a life span of 7 to 11 days 250,000 to 500,000 per cubic millimeter Essential in the formation of a blood clot

BLOOD CLOTTING When a blood vessel is damaged:
Platelets break apart releasing a chemical that converts a plasma protein (prothrombin) into an enzyme called thrombin Thrombin causes changes in another blood protein (fibrinogen) Thrombin and fibrinogen join together creating a long, threadlike molecule called fibrin Blood cells are tangled in the mesh Clot forms

Platelets and Blood Clotting
Blood is essential to life An injury can cause the body to lose this essential fluid Fortunately, blood has an internal mechanism to slow bleeding and begin healing A minor cut or scrape may bleed for a few seconds or minutes, but then it stops Clean it up with soap and water, cover it with a bandage, and it begins to heal Have you ever wondered why the bleeding stops?

The answer is that blood has the ability to form a clot The figure at right summarizes the process Blood clotting is made possible by plasma proteins and cell fragments called platelets There are certain large cells in bone marrow that can break into thousands of small pieces Each fragment of cytoplasm is enclosed in a piece of cell membrane and released into the bloodstream as a platelet

Blood Clotting Blood clotting is made possible by a number of plasma proteins and cell fragments called platelets Calcium and vitamin K aid in converting prothrombin into thrombin

Blood Clotting

When platelets come into contact with the edges of a broken blood vessel, their surfaces become very sticky, and a cluster of platelets develops around the wound These platelets then release proteins called clotting factors The clotting factors start a series of chemical reactions that are quite complicated In one reaction, a clotting factor called thromboplastin converts prothrombin, which is found in blood plasma, into thrombin Thrombin is an enzyme that helps convert the soluble plasma protein fibrinogen into a sticky mesh of fibrin filaments These filaments stop the bleeding by producing a clot The figure shows the tangle of microscopic fibers in an actual blood clot

Formation of a Blood Clot
Strands of fibrin trap blood cells, forming a net that prevents blood from leaving a damaged blood vessel.

Formation of a Blood Clot

Blood Clotting Problems
If the wound is small, within a few minutes the mesh of platelets and fibrin seals the wound, and bleeding stops Most of the time, this clotting reaction works so well that we take it for granted However, if one of the clotting factors is missing or defective, the clotting process does not work well Hemophilia is a genetic disorder that results from a defective protein in the clotting pathway People with hemophilia cannot produce blood clots that are firm enough to stop even minor bleeding They must take great care to avoid injury Fortunately, hemophilia can be treated by injecting extracts containing the missing clotting factor

Predicting the Success of Blood Transfusions
Although the first successful transfusions of human blood were carried out in the 1820s, many recipients had severe reactions to the transfused blood, and several died Today we know why We inherit one of four blood types—A, B, AB, or O—which are determined by antigens on our blood cells Antigens are substances that trigger an immune response People with blood type A have A antigens on their cells, those with type B have B antigens, those with AB blood have both A and B, and those with type O have neither A nor B antigens

BLOOD TYPES Protein (antigen) on surface of RBC Two types: A and B
Results in four different blood types Type A: RBC has antigen A Type B: RBC has antigen B Type AB: RBC has antigen A and B Type 0: RBC has no antigen

When blood types match, the transfusion is successful However, transfusions are successful in some cases even when the blood types of the donor and the recipient do not match

Drawing Conclusions: Which blood type is sometimes referred to as the “universal donor”? Which is known as the “universal recipient”?

Drawing Conclusions: In a transfusion involving the A and O blood types, does it make a difference which blood type belongs to the recipient and which to the donor?

Applying Concepts: Write a brief explanation for the results in the chart using information about phenotypes and genotypes in blood group genes (Hint: Review Section 14-1 if needed.)

Blood Transfusions

LYMPHATIC SYSTEM Tissue fluid (water, plasma protein, white blood cells, and molecules that have diffused from capillaries) Fluid through which many materials pass between the blood and body cells Network of vessels that returns tissue fluid to the blood circulation Thin walls Tissue fluid in the lymphatic vessels is called lymph Has no pump Skeletal muscles help squeeze the fluid One-way valves to help move fluid upwards Lymph transported to two large ducts (right lymphatic duct and thoracic duct) which empty into large veins in the upper chest near the heart Involved in the absorption of fat in villi of small intestine Lymph nodes: swellings in lymph vessels Concentrated in the neck, armpits, inner elbow, and groin Filters the lymph as it passes, catching foreign particles, microorganisms, and other tissue debris Produces lymphocytes

The Lymphatic System As blood circulates, some fluid leaks from the blood into the surrounding tissues This isn't an altogether bad thing A steady flow of fluid helps to maintain an efficient movement of nutrients and salts from the blood into the tissues However, more than 3 liters of fluid leak from the circulatory system into surrounding tissues every day! If this leakage continued unchecked, the body would begin to swell with fluid—not a very pleasant prospect

The Lymphatic System Fortunately, the interrelationship between two body systems does not allow this to happen A network of vessels, nodes, and organs called the lymphatic system collects the fluid that is lost by the blood and returns it back to the circulatory system The fluid is known as lymph Lymph collects in lymphatic capillaries and slowly flows into larger and larger lymph vessels Like large veins, lymph vessels contain valves that prevent lymph from flowing backward Ducts collect the lymph and return it to the circulatory system through two openings in the superior vena cava The openings are under the left and right clavicle bones just below the shoulders The figure at right shows the lymphatic system

The Lymphatic System The lymphatic system collects and returns fluid that leaks from blood vessels The spleen is an organ whose main function is to destroy damaged red blood cells and platelets Certain white blood cells called T cells mature in the thymus gland, which produces hormones that promote their development

The Lymphatic System

The Lymphatic System Along the length of the lymph vessels are small bean-shaped enlargements called lymph nodes Lymph nodes act as filters, trapping bacteria and other microorganisms that cause disease When large numbers of microorganisms are trapped in the lymph nodes, the nodes become enlarged If you have ever had “swollen glands,” you actually had swollen lymph nodes

The Lymphatic System Lymph vessels do not merely return excess fluid to the circulation They also play a very important role in nutrient absorption Lymph vessels lie near the cells that line the intestines, where they absorb fats and fat-soluble vitamins from the digestive tract and carry them to the blood Lymph moves through the lymphatic system under osmotic pressure from the blood and is pushed along by the contractions of nearby skeletal muscles It is important that there is a steady flow of lymph Edema, a swelling of the tissues due to the accumulation of excess fluid, can occur when lymphatic vessels are blocked due to injury or disease

The Lymphatic System In addition to the lymph vessels and lymph nodes, the thymus and spleen also have important roles in the lymphatic system The thymus is located beneath the sternum Certain lymphocytes called T cells mature in the thymus before they can function in the immune system T cells are the cells that recognize foreign “invaders” in the body The spleen helps to cleanse the blood and removes damaged blood cells from the circulatory system The spleen also harbors phagocytes that engulf and destroy bacteria and other microorganisms

The Respiratory System
When paramedics rush to the aid of an injured person, they check to see if the person is breathing If the person's chest is not rising and falling and they cannot feel or hear air being exhaled from the mouth or nose, it is likely that the person is not breathing Paramedics will ignore broken bones or burns to focus on breathing because there is no time to lose! If breathing stops for more than a few minutes, a life may be lost

Paramedics can do mouth-to-mouth rescue breathing to force air into the lungs They can do chest compressions to keep the blood circulating Cardiopulmonary resuscitation, or CPR, is rescue breathing combined with chest compressions

What Is Respiration? In biology, the word respiration is used in two slightly different ways Cellular respiration, which takes place in mitochondria, is the release of energy from the breakdown of food molecules in the presence of oxygen Without oxygen, cells lose much of their ability to produce ATP Without ATP, cells cannot synthesize new molecules, pump ions, or carry nerve impulses

EXTERNAL RESPIRATION Exchange of gases between the atmosphere and the blood Takes place in the alveoli of the lung Oxygen diffuses from the air into the blood Carbon dioxide diffuses from the blood into the air

INTERNAL RESPIRATION Gas exchange between the blood and the body cells
Oxygen diffuses from the blood into the cells Carbon dioxide diffuses out of the cells into the blood

CELLULAR RESPIRATION Chemical process that takes place in the mitochondria Oxygen combines chemically with food molecules releasing energy which is stored in ATP Carbon dioxide and water are produced as waste products

What Is Respiration? The blood carries oxygen from the lungs to the body's tissues, and carries carbon dioxide—a waste product of cellular respiration—in the opposite direction At the level of the organism, respiration means the process of gas exchange—the release of carbon dioxide and the uptake of oxygen between the lungs and the environment

The Human Respiratory System
The basic function performed by the human respiratory system is remarkably simple—to bring about the exchange of oxygen and carbon dioxide between the blood, the air, and tissues With each breath, air enters the body through the air passageways and fills the lungs, where gas exchange takes place The respiratory system consists of the nose, pharynx, larynx, trachea, bronchi, and lungs

The Human Respiratory System
The figure at right shows the structures of the respiratory system Air moves through the nose to a tube at the back of the mouth called the pharynx, or throat The pharynx serves as a passageway for both air and food Air moves from the pharynx into the trachea, or windpipe A flap of tissue called the epiglottis covers the entrance to the trachea when you swallow

PHARYNX Both the nasal passage and the mouth open into the pharynx
If the nasal passages are blocked, air can reach the lungs through the mouth which is not as effective in cleaning and warming the air

TRACHEA In the neck Also called windpipe Branches from the pharynx
Upper region is the location of the epiglottis which directs food into the esophagus and prevents food from entering the trachea Ringed by cartilage which prevents collapsing

LARYNX Just below the epiglottis Upper region of the trachea
Contains the vocal cords (voice box) Made of tough connective tissue flaps Vibrated by air passing over them which creates sound

The respiratory system is responsible for the exchange of oxygen and carbon dioxide Air moves through the nose, pharynx, larynx, trachea, and lungs After reaching the lungs, the trachea branches into smaller and smaller tubes called bronchioles, which end in alveoli, or air sacs

BRONCHUS Trachea carries air into the right and left bronchi
Bronchi branch into finer and finer tubes called bronchioles

LUNGS Organs of respiration Location of external respiration
Each lung is surrounded by a double membrane called pleura Outer pleura is attached to the chest wall Inner pleura is attached to the lungs Space between the two membranes contains a lubricating fluid allowing the lungs to move freely The heart occupies the space between the two lungs

NASAL CAVITY Many bony projections create a large surface area
Soft epithelial tissue which contains many capillaries covers these projections Mucus secreting cells are present Most dust, bacteria, and other particles are removed from the air and stick to the mucus Cilia moves the mucus to the back of the throat where it is swallowed Blood capillaries add moisture to incoming dry air and warmth to cold air preventing damage to the delicate lung tissue

Cilia and Mucus The respiratory passageways allow air to pass directly into some of the most delicate tissues in the body To keep the lung tissue healthy, air entering the respiratory system must be warmed, moistened, and filtered Large dust particles get trapped by the hairs lining the entrance to the nasal cavity Some of the cells that line the respiratory system produce a thin layer of mucus The mucus moistens the air and traps inhaled particles of dust or smoke Cilia sweep the trapped particles and mucus away from the lungs toward the pharynx The mucus and trapped particles are either swallowed or spit out These protective measures help keep the lungs clean and open for the important work of gas exchange

MUCUS Cells that secrete mucus line the trachea, bronchi, and bronchioles Coughing moves particles up to the glottis where swallowed

Respiratory Cilia

Respiratory Cilia In this cross section of the trachea, the cilia have been colored green

The Larynx At the top of the trachea is the larynx
The larynx contains two highly elastic folds of tissue known as the vocal cords When muscles pull the vocal cords together, the air moving between them causes the cords to vibrate and produce sounds Your ability to speak, shout, and sing comes from these tissues

The Bronchi From the larynx, air passes through the trachea into two large passageways in the chest cavity called bronchi (singular: bronchus) Each bronchus leads into one of the lungs Within each lung, the large bronchus subdivides into smaller bronchi, which lead to even smaller passageways called bronchioles Air moving along this path can be compared to a motorist who takes an exit off an eight-lane highway onto a four-lane highway, makes a turn onto a two-lane road, and ends up on a narrow country lane

The Bronchi The bronchi and bronchioles are surrounded by smooth muscle that helps to support them and enables the autonomic nervous system to regulate the size of the air passageways The bronchioles continue to subdivide until they reach a series of dead ends—millions of tiny air sacs called alveoli (singular: alveolus) Alveoli are grouped in little clusters, like bunches of grapes A delicate network of thin-walled capillaries surrounds each alveolus

Gas Exchange There are about 150 million alveoli in each healthy lung, providing an enormous surface area for gas exchange Oxygen dissolves in the moisture on the inner surface of the alveoli and then diffuses across the thin-walled capillaries into the blood Carbon dioxide in the bloodstream diffuses in the opposite direction, across the membrane of an alveolus and into the air within it This process is illustrated in the figure at right

GAS EXCHANGE (external)
Blood capillaries surround each alveolus Walls of the alveoli are thin and moist Gases can easily diffuse across the alveolar membrane External respiration takes place across the alveoli Air is approximately 80% nitrogen, 20% oxygen with traces of other gases (e.g. Carbon dioxide is approximately 0.03% of air)

Blood leaving the lungs is rich in oxygen Most oxygen binds to molecules of protein called hemoglobin which is located in RBC A small amount of oxygen dissolves in the plasma Blood is oxygenated (rich in oxygen, low in carbon dioxide) (bright red)

Gas Exchange Gas exchange occurs by diffusion across the membrane of an alveolus and a capillary Where is oxygen more concentrated, in an alveolus or in a capillary?

Blood entering the capillaries of the alveoli is deoxygenated (low in oxygen but high in carbon dioxide) Level of oxygen is higher in alveolar air than in the blood, so oxygen diffuses from the air into the blood Level of carbon dioxide is higher in the blood than in the alveolar air, so carbon dioxide diffuses from the blood into the air in the alveoli

ALVEOLI Cluster of microscopic, balloonlike air sacs at the end of each bronchiole

Gas Exchange

Gas Exchange The process of gas exchange in the lungs is very efficient The air that you inhale usually contains 21 percent oxygen and 0.04 percent carbon dioxide Exhaled air usually contains less than 15 percent oxygen and 4 percent carbon dioxide The lungs remove about one fourth of the oxygen in the air that you inhale and increase the carbon dioxide content of that air by a factor of 100

Gas Exchange Because oxygen dissolves easily, you may wonder why hemoglobin, the oxygen-carrying protein in blood, is needed at all The reason is efficiency Hemoglobin binds with so much oxygen that it increases the oxygen-carrying capacity of the blood more than 60 times Without hemoglobin to carry the oxygen that it uses, your body might need as much as 300 liters of blood to get the same result!

GAS EXCHANGE (internal)
When blood reaches the body cells During cellular respiration, cells use oxygen and produce carbon dioxide Oxygen concentration less in cytoplasm than blood Oxygen diffuses from blood to cytoplasm Carbon dioxide concentration higher in cytoplasm than blood Carbon dioxide diffuses from cytoplasm to blood

GAS EXCHANGE (internal)
Small amount of carbon dioxide dissolves in the blood plasma Some carbon dioxide attaches to hemoglobin Most carbon dioxide reacts with water and enzymes in the cytoplasm of the RBC forming carbonic acid CO2 + H2O + enzymes yields H2CO3 which ionizes to form hydrogen ions ( H+ ) + bicarbonate ions ( HCO3-) Ions accumulate in the RBC and diffuse into the plasma Deoxygenated blood ( dull purplish red) now returns to the lung alveoli In the lungs, the equation is reversed with enzymes forming water and carbon dioxide

Breathing Breathing is the movement of air into and out of the lungs
Surprisingly, there are no muscles connected to the lungs The force that drives air into the lungs comes from ordinary air pressure How does the body use this force to inflate the lungs? The lungs are sealed in two sacs, called the pleural membranes, inside the chest cavity At the bottom of the cavity is a large, flat muscle known as the diaphragm

MECHANISM OF BREATHING
INSPIRATION: phase of breathing during which air is taken into the lungs inhalation EXPIRATION: phase of breathing during which air is expelled from the lungs exhalation

INHALATION Diaphragm muscle contracts (flattens out)
Thoracic muscles contract moving ribs up and out Volume of the thoracic cavity increases reducing pressure in the pleural fluid Air rushes in Walls of the alveoli stretch

EXHALATION Diaphragm muscle relaxes returning to its dome shape
Thoracic muscles relax moving ribs down and in Volume of the thoracic cavity decreases Pressure in the pleural fluid increases Air rushes out of the lungs Walls of the alveoli return to their smaller size

Breathing As the figure shows, when you breathe in, or inhale, the diaphragm contracts and the rib cage rises up This expands the volume of the chest cavity Because the chest cavity is tightly sealed, this creates a partial vacuum inside the cavity Atmospheric pressure does the rest, filling the lungs as air rushes into the breathing passages

Breathing During inhalation the rib cage rises and the diaphragm contracts, increasing the size of the chest cavity This causes the pressure inside the lungs to decrease, and air enters

Breathing

Breathing Most of the time, exhaling is a passive event
When the rib cage lowers and the diaphragm muscle relaxes, the pressure in the chest cavity becomes greater than atmospheric pressure Air rushes back out of the lungs To blow out a candle, you need a greater force Muscles surrounding the chest cavity provide that extra force, contracting vigorously just as the diaphragm relaxes

CONTROL OF BREATHING RATE
Diaphragm and rib muscles are striated Under voluntary control Most of the time, breathing is an unconscious response where the breathing center in the brain controls the diaphragm and rib muscles automatically (involuntary) Nerve cells in the brain monitor the CO2 content of the blood and regulate the breathing rate

Breathing The system works only because the chest cavity is sealed
A puncture wound to the chest—even if it does not affect the lungs directly—may allow air to leak into the chest cavity and make breathing impossible This is one of the reasons chest wounds are always serious

How Breathing Is Controlled
You can control your breathing almost anytime you want, whether it's to blow up a balloon or to play a musical instrument But this doesn't mean that breathing is purely voluntary If you hold your breath for a minute or so, you'll see what happens Your chest begins to feel tight, your throat begins to burn, and the muscles in your mouth and throat struggle to keep from breathing Eventually your body takes over It “forces” you to breathe!

Breathing is such an important function that your nervous system will not let you have complete control over it The part of the brain that controls breathing is the medulla oblongata Autonomic nerves from the medulla oblongata to the diaphragm and chest muscles produce the cycles of contraction that bring air into the lungs How does the medulla oblongata “know” when it's time to breathe? Cells in its breathing center monitor the amount of carbon dioxide in the blood As the carbon dioxide level rises, nerve impulses from the breathing center cause the diaphragm to contract, bringing air into the lungs The higher the carbon dioxide level, the stronger the impulses If the carbon dioxide level reaches a critical point, the impulses become so powerful that you cannot keep from breathing

That the breathing center responds primarily to carbon dioxide can have dangerous consequences Consider a plane flying at high altitude Although the amount of oxygen in the air decreases as the altitude increases, the passengers do not need oxygen masks because the cabin is pressurized Oxygen is available for use in an emergency, but the passengers often have to be told to begin breathing the oxygen Although their bodies may be starving for oxygen, they have no more carbon dioxide in their blood than usual, so the breathing center does not sense a problem

Tobacco and the Respiratory System
The upper part of the respiratory system is generally able to filter out dust and foreign particles that could damage the lungs Millions of people engage in an activity—smoking tobacco—that damages and eventually destroys this protective system

Substances in Tobacco Tobacco smoke contains many substances that affect the body Three of the most dangerous substances are nicotine, carbon monoxide, and tar Nicotine is a stimulant drug that increases the heart rate and blood pressure Carbon monoxide is a poisonous gas that blocks the transport of oxygen by hemoglobin in the blood It decreases the blood's ability to supply oxygen to its tissues, depriving the heart and other organs of the oxygen they need to function Tar contains a number of compounds that have been shown to cause cancer

Substances in Tobacco Smoking tobacco brings nicotine and carbon monoxide into the upper respiratory system These compounds paralyze the cilia With the cilia out of action, the inhaled particles stick to the walls of the respiratory tract or enter the lungs

Substances in Tobacco Without cilia to sweep it along, smoke-laden mucus becomes trapped along the airways This explains why smokers often cough Irritation from the accumulated mucus triggers a cough that helps to clear the airways Smoking also causes the lining of the respiratory tract to swell, which reduces the air flow to the alveoli

Diseases Caused by Smoking
Only 30 percent of male smokers live to age 80, but 55 percent of male nonsmokers live to that age Clearly, smoking reduces life expectancy Smoking can cause such respiratory diseases as: Chronic bronchitis Emphysema Lung cancer

Chronic Bronchitis In chronic bronchitis, the bronchi become swollen and clogged with mucus Even smoking a moderate number of cigarettes on a regular basis can produce chronic bronchitis Affected people often find simple activities, such as climbing stairs, difficult

Long-term smoking can also cause a respiratory disease called emphysema Emphysema is the loss of elasticity in the tissues of the lungs This condition makes breathing very difficult People who have emphysema cannot get enough oxygen to the body tissues or rid the body of excess carbon dioxide

Smoking is an important, but preventable, cause of lung cancer Lung cancer is particularly deadly because its cells can spread to other locations By the time lung cancer is detected, it usually has spread to dozens of other places About 160,000 people in the United States are diagnosed with lung cancer each year Few will survive for five years after the diagnosis

Smoking and the Lungs Smoking can cause respiratory diseases such as chronic bronchitis, emphysema, and lung cancer The lung on the left is from a smoker The lung on the right is from a nonsmoker

Smoking and the Lungs

Smoking and the Lungs Smoking is also a major cause of heart disease
Smoking constricts, or narrows, the blood vessels This causes blood pressure to rise and makes the heart work harder There is a drastic change in body temperature and in circulation immediately after smoking a cigarette Smoking doubles the risk of death from heart disease for men between 45 and 65 Moreover, for men and women of all ages, the risk of death from heart disease is greater among smokers than among nonsmokers

Smoking and the Nonsmoker
In recent years, evidence has shown that tobacco smoke is damaging to anyone who inhales it, not just the smoker For this reason, many states have restricted smoking in restaurants and other public places

Smoking and the Nonsmoker
Passive smoking, or inhaling the smoke of others, is particularly damaging to young children because their lungs are still developing Studies now indicate that the children of smokers are twice as likely as children of nonsmokers to develop respiratory problems, such as asthma

Dealing With Tobacco Whatever the age of a smoker, and no matter how long that person has smoked, his or her health can be improved by quitting Nicotine is a powerful drug with strong addictive qualities that make it very difficult to quit smoking Thus, considering the cost, the medical dangers, and the powerful addiction, the best solution is not to begin smoking

Circulatory and Respiratory Systems

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Circulatory and Respiratory Systems

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