CIRCULATORY AND RESPIRATORY SYSTEMS

37-1 The Circulatory System

Functions of the Circulatory System• Organisms which have a small number of cells do not need a

circulatory system. Larger organisms need one. • Humans and other vertebrates have a closed circulatory system. This

means that the blood is contained inside of vessels.• The human circulatory system consists of the heart, a series of blood

vessels, and the blood that flows through them.

The Heart• Your heart is located near the center of your chest. The heart is made

up of mostly muscle. It 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. • Myocardium – thick middle muscle layer of the heart that pumps

blood through the circulatory system.

• The heart muscle contracts about 73 times a minute and pumps about 70 milliliters of blood with each contraction. • The septum divides the right and left sides of the heart. The septum

prevents the blood with little oxygen from mixing with blood rich in oxygen.

• Atrium – the upper chamber that receives the blood

• Ventricle – the lower chamber that pumps blood out of the heart.

• The right side of the heart pumps blood from the heart to the lungs. This is called pulmonary circulation (the word pulmonary refers to the lungs)• 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 is called systemic circulation.

Oxygen that returns to the right side of the heart has little oxygen because cells have absorbed a lot of the oxygen and loaded the blood with carbon dioxide. It now needs another trip to the lungs.

• Valves – flaps of connective tissue 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.• There are also valves that stops blood that has left the heart from

flowing back in. These valves keep the blood moving through the heart in one direction.

• There are two sets of muscle fibers in the heart, one in the atria and one in the ventricles. When a single fiber is stimulated, all the fibers are stimulated and all contract. Each contraction begins in a small group of cardiac muscle cells These cells are called the sinoatrial node, but also called the pacemaker, because it sets a pace for the heart to beat.• How fast your heart beats depends on how much oxygen-rich blood

your body needs.• For example, when you are exercising, your heart beat faster because

your body needs more oxygen.

Blood Vessels

• Aorta – a large blood vessel that the blood leaves the heart through • There are three types of blood vessels that blood flows through:

arteries, capillaries, and veins.

• Arteries – large vessels that carry blood away from the heart to the tissues of the body (Artery = Away)• Capillaries – the smallest of the blood vessels. They bring nutrients

and oxygen to the tissues and absorb carbon dioxide and other waste products from them.• Veins – carry blood to the heart after it has passed through the

capillary system.(think of a tv: To = Veins)

• Large veins contain valves that keep blood moving toward the heart.

Blood Pressure

Blood pressure is the force of the blood on the arteries’ walls. Blood pressure decreases when the heart relaxes, but there is still pressure. The pressure is needed to pump the blood throughout the body.

The body regulates blood pressure. When it is too high, the autonomic nervous system releases neurotransmitters that cause the smooth muscles in blood vessel walls to relax, which lowers the blood pressure. When blood pressure is too low, neurotransmitters are released that elevate blood pressure by causing these smooth muscles to contract.

Kidneys also help to regulate blood pressure. They remove more water from the blood when blood pressure is high. This reduces blood volume, which lowers the blood pressure.

Diseases of the Circulatory System• Cardiovascular disease (ex – heart disease and stroke) are among the

leading causes of death and disability in the US. High blood pressure and atherosclerosis are two main causes of cardiovascular disease.

• Atherosclerosis – fatty deposits, called plaque, build up on the inner walls of the arteries.• High blood pressure is also called hypertension. It forces the heart to

work harder, which can weaken or damage the heart and blood vessels. It increases the risk of heart attack or stroke.• Atherosclerosis is dangerous in the coronary arteries, which bring

oxygen and nutrients to the heart. If a coronary artery becomes blocked, the heart muscle may begin to die from lack of oxygen. If enough of the heart muscle is damaged, a heart attack can occur.

Symptoms of a heart attack are nausea, shortness of breath, and severe crushing chest pain

Blood clots that can form from atherosclerosis can break free and get stuck in one of the blood vessels leading to a part of the brain. This is called a stroke.

• To avoid a cardiovascular disease, get regular exercise, eat a balance diet, and DO NOT SMOKE!

37-2 Blood and the Lymphatic System

Blood Plasma• The Human body contains 4 to 6 liters of blood, about 8% of the total

mass of the body. 45% of blood is made up of cells and the other 55% is plasma.• Plasma – a straw-colored fluid which blood cells are suspended in• Plasma is 90% water and 10% dissolved gases, salts, nutrients,

enzymes, hormones, waste products, and proteins called plasma proteins.

Blood Cells

• Blood contains red blood cells, white blood cells, and platelets.

Red Blood Cells (erythrocytes)• The most numerous cells in the blood• Red blood cells transport oxygen.

They contain hemoglobin, which 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 are produced from cells in red bone marrow.

White Blood Cells (leukocytes)• There are much less white blood cells in the blood than there are red

blood cells (1000 to 1)• White blood cells are the “army” of the circulatory system. They

guard against infection, fight parasites, and attack bacteria.

• Lymphocytes – a special class of white blood cells that produce antibodies that are proteins that help destroy pathogens.• Antibodies are essential to fighting infection and help to produce

immunity to many diseases.

Platelets and Blood Clotting

• Blood has the ability to form a clot. Blood clotting is made possible by plasma proteins and cell fragments called platelets. • Platelet – cell fragment released by bone marrow that helps in blood

clotting.

When a platelets come into contact with the edges of a broken blood vessel, their surfaces become sticky, and a cluster of platelets develops around the wound. These platelets release proteins called clotting factors. A clot is formed and the bleeding is stopped.

• In small wounds, the wound is sealed and bleeding stops in a few minutes. • Hemophilia is a genetic disorder that results from a defective protein

in the clotting pathway. People with hemophilia can’t produce blood clots that are firm enough to stop even minor bleeding. Without clotting, they can bleed too much.

The Lymphatic System

• Blood can leak out into tissues. If nothing is done about this, the body can swell with fluid. The lymphatic system is a network of vessels, nodes, and organs that collects fluid that is lost by the blood and returns it back to the circulatory system. The fluid is called lymph.

Lymph nodes are small bean-shaped enlargements along the length of the lymph vessels. Lymph nodes act as filters, trapping bacteria and other microorganisms that cause disease. When a large number of microorganisms are trapped, the nodes become enlarged. Swollen glands are swollen 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 recognize foreign “invaders” in the body. The spleen helps to cleanse the blood and removes damaged blood cells from the circulatory system.

37-3 The Respiratory System

What is Respiration?• In cells, cellular respiration is the release of energy from the

breakdown of food molecules when oxygen is present.• In the human body, respiration is 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 of the human respiratory system is to bring about the exchange of oxygen and carbon dioxide between the blood, the air, and tissues.

• Pharynx – a passageway for air and food• Trachea – windpipe – air moves from the pharynx to the trachea. A

flap of tissue called the epiglottis covers the entrance to the trachea when you swallow.

To keep lung tissue healthy, air entering the respiratory system must be warmed, moistened, and filtered. Large dust particles get trapped by the hairs (cilia) lining the entrance to the nasal cavity. Some of the cells that line the respiratory system produce a thin layer of mucus. 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. This helps keep the lungs clean and open.

• Larynx – contains the vocal cords. Gives us the ability to makes sounds (speak, shout, sing…)• Bronchi – two large passageways in the chest cavity that air from the

trachea go into. Each bronchus leads into one of the lungs. • Bronchi lead into smaller passageways called bronchioles.

Bronchioles subdivide until they reach a series of dead ends, millions of tiny air sacs called alveoli. Alveoli looks like bunches of grapes.

Gas Exchange• There are about 150 million alveoli in each healthy lung. Oxygen

dissolves in the alveoli and then diffuses across the thin-walled capillaries in to the blood. Carbon dioxide in the bloodstream diffuses in the opposite direction across the membrane of an alveolus and into the air within it.

Breathing• Breathing is the movement of air into and out of the lungs. • Diaphragm – large flat muscle at the bottom of the chest cavity that

helps with breathing.• When you inhale, the diaphragm contracts and the rib cage rises up.

When you exhale, the diaphragm is relaxing and the rib cage lowers.

A puncture wound to the chest, even if it is not in the lungs, may allow air to leak into the chest cavity and make breathing impossible.

How Breathing is Controlled• Breathing isn’t totally voluntarily. We can control our breathing to an

extent, but if we hold our breath, our bodies force us to breath after some time. Also, breathing in our sleep in involuntary. • The medulla oblongata controls breathing. When carbon dioxide

levels rise, nerve impulses cause the diaphragm to contract, bringing air into the lungs. The higher the carbon dioxide level, the stronger the impulses. If carbon dioxide levels reaches a critical point, the impulses become so powerful that you cannot keep from breathing.

Tobacco and the Respiratory System

• The upper part of the respiratory system filters out dust and foreign particles that could damage the lungs. Smoking tobacco damages and eventually destroys this protective system.

• Tobacco smoke contains many substances. Three of the most dangerous are nicotine, carbon monoxide, and tar.• Nicotine – 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 has been shown to cause cancer.

Smoking paralyzes the cilia, causing the inhaled particles to stick to the walls of the respiratory tract or enter the lungs. Without cilia, smoke-laden mucus becomes trapped along the airways. This is why smokers often cough. Smoking also causes the lining of the respiratory tract to swell, reducing air flow to the alveoli.

Diseases Caused by Smoking

Smoking can cause chronic bronchitis, emphysema, and lung cancer.

In chronic bronchitis, the bronchi become swollen and clogged with mucus

Emphysema – the loss of elasticity in the tissues of the lungs. People with emphysema cannot get enough oxygen to the body tissues or rid the body of excess carbon dioxide.

About 160,000 people are diagnosed with lung cancer each year. By the time it’s detected, lung cancer usually spreads to other parts of the body. Few will survive for five years after the diagnosis.

Smoking is a major cause of heart disease. Smoking narrows the blood vessels, causing blood pressure to rise and makes the heart work harder.

Evidence has shown that tobacco smoke is damaging to anyone who inhales it, not just the smoker. This is called second-hand smoke.