The Human Circulatory System

Section 9-2

Human Circulatory System

• The human circulatory system is closed; it consists of: – A Heart.

– A Network of blood vessels (tubes).

– Blood that flows through them.

• All vertebrates have a closed circulatory system.

The Closed Circulatory System.

Human Blood Vessels

Human Blood Vessels• Three Kinds of Blood Vessels:– 1. Arteries: Blood vessels that carry blood

away from the heart to the organs and tissues of the body.

– 2. Veins: Blood vessels that carry blood from the body tissues back to the heart.

– 3. Capillaries: Tiny blood vessels that allow the exchange of nutrients, wastes, and gases between the circulatory system (the blood) and the body cells.

Arteries

• Arteries have very thick and elastic walls.

• Arteries consist of layers of connective tissue, muscle tissue, and epithelial tissue.

• Main arteries divide and branch into smaller and smaller arteries. The smallest arteries are called arterioles. – Arterioles branch into capillary networks (capillary beds).

Interesting Info• Humans turn pale when scared.– Most arterioles are in contact with nerve fibers. When these

nerves stimulate the muscle tissue to contract, the arteriole is constricted and blood flow decreases. This reduces the flow of blood to the face, and a person turns pale.

• Human blushing:– When the nerve fibers are inhibited, the arteriole muscles relax.

This increases blood flow.

Veins

• Veins have thinner, slightly elastic walls.

• Veins have flap-like valves that allow blood to flow in only one direction – toward the heart.

• The smallest veins are called venules.– Venules branch from capillary networks.

Valve

Capillaries

• Capillary networks connect arterioles (smallest arteries) and venules (smallest veins).

• Red blood cells pass through capillaries in single file.

Why is the blood oxygen rich and then oxygen poor?

Answer: Respiration! The cells of the body need oxygen to perform respiration (for energy).

A Comparison of Blood VesselsNot Drawn to Scale

Human Artery

Human Vein

Red Blood Cells Are Responsible For Oxygen Delivery To The Body’s Cells

.

Colour-enhanced scanning electron micrograph by Dave McCarthy and Annie Cavanagh

Human arteriole. LM, 160x. H&E stain. [G. W. Willis/BPS]

RBCs Pass Through Capillaries In Single File

Circulatory Facts

• Only 5-10% of the body’s capillaries have blood flowing in them at any given time. – Every part of the body still gets what it needs because of the

abundance of capillary beds in body tissues.

• A blood cell circulates in the body in about 30 seconds.

• Blood leaves the aorta at about 30 cm/second. Blood in the capillaries flows at about 0.026 cm/second. If you add up the rate in all the capillaries, it amounts to about 30 cm/second.

• Bone marrow makes about 2 million red blood cells per second.

The Heart

• The human heart is a complex and muscular pumping organ.– Consists mostly of cardiac muscle (aka heart

muscle).

– Cardiac muscle cells are somewhat elongated and contain a single nucleus.

– They are interconnected to form a network; this allows for high-powered contractions of the heart.

Cardiac Muscle Cells

The Beating Heart

• The heart beats (contracts) about 72 times a minute.

• Every heart beat pumps about 70 milliliters of blood.

• The heart beats about 3 million times a year.

• The human heart pumps enough blood to overflow an Olympic-sized swimming pool (2,000,000 L) every year – almost 3,000,000 liters!

EKG Simulator

The Atria and Ventricles

• The atria (upper chambers) receive incoming blood.– Atria are also called auricles.

• The ventricles (lower chambers) pump blood out of the heart.– This is why ventricles are more muscular than

atria.

Heart Valves

• Four flaplike valves exist in the heart. Their purpose is to control the direction of blood flow within the heart.– Two Atrioventricular Valves (A-V Valves)

• Tricuspid Valve Located on the right side, has three flaps.

• Bicuspid Valve (Mitral Valve) Located on the left side, has two flaps.

– Two Semilunar Valves.• Pulmonic Valve Located on the right side.

• Aortic Valve Located on the left side.

Heart Valves, Cont’d

• The A-V valves allow blood to flow only from the atria to the ventricles (not back).

• The semilunar valves allow blood to flow out of the ventricles and into arteries (not back).

A-V Valves

Semilunar Valves

Circulation Through the Body• The purpose of the heart is to send blood throughout the body.

• The heart actually serves as two different pumps:– The right ventricle pumps blood to the lungs.

• This Pathway is part of Pulmonary Circulation.– The left ventricle pumps blood to the rest of the body.

• This Pathway is part of Systemic Circulation.

The Two Circulation Pathways Pulmonary Circulation: The circulatory path

between the heart and the lungs.

Systemic Circulation: The circulatory path between the heart and the rest of the body.

–Includes:

•Coronary circulation (supply of blood to the heart itself).

•Renal circulation (supply of blood to the kidneys).

•Hepatic-portal circulation (supply of blood from the digestive tract to the liver).

Can you spot the two pathways?

Circulation Pathways (1)• Steps:– 1. Deoxygenated blood enters the right atrium of the

heart from the body tissues.• This blood reaches the heart through the superior and inferior

vena cava veins.

– 2. Deoxygenated blood is pumped from the right atrium to the right ventricle through an A-V valve.

– 3. Deoxygenated blood is pumped out of the heart to the lungs by the right ventricle.• This blood is pumped out through the pulmonary artery.

– 4. The lungs replenish the blood with oxygen. It is now oxygenated blood.

Circulation Pathways (2)• Steps:– 5. Oxygenated blood enters the left atrium of the heart

from the lungs.• This blood reaches the heart through the pulmonary veins.

– 6. Oxygenated blood is pumped from the left atrium to the left ventricle through an A-V valve.

– 7. Oxygenated blood is pumped out of the heart to the body tissues by the left ventricle.• This blood is pumped out through the aorta.

– 8. The body tissues use the oxygen carried by the red blood cells. The blood then becomes deoxygenated and must be returned to the heart where the cycle repeats.

Blue:Oxygen PoorBlood.

Red: Oxygen Rich Blood.

Lungs replenish the blood with oxygen. How it works: RBCs pick up O2 through diffusion across the capillary membrane.

Interesting Facts

• The pulmonary arteries are the only arteries that carry deoxygenated blood.

• The pulmonary veins are the only veins that carry oxygenated blood.

Simplified Sequence

• Blood flows fromRight Atrium Right Ventricle Lungs Left Atrium Left Ventricle Rest of Body Right Atrium again.

Pulmonary Circuit:Right Ventricle Lungs Left Atrium

Systemic Circuit:Left Ventricle Body Right Atrium

Can You Label The Parts?

Watch Encarta Animation

Heart and Blood Circulation

Watch Web Animation

Pulmonary and Systemic Circulation

http://www.pbs.org/wnet/redgold/journey/circulation_flash.html

Connections• The respiratory system and the circulatory system work together.

Can you think of how?

• The nervous system and the circulatory system work together. Can you think of how?

• The digestive system and the circulatory system work together. How?

• The excretory system and the circulatory system work together. How?

The two systems interact at the lungs (alveoli and the capillaries); the lungs give the blood oxygen.

The two systems interact at the heart and the brain; the brainstem coordinates the beating of the heart.

The two systems interact at the small intestine (in the villi); food molecules enter the bloodstream here.

The two systems interact in the kidneys; they filter the blood’s wastes.

The Circulatory System Interacts With Other Systems To Maintain Homeostasis.

0.5 cmNutrients

Digestivesystem

Lining of small intestine

MouthFood

External environment

Animalbody

CO2 O2

Circulatorysystem

Heart

Respiratorysystem

Cells

Interstitialfluid

Excretorysystem

Anus

Unabsorbedmatter (feces)

Metabolic waste products(nitrogenous waste)

Kidney tubules

10 µm

50 µ

m

Lung tissue

Volume rendering software and magnetic resonance imaging can be used to create 3-D images of body systems such as bone, soft tissue (organs), or anatomical structures (arteries). Can you spot some of the interactions?

Alveoli

A scanning electron micrograph reveals the tiny sacs known as alveoli within a section of human lung tissue. Human beings have a thin layer of about 700 million alveoli within their lungs. This layer is crucial in the process called gas exchange, exchanging oxygen and carbon dioxide with the surrounding blood capillaries. The subdivision of the lung into millions of tiny air sacs provides a greater surface area for gas exchange to take place. Microsoft ® Encarta ® Encyclopedia 2003. © 1993-

2002 Microsoft Corporation. All rights reserved.

Capillaries surround each alveolus for gas exchange to take place between the circulatory system and the respiratory system.

You have 700 million alveoli in your lungs. Their total surface area is the size of a tennis court!

Systole and Diastole

• Systole and Diastole are the two cycles of the heart (They are continuously alternating).

– Systole: the contraction of the heart by which the blood is forced onward and the circulation kept up. • Moment of Higher Blood Pressure (Systolic Pressure). Systole

is felt as your pulse.

– Diastole: the dilation of the heart chambers during which they fill with blood.• Moment of Lower Blood Pressure (Diastolic Pressure).

Blood pressure being measured with a sphygmomanometer and stethoscope. [N. Laing/BPS]

See Web Animation 1See Web Animation 2

Stethoscope and Heart Beat

http://sprojects.mmi.mcgill.ca/mvs/SHOCK/HRTSPLIT.HTM

http://www.smm.org/heart/heart/steth.htm

The ECG/EKG

• ECG (or EKG) stands for electrocardiogram. Electrical impulses coordinated by the nervous system control the beating of the heart. An EKG records these impulses.

• See Animation• http://www.medmovie.com/dqt77b/index.htm

Electrical Signals From The Nervous System Coordinate The Beating Of The Heart

Before We Continue

• It is important to realize that oxygen poor blood (deoxygenated blood) is not actually blue. It is just represented that way in diagrams.

• Deoxygenated blood is dark red/purple.

• Oxygenated blood is bright red.

Review

• Remember, if it’s a vein, the blood is flowing toward the heart.

• If it’s an artery, the blood is flowing away from the heart.

See Encarta Interactivity: The Circulatory System.

Comparative Anatomy

• Not all chordates have a separated four-chambered heart. Mammals and birds do, but fish, amphibians, and reptiles do not. The four-chambered design prevents oxygenated and deoxygenated blood from mixing, and is more efficient. Mammals and birds have a complete septum that separates the two sides of the heart. Without this heart design, they could not be warm-blooded creatures.

The Developing Heart of a Zebrafish Embryo

http://bioimaging.caltech.edu/index_content.html

Note: In Crocodilians, heart is actually completely separated. They can prevent blood from flowing through the pulmonary circuit while underwater by using a muscular valve.

Overview of Vertebrate Circulatory Systems

Disorders of the Circulatory System

• Disorders of the circulatory system are very common in this country.

• They are the leading cause of death in America every year.

Arteriosclerosis and Atherosclerosis.

• Arteriosclerosis: a condition involving the “hardening of the arteries.” When this happens, the heart must work harder to push blood through the circulatory system. In severe cases, the body is unable to get oxygen to all of its cells.

Most Common Type:• Atherosclerosis: a buildup of fat deposits (plaque)

in the innermost lining of medium and large arteries.– Plaque: material containing lipids (i.e. cholesterol) and

minerals such as calcium.– Thrombus: a clot of blood formed within a blood vessel

and remaining attached to its place of origin.

Atherosclerosis, cont’d

• When plaque and blood clots block part of or all of an artery, blood pressure goes up and blood flow can be reduced.

See Animation

Atherosclerosis (High Speed)

Plaque

Disorders, Cont’d

• Most disorders are a result of arteriosclerosis/atherosclerosis.

• They include high blood pressure, heart attack, and stroke.

High Blood Pressure

• Hypertension = High Blood Pressure.

• Hypertension makes the heart work harder, which can damage the heart and other tissues.

• Each pound of fat adds 1 mile of capillaries, forcing the heart to work harder.

Blood Pressure ClassificationClassification of blood pressure levels for adults 18 years and older. Systolic pressure, the higher number of a blood pressure reading, is the pressure as the heart pumps; diastolic pressure is the pressure when the heart relaxes between beats.

Normal* < 130 < 85

High normal 130-139 85-89

Hypertension

STAGE 1 (Mild) 140-159 90-99

STAGE 2 (Moderate) 160-179 100-109

STAGE 3 (Severe) 180-209 110-119

STAGE 4 (Very Severe) >209 >119

†Measured in millimeters of mercury

*Optimal blood pressure is less than 120/80 mm Hg. Unusually low readings should be evaluated by a physician.

Source: Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure; National Institutes of Health.

Microsoft ® Encarta ® Encyclopedia 2003. © 1993-2002 Microsoft Corporation. All rights reserved.

Category Systolic BP Diastolic BP

Coronary Heart Disease is a chronic illness in which the coronary arteries, the vessels that supply oxygen-carrying blood to the heart, become narrowed and unable to carry a normal amount of blood. When its blood supply is reduced, the heart does not receive sufficient oxygen. This oxygen deficit leads to two main consequences: chest pain known as angina pectoris, and heart attack, in which part of the heart dies because of oxygen deprivation. Coronary heart disease is the leading cause of death in the United States, responsible for nearly 460,000 deaths each year.Microsoft® Encarta® Encyclopedia 2003. © 1993-2002 Microsoft Corporation. All rights reserved.

Coronary Heart Disease/Heart Attack

See Web Animation

Coronary Artery Diseasehttp://www.umm.edu/careguides/cholesterol/dswmedia/corart_animation.html

Treatments for Coronary Heart Disease (CHD)

• Angioplasty: – “During angioplasty, the doctor threads a thin tube called a catheter through

your artery to insert a balloon. When the doctor inflates the balloon, it opens up the blocked part of the artery. Sometimes a small, flexible tube, called a stent, is placed in the artery and left there to help keep the blood vessel open. This procedure is called stenting. Doctors often recommend angioplasty, and possibly stenting, for people who have angina that isn't helped by medicines. Angina is another name for chest pain.” • Discovery Health

• Coronary Bypass Surgery: – “In bypass surgery, a length of blood vessel is removed from elsewhere in the

patient’s body—usually a vein from the leg or an artery from the wrist. The surgeon sews one end to the aorta and the other end to the coronary artery, creating a conduit for blood to flow that bypasses the narrowed segment. Surgeons today commonly use an artery from the inside of the chest wall because bypasses made from this artery are very durable.”• Microsoft® Encarta® Encyclopedia 2003. © 1993-2002 Microsoft Corporation. All

rights reserved.

Balloon Angioplasty

Angioplasty often involves a stent.

                     

See Animation

Angioplasty

http://www.healthscout.com/animation/68/38/main.html

Coronary Bypass Surgery

See Animation

Heart Bypass Surgery

http://www.healthscout.com/animation/68/36/main.html

Comparison of Treatments for CHDAngioplasty Bypass Surgery

Surgery Minor Major

Cost Less Expensive More Expensive

Length of Procedure

30 minutes - 2 hours 3 hours – 6 hours

Anesthesia Local (Less Risk) General (Greater Risk)

Hospital Stay 1-3 days 4-7 days

Recovery Time

Short Long (Many Weeks)

Effectiveness May need to be repeated in 6 months.

Results normally last longer.

Discovery Health

Symptoms of a Heart Attack

• Nausea

• Shortness of Breath

• Severe, Crushing Chest Pain

Dietary Approaches to Stop Hypertension (DASH).

Prevention

Stroke• A Stroke results when blood clots formed as a result of

atherosclerosis break free and get stuck in the blood vessels leading to a part of the brain. – This is called ischemic stroke. Ischemic strokes happen in about

80% of stroke cases.

• A stroke can also happen when a weakened artery in the brain bursts, flooding the area with blood.– This is called hemorrhagic stroke. Hemorrhagic stroke happens in

about 20% of stroke cases.

• Brain cells die from a lack of oxygen, and brain function in that region may be lost.

• Strokes can result in death.

Symptoms/Consequences of Strokes

• Paralysis

• Loss of the ability to speak

• Impaired speech

Ischemic Stroke

Embolic and thrombolic strokes are the two types of ischemic strokes. In embolic stroke, a blood clot from outside the brain or neck (i.e. heart) blocks a blood vessel of the brain. In thrombolic stroke, a blood clot from the brain or neck blocks a blood vessel of the brain.

Hemorrhagic StrokeIn hemorrhagic stroke, a blood vessel in the brain breaks and leaks blood into its surroundings, leaving a portion of the brain without oxygen. This is a more serious type of stroke than ischemic stroke, and often results from an aneurysm. An aneurysm is a localized enlargement of a blood vessel that forms a bulge or sac. Aneurysms are caused by disease, weakening of the vessel’s wall, injury, or an abnormality present at birth.

Aneurysms can be the precursors to hemorrhagic stroke.

Regions of the Brain Affected By Stroke

Interactivityhttp://www.klbschool.org.uk/interactive/science/heart.htm

Just For Fun: Watch Web

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St. Joseph Aspirin Commercialhttp://www.stjosephaspirin.com/images/stjoseph/pumpblood/index.html

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