Circulation and Cardiovascular Systems

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Chapter 29Circulation and

Cardiovascular

Systems



A Circulatory System Helps

Maintain Homeostasis

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29.1 A circulatory system

serves the needs of cells The circulatory system transports oxygen and

nutrients, such as glucose and amino acids, to

the cells It picks up wastes, which are later excreted from the

body by the lungs or kidneys

Both gas exchange and nutrient-for-wasteexchange occur across the walls of the smallest

blood vessels, capillaries No cell in the body of an animal is far from a capillary

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Figure 29.1 Exchanges of gases, nutrients, and wastes takes place

across capillary walls

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29.2 Some invertebrates do not

have a circulatory system Cnidarians, such as hydras, and flatworms, such as

planarians, do not have a circulatory system

In a hydra

The cells are either part of an external layer, or they linethe gastrovascular cavity

In either case, each cell is exposed to water and canindependently exchange gases and get rid of wastes

In a planarian

Trilobed gastrovascular cavity branches throughout thesmall, flattened body

No cell is very far from one of the three digestivebranches, so nutrient molecules can diffuse from cell tocell

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Figure 29.2 Invertebrates with a gastrovascular cavity

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29.3 Other invertebrates have an

open or a closed circulatory system

There are two types of circulatory fluid: Blood - always contained within blood vessels

Hemolymph - a mixture of blood and tissue fluid that flows into a bodycavity

Open circulatory system - found in arthropods and molluscs

Heart pumps hemolymph via vessels into tissue spaces and eventuallyhemolymph drains back to the heart

Slow delivery of oxygen and nutrients is sufficient for a sluggish animal(clam)

A grasshopper has colorless blood and doesn¶t depend on its opencirculatory system to deliver oxygen to its muscles

Tracheae open to outside and take oxygen directly to flight muscles

Closed circulatory system - found in annelids (earthworms) Heart pumps blood, which usually consists of cells and plasma, into a

system of blood vessels and valves prevent the backward flow of blood

Blood moves into capillaries, for exchanges with tissue fluid

Blood then moves from small veins into the dorsal blood vessel (a vein)

This dorsal blood vessel returns blood to the heart for repumping

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Figure 29.3A

Open circulatory

system in agrasshopper

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Figure 29.3B

Closed circulatory

system in an

earthworm

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29.4 All vertebrates have a

closed circulatory system Two different circulatory pathways in vertebrates Single-loop: heart only pumps blood to gills

Two-circuit: systemic circuit - heart pumps blood to all parts of thebody except for the lungs; the pulmonary circuit - heart pumps bloodto the lungs

Fishes - heart has a single atrium and a single ventricle Blood is fully enriched with oxygen when it leaves gills, the respiratory

organ for aquatic organisms

Amphibians and Reptiles - single ventricle pumps blood in thepulmonary circuit to the lungs Also pumps blood in the systemic circuit to the rest of the body

Although both O2 -rich and O2 -poor blood enter the single ventricle, it is

kept separate O2 -poor blood is pumped out of the ventricle to the lungs before O2-rich

blood enters and is pumped to the systemic circuit

Birds and Mammals Two atria and two ventricles in the heart and the complete separation of

the pulmonary and systemic circuits

Right ventricle pumps blood under pressure to the lungs, and the larger left ventricle pumps blood under pressure to the rest of the body 29-10



Figure 29.4A

Single-loop

circulatorypathway in fishes

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Figure 29.4B Two-

circuit pathway in

amphibians and

most reptiles

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Figure 29.4C Complete

separation of pulmonary

and systemic circuits in

birds, mammals, and

some reptiles

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The Mammalian Cardiovascular

System Consists of the Heartand Blood Vessels

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29.5 The mammalian heart

has four chambers All vertebrates have a closed circulatory system,

called a cardiovascular system because it

consists of a heart (cardio) and a system of

blood vessels (vascular ) Septum divides the heart into left and right sides

Right side of heart pumps O2-poor blood to lungs, and the left

side pumps O2-rich blood to tissues

Each side has two chambers Upper, thin-walled chambers are atria (sing., atrium)

Lower chambers are thick-walled ventricles

Atria receive blood; ventricles pump blood away from heart

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Heart Valves

Atrioventricular valves - between the atria andventricles

Semilunar valves - between the ventricles and their attached vessels

After the blood passes through the right atrioventricular valve, the right ventricle pumps it through the pulmonary semilunar valve into the pulmonary trunk andpulmonary arteries that take it to the lungs Pulmonary veins bring O2-rich blood back to the left atrium

After the blood passes through the left atrioventricular valve, the left ventricle pumps it through the aorticsemilunar valve into the aorta, which takes it to thetissues Heart murmur is often due to leaky atrioventricular valves,

which allow blood to pass back into the atria after they haveclosed 29

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Figure 29.5 Structure of the heart

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29.6 The heartbeat is rhythmic

The average human heart contracts, or beats, about 70 timesa minute, or 2.5 billion times in a lifetime Each heartbeat, called the cardiac cycle, can be divided into

three phases The atria contract (while the ventricles relax)

The ventricles contract (while the atria relax)

All chambers rest

Systole refers to contraction of the heart chambers, and theword diastole refers to relaxation of these chambers

When the heart beats, the familiar ³lub-dub ´ sound is heardas the valves of the heart close Pulse - wave effect that passes down walls of arterial blood

vessels following ventricular systole Rhythmic contraction of heart is due to cardiac conduction

system The SA (sinoatrial) node initiates the heartbeat every 0.85

seconds and is called the cardiac pacemaker

An electrocardiogram (ECG) is a recording of the electrical

changes that occur in the heart during a cardiac cycle29

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Figure 29.6A

The phases of

a heartbeat

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Figure 29.6B

Conduction

system of the

heart

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29.7 Blood vessel structure

is suited to its function Arteries (and arterioles) - carry blood away from the heart

to the capillaries Arteries have a much thick wall with elastic tissue that allows

arteries to expand and accommodate the sudden increase in bloodvolume that results after each heartbeat

Smaller arteries branch into a number of arterioles

Capillaries - permit exchange of material with tissues Extremely narrow (8±10 mm wide) and have thin walls composed

of single layer of epithelium with basement membrane

The thin walls of a capillary facilitate capillary exchange

Veins (and venules) - return blood from the capillaries tothe heart Venules (small veins) - drain blood from the capillaries; then join to

form a vein

Veins often have valves that allow blood to flow only toward theheart when open and prevent the backward flow of blood when

closed29

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Figure 29.7A

Types of

blood vessels

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Figure 29.7B Anatomy of a capillary bed

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29.8 Blood vessels form

two circuits in mammals The Pulmonary Circuit

O2-poor blood from all regions of body collects in right atrium andthen passes into right ventricle, which pumps it into the pulmonarytrunk

Pulmonary trunk divides into the right and left pulmonary arteries,

which carry blood to the lungs As blood passes through pulmonary capillaries, carbon dioxide is

given off and oxygen is picked up

O2-rich blood returns to left atrium of through pulmonary veins

The Systemic Circuit Aorta and the venae cavae (sing., vena cava ) are the major blood

vessels To trace the path of blood to any organ in the body, start with the

left ventricle, then go the aorta, then the proper branch of the aorta,the organ, and the vein returning blood to the vena cava, whichenters the right atrium

Portal systems begin and end in capillaries

Hepatic portal system takes blood from the intestines to the liver 29

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4



Figure 29.8

Path of blood

in the body

29

-2

5



29.9 Blood pressure is essential to

the flow of blood in each circuit Blood pressure is normally measured on the brachial

artery of the upper arm A blood pressure reading consists of two numbers that represent

systolic and diastolic pressures, respectively Systolic pressure results from blood being forced into the arteries

during ventricular systole Diastolic pressure is the pressure in the arteries during ventricular

diastole

Blood pressure accounts for the flow of blood from theheart to the capillaries As blood flows from the aorta into the various arteries and

arterioles, blood pressure falls Blood pressure in the veins is low and cannot move blood back

to the heart, especially from the limbs

Venous return depends upon three factors: Skeletal muscle contraction, presence of valves in veins, and

respiratory movements29-26



Figure 29.9A Velocity and blood pressure are related to the cross-

sectional area of the blood vessels

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Figure 29.9B How a valve affects the movement of blood in a vein

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APPLYING THE CONCEPTS²HOW BIOLOG Y IMPACTS OUR LIVES

29.10 Blood vessel deterioration

results in cardiovascular disease In U.S., about 20% of population suffers from

hypertension, high blood pressure Heredity and lifestyle contribute to hypertension

Hypertension is often seen in individuals who have atherosclerosis,which occurs when plaque protrudes into the lumen of a vessel andinterferes with the flow of blood

Plaque can cause a clot to form on the irregular arterial wall As long as the clot remains stationary, it is called a thrombus, but

when and if it dislodges and moves along with the blood, it is calledan embolus

A stroke often occurs when a small cranial arteriole burstsor is blocked by an embolus

Heart attack - when a coronary artery is completelyblocked, a portion of the heart muscle dies due to lack of oxygen

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APPLYING THE CONCEPTS²HOW BIOLOG Y IMPACTS OUR LIVES

29.11 Cardiovascular disease

can often be prevented The Don¶ts Smoking - When a person smokes, nicotine enters the

bloodstream and causes the arterioles to constrict and the bloodpressure to rise

Drug Abuse - Stimulants, such as cocaine and amphetamines,

can cause an irregular heartbeat and lead to heart attacks andstrokes

Weight Gain - in persons who are more than 20% above therecommended weight more tissues require servicing, and theheart sends the extra blood out under greater pressure

The Dos

HealthyD

iet - Physicians advise people to replace harmfulsaturated fats and trans fats with healthier ones, such asmonounsaturated fats (olive and canola oils) andpolyunsaturated fats (corn, safflower, and soybean oils)

Cholesterol Profile - Starting at age 20, all adults are advised tohave their cholesterol levels tested at least every five years

Exercise - People who exercise are less apt to have

cardiovascular disease29-30



Figure 29.11 Plaque buildup in a coronary artery

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Blood Has Vital Functions

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29.12 Blood is a liquid tissue

Blood¶s numerous functions include the following: Transports substances to and from the capillaries, where

exchanges with tissue fluid take place

Helps defend the body against invasion by pathogens

(e.g., disease-causing viruses and bacteria) Helps regulate body temperature

Forms clots, preventing a potentially life-threatening loss of blood

Blood has two main portions Plasma - composed mostly of water (90±92%) and

proteins (7±8%) Also contains smaller quantities of many types of molecules,

including nutrients, wastes, and salts

Formed elements - red blood cells, white blood cells, andplatelets

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Types of Blood Cells

Red blood cells (erythrocytes) - transport oxygen usinghemoglobin, which contains iron, and combines looselywith oxygen

White blood cells (leukocytes) - help fight infections

Neutrophils, which are amoeboid, squeeze through the capillarywall and enter the tissue fluid, where they engulf foreign material

Monocytes appear and are transformed into macrophages,large phagocytizing cells that release white blood cell growthfactors

Lymphocytes play important role in fighting infection T cells attack infected cells that contain viruses

B cells - produce antibodies Each B cell produces just one type of antibody, which is specific for one

type of antigen

An antigen, which is most often a protein but sometimes apolysaccharide, causes the body to produce an antibody to combinewith the antigen

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Figure 29.12 Composition of blood

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29.13 Blood clotting

involves platelets Platelets result from fragmentation of large cells in the bone marrow

called megakaryocytes Blood contains 150,000±300,000 platelets per mm3

When a blood vessel in the body is damaged platelets clump at the siteof the puncture and partially seal the leak

Platelets and the injured tissues release a clotting factor called prothrombinactivator that converts prothrombin to thrombin

Thrombin acts as an enzyme that severs two short amino acid chains fromeach fibrinogen molecule

These activated fragments then join forming long threads of fibrin that windaround the platelet plug in the damaged area of the blood vessel andprovide the framework for the clot

If blood is allowed to clot in a test tube, a yellowish fluid develops abovethe clotted material, called serum Contains all the components of plasma, except fibrinogen

Hemophilia is a well-known, inherited clotting disorder Due to the absence of a particular clotting factor, the slightest bump can

cause internal bleeding29-36



Figure 29.13 Blood clotting

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APPLYING THE CONCEPTS²HOW SCIENCE PROGRESSES

29.14 Adult stem cells

include blood stem cells A stem cell is a cell that is capable of becoming different

types of cells While embryonic stem cells possess the ability to become

virtually any cell type, adult stem cells are not quite as versatile

because they can become only certain other types of cell

Adult stem cells have been identified in many tissues,including the liver, skin, muscle, and even within thebrain, but the richest source is in the red bone marrow Adult stem cells from bone marrow are used to treat many white

blood cell and immune system disorders, including leukemia,certain blood cancers, and anemia

Like any organ transplant, a bone marrow transplant poses therisk of rejection

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Figure 29.14 Hematopoietic cells (adult stem cells in red bone

marrow) produce cells that become the various types of blood

cells.

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29.15 Capillary exchange

is vital to cells Capillary exchange occurs between a systemic capillary and

tissue fluid, the fluid between the body¶s cells Two forces control movement of fluid through capillary wall

Blood pressure, which tends to cause water to move out of a capillary intothe tissue fluid

Osmotic pressure, which tends to cause water to move from the tissue

fluid into a capillary Red blood cells and almost all plasma proteins remain in the

capillaries Fluid and other substances that leave a capillary contribute to the

tissue fluid

At the venous end of a capillary, blood pressure has fallen so

osmotic pressure is greater than blood pressure, and water tends to move into the capillary Some excess tissue fluid is always collected by the lymphatic

capillaries

Tissue fluid contained within lymphatic vessels is called lymph Lymph is returned to the systemic venous blood when the major lymphatic

vessels enter the subclavian veins in the shoulder region29-40



Figure 29.15A Capillary exchange

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Figure 29.15B A lymphatic capillary bed lies near a blood capillary

bed

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29.16 Blood types must be

matched for transfusions

ABO System

Presence or absence of type A and type B

antigens on red blood cells determines aperson¶s blood type

In the ABO system, there are four types of blood:

A, B, AB, and O

Type O blood has no antigens on the red blood cells andis sometimes called the universal donor

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Rh System and

Erythroblastosis Fetalis Rh System

Another important antigen in matching blood types is theRh factor

85% of the U.S. population have this particular antigen on

red blood cells and are called Rh-positive Erythroblastosis Fetalis

During pregnancy, if the mother is Rh-negative and thefather is Rh-positive, the child may be Rh-positive

Rh-positive red blood cells may begin leaking across theplacenta into the mother¶s cardiovascular system, sinceplacental tissues normally break down before and at birth

The mother produces anti-Rh antibodies, which may crossthe placenta and destroy the child¶s red blood cells duringa subsequent pregnancy

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Figure 29.16A No agglutination occurs when the donor and

recipient have the same type blood

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Figure 29.16B Agglutination occurs because blood typeB has

anti-A antibodies in the plasma

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Connecting the Concepts:

Chapter 29 It is possible to relate the type of cardiovascular system

to the lifestyle of an animal Some small, aquatic animals have no cardiovascular system²

external water passing in and out of a gastrovascular cavity issufficient to meet the needs of their cells

Grasshoppers have an open circulatory system, but they utilizetracheae to deliver oxygen directly to their muscles

We traced the evolution of the two-circuit circulatorypathway in vertebrates and saw that a two-circuitpathway allows blood to pass to the lungs and to thetissues under pressure This is particularly useful in birds and mammals, which maintain

a warm body and an active way of life

Body fluids make ideal culture media for the growth of infectiousparasites, and these fluids often have ways to ward off aninvasion. You already know that white blood cells are involved inthese endeavors

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Circulation and Cardiovascular Systems