The Circulatory System

The Nature of Blood Circulation

A circulatory system distributes materials throughout the vertebrate body (and some invertebrates)

Uses a transport medium called blood. A heart is a muscular organ that pumps the

transport medium (blood) through vessels. Blood and interstitial fluid (fluid between cells)

make up the body’s internal environment

Two Kinds of Circulatory Systems

Open circulatory system (arthropods, mollusks)• Blood moves through hearts and large vessels, but

also mixes with interstitial fluid

Closed circulatory system (annelids, vertebrates)• Blood remains inside heart and blood vessels • Materials diffuse between blood and interstitial fluid

at capillaries

Fig. 37-2a, p. 638

pumpaorta heart

spaces or cavities in body tissues

A In a grasshopper’s open system, a heart (not like yours) pumps blood through a vessel, a type of aorta. From there, blood moves into tissue spaces, mingles with interstitial fluid, then reenters the heart at openings in the heart wall.

Open Circulatory Systems

Fig. 37-2b, p. 638

dorsal blood vesselpump

large-diameter blood vessels

large-diameter blood vessels

two of five hearts

ventral blood vessels

gut cavity capillary bed (many small vessels that serve as a diffusion zone)

B The closed system of an earthworm confines blood inside pairs of muscular hearts near the head end and inside many blood vessels.

Closed Circulatory Systems

Evolution of Circulation in Vertebrates

Fishes• Heart with two chambers• Single circuit of circulation

Amphibians• Heart with three chambers• Two partially separated circuits

Birds and mammals• Heart with four chambers• Two fully separate circuits

Fig. 37-3a, p. 639

A In fishes, the heart has two chambers: one atrium and one ventricle. Blood flows through one circuit. It picks up oxygen in the capillary beds of the gills, and delivers it to capillary beds in all body tissues. Oxygen-poor blood then returns to the heart.

capillary beds of gills

heart

rest of body

Single Circuit of Circulation

Fig. 37-3b, p. 639

lungs B In amphibians, the heart has three chambers: two atria and one ventricle. Blood flows along two partially separated circuits. The force of one contraction pumps blood from the heart to the lungs and back. The force of a second contraction pumps blood from the heart to all body tissues and back to the heart.

right atrium

left atrium

ventricle

rest of body

Two Partially Circuits of Circulation

Circulation in Birds and Mammals

The four-chambered heart has two separate halves, each with an atrium and a ventricle

Each half pumps blood in a separate circuit• Pulmonary circuit: Blood flows from right half of

heart, to lungs (gains oxygen), to left half of heart • Systemic circuit: Blood flows from left half of

heart, to body (loses oxygen), to right half of heart

Fig. 37-3c, p. 639

C In birds and mammals, the heart has four chambers: two atria and two ventricles. The blood flows through two fully separated circuits. In one circuit, blood flows from the heart to the lungs and back. In the second circuit, blood flows from the heart to all body tissues and back.

lungs

right atrium

left atrium

right ventricle left ventricle

rest of body

Two Fully Separate Circuits of Circulation

Fig. 37-3d, p. 639

D Why flow slows in capillaries. Picture a volume of water in two fast rivers flowing into and out of a lake. The flow rate is constant, with an identical volume moving from points 1 to 3 in the same interval. However, flow velocity decreases in the lake. Why? The volume spreads out through a larger cross-sectional area and flows forward a shorter distance during the specified interval.

lake

river in river out

1 2 3 1 2 3

1 2 3

Analogy of Slowing Blood in Capillaries

Overview of Circulatory Systems

Fill in the blank.

Many animals have either an ________ or a ________ circulatory system that transports substances to and from all body tissues.

All vertebrates have a _______ circulatory system, in which blood is _______________________________.

Overview of Circulatory Systems

Many animals have either an open or a closed circulatory system that transports substances to and from all body tissues

All vertebrates have a closed circulatory system, in which blood is always contained within the heart or blood vessels

Characteristics of Blood

Blood, considering it is made of cells, can be called a large interconnect tissue.

Blood consists mainly of plasma, a protein-rich fluid that carries wastes, gases and nutrients.

Blood cells and platelets form in bone marrow and are transported in plasma.• Platelets are fragments of megakaryocytes,

active in clotting.

Blood Cells

Red blood cells (erythrocytes)• Contain hemoglobin that carries oxygen from

lungs to tissues• Quantified in cell count

White blood cells (leukocytes)• Defend the body from pathogens• Neutrophils, basophils, eosinophils, monocytes,

and lymphocytes (B and T cells)

Fig. 37-4, p. 640

Stepped Art

Components Amounts Main Functions

Plasma Portion (50-60% of total blood volume)

Cellular Portion (40-50% of total blood volume; numbers per microliter)

1. Water 91-92% of totalplasma volume

Solvent

2. Plasma proteins (albumins, globulins, fibrinogen, etc. 7-8%

Defense, clotting, lipid transport, extracellular fluid volume controls

3. Ions, sugars, lipids, amino acids, hormones, vitamins, dissolved gases, etc.

1-2%Nutrition, defense, respiration, extracellular fluid volume controls, cell communication, etc.

1. Red blood cells

Red blood cell

4,600,000-5,400,000Oxygen, carbon dioxide transport to and from lungs

2. White blood cells: Neutophils Lymphoctyes Monocytes (macrophages) Eosinophils Basophils

White blood cell

3,000-6,7501,000-2,700150-720100-38025-90

Fast-acting phagocytosisImmune responsesPhagocytosisKilling parasitic wormsAnti-inflammatory secretions

3. Plateletsplatelet

250,000-300,000 Roles in blood clotting

Components of Human Blood

Fig. 37-5, p. 641

stem cell in bone marrow

myeloid stem cell lymphoid stem cell

red blood cell granulocyte monocyteprecursor precursor precursor

megakaryocytes

platelets red blood cells (erythrocytes)

neutrophilseosinophils

basophils monocytes (immature

phagocytes)B lymphocytes (mature in bone

marrow)

T lymphocytes (mature in

thymus)

Cellular Components of Human Blood

Hemostasis

Hemostasis = Heme (blood) stasis (balance)• Keeping blood pressure/volume stable.

How do we stop bleeding? Initiated by a hormone cascade when an injury

is sustained and blood vessels are broken. Hemostasis is a three-phase process that stops

blood loss, constructs a framework for repairs• Damaged vessel constricts• Platelets accumulate• Cascading enzyme reactions involving plasma

proteins cause clot formation

Fig. 37-6, p. 642

Stepped Art

StimulusA blood vessel is damaged.

Phase 1 responseA vascular spasm constricts the vessel.

Phase 2 responsePlatelets stick together plugging the site.

Phase 3 responseClot formation starts:

2. Factor X converts prothrombin in plasma to thrombin

3. Thrombin converts fibrinogen, a plasma protein, to fibrin threads.

4. Fibrin forms a net that entangles cells and platelets, forming a clot.

1. Enzyme cascade results in activation of Factor X.

Three-Phase Process of Hemostasis

Blood Typing

Blood type• Genetically determined differences in molecules

on the surface of red blood cells

Agglutination• Clumping of foreign cells by plasma proteins• When blood of incompatible types mixes, the

immune system attacks the unfamiliar molecules

Agglutination

Light micrographs showing (a) an absence of agglutination in a mixture of two different yet compatible blood types and (b) agglutination in a mixture of incompatible types.

ABO Blood Typing

Blood type O is a universal donor; blood type AB can receive blood from any donor

Fig. 37-8, p. 643

Blood Type of DonorO A B AB

O

A

B

Blo

od

Typ

e o

f R

ecip

ien

t

AB

Mixing ABO Blood Types

Rh Blood Typing

An Rh- mother may develop Rh+ antibodies if blood from an Rh+ child enters her bloodstream during childbirth

These antibodies may attack the red blood cells of the next Rh+ fetus

Rh Complications of Pregnancy

How Rh differences can complicate pregnancy.

Blood Composition and Function

Fill in the blanks. Vertebrate blood is a fluid connective ________.

It consists of _______, ________, ________, and _________ (the transport medium)

_____ _______ cells function in gas exchange; _____ _______ cells defend tissues, and _________ function in clotting

Blood Composition and Function

Vertebrate blood is a fluid connective tissue

It consists of red blood cells, white blood cells, platelets, and plasma (the transport medium)

Red blood cells function in gas exchange; white blood cells defend tissues, and platelets function in clotting

Human Cardiovascular System

The term “cardiovascular” comes from the Greek kardia (for heart) and Latin vasculum (vessel)

In a cardiovascular circuit, blood flows from the heart through arteries, arterioles, capillaries, venules, veins, and back to the heart.

Two Circuits of the Human Cardiovascular System

Pulmonary circuit• Oxygen-poor blood flows from the heart, through

a pair of lungs, then back to the heart• Blood takes up oxygen in the lungs

Systemic circuit• Oxygenated blood flows from the heart (through

the aorta) into capillary beds where it gives up O2 and takes up CO2, then flows back to the heart

Fig. 37-10a, p. 644

right pulmonary artery left pulmonary artery

capillary bed of right lung

capillary bed of left lung

pulmonary trunk

to systemic circuit

from systemic circuit

pulmonary veins

heart

Pulmonary Circuit of the Human Cardiovascular System

Accessing the lungs to rid blood stream of excess CO2 & to replenish O2

Blood vessels carrying oxygenated blood are shown in red. Those that hold oxygen-poor blood are color-coded blue.

capillary beds of head, upper extremities

(pulmonary vessels to and from thoracic cavity)

to pulmonary circuit

aorta

from pulmonary circuit

heart

capillary beds of other organs in thoracic cavity(diaphragm, the

muscular partition between thoracic and abdominal cavities) capillary bed of liver

capillary beds of intestines

BSystemic Circuit for

Blood Flow capillary beds of other abdominal organs and lower extremities

Systemic Circuit of the Human Cardiovascular System

Pulmonary and systemic circuits of the human cardiovascular system. Blood vessels carrying oxygenated blood are shown in red. Those that hold oxygen-poor blood are color-coded blue.

Accessing the rest of the body to deliver O2

& to retrieve CO2

The Pulmonary CircuitDoes?

The Systemic CircuitDoes?

Deo

xyge

nate

d bl

ood

brou

ght t

o th

e lu

ngs

to re

plen

ish

O2

Oxygenated blood sent

to heart to distribute O2

throughout body

Blue = deoxygenatedRed = oxygenated

Fig. 37-12, p. 645

food, water intake oxygen intake

Digestive System Respiratory System elimination of carbon dioxide

nutrients, water, salts oxygen carbon dioxide

Circulatory System Urinary System

water, solutes

elimination of food residues

rapid transport to and from all living cells

elimination of excess water, salts, wastes

The Circulatory System and Homeostasis

Functional links between the circulatory system and other organ systems with major roles in maintaining the internal environment.

The Human Heart

A sac of connective tissue (pericardium) surrounds the heart muscle (myocardium)

Endothelium lines heart chambers and blood vessels

Heart valves keep blood moving in one direction• AV valves separate atria and ventricles• Semilunar valves separate ventricles and arteries

Fig. 37-13b, p. 646

right lung left lungribs 1–8

B The heart is located between the lungs in the thoracic cavity.

1

3

2

4

5

6

7

8pericardium

diaphragm

The Human Heart

Fig. 37-13a, p. 646

superior vena cava (flow from head, arms)

arch of aorta

trunk of pulmonary arteries (to lungs)right semilunar valve

(shown closed) to pulmonary trunk left semilunar valve

(closed) to aortaright pulmonary veins (from lungs) left pulmonary veins

(from lungs)

right atrium left atrium

right AV valve (opened)

left AV valve (opened)

right ventricle left ventricle

(muscles that prevent valve from everting)

endothelium and underlying connective tissue

inferior vena cava (from trunk, legs)

myocardium

septum (partition between heart’s two halves)

inner layer of pericardium

heart’s apex

The Human Heart

Fig. 37-13c, p. 646

C Outer appearance. Pads of fat on the heart’s surface are normal.

The Human Heart

The Cardiac Cycle

Cardiac cycle: Heart muscle alternates between diastole (relaxation) and systole (contraction)• Blood collects in atria• AV valves open, blood flows into ventricles• Contraction of ventricles drives blood circulation• Ventricles contract with a wringing motion from

bottom to top

Fig. 37-14, p. 647

D Ventricles relax. Semilunar valves close as atria begin filling for the next cardiac cycle.

A Atria fill. Fluid pressure opens the AV valves, blood flows into the ventricles.

B Next, atria contract. As fluid pressure rises in the ventricles, AV valves close.

C Ventricles contract. Semilunar valves open. Blood flows into aorta and pulmonary artery.

Stepped Art

The Cardiac Cycle

Cardiac Muscle

Cardiac muscle cells are striated (divided into sarcomeres) and have many mitochondria

Cells attach end to end at intercalated discs

Neighboring cells communicate through gap junctions that conduct waves of excitation

Fig. 37-15, p. 647

intercalated disk a branching cardiac muscle cell (part of one cardiac muscle fiber)

b Part of a gap junction across the plasma membrane of a cardiac muscle cell. The junctions connect cytoplasm of adjoining cells and allow electrical signals that stimulate contraction to spread swiftly between them.

Cardiac Muscle Cells and Gap Junctions

How the Heart Beats

Cardiac pacemaker (SA node)• A clump of noncontracting cells in the right

atrium’s wall spontaneously fires action potentials about 70 times per minute

Cardiac conduction system• Signal spreads from SA node to AV node and

junctional fibers in the septum, so heart contracts in a coordinated fashion

Fig. 37-16, p. 647

SA node (cardiac pacemaker)

AV node (the only point of electrical contact between atria and ventricles)

junctional fibers

branchings of junctional fibers (carry electrical signals through the ventricles)

The Cardiac Conduction System

The Human Heart and Two Flow Circuits

Fill in the blanks The ______-chambered human heart pumps

blood through _____ separate circuits of blood vessels

One circuit extends through _____________, the other through _______ tissue only.

Both circuits loop back to the __________, which keeps blood flowing through the _______ circuits.

The Human Heart and Two Flow Circuits

The four-chambered human heart pumps blood through two separate circuits of blood vessels

One circuit extends through all body regions, the other through lung tissue only.

Both circuits loop back to the heart, which keeps blood flowing through the two circuits.

Part II

Pressure, Transport, and Flow Distribution

Fig. 37-11, p. 645

Jugular Veins Carotid Arteries

Ascending Aorta Superior Vena Cava

Pulmonary Arteries

Pulmonary VeinsCoronary Arteries

Hepatic Vein Brachial Artery

Renal Vein Renal Artery

Inferior Vena Cava Abdominal Aorta

Iliac Veins Iliac Arteries

Femoral ArteryFemoral Vein

Major Blood Vessels of the Human Cardiovascular System

Pressure, Transport, and Flow Distribution

Contracting ventricles put pressure on the blood, forcing it through a series of vessels• Arteries carry blood from ventricles to arterioles• Arterioles control blood distribution to capillaries• Capillaries exchange substances• Venules collect blood from capillaries• Veins deliver blood back to heart

Fig. 37-17a, p. 648

outer coat

smooth muscle

basement membrane endothelium

Artery

elastic tissue elastic tissue

Human Blood Vessels

Fig. 37-17b, p. 648

outer coat

smooth muscle rings over elastic tissue

basement membrane endothelium

Arteriole

Human Blood Vessels

Fig. 37-17c, p. 648

basement membrane endothelium

Capillary

(venules have a similar structure)

Human Blood Vessels

Fig. 37-17d, p. 648

outer coat

smooth muscle, elastic fibers

basement membrane endothelium

Vein

valve

Human Blood Vessels

Blood Pressure

Blood pressure• The pressure exerted by blood on the walls of

blood vessels• Highest in arteries, then declines through circuit• Rate of blood flow depends on the difference in

blood pressure between two points, and resistance to flow

Fig. 37-18, p. 648

arteries capillaries veins

arterioles venules

Blood Pressure in the Systolic Circuit: Plot of fluid pressure for a volume of blood as it flows through the systemic circuit. Systolic pressure occurs when ventricles contract, diastolic when ventricles are relaxed.

Blood Flow

Thick, elastic arteries smooth out variations in blood pressure during the cardiac cycle

Arterioles respond to signals from the autonomic and nervous systems, and to chemical signals, to direct blood flow to different parts of the body

Fig. 37-19, p. 649

liver 6%

heart’s right half heart’s left half

lungs100%

skeletal muscle

brain13%

15%kidneys

20%digestive tract

21%

cardiac muscle3%

bone5%

skin 9%

all other regions 8%

Distribution of Cardiac Output in a Resting Person

Figure It Out: What percentage of the brain’s blood supply arrives from the heart’s right half? Answer: None

Controlling Blood Pressure

Blood pressure depends on total blood volume, how much blood the ventricles pump (cardiac output), and whether arterioles are constricted or dilated

Receptors in the aorta and carotid arteries monitor blood pressure and send signals to the medulla, which regulates cardiac output and arteriole diameter

Measuring Blood Pressure

Diffusion at Capillaries, Then Back to the Heart

Capillary• A cylinder of endothelial cells, one cell thick• Capillary beds are diffusion zones, where blood

exchanges substances with interstitial fluid• Hydrostatic pressure moves materials out

(ultrafiltration)• Osmotic pressure moves water in (capillary

reabsorption)

blood to venule

high pressure causes outward flow

inward-directed osmotic movementcells of

tissue

Bblood from arteriole

A

Fluid Movement at a Capillary Bed

Fluid movement at a capillary bed. Fluid crosses a capillary wall by way of ultrafiltration and reabsorption. (a) At the capillary’s arteriole end, a difference between blood pressure and interstitial fluid pressure forces out plasma, but few plasma proteins, through clefts between endothelial cells of the capillary wall. Ultrafiltration is the outward flow of fluid across the capillary wall as a result of hydrostatic pressure. (b) Reabsorption is the osmotic movement of some interstitial fluid into the capillary. It happens when the water concentration between interstitial fluid and the plasma differs. Plasma, with its dissolved proteins, has a greater solute concentration and therefore a lower water concentration. Reabsorption near the end of a capillary bed tends to balance ultrafiltration at the start of it. Normally, there is only a small net filtration of fluid, which vessels of the lymphatic system return to blood (Section 37.10).

Venous Pressure

Venules deliver blood from capillaries to veins

Veins deliver blood to the heart• Large-diameter, blood volume reservoirs• Valves help prevent backflow• Amount of blood in veins varies with activity level

Fig. 37-22a, p. 651

venous valve

Venous Valve ActionVenous valve action. (a) Valves in medium-sized veins prevent the backflow of blood. Adjacent skeletal muscles helps raise fluid pressure inside a vein. (b) These muscles bulge into a vein as they contract. Pressure inside the vein rises and helps keeps blood flowing forward. (c) When muscles relax, the pressure that they exerted on the vein is lifted. Venous valves shut and cut off backflow.

blood flow to heart

valve open

valve closed

valve closed

valve closed

Key Concepts Blood Vessel Structure and Function

The heart pumps blood rhythmically, on its own

Adjustments at arterioles regulate how blood volume is distributed among tissues

Exchange of gases, wastes, and nutrients between the blood and tissues takes place at capillaries

Blood and Cardiovascular Disorders

Red blood cell disorders• Anemias, beta-thalassemias, polycythemia

White blood cell disorders• Infectious mononucleosis, leukemias, lymphomas

Clotting disorders• Hemophilia, thrombus, embolus

Blood and Cardiovascular Disorders

Atherosclerosis• Buildup of lipids in the arterial wall that narrows

the lumen, may rupture and trigger heart attack

Fig. 37-23a, p. 652

wall of artery, cross-section

unobstructed lumen of a normal artery

Fig. 37-23b, p. 652

atherosclerotic plaque

blood clot sticking to plaque

narrowed lumen

Clogged Coronary Arteries

Fig. 37-24a, p. 653

coronary artery

The photo shows coronary arteries and other blood vessels that service the heart. Resins were injected into them. Then the cardiac tissues were dissolved to make an accurate, three-dimensional corrosion cast.

Fig. 37-24b, p. 653

aorta

coronary artery blockage

location of a shunt made of a section taken from one of the patient’s other blood vessels

The sketch shows two coronary bypasses (color-coded green), which extend from the aorta past two clogged parts of the coronary arteries.

Blood and Cardiovascular Disorders

Hypertension – a silent killer• Chronic blood pressure above 140/90

High blood pressure and atherosclerosis increase the risk of heart attack and stroke

Fig. 37-25, p. 653

one normal heartbeat

0 0.2 0.4 0.6 0.8a time (seconds)

bradycardia (here, 46 beats per minute)

tachycardia (here, 136 beats per minute)

b

cventricular fibrillation

d

Blood and Cardiovascular Disorders

Arrhythmias – abnormal heart rhythms• EKGs record

electrical activity of cardiac cycle

Risk Factors

Cardiovascular disorders are the leading cause of death in the United States

Risk factors• Tobacco smoking, family history, hypertension,

high cholesterol, diabetes mellitus, obesity, age, physical inactivity, gender

Key Concepts When the System Breaks Down

Cardiovascular problems include clogged blood vessels or abnormal heart rhythms

Some problems have a genetic basis; most are related to age or life-style