Circulation

Chapter 37

Impacts, Issues

And Then My Heart Stood Still

Each heartbeat starts with an electrical signal; in

sudden cardiac arrest, a defibrillator is needed

to restart the heart

37.1 The Nature of Blood Circulation

A circulatory system distributes materials

throughout the vertebrate body (and some

invertebrates)

A heart 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

Open and 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

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

Comparison of Flow Circuits

37.1 Key Concepts

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

37.2 Characteristics of Blood

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)

Components of Human Blood

Cellular Components of Human Blood

37.3 Hemostasis

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

Three-Phase Process of Hemostasis

37.4 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

ABO Blood Typing

Blood type O is a universal donor; blood type AB

can receive blood from any donor

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

37.2-37.4 Key Concepts

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

37.5 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

Pulmonary and Systemic Circuits

of the Human Cardiovascular System

Major Blood Vessels

of the Human Cardiovascular System

The Circulatory System and Homeostasis

37.6 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

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

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

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

The Cardiac Conduction System

37.5-37.6 Key Concepts

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

37.7 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

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

Blood Pressure in the Systolic Circuit

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

Distribution of Cardiac Output

in a Resting Person

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

37.8 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)

Fluid Movement at a Capillary Bed

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

Venous Valve Action

37.7-37.8 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

37.9 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

Clogged 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

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

37.9 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

37.10 Interactions With

the Lymphatic System

Vessels and organs of the lymphatic system

interact closely with the circulatory system

Lymph vascular system

• Lymph capillaries and vessels that collect water

and solutes from interstitial fluid and deliver them

to the circulatory system

Three Functions of

the Lymph Vascular System

Returns fluids and plasma proteins that leak out

of capillaries to the circulatory system

Delivers fats absorbed from the small intestine to

the blood

Transports cellular debris, pathogens, and

foreign cells to lymph nodes

Lymphoid Organs and Tissues

Lymph nodes

• Organs that filter lymph before it enters blood and

identify pathogens

Tonsils in throat and adenoids in nasal cavity

• Respond to inhaled pathogens

Lymphoid Organs and Tissues

Spleen

• Filters pathogens and worn out blood cells from

blood

Thymus gland

• Matures T lymphocytes essential to the immune

system

Components of the Lymphatic System

37.10 Key Concepts

Links With the Lymphatic System

A lymph vascular system delivers excess fluid

that collects in tissues to the blood

Lymphoid organs cleanse blood of infectious

agents and cellular debris