What Are The Major Features And Functions Of Circulatory Systems?

• A circulatory system evolved in multicellular animals to bring the external world to each metabolizing cell in the animal, so that nutrients, oxygen, and waste products could be exchanged.

What Are The Major Features And Functions Of Circulatory Systems?• Circulatory systems have three main components:

• Blood• Blood vessels• Heart

Anatomy of Circulatory Systems

• arteries - vessels that carry blood away from the heart

• capillaries - smallest blood vessels (microscopic) penetrate tissues

• extracellular fluid - fluid surrounding capillaries; dissolved substances in the blood are exchanged

• veins – vessels that move blood back toward the heart

vertebrate circulatory systems transport…

• oxygen from the lungs or gills to the tissues• carbon dioxide from the tissues to the lungs or gills• nutrients from the digestive system to the tissues• waste products & toxins to the liver & kidney for excretion• hormones from the glands and organs that produce them to the tissues on

which they act

Circulatory Systems also• Help to regulate body temperature by adjusting blood flow• Help to protect the body from bacteria and viruses by circulating the

cells and molecules of the immune system

How Does The Vertebrate Heart Work?• The vertebrate heart consists of muscular chambers.

• In vertebrate hearts, muscular chambers, called atria, collect blood.

• Blood flows from the atria to the ventricles, chambers whose contractions circulate blood through the body.

• The number of atria and ventricles differs among different classes of vertebrates.

How Does The Vertebrate Heart Work?• Four-chambered hearts, like the human heart, can be

thought of as two separate pumps.• One pump, consisting of the right atrium and right

ventricle, pumps oxygen-depleted blood to the lungs.• The other pump, consisting of the left atrium and left

ventricle, moves oxygen-rich blood from the lungs and through the aorta to the rest of the body.

How Does The Vertebrate Heart Work?• The human heart and its valves and vessels

Fig. 20-3

aorta

left atrium

pulmonary artery(to left lung)

semilunar valves

pulmonary veins(from left lung)

atrioventricularvalve

left ventricle

thicker muscleof left ventricle

descending aorta(to lower body)right ventricle

inferior vena cava

atrioventricular valve

superiorvena cava

pulmonary artery(to right lung)

pulmonary veins(from right lung)

right atrium

How Does The Vertebrate Heart Work?• The atria and ventricles contract in a coordinated way.

• The chambers of the heart alternatively contract and relax• two atria contract at the same time, emptying their contents

into the ventricles.• A fraction of a second later, the two ventricles contract,

forcing blood into arteries that exit the heart• Both atria and ventricles then relax briefly, and the cycle

repeats.

How Does The Vertebrate Heart Work?• The cardiac cycle

Fig. 20-4

Atria contract, forcingblood into the ventricles

Then the ventriclescontract, forcing bloodthrough the arteries to thelungs and the rest of the body

The cycle endsas the heart relaxes

Deoxygenated blood ispumped to the lungs

Blood fills theatria and beginsto flow passivelyinto the ventricles

Deoxygenatedblood from thebody enters theright ventricle

Oxygenated blood from thelungs enters the left ventricle

Oxygenated bloodis pumped to thebody

How Does The Vertebrate Heart Work?• The atria and ventricles contract in a coordinated way

• At a normal resting heart rate, the cycle lasts about 1 second.

• Blood pressure changes as the cycle proceeds• systolic pressure is measured during ventricular

contraction• diastolic pressure is measured between contractions.

How Does The Vertebrate Heart Work?• Measuring blood pressure

Fig. 20-5

A stethoscopedetectspulse sounds

The cuff is inflated,putting pressureon the artery

cuff

How Does The Vertebrate Heart Work?• Valves prevent blood from

moving in the wrong direction.• Atrioventricular valves separate

the atria from the ventricles• Semilunar valves allow blood to

enter the pulmonary artery and the aorta when the ventricles contract

How Does The Vertebrate Heart Work?• Electrical impulses coordinate the sequence of

contractions.• Contractions are coordinated by the pacemaker,

a cluster of specialized heart muscle cells that produce spontaneous electrical signals.

• The heart’s primary pacemaker is the sinoatrial (SA) node, located in the wall of the right atrium.

How Does The Vertebrate Heart Work?• Electrical impulses coordinate the sequence of

contractions• From the SA node, an electrical impulse creates a

wave of muscular contraction that spreads through the right and left atria until it arrives at the unexcitable tissue between the atria and ventricles.

• There, the excitation is channeled through the atrioventricular (AV) node.

How Does The Vertebrate Heart Work?• Electrical impulses coordinate the sequence of contractions

• From the AV node, the signal to contract spreads along excitable fibers to the base of the two ventricles.

• This signal causes the ventricles to contract in unison.• If the pacemaker fails, uncoordinated irregular contractions, called

fibrillation, occurs, and blood cannot be pumped out of the heart.

How Does The Vertebrate Heart Work?• The heart’s pacemaker and its connections

Fig. 20-6

Unexcitable tissueseparates the atriaand ventricles

AV node

The sinoatrial nodeelectrical signal startsthe atrial contraction

The atrioventricularnode transmits thesignal to the ventricleswith a slight delay

The signal travels tothe base of the ventricles

Excitable fibers transmitthe signals to ventricularcardiac muscle, causingcontraction from the baseupwards

The signal spreads,causing the atria tocontract

excitablefibers

What Is Blood?• Blood transports dissolved nutrients, gases, hormones,

and wastes through the body. • It has two major components:

• A fluid, called plasma• Cellular components—including red blood cells, white

blood cells, and platelets—which are suspended in the plasma

• The cellular components are produced in bone marrow and later move into the blood.

What Is Blood?• Blood cells

Fig. 20-9

platelets

megakaryocyte

neutrophil neutrophil

basophil

monocyte

eosinophil

lymphocyte

red blood cells

Erythrocytes White blood cells

Megakaryocyte forming platelets

(a) (b)

(c)

What Is Blood?• Plasma is primarily water and dissolved substances.

• Plasma is 90% water.• Dissolved in the plasma are proteins, hormones,

nutrients, salts, and wastes, such as urea.

What Is Blood?• Red blood cells carry oxygen from the lungs to the

tissues.• The most abundant cells in the blood are red blood

cells.• Red blood cells get their red color from hemoglobin,

an iron-containing protein that can bind up to four oxygen molecules.

• Hemoglobin picks up oxygen in the lungs, where oxygen is at high concentration, and releases it in other tissues of the body, where the oxygen concentration is low.

What Is Blood?• White blood cells help defend the body against disease.

• White blood cells, or leukocytes, make up less than 1% of blood cells but play a key role in the body’s resistance to disease.

• There are five types of white blood cells:• Neutrophils • Eosinophils • Basophils • Lymphocytes• Monocytes

What Is Blood?• Lymphocytes are responsible for the immune response against

disease.• Neutrophils and monocytes engulf foreign particles.

Fig. 20-10

What Is Blood?• Platelets are cell fragments that aid in blood clotting.

• Platelets are pieces of large cells, called megakaryocytes, that occur in the bone marrow and enter the blood, playing a key role in blood clotting.

• Blood clotting starts when platelets contact an irregular surface, such as a damaged blood vessel, where they partially block the opening.

What Is Blood?• The platelets and injured tissue initiate a complex sequence of

reactions among plasma proteins, which results in a fibrous network, called fibrin, that traps red blood cells and closes the wound.

Fig. 20-11

platelets white blood cell

red blood cell

fibrin strands

What Are The Types And Functions Of Blood Vessels?

• As it leaves the heart, blood travels from arteries to arterioles to capillaries to venules to veins, and finally, it returns to the heart.

jugular vein

aorta

superiorvena cava

carotid artery

lungcapillaries

pulmonaryartery

heart

kidney

femoral vein

intestine

inferiorvena cava

liver

femoral artery

What Are The Types And Functions Of Blood Vessels?• Arteries and arterioles carry blood away from the heart.

• These vessels have thick walls embedded with smooth muscle and elastic connective tissue.

• Arteries branch into vessels of small diameter called arterioles.

precapillarysphincters

arteriole

venule

artery vein

capillaryvalve

smooth muscle

connective tissue

smoothmuscle

crosssection

capillarynetwork

Fig. 20-13

What Are The Types And Functions Of Blood Vessels?• Structures and interconnections of blood vessels

Fig. 20-13

precapillarysphincters

arteriole

venule

artery vein

capillaryvalve

smooth muscle

connective tissue

smoothmuscle

crosssection

capillarynetwork

What Are The Types And Functions Of Blood Vessels?• Capillaries are microscopic vessels through which nutrients and

wastes are exchanged.• Diffusion of nutrients and wastes occurs in capillaries, the smallest of

all blood vessels.• Because their walls are only one cell thick, substances can cross a

capillary cell’s plasma membrane and easily move into or out of capillaries.

• Capillaries are so narrow that red blood cells pass through them in single file.

• The speed of blood flow drops very quickly as it moves through this narrow capillary network.

• The flow of blood in capillaires is regulated by tiny rings of smooth muscle, called precapillary sphincters, which surround the junctions between arterioles and capillaries.

What Are The Types And Functions Of Blood Vessels?• Red blood cells flow through a capillary.

Fig. 20-14

Red blood cells mustpass through capillariesin single file

Capillary walls are thinand permeable to gases,nutrients, and cellularwastes

What Are The Types And Functions Of Blood Vessels?• Venules and veins carry blood back to the heart.

• After picking up carbon dioxide and other cellular wastes from cells, capillary blood drains into larger vessels called venules, which empty into larger veins.

• To prevent blood from flowing away form the heart, veins are equipped with valves that allow blood to flow in only one direction.

What Are The Types And Functions Of Blood Vessels?• Blood pressure is low in veins

and contraction of skeletal muscle during exercise helps return blood to the heart by squeezing the veins and forcing blood through them.

• Valves direct the flow of blood in veins.

Fig. 20-15

valveclosed

valveclosed

valveopen

relaxedmuscle

musclecontractioncompressesvein