CHAPTER 23 CIRCULATION. OPEN AND CLOSED CIRCULATORY SYSTEMS Among the unicellular protists, oxygen...

CHAPTER 23

CIRCULATION

OPEN AND CLOSED CIRCULATORY SYSTEMS

• Among the unicellular protists, oxygen and nutrients are obtained directly by simple diffusion.

• Cnidarians and flatworms have cells that are directly exposed to either the external environment or to a body cavity that functions in digestion, the gastrovascular cavity.

Gastrovascular cavity

MouthPharynx

Planaria: gastrovascular cavity


• Large animals have tissues that are several cell layers thick so that many cells are too far away for surface exchange.• Instead, oxygen and nutrients are transported

from the environment and digestive cavity to the body cells by an internal fluid within a circulatory system.• There are two main types of circulatory

systems:• Open circulatory system• Closed circulatory system


• In open circulatory systems, there is no distinction between the circulating fluid (blood) and the extracellular fluid of the body tissues (interstitial fluid or lymph).• This fluid is called hemolymph.• Insects have a muscular tube that serves as a

heart to pump the hemolymph through a network of open-ended channels.

Insect: open circulation

Tubular heart


• In a closed circulatory system, the circulating fluid (blood) is always enclosed within blood vessels that transport blood away from and back to a heart.• Annelids and all vertebrates have a closed

circulatory system.Dorsal blood vessel

Lateralhearts Ventral blood

vessel

Earthworm: closed circulation


• Arteries carry blood away from the heart, and veins return blood to the heart; blood passes from the arterial system to the venous system in capillaries.

• The pressure of the blood forces some fluid out of the capillary walls.


• The pressure of the blood forces some fluid out of the capillary walls.• This fluid is called interstitial fluid.

• Some of it will return to the blood but some becomes lymph and travels through the lymph vessels.


• The functions of the circulatory system can be divided into three areas:• Transportation

• Substances essential for cellular functions are transported by the circulatory system.

Cold blood VeinsArtery

Capillarybed

5º CTemperature

of environment

Core bodytemperature

36º C Warm blood

VeinsArtery


• Regulation• The cardiovascular

system participates in temperature regulation, such as by countercurrent heat exchange.


• Protection• The circulatory system protects against injury

and foreign microbes or toxins introduced into the body.

ARCHITECTURE OF THE VERTEBRATE CIRCULATORY

SYSTEM• The vertebrate circulatory system (also

known as the cardiovascular system) is made up of three elements.• Heart—a muscular pump that pushes blood

through the body.• Blood vessels—a network of tubes through

which the blood moves.• Blood—fluid that circulates through the

vessels.


SYSTEM• Blood moves through the body in a cycle, from

the heart, through a system of vessels.• Blood leaves the heart in arteries.• From the arteries, blood passes into smaller arterioles.• Tiny vessels called capillaries connect arterioles to

venules, or small veins.• Venules and then veins carry blood back to the heart.

Heart

Veins

Venules

Capillaries

Arterioles

Arteries


SYSTEM• Although each capillary is very narrow, there are

so many of them that the capillaries have the greatest total cross-sectional area of any other type of blood vessel.


SYSTEM• Capillary beds can be opened or closed based on

the physiological needs of the tissues.• Precapillary sphincters can contract or relax

and affect whether blood flows into a capillary bed for exchange of gases and metabolites.

1

2

3Precapillarysphincters open

Through-flowchannel

Precapillarysphincters closed

Arteriole VenuleCapillaries

(a) Blood flows through capillary network (b) Blood flow in capillary network is limited


SYSTEM• An artery is more

than a simple pipe.• It needs to be able

to expand with and be strong against the pressure caused by contraction of the heart.

• For this reason, arteries have both elastic and smooth muscle layers.

Connectivetissue

Smooth muscle

Elasticlayer

Endothelialcells

(a) Artery


SYSTEM• Arterioles differ from arteries in that they

are smaller in diameter and respond to nervous and hormonal stimulation.• They can constrict or expand to affect blood

flow during periods of stress or body activity.

(b) Capillary

Endothelialcells

Endothelium


SYSTEM• Capillaries are where

O2 and food molecules are transferred from the blood to the body’s cells and waste CO2 is picked up.• Capillaries are narrow

and have thin walls for exchange.

• Almost all cells of the vertebrate body are no more than 100 micrometers from a capillary.

• The blood pressure is actually far lower in the capillaries than in the arteries.


SYSTEM

• Veins are vessels that return blood to the heart.• The walls of veins

are thinner because the blood pressure is not great.

(c) Vein

Connective tissue

Smooth muscle

Elastic layer

Endothelium

Blood flowstoward heart

Openvalve

Vein

Contractingskeletalmuscles

Valveclosed


SYSTEM• Veins have

unidirectional valves that prevent the flow of blood backwards.

THE LYMPHATIC SYSTEM: RECOVERING LOST FLUID

• The cardiovascular system is very leaky.• From capillary exchange, the

body loses about 4 liters of fluid each day.

• To collect and recycle this fluid, the body uses a second circulatory system called the lymphatic system.• The lymphatic system is

also a network of vessels filled with a fluid called lymph.

• Ultimately the lymph reenters the bloodstream through veins in the neck .

Lymph nodes

Lymphatic vessels

Thymus

Spleen

LYMPHATIC CAPILLARIES RECLAIM FLUID FROM INTERSTITIAL FLUID

Lymphaticcapillary

Blood pressurecauses net filtration

Excess interstitial fluidbecomes lymph

Osmosis due to plasmaproteins causes netabsorption

Interstitialfluid

Capillary

VenuleArteriole

Bloodflow

THE LYMPHATIC SYSTEM: RECOVERING LOST FLUID

• The lymphatic system has 3 important functions:• It returns proteins to circulation.

• If this protein remains in the tissues, it would cause swelling or edema.

• It transports fats absorbed from the intestine.• It aids in the body’s defense.

• Swellings along lymph vessels called lymph nodes and a lymph organ called the spleen are where bacteria and dead blood cells are destroyed.

• The thymus produces white blood cells.

BLOOD

• Blood plasma is a complex solution of water with three kind of substances dissolved in it:• Metabolites and wastes

• Glucose, vitamins, hormones, wastes.• Salts and ions

• Sodium, chloride, and bicarbonate.• Proteins

• Proteins help keep water in the plasma.• Serum albumin functions in maintaining

osmotic balance.

THREADS OF FIBRIN

• Other proteins found in blood include: antibodies, globulins, and fibrinogen.• Fibrinogen

(which converts into fibrin) is required for blood clotting.

BLOOD

• Nearly half the volume of blood is occupied by cells.• The three principal cell types are:

• Erythrocytes (red blood cells)• The blood’s hematocrit is the fraction of the

total volume of the blood that is occupied by red blood cells.

• In humans, the hematocrit is usually about 45%.

• Leukocytes (white blood cells)• Platelets (cell fragments)

BLOOD

• Erythrocytes resemble flat disks with a central depression on both sides.• Almost the entire interior is packed with

hemoglobin, which carries oxygen.• Because these cells have no nucleus they are

short-lived and must be replaced by new cells synthesized in the bone marrow.

BLOOD

• Leukocytes contain no hemoglobin and are essentially colorless.• There are several different kinds, all of which

help defend the body against invading microorganisms and other foreign substances.

BLOOD

• Platelets are cell fragments, pinched from large cells in the bone marrow, called megakaryocytes, that play a key role in clotting.

FISH CIRCULATION

• The chordates that were ancestral to the vertebrates have simple tubular hearts.

• The evolution of gills by fishes required a more efficient pump, a true chamber-pump heart.

A V

VA

Sinusvenosus Atrium Ventricle Conus

arteriosus

SV CA

Systemiccapillaries

Respiratorycapillaries

GillsBody

SV CA

(a)

FISH CIRCULATION

• The fish heart is essentially a tube with four chambers arrayed one after another.• The sinus venosus (SV) and

atrium (A) are collecting chambers, and the ventricle (V) and conus arteriosus (CA) are pumping chambers.• The SV and CA chambers are

reduced in higher vertebrates.• The chambers contract in a

peristaltic sequence.• The blood that is pumped to the

body is fully oxygenated because it passes through the gills first, but it has less pressure.

AMPHIBIAN AND REPTILE CIRCULATION

• The advent of lungs involved a major change in the pattern of circulation.• After blood is pumped by the heart to the lungs,

it does not go directly to the tissues of the body but instead returns to the heart.• Pulmonary circulation goes to and from the

heart and lungs.• Systemic circulation goes to and from the

heart and the rest of the body.


• The amphibian heart has structural features to prevent the mixing of deoxygenated blood from the body with oxygenated blood from the lungs.


• The atrium is divided by a septum that separates the blood coming from the body and from the lungs.

• There is a single, common ventricle, but little mixing of blood occurs because• Some species of

amphibians have folds in the ventricle that direct the flow of blood from the atria

• The conus arteriosus is branched


• Amphibians in water supplement the oxygenation of their blood by obtaining additional oxygen by diffusion across their skin.• This is called cutaneous respiration.


• The reptilian heart is additionally specialized. • There is a partial septum in the ventricle.• The conus arteriosus has become incorporated

into the large arteries leaving the heart.

MAMMALIAN AND BIRD CIRCULATION

• Mammals, birds, and crocodiles have a four-chambered heart with two complete pumping circuits.• This increased efficiency of the double

circulation in mammals and birds may have been important in the evolution of endothermy.• More efficient circulation is necessary to

support the high metabolic rate required.


• In the mammalian heart,• Oxygen-rich blood

returns from the lungs through pulmonary veins to the left atrium of the heart and flows through the mitral valve into the left ventricle.

• The thick-walled left ventricle contracts, sending oxygenated blood through a large artery called the aorta and out to the body.• Backflow of blood from

the aorta is prevented by the aortic semilunar valve.

Superiorvena cava

Aorticsemilunarvalve

Pulmonarysemilunar valve

Right atrium

Tricuspid valve

Inferiorvena cava Right ventricle

Left ventricle

Bicuspid(mitral) valve

Left atrium

Pulmonaryveins

Pulmonaryartery

Aorta


• Blood travels through the body and returns to the heart via the vena cavae, which drain into the right atrium.

• Blood flows from the right atrium through the tricuspid valve to the right ventricle.

• The right ventricle contracts, pushing blood through the pulmonary valve into pulmonary arteries that lead to the lungs.

Superiorvena cava

Aorticsemilunarvalve

Pulmonarysemilunar valve

Right atrium

Tricuspid valve

Inferiorvena cava Right ventricle

Left ventricle

Bicuspid(mitral) valve

Left atrium

Pulmonaryveins

Pulmonaryartery

Aorta

http://youtu.be/gn6QmETEm8s

THE HEART AND CIRCULATION OF MAMMALS AND BIRDS

Superiorvena cava

Carotid artery

Jugular vein

Aorta

Pulmonaryartery

Heart

Inferiorvenacava

Aorta

Femoralarteryandvein

Femoralvein

Greatsaphenousvein

Brachialartery

Hepaticportalsystem

Radialartery

Femoralartery


• The simplest way to monitor heartbeat is to listen using a stethoscope.– “Lub” is the sound made by the closing

of the bicuspid and tricuspid valves at the start of ventricular contraction.

– “Dub” is the sound made by the closing of the pulmonary and aortic valves at the end of ventricular contraction.

• A heart murmur is heard due to turbulence created by the valves not closing fully.


• Another way to examine the events of the heartbeat is to monitor the blood pressure.– A device called a sphygmomanometer is

used to measure the blood pressure in the brachial artery of the arm.

– Diastolic pressure is the low pressure when the atria are filling.

– Systolic pressure is the high pressure associated with the ventricles contracting.

0 0

321 Bloodpressuregauge

150

200

2500

50

100150

200

100

50

250

Cuff pressure: 75Sound stops:Diastolic pressure

Cuff pressure: 120Pulse sound:Systolic pressure

Cuff pressure: 150No sound:artery closed

Cuff

100 150

50 200

250

Stethoscope

MEASURING BLOOD PRESSURE


• The contraction of the heart consists of a carefully orchestrated series of muscle contractions.• First the atria contract, followed by the

ventricles.• The sinoatrial (SA) node is the pacemaker of

the heart and determines the rhythm of the heart’s beating.


• Contraction of the atria is initiated by the SA node.

• The wave of depolarization does not immediately spread to the ventricles because it must pass first through cardiac muscle called the atrioventricular (AV) node.• This delays the signal for about 0.1 sec until the

atria have finished contracting.


• The ventricles finally contract after the signal passes from the AV node to an atrioventricular bundle of muscle called the bundle of His.

• Bundle branches divide into fast-conducting Purkinje fibers which initiate the almost simultaneous contraction of the right and left ventricles.

• The electrical activity of the heart can be measured by a recording called an electrocardiogram (ECG or EKG).

HOW THE MAMMALIAN HEART CONTRACTS

1 2 3 4

P T

R R

Q S

P wave in ECG QRS wave in ECG

Purkinje fibers

AV nodeSA node

Bundle of His

1 sec

QRS wave

RV

RA

LA

LV

ECG

CHAPTER 23 CIRCULATION. OPEN AND CLOSED CIRCULATORY SYSTEMS Among the unicellular protists, oxygen...

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