gastrovascular cavity This cavity functions in both...

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Gastrovascular Cavities

• Simple animals, such as cnidarians, have a body

wall only two cells thick that encloses a

gastrovascular cavity

• This cavity functions in both digestion and

distribution of substances throughout the

body

• Some cnidarians, such as jellies, have elaborate

gastrovascular cavities


LE 42-2

Mouth Radial canal

Circular

canal

5 cm


Open and Closed Circulatory Systems

• More complex animals have either open or

closed circulatory systems

• Both systems have three basic components:

– A circulatory fluid (blood or hemolymph)

– A set of tubes (blood vessels)

– A muscular pump (the heart)


• In insects, other arthropods, and most molluscs

blood bathes the organs directly in an open

circulatory system

• There is no distinction between blood and

interstitial fluid, and this general body fluid is

more correctly called hemolymph

• In a closed circulatory system, blood is confined

to vessels and is distinct from the interstitial fluid

• Closed systems are more efficient at transporting

circulatory fluids to tissues and cells


LE 42-3

Hemolymph in sinusessurrounding organs

Heart

Anteriorvessel

Ostia

Tubular heart

An open circulatory system.

Lateralvessel

A closed circulatory system.

Auxiliary hearts Ventral vessels

Dorsal vessel(main heart)

Small branch vesselsin each organ

Interstitialfluid

Heart


Survey of Vertebrate Circulation

• Humans and other vertebrates have a closed

circulatory system, often called the

cardiovascular system

• Blood flows in a closed cardiovascular system,

consisting of blood vessels and a two- to four-

chambered heart

• Arteries carry blood to capillaries, the sites of

chemical exchange between the blood and

interstitial fluid

• Veins return blood from capillaries to the heart


LE 42-4

FISHES

Gill capillaries

AMPHIBIANS

Lung and skin capillaries

REPTILES (EXCEPT BIRDS)

Lung capillaries

MAMMALS AND BIRDS

Lung capillaries

Gillcirculation

Heart:Ventricle (V)

Atrium (A)

Artery

VeinSystemic

circulation

Systemic capillaries Systemic capillaries

Systemiccircuit

Pulmocutaneouscircuit

Right Left

AA

V

A

V

A

V

Systemic capillaries

Right Left

Pulmonarycircuit

Rightsystemic aorta

V

A

V

Systemic capillaries

Right Left

Pulmonarycircuit

A

Systemiccircuit

Leftsystemic aorta

Systemic circuits include all body tissues except lungs. Note that circulatory systems are depicted

as if the animal is facing you: with the right side of the heart shown at the left and vice-versa.


Mammalian Circulation: The Pathway

• Heart valves dictate a one-way flow of blood

through the heart

• Blood begins its flow with the right ventricle

pumping blood to the lungs

• In the lungs, the blood loads O2 and unloads CO2

• Oxygen-rich blood from the lungs enters the heart

at the left atrium and is pumped to the body

tissues by the left ventricle

• Blood returns to the heart through the right atrium


LE 42-5

Anterior

vena cava

Pulmonary

artery

Capillaries

of right lung

Aorta

Pulmonary

vein

Right atrium

Right ventricle

Posterior

vena cava

Capillaries of

abdominal organs

and hind limbs

Pulmonary

vein

Left ventricle

Left atrium

Aorta

Pulmonary

artery

Capillaries of

head and

forelimbs

Capillaries

of left lung


LE 42-6

Right

atrium

Posterior

vena cava

Pulmonary

veins

Anterior

vena cava

Pulmonary artery

Pulmonary

veins

Right

ventricle

Aorta

Semilunar

valve

Atrioventricular

valve

Pulmonary

artery

Left

atrium

Semilunar

valve

Atrioventricular

valve

Left

ventricle


• The heart contracts and relaxes in a rhythmic

cycle called the cardiac cycle

• The contraction, or pumping, phase is called

systole

• The relaxation, or filling, phase is called diastole

• The heart rate, also called the pulse, is the

number of beats per minute

• The cardiac output is the volume of blood

pumped into the systemic circulation per minute


• The sinoatrial (SA) node, or pacemaker, sets

the rate and timing at which cardiac muscle cells

contract

• Impulses from the SA node travel to the

atrioventricular (AV) node

• At the AV node, the impulses are delayed and

then travel to the Purkinje fibers that make the

ventricles contract

• Impulses that travel during the cardiac cycle can

be recorded as an electrocardiogram (ECG or

EKG)


LE 42-8

Pacemakergenerates wave ofsignals to contract.

Signals are delayedat AV node.

Signals passto heart apex.

Signals spreadthroughoutventricles.

SA node(pacemaker)

ECG

AV node

Bundlebranches Heart

apex

Purkinjefibers

The pacemaker is influenced by nerves, hormones, body

temperature, and exercise


LE 42-9

Endothelium

Endothelium

Smooth

muscle

Connective

tissue

Capillary

100 µm

Basement

membrane

Endothelium

Smooth

muscle

Connective

tissue

Valve

Artery

Arteriole Venule

Vein

Artery Vein


• Structural differences in arteries, veins, and

capillaries correlate with functions

• Arteries have thicker walls that accommodate the

high pressure of blood pumped from the heart

• In the thinner-walled veins, blood flows back to

the heart mainly as a result of muscle action

Blood Vessel Structure and Function


LE 42-10

Valve (open)

Skeletal muscle

Valve (closed)

Direction of blood flow

in vein (toward heart)


Blood Flow Velocity

• Physical laws governing movement of fluids

through pipes affect blood flow and blood pressure

• Velocity of blood flow is slowest in the

capillary beds, as a result of the high

resistance and large total cross-sectional area


LE 42-11

Systolic

pressure

Ve

na

e c

ava

e

Ve

ins

Ve

nu

les

Cap

illa

rie

s

Art

eri

ole

s

Art

eri

es

Ao

rta

Diastolic

pressure

Pre

ss

ure

(m

m H

g)

120100

806040200

Are

a (

cm

2)

5,000

4,000

3,000

2,000

1,000

0

Ve

loc

ity (

cm

/se

c)

50

40

30

20

10

0


Blood Pressure

• Blood pressure is the hydrostatic pressure that

blood exerts against the wall of a vessel

• Systolic pressure is the pressure in the arteries

during ventricular systole; it is the highest

pressure in the arteries

• Diastolic pressure is the pressure in the arteries

during diastole; it is lower than systolic pressure

• Blood pressure is determined by cardiac output

and peripheral resistance due to constriction of

arterioles


LE 42-12_4

Artery Artery

closed

Pressure

in cuff

above 120

120Rubber cuff

inflated

with air

Pressure

in cuff

below 120

120

Sounds

audible in

stethoscope

Pressure

in cuff

below 70

70

Blood pressure

reading: 120/70

Sounds

stop


Capillary Function

• Capillaries in major organs are usually filled to

capacity

• Two mechanisms regulate distribution of blood in

capillary beds:

– Contraction of the smooth muscle layer in the

wall of an arteriole constricts the vessel

– Precapillary sphincters control flow of

blood between arterioles and venules


LE 42-13ab

Precapillary sphincters Thoroughfare

channel

CapillariesVenuleArteriole

Sphincters relaxed

VenuleArteriole

Sphincters contracted


• The critical exchange of substances between the

blood and interstitial fluid takes place across the

thin endothelial walls of the capillaries

• The difference between blood pressure and

osmotic pressure drives fluids out of

capillaries at the arteriole end and into

capillaries at the venule end


LE 42-14

Capillary Red bloodcell

15 µm

Tissue cell

CapillaryNet fluidmovement out

INTERSTITIAL FLUID

Net fluidmovement in

Blood pressure

Osmotic pressure

Inward flow

Direction ofblood flow

Pre

ss

ure

Outward flow

Venous endArterial end of capillary


Fluid Return by the Lymphatic System

• The lymphatic system returns fluid to the body

from the capillary beds

• This system aids in body defense

• Fluid reenters the circulation directly at the venous

end of the capillary bed and indirectly through the

lymphatic system


Blood Composition and Function

• Blood consists of several kinds of cells suspended

in a liquid matrix called plasma

• The cellular elements occupy about 45% of the

volume of blood


Plasma

• Blood plasma is about 90% water

• Among its solutes are inorganic salts in the form of

dissolved ions, sometimes called electrolytes

• Another important class of solutes is the plasma

proteins, which influence blood pH, osmotic

pressure, and viscosity

• Various plasma proteins function in lipid transport,

immunity, and blood clotting


LE 42-15

SodiumPotassiumCalciumMagnesiumChlorideBicarbonate

Osmotic balance,pH buffering, andregulation ofmembranepermeability

Plasma 55%

Constituent Major functions

Water Solvent forcarrying othersubstances

Ions (blood electrolytes)

Albumin Osmotic balance,pH buffering

Plasma proteins

Fibrinogen

Immunoglobulins(antibodies)

Clotting

Defense

Nutrients (such as glucose, fatty acids, vitamins)

Waste products of metabolismRespiratory gases (O2 and CO2)Hormones

Substances transported by blood

Cellular elements 45%

Cell type Number Functionsper µL (mm3) of blood

5–6 million Transport oxygenand help transportcarbon dioxide

Leukocytes

(white blood cells)5,000–10,000

Defense andimmunity

Monocyte

Basophil

Eosinophil

Lymphocyte

Neutrophil

PlateletsBlood clotting250,000–

400,000

Erythrocytes

(red blood cells)

Separated

blood

elements


Cellular Elements

• Suspended in blood plasma are two types of cells:

– Red blood cells (erythrocytes) transport

oxygen

– White blood cells (leukocytes) function in

defense

• Platelets, a third cellular element, are

fragments of cells that are involved in clotting


• Red blood cells, or erythrocytes, are by far the

most numerous blood cells

• There are five major types of white blood cells, or

leukocytes: monocytes, neutrophils, basophils,

eosinophils, and lymphocytes

• They function in defense by phagocytizing

bacteria and debris or by producing antibodies

• Erythrocytes, leukocytes, and platelets all

develop from a common source, pluripotent

stem cells in the red marrow of bones


LE 42-16

Pluripotent stem cells

(in bone marrow)

Myeloid

stem cellsLymphoid

stem cells

B cells T cells

Lymphocytes

Erythrocytes

Eosinophils

Basophils

Neutrophils

MonocytesPlatelets


Blood Clotting

• When the endothelium of a blood vessel is

damaged, the clotting mechanism begins

• A cascade of complex reactions converts

fibrinogen to fibrin, forming a clot


LE 42-17

Endothelium of

vessel is damaged,

exposing connective

tissue; platelets adhere

Platelets form a plug Seal is reinforced by a clot of fibrin

Collagen fibers

Platelet plug

Platelet releases chemicalsthat make nearby platelets sticky

Clotting factors from:

PlateletsDamaged cellsPlasma (factors include calcium, vitamin K)

Prothrombin Thrombin

Fibrinogen Fibrin

Fibrin clot Red blood cell

5 µm


LE 42-18

Connectivetissue

Smoothmuscle Endothelium

50 µmNormal artery Partly clogged artery 250 µm

Plaque


• Hypertension, or high blood pressure, promotes

atherosclerosis and increases the risk of heart

attack and stroke

• A heart attack is the death of cardiac muscle

tissue resulting from blockage of one or more

coronary arteries

• A stroke is the death of nervous tissue in the brain,

usually resulting from rupture or blockage of

arteries in the head

Cardiovascular Disease


Gas exchange occurs across specialized respiratory surfaces

• Gas exchange supplies oxygen for cellular

respiration and disposes of carbon dioxide

• Animals require large, moist respiratory

surfaces for adequate diffusion of gases between

their cells and the respiratory medium, either air or

water


LE 42-19

Respiratory

medium

(air or water)

Organismal

level

Cellular level

Energy-rich

fuel molecules

from food

Respiratory

surface

Circulatory system

Cellular respiration

CO2O2

ATP


Gills in Aquatic Animals

• Gills are outfoldings of the body surface

specialized for gas exchange

• In some invertebrates, gills have a simple shape

and are distributed over much of the body

• Many segmented worms have flaplike gills that

extend from each segment of their body

• The gills of clams, crayfish, and many other

animals are restricted to a local body region


LE 42-20a

Gills

Coelom

Tube foot

Sea star


LE 42-20b

Gill

Parapodia

Marine worm


LE 42-20c

Gills

Scallop


LE 42-20d

Gills

Crayfish


• Effectiveness of gas exchange in some gills,

including those of fishes, is increased by

ventilation and the countercurrent flow of blood

and water


LE 42-21

Gill

arch

Water

flow Operculum

Gill

arch

Blood

vessel

Oxygen-rich

blood

Water flow

over lamellae

showing % O2

Gill

filaments

O2

Oxygen-poor

blood

Lamella

Blood flow

through capillaries

in lamellae

showing % O2

Countercurrent exchange


Tracheal Systems in Insects

• The tracheal system of insects consists of tiny

branching tubes that penetrate the body

• The tracheal tubes supply O2 directly to body

cells


LE 42-22a

Air sacs Tracheae

Spiracle


LE 42-22b

Bodycell

TracheoleAirsac

Trachea

Air Body wall

MyofibrilsTracheoles Mitochondria

2.5 µm


Lungs

• Spiders, land snails, and most terrestrial

vertebrates have internal lungs

• An amphibian such as a frog ventilates its lungs by

positive pressure breathing, which forces air down

the trachea


Mammalian Respiratory Systems: A Closer Look

• A system of branching ducts conveys air to the

lungs

• Air inhaled through the nostrils passes through the

pharynx into the trachea, bronchi, bronchioles,

and dead-end alveoli, where gas exchange occurs


Branchfrompulmonaryvein(oxygen-richblood)

Terminalbronchiole

Branchfrompulmonaryartery(oxygen-poorblood)

Alveoli

Colorized SEMSEM

Nasalcavity

Leftlung

Heart

Larynx

Pharynx

Esophagus

Trachea

Rightlung

Bronchus

Bronchiole

Diaphragm


How a Bird Breathes

• Birds have eight or nine air sacs that function as

bellows that keep air flowing through the lungs

• Air passes through the lungs in one direction only

• Every exhalation completely renews the air in the

lungs


LE 42-25

Anteriorair sacs

LungsPosteriorair sacs

Trachea

Air

Lungs

Air

Air tubes(parabronchi)in lung 1 mm

EXHALATIONAir sacs empty; lungs fill

INHALATIONAir sacs fill


How a Mammal Breathes

• Mammals ventilate their lungs by negative

pressure breathing, which pulls air into the lungs

• Lung volume increases as the rib muscles and

diaphragm contract


LE 42-24

Rib cageexpands asrib musclescontract

Airinhaled

Lung

Diaphragm

INHALATIONDiaphragm contracts

(moves down)

Rib cage getssmaller asrib musclesrelax

Airexhaled

EXHALATIONDiaphragm relaxes

(moves up)


Control of Breathing in Humans

• In humans, the main breathing control centers

are in two regions of the brain, the medulla

oblongata and the pons

• The medulla regulates the rate and depth of

breathing in response to pH changes in the

cerebrospinal fluid

• The medulla adjusts breathing rate and depth to

match metabolic demands


LE 42-26

Breathingcontrolcenters

Cerebrospinalfluid

Medullaoblongata

Pons

Carotidarteries

Aorta

Diaphragm

Rib muscles


The Role of Partial Pressure Gradients

• Gases diffuse down pressure gradients in the

lungs and other organs

• Diffusion of a gas depends on differences in a

quantity called partial pressure

• A gas diffuses from a region of higher partial

pressure to a region of lower partial pressure

• In the lungs and tissues, O2 and CO2 diffuse from

where their partial pressures are higher to where

they are lower


LE 42-27

Inhaled air

Bloodenteringalveolar

capillaries

Alveolarepithelialcells

Alveolar spaces

Alveolarcapillaries

of lung

Exhaled air

Bloodleavingalveolar

capillaries

Pulmonaryveins

Pulmonaryarteries

Tissuecapillaries

HeartSystemicveins

Systemicarteries

Bloodleavingtissue

capillaries

Bloodenteringtissue

capillaries

Tissuecells

CO2O2

CO2O2

O2 CO2

CO2O2

< 40 > 45

40 45

CO2O2

100 40

CO2O2

40 45

CO2O2

104 40

CO2O2

CO2O2

CO2 O2

104 40

120 27160 0.2


Respiratory Pigments

• Respiratory pigments, proteins that transport

oxygen, greatly increase the amount of oxygen

that blood can carry

• The respiratory pigment of almost all vertebrates

is the protein hemoglobin, contained in

erythrocytes

• Like all respiratory pigments, hemoglobin must

reversibly bind O2, loading O2 in the lungs and

unloading it in other parts of the body


LE 42-28

Polypeptide chain

O2 unloadedin tissues

O2 loadedin lungs

Iron atomHeme group


• Loading and unloading of O2 depend on

cooperation between the subunits of the

hemoglobin molecule

• The binding of O2 to one subunit induces the other

subunits to bind O2 with more affinity

• Cooperative O2 binding and release is evident in

the dissociation curve for hemoglobin

• A drop in pH lowers affinity of hemoglobin for O2


LE 42-29a

O2 unloaded fromhemoglobinduring normalmetabolism

O2 reserve that canbe unloaded fromhemoglobin totissues with highmetabolism

P and hemoglobin dissociation at 37°C and pH 7.4O2

P (mm Hg)O2

Tissues duringexercise

Tissues at rest

Lungs

1008060402000

20

40

60

80

100

O2

satu

rati

on

of

hem

og

lob

in (

%)


LE 42-29b

Bohr shift:additional O2

released fromhemoglobin atlower pH(higher CO2

concentration)

pH and hemoglobin dissociation

P (mm Hg)O2

1008060402000

20

40

60

80

100

O2

satu

rati

on

of

hem

og

lob

in (

%)

pH 7.2

pH 7.4


Carbon Dioxide Transport

• Hemoglobin also helps transport CO2 and assists

in buffering

• Carbon from respiring cells diffuses into the blood

plasma and then into erythrocytes and is

ultimately released in the lungs


LE 42-30

CO2 transportfrom tissuesCO2 produced

Tissue cell

CO2

CO2

CO2

Interstitialfluid

Blood plasmawithin capillary

Capillarywall

Hemoglobinpicks up

CO2 and H+

CO2 transportto lungs

To lungs

H2CO3

Carbonic acid

H2O

Hb

HCO3–

Bicarbonate

Redbloodcell

H++

HCO3–

HCO3–

Hemoglobinreleases

CO2 and H+

H++HCO3–

CO2

H2CO3

H2O

CO2

CO2

CO2

Hb

Alveolar space in lung

gastrovascular cavity This cavity functions in both...

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