Circulation and Gas Exchange
Chapter 42 (all)
4-17-06
• Overview: Trading with the Environment
• Every organism must exchange materials
with its environment (whether it be
nutrients or gases (oxygen and carbon
dioxide)
– And this exchange ultimately occurs at the
cellular level
• In unicellular organisms
– These exchanges occur directly with the environment
across the cell membrane. Diffusion is adequate for
necessary rapid exchange.
• For most of the cells making up multicellular
organisms direct exchange with the environment
is not possible because diffusion distances are too
great! Therefore specialized exchange and
transport systems have evolved!
Gills as exchange sites in aquatic animals!
• The feathery gills projecting from a salmon
– Are an example of a specialized exchange system
found in animals
Gill arch with
filaments which
have lamellae on
both sides!
Surface area of gill
equal body skin
surface area!
Figure 42.1
• Transport systems
– Functionally connect the organs of exchange
with the body cells where nutrients and
oxygen required!
• Most complex animals have internal
transport systems providing a conduit
between the evironment and the cell
cytoplasm!
Invertebrate Circulation
• The wide range of invertebrate body size
and form is paralleled by a great diversity
in circulatory systems. Water vascular
system in star fish, open circulatory
systems in insects and closed circulatory
systems in earth worms and squids.
Gastrovascular Cavities
• Simple animals, such as cnidarians
– Have a body wall only two cells thick that
encloses a gastrovascular cavity (recall sea
anemone sac with a mouth!)
• The gastrovascular cavity
– Functions in both digestion and distribution of
substances throughout the body. Also gas
exchange for cells lining the cavity.
• Some cnidarians, such as jellies
– Have elaborate gastrovascular cavities with
canals radiating off the central sac!
Circular
canal
Mouth
Radial canal
5 cm
Figure 42.2
Open and Closed Circulatory
Systems
• More complex animals
– Have one of two types of circulatory systems:
open or closed
• Both of these types of systems have three
basic components
– A circulatory fluid (blood)
– A set of tubes (blood vessels)
– A muscular pump (the heart)
Open circulatory systems
• In insects, other arthropods, and most molluscs
– Blood bathes the organs and tissues directly in an
open circulatory system
Heart
Valves in heart so
blood flow is
unidirectional
Hemolymph in sinuses
surrounding ograns
Anterior
vessel
No interstitial
space or fluid!
Figure 42.3a
Lateral
vessels
Ostia
Tubular heart
(a) An open circulatory system
Closed Circulatory System
• In a closed circulatory system
– Blood is confined to vessels and is distinct
from the interstitial fluid
Heart
Closed systems
are more efficient at
transporting
circulatory fluids to
tissues and cells.
Interstitial
fluid
Small branch vessels
in each organ
Dorsal vessel
(main heart)
Earthworm an
annelid is the first
time we see a
closed circulatory
system!
Figure 42.3b
Auxiliary hearts
Ventral vessels
(b) A closed circulatory system
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 fourchambered heart.
• Arteries carry blood from heart to capillaries
– The capillaries are the sites of chemical exchange
between the blood and interstitial fluid
• Veins collect blood from capillaries and return
blood to the heart.
– Types of hearts!
Vertebrate circulatory systems
AMPHIBIANS
REPTILES (EXCEPT BIRDS)
MAMMALS AND BIRDS
Lung and skin capillaries
Lung capillaries
Lung capillaries
FISHES
Gill capillaries
Artery
Pulmocutaneous
circuit
Gill
circulation
Heart:
ventricle (V)
A
Atrium (A)
Systemic
Vein circulation
Systemic capillaries
Right
systemic
aorta
Pulmonary
circuit
A
A
V
Right
V
Left
Right
Systemic
circuit
Systemic capillaries
Figure 42.4
Pulmonary
circuit
Left
Systemic
V aorta
Left
A
Systemic capillaries
A
V
Right
A
V
Left
Systemic
circuit
Systemic capillaries
Fishes- two chambered heart!
• A fish heart has two main chambers
– One ventricle and one atrium and blood
pumped from the ventricle through the gills
where it is loaded with oxygen and unloadsf
CO2. It then travels through the dorsal aorta
to the organs and tissues thru capillary beds
and is returned to the heart as venous blood.
Where does heart get its oxygen? Enough
remains in the venous blood. In some active
species (Tuna fishes) a branch off the ventral
aorta supplies oxygenated blood to the heart.
Amphibians
• Frogs and other amphibians have a threechambered heart, with two atria and one ventricle
• The ventricle pumps blood into a forked artery that
splits the ventricle’s output into the
pulmocutaneous circuit (lung and skin) and the
systemic circuit. Thus a certain amount of mixing
of oxygenated and oxygen poor blood occures.
Reptiles (Except Birds)
• Reptiles have double circulation
– With a pulmonary circuit (lungs) and a
systemic circuit
• Turtles, snakes, and lizards
– Have a three-chambered heart.
Mammals and Birds
• In all mammals and birds
– The ventricle is completely divided into
separate right and left chambers
• The left side of the heart pumps and
receives only oxygen-rich blood
– While the right side receives and pumps only
oxygen-poor blood
• A powerful four-chambered heart
– Was an essential adaptation of the
endothermic way of life characteristic of
mammals and birds. Reason is because of
metabolism being almost 10 times greater
than the ectotherms!
• A powerful four-chambered heart was an essential
adaptation of the endothermic way of life
characteristic of mammals and birds. Reason is
because of metabolism being almost 10 times
greater than the ectotherms!
• Double circulation in mammals depends on the
anatomy and pumping cycle of the heart (Good
model).
• 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
The mammalian cardiovascular system
7
See text for
description of
sequential
events
Capillaries of
head and
forelimbs
Anterior
vena cava
Pulmonary
artery
Aorta
Pulmonary
artery
9
6
Capillaries
of right lung
Capillaries
of left lung
2
4
3
Pulmonary
vein
5
1
Right atrium
3
11
Left atrium
Pulmonary
vein
10
Left ventricle
Right ventricle
Aorta
Posterior
vena cava
8
Figure 42.5
Capillaries of
abdominal organs
and hind limbs
The Mammalian Heart: A Closer Look
• A closer look at the mammalian heart
– Provides a better understanding of how
double circulation works
Pulmonary artery
Aorta
Pulmonary
artery
Anterior vena cava
Left
atrium
Right atrium
In fetus ductus
artieriosus shunts
blood from
pulmonary artery
into the aorta.
Closes off at birth
when the lungs
inflate!
Figure 42.6
Pulmonary
veins
Pulmonary
veins
Semilunar
valve
Semilunar
valve
Atrioventricular
valve
Atrioventricular
valve
Posterior
vena cava
Right ventricle
Left ventricle
• The heart contracts and relaxes
– In a rhythmic cycle called the cardiac cycle
• The contraction, or pumping, phase of the
cycle
– Is called systole
• The relaxation, or filling, phase of the cycle
– Is called diastole
• The cardiac cycle: filling of chambers longest!
2 Atrial systole;
ventricular
diastole
Semilunar
valves
closed
0.1 sec
Semilunar
valves
open
0.3 sec
0.4 sec
AV valves
open
1 Atrial and
ventricular
diastole
Figure 42.7
AV valves
closed
3 Ventricular systole;
atrial 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 and depends
on the rate of contraction and the stroke
volume (how much blood is “loaded” into the
ventricle during diastole).
Maintaining the Heart’s Rhythmic Beat
• Some cardiac muscle cells are self-excitable (myogenic)
– Meaning they contract without any signal from the
nervous system (heart transplant).
• A region of the heart called the sinoatrial (SA) node, or
pacemaker sets the rate and timing at which all cardiac
muscle cells contract
• Impulses from the SA node spread across the atria to the
atrioventricular (AV) node
• At the AV node, the impulses are delayed and then travel
down bundle fiber to the the Purkinje fibers that make the
ventricles contract
• The impulses that travel during the cardiac
cycle
– Can be recorded as an electrocardiogram
(ECG or EKG)
The control of heart rhythm
• The impulses that travel during the cardiac cycle
can be recorded as an electrocardiogram (EKG)
1 Pacemaker generates
2 Signals are delayed
wave of signals in the atria
to contract.
SA node
(pacemaker)
3 Signals pass
at AV node.
AV node
to heart apex.
4 Signals spread
throughout
ventricles.
Bundle
branches
Heart
apex
ECG
Figure 42.8
Purkinje
fibers
• The pacemaker is influenced by
– Nerves, hormones, body temperature, and
exercise
Blood Circulation
• The same physical principles that govern
the movement of water in plumbing systems
– Also influence the functioning of animal
circulatory systems.
– Structure of circulatory system is a network of
vessels that are differ in structure to
accommodate function.
• The velocity of blood flow varies in the
circulatory system
Systolic
pressure
Veins
Venules
Arterioles
Capillaries
Diastolic
pressure
Arteries
120
100
80
60
40
20
0
Aorta
Area (cm2)
Velocity (cm/sec)
50
40
30
20
10
0
Venae cavae
Figure 42.11
5,000
4,000
3,000
2,000
1,000
0
Pressure (mm Hg)
– And is slowest in the capillary beds as a result of
the high resistance and large total cross-sectional
area
• All blood vessels
– Are built of similar tissues
– Have three similar layers
Artery
Arteries have thicker
walls to accommodate
the high pressure of
blood pumped from the
heart. Veins thinner
walls.
Basement membrane
composed of
mucopolysaccharides
and collagen fibers.
Not a barrier to
diffusion of molecules.
Vein
Basement
membrane
Endothelium
100 µm
Valve
Endothelium
Smooth
muscle
Connective
tissue
Endothelium
Capillary
Smooth
muscle
Connective
tissue
Artery
Vein
Venule
Figure 42.9
Arteriole
• In the thinner-walled veins
– Blood flows back to the heart mainly as a
result of muscle action
Direction of blood flow
in vein (toward heart)
Valve (open)
Skeletal muscle
Valve (closed)
Figure 42.10
Blood Flow Velocity
• Physical laws governing the movement of
fluids through pipes
– Influence blood flow and 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
– Is the highest pressure in the arteries
• Diastolic pressure
– Is the pressure in the arteries during diastole
– Is lower than systolic pressure
• Blood pressure
– Can be easily measured in humans
1 A typical blood pressure reading for a 20-year-old
is 120/70. The units for these numbers are mm of
mercury (Hg); a blood pressure of 120 is a force that
can support a column of mercury 120 mm high.
4 The cuff is loosened further until the blood flows freely
through the artery and the sounds below the cuff
disappear. The pressure at this point is the diastolic
pressure remaining in the artery when the heart is relaxed.
Blood pressure
reading: 120/70
Pressure
in cuff
above 120
Rubber cuff
inflated
with air
120
Pressure
in cuff
below 120
Pressure
in cuff
below 70
120
70
Sounds
audible in
stethoscope
Artery
Artery
closed
2 A sphygmomanometer, an inflatable cuff attached to a
pressure gauge, measures blood pressure in an artery.
The cuff is wrapped around the upper arm and inflated
until the pressure closes the artery, so that no blood
flows past the cuff. When this occurs, the pressure
exerted by the cuff exceeds the pressure in the artery.
Figure 42.12
3 A stethoscope is used to listen for sounds of blood flow
below the cuff. If the artery is closed, there is no pulse
below the cuff. The cuff is gradually deflated until blood
begins to flow into the forearm, and sounds from blood
pulsing into the artery below the cuff can be heard with
the stethoscope. This occurs when the blood pressure
is greater than the pressure exerted by the cuff. The
pressure at this point is the systolic pressure.
Sounds
stop
• Blood pressure is determined partly by cardiac
output
– And partly by peripheral resistance due to variable
constriction of the arterioles (anaphylactic shock).
– For high blood pressure try and reduce peripheral
resistance using smooth muscle relaxants!
Capillary Function
• Capillaries in major organs are usually
filled to capacity
– But in many other sites, the blood supply
varies. Homeostatic mechanisms involved to
keep blood pressure constant!
Control of Blood Flow Through Capillaries
• Two mechanisms
– Regulate the distribution of blood in capillary
beds
• In one mechanism
– Contraction of the smooth muscle layer in the
wall of an arteriole constricts the vessel
• In a second mechanism
– Precapillary sphincters control the flow of
blood between arterioles and venules
Precapillary sphincters
Thoroughfare
channel
(a) Sphincters relaxed
Arteriole
Venule
Capillaries
Arteriole
Venule
(b) Sphincters contracted
(c) Capillaries and larger vessels (SEM)
Figure 42.13 a–c
20 m
• 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
Tissue cell
Capillary
Capillary
Red
blood
cell
INTERSTITIAL FLUID
Net fluid
movement out
Net fluid
movement in
15 m
Direction of
blood flow
Pressure
At the arterial end of a
capillary, blood pressure is
greater than osmotic pressure,
and fluid flows out of the
capillary into the interstitial fluid.
At the venule end of a capillary,
blood pressure is less than
osmotic pressure, and fluid flows
from the interstitial fluid into the
capillary.
Blood pressure
Osmotic pressure
Inward flow
Outward flow
Figure 42.14
Arterial end of capillary
Venule end
Osmotic pressure
in capillary due to
plasma proteins!
Fluid Return by the Lymphatic
System
• The lymphatic system
– Returns fluid to the body from the capillary beds
– Aids in body defense because it passes through
lymph nodes where white blood cells take out any
pathogens or foreign material!
• Fluid reenters the circulation
– Directly at the venous end of the capillary bed and
indirectly through the lymphatic system
Blood
• The cellular elements of mammalian blood
Cellular elements 45%
Cell type
Separated
blood
elements
Number
per L (mm3) of blood
Functions
Erythrocytes
(red blood cells)
5–6 million
Transport oxygen
and help transport
carbon dioxide
Leukocytes
(white blood cells)
5,000–10,000
Defense and
immunity
Lymphocyte
Basophil
Eosinophil
Neutrophil
Monocyte
Platelets
Figure 42.15
250,000
400,000
Blood clotting
Plasma
• Blood plasma is about 90% water
• Among its many solutes are
– Inorganic salts in the form of dissolved ions,
sometimes referred to as electrolytes
• The composition of mammalian plasma
Plasma 55%
Constituent
Major functions
Water
Solvent for
carrying other
substances
(blood electrolytes)
Sodium
Potassium
Calcium
Magnesium
Chloride
Bicarbonate
Plasma proteins
Albumin
Fibringen
Immunoglobulins
(antibodies)
Osmotic balance
pH buffering, and
regulation of
membrane
permeability
Separated
blood
elements
Osmotic balance,
pH buffering
Clotting
Defense
Substances transported by blood
Nutrients (such as glucose, fatty acids, vitamins)
Waste products of metabolism
Respiratory gases (O2 and CO2)
Hormones
Figure 42.15
Erythrocytes
• Red blood cells, or erythrocytes
– Are by far the most numerous blood cells
– Transport oxygen throughout the body
– Platelets function in blood clotting
Blood Clotting
• A cascade of complex reactions
– Converts fibrinogen to fibrin, forming a clot
1 The clotting process begins
when the endothelium of a
vessel is damaged, exposing
connective tissue in the
vessel wall to blood. Platelets
adhere to collagen fibers in
the connective tissue and
release a substance that
makes nearby platelets sticky.
2 The platelets form a
plug that provides
emergency protection
against blood loss.
3 This seal is reinforced by a clot of fibrin when
vessel damage is severe. Fibrin is formed via a
multistep process: Clotting factors released from
the clumped platelets or damaged cells mix with
clotting factors in the plasma, forming an
activation cascade that converts a plasma protein
called prothrombin to its active form, thrombin.
Thrombin itself is an enzyme that catalyzes the
final step of the clotting process, the conversion of
fibrinogen to fibrin. The threads of fibrin become
interwoven into a patch (see colorized SEM).
A baby aspirin per day
makes the platelets lazy!
Collagen fibers
Platelet
plug
Platelet releases chemicals
that make nearby platelets sticky
Fibrin clot
Red blood cell
Clotting factors from:
Platelets
Damaged cells
Plasma (factors include calcium, vitamin K)
Prothrombin
Figure 42.17
Thrombin
Fibrinogen
Fibrin
5 µm
Hemophiliacs