Download blood pressure

Chapter 42: Circulation and Gas Exchange
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Trading with the Environment
• Every organism must exchange materials with
its environment
– And this exchange ultimately occurs at the
cellular level
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Unicellular organisms
– Exchanges occur directly with the environment
• Multicellular organisms
– Direct exchange not possible
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Salmon gills
– example of a specialized exchange system
Figure 42.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Circulatory systems reflect phylogeny
• Transport systems connect the organs of
exchange with the body cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Complex animals have internal transport
systems
– circulate fluid, lifeline between the aqueous
environment of cells and the exchange organs,
such as lungs, that exchange chemicals with the
outside environment
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Invertebrate Circulation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Gastrovascular Cavities
• Simple animals, e.g. cnidarians are two cells
thick
•  gastrovascular cavity
– digestion and distribution of substances
throughout the body
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Circular
canal
Radial canal
Mouth
5 cm
Figure 42.2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Open and Closed Circulatory Systems
• Found in more complex animals
• 3 basic components
– circulatory fluid (blood)
– set of tubes (blood vessels)
– muscular pump (the heart)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Arthropods, and most molluscs
– Open circulatory system
Heart
Hemolymph in sinuses
surrounding ograns
Anterior
vessel
Lateral
vessels
Ostia
Tubular heart
Figure 42.3a
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(a) An open circulatory system
• Closed circulatory system
– Blood is confined to vessels and is distinct
from the interstitial fluid efficient
Heart
Interstitial
fluid
Small branch vessels
in each organ
Dorsal vessel
(main heart)
Auxiliary hearts
Figure 42.3b
Ventral vessels
(b) A closed circulatory system
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Vertebrate Circulation
• Vertebrates have a closed circulatory system
–
called the cardiovascular system
• Blood vessels and a 2-4-chambered heart
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Arteries  capillaries (sites of chemical
exchange)veinsheart
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fishes
• 2 chamber heart
– One ventricle and one atrium
• Ventricle gills (picks up O2 and disposes of
CO2) body atrium
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Amphibians
• 3-chambered heart, with two atria and one
ventricle
• Ventricle pumps blood into a forked artery,
splits the ventricle’s output into the
pulmocutaneous circuit and the systemic circuit
 double circulation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Reptiles (Except Birds)
• Double circulation
– With a pulmonary circuit (lungs) and a
systemic circuit
• Turtles, snakes, and lizards
– 3-chambered heart
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mammals and Birds
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 4-chambered heart
– essential adaptation of the endothermic way of
life characteristic of mammals and birds
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Vertebrate circulatory systems, fig. 42.4
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Pulmonary
circuit
Left
Systemic
V aorta
Left
A
Systemic capillaries
A
V
Right
A
V
Left
Systemic
circuit
Systemic capillaries
Mammalian Circulation: The Pathway
• Heart valves
– one-way flow of blood through the heart
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Blood begins at right ventricle  lungs (blood
loads O2 and unloads CO2)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Oxygen-rich blood from the lungs heart at
the left atrium  left ventricle  body heart
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• mammalian cardiovascular system
7
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Capillaries of
abdominal organs
and hind limbs
The Mammalian Heart: A Closer Look
Pulmonary artery
Aorta
Pulmonary
artery
Anterior vena cava
Right atrium
Left
atrium
Pulmonary
veins
Pulmonary
veins
Semilunar
valve
Semilunar
valve
Atrioventricular
valve
Atrioventricular
valve
Posterior
vena cava
Right ventricle
Figure 42.6
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Left ventricle
Cardiac cycle
• Contraction, or pumping, phase of the cycle
– Is called systole
• Relaxation, or filling, phase of the cycle
– Is called diastole
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The cardiac cycle (~ 0.8 sec.)
2 Atrial systole;
Semilunar
valves
closed
ventricular
diastole
0.1 sec
Semilunar
valves
open
0.3 sec
0.4 sec
AV valves
open
1 Atrial and
ventricular
diastole
Figure 42.7
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
AV valves
closed
3
Ventricular systole;
atrial diastole
• Heart rate, also called the pulse
– number of beats per minute
• Cardiac output
– volume of blood pumped
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Maintaining the Heart’s Rhythmic Beat
• Cardiac muscle cells are self-excitable
– contract without any signal from the nervous
system
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Sinoatrial (SA) node, or pacemaker
– Sets the rate and timing
• 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 
ventricles contract
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Impulses recorded as an electrocardiogram
(ECG or EKG)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The control of heart rhythm
1 Pacemaker generates
wave of signals
to contract.
SA node
(pacemaker)
2 Signals are delayed
3 Signals pass
at AV node.
to heart apex.
4 Signals spread
Throughout
ventricles.
Bundle
branches
AV node
Heart
apex
ECG
Figure 42.8
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Purkinje
fibers
Blood Vessel Structure and Function
• The “infrastructure” of the circulatory system
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• All blood vessels
– Have three similar layers
Vein
Artery
Basement
membrane
Endothelium
100 µm
Valve
Endothelium
Smooth
muscle
Connective
tissue
Endothelium
Smooth
muscle
Capillary
Connective
tissue
Artery
Vein
Venule
Figure 42.9
Arteriole
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Arteries have thicker walls
–  high pressure of blood pumped from the
heart
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• velocity of blood flow slowest in the capillary beds
Systolic
pressure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Veins
Venules
Venae cavae
Figure 42.11
Capillaries
Diastolic
pressure
Arterioles
120
100
80
60
40
20
0
Arteries
50
40
30
20
10
0
Aorta
Velocity (
5,000
4,000
3,000
2,000
1,000
0
Pressure
Area
as a result of the high resistance and large total
cross-sectional area
• Systolic pressure
– pressure in the arteries during ventricular
systole
• Diastolic pressure
– pressure in the arteries during diastole
– lower than systolic pressure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Blood pressure measurement
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
Pressure
in cuff
below 120
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Capillaries
Precapillary sphincters
Thoroughfare
channel
(a) Sphincters relaxed
Venule
Arteriole
Capillaries
(b) Sphincters contracted
Arteriole
Venule
(c) Capillaries and larger vessels (SEM)
Figure 42.13 a–c
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
20 m
• 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
INTERSTITIAL FLUID
Net fluid
Net fluid
Capillary
Red
blood
cell
out
movement
in
15 m
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.
Direction of
blood flow
Pressure
Capillary
movement
Figure 42.14
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Blood pressure
Osmotic pressure
Inward flow
Outward flow
Arterial end of capillary
Venule end
Fluid Return by the Lymphatic System
• Returns fluid to the body from the capillary
beds
• Aids in body defense
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Blood is a connective tissue with cells
suspended in plasma (matrix)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Blood Composition and Function
• The cellular elements
– Occupy about 45% of the volume of blood
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Plasma
• 90% water
• Also, dissolved ions, sometimes referred to as
electrolytes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• mammalian plasma
Plasma 55%
Constituent
Major functions
Water
Solvent for
carrying other
substances
Icons (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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 42.15
Cellular Elements
• Red blood cells, which transport oxygen
• White blood cells, which function in defense
• Platelets
– (fragments of cells that are involved in clotting)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• cellular elements of mammalian blood, fig.
42.15
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
250,000
400,000
Blood clotting
Erythrocytes (red blood cells)
• Most numerous blood cells
– Transport oxygen
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Leukocytes
• 5 types of white blood cells, or leukocytes
– Monocytes, neutrophils, basophils,
eosinophils, and lymphocytes, which function
in defense by phagocytizing bacteria and
debris or by producing antibodies
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Platelets
• blood clotting
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Erythrocytes, leukocytes, and platelets all
develop from a common source
– pluripotent stem cells in the red marrow of
bones
Pluripotent stem cells
(in bone marrow)
Lymphoid
stem cells
Myeloid
stem cells
Basophils
B cells
T cells
Lymphocytes
Eosinophils
Neutrophils
Erythrocytes
Figure 42.16
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Platelets
Monocytes
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).
Collagen fibers
Platelet
plug
Platelet releases chemicals
that make nearby platelets sticky
Fibrin clot
Clotting factors from:
Platelets
Damaged cells
Plasma (factors include calcium, vitamin K)
Prothrombin
Figure 42.17
Thrombin
Fibrinogen
Fibrin
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
5 µm
Red blood cell
Cardiovascular Disease
•  more than half the deaths in the United
States
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• atherosclerosis
– Is caused by the buildup of cholesterol within arteries
Connective
tissue
Smooth muscle
Plaque
Endothelium
(a) Normal artery
50 µm
(b) Partly clogged artery
Figure 42.18a, b
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
250 µm
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Gas Exchange
• Across specialized respiratory surfaces
• Supplies oxygen for cellular respiration and
disposes of carbon dioxide
Respiratory
medium
(air of water)
O2
CO2
Respiratory
surface
Organismal
level
Circulatory system
Cellular level
Energy-rich
molecules
from food
Figure 42.19
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Cellular respiration
ATP
• Animals require large, moist respiratory
surfaces for the adequate diffusion of
respiratory gases
– Between their cells and the respiratory
medium, either air or water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Gills in Aquatic Animals
• Outfoldings of the body surface
– Specialized for gas exchange
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Some invertebrates
– gills have a simple shape and are distributed
over much of the body
(a) Sea star. The gills of a sea
star are simple tubular
projections of the skin.
The hollow core of each gill
is an extension of the coelom
(body cavity). Gas exchange
occurs by diffusion across the
gill surfaces, and fluid in the
coelom circulates in and out of
the gills, aiding gas transport.
The surfaces of a sea star’s
tube feet also function in
gas exchange.
Gills
Coelom
Figure 42.20a
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Tube foot
• Many segmented worms have flaplike gills
– That extend from each segment of their body
(b) Marine worm. Many
polychaetes (marine
worms of the phylum
Annelida) have a pair
of flattened appendages
called parapodia on
each body segment. The
parapodia serve as gills
and also function in
crawling and swimming.
Parapodia
Figure 42.20b
Gill
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The gills of clams, crayfish, and many other
animals
– Are restricted to a local body region
(c) Scallop. The gills of a
scallop are long,
flattened plates
that project from the
main body mass
inside the hard shell.
Cilia on the gills
circulate water around
the gill surfaces.
(d) Crayfish. Crayfish and
other crustaceans
have long, feathery
gills covered by the
exoskeleton. Specialized
body appendages
drive water over
the gill surfaces.
Gills
Gills
Figure 42.20c, d
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Effectiveness of gills is increased by ventilation
and countercurrent flow of blood and water
Oxygen-poor
blood
Gill arch
Oxygen-rich
blood
Lamella
Blood
vessel
Gill
arch
Water
flow
Operculum
O2
Water flow
over lamellae
showing % O2
Figure 42.21
Gill
filaments
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Blood flow
through capillaries
in lamellae
showing % O2
Countercurrent exchange
Tracheal Systems in Insects
• The tracheal system of insects
– tiny branching tubes that penetrate the body
Air sacs
Tracheae
Spiracle
(a) The respiratory system of an insect consists of branched internal
tubes that deliver air directly to body cells. Rings of chitin reinforce
the largest tubes, called tracheae, keeping them from collapsing.
Enlarged portions of tracheae form air sacs near organs that require
a large supply of oxygen. Air enters the tracheae through openings
called spiracles on the insect’s body surface and passes into smaller
tubes called tracheoles. The tracheoles are closed and contain fluid
(blue-gray). When the animal is active and is using more O2, most of
the fluid is withdrawn into the body. This increases the surface area
of air in contact with cells.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 42.22a
• The tracheal tubes
– Supply O2 directly to body cells
Body
cell
Air
sac
Tracheole
Trachea
Air
Tracheoles
Mitochondria
Body wall
Myofibrils
(b) This micrograph shows cross
sections of tracheoles in a tiny
piece of insect flight muscle (TEM).
Each of the numerous mitochondria
in the muscle cells lies within about
5 µm of a tracheole.
Figure 42.22b
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2.5 µm
Lungs
• Spiders, land snails, and most terrestrial
vertebrates have internal lungs
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mammalian Respiratory Systems: A Closer Look
• A system of branching ducts
– Conveys air to the lungs
Branch
from the
pulmonary
artery
(oxygen-poor
blood)
Branch
from the
pulmonary
vein
(oxygen-rich
blood)
Terminal
bronchiole
Nasal
cavity
Pharynx
Left
lung
Alveoli
50 µm
50 µm
Larynx
Esophagus
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
SEM
Heart
Figure 42.23
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Colorized SEM
• Air inhaled through the nostrils pharynx
trachea bronchi bronchioles alveoli,
where gas exchange occurs
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
How an Amphibian Breathes
• Ventilates its lungs by positive pressure
breathing, which forces air down the trachea
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
How a Mammal Breathes
• Negative pressure breathing, which pulls air
into the lungs
Rib cage
expands as
rib muscles
contract
Air inhaled
Rib cage gets
smaller as
rib muscles
relax
Air exhaled
Lung
Diaphragm
INHALATION
Diaphragm contracts
(moves down)
Figure 42.24
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
EXHALATION
Diaphragm relaxes
(moves up)
• Lung volume increases
– As the rib muscles and diaphragm contract
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
How a Bird Breathes
• Besides lungs, bird have eight or nine air sacs
– That function as bellows that keep air flowing
through the lungs
Air
Air
Anterior
air sacs
Trachea
Posterior
air sacs
Lungs
Lungs
Air tubes
(parabronchi)
in lung
EXHALATION
Air sacs empty; lungs fill
INHALATION
Air sacs fill
Figure 42.25
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1 mm
Control of Breathing in Humans
• 2 regions of the brain, the medulla oblongata
and the pons
Cerebrospinal
fluid
1 The control center in the
medulla sets the basic
rhythm, and a control center
in the pons moderates it,
smoothing out the
transitions between
inhalations and exhalations.
Pons
2 Nerve impulses trigger
muscle contraction. Nerves
from a breathing control center
in the medulla oblongata of the
brain send impulses to the
diaphragm and rib muscles,
stimulating them to contract
and causing inhalation.
Breathing
control
centers
Medulla
oblongata
4 The medulla’s control center
also helps regulate blood CO2 level.
Sensors in the medulla detect changes
in the pH (reflecting CO2 concentration)
of the blood and cerebrospinal fluid
bathing the surface of the brain.
5 Nerve impulses relay changes in
CO2 and O2 concentrations. Other
sensors in the walls of the aorta
and carotid arteries in the neck
detect changes in blood pH and
send nerve impulses to the medulla.
In response, the medulla’s breathing
control center alters the rate and
depth of breathing, increasing both
to dispose of excess CO2 or decreasing
both if CO2 levels are depressed.
Carotid
arteries
Aorta
Figure 42.26
3 In a person at rest, these
nerve impulses result in
about 10 to 14 inhalations
per minute. Between
inhalations, the muscles
relax and the person exhales.
Diaphragm
Rib muscles
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
6 The sensors in the aorta and
carotid arteries also detect changes
in O2 levels in the blood and signal
the medulla to increase the breathing
rate when levels become very low.
• Sensors in the aorta and carotid arteries
– Monitor O2 and CO2 concentrations in the
blood
– Exert secondary control over breathing
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Inhaled air
Exhaled air
160 0.2
O2 CO2
120 27
Alveolar spaces
O2 CO2
104
Alveolar
epithelial
cells
40
O2 CO2
Blood
entering
alveolar
capillaries
40
O2
CO2
2
1
O2
Alveolar
capillaries
of lung
45
O2 CO2
104
Pulmonary
veins
Systemic
arteries
Systemic
veins
CO2
40
40
O2 CO2
Pulmonary
arteries
Blood
leaving
tissue
capillaries
Blood
leaving
alveolar
capillaries
Heart
Tissue
capillaries
O2
3
4
45
O2
CO2
Tissue
cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
100
40
O2 CO2
O2 CO2
Figure 42.27
Blood
entering
tissue
capillaries
<40 >45
O2 CO2
Respiratory Pigments
• Proteins that transport oxygen
– Greatly increase the amount of oxygen that
blood can carry
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Oxygen Transport
• Respiratory pigment of vertebrates is
hemoglobin, contained in the erythrocytes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Hemoglobin must reversibly bind O2, loading
O2 in the lungs and unloading it in other parts
of the body
Heme group
Iron atom
O2 loaded
in lungs
O2 unloaded
In tissues
Figure 42.28
Polypeptide chain
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
O2
O2
Carbon Dioxide Transport
• Hemoglobin also helps transport CO2
– And assists in buffering
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1
2
Carbon dioxide produced by
body tissues diffuses into the
interstitial fluid and the plasma.
Over 90% of the CO2 diffuses
into red blood cells, leaving only 7%
in the plasma as dissolved CO2.
Tissue cell
Some CO2 is picked up and
transported by hemoglobin.
1
Blood plasma CO
2
within capillary
Capillary
wall
2
CO2
Carbonic acid dissociates into a
biocarbonate ion (HCO3–) and a
hydrogen ion (H+).
HCO3–
7
Hemoglobin binds most of the
H+ from H2CO3 preventing the H+
from acidifying the blood and thus
preventing the Bohr shift.
Figure 42.30
9
Carbonic acid is converted back
into CO2 and water.
10
CO2 formed from H2CO3 is unloaded
from hemoglobin and diffuses into the
interstitial fluid.
To lungs
CO2 transport
to lungs
HCO3–
8
H2CO3
Hb
9
11 CO2
Hemoglobin
releases
CO2 and H+
H2O
CO2
6
In the HCO3– diffuse
from the plasma red blood cells,
combining with H+ released from
hemoglobin and forming H2CO3.
6
HCO3– + H+
5
8
Red
Hemoglobin
H2CO3
blood Carbonic acid Hb
picks up
cell
CO2 and H+
5
+ H+
Bicarbonate
However, most CO2 reacts with water
in red blood cells, forming carbonic
acid (H2CO3), a reaction catalyzed by
carbonic anhydrase contained. Within
red blood cells.
Most of the HCO3– diffuse
into the plasma where it is
carried in the bloodstream to
the lungs.
3
4
HCO3–
4
7
Interstitial CO
2
fluid
H2O
3
CO2 transport
from tissues
CO2 produced
CO2
CO2 10
CO2 11
Alveolar space in lung
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
diffuses into the alveolar
space, from which it is expelled
during exhalation. The reduction
of CO2 concentration in the plasma
drives the breakdown of H2CO3
Into CO2 and water in the red blood
cells (see step 9), a reversal of the
reaction that occurs in the tissues
(see step 4).
Diving Mammals
• Deep-diving air breathers
– Stockpile O2 and deplete it slowly
– Myoglobin
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings