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The Circulatory and
Respiratory Systems
Chapter 49
Invertebrate Circulatory Systems
Sponges, Cnidarians, and nematodes lack a
separate circulatory system
-Sponges circulate water using many
incurrent pores and one excurrent pore
-Hydra circulates water through a
gastrovascular cavity (also for digestion)
-Nematodes are thin enough that the
digestive tract can also be used as a
circulatory system
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Invertebrate Circulatory Systems
Larger animals require a separate circulatory
system for nutrient and waste transport
-Open circulatory system = No distinction
between circulating and extracellular fluid
-Fluid called hemolymph
-Closed circulatory system = Distinct
circulatory fluid enclosed in blood vessels &
transported away from and back to the heart
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Vertebrate Circulatory Systems
Fishes evolved a true chamber-pump heart
-Four structures are arrayed one after the
other to form two pumping chambers
-First chamber consists of the sinus
venosus and atrium, and the second,
of the ventricle and conus arteriosus
-These contract in the order listed
-Blood is pumped through the gills, and
then to the rest of the body
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Vertebrate Circulatory Systems
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Vertebrate Circulatory Systems
The advent of lungs in amphibians required a
second pumping circuit, or double
circulation
-Pulmonary circulation moves blood
between the heart and lungs
-Systemic circulation moves blood
between the heart and the rest of the body
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Vertebrate Circulatory Systems
The frog has a three-chambered heart,
consisting of two atria and one ventricle
-Oxygenated and deoxygenated blood mix
very little
Amphibians living in water obtain additional
oxygen by diffusion through their skin
Reptiles have a septum that partially
subdivides the ventricle, thereby further
reducing the mixing of blood in the heart
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Vertebrate Circulatory Systems
Mammals, birds and crocodilians have a fourchambered heart with two separate atria
and two separate ventricles
-Right atrium receives deoxygenated blood
from the body and delivers it to the right
ventricle, which pumps it to the lungs
-Left atrium receives oxygenated blood
from the lungs and delivers it to the left
ventricle, which pumps it to rest of the body
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The Cardiac Cycle
The heart has two pairs of valves:
-Atrioventricular (AV) valves guard the
openings between atria and ventricles
-Tricuspid valve = On the right
-Bicuspid, or mitral, valve = On the left
-Semilunar valves guard the exits from the
ventricles to the arterial system
-Pulmonary valve = On the right
-Aortic valve = On the left
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The Cardiac Cycle
These valves open and close as the heart
goes through the cardiac cycle of rest
(diastole) and contraction (systole)
-“Lub-dub” sounds heard with stethoscope
Right and left pulmonary arteries deliver
deoxygenated blood from the right ventricle
to the right and left lungs
-Pulmonary veins return oxygenated blood
from the lungs to the left atrium
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The Cardiac Cycle
The aorta and all its branches are systemic
arteries, carrying oxygen-rich blood from the
left ventricle to all parts of the body
-Coronary arteries supply the heart muscle
itself
Superior vena cava drains the upper body
Inferior vena cava drains the lower body
These veins empty into the right atrium,
completing the systemic circulation
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The Cardiac Cycle
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The Cardiac Cycle (Cont.)
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The Cardiac Cycle
Arterial blood pressure can be measured with
a sphygmomanometer
-Systolic pressure is the peak pressure at
which ventricles are contracting
-Diastolic pressure is the minimum
pressure between heartbeats at which the
ventricles are relaxed
Blood pressure is written as a ratio of systolic
over diastolic pressure
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Contraction of Heart Muscle
Contraction of the heart muscle is stimulated
by membrane depolarization
-Triggered by the sinoatrial (SA) node, the
most important of the autorhythmic fibers
-Located in the right atrium, the SA node
acts as a pacemaker for rest of the heart
-Produces spontaneous action
potentials faster than other cells
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Contraction of Heart Muscle
Depolarization travels to the atrioventricular
(AV) node
-It is then conducted rapidly over both
ventricles by a network of fibers called the
atrioventricular bundle, or bundle of His
-Relayed to the Purkinje fibers
-Directly stimulate the myocardial
cells of both ventricles to contract
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Contraction of Heart Muscle
The electrical activity can be recorded on an
electrocardiogram (ECG or EKG)
-First peak (P) is produced by depolarization
of atria (atrial systole)
-Second, larger peak (QRS) is produced by
ventricular depolarization (ventricular systole)
-Last peak (T) is produced by repolarization
of ventricles (ventricular diastole)
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Characteristics of Blood Vessels
Blood leaves heart through the arteries
-Arterioles are the finest, microscopic
branches of the arterial tree
-Blood from arterioles enters capillaries
-Blood is collected into venules,
which lead to larger vessels, veins
-Carry blood back to heart
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Characteristics of Blood Vessels
Arteries and veins are composed of four
tissue layers
-Endothelium, elastic fibers, smooth muscle,
and connective tissue
Capillaries are composed of only a single
layer of endothelial cells
-Allow rapid exchange of gases and
metabolites between blood and body cells
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Characteristics of Blood Vessels
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Characteristics of Blood Vessels
(Cont.)
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Characteristics of Blood Vessels
Arteries and arterioles
-Contraction of the smooth muscle layer
results in vasoconstriction, which greatly
increases resistance & decreases blood flow
-Chronic vasoconstriction can result in
hypertension (high blood pressure)
-Relaxation of the smooth muscle layer
results in vasodilation, decreasing
resistance & increasing blood flow to organs
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Characteristics of Blood Vessels
Veins and venules
-Have thinner layer of
smooth muscles than
arteries
-Return blood to the
heart with the help of
skeletal muscle
contractions and oneway venous valves
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The Lymphatic System
The lymphatic system consists of lymphatic
capillaries, lymphatic vessels, lymph nodes,
and lymphatic organs
-Excess fluid in the tissues drains into blindended lymph capillaries
-Lymph passes into progressively larger
vessels with one-way valves
-Eventually drains into subclavian veins
Lymph nodes contain germinal centers
-Site of lymphocyte activation
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Cardiovascular Diseases
Heart attacks (myocardial infarctions)
-Main cause of cardiovascular deaths in US
-Insufficient supply of blood to heart
Angina pectoris (“chest pain”)
-Similar to but not as severe as heart attack
Stroke
-Interference with blood supply to the brain
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Cardiovascular Diseases
Atherosclerosis
-Accumulation of fatty material within arteries
Arteriosclerosis
-Arterial hardening due to calcium deposition
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Blood Flow and Blood Pressure
Blood flow and pressure are regulated by the
autonomic nervous system
The cardiac center of the medulla oblongata
modulates heart rate
-Norepinephrine, from sympathetic neurons,
increases heart rate
-Acetylcholine, from parasympathetic
neurons, decreases heart rate
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Blood Flow and Blood Pressure
Cardiac output is the volume of blood
pumped by each ventricle per minute
-Increases during exertion because of an
increase in both heart rate & stroke volume
Arterial blood pressure (BP) depends on the
cardiac output (CO) and the resistance (R)
to blood flow in the vascular system
BP = CO x R
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Blood Flow and Blood Pressure
The baroreceptor reflex is a negative
feedback loop that responds to BP changes
-Baroreceptors detect changes in arterial BP
-If BP decreases, the number of
impulses to cardiac center is decreased
-Ultimately resulting in BP increase
-If BP increases, the number of
impulses to cardiac center is increased
-Ultimately resulting in BP decrease
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Blood Flow and Blood Pressure
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Blood Flow and Blood Pressure
Blood pressure increases with blood volume
Blood volume is regulated by four hormones
-Antidiuretic hormone (ADH)
-Aldosterone
-Atrial natriuretic hormone
-Nitric oxide (NO)
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The Components of Blood
Blood is a connective tissue composed of a
fluid matrix, called plasma, within which are
found different cells and formed elements
The functions of circulating blood are:
1. Transportation of materials
2. Regulation of body functions
3. Protection from injury and invasion
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The Components of Blood
Plasma is 92% water, but it also contains the
following solutes:
-Nutrients, wastes, and hormones
-Ions
-Proteins
-Albumin, alpha (a) & beta (b) globulins
-Fibrinogen
-If removed, plasma is called serum
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The Components of Blood
The formed elements of the blood include red
blood cells, white blood cells and platelets
Red blood cells (erythrocytes)
-About 5 million per microliter of blood
-Hematocrit is the fraction of the total blood
volume occupied by red blood cells
-RBCs of vertebrates contain hemoglobin, a
pigment that binds and transports oxygen
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The Components of Blood
White blood cells (leukocytes)
-Less than 1% of blood cells
-Larger than erythrocytes and have nuclei
-Can also migrate out of capillaries
-Granular leukocytes
-Neutrophils, eosinophils, and basophils
-Agranular leukocytes
-Monocytes and lymphocytes
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The Components of Blood
Platelets are cell fragments that pinch off
from larger cells in the bone marrow
-Function in the formation of blood clots
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The Components of Blood
All of the formed elements develop from
pluripotent stem cells
Hematopoiesis is blood cell production
-Occurs in the bone marrow, and produces:
-Lymphoid stem cell  Lymphocytes
-Myeloid stem cell  All other blood cells
-Red blood cell production is called
erythropoiesis
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Gas Exchange
The rate of diffusion between two regions is
governed by Fick’s law of diffusion
D A Dp
R=
d
R = Rate of diffusion
D = Diffusion constant
A = Area over which diffusion takes places
Dp = Pressure difference between two sides
d = Distance over which diffusion occurs 50
Gas Exchange
Gases diffuse directly into unicellular organisms
However, most multicellular animals require
system adaptations to enhance gas exchange
-Amphibians respire across their skin
-Echinoderms have protruding papulae
-Insects have an extensive tracheal system
-Fish use gills
-Mammals have a large network of alveoli
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Gills
Gills are specialized extensions of tissue that
project into water
External gills are not enclosed within body
structures
-Found in immature fish and amphibians
-Two main disadvantages
-Must be constantly moved to ensure
contact with oxygen-rich fresh water
-Are easily damaged
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Gills
The gills of bony fishes are located between
the oral (buccal or mouth) cavity and the
opercular cavities
-These two sets of cavities function as
pumps that alternately expand
-Moving water into the mouth, through
the gills, and out of the fish through the
open operculum or gill cover
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Gills
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Gills
There are four gill arches on each side of a
fish’s head
-Each is composed of two rows of gill
filaments, which consist of lamellae
-Within each lamella, blood flows
opposite to direction of water movement
-Countercurrent flow
-Maximizes oxygenation of blood
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Gills
Many amphibians use cutaneous respiration
for gas exchange
In terrestrial arthropods, the respiratory
system consists of air ducts called trachea,
which branch into very small tracheoles
-Spiracles (openings in the exoskeleton)
can be opened or closed by valves
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Lungs
Gills were replaced in terrestrial animals
because
1. Air is less supportive than water
2. Water evaporates
The lung minimizes evaporation by moving
air through a branched tubular passage
-A two-way flow system
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Lungs
Air exerts a pressure downward, due to gravity
-A pressure of 760 mm Hg is defined as one
atmosphere (1.0 atm) of pressure
Partial pressure is the pressure contributed
by a gas to the total atmospheric pressure
-Based on the % of the gas in dry air
-PN2 = 760 x 79.02% = 600.6 mm Hg
-PO2 = 760 x 20.95% = 159.2 mm Hg
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-PCO2 = 760 x 0.03% = 0.2 mm Hg
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Lungs
Lungs of amphibians are formed as saclike
outpouchings of the gut
Frogs have positive pressure breathing
-Force air into their lungs by creating a
positive pressure in the buccal cavity
Reptiles have negative pressure breathing
-Expand rib cages by muscular contractions,
creating lower pressure inside the lungs
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Lungs
Lungs of mammals are packed with millions
of alveoli (sites of gas exchange)
-Inhaled air passes through the larynx,
glottis and trachea
-Bifurcates into the right and left
bronchi, which enter each lung and
further subdivide into bronchioles
-Surrounded by an extensive
capillary network
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Lungs
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Lungs
Lungs of birds channel air through very tiny air
vessels called parabronchi
-Unidirectional flow
-Achieved through the action of anterior
and poster sacs (unique to birds)
-When expanded during inhalation,
they take in air
-When compressed during exhalation,
they push air in and through lungs 69
Lungs
Respiration in birds occurs in two cycles
-Cycle 1 = Inhaled air is drawn from the
trachea into posterior air sacs, and exhaled
into the lungs
-Cycle 2 = Air is drawn from the lungs into
anterior air sacs, and exhaled through the
trachea
Blood flow runs 90o to the air flow
-Crosscurrent flow
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Lungs
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Gas Exchange
Gas exchange is driven by differences in
partial pressures
-As a result of gas exchange in the lungs,
systemic arteries carry oxygenated blood
with relatively low CO2 concentration
-After the oxygen is unloaded to the tissues,
systemic veins carry deoxygenated blood
with a high CO2 concentration
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Lung Structure and Function
The outside of each lung is covered by the
visceral pleural membrane
-The inner wall of the thoracic cavity is lined
by the parietal pleural membrane
-The space between the two membranes
is called the pleural cavity
-Normally very small and filled with
fluid
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Lung Structure and Function
During inhalation, thoracic volume increases
through contraction of two muscle sets
-Contraction of the external intercostal
muscles expands the rib cage
-Contraction of the diaphragm expands the
volume of thorax and lungs
-Produces negative pressure which
draws air into the lungs
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Lung Structure and Function
Thorax and lungs have a degree of elasticity
-Expansion during inhalation puts these
structures under elastic tension
-Tension is released by the relaxation of
the external intercostal muscles and
diaphragm
-This produces unforced exhalation,
allowing thorax and lungs to recoil
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Lung Structure and Function
Tidal volume = Volume of air moving in and
out of lungs in a person at rest
Vital capacity = Maximum amount of air that
can be expired after a forceful inspiration
Hypoventilation = Insufficient breathing
-Blood has abnormally high PCO2
Hyperventilation = Excessive breathing
-Blood has abnormally low PCO2
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Lung Structure and Function
Each breath is initiated by neurons in a
respiratory control center in the medulla
oblongata
-Stimulate external intercostal muscles and
diaphragm to contract, causing inhalation
-When neurons stop producing impulses,
respiratory muscles relax, and exhalation
occurs
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Lung Structure and Function
Neurons are sensitive to blood PCO2 changes
-A rise in PCO2 causes increased production
of carbonic acid (H2CO3), lowering the pH
-Stimulates chemosensitive neurons in
the aortic and carotid bodies
-Send impulses to control center
Brain also contains central chemoreceptors
that are sensitive to changes in the pH of
cerebrospinal fluid (CSF)
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Respiratory Diseases
Chronic obstructive pulmonary disease
(COPD) refers to any disorder that obstructs
airflow on a long-term basis
-Asthma = An allergen triggers the release
of histamine, causing intense constriction of
the bronchi and sometimes suffocation
-Emphysema = Alveolar walls break down
and the lung exhibits larger but fewer alveoli
-Lungs become less elastic
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Respiratory Diseases
Lung cancer follows or accompanies COPD
-The number one cancer killer
-Caused mainly by cigarette smoking
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Hemoglobin
Hemoglobin consists of four polypeptide
chains: two a and two b
-Each chain is associated with a heme
group, and each heme group has a central
iron atom that can bind a molecule of O2
Hemoglobin loads up with oxygen in the
lungs, forming oxyhemoglobin
-Some molecules lose O2 as blood passes
in capillaries, forming deoxyhemoglobin
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Hemoglobin
In a person at rest, about one-fifth of the
oxygen is unloaded in the tissues
-Leaving four-fifths of the oxygen in the
blood as a reserve
-This reserve enables the blood to supply
body’s oxygen needs during exertion
The oxyhemoglobin dissociation curve is a
graphic representation of these changes
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Hemoglobin
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Hemoglobin
Hemoglobin’s affinity for O2 is affected by pH
and temperature
-The pH effect is known as the Bohr shift
-Caused by H+ binding to hemoglobin
-Results in a shift of oxyhemoglobin
dissociation curve to the right
-Facilitates oxygen unloading
-Increasing temperature has a similar effect
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Hemoglobin
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Transportation of Carbon Dioxide
About 8% of the CO2 in blood is dissolved in
plasma, and 20% is bound to hemoglobin
-Remaining 72% diffuses into red blood cells
-The enzyme carbonic anhydrase
combines CO2 with H2O to form H2CO3
-H2CO3 dissociates into H+ and HCO3–
-H+ binds to deoxyhemoglobin
-HCO3– moves out of the blood, and
into plasma
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Transportation of Carbon Dioxide
When the blood passes through pulmonary
capillaries, these reactions are reversed
-The result is the production of CO2 gas,
which is exhaled
Other dissolved gases are also transported
by hemoglobin
-For example, nitric oxide (NO) and carbon
monoxide (CO)
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