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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 &
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transported away from and back to the heart
Vertebrate Circulatory Systems
Mammals, birds and crocodilians have a
four-chambered 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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Later-Evolved Vertebrate Circulatory Systems
-Oxygenated and deoxygenated blood don’t mix in heart5
Heart Valves
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
-Systolic pressure is the peak pressure at which
ventricles are contracting AV valves close (to prevent
backwash)= “lub”
-Diastolic pressure is the minimum pressure
between heartbeats at which the ventricles are
relaxed, semilunar valves close = (to prevent
backwash)“dub”
-Blood pressure is written as a ratio of systolic over
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diastolic pressure
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Contraction of Heart Muscle
Autorhythmic SA node
Initiates
depolarization
Electrocardiogram (ECG or EKG)
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Characteristics of Blood Vessels
*Arteries and veins are composed of four tissue layers
*Capillaries are composed of only a single layer of
endothelial cells...They allow for rapid exchange of
gases and metabolites between blood and body cells
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Arteries and Arterioles Regulate Heat Loss
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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
...and vice versa.
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Veins and Venules
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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What is Blood?
A connective tissue
composed of a fluid
extracellular 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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White Blood Cells
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
Prothrombin
Thrombin
Fibrinogen
Thrombin
Fibrin
1. Vessel is
damaged,
exposing
surrounding
tissue to blood.
2. Platelets
adhere and
become
sticky, forming
a plug.
3. Cascade of
enzymatic
reactions is
triggered by
platelets,
plasma factors,
and damaged
tissue.
4. Threads of
fibrin trap
erythrocytes
and form
a clot.
5. Once tissue
damage
is healed,
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the clot is
dissolved.
Making Blood “Formed Elements”
All of the “formed elements”
develop from pluripotent
stem cells
Hematopoiesis is blood
cell production
-Occurs in the bone
marrow of (medullary bone),
and produces:
-Lymphoid stem cell...Lymphocytes
-Myeloid stem cell...All other blood cells
Red blood cell production
is called erythropoiesis
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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
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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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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 31
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
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-Surrounded by an extensive capillary network
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
-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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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
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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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
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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Lung Structure and Function
-Each breath is initiated by
neurons in a respiratory control
center in the medulla oblongata
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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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RBCs of vertebrates contain Hemoglobin,
a pigment that binds and transports
oxygen
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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Gas Exchange Biochemistry
In Tissue Cells
-Mitochondria release CO2 after pyruvate oxidation and the
Krebs Cycle
Mitochondria also reduce
oxygen to H20 (water)
at the end of the electron
transport chain.
C02 leaves tissue cells
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Gas Exchange Biochemistry
In Red Blood Cells & Plasma
-The enzyme carbonic anhydrase combines CO2 with H2O to form
H2CO3
-H2CO3
into H+
dissociates
and HCO3–
-H+ binds to deoxyhemoglobin
making O2 get into tissue
-HCO3– moves out of the
blood, and into plasma
acts as buffer
72% of the CO2 in blood is
“hidden” in HCO3
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Gas Exchange Biochemistry
Into Alveoli
-CO2 goes into Alveoli...HCO3– moves INTO red blood cells
-H+ and HCO3– associate
into H2CO3
-H2CO3 changes into CO2
with H2O
-CO2 leaves Red Blood Cells
and goes into the alveoli
THEN YOU EXHALE IT
...Bronchioles, bronchi,
trachea, pharynx, mouth,
atmosphere!!
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Transportation of Carbon Dioxide
When 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)...so these molecules compete
with, oxygen, the terminal electron acceptor
in the electron transport chain...can be deadly
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