Transcript Slide 1

CIRCULATION AND GAS
EXCHANGE
Chapter 42
Gas Exchange Systems of Different Animals
• Gastrovascular Cavities
– (Platyhelminthes, Cnidarians, simple animals)
• Open and Closed Circulatory Systems
– Open – Arthropods such as insects, Molluscks
– Closed – Annelids such as earthworms, Cephalopods such as squid
and octopi, vertebrates
Open vs. Closed
Various Closed Circulatory Systems
Fish
2-chambered heart
Amphibian and Reptiles
3-chambered heart
Mammal
4-chambered heart
The Mammalian Heart
THE HEART
•Made up of cardiac muscle (most of it)
•4-chambered (2 atria on top of, 2 ventricles)
•4 valves
-The 2 Atrioventricular valves are
between the atria and ventricles
-The tricuspid on the right
-The bicuspid on the left
-The 2 Semilunar valves are located at
the 2 exits of the heart
-The Pulmonary valve that leads to
the pulmonary artery
-The Aortic valve that leads to the
aorta
Endotherms (Hometherms) require 4-chambered hearts
(Pulmonary Valve)
(Tricuspid Valve)
(Aortic Valve)
(Bicuspid or Mitral Valve)
Heart Chambers and Valves
• The heart has four internal chambers: two atria on top
and two ventricles below.
– Atria receive blood returning to the heart and have thin walls and
ear-like auricles projecting from their exterior.
– The thick-muscled ventricles pump blood to the body.
• A septum divides the atrium and ventricle on each side.
Each also has an atrioventricular (A-V) valve to ensure
one way flow of blood.
– The right A-V valve (tricuspid) and left A-V valve (bicuspid or
mitral valve) have cusps to which chordae tendinae attach.
– Chordae tendinae are, in turn, attached to papillary muscles in
the inner heart wall that contract during ventricular contraction to
prevent the backflow of blood through the A-V valves.
Path of Blood through the Heart
• Blood low in oxygen returns to the right atrium via the venae cavae
and the coronary sinus.
• The right atrium contracts, forcing blood through the tricuspid valve
into the right ventricle.
• The right ventricle contracts, closing the tricuspid valve, and forcing
blood through the pulmonary valve into the pulmonary trunk and
arteries.
• The pulmonary arteries carry blood to the lungs where it can rid itself
of excess carbon dioxide and pick up a new supply of oxygen.
• Freshly oxygenated blood is returned to the left atrium of the heart
through the pulmonary veins.
• The left atrium contracts, forcing blood through the left bicuspid valve
into the left ventricle.
• The left ventricle contracts, closing the bicuspid valve and forcing open
the aortic valve as blood enters the aorta for distribution to the body.
Blood Supply to the Heart
• The first branches off of the aorta, which carry freshly
oxygenated blood, are the right and left coronary arteries
that feed the heart muscle itself.
• Branches of the coronary arteries feed many capillaries
of the myocardium.
• The heart muscle requires a continuous supply of freshly
oxygenated blood, so smaller branches of arteries often
have anastomoses as alternate pathways for blood,
should one pathway become blocked.
• Cardiac veins drain blood from the heart muscle and
carry it to the coronary sinus, which empties into the right
atrium.
Direction of Blood Flow
• The superior and inferior vena cavae bring blood from
the body to the right atrium.
• The right ventricle has a thinner wall than does the left
ventricle because it must pump blood only as far as the
lungs, compared to the left ventricle pumping to the
entire body.
• At the base of the pulmonary trunk leading to the lungs is
the pulmonary valve, which prevents a return flow of
blood to the ventricle.
• The left atrium receives blood from four pulmonary veins.
• The left ventricle pumps blood into the entire body
through the aorta, guarded by the aortic valve that
prevents backflow of blood into the ventricle.
The Path Blood Travels
Terminology
1. Cardiac Cycle – one complete sequence
of pumping out of blood and filling up
with blood
2. Systole – the contraction of the heart
chamber muscle
3. Diastole – the relaxation of the heart
chamber muscle
4. Cardiac Output – the volume of blood
pumped by the heart
The Rhythm is going to get you!
Specialized muscle tissue in the region of the heart called
the sinoatrial node (SA) is the pacemaker. It maintains
the heart’s pumping, by setting the pace at which
cardiac muscle cells contract.
1. The SA node sends electric impulses anywhere
between 60 and 100 times a minute
2.
3.
4.
The impulses spread throughout the atria
The atrioventricular (AV) node intercepts these signals
and relays them to the apex of the heart, via
specialized muscle fibers called Bundle branches and
Purkinje fibers
The signal then spreads throughout the ventricles
Artial Systole, Ventricular diastole
“DUPP”
Atrial Diastole, Ventricular systole
“LUBB”
Cardiac Cycle
• During the cardiac cycle, pressure within the heart
chambers rises and falls with the contraction and
relaxation of atria and ventricles.
• When the atria fill, pressure in the atria is greater than
that of the ventricles, which forces the A-V valves open.
• Pressure inside atria rises further as they contract,
forcing the remaining blood into the ventricles.
• When ventricles contract, pressure inside them
increases sharply, causing A-V valves to close and the
aortic and pulmonary valves to open.
– As the ventricles contract, papillary muscles contract, pulling on
chordae tendinae and preventing the backflow of blood through
the A-V valves.
Heart Sounds
• Heart sounds are due to vibrations in heart tissues as
blood rapidly changes velocity within the heart.
• Heart sounds can be described as a "lubb-dupp" sound.
• The first sound (lubb) occurs as ventricles contract, atria
relax. The A-V valves are closing and the pulmonary and
aortic valves are opening.
• The second sound (dupp) occurs as ventricles relax,
atria contract. The aortic and pulmonary valves are
closing and the A-V valves are opening.
Cardiac Conduction System
• Specialized cardiac muscle tissue conducts impulses
throughout the myocardium and comprises the cardiac
conduction system.
• A self-exciting mass of specialized cardiac muscle called the
sinoatrial node (S-A node or pacemaker), located on the
posterior right atrium, generates the impulses for the
heartbeat.
• Impulses spread next to the atrial syncytium, it contracts, and
impulses travel to the junctional fibers leading to the
atrioventricular node (A-V node) located in the septum.
– Junctional fibers are small, allowing the atria to contract
before the impulse spreads rapidly over the ventricles.
• Branches of the A-V bundle give rise to Purkinje fibers leading
to papillary muscles; these fibers stimulate contraction of the
papillary muscles at the same time the ventricles contract.
Cardiac Conduction System
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Atrial Syncytium
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Ventricular Syncytium
The control of heart rhythm
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The Structure of Blood Vessels
Blood Vessels
Arteries and Arterioles
• Arteries are strong, elastic vessels adapted for
carrying high-pressure blood.
• Arteries become smaller as they divide and give rise
to arterioles.
• The wall of an artery consists of an endothelium,
tunica media (smooth muscle), and tunica externa
(connective tissue).
• Arteries are capable of vasoconstriction as directed
by the sympathetic impulses; when impulses are
inhibited, vasodilation results.
Capillaries
• Capillaries are the smallest vessels, consisting only of a layer of
endothelium through which substances are exchanged with tissue
cells.
• Capillary permeability varies from one tissue to the next, generally
with more permeability in the liver, intestines, and certain glands,
and less in muscle and considerably less in the brain (blood-brain
barrier).
• The pattern of capillary density also varies from one body part to the
next.
• Areas with a great deal of metabolic activity (leg muscles, for
example) have higher densities of capillaries.
• Precapillary sphincters can regulate the amount of blood entering a
capillary bed and are controlled by oxygen concentration in the area.
– If blood is needed elsewhere in the body, the capillary beds in
less important areas are shut down by the precapillary
sphincters.
Exchanges in the Capillaries
• Blood entering capillaries contains high concentrations of
oxygen and nutrients that diffuse out of the capillary wall
and into the tissues.
– Plasma proteins remain in the blood due to their large
size.
• Hydrostatic pressure drives the passage of fluids and
very small molecules out of the capillary at this point.
• At the venule end, osmosis, due to the osmotic pressure
of the blood, causes much of the tissue fluid to return to
the bloodstream.
• Lymphatic vessels collect excess tissue fluid and return it
to circulation.
Venules and Veins
• Venules leading from capillaries merge to
form veins that return blood to the heart.
• Veins have the same three layers as arteries
have and have a flap-like valve inside to
prevent backflow of blood.
– Veins are thinner and less muscular than arteries;
they do not carry high-pressure blood.
– Veins also function as blood reservoirs.
Blood Pressure
• Blood pressure is the force of blood against the inner
walls of blood vessels anywhere in the cardiovascular
system, although the term "blood pressure" usually
refers to arterial pressure.
• Arterial blood pressure rises and falls following a pattern
established by the cardiac cycle.
– During ventricular contraction, arterial pressure is at its highest
(systolic pressure).
– When ventricles are relaxing, arterial pressure is at its lowest
(diastolic pressure).
• The surge of blood that occurs with ventricular
contraction can be felt at certain points in the body as a
pulse.
Blood Flow in
capillary beds
•Capillaries are composed of a single
layer of epithelium surrounding a lumen
of a few micrometers.
•The average capillary is only about 1
mm long.
•The capillary beds are the region of
exchange of materials with the tissues.
O2 and nutrients are supplied to the
cells, and CO2 and other waste products
are taken away.
•Some materials are transported across
the endothelial membrane by diffusion,
but material (especially water) also
leaves through pores in the capillary
walls.
•Capillaries supply brain, heart, kidneys
and liver with blood constantly, but their
supply to other parts varies based on
need.
Composition of Mammalian Blood
Differentiation of blood cells
(release Histamine in response to tissue injury)
The Kidneys
convert a plasma
protein into a
hormone called
erythropoietin,
which stimulates
the bone marrow
to produce
erythrocytes
(Destroy larger invaders by
Secreting destructive enzymes)
(Become macrophages
“big eaters”)
(Phagocytes)
Blot Clotting
Atherosclerosis
Platelets and can clump and fibrin can coagulate within a blood vessel
to form a clot. This clot is called a thrombus. These clots can cause
cardiovascular diseases.
Myocardial Infarction (heart attack) is the death of cardiac muscle and a
Stroke is the death of nervous tissue in the brain
Gas exchange in the lungs
SEM of Pulmonary Alveoli
Alveoli are lung air sacs made
of simple squamous epithelial
cells for diffusion of gases.
Capillaries plus alveoli form the
respiratory membrane for the
exchange of gases between the
blood and the lungs.
Alveolus
Gas Exchange in the Alveoli
Capillary beds run around the outside of the entire alveolus. The capillary
bed is from arteriole to venule, and is depicted as running from top left, down
and to the right, and reaching the venule at the top right. Remember,
pulmonary arterioles contain deoxyhemoglobin and are color coded in blue,
while pulmonary venules contain oxyhemoglobin and are color coded in red.
Alveolar Gas Exchange
The gases only have to travel through a 2-cell thick region
(one-cell thick capillary wall and a one-cell thick alveolar
wall - with just the basement membrane between
them). This 2-cell-thick-material is called the respiratory
membrane.
CO2 Transport
Carbon dioxide (CO2) combines with water forming carbonic acid, which
dissociates into a hydrogen ion (H+) and as bicarbonate ions:
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3−
95% of the CO2 generated in the tissues is carried in the red blood cells:
It probably enters (and leaves) the cell by diffusing through
transmembrane channels in the plasma membrane.
Once inside, about one-half of the CO2 is directly bound to
hemoglobin (at a site different from the one that binds oxygen).
The rest is converted — following the equation above — by the enzyme
carbonic anhydrase into bicarbonate ions that diffuse back out into the
plasma and hydrogen ions (H+) bind to the protein portion of the
hemoglobin (thus having no effect on pH).
Only about 5% of the CO2 generated in the tissues dissolves directly in
the plasma. (A good thing, too: if all the CO2 we make were carried this
way, the pH of the blood would drop from its normal 7.4 to an instantlyfatal 4.5!)
When the red cells reach the lungs, these reactions are reversed and
CO2 is released to the air of the alveoli.
The Breathing Mechanism
What makes you
take a breath?
Conclusion: Increased levels of
CO2 lead to taking a breath.
In fish, the oxygenated blood from the gills does not need
to return to the heart to get pumped to the rest of the body.
It can go to all body tissues directly from the gills.
When CO2 levels in he blood increase, blood pH
drops. This causes an additional release of O2
from hemoglobin.
Conclusion: The greater the need for O2, the more it is released from hemoglobin.
Fetal hemoglobin binds O2 better
than maternal (adult) hemoglobin
THE END