Circulatory Systems By: Tim Nguyen Ezequiel Jauregui
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What is the Circulatory System? The circulatory system is an
organ system that passes nutrients (such as amino acids,
electrolytes, and lymph), gases, hormones, blood cells, etc. to and
form cells in the body to help fight diseases, stabilize body
temperature and pH, and to maintain homeostasis.
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Importance The timely delivery of oxygen to the bodys organs is
critical. For example, brain cells die within a few minutes if
their oxygen supply is interrupted. Thus, maintaining heart
function is crucial for survival.
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Circulatory systems All animals have: o circulatory fluid =
blood o tubes = blood vessels o muscular pump = heart
openclosed
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Open circulatory system Taxonomy o invertebrates insects,
arthropods, mollusks Structure o no separation between blood &
interstitial fluid hemolymph
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Closed circulatory system Taxonomy o invertebrates earthworms,
squid, octopuses o vertebrates Structure o blood confined to
vessels & separate from interstitial fluid 1 or more hearts
large vessels to smaller vessels material diffuses between blood
vessels & interstitial fluid closed system = higher
pressures
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The Mammalian Heart Figure 42.6 Aorta Pulmonary veins Semilunar
valve Atrioventricular valve Left ventricle Right ventricle
Anterior vena cava Pulmonary artery Semilunar valve
Atrioventricular valve Posterior vena cava Pulmonary veins Right
atrium Pulmonary artery Left atrium
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Vertebrate cardiovascular system Chambered heart o atrium =
receive blood o ventricle = pump blood out Blood vessels o arteries
= carry blood away from heart arterioles o veins = return blood to
heart venules o capillaries = thin wall, exchange / diffusion
capillary beds = networks of capillaries
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Mammalian Circulation pulmonary systemic
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Mammalian Circulation: The Pathway 1.The Right ventricle pumps
blood to the lungs Lungs 1
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Mammalian Circulation: The Pathway 2 & 3. Leads to the
pulmonary arteries as the blood flows through capillary beds in the
left and right lungs. It loads O2 and unloads CO2.
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Mammalian Circulation: The Pathway 4. Oxygen rich blood returns
from the lungs via the pulmonary veins to the left atrium of the
heart. Lungs 4
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Mammalian Circulation: The Pathway 5. Next, the oxygen-rich
blood flows into the left ventricle as the ventricle pumps the
oxygen-rich blood out to body tissues through the systemic circuit.
Lungs 5
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Mammalian Circulation: The Pathway 6. Blood leaves the left
ventricle via the aorta, which conveys blood to arteries leading
throughout the body. The first branches from the aorta are the
coronary arteries (not shown), which supply blood to the heart
muscle itself. 6
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Mammalian Circulation: The Pathway 7. Then come branches
leading to the capillary beds in the head and arms
(forelimbs).
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Mammalian Circulation: The Pathway 8. The aorta continues in a
posterior direction, supplying oxygen- rich blood to arteries
leading to arterioles and capillary beds into the abdominal organ
and legs.
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Mammalian Circulation: The Pathway 9 & 10. Two other large
veins called the anterior (or superior) vena cava and posterior (or
inferior) vena cava drains blood back to the heart.
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Mammalian Circulation: The Pathway 11. The two vena cava empty
their blood into the right atrium, from which the oxygen-poor blood
flows into the right ventricle. 9 10 11
Arteries: Built for high pressure pump Arteries o thicker walls
provide strength for high pressure pumping of blood o narrower
diameter o elasticity elastic recoil helps maintain blood pressure
even when heart relaxes
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Veins: Built for low pressure flow Veins o thinner-walled o
wider diameter blood travels back to heart at low velocity &
pressure lower pressure o distant from heart o blood must flow by
skeletal muscle contractions when it move squeeze blood through
veins o valves in larger veins one-way valves allow blood to flow
only toward heart Open valve Blood flows toward heart Closed
valve
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Capillaries: Built for exchange Capillaries o very thin walls
lack 2 outer wall layers only endothelium o enhances exchange
across capillary o diffusion exchange between blood &
cells
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Mammalian Circulation: The Pathway Heart valves o Dictate a
one-way flow of blood through the heart
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Cardiac cycle 1 complete sequence of pumping o heart contracts
& pumps o heart relaxes & chambers fill o contraction phase
systole ventricles pumps blood out o relaxation phase diastole
atria refill with blood
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Blood Pressure Blood pressure o Is the hydrostatic pressure
that blood exerts against the wall of a vessel Blood pressure is
determined partly by cardiac output o And partly by peripheral
resistance due to variable constriction of the arterioles
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Systolic pressure o Is the pressure in the arteries during
ventricular systole o Is the highest pressure in the arteries
Diastolic pressure o Is the pressure in the arteries during
diastole o Is lower than systolic pressure
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Blood pressure Figure 42.12 Artery Rubber cuff inflated with
air Artery closed 120 Pressure in cuff above 120 Pressure in cuff
below 120 Pressure in cuff below 70 Sounds audible in stethoscope
Sounds stop Blood pressure reading: 120/70 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. 1 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. 2 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. 3 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. 4 70 systolic
________ diastolic pump (peak pressure) _________________ fill
(minimum pressure) 110 ____ 70
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The heart rate, also called the pulse o Is the number of beats
per minute The cardiac output o Is the volume of blood pumped into
the systemic circulation per minute
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The cardiac cycle Semilunar valves closed AV valves open AV
valves closed Semilunar valves open Atrial and ventricular diastole
1 Atrial systole; ventricular diastole 2 Ventricular systole;
atrial diastole 3 0.1 sec 0.3 sec 0.4 sec
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Maintaining the Hearts Rhythmic Beat Some cardiac muscle cells
are self-excitable o Meaning they contract without any signal from
the nervous system
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A region of the heart called the sinoatrial (SA) node, or
pacemaker o Sets the rate and timing at which all cardiac muscle
cells contract Impulses from the SA node o Travel to the
atrioventricular (AV) node At the AV node, the impulses are delayed
o And then travel to the Purkinje fibers that make the ventricles
contract
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The pacemaker is influenced by o Nerves, hormones, body
temperature, and exercise The impulses that travel during the
cardiac cycle o Can be recorded as an electrocardiogram (ECG or
EKG)
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The control of heart rhythm Figure 42.8 SA node (pacemaker) AV
node Bundle branches Heart apex Purkinje fibers 2 Signals are
delayed at AV node. 1 Pacemaker generates wave of signals to
contract. 3 Signals pass to heart apex. 4 Signals spread Throughout
ventricles. ECG
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Capillary Function Capillaries in major organs are usually
filled to capacity o But in many other sites, the blood supply
varies Two mechanisms o Regulate the distribution of blood in
capillary beds In one mechanism o Contraction of the smooth muscle
layer in the wall of an arteriole constricts the vessel In a second
mechanism o Precapillary sphincters control the flow of blood
between arterioles and venules
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Figure 42.13 ac Precapillary sphincters Thoroughfare channel
Arteriole Capillaries Venule (a) Sphincters relaxed (b) Sphincters
contracted Venule Arteriole (c) Capillaries and larger vessels
(SEM) 20 m
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Platelets Platelets function in blood clotting When the
endothelium of a blood vessel is damaged o The clotting mechanism
begins
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Blood Clotting blood contains self-sealing materials that plug
up leaks when blood vessels are injured. Clotting response is vital
to survival. Hemophiliacs = lack a key component of clotting
response; susceptible to excessive bleeding during minor
injuries.
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sealants are always present in the blood: include: platelets:
circulating cell fragments which form temporary plugs at site of
injury. fibrinogen: when blood vessels are injured, a chain of
reactions (cascade) leads to conversion of a soluble fibrinogen
into fibrous, insoluble fibrinogen, which is deposited around
injury site and traps platelets and white blood cells, forming a
clot, until connective tissue forms a permanent patch.
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A cascade of complex reactions Converts fibrinogen to fibrin,
forming a clot Platelet plug Collagen fibers Platelet releases
chemicals that make nearby platelets sticky Clotting factors from:
Platelets Damaged cells Plasma (factors include calcium, vitamin K)
Prothrombin Thrombin Fibrinogen Fibrin 5 m Fibrin clot Red blood
cell 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. 1 The
platelets form a plug that provides emergency protection against
blood loss. 2 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). 3 Figure 42.17
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Cardiovascular Disease Cardiovascular diseases o Are disorders
of the heart and the blood vessels o Account for more than half the
deaths in the United States
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One type of cardiovascular disease, atherosclerosis o Is caused
by the buildup of cholesterol within arteries Figure 42.18a, b (a)
Normal artery (b) Partly clogged artery 50 m250 m Smooth muscle
Connective tissue Endothelium Plaque
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Hypertension, or high blood pressure o Promotes atherosclerosis
and increases the risk of heart attack and stroke A heart attack o
Is the death of cardiac muscle tissue resulting from blockage of
one or more coronary arteries A stroke o Is the death of nervous
tissue in the brain, usually resulting from rupture or blockage of
arteries in the head
