BIO 012 Lecture Notes - Lecture 20: Systolic Geometry, Carbonic Anhydrase, Skeletal Muscle
19 Jun 2018
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Chapter 50
p. 1026 1.) What is a circulatory system and what is its function? 2.) Do all animals have a circulatory
system? Why or why not? 3.) What is the difference between an open and closed circulatory
system? In closed circulatory systems, what is the difference between extracellular fluid and
interstitial fluid? 4.) What is the function of a heart and is one required in open circulatory
systems? What are ostia valves and why are they important? 5.) What is hemolymph? 6.) How
do nutrients and water get out of a closed circulatory system into tissues? 7.) How many hearts
do earthworms have and what is their function? 8.) What allows blood to be circulated in only
one direction in closed circulatory systems?
1.) A circulatory system is a system used to transport oxygen, hormones, nutrients, immune cells,
waste, and heat. It includes a muscular pump (heart), fluid (blood) and conduits through which
fluid moves (vessels). 2.) All animals do not have a circulatory system because some organisms
are able to survive with no circulatory system based on their structure or location. 3.) An open
system is one where the ECF is the same as the fluid in the circulatory system and it is called
hemolymph; the fluid leaves vessels, filters between cells through tissues and goes back to the
heart. A closed system keeps the blood separate from the interstitial fluid and it is pumped by 1
or more hearts. Some things diffuse out of the blood, but many stay in the vessels. In the closed
system, the extracellular fluid in the circulatory system is called blood plasma, and the
extracellular fluid around the cells is called interstitial fluid. Interstitial fluid is tissue fluid around
the tissue cells and it is a type of ECF. 4.) The function of the heart is to aid in circulation by
pumping blood throughout the body. A heart is required in an open circulatory system because
as the heart expands, the ostia valve opens, and hemolymph can come in. Ostia valves are one-
way valves where hemolymph can only flow in. 5.) Hemolymph is a fluid equivalent to blood in
most invertebrates and it is in the hemocoel. 6.) In the closed system, nutrients and water go
from the blood vessels to the interstitial fluid to the tissues. 7.) Earthworms do not have a
multichambered heart like mammals or reptiles but instead have a series of single-chambered
aortic arches, or “pseudohearts,” that pump blood through the circulatory system. The
earthworm has five of these circulatory-system structures arranged consecutively. So sometimes
it is considered five hearts that they have, and all 5 hearts pump blood throughout the blood
vessels of the worm. 8.) Arteries and veins allow blood to be circulated in only one direction in
closed circulatory systems. Majority of the time, arteries are taking oxygenated blood away from
the heart to the organs (exception is the pulmonary artery which takes deoxygenated blood to
the lungs); and the veins usually take deoxygenated blood from the body to the heart which
sends it to the lungs (exception is the pulmonary vein which brings oxygenated blood to the heart
form the lungs). Veins have low pressure and depend on valves to prevent backflow.
p. 1026 What are the three main advantages closed circulatory systems have over open circulatory
systems? If open circulatory systems are less efficient than closed circulatory systems in
nurturing tissues, why are animals with open circulatory systems so active? (why are animals
who have open circulatory systems so small?)
Three advantages of closed circulatory systems are that fluid moves more quickly through vessels
than tissues; the diameter of the vessels can change which helps control flow of blood to tissues
and organs; and specialized cells and large molecules that aid in transporting hormones and
nutrients can stay in vessels but drop their cargo. Animals with open systems are active because
they don’t need circulatory systems for gas exchange. They just need a higher concentration
gradient so gas can move from blood to tissues. Organisms with open systems are smaller
because they have a direct exchange with their environment; they also have ostia so gas can
move in and out of their bodies.
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p. 1027 As we investigate closed circulatory systems through different classes of vertebrates, what
major theme emerges in the evolution of the how these systems get organized? What is the
difference between a pulmonary circuit and a systemic circuit?
All vertebrates have a closed circulatory system and they will have a heart with 2 or more
chambers. As circulatory systems become more complex, blood that flows to gas exchange
organs become is more separates from blood that goes to the rest of the body. Earlier system
was not too separate and had a lot of mixing, later systems had to have less and less mixing to
help better gas exchange occur. The pulmonary circuit is where blood is sent to the lungs and
back to the heart while the systemic system is where blood is sent from the heart to the body
and back to the heart.
p.1027 What are the five different types of blood vessels and what are their general functions? How
many blood flowing circuits do fish have?
Five different types of blood vessels are: arteries take blood away from the heart; arteries
branch into arterioles which feed blood into capillary beds; capillaries are the tiny, thin-walled
vessels where materials are exchanged between the blood and the tissue fluid; small vessels
called venules drain capillary beds; the venules join to form larger vessels called veins that deliver
blood back to the heart. The fish has just one blood flowing circuit.
p. 1028 What are the chambers of the fish heart? What path does blood take in the fish (start at the
heart and go through the major structures and return back to the heart) What allows the blood
to flow one way in the fish? Where is the blood pressure the highest in the fish? Where does
this pressure dissipate the most as it travels and why?
The fish heart has four chambers: the sinus venosus, an atrium, a ventricle, and the bulbus
arteriosus. Blood returning from the body goes to the atrium, which contracts and pushes blood
into the ventricle. Contraction of the ventricle pushes blood into the bulbus arteriosus. The
arterial blood leaving the bulbus arteriosus under pressure flows through the gills. It leaves the
gills in a large artery, the aorta, which distributes the blood to smaller arteries and arterioles
leading to all the organs and tissues of the body. It then comes back in through the ventricle and
moves to the atrium. The process then restarts. The unidirectional flow of blood in this circuit is
enabled by one-way valves between the sinus venosus and the atrium, between the atrium and
the ventricle, and between the ventricle and the bulbus arteriosus. Most of the pressure to the
blood is done by the contraction of the ventricle but it is dissipated as a result of resistance to
flow in the many narrow spaces in the gills. Therefore, blood leaving the gills and entering the
aorta is under low pressure, limiting the capacity of the fish circulatory system to supply the
tissues with oxygen and nutrients. This loss of pressure cause there to be a limited ability in
delivering O2.
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p.1029 1.) Which fish contain a functional lung? How does the path of blood differ in these fish
compare to regular fish and why? How does the heart of these fish differ from regular fish and
why? 2.) How does the heart of amphibians differ from that of fish which only use gill
respiration, and that of air breathing fish? 3.) What function do these differences serve for
amphibian function? 4.) Aside from circulation through the lungs, how else do amphibians get
oxygen to their tissues? (In thinking a little more advanced, how does this explain the size of
amphibians?)
1.) The lungfish has a functional lung. The path of blood differs in these fish because the lung has
many thin-walled blood vessels so blood flowing through those vessels can pick up oxygen from
air gulped into the lung. The lungfish heart partially separates its flow of blood into pulmonary
and systemic circuits, so it has a partially divided atrium. The left side receives oxygenated blood
from the lung and the right side receives deoxygenated blood form the sinus venosus. These two
blood streams stay mostly separate and as a result, oxygenated blood goes mostly to the anterior
gill arteries leading to the dorsal aorta, and deoxygenated blood goes mostly to the other gill
arches that have functional gills as well as to the gill arteries that serve the lung. 2.) The heart of
amphibians differs from fish that use only gill respiration or breath air because these amphibians
have a single ventricle that pumps blood to the lungs and the body, but two atria receive blood
returning to the heart. The left atrium receives O2 while the right atrium receives de-O2. B/c
both atria deliver blood to the same ventricle, the O2 and de-O2 can mix, in which case blood
going to the tissues would not carry a full load of oxygen. 3.) Partial separation of pulmonary and
systemic circulation has the advantage of allowing blood destined for the tissues to sidestep the
large pressure drop that occurs in the gas exchange organ. Blood leaving the heart to the tissues
moves directly to the aorta and then the body at a higher pressure than if it had gone through
the lungs. 4.) Another adaptation would be that amphibians can pick up a considerable amount
of oxygen in blood flowing through small vessels in their skin.
p. 1030 What are the advantages of a 4-chambered heart? What is the pathway of blood as it flows
through the body, the heart, and the lungs (in mammals).
The advantages of a four-chambered heart are that O2 and de-O2 can’t mix; therefore the
systemic circuit always receives blood with the highest oxygen content; respiratory gas exchange
is maximized b/c the blood with the lowest oxygen content and highest CO2 content is sent to
the lungs; and separate systemic and pulmonary circuits can operate at different pressures. De-
O2 blood flows form the vena cavas to the RA, it goes through the atrioventricular valves to the
RV. Then blood goes through the semilunar valve to the pulmonary artery which takes the de-O2
blood to the lungs. O2 blood is brought from the lungs to the heart through the pulmonary vein
to the LA. The O2 then goes through the atrioventricular valves to the LV. It then goes out the
semilunar valve to the aorta and to the rest of the body.
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Document Summary
A circulatory system is a system used to transport oxygen, hormones, nutrients, immune cells, waste, and heat. It includes a muscular pump (heart), fluid (blood) and conduits through which fluid moves (vessels). All animals do not have a circulatory system because some organisms are able to survive with no circulatory system based on their structure or location. An open system is one where the ecf is the same as the fluid in the circulatory system and it is called hemolymph; the fluid leaves vessels, filters between cells through tissues and goes back to the heart. A closed system keeps the blood separate from the interstitial fluid and it is pumped by 1 or more hearts. Some things diffuse out of the blood, but many stay in the vessels. In the closed system, the extracellular fluid in the circulatory system is called blood plasma, and the extracellular fluid around the cells is called interstitial fluid.
