BIOA02H3 Lecture Notes - Circulatory System, Extracellular Fluid, Pulmonary Artery

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26 Jun 2011

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Chapter 49
49.1 –Why do animals need a circulatory system?
-a circulatory system consists of a muscular pump (the heart), a fluid (the
blood), and a series of conduits (blood vessels) through t which the fluid can be
pumped around the body
-cardiovascular system where the heart, blood and vessels are also known as
-circulatory systems is to transport things around the body
otransports heat, hormones, reparatory gases, blood cells, platelets and
elements of the immune system
-single cell organisms serve all of their need through direct exchanges with the
omostly found in aquatic environments, or moist terrestrial environment
-multicellular organisms a circulatory system is not necessary if all of their cells
are close enough to the external environment that nutrients, respiratory gases, and
wastes can diffuse between the cells and the environment
-small aquatic invertebrates have structures and body shapes that permit direct
exchanges between cells and environment
ohave flattened, thin body shapes that maximize the amount of surface area
that is in contact with the environment
osome other aquatic invertebrates are served by highly branched central
cavities called gastrovasular systems bring the external environment
into the animal
-very small animals without circulatory systems can maintain high levels of
metabolism and activity, but bigger animals without circulatory systems such as
sponges, coelenterates, and flatworms tend to be inactive, slow, or even sedentary
-larger and more active animals must support the metabolism of their cells by
delivering nutrients to them and taking wastes away from them with circulatory
-extracellular fluid contains oxygen, fuel, essential molecules
oit is continuous with the fluid in the circulatory system
othe vessels of these animals empty their fluid directly into the tissues
oopen where the extracellular fluid flows back into the circulatory
system to be pumped back out again
oclose completely contain the circulating fluid, blood, in a continuous
system of vessels
liquids and low-molecular weight solutes are exchanged between
the blood and the extracellular fluid even though it’s closed
-extracellular fluid refers to both the fluid in the circulatory system (blood plasma)
and the fluid between the cells of the body (interstitial fluid)
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-a normal 70 kg human contains 14 L of extracellular fluid, and 3 L is blood
-open circulatory systems extracellular fluid squeezes through intercellular
spaces as the animal moves
othe contraction of this simple heart propel the extracellular fluid through
cessels leading to different regions of the body, but the fluid leaves those
vessels to trickle through the tissues and eventually return to the heart
oare found in arthropods, mollusks, and some invertebrates groups
in arthropods, fluid returns to the heart through valved opening
called ostia
in mollusks, open vessels aid in the return of extracellular fluid to
the heart
-closed circulatory system a system vessels keeps circulating blood separate
from the interstitial fluid
oblood is pumped through this vascular system by one or more muscular
hearts, and some components of the blood never have the vessels
oare characterize vertebrates, annelids, and some other invertebrates groups
oin earthworms, one large ventral blood vessel carries blood from its
anterior end to its posterior end
smaller vessels branch off and transport the blood to even smaller
in the smaller vessels, respiratory gases, nutrients, and metabolic
wastes diffuse between the blood and the interstitial fluid
the blood then flows from these vessels into larger vessels that lead
into one large dorsal vessel, which carries the blood from the
posterior to the anterior end of the body
five paris of muscular vessels connect the large dorsal and ventral
vessels in the anterior end, thus completing the circuit
the doral vessel and the five connection vessels serve as hearts for
the earthworm
-closed circulatory systems have several advantages over open systems
ofluid can flow more rapidly through vessels than through intercellular
spaces, and can therefore transport nutrients and wastes to and from
tissues more rapidly
oby changing resistance in the vessels, closed systems can be selective in
directing blood to specific tissues
ospecialized cells and large molecules that aid in the transport of hormones
and nutrients can be kept within the vessels, but can drop their cargo in the
tissues where it is needed
-closed circulatory systems can support higher levels of metabolic activity than
open systems can
49.2 – How have vertebrate circulatory systems evolved?
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-vertebrates have closed circulatory systems and hearts with two or more chambers
-when the heart chamber contracts, it squeezes the blood, putting it under pressure
othen the blood flows out of the heart and into vessels where pressure is
ovalves prevent backflow of blood as the heart cycles between contraction
and relaxation
-as circulatory systems become more complex, the blood that flows to the gas
exchange organs becomes more completely separated from the blood that flows to
the rest of the body
oin fish, blood is pumped from the heart to the gills and then to the tissues
of the body and back to the heart
oin birds and mammals, blood is pumped from the heart to the lungs and
back to the heart in a pulmonary circuit
and then from the heart to the rest of the body and back to the heart
in a systemic circuit
-the closed vascular system of vertebrates begins with vessels called arteries
-arteries give rise to smaller vessels called 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
ojoin together to form larger vessels called veins, which deliver blood
back to the heart
-the fish heart has two chambers
oan atrium receives blood from the body and pumps it into a more
muscular chamber the ventricle
othe ventricle pumps the blood to the gills, where gases are exchanged
oblood leaving the gills collects in a large dorsal artery the aorta, which
distributes blood to smaller arteries and arterioles leading to all the organs
and tissues of the body
oin the tissues, blood flows through beds of tiny capillaries, collects in
venules and veins, and eventually returns to the atrium of the heart
osince there are only narrow spaces in the gill lamellae through which
blood flows, therefore blood leaving the gills and entering the aorta is
under low pressure, limiting the maximum capacity of the fish circulatory
-the lungfish heart has two atria, one receiving oxygenated blood from the lung
and one receiving deoxygenated blood from the body
othe lung contains many thin-walled blood vessels, so blood flowing
through those vessels can pick up oxygen from air gulped into the lung
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