This is a comprehensive and detailed note on Chapter 48; circulatory system for Biol 105.
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48.1 Circulatory Systems Serve Many Functions
muscular pump – the heart
fluid – blood
series of conduits – blood vessels
it transports heat, hormones, respiratory gases, blood cells, platelets,
immune system components, nutrients, and waste products around the body
= cardiovascular system
some very small animals don’t need circulatory systems; all cells are close to
the environment to allow exchange
some larger aquatic organisms have branched gastrovascular systems that
bring external environment inside the animal (sponges)
larger animals without a circulatory system tend by sedentary or sessile
large active animals must have circulatory systems to deliver nutrients to all
cells and remove wastes
o cells exchange nutrients and wastes with the extracellular fluid
o a circulatory system has a muscular chamber or heart to move the
extracellular fluid around the body
open circulatory system – fluid leaves the circulatory system and moves
between the cells
closed circulatory system – fluid is contained in a continuous system of
vessels
o extracellular fluid in a closed system refers to the fluid in the
circulatory system (blood plasma) plus the fluid around cells
(interstitial fluid)
open circulatory systems (arthropods, mollusks)
o a heart moves hemolymph through vessels to different regions
o fluid leaves vessels and filters through the tissues
o in arthropods, hemolymph returns to the heart through openings
(ostia) which have one-way valves
o mollusks have open vessels that collect the hemolymph
, closed circulatory systems (vertebrates, annelids)
o blood is kept separate from the interstitial fluid, pumped through the
vascular system by one or more hearts
o cellular and macromolecular components of the blood never leave the
vessel
advantages of closed systems:
o faster transport of material through vessels
o blood can be directed to specific tissues by varying resistance
(diameter of blood vessel)
o specialized carriers can travel in the vessels and transport hormones or
nutrients to specific sites
48.2 Vertebrate Circulatory Systems Evolved from Single to Double
Circuits
vertebrates circulatory systems:
o heart with multiple chambers and one-way valves to prevent backflow
o blood flows into arteries that branch into arterioles that feed into
capillaries – tiny, thin-walled vessels where materials are exchanged
between blood and interstitial fluid
o capillary beds are drained by venules, which join to form veins that
return blood to the heart
in fish, the heart pumps blood to the gills and then the rest of the body in a
single circuit
in birds and mammals, blood is pumped from heart to lungs and back in a
pulmonary circuit, and from the heart to the rest of the body in a systemic
circuit
fish circulatory system:
o heart has 4 chambers connected in series
o arterial blood leaves bulbus arteriosus and moves through gills, then to
the aorta and on to body tissues
o unidirectional flow of blood is enabled by one-way valves between the
heart chambers
lungfish show the transition from breathing water to breathing air
o an outpocketing of the gut forms a lung
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