BIOL 005B Lecture Notes - Lecture 17: Gastrovascular Cavity, Hemolymph, Cellular Respiration
BIOL 005B Lecture 17: Circulation
●All organisms must exchange materials with the environment. The exchanges of gases
used in cellular respiration (O2 and CO2) is one of the most important processes in an
animal’s physiology
○Most gases move easily through membranes by diffusion
○Although diffusion requires no energy, it is a random process and is relatively
slow
○Therefore, diffusion is fine for single celled and very small animals
○Larger animals must build distributive systems for the transport of gas and other
materials
■Distributive systems take advantage of convection (bulk flow
) through
circulating blood to carry materials from one place to another in the body
quickly and efficiently
●Circulatory systems link exchange surfaces with cells throughout the body
○In small and/or thin animals, cells can exchange materials directly with the
surrounding medium
○In most animals, transport systems connect the organs of exchange with the body
cells
○Most complex animals have internal transport systems that circulate fluid
○Diffusion is only viable if it is fast enough
to support cellular and organismal
processes
○In almost all animals that distance is less than 10 nm and effective over only one
or two cell layers
○Gastrovascular Cavities
■Simple animals, such as cnidarians, have a body wall that is only two cells
thick. It encloses a gastrovascular cavity - here diffusion might be possible
■This cavity functions in both digestion and distribution of substances
throughout the body
■Cnidarians, such as jellies, have elaborate gastrovascular cavities
■Flatworms have a gastrovascular cavity and a large surface area to volume
ratio
○Open and Closed Circulatory Systems
■Complex animals have either open or closed circulatory systems
■Both systems have three basic components:
●A circulatory fluid (blood or hemolymph)
●A set of tubes (blood vessels)
●A muscular pump (the heart)
■Open Circulatory Systems
●In insects and other arthropods, and most molluscs, blood
bathes the organs directly in an open circulatory system
●In an open circulatory system, the general body fluid is called
hemolymph
■Closed Circulatory Systems
●In a closed circulatory system, blood is confined to vessels and is
distinct from the interstitial fluid
●Closed systems are more efficient at transporting circulatory fluids
to tissues and cells
○Organization of Vertebrate Circulatory Systems
■Humans and other vertebrates have a closed circulatory system, often
called the cardiovascular system
●The three main types of blood vessels are arteries, veins and
capillaries
●Arteries branch into arterioles and carry blood to capillaries
(arterial system)
●Networks of capillaries called capillary beds are the sites of
chemical exchange between the blood and interstitial fluid
●Venuoles converge into veins and return blood from capillaries to
the heart (venous system)
○General Goals of Circulation
■Gas Exchange
●Deliver respiratory gases to the tissues in the body for cellular
respiration
●Remove the gases that are a byproduct of cellular respiration to the
respiratory surfaces for disposal
■Energy Balance
●Deliver the byproducts of digestion and absorption to the liver and
other body tissues for processing
●Remove the waste products of nutrient breakdown during cellular
respiration to the kidney for excretion
■Osmoregulation
●Carry water, other ions, and molecular signal molecules throughout
the body
○Different ways for the vertebrate heart to meet the goals of circulation in different
vertebrate classes
■Gas Exchange (two plans)
●Single circuit: pumps blood to the respiratory surfaces so it can
dump CO2 and pick up O2 for delivery directly to tissues; low
pressure throughout
●Two circuits
:
○First pumps blood at low pressure
to the lungs for
exchange of gases
○Second pumps blood at high pressure
to the body for
delivery of gases to tissues (and takes CO2 to the heart and
then lungs)
■Energy Balance (two results)
●Single circuit: low pressure means slow delivery
. This is found in
animals with relatively low metabolic rates
Document Summary
All organisms must exchange materials with the environment. The exchanges of gases used in cellular respiration (o 2 and co 2 ) is one of the most important processes in an animal"s physiology. Most gases move easily through membranes by diffusion. Although diffusion requires no energy, it is a random process and is relatively. Therefore, diffusion is fine for single celled and very small animals. Larger animals must build distributive systems for the transport of gas and other slow materials. Distributive systems take advantage of convection ( bulk flow ) through circulating blood to carry materials from one place to another in the body quickly and efficiently. Circulatory systems link exchange surfaces with cells throughout the body surrounding medium. In small and/or thin animals, cells can exchange materials directly with the. In most animals, transport systems connect the organs of exchange with the body. Most complex animals have internal transport systems that circulate fluid.
