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Circulatory Systems in Animals
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Covers the different types of circulatory systems in different animals and how they function.
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Comparative Anatomy and Physiology in AnimalsLecture 3 Circulatory Systems of Animals 20/10/20
- All cells need nutrients and oxygen and to have waste products, such as CO2, to be removed.
- Size and structural complexity is critical to the evolution and organisation of circulatory
systems.
Definitions
- Blood vessel- a tubular structure carrying blood through the tissues and organs (a vein, an
artery, or a capillary).
- Heart- a muscular organ in most animals, which pumps blood through the blood vessels of
the circulatory system.
- Blood- a body fluid in animals that delivers necessary substances such as nutrients and
oxygen to the cells and transports metabolic waste products away from those same cells.
- Haemolymph- a body fluid that is a mixture of blood and interstitial fluid.
Platyhelminthes and Nematoda
- Flatworms have relatively short distances between organs and so rely on diffusion for gas
exchange and nutrient delivery.
- In large turbellaria, diffusion distances are increased so they have gut ceca in which cilia
move digestion products nearer the edges of the body.
- Nematodes are small (most <2.5mm long) and do not need a circulatory system.
Annelida
- Annelid worms are large and segmented and require a circulatory system.
- Each segment has a coelom filled with fluid, which is circulated by cilia on the internal walls,
and muscle contractions.
- Body organisation requires a well-developed haemal system of blood vessels and hearts to
provide transport through the body.
- Annelids have blood enclosed in a network of blood vessels that is a closed system. Blood is
pushed through the dorsal blood vessel from the anterior (head) end by the contractile walls
of the blood vessel itself.
- Within a segment blood then flows into a capillary network around the gut and then enters
the ventral blood vessel, in which it moves towards the posterior (tail) end of the worm. In
this way respiratory gases, nutrients, and waste products can be transported around the
body to all tissues.
- The blood is pushed through the vessel via peristalsis.
Molluscs
- Increased size and body plan complexity mean that molluscs have a well-developed
circulatory system.
- Heart with pair of atria and a medial ventricle with a dorsal aorta. Other vessels transport
haemolymph but connect to haemocoel, such as the dorsal aorta, blood vessels and
haemolymph.
- The heart has one or more pairs of atria, which receive oxygenated blood from the gills.
- These empty into the medial ventricle, which is continuous aorta, which branches to smaller
vessels to deliver blood to haemocoelic sinuses in the head, foot and bathe the visceral
mass.
- Blood then passes over the nephridia and returns to the heart by afferent branchial vessels.
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