Transport in Invertebrates

1. Transport in Invertebrates Invertebrates such as sponges, cnidarians (e.g. hydras, sea anemones), and flatworms don’t have circulatory systems not necessary with their thin body walls their bodies are so small they can use their specialized cells to spread nutrients, excrete waste products, and respire through diffusion Coelomate echinoderms (sea urchins, sea cucumbers, starfish) rely on the movement of coelomic fluid within their body cavities as a circulatory system

2. Invertebrates with a Circulatory System • Most animals have a circulatory system • Circulatory system transports oxygen and nutrients (i.e. glucose and amino acids) to the cells, and carries wastes away from the cells • Wastes later excreted from body by lungs or kidneys • Two types of circulatory fluids: • Blood, which is always contained within blood vessels • Hemolymph (mixture of blood and tissue fluid), which flows into a hemocoel- a body cavity found in many invertebrates

3. Open Circulatory System • Hemolymphfound in animals, especially molluscs and arthropods, with an open circulatory system that consists of blood vessels and open spaces • The heart pumps hemolymph via vessels into tissue spaces, sometimes enlarging them; the hemolymph eventually drains back to the heart • The book uses a grasshopper as the main example (next slide) • A grasshopper’s hemolymph is colorless because it contains no hemoglobin or other respiratory pigment • It’s hemolymph carries nutrients, but not oxygen • Oxygen is taken to cells and carbon dioxide removed from them via the tracheae- air tubes found throughout the body • The tracheae provide transport and delivery of respiratory gases while restricting water loss

4. Grasshopper • It’s dorsal tubular heart pumps hemolymphinto the dorsal aorta, which empties it into the hemocoel • When the heart contracts, its openings (called ostia) close • When the heart relaxes, the hemolymphis sucked back into the heart through the ostia

5. Closed Circulatory System • Consists of blood vessels only, no hemolymph • Blood, which is composed of cells and plasma, is pumped into a system of blood vessels by the heart • Valves prevent blood from flowing backward • In annelids such as the earthworm and in some molluscs such as squid and octupuses • The book uses the earthworm as the main example (next slide) • An earthworm’s blood is red because it contains the respiratory pigment hemoglobin, which is dissolved in the blood, not contained within cells • The earthworm has no specialized organs, such as lungs, so gas exchange takes place across the body wall

6. Earthworm • Its 5 pairs of anterior hearts pump blood into the ventral blood vessel, which has a branch (lateral vessel) in each segment of the worm’s bodies • Blood moves from these branches into capillaries*- the thinnest of the blood vessels, where exchanges with tissue fluid take place • Gas exchange & nutrient-for-waste exchange occur across capillary walls • The blood then moves from the capillaries to small veins, and into the dorsal blood vessel (which is a vein) • The dorsal blood vessel returns the blood to the heart for repumping *no cell is far from a capillary in animals with closed circulatory systems

7. Transport in Vertebrates • All vertebrates have a closed circulatory system called a cardiovascular system • It includes a strong, muscular heart in which the atria receive blood and the muscular ventricles pump blood through the blood vessels • Three kinds of blood vessels: • Arteries carry blood away from the heart • Capillaries exchange materials with tissue fluid • Veins return blood to the heart

8. Arteries & Veins • Arteries and veins both have three distinct layers • Outer layer consists of fibrous connective tissue that is rich in elastic & collagen fibers • Middle layer consists of smooth muscle and elastic tissue • Endothelium (innermost layer) is similar to squamous epithelium (thin, flat cells) • Arteries are thick-walled, and those attached to the heart are resilient- able to expand and accommodate the sudden increases in blood volume after each heart beat

9. Arterioles & Capillaries • Arterioles- small arteries whose diameters can be regulated by the nervous system • Arteriole constriction and dilation generally affect blood pressure • A greater number of vessels dilated means lower blood pressure • Arterioles branch into capillaries- extremely narrow, microscopic tubes with walls made of only one layer of cells • Capillary beds are made of many interconnected capillaries; they are so prevalent that all cells in a human are within 60-80 μm of a capillary • But only 5% of capillary beds are open at the same time • Capillaries, usually so narrow that red blood cells pass through them single file, allow the exchange of nutrients and wastes across their walls

10. Venules & Veins • Venules drain blood from the capillaries, then join to form veins • Vein walls are much thinnner than those of arteries, which may be associated with a lower blood pressure in the veins • There are valves within the veins that point open towards the heart, preventing a backflow of blood

12. Two Types of Circulatory Pathways • Fish have a one-circuit circulatory pathway through the body • Ventricle pumps blood under pressure to the gills, where gas exchange occurs • Blood returns to aorta, distributed throughout the body • Atrium pumps oxygen-poor blood back to the ventricle • Advantage: gill capillaries receive oxygen-poor blood while systemic capillaries receive oxygen-rich blood • Disadvantage: blood is under reduced pressure after leaving the gills • A result of evolutionary changes, other vertebrates (birds, mammals, crocodilians) have a two-circuit circulatory pathway • Systemic circuit- the heart pumps blood to the tissues • Pulmonary circuit- the heart pumps blood to the lungs • This double pumping action was adapted for breathing air on land • Provides adequate blood pressure for both the pulmonary and systemic circuits

13. Frog and bird two-circuit circulatory pathways • Oxygen-poor blood is pumped via the veins into the right atrium • That blood is then delivered to the lungs, & possibly the skin, to be oxygenated • Oxygen-rich blood returning from the lungs passes through the left atrium to the ventricle, where it is pumped out for distribution through the body • Frog • Though both atria empty into the same ventricle, they stay somewhat separated because oxygen-poor blood is pumped out of the ventricle before the oxygen-rich blood enters • Bird • A septum divides the ventricle in two, which prevents the oxygen-rich and oxygen-poor bloods from mixing

14. Sources Pictures: • http://knowyourmeme.com/photos/520436-surprised-patrick • http://www.pixarpost.com/2012/07/directors-commentary-track-review.html • http://trussty-jasmine.blogspot.com/2012/04/sea-urchins-usability-study.html#axzz2Qa74xqAJ • http://www.bigstockphoto.com/image-28235060/stock-photo-red-knobbed-starfish • http://www.healtone.com/categories/Blood/ • http://idratherbewriting.com/2007/07/31/grasshoppers-that-look-like-aliens/ • http://www.ryanphotographic.com/squid.htm • http://education-portal.com/academy/lesson/open-circulatory-systems-definition-lesson-quiz.html • http://www.tutorvista.com/content/biology/biology-ii/transportation/blood-vessels.php • http://www.passmyexams.co.uk/GCSE/biology/capillaries.html • http://biologytb.net23.net/text/chapter30/concept30.1.html Information: Mader, Sylvia S. "32 Circulation and Cardiovascular Systems." Biology. Tenth ed. New York: McGraw-Hill Higher Education, 2010. 594-97. Print.