13-chapter 10 - Chapter 10: The Circulatory System Purpose...

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Chapter 10: The Circulatory System Purpose Become familiar with the basic vertebrate circulatory system. Understand the basic pattern of blood flow in vertebrates. Note circulatory changes associated with respiratory changes in a phylogenetic sequence. Understand the evolution of the craniate heart in a phylogenetic context. Introduction Mammalian Anatomy: The Cat -Circulatory System chapter Ch. 10 Circulatory System slide guide Liquids in the body are carried by two distinct pathways, both considered part of the circulatory system: the lymphatic system and blood-vascular system. Because it is so difficult to see its vessels in our dissections, the lymphatic system will not be dealt with in depth here. However, you have encountered in your cats a number of small, rounded, brownish glands scattered throughout the viscera, particularly around the small intestine and colon. These are lymph nodes . In many disease states, these organs are where bacteria or cancer cells can accumulate. The circulatory system, composed of the heart and associated blood vessels, carries an enormous range of structures and substances including blood cells (erythrocytes, leukocytes, and thrombocytes), oxygen (using proteins within the erythrocytes as carriers), carbon dioxide (stored as the bicarbonate ion), food molecules ( e.g. , lipids, monosaccharides, and amino acids), and hormones. Structurally, the blood vessels are broken down into three categories: arteries , defined as any blood vessel carrying blood away from the heart, irrespective of its oxygen content; veins , defined as a blood vessel carrying blood towards the heart, irrespective of its oxygen content; and capillaries , thin vessels in which the exchange of material between blood and other cells of the body occurs. Typically, the walls of arteries are very rigid and have low compliance (stretchiness); the opposite is true of veins. Why is this important? Arteries are not uniform in size, but show a progressive shift in size from larger to smaller as they approach the capillaries; a reverse pattern is found in the veins. You are responsible for knowing the vessels of both Squalus and Felis , the sheep heart, and the plastic heart models found in the laboratory. Primitive Condition Blood leaves the heart anteriorly via a single ventral aorta , then passes dorsally through aortic arches . The primitive condition (presumably intermediate between early craniates and vertebrates) involves six pairs of aortic arches (six left and six right). The retention of 6 pairs of aortic arches in the developing embryo serves as the foundation for the adult circulatory system. In typical aquatic organisms the aortic arches pass through the gill region via capillary beds where gas exchange occurs. In these aquatic forms the vessels leading to the gills are afferent branchial arteries, and the vessels leading away from the gills are efferent branchial arteries . In adult craniates blood
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13-chapter 10 - Chapter 10: The Circulatory System Purpose...

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