38 - Chapter 38. Circulation, Respiration, and Excretion in...

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Chapter 38. Circulation, Respiration, and Exc re t ion in Ch ickens The comparable life support systems of birds will be described briefly using the domestic chicken as the type species. In general, the requirements of these systems are similar to those for mammals, but considerable structural specialization has attended their evolution. A. Cardiovascular The blood of chickens contains relatively few erythrocytes (about half the concentration found in mammals), the cells are smaller, they retain their nuclei, and they are not biconcave disks. Circulating erythrocytes are capable of continued synthesis of hemoglobin. The lymphocyte is the dominant leukocyte and there are no platelets because thrombocytes are present as intact cells and are not fragmented as in the case of mammals. Blood cell formation is confined to the sparse amount of marrow found in just a few of the bones, as noted in Chapter 7, Section B. Chickens lack definitive lymph nodes equivalent to those of mammals, but there are specialized lymphoid tissues associated with the digestive tract (described later in Chapter 48). Chickens have a high metabolic rate and, because of the low oxygen carrying capacity of the blood, the needs of tissues are met by the cardiovascular system operating at a
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38 - Chapter 38. Circulation, Respiration, and Excretion in...

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