The Human Spleen During Physiological Stress

Many mammals have the ability to autotransfuse a large quantity of red blood cells from the spleen into the active circulation during times of stress. This enhancement of the oxygen transport system has benefited the athletic mammal, that is, the thoroughbred horse, fox and greyhound in an improved aerobic performance. The role of the spleen in sequestering 50% of the total red cell volume in seals and horses, during times of inactivity, dramatically reduces the viscosity of the blood and therefore the work of the heart. In comparison, the human spleen contains only a small percentage of red blood cells, and has been primarily thought of as a lymphoid organ. The aim of this review is to emphasise the similarities between the human spleen and that of several athletic mammalian species during acute physiological stress. In the athletic mammalian model the expulsion of blood from the spleen is facilitated via the sympathetic nervous system resulting in contraction of smooth muscle within the splenic capsule. In comparison, the lack of smooth muscle contained within the human splenic capsule has meant that active contraction of the spleen has historically been viewed as unlikely, although evidence of contractile proteins within the red pulp have suggested otherwise. Exercise results in haemoconcentration, which has been attributed solely to areduction in plasma volume. Indirect calculation of plasma volume changes utilise haemoglobin and haematocrit and assume that the circulating red cell volume remains constant.However, several studies have suggested that the human spleen could account for 30% of the increase in haematocrit. This would result in a substantial overestimation of the reduction in plasma volume, indicating that the expulsion of red blood cells from the spleen must not be overlooked when utilising these equations

FAMILY, FEMINISM, AND RACE IN AMERICA

Feminist scholarship has advanced our understanding of the family's relationship to the economy and the state over different historical periods. Theorizing about gender, class, and family life has led us to conclude that global explanations of the family are false. Our knowledge about the meaning of racial stratification for family life, however, still remains fragmented. This article asks, What does including race have to offer the study of the family? Analysis of two streams of revisionist family scholarship demonstrates the need for reconceptualizing racial diversity in a way that embraces the experiences of White families as well as racial ethnic families. Family upheavals created by industrialization and deindustrialization offer concrete examples of the importance of race in theorizing family life throughout American society.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66994/2/10.1177_089124390004001006.pd