[填空题]Blood is vital to maintaining a stable body temperature; in humans, body temperature normally fluctuates within a degree of 37.0℃. Heat production and heat{{U}} (36) {{/U}}in various parts of the body are balanced out by heat transfer{{U}} (37) {{/U}}tile bloodstream. This is accomplished by varying the{{U}} (38) {{/U}}of blood vessels in the skin. When a person becomes{{U}} (39) {{/U}}, the vessels dilate(膨胀) and an increased volume of blood flows through the skin. Heat dissipates(消散) through the skin, effectively{{U}} (40) {{/U}}the body temperature. The increased flow of blood in the skin makes the skin appear{{U}} (41) {{/U}}or flushed. When a person is cold, the skin may become pale as the{{U}} (42) {{/U}}narrow, diverting blood from the skin and reducing heat loss. About 55 percent of the blood is{{U}} (43) {{/U}}of a liquid known as plasma(血浆).{{U}} (44) {{/U}} : red blood cells, white blood cells, and platelets. Blood, vital fluid found in humans and o

[填空题]Blood is vital to maintaining a stable body temperature; in humans, body temperature normally fluctuates within a degree of 37.0℃. Heat production and heat{{U}} (36) {{/U}}in various parts of the body are balanced out by heat transfer{{U}} (37) {{/U}}tile bloodstream. This is accomplished by varying the{{U}} (38) {{/U}}of blood vessels in the skin. When a person becomes{{U}} (39) {{/U}}, the vessels dilate(膨胀) and an increased volume of blood flows through the skin. Heat dissipates(消散) through the skin, effectively{{U}} (40) {{/U}}the body temperature. The increased flow of blood in the skin makes the skin appear{{U}} (41) {{/U}}or flushed. When a person is cold, the skin may become pale as the{{U}} (42) {{/U}}narrow, diverting blood from the skin and reducing heat loss. About 55 percent of the blood is{{U}} (43) {{/U}}of a liquid known as plasma(血浆).{{U}} (44) {{/U}} : red blood cells, white blood cells, and platelets. Blood, vital fluid found in humans and o

[单项选择]→ Mammals and birds generally maintain body temperature within a narrow range (36-38℃ for most mammals and 39-42℃ for most birds) that is usually considerably warmer than the environment. Because heat always flows from a warm object to cooler surroundings, birds and mammals must counteract the constant heat loss. This maintenance of warm body temperature depends on several key adaptations. The most basic mechanism is the high metabolic rate of endothermy itself. Endotherms can produce large amounts of metabolic heat that replace the flow of heat to the environment, and they can vary heat production to match changing rates of heat loss. Heat production is increased by such muscle activity as moving or shivering. In some mammals, certain hormones can cause mitochondria to increase their metabolic activity and produce heat instead of ATP. This nonshivering thermogenesis (NST) takes place throughout the body, but some mammals also have a tissue called
A. describing the evolution in our ancestors
B. giving an example of heat loss in the extremities
C. comparing the process in humans and animals
D. identifying various types of insulation