Critical Thinking Questions 1 & 4

1) The membranes involved in John's condition are the parietal serosa which folds in on itself to form the visceral serosa, covering the organs in the cavity. In the body, the serous membranes are separated by a thin layer of lubricating fluid, called the serous fluid, which is secreted by both membranes. The serous fluid allows the organs to slide without friction across the cavity walls and one another as they carry out their routine functions. This freedom of movement is important for mobile organs. John is in agonizing pain because his condition called pleurisy prevents the serous membrane from secreting serous fluid and therefore creates friction across the cavity walls.

4) The sensation of thirst is a positive feedback control system because the thirst sensation is increased to communicate that the body is thirsty and needs more water. If the thirst sensation was a negative feedback control system, the sensation of thirst would be reduced without the dehydrated person even taking in water. The body cannot generate water on its own, therefore water has to be taken in. Positive feedback helps to communicate this to keep the body functioning normally.