1. Describe one physiological adaptation marine animals such as whales and dolphins adopt to maintain body temperature.

· Whales and dolphins also maintain their body temperature by using a countercurrent exchange system (逆流热交换).

· In this countercurrent exchange system, heat in the blood coming from the core flows to the blood that is returning from the skin to the body core.

· This warms the blood flowing in from the skin and so prevents the venous blood from cooling the internal organs and muscles.

· At the same time, the blood moving out to the skin is cooled and so the loss of heat across the skin is reduced.

简而言之， 鳍，尾部的动脉，静脉互相接触，在末梢部分极度冷却的静脉血被热的动脉血温暖，然后流向身体中心。防止了身体中心被冷却，也同时阻止温度的流失。

2. Where are vasopressin and renin formed and what is the role of each in water balance?

· The two significant compounds involved in water balance and blood pressure control are an antidiuretic hormone (ADH) (抗利尿激素), also called vasopressin, and renin.

· Vasopressin is produced in the hypothalamus（下丘脑） of the brain when osmoreceptors 渗透压感受器）detect a rise in blood solute. Vasopressin flows through the axons of the neurosecretory cells to the posterior pituitary gland (脑垂体), where it is released into the bloodstream.it is transported to the kidneys where it increases the permeability （渗透性）of distal tubules and collecting ducts to water.

· When blood pressure falls. A fall in blood pressure reduces glomerular filtration. Pressure-sensitive receptors in the kidney register this and afferent arteriole cells secrete renin (肾素) Renin initiates chemical reactions that cause the adrenal cortex of adrenal glands（肾上腺） to release aldosterone. Aldosterone (醛丙酮) acts on nephron （肾小体） distal tubules, sodium ions are actively reabsorbed from the tubules, water follows and hence blood pressure rises.