You are hiking in the mountains on a warm summer day. As you are walking up a st

Question

You are hiking in the mountains on a warm summer day. As you are walking up a steep incline, your leg muscles are working pretty hard. They need to produce a lot more ATP than usual in order to propel you upward. Your breathing becomes deeper and more rapid as you work to bring in more air. You also notice that you are getting warm and starting to sweat. You have water with you and decide to stop for a water and snack break. Your snack consists of a power bar that contains a good mix of carbs, proteins, and lipids - just what your body needs! As you sit and replenish your nutrients and water, you marvel at the beauty of your surrounds and feel a sense of appreciation that your body is healthy and able to adjust its activities to meet your ongoing needs.

(35 points) Prior to taking a break, your body was losing water thru sweat.

a. Describe how the kidneys would adjust their activities to reduce the loss of water thru urination, and reduce the potential for dehydration.

b. Describe a regulatory mechanism that would explain how this adjustment would be made.

c. What would happen to blood volume and osmolarity if the kidneys couldn't conserve water when sweating increases and how would that affect cell volume and function?

Explanation / Answer

a. A person's plasma osmolality reflects the state of hydration. A healthy body maintains plasma osmolality with a narrow range by regulating both water intake and output. Osmoreceptors are sensory receptors that monitor the concentration of solutes of the blood. If blood osmolality increase above its ideal value, the hypothalamus transmits signals resulting in awareness of thirst.

b. The hypothalamus of a dehydrated person also releases ASH through the posterior pituitary gland. This hormone signals kideny to recover water from urine effectively diluting the blood plasma. To conserve water, hypothalamus signals through sympathetic nervous system to salivary glands in the mouth which leads to decrease in watery, serous output.

c. Decreased bllod volume results in activating baroreceptors in the arch of aorta and the carotid arteries in the neck detect decrease in blood pressure that results from decreased blood volume.

Kidneys have renin-angiotensin hormonal system that increases the production of the active form of the hormone angiotensin which helps stimulate thirst but also releases aldosterone. This hormone increase sodium reabsorption in the distal tubules of kidney.

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