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 nice mix of carbs, proteins, and lipids. Just what your body needs! As you sit and replenish your energy 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. 1. Oxygen is needed for ATP production by your muscles. Describe how the lungs are working to increase the inflow of fresh air, so that more oxygen can be delivered to your muscles. Describe a regulatory mechanism that would explain why your breathing became deeper and more rapid while you were hiking. 2. Prior to taking a break, your body was losing water thru sweat. Describe how the kidneys would adjust their activities to reduce the loss of water thru urination, and reduce the potential for dehydration. Describe a regulatory mechanism that would explain how this adjustment would be made. 3. The nutrients in the power bar and the water are taken in thru the digestive tract to help meet your body's energy needs and help to keep you hydrated. Describe where in the digestive tract each of the nutrients is broken down into an absorbable form and where the nutrients and water are absorbed. Describe a hormonal regulatory mechanism that would help to make the digestion of these nutrients possible. Make sure to include detail about the anatomical structures involved to provide a thorough picture of the processes taking place and complete pathways for the regulatory mechanisms (i.e. the trigger for the pathway, the control center, the efferent pathway, and the effector/effector response).

Explanation / Answer

1.

While hiking a mountain, the body needs to spend more energy since there is vertical movement also involved. Therefore, more energy is required to climb up the mountain. Initially, the body depends on anaerobic glycolysis to produce the energy required. However, gradually it shifts to aerobic breakdown of glucose or combined aerobic and anaerobic metabolism (simultaneously, it also uses ATP – creatine phosphate system).

Since the body shifts from anaerobic glycolysis to aerobic ATP synthesis, the demand for oxygen increases.

This demand for oxygen can be met in two different ways. The nitric oxide induced increase in pulmonary ventilation is one way. Under stress conditions, the lungs increase the synthesis and release of nitric oxide which increases blood flow and from pulmonary circulation and thus, more oxygen is delivered to tissues. On the other hand, oxygen supply is increased through increase in VO2 max, heart rate, or stroke volume. Since the VO2 max has a saturation limit, it cannot be increased further if the person is already in his peak VO2 max. Therefore, further increase in oxygen delivery to tissues is achieved through increase in cardiac output.

2.

When a person sweats profusely, there is loss of fluid which leads to increase in extracellular fluid osmolality above the normal. The osmoreceptors in the kidneys and other organs detect this change and stimulate the hypothalamus to secrete anti diuretic hormone. The hormone acts on nephrons by increasing the permeability of the distal tubules and collecting ducts to water. Therefore, more water is reabsorbed and only small volume of concentrated urine is excreted.

3.

Digestion of proteins – start in stomach through acid hydrolysis. The acidic pH in the stomach hydrolyzes proteins. The enzyme pepsin in the stomach digests proteins. In the small intestine, other peptidases like trypsin and chymotrypsin digest the remaining peptides.

Carbohydrates: Their digestion starts in the mouth by the enzyme ptyalin or amylase. In the stomach, the mechainical churning action makes the carbohydrates into pieces or small parts. In the intestine, the pancreatic amylase, and the enzymes like lactase, sucrase, and maltase break down most of the starches and polysaccharides into sugars. Those carbohydrates that are not digested reach the colon and may be fermented by intestinal flora.

Lipids: lipid digestion starts only in the intestines. At the duodenum, the bile secretions emulsify the lipids and make them suitable for enzyme action. The pancreatic lipases act on the lipids in the small intestine and facilitate their digestion.

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