A hiker walks for hours in the heat and sweats a lot…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A hiker walks for hours in the heat and sweats a lot. She does not drink.
- Which gland releases ADH, and what does ADH do in the kidney?
- Which hormone of the adrenal cortex helps to keep sodium, and where does it act?
- What happens to the volume and the concentration of her urine?
- When she drinks water, what happens to the release of ADH? Name the kind of feedback.
- Why do the nervous system and the endocrine system both take part in her response?
Need a reminder? The key ideaShow
Negative feedback keeps a level near a set point. Positive feedback drives a process to its end, as oxytocin does in childbirth. Insulin and glucagon, and PTH and thyrocalcitonin, work in opposite ways. The hypothalamus joins the nervous system to the endocrine system.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The posterior pituitary releases ADH, which was made in the hypothalamus. It makes the distal tubules of the kidney reabsorb water.
Step 2. (b) Aldosterone. It acts on the renal tubules and keeps sodium ions and water.
Step 3. (c) The urine is small in volume and concentrated.
Step 4. (d) The release of ADH is switched down. This is negative feedback.
Step 5. (e) The hypothalamus, which belongs to the nervous system, senses the water of the body and controls the pituitary. The hormones then act on the kidney.
Answer: (a) posterior pituitary, more water taken back; (b) aldosterone at the renal tubules; (c) small volume, concentrated; (d) ADH falls, negative feedback; (e) the hypothalamus joins the two systems.
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