Ella has just finished running a half marathon. She hasn't been drinking enough water so is dehydrated and is feeling incredibly hot. Describe how her body responds to these changes. (6)

She is dehydrated so osmoreceptors in the hypothalamus shrink, this causes ADH to be secreted by the pituitary gland. The ADH travels in the blood stream and acts on the collecting ducts of the kidney nephrons to make them more permeable to water. Thus, more water is reabsorbed from the filtrate back into the blood stream. As she is hot, her arterioles will dilate, hair erector muscles lie flat and sweat is secreted onto the skin.