The Role of the Kidney in the Regulation of Plasma Osmolality

Transcription

1 The Role of the Kidney in the Regulation of Plasma Osmolality Model 1: ADH Production, Storage, and Release Hypothalamus Neurons in hypothalamus produce antidiuretic hormone; stored in posterior pituitary for future use Anterior Pituitary Posterior Pituitary 1. Which organ of the body produces ADH? The hypothalamus is responsible for the production of ADH. 2. Which organ is responsible for the storage and release of ADH? The posterior pituitary stores and also releases ADH as needed.

2 Model 2: ADH s Effect on a Nephrons Water Permeability Low ADH High ADH Low ADH 3. Where in the nephron does ADH act? On the wall of the collecting duct 4. When water is reabsorbed in the nephron where does it travel first? The interstitial fluid/space 5. What effect does increasing levels of ADH have on the water permeability of the nephron? The nephron becomes more permeable to water, which causes the body to retain more water.

3 6. If the plasma osmolality increases predict what happens to ADH levels? If the plasma osmolality decreases predict what happens to ADH levels? As plasma osmolality increases, ADH levels increase and the opposite would be true. Model 3: Plasma Osmolality versus ADH Concentration Data was collected by increasing plasma osmolality from the normal value of 300 mosm/kg and measuring the effect of ADH levels a short time later. 7. How do ADH levels change when plasma osmolality increases? Was your prediction from question 6 correct? As plasma osmolality levels increase so do ADH levels. Our prediction was correct. 8. Predict what will happen to plasma ADH levels if plasma osmolality falls below 300 mosm. The posterior pituitary will be stimulated to release ADH 9. Describe a condition/situation that might lead to a rise in plasma osmolality. Explain your answer. Someone could have been in an accident and lost a lot of blood causing their blood pressure to decrease. The body s response would be to retain as much fluid as possible, which would mean ADH would be released from the posterior pituitary gland causing the wall of the collecting duct to retain more water.

4 Model 4: Plasma Osmolality Homeostasis Negative Feedback Loop Hypothalamus signals posterior pituitary to adjust release of ADH Activate osmoreceptors in hypothalamus ADH levels in blood increase Osmolality of blood Permeability of the wall of the collecting duct increases Change in urine output and shift in plasma osmolality back toward 10. In the above feedback system, what variable is being monitored? Plasma osmolality 11. Where in the body is the variable monitored? The hypothalamus

5 12. Being a negative feedback loop, how will the posterior pituitary respond if osmolality of the blood increases? It will release ADH. 13. When the osmolality of blood decreases, draw a negative feedback cycle diagram showing how osmolality returns toward the set point. Osmoreceptor senses a decrease decreased ADH release permeability decreases higher urine output increased blood osmolality 14. Alcohol inhibits the release of ADH. How will this affect plasma and urine osmolality? Both plasma osmolality and urine output will increase. 15. Bill likes to reward himself after moving the lawn with a couple of beers. He follows this routine on a very hot summer day and again, on a cool, crisp fall day. Assuming that his hydration prior to mowing was similar; would his urinary output be similar or different on those two occasions? a. Explain with grammatically correct sentences. The beer will affect him more during the summer because even with hydration, perspiring will make his body lose water. His urine output will decrease as his body tried to maintain water. b. List any other possible physiological effects or differences between the two seasons. Concentrate urine, thirst response, constrict blood vessels 16. With Diabetes Insipidus the pituitary gland fails to secrete ADH or the collecting duct receptors fail to detect ADH. a. How would the urine volume and concentration in a patient with Diabetes Insipidus compare with that of a healthy person? Urine volume will increase and be more dilute due to less solutes in the urine. b. Will increasing fluid intake restore water balance in these patients? Explain why. In the short term yes, in the long term no because ADH will not respond.