Water Handling - Kidneys Flashcards
What is the osmolarity of all the parts of the tubule?
Proximal: 300mOsm Descending: 300-1400mOsm Ascending: 800-200mOsm DCD: 200-100mOsm Collecting: 100-1400mOsm
Why is osmosis important in water handling?
Water moves by osmosis out of the tubule to match the osmolarity of the medulla
What happens to water reabsorption of ADH is present?
Present: water will be reabsorbed out of the collecting duct and match the osmolarity of the surrounding medulla as it increases in [] on the way down. Urine will be low volume and high concentration of solutes
Not present: Water will not be reabsorbed because there will be no aquaporin channels to allow the water out of the collecting duct. Urine will be high volume but low concentration because osmolarity of the surrounding medulla will not have as strong an effect
How are water and salt regulated different than any other process in the body?
They both can be regulated independently to maintain homeostasis
What is the average expulsion of urine a day?
- 5-2L
- low as 0.4L
- high as 25L
Where does most of our water come form?
What we drink and what we eat
Where do we lose most of our water from?
Urine
Skin & Lungs
How do kidneys and blood volume relate?
Kidneys can control the blood volume. If total body water decreases the ECF (blood plasma) volume decreases, blood pressure decreases.
If total body water increases, blood volume increases
-help by not constricting fluids in the tubules
How do kidneys know when ADH is required?
Kidneys rely on pressure differences to determine whether or not ADH is required
Where is ADH
- Made
- Stored
- Hormone properties
- Stimulus
- Action
Made: In the hypothalamus
Stored: In the posterior pituitary
Properties: Peptide hormone, receptors on the outside of the cells, released directly to the blood
Stimulus: high plasma osmolarity and low ECF volume (resulting in low BP)
Action: Increases the number of AQII channels on the luminal membrane of the collecting duct
What are the sensors for ADH?
Osmoreceptors: Located in the hypothalamus, Increased plasma osmolarity causes receptors to shrink in volume triggering ADH release
-when plasma is higher than normal, causes receptors to decrease in volume causing ADH release because the solution around the cell is a higher osmolarity
Baroreceptors: Located in the aortic arch and carotid sinus, when ECF decreases ADH is released because there are fewer action potentials sent to the hypothalamus via these receptors
How does ADH cause more water reabsorption in the collecting duct?
When ADH is present it is released from the posterior pituitary, binds extracellular receptors, increases the number of AQII channels on the luminal membrane in the collecting duct
-AQII are in vesicles in the cytoplasm of tubule cells
What happens when plasma osmolarity is higher than normal?
ADH is released
What is the flow chart outlining the stops that cause an increase in water reabsorption in the collecting duct starting with an increase in plasma osmolarity
Increase in plasma osmolarity, osmoreceptors shrivel, ADH is released, ADH binds receptors in the collecting duct, More AQII channels move to luminal membrane, More water is reabsorbed
What is the flow chart outlining the steps that cause an increases in water reabsorption in the collecting duct beginning with a decrease in total body water
Decrease in total body water, decrease in BP and ECF, senses by baroreceptors in arctic arch and carotid, decrease in AP’s sent to the hypothalamus from baroreceptors triggers the release of ADH, stimulates kidneys to take up more water via more AQII channels
