Regulation of Osmolarity Flashcards
What is water controlled by ?
ADH
How does plasma osmolarity affect ADH?
Increased plasma osmolarity causes an increased rate of ADH secreting hormones. and then ADH increases
Where are osmoreceptors found?
The anterior hypothalamus
What occurs when the volume of osmoreceptors changes?
There is a change in osmoreceptor discharge
What is the rate of normal plasma osmolality?
280-290mOsm/kg H2O
What occurs when you increase NaCl concentration?
There is a decrease in plasma volume, an increase in discharge and an increase in ADH
Why is osmolarity uneffective without tonicity?
No osmotic drag is created without tonicity
The amount of urine produces is dependent on what?
ADH concentration and the amount of solute to be excreted
What does the ingestion of hypertonic solition do to the body?
Increases urine flow which induces dehydration
Where is the site of water regulation?
The collecting duct
What occurs when vasopressin binds to the membrane receptor?
cAMP is activated and cells insert AQP2 water pores into the apical membrane. Water is then absorbed by osmosis into the blood
When is [ADH] at a maximum level?
During a water deficit. It effectively adds pure H2O into the ECF
Describe the oncotic pressure level of the vasa recta during a water deficit?
It is increased
What happens when ADH is absent?
Collecting ducts are impermeable to h20 so a large volume of dilute urine is excreted, compensating for H2O excess
Why is urea retained during anti-diuresis?
To save water and reinforce medullary gradient in region of thin ascending limb of LoH
Why is it important for urea to be reabsorbed?
If it remained in the tubule, it would exert an osmotic effect to hold h2o in the tubule. This reduces potential for rehydration
What does an increase in ecf volume have on ADH?
Decreased ADH
What does a decrease in ECF volume have on ADH/?
Increases ADH
Where are low pressure receptors found?
Left and Right atria, great veins
Where are high pressure receptors found?
The Carotid and Aortic branches
What does a moderate decrease in ECF volume cause?
Primarily affects the atrial receptors
Decrease in ECF, Decrease in Atrial Receptor Discharge and an Increase in ADH
What increases ADH?
Pain, emotion, stress, exercise, nicotine, morphine
Traumatic surgery can also cause inappropriate ADH secretion
What decreases ADH?
Alcohol
What is an ADH deficiency also known as ?
Diabetes Insipidus
What can cause Diabetes Insipidus?
Tumours or meningitis.
Surgery can cause damage = CENTRAL DIABETES INSIPIDUS
What are the characteristics of Diabetes Insipidus?
Polyuria and polydipsia
How is Diabetes Insipidus treated?
Giving synthetic ADH
How would drinking a large amount of water affect osmolarity and ecf volume?
Decreased osmolarity and increased volume
