Polydipsia/ Polyuria (part 1)

what is the countercurrent system?

- Loops of Henle - water reabsorbed along concentration gradients that are established in renal medulla - decreases osmolality

what is secondary thirst?

- NOT well understood but IS the more common cause of Pd! - anticipates water needs prior to actual deficiencies!

what is primary thirst?

- well understood but not the primary mechanism! - intracellular dehydration - left atrial volume and pressure receptors detect 8-10% decrease in blood volume to induce thirst (and incr. ADH)

what could hypercalcium be indicative of?

Cushing's disease or cancer

what could be some causes of pseudopsychogenic Pd/ compulsive water drinking?

anxiety, boredom, compulsion, crazy owners lol

in the case of primary polydipsia, what is the secondary result?

compensatory polyuria

what is polydipsia?

excessive thirst for long periods of time, constant drinking

what does ADH do and what is it controlled by?

helps concentrate urine, controlled by extracellular osmolality

where is the thirst center located?

hypothalamus (stimulates drinking)

describe the process used by the ADH osmoreceptor control system

incr. extracellular osmolality --> incr. ADH release --> incr. collecting tubule permeability (in kidney) --> water is reabsorbed

what is polyuria?

passage of large amounts of urine, typically with decreased specific gravity

what is the name for the specialized neurons in the hypothalamus that produce ADH?

pituicytes (stored in the nerve endings)

is polydipsia or polyuria the primary disorder?

polyuria (polydipsia is the secondary result)

what is pathologic thirst?

primary polydipsia (direct effect on thirst center)

what are two examples of dipsinogenic compounds?

renin and angiotensin

what happens when aldosterone increases?

sodium and water retention increase, potassium decreases

what is a dipsinogenic compound?

stimulates thirst by direct action on neurons in the thirst center

what are some causes of neuronal/ hypothalamic irritation causing primary Pd?

tumor, trauma, inflammation/ infection of the brain

what are two types of renal concentrating mechanisms?

1. ADH Osmoreceptor control system 2. countercurrent system

what are 5 possible causes of pathologic thirst?

1. neuronal irritation (hypothalamic) 2. compulsive water drinking/ pseudopsychogenic Pd 3. increased plasma renin 4. hypercalcemia 5. thoracic caval constriction

what are the two basic principles of the "bar-scene syndrome"?

1. water in = water out (alcohol in = alcohol + water out) 2. over-hydration vs dehydration (intracellular)

what specific gravity indicated polyuria?

1.035 or lower

how much urine is produced by a 25 lb dog taking in 68 liters of fluid?

500 ml produced (very efficient process!)

what is ADH?

antidiuretic hormone

what could be the cause of thoracic caval constriction?

a mass in the chest

what increase in serum osmolality results in max release of ADH?

about 1-2% increase in osmolality

where is the ADH control center located?

adjacent to the thirst center (hypothalamus)

what happens to the body when you drink alcohol in excess?

alcohol AND water leave (since its a diuretic), as well as loss of electrolytes