L7 Control Of ECFII Flashcards
Changes in ECF volume and osmolarity
Volume contraction - decreases in ECF volume
Volume expansion - increase in ECF volume
When a disturbance is called isosmotic, hyperosmotic, or hyposmotic, the terms refer to the osmolarity of the ECF
Hyperosmotic volume contraction
Dehydration
Volume is low
Hyperosmotic
Hyperosmotic volume contraction
Diabetes insipidus
ADH very low or ineffective (can’t conc urine)
Presentation: high plasma osmolality, low urine osmolality, polyuria, polydipsia
2 types of causes: neurogenic and nephrogenic
Neurogenic (=central) DI
Plasma ADH low due to hypothalamic-pituitary injury
Patient cannot secrete sufficient amounts ADH
Will respond to exogenous ADH agonist (ie desmopressin)
Nephrogenic DI
Renal in origin- kidney unable to respond to ADH or desmopressin
Several causes:
Defect in V2 receptor or elsewhere
Lithium toxicity
Hypercalcemia
Plasma ADH high since pituitary is functioning normally
Hyposmotic volume expansion
SIADH- syndrome of inappropriate ADH secretion
Head injury and some lung tumors can cause excessive amounts of ADH to be secreted
Result: chronic ECF dilution
Hyponatremia
ECF volume may transiently expand, but euvolemia common
Excess renal Na loss (decreases aldosterone, increased ANP)
Dilution of the ECF but no hypertension
Constancy of Pna
Plasma Na must be carefully controlled
Na the major action of the ECF, determines volume of ECF compartment
Na loss is often isotonic (diarrhea, vomiting)
Changes in Na conc of ECF generally caused by changes in body water content rather than changes in Na content
Hyponatremia
<135mEq/L
Common causes:
Secondary to blood volume depletion- high ADH(maximal reabsorption of water), thirst (ingested water and dilution of ECF [Na])
Secondary to excessive water conservation (ie SIADH)
Secondary to excessive water intake (water intoxication, exercise associated)
Hypernatremia
> 145mEq/L
Causes:
Loss of water (dehydration, DI)
Gain of sodium
Rarely produce persistent hypernatremia in normal subjects
Excess Na causes hyper osmolarity and thirst.
Drinking water will quickly dilute plasma conc to normal
Passage of urine from kidney to bladder
Renal calyxes and pelvis possess smooth muscle
As urine collects, smooth muscle is stretched and inherent pacemaker activity is stimulated
Peristaltic contraction forces urine into the bladder
Stretching of trigone will create urge to urinate
Micturition
Urge to void felt at volume of 150ml
Max bladder volume = 500-800ml
Sympathetic fibers: relax detrusor muscle (inhibit) during filling, contract internal sphincter during filling
PNS is responsible for micturition: PNS causes detrusor to contract and causes relaxation of internal sphincter
