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42 Cards in this Set

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Location of osmoreceptors. How are these stimulated?
Anterior hypothalamus (AV3V) near the supraoptic nucleus.
Increased osmolarity causes the cells to shrink, causing them to fire an AP to the supraoptic nucleus
Where in the kidney do ADH receptors increase water reabsorption?
Distal collecting tubules, cortical collecting tubules and medullary collecting ducts.
How is ADH released?
Stimulation of the magnocellular neurons of the supraoptic and paraventricular nuclei, causes an AP and thus their membrane permeability to increase. Ca2+ enters the cell and ADH stored in secretory vesicles is released into the capillaries of the Posterior Pituitary.
Lesions in what region cause multiple deficits in the control of ADH secretion, thirst, sodium appetite, and blood pressure.
Anteroventral region of the third ventricle (AV3V)
Send nerve signals to the supraoptic nucleus to control their firing and secretion of ADH
osmoreceptors of the AV3V
Median preoptic nucleus
Multiple nerve connections with the two organs, the supraoptic nuclei, and the BP control centers of the medulla
Location of median preoptic nucleus
Between the subfornical organ and the organum vasculosum of the lamina terminalis
Area whose vscular supplies lacks the typical blood-brain barrier. Why is this important?
Subfornical organ and the organum vasculosum:
Allows ions and other solutes to pass between the blood and the interstitial fluid, allowing osmoreceptors to react rapidly.
How does blood pressure and blood volume effect ADH secretion? Mechanism?
Decreased BV and BP increase the release of ADH. This occurs via receptors in the high pressure aortic arch and carotid sinus, and the low pressure cardiac atria that sense the drops. This causes these areas to send Afferent signals through the vagus and glossopharyngeal nerves to the Nuc Solitarius, which relays the signals to the hypothalamus
Is ADH secretion more sensitive to osmolarity or decreases in BV?
It is much more sensitive to osmolarity. Decreased BV, however, greatly enhances the ADH response to increased osmolarity.
How does nausea effect ADH secretion?
Increases ADH
Drugs that stimulate ADH release?
Inhibit?
Increase: Morphine, Nicotine, cyclophosphamide
Decrease: Alcohol, Haloperidol, and Clonidine
Fluid intake is regulated by what mechanism?
Thirst, which acts together with the osmoreceptor-ADH mechanism
Inability to produce or release ADH from the posterior pituitary. What mechanism keeps the body in homeostasis?
Central diabetes insipidus
Thirst mechanism
Where does desmopressin act?
On V2 receptors of the epithelium of the kidney
How does renal disease cause Diabetes Insipidus
Damage to the renal medulla impairs the concentrating mechanism and thus the urine is unable to become hyperosmotic. This is a form of nephrogenic diabetes insipidus.
Action of diuretics
Inhibit electrolyte reabsorption in the loop of henle
Regulation of extracellular fluid osmolarity is linked with what ion. Calculation of Plasma osmolarity?
Na
Posm= 2.1 x plasma Na concentration
Threshold for drinking
When the osmolarity increases 2mEq/L above normal, the thirst mechanism is activated.
Increased CSF osmolarity may activate the thirst mechanism via what area
The organum vasculosum of the lamina terminalis
Affects of angiotensin II and aldosterone on plasma osmolarity
Because these hormones increase both sodium and water reabsorption, they have little effect on the sodium concentration, except under extreme conditions.
During Addison's disease, how does the extracellular fluid environment become hypo-osmolaric?
Loss of extreme amounts of Na, leads to decreased blood volume and pressure, which activates the cardiovascular reflexes. Once activated, the reflexes work to stimulate thirst, leading to further dilution of the plasma Na concentration.
What stimuli drive the salt appetite?
Decreased extracellular fluid Na concentration and decreased blood volume or pressure
How does excess water effect ADH secretion and kidney permeability?
Decreases ADH secretion, causing the distal tubules and collecting ducts to be impermeable to water.
How does drinking large amounts of water affect the reabsorption of solutes?
It doesnt
Initial glomerular filtrate has an osmolarity equal to what?
Plasma
Fluid osmolarity in the proximal tubule. When does the tubular fluid first become hypertonic?
Isotonic, this is because both solutes and water are reabsorbed.
As it passes down the descending loop of henle.
As fluid reaches the renal medulla, what is its tonicity
Hypertonic
Is fluid leaving the early distal tubule hyper or hypo osmotic? Is this influenced by ADH
Hypo-osmotic
NO!
Most solutes are reabsorbed in what part of the kidney?
Ascending limb of the loop of henle
In healthy kidneys, where is fluid always dilute?
In the ascending limb and early distal tubule
Maximum urine osmolarity
1200-1400 mOsm/L
Basic requirements for forming a concentrated urine
High level of ADH
High osmolarity of the renal medullary interstitial fluid. This provides the osmotic gradient necessary for water reabsorption.
ADH increases the permeability of urea where?
Inner medullary collecting duct
Most important cause of high medullary interstitial osmolarity
Active transport of solutes from the thick ascending loop of henle into the interstitium
ADH increases urea reabsorption how?
In the presence of ADH, water is reabsorbed creating a high urea tubular concentration. At the inner collecting medullary duct, ADH activates UT-AI urea transport receptors that work to rebasorb urea.
Malnutritions effects on urine concentration
When protein malnutrition occurs, there are low amounts of nitrogenous urea formed as protein waste. This hinders the ability of urine
During dehydration how is urea reabsorbed?
By passive diffusion due to presence of ADH
How is urea concentration affected during kidney disease?
A decreased GFR raises the plasma urea concentration, which allows for the continued excretion of urea despite a decreased GFR
How do the vasa recta contribute to the medullary interstitial hyperosmolarity?
They prevent it from being dissipated
How does medullary blood flow affect the medullary osmolarity?
Slow blood flow through the medulla minimizes solute loss
How do vasodilators affect medullary osmolarity?
They markedly increase medullary blood flow causing the an increase in absorption of solutes from the medullary interstitium. This decreases the urines concentrating ability