1.4.1 Regulation of Extracellular Fluid and Electrolytes I Flashcards
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What is the pathway through which sympathetic nerve activity decreases salt and water excretion?
What are the net effects of aldosterone?
Na+ and water absorption
K+ secretion
Increase blood volume and BP
What are the three net effects of the renin-angiotensin-aldosterone system in volume control?
Decreased salt and water excretion
Increased salt and water absorption
Increased peripheral resistance
What are the net effects of ANP release?
Increased salt and water excretion
Decreased BP
Describe the cascade set off by increased blood volume that leads to the release of ANP.
What is the physiological response to acute volume expansion?
The response to acute expansion of ECF volume begins also with the two major stimuli: the change in atrial volume and the change in arterial pressure. The atrial response is probably triggered first as ECF volume rises; the increase in arterial pressure occurs at a higher level of volume expansion. The two major response systems are the sympathetic nervous system and the juxtaglomerular apparatus. The atrial secretion of ANP also plays a role. A major cause of the resulting diuresis is probably the change in peritubular capillary pressures.
As a conclusion, it is important to realize that physiological maintenance of ECF volume in a healthy individual implies complex interrelationships among the various stimuli, pathways and effectors, and that none of them operates in isolation of the others.
What are the four sensor/effector mechanisms that control effective circulating volume?
- ADH, AVP (pituitary)
- Natriuretic peptides (ANP, BNP)
- Renin-Aldosterone Release
- Sympathetic nervous system
What is the mechanism of NPs on vascular cells?
NPs bind their NPR on vascular cells. This binding stimulates the formation of cGMP which results in protein phosphorylation and decreased Ca++ levels. This results in relaxation/vasodilation
On what part of the kidney does ADH act? How does it alter the volume and osmolarity of urine?
ADH acts on the distal tubule and collecting duct
Decreases volume of urine while increasing its osmolarity
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What are the four natriuretic peptides and their organ of origin?
ANP: Atria
BNP: Ventricle
CNP: Brain
Urodilatin: Kidney
What is the physiological response to severe volume depletion?
Describe the physiological In severe volume depletion, there are two major triggering stimuli: the fall in arterial pressure and the fall in atrial volume. These stimuli activate two Interrelated major systems, the sympathetic nervous system and the juxtaglomerular apparatus (the sympathetic nervous system stimulates the juxtaglomerular apparatus). As a result, the activity of the renin-angiotensin-aldosterone axis is increased. The peritubular capillary pressures are altered so that reabsorption is stimulated. These, and a constellation of other effector mechanisms, reduce the excretion of salt and water. In addition, total peripheral resistance is raised by the sympathetic neural and humoral activity in combination with angiotensin and ADH, so that the effect of the loss of circulating blood volume is minimized. The sympathetic nervous system also decreases venous compliance and increases the pumping activity of the heart.response to severe volume depletion.
What are the four locations of the volume receptors? Where are the baroreceptors located?
Volume receptors: Venous, R. Atrium, Pulmonary, L. Atrium
Baroreceptors: Carotid sinus, Aortic Arch
What is the cellular mechanism of ADH?
ADH binds to the V2 receptor on the basolateral surface of pricipal cells of the distal tubule/collecting duct. This activates AC which increases the intracellular level of cAMP. Increased cAMP aids in the phosphorylation of aquaporin vesicles, which leads to their insertion on the apical suface. The insertion of aquaporins on the apical surface favors water reabsorption
What is the MOA of aldosterone?
Aldosterone enters distal tubular (main effect is on the collecting duct) cells binds its receptor. The bound receptor alters DNA txn upregulating Na-K ATP-ases on the basal surface and Na+ channels on the apical suface. Ultimately, K+ is secreted will Na+ is reabsorbed.
What is the mechanism of Urodilatin on the collecting duct cells?
Urodilatin binds its NPR. This binding then favors the formation of cGMP. The cGMP levels inhibit ENac inhibiting the resorption of Na+.
What factors influence ADH secretion? What is ADH most responsive to?
ADH responds to changes in volume, pressure, and osmolality. ADH is most sensitive to osmolality
What are the three stimulators of aldosterone secretion?
- Decreased Na+ levels
- Decreased blood volume and BP
- ACTH from the pituitary
Describe the pathway from angiotensinogen to aldosterone.
