Physiology - Plasma Regulation Flashcards
hyperkalemia is defined as what?
- high K+ levels above 5.0 mM
- decreass outwardly directed K+ gradient
- depolarized resting membrane potential
- may cause hyperexcitable muscle contraction
- may cause metabolic acidosis
hypokalemia is defined as what?
- low K+ levels, below 3.5 mM
- increases outwardly directed K+ gradient
- hyperpolarizes resting membrane potential
- may cause hypoexcitability - weakened muscle contraction
- may cause metabolic alkalosis
describe the cellular mechanisms relating to the H+ - K+ exchange, with increased cellular uptake of H+ (acidemia) ? with decreased cellular uptake of H+ (alkalemia)
increased H+ cell uptake blocks the (Na/K/Cl) and Na/K ATPase transporters- the inhibition lowers the K+ uptake into the cell, increasing K+ in plasma (may lead to hyperkalemia)
alkalemia (decreased H+ cell uptake) stimulates (Na/K/Cl) and Na/K ATPase transporters, K+ pulled into cell even more - hypokalemia may result
describe the role of aldosterone on K+ secretion
aldosterone acts in the distal nephron, results in simultaneous Na+ reabsorption and K+ secretion
describe generally hypernatremia?
it is an increase in sodium concentration (Na) to a level above normal range 135 - 145 mEq/L. Caused by inadequate water consumption or an increase in water excretion
A person comes in with hypernatremia, what are their symptoms?
lethargy, weakness and irritability, sever cases - seizure and coma
what can cause hypovolemic hypernatremia?
Due to 1. inadequate water consumption 2. extreme sweating 3. severe diarrhea 4. polyuria ( excess renal excretion of h20)
excessive renal excretion may result from central diabetes insipidus, describe this disorder?
central diabetes insipidus - low release of ADH/AVP from posterior pituitary in response to increased plasma osmolarity
excess renal secretion can also cause nephrogenic diabetes insipidus, describe it?
nephrogenic diabetes refers to an inability of the collecting tubule/duct to respond to ADH/AVP -
what can cause hypervolemic hypernatremia?
excessive hypertonic fluid consumption (seawater), or IV infusion of hypertonic saline, hyperaldosteronism (high levels of aldosterone – inappropriate Na+ reabsorption and volume expansion )
describe hyponatremia generally?
characterized by a decrease in plasma sodium concentration below normal range 135 - 145 mEq/L. Due to a gain of water in excess of solutes in the plasma, dilutes plasma Na+ concentration
name two causes of general hyponatremia
- extreme excess consumption of water (polydipsia) 2. an inappropriate increase in free water rebasorption by kidney (SIADH syndrome - too much ADH release )
describe hypervolemic hyponatremia
Leads to an inappropriate reabsorption of water, which increases plasma volume, and dilutes plasma Na+
describe hypovolemic hyponatremia
- Leads to extreme plasma reduction ( hemorrhage, diuretic drug therapy) , water consumption/reabsorption not enough to correct depleted volume, but can decrease plasma Na+ 2. Addisons disease (hypoaldosteronism/adrenal insufficiency) 3. severe vomiting or diarrhea
what do ECF volume barorecpetors sense?
they sense changes in pressure and effect changes in ECF volume, including effective circulating volume – can be increased or decreased depending on pressure
where are central vascualar sensors of BP for low pressure located ?
these sensors are located in the atria and the pulmonary vasculature
Aldosterone - where is it secreted from and what does it regulate?
aldosterone is a mineralocorticoid, it is secreted from the adrenal cortex, it increases Na+ reabsorption and increases K+ excretion, acts in the distal nephron
What are some of the actions of Angiotensin II?
- stimulates aldosterone release 2. acts on hypothalamus - increase thirst and release of ADH/AVP 3. potent vasoconstrictor 4. increases Na+ reabsorption
which two substances lead to sodium retention
its promoted by Angiotensin II in proximal tubule (Na+ H+ exchange) and Aldosterone in the distal tubule and collecting duct
what is the most important factor controlling Angiotensin II levels in the plasma?
renin release! from the JGA cells.
AVP/ADH - how does this act?
acts by increasing water reabsorption
how does atrial natriuretic peptide work? with decreased effective circulating volume , how does ANP work?
it causes Na+ to be excreted in the urine. it is inhibited wuth decreased effective circulating volume
how does the body get rid of excess Na+?
the body can only decrease Na+ reabsorption, renal handling does not include secretion
describe the cellular actions of aldosterone
Aldosterone diffuses easily into the cell from the blood, it creates a Aldo-MR complex that stimulates transcription, and results in synthesis of Na+ channels, mitochondrial enzymes, and Na-K pumps.
describe positive water balance
when the gain of water exceed the loss of water, and total body water increases (TBW)
describe negative water balance
when loss of water is greater than its gain, TBW decreases
excretion of water by the kidney depends on whether
the plasma is hypo-osmotic or hyper-osmotic
