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Atrial Natriuretic Peptide (ANP)
- DIURETIC (Na+ and Water)
- released by the heart in response to stretch of atria (i.e. high BP)
- causes a decrease in Na and water reabsorption and overall drop in BP
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aldosterone
- ANTIDIURETIC
- increases Na retention and increases potassium excretion
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ADH, Antidiuretic hormone/ AVP arginine vasopressin
- ANTIDIURETIC
- promotes water reabsorption in the tubules by increasing number of aquaporins
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What is the physiological response to fluid depletion
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apparent ECF osmolality formula & when is it valid
2[Na+] + 2[k+] + [glucose] + [urea]
is only valid if the patient doesnt have hyperproteinureia or hyperlipidemia
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Major electrolytes of ICF and ECT and app. volumes
- ICF: 28L, K+, phosphate, Proteins
- ECF: 14L, Na, Cl, HCO3-
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response to dehydration
- post. pit. to secrete ADH --> water reabsorption
- adrenal glands secrete aldosterone --> Na reabsorption
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what happens when you lose ECF pure water only + symptoms
pure water is lost , Na+ content is the same, thus [Na+] increases --> changes osmolality of ECF --> ICF water travels to the ECF to balance osmolality. loss of ICF
- SYMPTOMS:
- cell dysfunction, muscular cell dysfunction --> lethargy, CNS cell dysfunction --> confusion, coma
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what happens when you lose isotonic Water + Na+
changes the ECF only because there is no osmolality difference, osmolality of both compartments remain the same. There is no net water movement. Only the ECF loses volume.i.e. hypovolemia
- SYMPTOMS
- circulatory collapse, renal shutdown, shock
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3 types of dehydration
- Hypertonic, >water loss than Na+
- isotonic water=na+ loss
- hypotonic >Na loss than water
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Presentation of dehydration and causes
presentation: hypernatremia, hyperosmolality, decrease volume in ECF and ICF
- CAUSES:
- Inadequate intake:
- Abnormal loss:
- - lungs, skin, gut (diarrhea)
- - renal tract (diabestes insipidus which is a deficiency of ADH)
- - Li therapy, increase in osmotic load (alot of glucose, needs a lot of water to be excreted), DM, diuretics
- - third space losses
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causes of water excess
- excessive intake (polydispia)
- - oral or parenteral (e.g. hypotonic IV infusion)
- renal retention
- - XS ADH secretion - SIADH
- - hypoadrenalism
- - hypothyroidism
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water intoxication
- - dilutional hyponatremia and hyposmolality of the ECF
- - expansion of both ICF and ECF
- - Na+ falls ~ 120-125mmol/L --> nausea, vomiting, abdominal cramps
- - seizures & coma result from the changes in water content of brain, i.e. cerebral oedema
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The three types of hyponatremia
- 1. hypovolemic hyponatremia
- - low TBW & Na with a relatively greater decrease in Na & therefore decreased ECF.
- - due to renal or extra renal Na+ loss
- - renal: urine [Na+] > 20mmol/L
- - extra renal:urine [Na+]<20mmol/L
- - no oedema
- 2. Euvolemic hyponatremia (dilutional)
- - high TBW with near normal total body Na therefore normal ECF
- - due to excessive water retention
- causes:
- - acute: post-op water admin
- - chronic: antiduiretic drugs, opiates, SIADH
- 3. hypervolemic hyponatremia
- - high total body Na (therefore high ECF) with a relatively greater increase in TBW.
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SIADH
- syndrome of innappropriate ADH secretion --> hyponatremia
- - secretion of ADH without hypernatremia or fluid depletion due to failure of the neg. feedback system that regulates ADH release
- signs:
- - low plasma Na
- - high urine osmolality
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hyperosmolar hyponatremia
- due to other substances into the plasma and causing a shift of water from ICF to ECF.
- e.g. hyperglycemia in uncontrolled DM
- - assessed by calculating osmolal gap
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pseudohyponatremia
* CLARIFY**
- fake hyponatremia due to hyperlipidemia and hyperproteinemia occupying plasma volume
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causes of hypernatremia
- oral intake (sea water near-drowning, salt tablets, hypertonic NaCl (rare)
- parenteral
- renal retention: renal failure, cushings syndrome (XS aldosterone), 2ndary hyperaldosteronism
- pregnancy
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