Podcast Beta
Questions and Answers
What primarily regulates sodium levels in the body?
What is a common clinical manifestation of hypernatraemia?
What is characterized as a more acute condition influenced by sodium regulation?
What condition is associated with a decrease in ECF volume?
Signup and view all the answers
Which hormone is primarily involved in water regulation in relation to osmolality?
Signup and view all the answers
What physiological response is initiated by baroreceptors concerning sodium regulation?
Signup and view all the answers
In a state of hyponatraemia, what is a potential clinical symptom?
Signup and view all the answers
What triggers the secretion of Atrial Natriuretic Peptide (ANP)?
Signup and view all the answers
What condition results from a chronic deficit in water regulation?
Signup and view all the answers
Which parameter is a crucial indicator of sodium levels imbalance?
Signup and view all the answers
What is the primary consequence of severe shrinkage in cells related to blood volume?
Signup and view all the answers
What treatment method is suggested for managing high sodium levels in the extracellular fluid?
Signup and view all the answers
Which statement best describes the impact of sodium content in the extracellular fluid?
Signup and view all the answers
What condition may arise as a result of vascular rupture due to cellular dehydration?
Signup and view all the answers
In the context of severe cellular dehydration, what is a visible symptom related to blood pressure?
Signup and view all the answers
What is the possible physiological effect caused by free water intake in a patient with high extracellular sodium levels?
Signup and view all the answers
Which physiological response is expected in reaction to elevated blood volume due to sodium retention?
Signup and view all the answers
What is a primary concern in managing a patient experiencing symptoms of pulmonary edema?
Signup and view all the answers
What is the primary purpose of the fluid deprivation test in assessing diabetes insipidus (DI)?
Signup and view all the answers
Which treatment is specifically indicated for central diabetes insipidus?
Signup and view all the answers
What indicates nephrogenic diabetes insipidus in the results of the fluid deprivation test?
Signup and view all the answers
What is a potential consequence of acute or extreme hyponatremia?
Signup and view all the answers
Which of the following statements about collecting urine samples during the fluid deprivation test is correct?
Signup and view all the answers
In managing nephrogenic diabetes insipidus, which medication is primarily used to enhance the uptake of sodium in the proximal tubule?
Signup and view all the answers
What distinguishes primary polydipsia from diabetes insipidus during the fluid deprivation test?
Signup and view all the answers
What is the ideal daily fluid restriction for treating a patient with inappropriate ADH secretion?
Signup and view all the answers
What defines osmolality in a biological context?
Signup and view all the answers
Which of the following correctly describes the effect of Na+ as an osmole?
Signup and view all the answers
What is the maximum urine osmolality under normal conditions?
Signup and view all the answers
What is the normal osmol gap (OG) range for healthy adults?
Signup and view all the answers
Which hormone is primarily responsible for water reabsorption in the kidneys?
Signup and view all the answers
In cases of diabetes insipidus, what is the predominant symptom?
Signup and view all the answers
Which of the following conditions can lead to syndrome of inappropriate ADH secretion (SIADH)?
Signup and view all the answers
What is a significant consequence of hypernatremia on water movement?
Signup and view all the answers
Which statement about urea in relation to osmolality and tonicity is true?
Signup and view all the answers
Which of the following accurately describes the physiological response to a 1% change in osmolality?
Signup and view all the answers
What is the effect of severe hypovolemia on ADH secretion?
Signup and view all the answers
What primarily stimulates the thirst mechanism in the body?
Signup and view all the answers
What is the daily obligatory water loss from skin mostly attributed to?
Signup and view all the answers
Which of the following urine osmolality values indicates the highest concentration of solutes?
Signup and view all the answers
What is a critical factor to consider when assessing the osmol gap for abnormal results?
Signup and view all the answers
Study Notes
Osmolality and Tonicity
- Osmolality: concentration of osmotically active particles in a solution, measured by freezing point thermodynamics.
- Plasma osmolality: 275 – 295 mOsm/kg
- Urine osmolality: 50 – 1200 mOsm/kg
- Calculated osmolality = (2 x [Na] + [urea] + [glucose]) of plasma
- Osmol gap (OG): measured osmolality - calculated osmolality
- Normal OG < 10: osmolality generated by ions e.g. Cl-, K+, Ca2+; serum proteins and lipids
- OG > 10: presence of exogenous substances that are osmotically active, e.g. alcohols, sugars, lipids, proteins
- Tonicity: determines water movement across compartments, caused by effective osmoles (osmotic gradient; dependent on how penetrable solutes are; hypertonic – water leaving cell, hypotonic – water entering cell)
- Effective osmoles: Na+, K+, glucose (in diabetics), urea (in extremely high level)
- Ineffective osmoles (but osmotically active): glucose (in normal individuals), urea, alcohol
Water Metabolism
- Daily water requirements: 1500 mL
- Obligatory losses: 1500 mL
- Skin: 500 mL
- Lungs: 400 mL
- Gut (faeces): 100 mL
- Kidney (urine): 500 mL
- Sources: 1500 mL
- Water from oxidative metabolism: 400 mL
- Minimum in diet: 1100 mL
- Obligatory losses: 1500 mL
- Minimum urine output: 0.5 L
Antidiuretic Hormone (ADH)
- Produced in the hypothalamus, stored in the posterior pituitary
- Stimulated by:
- Osmolality (1% change),
- Non-osmotic stimuli (blood volume (10%), stress, nausea)
- Severe hypovolemia: ADH is secreted to preserve plasma volume at the expense of osmolality and Na regulation
- Actions:
- Water reabsorption: via AQP-2 channels at the collecting duct & distal convoluted tubule
- Vasoconstriction: via V1a receptors, ↑ peripheral vascular resistance
Thirst
- Osmolality à sensed by osmoreceptors à hypothalamic thirst centre (outside of BBB) à activate median preoptic nucleus
Disorders of Water Metabolism
Diabetes Insipidus (DI)
- Cause:
- Cranial: (50% idiopathic) X hypothalamus/pituitary gland
- 1o hypothalamic (more common): Tumor, vascular, head injury (HI), etc.
- Nephrogenic: (kidney cannot respond; tubular injury)
- Familial
- Metabolic (hypoK, hyperCa)
- Li toxicity
- Cranial: (50% idiopathic) X hypothalamus/pituitary gland
- Manifestation:
- Polyuria of dilute urine (>3L/24h)
- Polydipsia
- Euvolemic, normal Na & osmo. (dehydrated, Na if insufficient water intake)
- Investigation: Fluid deprivation test
- Treatment: Treat underlying cause
- Cranial DI: Desmopressin (DDAVP)
- Nephrogenic DI: thiazide diuretics (↑ Na+ excretion), amiloride (↓K+ loss)
Syndrome of Inappropriate ADH Secretion (SIADH)
- Cause:
- CNS: encephalitis, stroke
- Lung: pneumonia, TB
- Drugs: SSRI, carbamazepine, morphine, etc
- Surgerysmall cell lung cancer
- Ectopic: SCLC, Ca prostate, Ca thymus
- Manifestation:
- Concentrated urine
- Euvolemic, hypotonic hypoNa (dilutional hypoNa)
- If acute/extreme: cerebral oedema
- Investigation: Urine Na, urine osmolality
- Treatment: Treat underlying cause
- Fluid restriction: 1200ml/day
- Salt: PO, hypertonic IV (rare)
Water and Sodium Regulation
Sensing Parameter
- Water
- Osmolality: by osmoreceptors
- Sodium
- Intravascular volume: by baroreceptors, chemoreceptors
- Vasoconstriction
- Intravascular volume: by baroreceptors, chemoreceptors
Endocrine regulator
- Water
- ADH
- Sodium
- RAAS (renal-angiotensin-aldosterone system)
- Angiotensin II
- ADH
- ANP (atrial natriuretic peptide)
- Sense: BP + volume in heart atrium
- Natriuresis and diuresis
- RAAS (renal-angiotensin-aldosterone system)
Major compartment affected
- Water
- ECF + ICF
- Sodium
- ECF
Manifestations
- Water
- Dehydration (more chronic)
- Sodium
- Hypovolemia (more acute)
Parameter Affected
- Water
- [Na] < /35 mEq/L
- Hypernatraemia
- Sodium
- ECF volume
- Hyponatraemia
- Hypervolemia
- Hypovolemia
Clinical Presentations
- Water
- Lethargy, coma due to brain cellular dehydration
- Vascular rupture
- Seizure, coma due to brain swelling
- Sodium
- Mild: nausea, lethargy
- Severe: ¯ GCS, seizure, coma
- Oedema
- Weight gain
- ↑ jugular venous pressure (JVP)
- ↑ R pressure
- ↑ blood volume
- ¯ GFR
- Poor skin turgor
- Tachycardia
- Orthostatic ¯BP (standing: ¯BP)
- ¯ capillary refill
Implications in treatment
- Water
- Free water, e.g. Water restriction, D5W
- Sodium
- Sodium restriction (since higher water content – dilute Na)
- Normal saline (NS)
Notes
- ^ECF sodium content (or total sodium content as intracellular contains little sodium c.f.ECF) bears no relationship with [Na]
- Measured by indirect ion-selective electrodes or flame photometry
- This can be viewed as a clinical spectrum:
-
Fluid deprivation test: used to differentiate between primary polydipsia and DI.
- Procedures: Supervised water deprivation x 8h, monitor BW, urine volume & osmolality, stop if ¯BW > 5%
- To further differentiate between central vs nephrogenic DI, give DDAVP (desmopressin)
- Results:
- Uosm 300-750 Primary polydipsia
- Normal: Uosm > 750 8h water deprivation
- Uosm > 50% increase Central DI (polyuria)
- Uosm < 300
- DDAVP inj.(no increase) Uosm < 50% increase Nephrogenic DI
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Test your understanding of osmolality and tonicity, important concepts in physiology that regulate fluid balance in the body. This quiz covers the definitions, calculations, and implications of osmolality, as well as the significance of effective and ineffective osmoles in various conditions. Perfect for students studying biology or medicine.
