SIMARA CLOUDHURY – DEHYDRATION Adam Reynolds M1900276@sgul.ac.uk Will Nash m1902620@sgul.ac.uk
OVERVIEW • Our top tips for the year • Useful resources • Practice SBA Questions • Questions
TOP TIPS FOR THIS YEAR (1) • DR DEAC PIMP – Nice way to summarize a disease • Definition • Risk Factors • Differential Diagnosis • Epidemiology • Aetiology • Clinical Features • Pathophysiology • Investigations • Management • Prognosis
TOP TIPS FOR THIS YEAR (2) • MICRA – Nice way to summarize drugs • Mechanism of Action – How it works • Indications – What it is used for • Contraindications – Who should NOT have this drug • Route of Administration – How the drug is given • Adverse Effects/Side Effects – What the side effects of this are (they love exam questions on this!!) • Go over the PBL Cases and try to understand the actions the doctors take
USEFUL RESOURCES • Armando • Osmosis – Need to pay but get a group together – worth it! • PassMedicine - Question Banks – more for later years • Anki • T each Me Anatomy • AMBOSS • BMJ Best Practice • Zero to Finals – Great podcast • Geeky Medics – OSCE • Leeds University - Histology • T extbooks • T op 100 Drugs • USMLE First Aid • Kumar and Clark
MEET YOUR GEP PARENTS! • Wednesday 9 th September at Tooting Common • Come and meet your GEP Parents • Due to social distancing there will be time slots for you to come and meet your parents. • All details are on your GEP Facebook page!
KEY AREAS OF THE WEEK • Fluid Compartments, Fluid Balance and Fluid Movement • Intro to Structure and Function of the Kidney • Pharmacology • Autonomic Nervous System • Anatomical T erminology
• Everything this week (and in the foundation module) will be repeated. • Don’t worry if you don’t understand everything perfectly this week, you will come back to it and it will be much clearer! • Use the Foundation Module to develop your own system to learn medicine!
FLUID LOSSES • Fluid Losses • Insensible - ~700 – 800 ml/day • Evaporation from the respiratory tract – respiratory droplets • Diffusion through the skin • Sensible – Much more variable • Sweat – Can depend on climate or physical exertion. Usually ~100 ml/day but can be 1-2 L/day following strenuous activity. • Faeces – Usually only a small amount but can be up to 5-7 L/day in severe diarrhoea. • Urine (Kidneys) – Highly variable depending on level of hydration or diseases.
FLUID REQUIREMENTS • Fluid Requirements • Generally, 2 – 2.5 L of water a day, but this is highly variable • Majority of water gained is from ingestion. • We make a small amount from the oxidation of carbohydrates, ~200ml/day
FLUID COMPARTMENTS • 2 main stores of fluid in the body • Intracellular (2/3 of total fluid) • Water inside cells • Extracellular (1/3 of total fluid) • Plasma – fluid component of blood • Interstitial Fluid – fluid surrounding cells • Only separated by thin capillary membrane • 60, 40, 20 Rule • 60% of the body is water, 40% (2/3) of this water is intracellular, 20% (1/3) of this water is intracellular!
IONIC COMPOSITION OF EXTRACELLULAR AND INTRACELLULAR FLUID • Extracellular – What we measure in blood tests • Na + (Low sodium = hyponatraemic, High sodium = hypernatraemic) • Cl - • HCO3 - - Buffer • Intracellular • K + (Potassium) – Cardiac Arrest if high extracellular levels! (Hyperkalaemia) • PO4 3- (Phosphate) – Used for many intracellular reactions • Lots of Proteins
DIFFUSION AND OSMOSIS • Diffusion • The movement of MOLECULES in a solution from a high to low gradient • Facilitated Diffusion – When diffusion occurs across a membrane, utilizing a carrier protein (Ion Channels) • Osmosis • The movement of WATER across a cell membrane • Nature likes things to be equal – equal concentrations on both sides of a membrane • Charged molecules cannot move across the cell membrane to equalize concentrations • Therefore, water moves across the membrane to equalize concentrations • Water leaves the dilute solution to enter the more concentrated solution • Makes the dilute solution more concentrated and the more concentrated solution more dilute àà Concentrations equalize across the membrane
MOLARITY AND OSMOLARITY • Molarity is a measure of the MOLES of a solution in a given volume • Basically, how many moles there are in one litre • Expressed in moles per litre (mol/L or M) • In reality, when ionic compounds are dissolved in water they dissociate. • Sodium Chloride (salt) is NaCl, when it is dissolved in water it splits into Na+ ions and Cl- ions. • Each ion exerts a force, we need to consider individually. • This is Osmolarity, it considers the number of PARTICLES in a given volume • Basically, how many particles there are in one litre • 1 mol of NaCl dissolved in 1 litre will have a molarity of 1 mol/L but an osmolarity of 2 Osmol/L (splits into Na+ and Cl-, 2 particles) • 1 mol of Glucose dissolved in 1 litre will have a molarity of 1 mol/L and also an osmolarity of 1Osmol/L (it doesn’t split and remains 1 particle)
OSMOLALITY • Molarity and Osmolarity • Moles and osmoles per VOLUME (Litres) • Molality and Osmolality • Moles and osmoles per WEIGHT (Kg) • Osmolality technically more accurate, but physiologically speaking no difference • For purposes of Medicine: Osmolarity = Osmolality
TONICITY • Tonicity is the ability of a solution to make water move in or out of it by osmosis • This has implications for how water moves in and out of a cell • Similar to Osmolarity, tonicity refers to the direction in which water would travel • Think of tonicity as the affects of osmolarity! • A hypertonic solution is a solution that is very concentrated, a hypotonic solution is a solution that is dilute. • If a cell is in a hypertonic solution, water will move out of the cell (Osmosis) • If a cell is in a hypotonic solution, water will move into the cell (Osmosis) • An isotonic solution is one in which the osmolarity of intracellular and extracellular fluids are the same - no net movement of water.
MOVEMENT BETWEEN FLUID COMPARTMENTS ACCORDING TO OSMOSIS/TONICITY • Extracellular and Intracellular Fluid are linked by Osmosis/Tonicity • Alterations to Extracellular Fluid can result in changes to Intracellular Fluid – we take advantage of this clinically. • Water is lost from the Extracellular Fluid, with the Intracellular Fluid changing according to what has been lost. • If more salt than water lost – Hypotonic Dehydration • Water ENTERS cells via osmotic pressure to equalize osmolarities across the cell • This video summarises nicely – membrane tricky concept • If more water than salt lost – Hypertonic Dehydration • Water LEAVES cells via osmotic pressure to equalize osmolarities across the cell membrane
TYPES OF DEHYDRATION • Salt and Water Depletion (Isotonic Dehydration) • Water and Salt are lost in equal measure à No change in concentration of Extracellular Fluid à No change in osmotic pressure à No change in volume of Intercellular Fluid • Water Depletion (Hypertonic Dehydration) • More water than salt lost à Extracellular Fluid becomes more concentrated à Increased Osmolarity à Hypertonic Solution à Water moves into Extracellular Fluid to compensate, from Intracellular Fluid à Decrease in Intracellular Volume à Cells Shrink • Salt Depletion (Hypotonic Dehydration) • More salt than water lost à Extracellular fluid becomes more dilute à Decreased Osmolarity à Hypotonic Solution à Water moves out of Extracellular Fluid, into Intracellular Fluid à Increase in Intracellular Volume à Cells expand, risk of lysis • Blood T ests reveal which type: • Normal Electrolyte Levels – Isotonic • High Electrolyte Levels – Hypertonic • Low Electrolyte Levels – Hypotonic
CLINICAL RELEVANCE – FLUIDS • Isotonic Saline (0.9% Saline) • Isotonic Dehydration • Hypertonic Saline (>0.9% Saline) • Hypotonic Dehydration • Hypotonic Saline (<0.9% Saline) • Hypertonic Dehydration
SBA PRACTICE QUESTION • An 89 Year-Old woman is brought to an emergency department after falling at home and was found to have Hypertonic Dehydration. Which of the following will describe the changes to intracellular fluid following this type of dehydration? • A) No Change in Intracellular Fluid Volume • B) Decrease in Intracellular Fluid Volume • C) Increase in Intracellular Fluid Volume • D) Intracellular Fluid will increase pH • E) Intracellular Fluid will decrease pH
SBA PRACTICE QUESTION • An 89 Year-Old woman is brought to an emergency department after falling at home and was found to have Hypertonic Dehydration. Which of the following will describe the changes to intracellular fluid following this type of dehydration? • A) No Change in Intracellular Fluid Volume • B) Decrease in Intracellular Fluid Volume • C) Increase in Intracellular Fluid Volume • D) Intracellular Fluid will increase pH • E) Intracellular Fluid will decrease pH
EXPLANATION
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