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Homeostasis-A Water Balance and Body Fluid Compartments Year 2, Unit I 2024 – 2025 12/09/2024 Prof. Rima Abdul Razzaq, Physiology Dept, CMHS, AGU  Week 2 - Homeostasis A disruption in...

Homeostasis-A Water Balance and Body Fluid Compartments Year 2, Unit I 2024 – 2025 12/09/2024 Prof. Rima Abdul Razzaq, Physiology Dept, CMHS, AGU  Week 2 - Homeostasis A disruption in body fluids Problem 1: A 9-month-old boy is brought to the emergency department 1. Guyton, Textbook of Medical with a chief complaint of diarrhea and vomiting for 2 days. Physiology 14th Ed., (2021). He has a fever, tachycardia, and an increased respiratory rate. The anterior fontanel is sunken, and his skin turgor is slightly diminished. He is given intravenous glucose saline in the Transport of substances through cell emergency department and is then hospitalized for further membrane, Chap. 4 Pp. 51 – 62. management. Body fluids compartments, Chap. 25 Pp. 305 – 316. Problem 2: An 86-year-old man was admitted to the hospital because he 2. Lab 2 in Physiology Manual (Practical) had become lethargic, confused, and was refusing to drink 3. Lab 3 in Physiology Manual fluids. On admission, his skin felt hot and doughy, his eyes were sunken, and his mouth was dry. Serum electrolytes (Cases/Calculations) revealed hypernatremia, hyperchloremia, and increased plasma osmolarity. 5% glucose in saline solution was given intravenously as prescribed.  Homeostasis Homeostasis: Constant maintenance of the internal environment of the body within the physiological limits. Example ❖ The pH of the ECF has to be maintained at the critical value of 7.4. bouz temp denatures protein ❖ Body temperature must be maintained at 37.5°C. high ❖ Adequate amount of nutrients must be supplied to the cells. ❖ Adequate amount of oxygen should be made available to the cells for the metabolism of the nutrients. Homeostatic mechanisms in the body rely on feedback signals. ❖ Water and electrolyte balance (Osmolarity of body fluids) should be maintained optimally.  Water Balance Input us output of water is same When the body is in 'water balance', the intake and output of Input output water are equal. Disorders of water homeostasis result in electrolyte disturbances (e.g: hypo- or hypernatremia). of body electrolytes Inbalance water in the causes disturbance Water Loss Ingestion of a normal diet results in the generation of 600 mosmol of solute per day, containing primarily Na+ and K+, urea, etc… we don't need these 600 mosmol of solute and it has to get out of the body ; thus , sodium Potassium meaning the body These 600 mosmols must be excreted daily through the kidneys. osmol can't It regulate Since the maximal urine osmolality is 1200 mosmol/kg (liter). 1200 is released In 1 litre , will So the 600 mosmol This is called 0 5 litre be released in water loss Obligatory. If someone doesn't produce 500 m of vrine a day , he has renal failure ~ the excess and toxins will build up in the body like Sodium A minimum urine output of 500 mL/day is required for neutral Potassium and urea and will have renal fallure solute balance. This is called “Obligate water loss”.  Distribution of Body Fluids there's exchange Variations exist depending on age, sex, and % of body fat. between plasma and interstitial fluid based on : water - more body fat=less water - women have less body because they have more fat of 42 The 60-40-20 Rule for me : 60 % TORg IS theres exchange between 50 % of GORg IS 30L interstitial fluid and intracellular M 40% Of 70 = 28 20 % Of 70 = 14 Water accounts for approximately 60% of body weight in men and 50% of body weight in women. blood Intracellular (ICF: 40% of body weight) 60 24L 40% of = ICF Extra cellular compartment (ECF: 20% of body weight). Transcellular compartments or spaces, i.e. 20% of 60 = 121 ECf synovial, peritoneal, pericardial, and intraocular spaces, as well as the blood cerebrospinal fluid. Intracellular is bigger (40%) remember alot of cells because we have 12/09/2024  body fluids Composition of Body Fluids electrolytes and non-electrolytes b cons gamiat or Non-electrolytes of Electrolytes: Each fluid compartment of the body has a distinctive pattern of the plasma electrolytes. Positive negative Extracellular Fluids in Sodium is extracellular more Potassium is more in Intracellular ECFs are similar except for the high protein content of plasma. Sodium (Na+) is the major cation Chloride (Cl-) is the major anion Intracellular Fluids Have low sodium and chloride Proteins Potassium (K+) is the chief carry negative a charge cation Phosphate (PO4-) is the chief anion - bicarbonate is In same ICF & ECF - Protein in intracellular is more  Intracellular and extracellular fluid electrolyte concentrations Intracellular extracellular - Potassium - sodium - magnesium - Chloride - Phospholipid - bicarbonate  Measuring Volumes of the Body’s Compartments conservation of mass : -mass is the volume same changes , only EXAMPLE: Conservation of Mass Principle If 1 milliliter of a solution containing 10 mg/ml of dye is The volumes of some of the dispersed into chamber B and the final concentration in compartments can be the chamber is 0.01 mg/ml fluid, the unknown volume of measured by the dilution concentration in small dilution happen the chamber can be calculated as follows: volume ; method. outside concentration in big Addition of an extrinsic, volume measurable, compound (indicator substance) that is fully within the compartment of interest. Properties of the indicator substance = It disperses evenly throughout the compartment. It disperses only in the compartment that is being measured. It is not metabolized or excreted. know this ; maybe coming in exam 12/09/2024 =  Basic Principles for Osmolality/Osmolarity /Osmotic Pressure measure of concentration RG Osmolality describes the total concentration of all particles that are free in a solution. If Particle is bound and Number of solute particles not to free , osmolarity osmolality it doesn't contribute or 1 kg of solvent only solute water moves not Particles bound to macromolecules do not contribute at all to osmolality. The difference in the concentration of impermeant particles (which exert Osmotic Pressure) determines the osmotic movement of water across the me membrane. water will concentration go from to low solute high solute concentration until equilibrium is found Lire Osmolarity refers to the concentration of a solution, from 2 to 4 expressed as: Breaks down No. of particles a Number of solute particles (mosmoles) 2 sodium 2 chloride solute dissociates 1 L of solvent L from 2 to 2 into when dissolved in water. 1 osmol/L causes 19, 300 mm Hg osmotic pressure in the solution. glucose here doesn't 12/09/2024 break down Osmolarity of Body Fluids We measure It from Plasma Osmolar Substances in ECF and ICF Plasma Osmolarity Plasma osmolarity measures the body's electrolyte–water balance. Plasma osmolarity is mainly determined by: serum sodium, chloride, blood glucose, and blood nitrogen urea. sodium de NaCl represents most of the effective osmolarity of ECF (Plasma) (80%). 12/09/2024 Fluid Exchange Across Membranes pressure - hydrostatic does not change. osmotic pressure changes - Osmotic Equilibrium Between ECF and ICF Two major factors contribute All body fluids have the same osmolarity. Exchange of fluid between ISF - Hydrostatic pressure in the cells and surrounding ISF is spaces and cells (ICF) to fluid movement from one ordinarily equal and remains stable. compartment to another: - Osmotic pressure by impermeant electrolytes controls the distribution of fluid between ECF and ICF. 1. Hydrostatic pressure - Water moves between these 2 compartments only when 2. Osmotic pressure an osmotic pressure gradient exists. greater when Is one compartment than the other Past slides , - Equilibration of ICF and ECF osmolarity occurs primarily by water shifts, not solute shifts. equilibrium , same , no gradient found Exchange of fluid between plasma and interstitial spaces (ISF) – Water enters and exits the cell with relative ease. water water moves - Some water molecules slip between moves outside inside adjacent membrane phospholipid molecules. - Others are swept along with solutes in ion channels and transporters. cellular Awl edema - Most cells also happens express aquaporins in their surface membrane. 1. S110 (Passive). lon channels 2 (facilitated diffusion) 3. aquaporins (pores)  Regulation of Total Body Water Content/Balance To maintain a steady state, water intake must equal water excretion. Depends upon hypothalamic mechanisms: I 1. Thirst mechanisms, regulated by the hypothalamus, control the I oral intake of water. Not physiologically stimulated until: you will feel thirsty and want to drink when mosmol greater Plasma osmolarity >290 mosmol/L than 290 · antidiuretic normone 2. Vasopressin (ADH) released by the hypothalamus controls water excretion (Output) by the kidneys. The primary means of regulating water output is urine production These two mechanisms collaborate to maintain normal water content and consequently body fluid osmolarity. 12/09/2024 Mechanisms to Regulate ECF Volume The volume of the extracellular fluid (ECF) is mainly dependent on two factors: 1. Total body water (TBW) content, which is: Carefully regulated by : Thirst mechanism Vasopressin through adjusting the renal handling of water Important for maintaining body fluid osmolarity constant 2. Osmotic forces, i.e. how much of the total body water (TBW) is osmotically drawn into the ECF, which is: the function of the osmotically active content of the ECF (mainly sodium and chloride) mainly regulated by neurohumoral mechanisms that control the renal handling of sodium: 1. The renin-angiotensin system 2. Aldosterone which enhances renal reabsorption of Na+ ( [Na+]= expansion of ECF volume) 3. Natriuretic peptides (Increases Na+ excretion by the kidney) toa Causes of ECF and ICF Volume Changes 1. Excess ingestion of water 2. Renal retention of water 3. Dehydration 4. Intravenous infusion of solutions 5. Loss of fluid : From GI tract (Diarrhea, vomiting..) By sweating Through the kidneys Clinical Abnormalities of Fluid Volume Regulation Plasma [Na+] is a reasonable indicator of plasma osmolarity. OPEN RECORDING OF THIS SLIDE Edema Hyponatremia: Most common electrolyte disorder encountered in clinical practice. Causes: a in 1. Excess water = Hyponatremia - Overhydration: Water retention (Excessive secretion of ADH). 2. Loss of Na+ = Hyponatremia - Dehydration: Diarrhea, vomiting, overuse of diuretics, or Addison disease (Reduced aldosterone secretion). Effects: ECF volume shrinkage and Cell edema (Serious complication = Brain edema) Shrinkage Hypernatremia: Much less common than hyponatremia. Causes: 1. Water loss from ECF = Hypernatremia - Dehydration: Low secretion of ADH (Central diabetes insipidus) or kidney cannot respond to ADH (Nephrogenic diabetes insipidus). 2. Excess Na+ = Hypernatremia – Overhydration: Excessive secretion of aldosterone (Effect is mild because Na+ pulls water to ECF which induces secretion of ADH leading to water reabsorption). 3. Patients with hypothalamic lesions that impair the sense of Thirst. Effects: ECF volume expansion and Cell shrinkage