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Fluid compartment, function & balance

Fluid compartment, function & balance . Prepared by, Dr. Nicole Seng Lai Giea. What so important?. Loss of 10% -- disturbance of body function Loss of 6-8% -- sensation of thirst , headache and muscular incoordination, rise of body temperature Loss of 20% -- delirium, coma, death.

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Fluid compartment, function & balance

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  1. Fluid compartment, function & balance Prepared by, Dr. Nicole Seng Lai Giea

  2. What so important? • Loss of 10% -- disturbance of body function • Loss of 6-8% -- sensation of thirst, headache and muscular incoordination, rise of body temperature • Loss of 20% -- delirium, coma, death

  3. Variations in Water Content • Variation due to Age • Variation between Individuals (adipose tissue) • Habitat

  4. Functions • Transfer medium ( dissolved nutrients and waste products) • Secretion and excretion ( glandular product) • Temperature regulation • Lubricant for body surface

  5. Homeostasis of body water • Removal or excess water (kidney, alimentary, lung, skin, sweat, mammary glands) • All these mechanisms except lungs can be inhibited to enhance water conservation

  6. FluidCompartments 20% extracellular fluid -5% plasma -15% interstitial volume Total body water (60% bodyweight) 40% intracellular fluid

  7. Total body water • Intracellular: 70% • The cytosol has no single function • the site of multiple cell processes • Extracellular: 30% • ECF is divided into several smaller compartments (eg plasma, Interstitial fluid, digestive fluid and transcellular fluid)

  8. 1 gm = 1 ml; 1 kg = 1 liter; 1 kg = 2.2 lbs • total body water: 55-75% (60%) of body weight • intracellular water: 30-40% of body weight • extracellular water (plasma water + interstitial water): 23-33% (30%) of body weight • interstitial water: 15-25% of body weight • plasma water: 5% of body weight • blood volume: 8-10% of body weight (blood volume = plasma water + red blood cell volume) •  The ratio of ICF to ECF is 55:45.

  9. major division is into Intracellular Fluid (ICF) and Extracellular Fluid (ECF), separated by the cell membranes

  10. ECF -- Interstitial fluid •  20% in total body fluid and interstices of all body tissues •  link between the ICF and the intravascular compartment • Oxygen, nutrients, wastes and chemical messengers all pass through the ISF • low protein concentration (in comparison to plasma) •  Lymph is considered as a part of the ISF. The lymphatic system returns protein and excess ISF to the circulation

  11. ECF -- Plasma • 5% in total and it differs from ISF in its much higher protein content and its high bulk flow (transport function) • Blood contains suspended red and white cells so plasma has been called the ‘interstitial fluid of the blood’ • The fluid compartment called the blood volume is interesting in that it is a composite compartment containing ECF (plasma) and ICF (red cell water).

  12. ECF -- Transcellular fluid  • Transcellular fluid (<1%) formed from the transport activities of cells. It is contained within epithelial lined spaces and produced by secretory cells • It includes CSF, GIT fluids, bladder urine, aqueous humour and joint fluid. The electrolyte composition of the various transcellular fluids are quite dissimilar

  13. Aqueous humour • thick watery substance filling the space between the lens and the cornea • Maintains the intraocular pressure • Provides nutrition (e.g. amino acids and glucose) for the avascular ocular tissues; posterior cornea, trabecular meshwork, lens, and anterior vitreous. • May serve to transport ascorbate in the anterior segment to act as an anti-oxidant agent. • Presence of immunoglobulins to defend against pathogens. • Provides inflation for expansion of the cornea and thus increased protection against dust, wind, pollen grains and some pathogens. • for refractive index.

  14. CSF •  clear, colourless, salty fluid that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord • In essence, the brain "floats" in it • It constitutes the content of all intra-cerebral (inside the brain, cerebrum) ventricles, cisterns, and sulci as well as the central canal of the spinal cord • It acts as a "cushion" or buffer for the cortex, providing a basic mechanical and immunological protection to the brain inside the skull • It is produced in the choroid plexus

  15. Functions of CSF • Buoyancy • Protection: CSF protects the brain tissue from injury when jolted or hit • Chemical stability: CSF flows throughout the inner ventricular system in the brain and is absorbed back into the bloodstream, rinsing the metabolic waste from the central nervous system through the blood-brain barrier • Prevention of brain ischemia

  16. Joint fluid • Synovial fluid is a viscous, fluid found in the cavities of synovial joints with its yolk-like consistency  • the principal role is to reduce friction between the articular cartilage during movement

  17. ECF – gut water •  6-8% in total • Ruminant and monogastric herbivore with large ceca have higher in percentage

  18. Regulation of fluid balance • To maintain an ionic environment suitable for the functioning of the various cells of body • Components of Daily Obligatory Water Loss • Insensible loss: 800 mls • Minimal sweat loss: 100 mls • Faecal loss: 200 mls • Minimal urine volume to excrete solute load: 500 mls • Total: 1,600 mls • Fluid input is from 2 major sources: • External: Oral intake of fluids and food (and/or IV fluids) • Internal: Metabolic water production

  19. Basic control system • Sensors -these are receptors which respond either directly or indirectly to a change in the controlled variable • Central controller -this is the coordinating and integrating component which assesses input from the sensors and initiates a response • Effectors -these are the components which attempt, directly or indirectly to change the value of the variable.

  20. Sensors • The main sensors that are involved in control of water balance in the body are: • Osmoreceptors • Volume receptors (low pressure baroreceptors) • High pressure baroreceptors

  21. Central controller •  central controller for water balance is the hypothalamus • The key parts of the hypothalamus involved in water balance are: • Osmoreceptors  • Thirst centre • OVLT & SFO (respond to angiotensin II) • Supraoptic & paraventricular nuclei (for ADH synthesis)

  22. Effector mechanisms • The major effector mechanisms are: • Control of Water Input : ThirstThirst is a mechanism for adjusting water input via the GIT • Control of Water Output : ADH & the KidneyADH provides a mechanism for adjusting water output via the kidney. Note that ADH is often called 'vasopressin' - this term refers to the vasoconstrictive properties of very large doses ('pharmacological doses') of the hormone

  23. Fluid balance • Plasma osmolality • Three major effectors alter effective circulating volume 1) The sympathetic nervous system, 2) angiotensin II, and 3) renal sodium excretion • (Dog) colloid osmotic pressure: 25-30mmHg Osmolarity: 280-310 mOsm/l

  24. Stimuli to Thirst • The 4 major stimuli to thirst are: • Hypertonicity: Cellular dehydration acts via an osmoreceptor mechanism in the hypothalamus • Hypovolaemia: Low volume is sensed via the low pressure baroreceptors in the great veins and right atrium • Hypotension: The high pressure baroreceptors in carotid sinus & aorta provide the sensors for this input • Angiotensin II: This is produced consequent to the release of renin by the kidney (eg in response to renal hypotension)

  25. ADH in the Hypothalamus & Posterior Pituitary • The secretory granules containing the ADH and neurophysin move down the axons (axonal transport) to the nerve terminals in the posterior pituitary from where they are secreted into the systemic circulation by a process of exocytosis (involving calcium)

  26. Renal Actions of ADH • ADH-dependent water permeability of the collecting duct cells • Aquaporin-2 is the protein which is the vasopressin responsive water channel in the collecting duct • forms a channel which allows rapid water movement

  27. In the absence of ADH, the apical membranes of the cells in the cortical and medullar collecting tubules have very low water permeability • In the presence of ADH, the cells are much more permeable to water. At maximal ADH levels, less then 1% of the filtered water is excreted (urine volume 500mls/day) • Feedback loop: Reabsorption of water reduces plasma [Na+] and this is detected by the osmoreceptors in the hypothalamus

  28. Renal Water Regulation • The major additional mechanisms which act at the local renal level are: • Glomerulotubular Balance • Autoregulation • Intrinsic Pressure-Volume Control System

  29. Summary • Importance and function • Fluid compartment • Fluid balance regulation

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