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Hypertensive emergency- increase in systolic and diastolic blood pressure leading to end-organ damage A discount levitra professional 20mg line impotence tumblr. The clinical differentiation between these two entities is the presence or absence of end organ damage not the level of blood pressure elevation buy cheap levitra professional 20mg on-line erectile dysfunction evaluation. The aim is to lessen pulsatile load and force of left ventricular contraction to slow the propagation of the dissection. Definition: Hyponatremia is generally defined as a plasma sodium level of less than 135 mEq per L (135 mmol per L). Pseudohyponatremia: This condition results from increased percentage of large molecular particles in the serum relative to sodium. These large molecules do not contribute to plasma osmolality resulting in a state in which the relative sodium concentration is decreased, but the overall osmolality remains unchanged. Glucose molecules exert an osmotic force and draw water from the intracellular compartment into the plasma, thereby causing a diluting effect. Hypervolemic hyponatremic conditions: congestive heart failure, liver cirrhosis, and renal diseases such as nephrotic syndrome. Treatment: Step 1: Based on Na levels and severity of symptoms decide whether immediate treatment is required. In patients with chronic hyponatremia, overzealous and rapid correction should be avoided because it can lead to central pontine myelinolysis. In central pontine myelinolysis, neurologic symptoms usually occur one to six days after correction and are often irreversible. In patients with hypernatremia and depletion of total body Na content (ie, who have volume depletion), the free water deficit is greater than that estimated by the formula. Dialysis (diffusion): The movement of solutes from a high concentration compartment to a low concentration compartment. An electrolyte solution (dialysate) runs countercurrent to blood across a semi-permeable (small pore) filter. Ultra-filtration (convection) – Solute is carried (in solution) across a semipermeable membrane in response to a transmembrane pressure gradient (a process known as solvent drag). The rate of ultrafiltration depends upon the porosity of the membrane and the hydrostatic pressure of the blood. Intermittent hemodialysis is the most efficient – Large amounts of fluid can be removed and electrolyte abnormalities can be rapidly corrected. Continuous Renal Replacement Therapy: The concept behind continuous renal replacement techniques is to dialyse patients in a more physiologic way, slowly, over 24 hours, just like the kidney. The ultrafiltration rate is high, and replacement electrolyte solution is required to maintain hemodynamic stability. It is hypothesized that removal of mid sized inflammatory cytokines may play a role in improving outcome in sepsis. Pathophysiology: premature activation of trypsin in pancreatic acinar cells sets of inflammatory cascade. Confirmed infected necrosis can be treated with imipenem, fluouroquinolone+flagyl, or cephalosporin + flagyl, all +/- vanco. Likely to decrease bleeding from esophageal varices but does not change mortality Pitressin (Vasopressin) • For gastric ulcers, stress ulcers and gastritis initiate at 0. Definition: A group of syndromes characterized by increased pressure within a closed anatomical space resulting in local ischemia (limb compartment syndrome) or local and systemic complications (abdominal compartment syndrome). Injury (trauma, hemorrhage, ischemia-reperfusion, venous obstruction) leads to swelling and increased pressure within a compartment. The increased pressure collapses venules, and as hydrostatic pressure increases, eventually collapses arterioles causing limb ischemia. Most common cause is fracture of tibia or distal radius/ulna, in which compartment syndrome has been described in 2-30% of fractures c. Can occur with dilated loops of bowel in absence of trauma, rarely with ascites, peritonitis, pancreatitis. Pressure=Force (fluid volume, cardiac output)/ area (vasodilation) When one part fails, others try to compensate (hopefully). Definition: use of invasive device for continuous, detailed assessment of hemodynamics in order to guide treatment decisions. Exam: generally poor at predicting volume responsiveness and estimating cvp, except maybe the abdomino-jugular reflux Which is a fair estimate of cvp/pcwp. Above 5, it’s 50/50 whether bolus will be effective (see graph below from Heenan et al Crit Care 2006). Change in Pulse Pressure: Mechanically ventilated patients who are not initiating breaths and have variations in pulse pressure during their respiratory cycle have been shown to respond to volume challenges. Notably, recent evidence suggests that changes in 02 sat waveform may also be a useful to guide treatment (Natalini et al. Conclusion: Little evidence exists for utilizing static measurements to predict beneficial response to volume expansion. Consider empiric antibiotics +/- cortisol replacement (hydrocortisone 50- 100mg every 8 hrs) 80 Major complications: 1. E Ingestions and Toxins Standard approach to all ingestions: 1) Assume there is more than one toxin; however, statistics show that greater than 90% of all accidental and intentional ingestions are only one substance. Gastric lavage should only be performed in patients that present early after ingestion 6) It is still recommended that everyone receive charcoal (1 g/kg). Controversy exists because recommendation is not supported by randomized clinical trial and some opponents say charcoal increases patients risk of aspiration pneumonia. It is reasonable to withhold charcoal in patients who present late after ingestion 7) Do a more thorough physical exam to look for classic signs of toxic syndromes. Pupils - Pupillary size (normal 3-4 mm in diameter) and reactivity is dependent on sympathetic parasympathetic innervation. Brain stem reflexes, such as the pupillary reaction to light offer clues to the location of the lesion responsible for the coma. If the dilated pupil does not react to light or reacts slowly, it usually indicates a rapidly expanding lesion on the ipsilateral side as in subdural or middle meningeal hemorrhage or brian tumor, that is compressing the midbrain or oculomotor nerve directly or by mass effect. Upper airway has great heat exchanging properties so when thermal injuries occur it is rare from them to damage anything but the upper respiratory tract. Typical problems result from persistent edema causing stridor and superinfection from airway ulceration. However, the low o2 concentration may potentiate the toxicities of carbon monoxide and hydrogen cyanide which compete with the oxygen for the heme molecule. Much later complications: bronchiectasis, tracheal stenosis, bronchiolitis obliterans and pulmonary fibrosis. Deficiency of insulin -Induces increased hepatic production of glucose -Decreased peripheral utilization of glucose -Induces lipolysis whcih generates ketoacids (acetoacetate, B- hydroxybutyrate, and acetone) which causes acidemia 2. Increased counter regulatory hormones -Glucagon and catecholamine levels increase inducing glycogen phosphorylase to break down hepatic glycogen stores -Growth hormone levels increase which worsen hyperglycemia -Cortisol level is increased which stimulates protein catabolism which provides amino acids for gluconeogenesis As a result of the insulin deficiency and increased counter regulatory hormones, there is hyperglycemia.

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The usual pattern of early visual loss is therefore arcuate scotoma reflecting damage to these axon bundles that branch around the fovea purchase levitra professional amex erectile dysfunction treatment caverject. Retinal vascular narrowing is the earliest sign of this disturbance of outer retinal layer or retinal pigment epithelium function discount levitra professional 20mg with amex erectile dysfunction song. Also known as pigmentary retinopathy, retinal degeneration is accompanied by release of pigment from damaged retinal pigment epithelial cells that can migrate into the retina, appearing as focal pigment aggregates or larger “bone spicules. Slide 28 Obstruction of the central retinal artery, usually due to embolic or inflammatory disease, causes sudden complete loss of vision and infarction of the inner retina. The outer retina receives its oxygen supply from the underlying choroid by passive 149 diffusion and survives. The retinal pallor surrounds residual hyperemia beneath the fovea where only cones and glial Muller cells, components of outer retina, survive. Recanalization of the obstructed vessel often occurs, leaving a fundus with ghost vessels, vascular narrowing, and optic atrophy. Causes of elevated intracranial pressure include structural, neoplastic, inflammatory, hemorrhagic, thrombotic, and infectious disorders. The earliest sign of papilledema is increased hyperemia of the optic disc and obliteration of the optic disc cup. Slide 30 Papilledema develops when increased intracranial pressure causes distension of the subarachnoid space leading to centripetal rotation of the meninges and scleral canal, effectively choking the optic disc. Slide 31 Swelling of the optic disc with hemorrhages, exudates, and vascular distension can be marked as in this obese 12-year-old boy with idiopathic intracranial hypertension. Slide 32 In addition to elevated intracranial pressure, swelling of the optic discs occurs in the presence of inflammatory, ischemic, thrombotic, infiltrative, and hypertensive diseases. There are also normal variants of optic disc structure that create the appearance called pseudo-papilledema. Slide 33 The remaining types of visual field loss as illustrated in figures B-H can now be understood with knowledge of visual system anatomy from optic chiasm to visual cortices. Each example has temporal arcuate field loss due to involvement of nasal retinal axons that cross the midline in the chiasm. Figure B occurs when a single lesion involves all of the superior fibers of the right intracranial optic nerve and its inferior nasal fibers that begin to cross the midline just as they enter the chiasm. Figure C, bitemporal hemianopia, occurs when the nasal crossing fibers in the chiasm are asymmetrically involved. Inflammatory disease such as sarcoidosis can also cause isolated chiasmal syndromes. Slide 35 Optic tract syndromes and lesions downstream along the visual pathway cause homonymous hemianopia, visual field loss through each eye restricted to the same side of the visual world. For example, complete congenital absence of an optic tract causes 150 completely congruous homonymous hemianopia. Acquired homonymous hemianopic field loss due to optic tract disease is usually grossly incongruous. For example, a left optic tract syndrome typically can cause nearly complete right-sided homonymous visual field loss through the right eye with incomplete right-sided homonymous field loss through the left eye. This pattern of field loss is termed incongruous and results because axons forming the optic tract are still relatively spatially segregated according to right and left eyes, hence a small lesion can affect axons from one eye more than axons from the other eye. Because of this spatial segregation of visual information, optic tract lesions can be associated with mild asymmetry in pupillary responses to light. Etiologies are usually structural or vascular, most commonly neoplasia in children and vascular compromise in adults. Slide 36 We can now appreciate that the completely congruous homonymous hemianopic visual field loss in figure D has limited localizing value. This pattern can result from large optic tract lesions that encompass all axons from each eye as well as from smaller lesions in the optic radiations where there is homogeneous mixing of axons carrying information from each eye to the level of individual ocular dominance columns. Localization in the presence of such congruity is accomplished by combining the pattern of visual loss with other deficits such as somatosensory or motor loss. Figures F-H are typical of lesions affecting the temporal, parietal, and occipital lobes. The lesion in Figure F involves the right optic radiation beneath the temporal lobe. The lesion in Figure G is due to watershed infarction following cardiac arrest at the right parietal- occipital junction with sparing of the macular representation. The lesion in Figure H is bilateral, asymmetric homonymous hemianopia with central macular preservation following bilateral infarction in the posterior cerebral artery circulations. Copper released from liver associated with Wilson’s disease does not only end up in peripheral Descemet’s membrane as Kayser-Fleischer rings. It becomes deposited throughout the body with early symptoms usually associated with predilection for deposition in basal ganglia. Slide 38 The description “cherry red spot” is not specific for acute retinal infarction immediately following central retinal artery obstruction. Storage material accumulates within retinal ganglion cell bodies in several metabolic lysosomal disorders. Because the ganglion cell layer is normally thickened in the macula, these distended cell bodies create a visible perifoveal opacification of the otherwise transparent retina. The prominence of the normal choroidal vasculature beneath the fovea is also described as a cherry red spot. Slides 39-40 Diseases causing pigmentary retinal degeneration share the disturbance of pigment within retinal pigment epithelium cells as well as migration of pigment from devitalized cells into the retina. Microaneurysms, tiny ectasias in capillary walls that develop after pericyte death, are the earliest clinical sign. Exudation of serum proteins and hemorrhage occur with moderately advanced disease. Ischemic retina produces angiogenic factors that promote growth of fragile neovascular tissue that bleeds, scars, and disturbs ocular anatomy and function. Similar compromise of the optic disc called diabetic papillitis results in swelling of the optic disc. Neovascular glaucoma develops when peripheral iris becomes scarred to peripheral cornea thereby blocking access of aqueous humor to the trabecular meshwork. Fluctuating serum glucose levels cause similar fluctuations in aqueous humor with correspond swelling and shrinkage of the crystalline lens leading to cataract formation. The earliest sign in the retinal vasculature is arteriolar narrowing because of auto-regulation and arteriolar spasm. Hemorrhage, exudation of large serum proteins, choroidal infarction, and swelling with eventual infarction of the optic disc can occur when the normal mechanisms of auto- regulation are overwhelmed. Slide 44 The phacomatoses, disorders characterized by hamartomas, abnormally organized masses of tissue normally found in that area of the body, often have ophthalmic involvement. Lisch nodules, tiny hamartomas within the iris stroma best detected with a slit lamp, are visually insignificant but diagnostically important. When present, visual loss is usually associated with the presence of optic nerve glioma, a typically indolent tumor. Slide 45 Tuberous sclerosis is characterized by hamartomas in skin, kidney, eye, brain, and heart.

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Attention to technical details correct interpretation of data discount 20mg levitra professional erectile dysfunction zyprexa, and its application in selecting therapy should be individualized within the clinical context cheap levitra professional 20mg line impotence age 40. In addition, presence of arterial catheter enables frequent sampling of arterial blood without arterial punctures in critically ill patients. Set up of the pressure tranducing system o The pressure transducing assembly consists of a coupling system, pressure transducer, amplifier and signal conditioner, analog to digital converter, microprocessor which convert the signal received from the vein or artery into a waveform on the a bedside monitor o The flushing system – is set up using a 500 ml saline bottle encased in a bag 65 pressurized to 300 mm Hg. At this pressure the catheter will be flushed with 3 ml saline per hour and help keep the catheter patent. Heparinised saline is no longer routinely used  The reference point is usually at the level of the heart where the transducer is zeroed. Other veins that may be used are the arm veins (basilic, cephalic), external jugular and femoral veins. The fluid challenge is performed in 4 steps: o Select the type of fluid: usually normal saline or a colloid o Infuse rapidly. Rate of infusion: 500ml of crystalloid or 200 ml of colloid over 20-30 minutes o Target the Desired therapeutic response: the parameters are set empirically by the physician. This brought the catheter out of the domain of radiologists and at the bedside of the patients in intensive care. An SvO2 below 65% implies low oxygen delivery, while a value below 60% indicates that there is a serious risk of tissue hypoxia if corrective measures are not taken. In some disease states, cells in some tissues are unable to assimilate and/or process the needed oxygen. Indications  Management of complicated myocardial infarction • Hypovolemia vs cardiogenic shock • Severe left ventricular failure  Assessment of type of shock  Septic shock  Assessment of therapy • Afterload reduction • Vasopressors • Beta blockers • Intra-aortic balloon counterpulsation  Assessment of fluid requirement in critically ill patients • Hemorrhage • Sepsis • Acute renal failure • Burns  Management of postoperative open heart surgical patients Methods of monitoring cardiac output  Thermodilution (intermittent or continuous) using the pulmonary artery catheter has been the classical method of cardiac output monitoring. A central venous catheter, special thermistor tipped femoral artery catheter and monitor are required. The additional advantages are the values of extravascular lung water, global end-diastolic volume and the stroke volume variation (a dynamic measure of preload). They are not reliable in patients ventilated with low tidal volume and in patients with increased intraabdominal pressure  In these cases Passive leg raising is an alternative choice. Line 70 0 70 Saline, syringes 400 200 200 Total Initial Set up 11,470 12750 9770 Cost (Does not Add Presep include capital cost of continuous hemodynamic ScvO2 catheter monitors) 8000 Total: 17700 Daily monitoring cost 4500-5000 4500-5500 3500-4000 (based on an average of 3 days monitoring, 6000-7000 does not include including professional fees) Presep Further reading: 1. Minimally invasive hemodynamic monitoring for the intensivist: Current and emerging technology Crit Care Med 2002; 30:2338 –2345 6. Equipment review: New techniques for cardiac output measurement – oesophageal Doppler, Fick principle using carbon dioxide, and pulse contour analysis. Hemodynamic monitoring in shock and implications for management International Consensus Conference, Paris, France, 27–28 April 2006. It should be suspected anytime there is hypotension accompanied by an elevated central venous pressure (or neck vein distension), which is not otherwise explained by acute myocardial infarction, tension pneumothorax, pericardial tamponade, or a new arrhythmia. The concern about radiation is overcome by the hazard of missing a potentially fatal diagnosis or exposing the mother and fetus to unnecessary anticoagulant treatment. Despite the advances in the treatment and the understanding of the pathophysiology of sepsis, the mortality has remained unforgivably high. The site of infection is difficult to estimate and even among those patients where the site is strongly suspected, cultures might be negative or of questionable significance. Though a positive blood culture would be diagnostic, the rate of positivity is only 30 to 50 % percent. It is easy to confuse the diagnosis of sepsis with conditions that simulate it such as pancreatitis or anaphylactic reactions or drug fever. Early identification and prompt treatment is the key to reduce mortality a) Case definition: Till 2001 there was no clear definition of sepsis. Although making the distinction of the above conditions from true sepsis becomes difficult, using different biomarkers and imaging studies might be helpful in making the diagnosis. Close monitoring and optimising the patient physiological variables will give us time to identify the exact insult. Organ dysfunction variables:  Respiratory –Decreased oxygen saturation  Renal – Acute oliguria urine output <0. Rapid diagnosis, expeditious treatment multidisciplinary approaches are critical and necessary in the treatment of sepsis. Diagnosis 1) Cultures with gram stain- Obtain appropriate cultures before starting antibiotics provided this does not significantly delay antimicrobial administration. Begin intravenous antibiotics early within the first hour of recognizing Severe sepsis or septic shock. Early and appropriate antibiotic therapy and control of the source of infection arethe major therapies shown to improve survival in sepsis. Source of infection should be established as rapidly as possible and start measures to control the source within the first 6 hours of presentation as soon as the initial resuscitation is done e. Source control measures must be directed at achieving maximal efficacy with minimal physiological upset. Epinephrine, phenylephrine, or vasopressin should not be used as the initial vasopressor in septic shock 3. In case of myocardial dysfunction as evidenced by increased cardiac filling pressures and decreased cardiac output dobutamine can be used. Do not use steroids to treat sepsis in the absence of shock and wean it once vasopressors are no longer required 3. But its use for correcting laboratory clotting abnormalities is contraindicated unless an invasive procedure is planned. Lung protective ventilation strategy using low tidal volume ventilation reduces ventilator- induced lung injury like volutrauma, barotrauma, atelectrauma and biotrauma. This is the only ventilator manipulation that has been shown definitively to reduce injury and absolute mortality reduction of 9%. Do not use bicarbonate therapy to improve hemodynamics or reducing vasopressor requirements with lactic acidemia and pH < 7. Use a mechanical prophylactic device, such as compression stockings or an intermittent compression device, when heparin is contraindicated. Serum procalcitonin measurement as diagnostic and prognostic marker in febrile adult patients presenting to the emergency department. Introduction Community acquired pneumonia affects 2 to 3 million patients per year and carries high mortality of around 30% in severe cases. Case Definition Patient usually presents with a constellation of respiratory symptoms like cough, purulent sputum and sometimes pleuritic pain associated with constitutional symptoms like fever, lack of appetite and myalgia. Presentation: Preceding airway symptoms, myalgias, fever without chills, headache, unproductive cough. Chest x- ray shows- diffuse, patchy or ground glass shadows Assessment of Severity This is a crucial step as it will help in identifying patient who are prone to get complication and should be admitted in intensive care unit. D Dimer Treatment: Initial Choice of Antibiotic A detailed history should be taken to identify patients who are at high risk of drug resistant infection. Duration of Antibiotic therapy: Duration of antibiotic should be individualized based on clinical response,type of organismbiomarker response, development of complications and comorbidities. Prolonged antibiotics upto two 100 weeks should be considered inselected cases like slow responders, pseudomonas and staph infection,lung abscess , empyema,metastatic infection.

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Experiments showed that the surface tension of the biological membranes are lower than that of the pure lipid bilayers buy levitra professional 20mg otc erectile dysfunction vyvanse, suggesting the presence of proteins in them cheap levitra professional 20mg without a prescription erectile dysfunction videos. With this observation, Robertson formulated a unit membrane model, which states that the proteins are present on either side of the lipid bilayer. According to this model, the membrane will be like a lipid layer sandwiched between two protein layers. Phospholipids act as a fuid matrix, in which some proteins are integral and others are associated with the surface of the membrane. The membrane is asymmetric in nature, the outer and inner leafets of the bilayer differ in composition. Uncharged large polar molecules and charged molecules do not diffuse and they need proteins to get transported. Outside cell Carbohydrate Chain Glycolipid Phospholipid bilayer 5 nm Peripheral Protien Integral Integral (transmembrane) membrane glycoprotein protien Cholesterol Inside cell Fig. In passive transport, the substances move from higher concentrations to lower concentrations generally without the help of any protein. The transport continues until the concentration of the substance becomes same on both the sides of the membrane. Pinocytosis, in which the fuid material is engulfed and phagocytosis, in which large sized solid material is engulfed. During the process, the plasma membrane invaginates into tiny pockets, which draw fuids from the surroundings into the cell. Finally, these pockets pinch off and are known as pinosomes or phagosomes, which fuse with lysosomes and liberate their contents into the cell cytosol. Vesicles containing secretory materials fuse with the plasma membrane and discharge their contents into the exterior. Table 1 Similarities and differences between facilitated diffusion and active transport Facilitated Diffusion Active Transport 1. Needs a carrier protein and they are Needs a carrier protein and they are named as transporters or channels. Solutes are transported from high Solutes are transported from low concentrations to low concentrations concentrations to high concentrations 6. The co-effcient of viscosity of a liquid is defned as the force in dynes required to maintain the streamline fow of one fuid layer of unit area over another layer of equal area separated from one another by 1 cm at a rate of 1cm/sec. If a small sphere of radius ‘r’ and density ‘r’ falls vertically through a liquid with the density ‘r’at a steady velocity ‘u’, inspite of the acceleration due to gravity (g), the co-effcient of viscosity and density are related as follows. The lubricating property of the synovial fuid is achieved mainly by the viscous nature of the mucopolysaccharides present in the synovial fuid. But a surface molecule (b) suffers a much greater intermolecular 7 attraction towards the interior of the liquid than towards the vapour phase, because fewer molecules are present in the vapour phase. Surface tension (¡) is defned as the force acting perpendicularly inwards on the surface layer of a liquid to pull its surface molecules towards the interior of the liquid mass. Density - Macloed’s equation relates surface tension to the density of the liquid (r) and that of its vapour (r’). As the temperature of the liquid increases, the surface tension decreases and becomes zero at the critical temperature. Solutes - Solutes that enter the liquid raise the surface tension of the solvent, while solutes that concentrate on the surface lower the surface tension. Emulsifcation of fats by bile salts - Bile salts lower the surface tension of the fat droplets in the duodenum, which aids in digestion and absorption of lipids. Surface tension of plasma: The surface tension of plasma is 70 dynes/cm, which is slightly lower than that of water. Hay’s test for bile salts - The principle of surface tension is used to check the presence of bile salts in urine. When fne sulphur powder is sprinkled on urine containing bile salts ( as in jaundice), it sinks due to the surface tension lowering effect of bile salts. Dipalmitoyl lecithin is a surfactant that is secreted by the lung alveoli, which reduces the surface tension and prevents the collapse of lung alveoli during expiration. Osmosis is a colligative property of solution that depends on the number of molecules or ions of the solute in the solutions. A solution having lower or higher osmotic pressure with respect to the other is called as hypo-osmotic or hyperosmotic solutions respectively. The osmotic pressure exhibited by these impermeable solutes is called as the tonicity of the solution. A solution having lower or higher tonicities with respect to the other is called as hypotonic or hypertonic solutions respectively. The ability of the membrane to withstand hypotonic solution depends upon the integrity of the membrane. Certain genetic disorders like sickle cell anemia and defciency of vitamin E makes the erythrocyte membrane more fragile. Osmotic pressure of blood is largely due to its mineral ions such as sodium, potassium, chloride, calcium and protein. The osmotic pressure exerted by proteins is of considerable biological signifcance owing to the impermeability of the plasma membrane to the colloidal particles. The net difference in the hydrostatic pressure and osmotic pressure is responsible for the fltration of water at the arterial end of the capillary and the reabsorption of the same at the venous end. The renal excretion of water is regulated partly by the osmotic pressure exerted by the colloids in the blood plasma. Increased urination (polyuria) occurring in diabetes patients is due to the increased water retention by the urinary glucose. Donnan Membrane Equilibrium Let us consider two compartments separated by a semi permeable membrane, which is permeable to water and crystalloids, but not to colloidal particles. One of the compartment (A) is flled with a moles of NaCl, and the other compartment (B) is flled with b moles of NaR, in which R happens to be a non diffusible ion. So, the ionic concentration at equilibrium in both the compartments will be as follows, (A) (B) a-x Na+ Na+ b + x a-x Cl- R- b. Due to imbalance in the electrolytes, swelling of proteins occur, which is called as Donnan osmotic effect. Due to metabolism and dietary intake, large quantities of acids and bases are produced in the body and they have to be transported through blood for elimination. This is effectively done in the body by means of the buffers present in the blood and by two mechanisms, namely the respiratory mechanism and the renal mechanism. Since the concentrations of phosphate and organic acids are low in plasma, they do not play a major role in regulation of pH. Hemoglobin buffer system The buffering capacity of hemoglobin is due to the presence of imidazole groups in its histidine residues. When the blood returns to the lungs, O2 tension in the lungs is high resulting in the oxygenation of Hb.