PhysiologyMCEMA.txt

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PhysiologyMCEMA.txt
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2013-12-06 21:25:04
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Physiology MCEM
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Physiology MCEM A
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  1. The intracellular compartment contains approximately
    •25-28 L of fluid.
  2. The third space is the space in the body where fluid does not usually collect, examples include the
    • peritoneal and pleural cavities.
  3. The action potential can be summarized as follows:
    • 1. Resting potential. Small subset of potassium channels open, permitting K+ to enter and exit the cell based on electrochemical forces. There is no net movement of K+ ions.
    • 2. Threshold. As a depolarizing stimulus arrives a few Na+ channels open allowing Na+ ions to enter the neurone. The increase in positive ions inside the cell depolarized the membrane potential and brings it closer to the threshold at which the action potential is generated ( -55mV).
    • 3. Depolarisation phase. After the threshold potential is reached additional voltage gated sodium channels open and Na+ ions rush into the cell. The voltage across the membrane rapidly reverses and reaches its most positive value.
    • 4. Repolarisation phase. At the peak of the action potential, two processes occur simultaneously. Many of the voltage-gated sodium channels begin to close and more potassium channels open. This allows positive ions to leave the cell and causes the membrane potential to shift back towards the resting membrane potential. As the membrane potential approaches the resting potential the potassium channels channels are maximally activated and open.
    • 5. Hyperpolarisation phase. The membrane potential then hyperpolarizes beyond the resting membrane voltage as more potassium channels are open at this point than during the membranes resting state, allowing more positively charged potassium ions to leave the cell.
    • 6. Recovery. A return to steady state occurs as the additional potassium channels opened during the action potential close. The membrane potential is now determined by the subset of potassium channels that are normally open during the membranes resting state.
  4. The velocity of the action potential increases with
    • •increasing axonal diameter.
    • •The velocity also increases if the neurone is myelinated.
  5. The following factors promote gastric emptying:
    • • Increased food volume in the stomach
    • • Gastrin
    • • Motilin
    • • Parasympathetic innervation (via the vagus nerve)
    • • Prokinetics such as metoclopramide and erythromycin
    • • Proteins empty fastest and fats slowest
  6. Prolongation of the QT interval can be caused by
    •NON-sedating antihistamine drugs such as terfenadine and astemizole.
  7. Cocaine increase QT intervals ?
    •acute intoxication but not in chronic abuse.
  8. Decreased oxygen tension causes
    vasodilatation of arterioles.
  9. Locally released serotonin causes
    • vasoconstriction of arterioles.
    • An area with no ventilation is termed a
    • shunt.
  10. An area with no perfusion is termed
    dead space.
  11. This is the ideal V/Q.
    At approximately 2/3 of the way up the chest the V/Q = 1.
  12. At the apex the V/Q =
    V/Q = 3
  13. and at the base V/Q = 0.6.
    V/Q = 0.6.
  14. The criteria for the systemic inflammatory response syndrome are:
    • • Temperature < 36°C or > 38°C
    • • Heart rate > 90 bpm
    • • Respiratory rate > 20/min or PaCO2 < 4.3 kPa
    • • White cell count < 4 x 109/l or > 12 x 109/l (or 10% bands)
  15. ECG criteria for LVH have good
    • •specificity but poor sensitivity for actual left ventricular hypertrophy.
    • •Many people who actually have LVH do have ECGS which reveal it.
  16. The Sokolow-Lyon index is positive for LVH if the
    •S wave in V1 plus the R wave in V5 or V6 > 35 mm (7 large squares).
  17. LVH is present if the R wave in aVL is greater than
    •12 mm.
  18. EKG vs Echocardiography LVH?
    •Echocardiography-> gold standard for diagnosis of LVH.
  19. ‘P mitrale is indicative of
    • · left atrial enlargement-> delay in left atrial activation,->broad, bifid or notched P wave
    • · ECG changes are most prominent in the inferior leads.
  20. ‘P mitrale’ is typically caused by
    · mitral regurgitation, which results in left atrial enlargement.
  21. Vitamin D is metabolized in the kidney to
    1,25-dihydroxycholecalciferol.
  22. Renin is produced by the
    juxtaglomerular apparatus and promotes the formation of angiotensin.
  23. Erythropoietin in synthesized by
    Interstitial cells in the renal cortex. It is a hormone that regulates red blood cell production.
  24. PTH reduces re-absorption of
    phosphate in the proximal convoluted tubule.
  25. Thiazide diuretics inhibit re-absorption of
    • Na and Cl ions in the distal convoluted tubule
    • blocking the thiazide sensitive Na/Cl co-transporter.
  26. A polysnaptic reflex occurs when more than one synapse connects the afferent (sensory) and efferent (motor) signals. Examples of polysynaptic reflexes include:
    • • Pupillary light reflex
    • • Accommodation reflex
    • • Corneal reflex
    • • Vestibulo-ocular reflex
    • • Gag reflex
    • • Withdrawal reflex
  27. The following are the classic criteria of left anterior fascicular block on ECG:
    • • Dominant negative deflection of QRS complex in lead II (i.e. axis < -30°)
    • • Q waves in lead I and aVL
    • • R waves in leads II, III and aVF
  28. are ECG criteria for LBBB:
    • • Widened QRS (> 0.12 seconds)
    • • RSR pattern in V4-V6
    • • Q wave in V1
    • • Dominant R wave in V6
    • • Upright and notched lead I (‘M pattern’)
  29. The commonest causes of LBBB are:
    • • Coronary artery disease
    • • Hypertension
    • • Cardiomyopathy
  30. The third heart sound can be physiological in
    • children where it is due to the presence of a supple ventricle that can undergo rapid filling.
    • When heard in older adults ->sign of increased ventricular filling secondary to disease such as heart failure or mitral regurgitation.
  31. The fourth heart sound is due to conditions which cause
    • stiffness of the ventricles.
    • ventricular hypertrophy
    • aortic stenosis
    • ventricular fibrosis
    • heart failure.
  32. EDRF (nitric oxide) is produced and released by the endothelium to promote
    • smooth muscle relaxation.
    • released in response to <- calcium, bradykinin and histamine, and also in response to painful stimuli.
  33. Endothelin-1 is a potent
    vasoconstrictor released by the endothelium.
  34. Thromboxane A2 is a potent
    vasoconstrictor released by the endothelium.
  35. The kidneys receive approximately
    • 1.2 L of blood flow per minute
    • 20-25% of the cardiac output.
  36. The blood flow in the renal cortex is approximately
    20 times greater in the renal cortex than in the medulla.
  37. The kidney is approximately
    • 11-14 cm in length
    • 6 cm wide
    • 4 cm thick.
  38. The intracelleular compartment contains approximately
    • 55%
    • 25 L of fluid.
  39. the extracellular compartment contains approximately
    45%.
  40. Lymph is an example of an
    interstitial fluid.
  41. Transcellular fluids are fluids that are formed from the transport activities of cells. Examples include:
    CSF, GIT fluids, bladder urine, aqueous humour and joint fluids.
  42. The normal value of the CVP is
    2-8 mmHg.
  43. The tip of the catheter must be in the
    junction between the superior vena cava and the right atrium.
  44. Cannon a waves are very large a waves that occur when the right atrium contracts against a closed tricuspid valve. They occur in:
    • • Complete heart block
    • • Ventricular tachycardia
    • • Junctional tachycardia
  45. Both gelofusine and 0.9% saline contain
    • 154 mmol/l of sodium.
    • 125 mmol/l of chloride compared with 0.9% saline which contains 154 mmol/l.
    • PH 7.4
    • molecular weight 30,000.
  46. The average molecular gelatine weight of gelofusine is
    30,000.
  47. Regarding class II haemorrhage in a 70 kg male:
    • 750-1500 mL of blood would have lost.
    • pulse rate 100-120 with a normal blood pressure.
    • Urinary output is only mildly affected and usually in the region of 20-30 mL/hour.
    • pulse pressure is usually decreased.
    • respiratory rate 20-30.
  48. Cerebral perfusion pressure (CPP) = mean arterial pressure (MAP) – intracranial pressure (ICP). CPP is reduced by:
    • • Reduced MAP
    • • Increased ICP
    • • High pCO2 (due to resultant vasodilatation)
  49. Regarding the electrical basis of cardiac contractility
    • •Cell membrane potentials are determined primarily by 3 factors.
    • ? These are the concentrations of ions inside and outside the cell.
    • ? The permeability of the cell membrane to those ions through specific ion channels.
    • The activity of electrogenic pumps.
    • •The first phase of a cardiac action potential is a rapid rise in sodium permeability.
    • •The second phase in a cardiac action potential is a rapid fall in sodium permeability and a slight rise in potassium permeability.
  50. The resting membrane potential of a ventricular myocyte is
    •-90mV.
  51. An increase in cardiac output can generally be attributed to an increase in
    •heart rate.
  52. Alkalosis is a
    •negative inotropic factor.
  53. The effect of increased sarcomere length on the contractile proteins is termed
    • •length-dependent activation.
    • Terminal arterioles/Post capillary venules are small vessels measuring
    • •10-50µm.
    • Albumin generates about
    • •70% of oncotic pressure.
  54. In most capillary systems of the body there is a net filtration of fluid of about --% from the intravascular compartment to the extravascular compartment.
    •10%.
  55. Normal coronary blood flow is around
    • •200ml/minute at rest.
    • Coronary blood flow may increase up to 5 times during exercise.
    • •5 times during exercise.
    • An increase in carbon dioxide leads to cerebral
    • •vasodilatation.
    • An increase in potassium leads to cerebral
    • •vasodilatation.
    • Regarding skeletal muscle blood flow
    • •At rest it accounts for approximately 20% cardiac output.
    • During swallowing the nasopharynx is
    • •It is sealed by elevation of the soft palate
    • •superior constrictor muscle contraction.
    • The primary peristaltic wave forces the food bolus down the oesophagus into the stomach in a wave that last approximately
    • •8-9 seconds.
    • CCK inhibits
    • •gastric emptying and gastric acid secretion.
  56. Each villus is approximately
    •0.5-1.6 (millimetres) in length.
  57. An example of secondary active transport is the glucose symporter SGLT1, which co-transports
    • •one glucose molecule into the cell for every two sodium ions it imports into the cell.
    • The Thin descending Henle displays a high permeability to
    • •water and solutes
    • •20% of water resorption
  58. The normal value for arterial blood pH is
    • •7.34-7.44.
    • The normal value for arterial blood PaCO2 is
    • •4.6-6.
    • The normal level for total serum calcium is
    • • 2.2-2.6 mmol/L.
    • calcium that enters the body in a normal diet is absorbed by the small intestine.
    • •About 40% is absorbed
    • The pituitary gland weighs approximately
    • •0.5g
    • Head trauma is the cause of neurogenic diabetes insipidus in
    • •17% of cases.
    • Regarding SIADH
    • •hyponatraemia.
    • •Small cell lung cancer is a common cause.
    • Symptoms of SIADH include
    • •headache, nausea, vomiting, convulsions and coma.
    • Management of SIADH includes the use of
    • •demeclocycline.
    • The combined weight of the adrenal glands ranges from
    • • 7-10 grams.
    • Regarding Cushing’s syndrome Patients often suffer with psychological disturbances such as
    • •euphoria and psychosis.
    • •Anxiety and depression are also common.
    • the most common non iatrogenic cause of Cushing’s syndrome.
    • •Pituitary adenomas
    • Antifungal treatment for Cushing’s syndrome.
    • •Ketoconazole->It inhibits cortisol synthesis but is of limited efficacy.
    • Regarding phaeochromocytoma may be familial.
    • •Up to 25% may be familial.
    • Delta cells of the pancreas secrete
    • •Somatostain.
  59. Proinsulin ->insulin by
    • •cellular endopeptidases.
    • In the maturation of insulin there is release of a fragment termed the
    • • C-peptide.
    • Insulin acts to increase the
    • •secretion of hydrochloric acid by parietal cells in the stomach.
    • cholecystokinin stimule vs inhibit-> Glucagon
    • •Stimulated
  60. increased urea production-> stimule vs inhibit-> Glucagon
    •Inhibited
  61. Regarding IDDM male/female incidence
    • •There is an equal incidence in males and females.
    • NIDDM accounts for --% of cases of diabetes.
    • •90% of cases.
    • Regarding NIDDM The pathophysiology includes an
    • •inability of cells to respond to normal levels of insulin i.e. they are insulin resistant.
  62. NIDDM Dx
    • •A fasting blood sugar of > 7mmol/L suggests the diagnosis.
    • The primary mechanism of action of metformin is
    • •---> suppress glucose production by the liver.
    • •also Increasing insulin sensitivity is an important action
  63. Efferent arteriole is narrower vs widther than the afferent,
    •Narroweer ->creating a capillary hydrostatic pressure of about 7.3kPA.
  64. Glomerular Filtration->The osmotic pressure of the blood is around
    • 4kPA and is provided mainly by plasma proteins.
  65. Glomerular Filtration Less than --% of the glomerular filtrate is excreted as urine.
    • •< 1%
    • Atrial natriuretic peptide
    • •decreases reabsorption of sodium and water from the Distal convoluted tubule and collecting ducts.
  66. ACTH with highest levels at around
    • •8am in the morning.
    • The release of thyroid stimulating hormone is at it’s highest in the
    • •early evening is at it’s lowest
    • •highest during the night.
  67. Calcitonin is secreted by the
    •parafollicular C cells in the thyroid gland.
  68. At the arterial end of a capillary the hydrostatic pressure is around
    • 5kPa.
  69. The osmotic pressure of the blood at the arterial end is around
    •3kPA.
  70. Hydrostatic pressure at the venous end of a capillary is around
    • 2kPa.
  71. % of carbon dioxide in the blood is dissolved in the water of the plasma.
    •7%
  72. % of carbon dioxide in the blood is transported in combination with haemoglobin.
    •23%
  73. % of carbon dioxide is transported in the blood in the form of sodium bicarbonate.
    • •70%
    • The normal platelet count is between
    • •200 and 350 x 109/L.
    • The lifespan of a platelet is between
    • •8 and 11 days, after which time they are destroyed by macrophages mainly in the spleen.

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