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Cardiovascular system

  1. S.A node is located at the junction of SVC with right atrium. The action potential in SA & AV nodes are due to Ca++, with no contribution by Na+influx.
  2. Conduction rate in decreasing order: Purkinje fibers > bundle of His = Ventricular muscle = Atrial pathway > SA node > AV node.
  3. When the sum of voltage of all the QRS complexes of the three standard leads is greater than 4 millivolts, the ECG is considered as high voltage electrocardiogram. Most often due to increased cardiac muscle mass.
  4. Cardiac output : Amount of blood pumped by each ventricle per min.MCQ CO = stoke vol x heart rate ( 5-6 litres/min)
  5. Measured by 1) Fick method 2) dye dilution/ thermodilution(Stewart method) 3) Doppler
  6. Regulated by a) control of HR b) control of stroke vol. : hetero and homo-metric regulation
    a. heterometric regulation : Frank Starling’s law MCQ. More preload (EDV) more is SV.
    b. Homometric regulation   The S V changed fibre length same. example, positively inotropic agents like catecholamines. xanithines, and digitalis MCQ increase the S.V , negatively inotropic states like hypercapnia. hypoxia, acidosis MCQ, certain drugs (eg barbiturates, quinidine MCQ) myocardial infarction, decrease the S.V.
  7. Cardiac index = CO/body surface area. Normal 3.2 L/min/m2
  8. Blood pressure measured by auscultatory method using sphygmomanometer tends to be higher than intra-arterial pressure measured by arterial cannulation, because some cuff pressure gets dissipated between the cuff and artery.
  9. Systolic pressure is best indicated by lst Korotkoff's sound and diastolic pressure in adults by 5th korotkoffs sound
  10. Using relatively small cuff, obesity and person with thick calcified & sclerotic vessels that are difficult to compress (eg in elderly, atherosclerosis, diabetic and Monckeberg's arteriosclerosis) are the reasons of spuriously high blood pressure (pseudohypertension). Pressure in SI unit is measured in pascal (Pa), blood pressure in SI unit is measured in KPa.
  11. B.P = CO x PR
    a. Pulse pressure = Systolic pressure - Diastolic pressure MCQ
    b. Mean pressure = Diastolic B.P. + 1/3 Pulse pressure MCQ
  12. maximum pressure drop in the vascular circuit is at the level of the arterioles (as the maximum resistance is at the arterioles)
  13. Effect of gravity on B.P.: Above the heart level, the BP falls and below the heart level, the BP increases. The value is 0.77mmHg per cm MCQ. This is true for arterial as well as for venous pressure.
  14. Carotid sinus nerve and vagal fibres from aortic arch commonly called Buffer nerves.
  15. Endothelin 1 is brocho constrictor (not bronchodilator) &vasoconstrictor (so decrease GFR).
  16. NO (nitric oxide) is also called as EDRF (endothelial derived relaxing factor)
  17. NO is produced from arginine by enzyme NO synthetase. It has a short half life t1/2 = 4 seconds
  18. NO acts as – Neurotransmitter free radical, vasodilator, oxidizing agent and catalyst.
  19. High capillary hydrostatic pressure & interstitial fluid colloid osmotic pressure tend to cause osmosis (Alteration) of fluid outward through capillary membrane.
  20. Urine output is quantitative and relatively reliable indicator of organ perfusion.
  21. Blood Vessels Types :     
    a. Wind kessel vessels MCQ: show elastic recoil eg aorta, major arteries (2 % in aorta MCQ, 8% in rest)
    b. Resistance vessels MCQ: innervated, eg arterioles. (max. smooth muscle MCQ)
    c. Precapillary sphincters MCQ : not innervated, affected by local metabolites
    d. Exchange vessels : capillaries, not innervated (5 % of blood vol. MCQ)
    e. Capacitance vessels MCQ: veins, thin walled, poor innervation (55 % of blood vol. MCQ)
    f. Shunt vessels MCQ: A-V anastomoses (bypass capillaries), in skin for temp. regulation
  22. Cross sectional area : is minimum for aorta and maximum for capillaries MCQ
  23. Capillaries
    a. Maximum cross- sectional area (1000 times of aorta)
    b. Minimum velocity in circulation is seen in capillaries (inversely relation to cross- sectional area)
    i. Are lined by single layer of endothelial cells.
  24. Critical closing pressure : It is the pressure below which flow completely stops, the value of this pressure is just above zero.
  25. Law of Laplace : This gives the relationship between the distending pressure (P), the wall tension (T), the wall thickness (w) and the radius in a hollow viscous organ. T=Pr/w imp: in dilated heart work done inc. MCQ.
  26. Blood supply of liver through (1500 ml/min) : Portal vein is 80% and Hepaticartery is 20%
  27. The direct vasodilator action of C02 is most pronounced in the skin and brain.
  28. RBC are produced in marrow of membranous flat bones such as vertebrae, sternum,ribs etc
  29. Alkali denaturation test(ADT) - done for fetal hemoglobin. HbFis alkali denaturation resistant. Thrombosthenin - is a contractile protein found within platelets.
  30. Lysozyme is an enzyme found in neutrophils of eukaryotes, plants & in bacteriophage virus. The average half life of neutrophils in the circulation is 6hr. Half life of transfused platelet is 4 days.
  31. Vit. K dependent factors: Factor II (prothrombin), VII, IX, X protein C and S.
  32. PT is first to be prolonged in Vit K deficiency. 
  33. Factors causing increase venous return
    a. Increase total blood vol
    b. Increase venous tone
    c. Increase -ve intrathoracic pressure
    d. Factors decreasing venous return l.Standing,2.Decrease ventricular compliance
  34. When a person changes posture from standing to lying down position 1st change is in VR, venous return to heart rises, so in CHF lying down causes more cough.
  35. Neural regulation of CVS , Site: medulla
    a. Vasomotor centre(VMC) – in rostral ventrolateral medulla, causes symp. stimulation of heart, vessels
    b. Cardio inhibitory centre(CIC) – nucleus of Vagus N. – inhibitory to VMC and heart ,dec. HR & BP
  36. BARORECEPTORS – inhibit VMC, stimulate CIC. Causes dec. in BP
  37. CHEMORECEPTORS – normally inhibit VMC but in hypoxia stimulate VMC inc. in BP
  38. Neurogenic Hypertension – cutting of sinus nerves, damage to BARORECEPTORS.
  39. Resting Vagal Tone – HR is low due to this, cutting vagus inc. HR to 100/min
  40. 2 ,3 DPG doesnot bind to HbF
  41. Blood brain barrier is made up of astrocytes & Tight junctions. Blood testis barrier is formed by Sertoli cells.
  42. Heart rate is maximum in a normal foetus.
  43. For smooth muscle contraction presence of cellular calcium is essential to cause contraction
  44. Force of muscle contraction is independent of amplitude of action potential.
  45. Central venous pressure : close to JVP
    a. Normal Range - -2 cm H20 to 12 cm H20
    b. Causes of decrease CVP - non cardiogenic shock
    c. Causes of increase CVP - heart failure, expansion of blood volume, PEEP
  46. At isometric contraction – start: Mitral and tricuspid valves close, It end:  when aortic and pulmonary valves open.
  47. At isometric relaxation - mitral and tricuspid valves open and aortic and pulmonary valves close
  48. Depolarization is from endocardium to epicardium. And repolarization is also from endocardium to epicardium.
    a. lst heart sound occurs during isometric contraction and ejection period
    b. 2nd heard sound occurs during protodiastole and part of isometric relaxation
    c.3 rd heart sound is due to rapid ventricular filling
    d. 4th heart sound is due to rapid ventricular distension caused by forceful atrial contraction. Heard during ventricular filling phase.

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