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Time bio n chem


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Time bio n chem

  1. 1. Chemical and biochemicalchanges
  2. 2. Medic- legally death is not only the absence of life-it isdefinedas permanent and irreversiblecessation of functions of thethree interlinked vital systemsof the body(tripod of life),Namely: the nervous, circulatory,and respiratory systems.
  3. 3. • Estimation of time since death can directly or indirectly help to find out time of assault , by additional findings related with the stage of healing of an injury, which is equal to period for which the victim survived after sustaining the injury.• This is helpful for the investigating officer to locate an accused or verify any alibi of the accused.
  4. 4. • MECHANISM: It is bluish-purple or reddish-purple discolouration due to capillo-venous distension with blood at the undersurface of skin of the dependent parts of the body for settling of blood in those areas due to the pull of gravity, when circulation to keep the blood in motion ceases.• Bluish discoloration is NOT due to asphyxia• In dead bodies o₂ dissociation continues and there may be reflux of deoxygenated venous blood in capillaries and dependent parts, is reddish purple• Sites: Body surface & internal organs.• It appears in about 1-2hours & fully established in 6-12 hours• Fixation of levidity: The fluid may be displaced but there
  5. 5. • Sign of death• Time of death: 1-2 hours: It appears• 6-12hours: fully established• Position of the body can be determined: eg. In case of hanging, the PMS will be present on lower limbs & lower part of upper limbs.• Colour of staining can indicate cause of death: Due to CO poisoning- cherry red or pinkish In cyanide poisoning- Brick red Phosphorous,pot.chlorate,nitrate and aniline- dark brown H₂s poisonig greenish blue septicaemia: bronze Due to exposure to cold- bright red due to non utilisation of oxygenated blood,due to lack of metab. Drowning- red,formation of oxyHb in blood capillaries,due to absorption of O₂ through the body surface
  6. 6. • It is that state of the muscles (involuntary & voluntary) of a dead body when they become stiff or rigid with some degree of shortening.• After death there is breakdown of ATP, stiffening of muscles occur when ATP is reduced to <85% . If glycogen is available there is re-synthesis of ATP• Once the muscle glycogen is exhausted re-synthesis is not possible and muscle loose elasticity, softness and extensibility due to formation of viscid acto-myosin complex.• Since Calcium is not available , actomyosin complex become semi permanent till it is broken or destroyed due to decomposition.• *How to test for rigor mortis
  7. 7. • Sequence of appearance:• 1st in the heart (left ventricle)after 1 hour small muscles of face after 3-5 hours upper limbs lower limbs within 5-7 hours fully established in 12 hours.• RULE OF 12:• The approximate time after death can be estimated using the appearance & disappearance of rigor mortis. It fully appears in 12 hours, persists for another 12 hours and disappears in te next 12 hours.• 12 + 12+ 12 = 36 hours
  8. 8. • There is decomp. of proteins by putrefying bacteria resulting in production of amines(purescine and cadaverine)having putrid odour.• Cl. Welchii is responsible for decomposition.• H₂S,CO₂,CO,NH₃,marsh gas are produced.• After death at the ileocaecal zone Cl. Welchii,invade throgh the intestinal wall and reach bvs,breaking tissue structure producing H2S gas which combines withHB to form sulphmethaemoglobin which discolours.• Diffusion of gases causes spreading of
  9. 9. • Invasion of blood vessels by by the organisms and production of H₂S gas and formation of sulphmethaemogloin causing greenish brown staining of the inner walls of the vessels.• This makes superficial veins prominent and colourful• This gives a marbled appearance of skin.• Prominent after 36-48 hours.
  10. 10. • Formation of soft,whitish,crumbly,waxy and greasy material occuring in fatty or fat containing tissues of dead body.• Consists of fatty acids formed due to hydrolysis and dehydrogenation of body fats.• Initially the process needs water and body utilises its fluid and hence other soft tissues become mummified.• Normal body fat contains 0.5%FFA but in adepocere it is 70%
  11. 11. • Blood pH falls due to glycogenolysis,glycolysis,terminal accumulation of co₂,lactic acid,phosphoric acid and splitting of a.a. and f.a.• Blood pH rises again during secondary relaxation due to accumulation of ammonia.• Soon after death,plasma and RBC chloride levels are equal,by 3rd day level drops to half due to extra vascular diffusion and by dis Mg level rises 8fold.• 12hrs after death,level of a.a nitrogen in blood is about 10mg%,NPN 40mg% and creatine 10mg%.
  12. 12. • Levels of NPN,amino acid nitrogen and phosphorus levels in CSF are same as in blood.• CSF analysis for time of death is more dependable than that of blood because the levels of the constituents in CSF are less vulnerable to variation.
  13. 13. • Biochemical estimation of some of the constituents of vitreous humor. These are: • LEVEL OF ASCORBIC ACID: level falls after death • LEVEL OF PYRUVIC ACID: level falls after death • LLEVEL OF POTASSIUM: level rises to a moderate extent constantly,for about 100hrs after death.
  14. 14. • Growth of facial hair occurs at the rate of 0.4 mm/day.• Therefore by measurement of facial hair in subjects habituated of shaving it can be said for what period he survived after his last shave.
  15. 15. • From the state of digestion of food in stomach and approximate quantity of food emptied from stomach, it can be estimated the time after which the person survived after taking his last meal.• Therefore if the time of last meal is known approximate time of his death can be made out indirectly.• Carbohydrate passes out earliest from stomach.• Protein take some more time• Fat empties last.
  16. 16. • Normal emptying time for an average Indian mixed diet:• 1)half of food to pass through pylorus-45 min/1 hr• 2) half of rest-1/2 hr• 3) half of rest-3rd hr• 4) remains within an hour• So, total emptying time- 4-5 hrs.
  17. 17. • Digested food residue reaches:• Ascending colon by: 6-8 hrs• Left flexure of transverse colon: 9-10 hrs• Pelvic colon by: 12 hrs• Here food remains as faeces for upto 12 hrs.
  18. 18. • Radioactvie carbon is deposited in living tissues and maintains a near equilibrium level all along the life.• After death there is no further deposition of c₁₄ and its conc. gradually decreases.• In bone it reaches its half life in about 5600 years and estimation of bones of a person who died several years back,to study the strength of C ₁₄ in the bones may give some idea when the person died.