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Forensic Biology Exam 1 Material, Lecture notes of Forensics

Southeastern Louisiana University Forensics

Covers all material for exam 1. Stages of decay, role of pathologist, forensic anthropology, forensic odontology, forensic taphonomy, etc.

Typology: Lecture notes

2021/2022

Available from 03/03/2022

victoria-hart 🇺🇸

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Exam 1 Lecture Materials

Stages of Decay

Human Decomposition Stages

Taphonomy~

• Study of the transition of animal remains postmortem (after death)

Stages of decay are not discrete, described from 2-8 stages but 5 stages most common

Five stages of decay~

• Fresh, bloat, active decay, advanced decay, putrid/dry remains

• Also referred to as:

•autolysis, putrefaction, diagenesis

• autolysis: cell death

• putrefaction: breakdown of soft tissues

• diagenesis: breakdown of hard tissues

• Fresh (autolysis), bloat (putrefaction), decay (putrefaction &

carnivore/scavenging activities), dry (diagenesis)

• Recycling of tissues to simplest building blocks

• organic molecules of carbohydrates, proteins, lipids, nucleic acids

Stages of decay

Rate of decay varies according to:

• Temperature & relative humidity: season, geography, elevation

• Dry heat: turns tissue leather-like, mummifies

• Corpse/carcass condition: intact, dismembered, burned, etc.

• Decay faster intact than dismembered (flies prefer large bodies to lay

eggs)

• Clothing accelerates decomposition (holds in moisture)

• Corpse/carcass size & biomass

• Presence of clothing, physical barriers, etc.

Partial preview of the text

Download Forensic Biology Exam 1 Material and more Lecture notes Forensics in PDF only on Docsity!

Exam 1 Lecture Materials

Stages of Decay

Human Decomposition Stages

Taphonomy~

Study of the transition of animal remains postmortem (after death) Stages of decay are not discrete, described from 2-8 stages but 5 stages most common Five stages of decay~
Fresh, bloat, active decay, advanced decay, putrid/dry remains
Also referred to as:
autolysis, putrefaction, diagenesis
autolysis: cell death
putrefaction: breakdown of soft tissues
diagenesis: breakdown of hard tissues
Fresh (autolysis), bloat (putrefaction), decay (putrefaction & carnivore/scavenging activities), dry (diagenesis)
Recycling of tissues to simplest building blocks
organic molecules of carbohydrates, proteins, lipids, nucleic acids

Stages of decay

Rate of decay varies according to:

Temperature & relative humidity: season, geography, elevation
- Dry heat: turns tissue leather-like, mummifies
Corpse/carcass condition: intact, dismembered, burned, etc.
- Decay faster intact than dismembered (flies prefer large bodies to lay eggs)
- Clothing accelerates decomposition (holds in moisture)
Corpse/carcass size & biomass
Presence of clothing, physical barriers, etc.

Placement of corpse/carcass: terrestrial, aquatic, buried, hung, indoors, shade-vs- sunlit areas, etc.
Availability to insects, vertebrate scavengers, bacteria, fungi Fresh~
Internal Changes
Cells begin dying ~3-7 mins PM due to lack of O 2 (brain cells die 1st, epithelium can survive up to 24 hrs PM)
Corpse appears normal externally, yet cellular death & microbial activities are occurring internally
Decay initiated by ‘autolysis’ (self-digestion by lysosomal enzymes)
As cells die, [CO 2 ] increases in blood, pH decreases, & cellular byproducts accumulate
causing more cell death
Autolysis externally observable ~few days PM: skin blistering, slippage, or ‘gloving’
Skin blistering: breakdown of epidermis from dermis
Rate of tissue degradation in liver (i.e., breakdown of DNA) used as a PM indicator
high [enzyme] in organ leads to linear correlation btw degree of degradation & PMI
Algor mortis, livor mortis, rigor mortis most common methods of PMI during fresh decay
Algor mortis= body temperature acclimates to ambient temp
Body temp drops 2° F after the first hour after death and 1.5° F every hour after
Livor mortis= blood pools in vessels due to gravity, causes discoloration of skin (reddish-purple coloring)
Observable ~20-120 mins PM as blotches, then spreads & deepens in color w/ time….’fixed’ @ ~10-12 hrs PM
RBC’s decay & diffuse across vessels into surrounding tissues
Helps indicates initial position of body PM (‘ pressure pallor’ )

Aerobic & anaerobic bacteria flourish, insect activity dominates w/ fly larvae consuming majority of soft tissue
‘Black putrefaction ’ refers to darkening of skin due to continued tissue breakdown - Typically appears first in head region as colonization of fly larvae (Calliphoridae) in area accelerates decay
Escaping gases produce a very strong odor, NH 3 most noticeable Advanced decay~
Marked by mass migration of fly larvae away from corpse to pupate
remains now resemble a ‘collapsed’ corpse/carcass
remaining portions of internal organs, bone, tendons, ligaments, & limited amount of muscle, skin
Adipocere present but ranges from crumbly (rapid decay) to soft, paste-like (slower decay)
waxy, fatty substance formed by glycerol & fatty acids
produces a ‘cheesy’ odor associated with the remains
Mold, fungi, & other microbes become apparent on drying surfaces
Surfaces of skin, hide, bone; on clothing, soil surface, etc.
Insect activity still very important, though species change as ‘food’ & ‘habitat’ resources vary Putrid/dry remains~
Dry or nearly dried remains:
bone, tendons, ligaments, hair (hide), nails (hooves, horns)
sinew= shreds of dried tissues attached to bone, hides
Putrid remains tend to have layer of adipocere present on soil or ground surface, bones, clothing, etc.)
Dry remains typically include sun bleached bone & mummified tissues (if remain) resting on ‘dried soils’ devoid of adipocere
remains have now become ‘skeletonized’

Aquatic environments

Aquatic environments~

Remains decay ~2x slower than terrestrial habitats due to cooler temps, low [O 2 ], & inhibition of insect activity 6 stages of decomposition in freshwater ecosystems:
Submerged fresh= carcass sinks to bottom of pond, etc.
Early floating= carcass floats to surface as gases accumulate in abdomen; flies begin to lay eggs on exposed flesh
Floating decay= ‘active decay’ w/ fly larvae feeding on exposed flesh
Bloated deterioration= carcass still floating though fly larvae have consumed exposed skeletal muscle; limbs begin to disarticulate, body fluids leak from orifices
Floating remains= disarticulated limbs, skin, internal organs, fatty tissues, etc. ‘float’ as a mass; exposed remains now have little/no insects associated w/ it
Sunken remains= bones, bits of skin, etc. sink to bottom of pond Marine ecosystems~
Crustaceans, fish, gastropods, & echinoderms (starfish) main decomposers of carrion
Recovery of human remains rare & limited research on forensic taphonomy in marine environments Burned bodies~
A ‘complete’ burn extremely difficult to achieve
Typically, flies will still oviposit on the non-burned tissues (bloating of carcass exposes ‘fresh tissues’) Confined/wrapped, buried, hung, dismembered, chemicals (embalmed), etc. all will alter decay~

Late changes: algor, livor, & rigor mortis
- Algor mortis: ‘cooling of the body’; internal body temperature acclimates to ambient temp
- Livor mortis: ‘skin discoloration’; blood pools in vessels due to gravity, causing discoloration of skin on ‘dependent’ parts of the body
- Observable ~20-120 mins postmortem (PM) as reddish-purple blotches
- Spreads & deepens in color w/ time…‘fixed’ @ ~10-12 hrs PM
- RBC’s decay & diffuse into surrounding tissues
- Helps indicate initial position of body PM…’pressure pallor’
Rigor mortis: ‘stiffening of muscles & joints’
- Shortening of muscle fibers (contraction) leads to rigidity
- Onset begins ~2-6 hrs PM w/ muscles of eyelids, neck, jaw
- Spreads to all muscles w/in hrs
- Rigidity persists ~24-84 hrs (temperature dependent)
- Muscle contraction is produced by shortening of sarcomeres
- Contractile unit consisting of actin (thin) & myosin (thick) filaments that ‘slide across’ each other
- Ca2+^ stored in sarcoplasmic reticulum (SR) of muscle cells leak into cytoplasm
- Bind to troponin-tropomyosin complex, causing ‘active site’ on actin to be exposed
- In the presence of ATP, myosin ‘heads’ bind to actin, causing filaments to ‘slide across’ each other (= contraction)
- Requires ATP to break bond & relax muscle fiber
- Remain attached w/ no more ATP synthesis.…= rigor

Structural framework of sarcomeres start to breakdown (reverse of rigor mortis)
Rigor reverses itself over time as filaments degrade
Thin filaments (actin) ‘detach’ from ends of each sarcomere, allowing contractile unit to lengthen again
Muscles relax in approx. same order as stiffened
Onset & duration determined by ambient temp & metabolic activity @ time of death
Cold temps accelerates onset & prolongs rigor
Warm, hot temps delay it, or potentially never fully develops
Rigor may accelerate if fever or vigorous activity @ death:
increase [lactic acid] in muscle cells
decrease [glucose]
Ca2+^ released into sarcoplasm

Postmortem tissue changes

Postmortem tissue changes~

Decomposition
- autolysis & putrefaction
Mummification
Skeletonization
Adipocere formation Decomposition:
Cells begin dying ~3-7 mins PM due to lack of O 2
Corpse/carcass appears normal externally, yet cellular death & microbial activities are occurring internally
Autolysis: ‘ self-digestion’ ; process by which digestive enzymes w/in cells break down carbohydrates & proteins
Tissue decay initiated by cells w/ high [lysosomal enzymes] As [CO 2 ] increases, pH decreases, & membranes become ‘leaky

White-, grey- or yellowish w/ consistency ranging from crumbly (rapid decay) to soft, paste-like (slower decay-like buried body) - Produces a ‘cheesy’ odor
Can inhibit further decomposition, causing body to remain virtually unchanged for years

Medical examiner & coroner systems

Coroners:

Elected lay persons who rely upon medical personnel available to assist in investigations & perform autopsies Medical examiners:
Appointed physicians & pathologists typically w/ special training in medicolegal death investigations & forensic autopsy performance
Most general pathology training includes limited or no exposure to forensic pathology
Thus, ME’s should be a board certified forensic pathologist
A ‘Medical Examiner’s Law ’ stating that the ME has the right to perform autopsies in all deaths where a physician was not present At minimum, the ME will perform the following~
Complete external examination
X-rays
Sampling & toxicological analysis of body fluids
Blood, urine, bile, vitreous Violent homicides, deaths of children, etc.~
ME may visit crime scene
Perform autopsies
Photograph injuries
Submit report

Definitions of death

Cause of death:

Any injury or disease that is responsible for initiating series of events that results in death Mechanism of death:
Physiological derangement produced by the cause of death that results in death Manner of death:
An opinion based on known facts concerning circumstances leading up to & surrounding death, in conjunction w/ findings @ autopsy & lab tests

Types of Death

Types of death~

Natural: death resulting from natural causes
Accidental: unexpected death resulting from a lawful act performed under a reasonable belief that no harm is possible
Suicide: deliberate termination of one’s existence
Homicide: killing of one human being by the act or omission of another (doesn’t equal ‘murder’)
Undetermined: when investigation, autopsy, & other tests fail to identify a commonly accepted cause or manner of death
Unclassified: when circumstances of death fail to fit into the definition of any other manner of death

Forensic Pathology

Definition: “A branch of medicine that applies the principles & knowledge of the medical sciences to problems in the field of law.” (DiMaio & DiMaio)

Or, a subspecialty of pathology involved in the investigation of deaths that are sudden, unexpected, unexplained or violent 5 Specific goals of a forensic autopsy~
Identify victim (‘who’)
Determine cause of death (‘what’)
Time of death (‘when’)
Correlation of body & its environment (‘where’)
Manner of death (‘how’)

Rigor, livor, & algor mortis, & decomposition
Rigor mortis: PM stiffening of muscles & joints
- Timeline for onset & relaxation subject to variables
- Graded as: absent (limp), minimal (some stiffness), moderate (stiffer but breakable), full (complete stiffening)
Lividity (livor mortis): discoloration on ‘dependant’ areas
- Color varies, but normally reddish-purple
- Discoloration does not disappear & timeline subject to variables
- Graded as: absent, faint, full, fixed/unfixed
Body cooling (algor mortis): 1.5-2 degrees/hr PM
- Use lab thermometer or electronic meter for core temp (rectum, liver)
- Timeline subject to variables:
  - ambient temperature, humidity, & air currents; location (air, water, ground); body mass & clothing; time elapsed Postmortem changes indicating time of death (‘when’):
Decomposition: observable changes on external surface
~ 24 hrs, green discoloration of lower abdomen (caecum)
~48 hrs, entire abdomen w/ green discoloration
~72 hrs, torso green Correlation of body & its environment (‘where’):‘
May or may not be possible Identification (‘who’):
Visual, fingerprints, dental, medical, circumstantial, anthropological, DNA Cause of death (‘what’):
Injury or disease process that initiates chain of events sufficient to result in death
Natural causes: heart attack, lung cancer
Medicolegal causes of death: gunshot or stab wounds, asphyxia by hanging, blunt force trauma Manner of death (‘how’):

Medical classification of a death according to circumstances surrounding the death
Standard of certainty= ‘reasonable medical certainty’

Time of death indicators

Forensic pathologist~

Rigor mortis, livor mortis, algor mortis, decomposition, changes in vitreous humor, & gastric emptying Forensic entomologist~
Development rates & succession patterns of necrophilous insects Forensic anthropologist~
Taphonomic processes (observable changes in tissues) Other info~
Last seen alive, scene markers (mail, newspaper, etc.), etc.

longer to warm/cool than adjacent lands
Buffers changes in pH in tissues & environment= dilutes [chemical] intra/extracellularly
Source of H+^ for biochemical rxtn in all cells (plants, animals, bacteria)
Accelerates or retards decomposition according to:
submerged or partial; salt or fresh; moving or still; varying from normal pH
salt water have preserving effects on tissues
Decomposition gases (VOC’s) are H 2 O-soluble= inc humidity, soil moisture aids in detection of carrion
Presence of moisture encourages floral, microbial growth
Amount of H 2 O present directly affects activity of hydrolases (metabolize carb’s, lipids, proteins) by altering pH & [enzyme]
submerged or relative humidity (on land)
High moisture content promotes adipocere formation:
H 2 O reduces oxidation of fatty acids, & so, lipids available for binding of salts @ low pH pH (acidity & alkalinity) ~
Includes changes in intra/extracellular & environmental pH
Intracellular pH lowers…leading to decreased enzymatic activities & slower metabolic rxtn
stops completely as enzymes denature/coagulate
½ life of intracellular enzymes ~few hrs
Fermentation by anaerobic & facultative bacterial in soil further contribute to lower pH (lactic acid, etc.)
Lowered soil pH encourages: 1) fungal growth on remains/clothing/adjacent soils;

nutrient uptake in rootlets

Plant rootlets & fungi may eventually invade tissues, helping to further physical breakdown of remains
decaying vegetation also adds humic acids to soil
Buried corpses/carcasses create an acidic environment early in decay

However, weeks or months PM surrounding soil become more alkaline
- useful for detecting buried remains according to location of ‘more basic’ soils (alkaline) Partial pressure of O 2 ~
Oxidation of tissues slows in low-O 2 environments like deep burials, submerged, high altitude; thus, slower rates of decay
H 2 O & H 2 O-logged soils are depleted of O 2 , & so have low redox potential
Soils & H 2 O w/ decaying organic matter tend to be acidic, & so are ‘reducing environments’
Dry soils have a high redox potential
Depletion of O 2 initiates decay, w/ anaerobic environment stimulating bacterial decomposers
Autolysis process begins @ enzyme failure due to lack of O 2

Autolysis & cell death

Autolysis & cell death~

In living cells, ATP is constantly being formed via e--transport chain in mitochondria
Process called ‘oxidative phosphorylation’ & requires O 2 in final step of ATP synthesis
W/o^ O 2 (anoxia), process disrupted & cellular activities halt
- shift to fermentation does produce some ATP for a while, but not enough to sustain cellular activities
Autolysis occurs 1st^ in areas of high rates of ATP synthesis; in cells storing hydrolytic enzymes (secretory cells, macrophages)

Ultrastructural correlates of autolysis

2 stages of cellular death~

- Stage 1 (early reversible): ATP synthesis drastically reduced due to anoxia &/or direct damage to mitochondria - cellular activities fail w/o ATP & cells swell due to osmotic imbalance (membrane pumps fail) - anaerobic fermentation produces lactic acid (lowering pH)

Decay slows once reduced to hard tissues: bone, cartilage, mummified tissue
Skeletal remains affected initially by scavengers
- small bones removed, marrow eaten
- larger bones (limbs, skull, etc.) tend to resist destruction more than small bones
- flat bones easily carried away by water currents, wind
Complete decomposition in terrestrial environment
- fossilization can occur (.001 %) in extremely low temps, low O 2 , little/no moisture
Bacteria eventually consumes all collagen (protein in matrix of bone), leaving only inorganic salts
Then interactions w/ soil & water alter the inorganic chemistry of the bones/fragments Chemical weathering & diagenesis~
Calcium phosphate exchange w/ surrounding soils controlled by chemistry of soil & bacteria present
Demineralization of bone is a function of changing ratios of calcium phosphate in bone & soil

Anthropology

Forensic Anthropology

“Bones are the silent witnesses from the dead. They never forget and they

never lie.”

Dr. Clyde Snow, Forensic Anthropologist

Forensic Anthropology~

Application of knowledge of human biology to criminal and civil investigations (of legal matters)
Obtain info from skeleton to answer the following:
- Identification of the deceased
- Establish cause of death
- Establish manner of death
FA consultants contribute to investigations by:
- Determining if remains are human
- Recovery of remains
- Estimating potential PMI & ID of deceased; providing info on cause & manner of death

Questions to Ask About Remains

Questions to ask~

Is it human?
- Typically easy to determine if trained in comparative anatomy
- Depends on completeness & condition of the skeleton
How old is it?
- Knowledge of growth & development, maturation, & degenerative changes of bones
Is it of interest to law enforcement? Recall the most common methods for estimating PMI:
Associative evidence; witness statements; rigor, livor, & algor mortis; stomach contents; entomological info; & anthropological info

Forensic Biology Exam 1 Material, Lecture notes of Forensics

Related documents

Partial preview of the text

Download Forensic Biology Exam 1 Material and more Lecture notes Forensics in PDF only on Docsity!

Exam 1 Lecture Materials

Stages of Decay

Human Decomposition Stages

Stages of decay

Aquatic environments

Postmortem tissue changes

Medical examiner & coroner systems

Coroners:

Definitions of death

Types of Death

Forensic Pathology

Time of death indicators

Autolysis & cell death

Ultrastructural correlates of autolysis

Anthropology

Forensic Anthropology

“Bones are the silent witnesses from the dead. They never forget and they

never lie.”

Dr. Clyde Snow, Forensic Anthropologist

Questions to Ask About Remains