Nature of Blood and Presumptive Tests

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Questions and Answers

What percentage of blood volume is composed of plasma?

60%

55% (correct)

45%

50%

What is the primary function of red blood cells (RBC)?

Aid in blood clotting

Produce antibodies

Carry respiratory gases (correct)

Fight disease

At what percentage of blood loss is irreversible shock (death) likely to occur?

30%

50%

20%

40% (correct)

What is the role of platelets in the blood?

Aid in coagulation Signup and view all the answers

What percentage of total body weight does blood constitute?

8% Signup and view all the answers

What component of blood is primarily responsible for transporting oxygen?

Red blood cells Signup and view all the answers

Which condition leads to blood clotting?

Fibrin traps red blood cells Signup and view all the answers

What is the primary component of the blood's liquid portion?

Water Signup and view all the answers

What blood type is characterized by mixed ancestry and a combination of type A and type B?

Type AB Signup and view all the answers

What does a blue coloration in the Benzidine test indicate?

Presence of peroxidase Signup and view all the answers

Which test is sensitive to very old blood stains and yields a blue coloration?

Guaiacum test Signup and view all the answers

In the Kastle-Meyer test, which substance is initially added to the blood stain?

Ethanol Signup and view all the answers

What is the role of hydrogen peroxide in the Kastle-Meyer test?

It serves as a solvent Signup and view all the answers

Which of the following statements about the Van Deen’s test is true?

It requires hydrogen peroxide to produce results. Signup and view all the answers

What does a violet color in the Kastle-Meyer test imply?

Presence of hemoglobin Signup and view all the answers

What is the main disadvantage of the Guaiacum test?

It can yield false negatives with old stains. Signup and view all the answers

What is the main purpose of a Hemastix test strip?

To conduct a field test for blood Signup and view all the answers

What color results from the luminol test when blood is present?

Bright violet Signup and view all the answers

Which test is characterized by the formation of malachite green?

Leucomalachite green test Signup and view all the answers

What type of crystals are produced in the Takayama test?

Large rhombic salmon-colored crystals Signup and view all the answers

Which test is considered not very sensitive for blood detection?

Leucomalachite green test Signup and view all the answers

What reagent is used in the Hemin crystal test?

Acetic acid Signup and view all the answers

What is a common characteristic of the acetone-Haemin or Wagenhaar test?

Production of small dark dichroic crystals Signup and view all the answers

Which test includes the use of a spray reagent for blood detection?

Luminol test Signup and view all the answers

What is the quantity of semen typically present in a single ejaculation?

1.5 to 3.5 ml Signup and view all the answers

Which method of examination can detect the presence of seminal stains under ultraviolet light?

Ultraviolet examination Signup and view all the answers

What is a limitation of the Florence test for examining semen?

Specimen should not be mixed with blood Signup and view all the answers

What characterizes semen when it is first collected?

Viscid and gelatinous Signup and view all the answers

What effect does enzyme action have on semen after exposure?

Causes it to become more liquid Signup and view all the answers

What crystal shape is associated with the Barberios test?

Rhombic needle Signup and view all the answers

To maintain the integrity of evidence, how should clothing with stains be stored?

Air dried without sunlight and wrapped with paper Signup and view all the answers

In assessing sperm diseases, which terms refer to a lack of sperm production?

Aspermia and Oligospermia Signup and view all the answers

What are the three subfields of forensic entomology?

Urban, Stored-product, and Medico-legal Signup and view all the answers

Which type of forensic entomology deals with pest infestations that may lead to litigation between landlords and tenants?

Urban forensic entomology Signup and view all the answers

How can stored-product forensic entomology be defined?

It deals with insects contaminating commercially distributed foods. Signup and view all the answers

What is the role of medico-legal forensic entomology?

To analyze insect activity related to violent crimes. Signup and view all the answers

What significant contribution to forensic entomology is attributed to Sung Tz’u?

Documentation of the first medico-criminal entomology case. Signup and view all the answers

In forensic investigations, which insects are specifically mentioned as being necrophagous?

Flies and Wasps Signup and view all the answers

What information can forensic entomology provide in murder investigations?

The time of death and location related to insect activity. Signup and view all the answers

What method did Sung Tz’u use to solve the murder case he documented?

He gathered sickles from villagers to attract flies. Signup and view all the answers

Study Notes

Nature of Blood

Blood is a specialized circulating tissue made of cells, enzymes, proteins, and inorganic substances in a fluid medium.
Blood volume constitutes about 8% of body weight: approximately 5-6 liters in males and 4-5 liters in females.
Blood components include:
- Plasma (55%): the fluid portion mainly composed of water, enzymes, and glucose.
- Cells (45%): consist of red blood cells (RBC), white blood cells (WBC), and platelets.
  - RBCs: transport respiratory gases; contain hemoglobin, giving blood its red color.
  - WBCs: responsible for immune defense against diseases.
  - Platelets: cell fragments crucial for blood clotting.
Loss of 40% blood volume can lead to irreversible shock; 1.5 liters loss causes incapacitation.
Clotting occurs when fibrin in plasma traps red blood cells, forming a solid clot separating serum.
Blood type AB indicates mixed ancestry, consisting of A and B types.

Presumptive Tests for Blood

Benzidine Test: Blue coloration indicates the presence of peroxidase enzyme in blood.
Kastle-Meyer Test: Involves ethanol and phenolphthalein; violet color results from alcohol solvent reacting with hemoglobin.
Guaiacum Test: Detects blood through blue coloration; less effective on older stains.
Hemastix: Test strips become color bands when in contact with blood.
Luminol Test: Produces bright blue color under UV light, indicating blood presence.
Leucomalachite Green Test: Oxidation gives peacock blue color; less sensitive than benzidine test.

Microcrystalline Tests

Teichmann Test: Evaporation of salt and acetic acid yields reddish-brown hemin crystals.
Takayama Test: Addition of Takayama reagent results in large rhombic crystals with salmon color.
Acetone-Haemin Test: Formation of small dark dichroic crystals.

Confirmatory Tests for Blood

Stains on clothing should be air-dried, avoiding sunlight, and wrapped in paper for preservation.
Soil exhibits the same care as other samples; store in glass containers or new paint cans, maintaining chain of custody.

Forensic Characterization of Semen

Semen is viscous and gelatinous, becoming more liquid over time due to enzymes.
Normal ejaculation volume ranges 1.5 to 3.5 ml, containing spermatozoa, epithelial cells, choline, and lecithin; slightly alkaline.
The healthy male produces approximately 400 to 500 million sperm per ejaculation.
Sperm conditions include aspermia (absence of sperm) and oligospermia (low sperm count).

Examination of Semen and Seminal Stains

Physical Examination:
- Microscopic examination stains sperm cells for observation under high power.
- Ultraviolet examination reveals bright bluish fluorescence in seminal stains.
Chemical Examination:
- Florence Test: Tests for choline by forming dark brown rhombic crystals; limited by specimen handling and blood contamination.
- Barberios Test: Identifies spermine picrate via slender yellow rhombic needles.

Forensic Entomology

Medico-legal forensic entomology involves insects in crime investigations, including murder, suicide, and physical abuse.
- It assesses insect activity on bodies to estimate time of death (postmortem interval) and location.

History of Forensic Entomology

Sung Tz’u (1235 AD): Early death investigator noted for using insect behavior to solve a murder case.
The case described involved flies being attracted to sickles, leading to a confession.
Importance of necrophagous insects in determining crime scene details was highlighted.

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Description

Explore the essential components of blood, including its volume, composition, and the critical role of blood cells in the body. This quiz also covers key presumptive tests used to detect blood, highlighting their importance in forensic science. Test your knowledge on these crucial topics in biology and medicine!