Forensic Serology: Notes 1 - Structure of Blood

Introduction to Blood in Serology

Overview of Blood

• The focus of this segment is on blood, specifically within the context of serology, which often includes other bodily fluids but will primarily concentrate on blood.

• An average adult human has about ten pints (approximately 5.5 liters) of blood, providing a visual reference for understanding blood volume.

Composition of Blood

• Blood consists of two main components: cells and plasma. Understanding these components is crucial for forensic applications.

Production and Functionality

• Blood cells are produced mainly in the bone marrow located in the pelvis and sometimes in the upper femur; other bones have inactive marrow.

• Bone marrow transplants can lead to unique DNA situations where a recipient's blood DNA may differ from their body DNA due to donor-derived red blood cells.

Types of Blood Cells

Red Blood Cells (Erythrocytes)

• Erythrocytes are vital as they carry oxygen throughout the body; they lack a nucleus to enhance flexibility while navigating through vessels.

• Hemoglobin within red blood cells binds oxygen, facilitating its transport; however, no nuclear DNA can be extracted from them.

Testing Red Blood Cell Volume

• A hematocrit test measures the percentage of red blood cells in total blood volume; males typically have around 45% compared to females who generally have lower counts due to menstruation.

White Blood Cells (Leukocytes)

• Leukocytes are larger than red blood cells and play a critical role in immune defense against infections; they contain nuclei that allow for DNA extraction during testing.

Platelets

• Platelets are cell fragments essential for clotting; they become sticky upon activation by chemicals released during injury, forming barriers that prevent excessive bleeding.

Understanding Blood Components

Overview of Blood Composition

• The blood consists of three main cellular components: red blood cells, white blood cells, and platelets. Additionally, plasma is the liquid portion containing various dissolved substances.

Key Proteins in Plasma

Albumins and Globulins

• Two primary proteins in plasma are albumins and globulins. Despite their structural differences, they perform similar functions within the bloodstream.

• Both albumins and globulins act as buffers to maintain pH levels in the blood, preventing fluctuations that could be harmful.

Transport Functions

• These proteins bind and transport essential substances such as lipids, hormones, vitamins, and metals (e.g., iron), ensuring they are not freely floating but rather securely carried through the bloodstream.

Role in Clotting and Immune Response

• Some albumins and globulins contribute to clotting responses alongside platelets; others function as enzymes or hormones. Notably, antibodies—produced by certain globulins—are crucial for immune defense.

Fibrinogen's Role in Clotting

• The final key protein discussed is fibrinogen. It plays a vital role during clot formation by becoming stringy when activated, helping create a mesh that facilitates scab formation after injury.

• This interaction between sticky platelets and fibrinogen fibers is essential for effective wound healing processes.