Biology Chapter: Blood Functions and Composition

Blood

• Blood is considered to be a specialized type of connective tissue
• Blood contains blood cells and plasma
• Blood plasma is the extracellular matrix of blood

Blood Functions

• Transports nutrients and gases around the body
• Transports waste products to organs and tissues for recycling or excretion
• Transports hormones around the body
• Transports immune cells throughout the body
• Helps regulate body temperature
• Maintains acid-base and osmotic balance

Blood Volume and Movement

• The average adult has approximately 5-6 liters of blood
• Blood is propelled through the circulatory system by rhythmic contractions of the heart
• Blood flows unidirectionally throughout the closed circulatory system

Blood Composition

• Anticoagulants prevent blood from clotting
• Centrifuging blood with anticoagulants separates it into layers
• Blood is a heterogeneous mixture

Erythrocytes

• Erythrocytes are also known as red blood cells (RBCs)
• Erythrocytes are biconcave discs containing hemoglobin
• Erythrocytes have a low number of enzymes
• Erythrocytes contain a plasma membrane that is critical for gas transport and maintenance
• Erythrocytes stain pink/red (acidophilia) due to the high content of hemoglobin (basic protein)
• The central region of the erythrocyte appears pale due to its biconcave shape
• The pale staining erythrocytes are called "Normochromic RBCs"
• Erythrocytes consist of a meshwork of proteins (spectrin and ankyrin) that form a cytoskeleton
• The submembranous meshwork stabilizes the membrane, maintains the cell shape, and provides elasticity for passage through capillaries
• Erythrocytes are called "Normocytic RBCs"
• Erythrocytes are 6-9µm (7.5µm) in diameter
• Erythrocytes are 2.6µm thick at the rim, but only 0.75µm thick in the center
• Erythrocytes can be used as a reference for cell size

Erythrocyte Abnormalities

• Mutations in membrane proteins like spectrin and ankyrin can cause abnormal erythrocyte shapes

Erythrocyte Membranes

• Erythrocytes are covered in a glycocalyx (a covering composed of glycoproteins and glycolipids)

Erythrocyte Appearance

• Erythrocytes appear rounded and non-nucleated when viewed under a light microscope
• Erythrocytes are stained with Leishman stain
• There is no nucleus present within the cell

Leukocytes

• Leukocytes are also known as white blood cells (WBCs)
• Leukocytes are divided into granulocytes and agranulocytes
• Granulocytes have cytoplasmic granules
• Granulocytes contain azurophilic granules (lysosomes) and specific/secondary granules
• Agranulocytes lack cytoplasmic granules
• The three main types of granulocytes:
  • Neutrophils
  • Eosinophils
  • Basophils

Neutrophils

• Neutrophils are the most common leukocyte
• Neutrophils have a multi-lobed nucleus with 2-5 lobes connected by strings of nuclear material
• Neutrophils have a light pink cytoplasm
• Neutrophils cytoplasm stains equally red (acidic) and blue (basic)
• Neutrophils are specialized for destroying bacterial invasions
• Neutrophils respond to acute infections
• Neutrophils are short-lived with a 6-8 hour half-life in blood and a 1-4 day lifespan in connective tissues
• Neutrophils die by apoptosis
• Neutrophils are the first WBCs to leave the blood in large numbers when there is an infection

Basophils

• Basophils stain blue in color

Eosinophils

• Eosinophils are stained red/orange using eosin
• Eosinophils are involved with allergies

MHC

• MHC (major histocompatibility complex)
• MHC-I molecules are present on all of the cells in the body except for red blood cells
• MHC-I molecules bind to viral peptides or mutant peptides
• MHC-I molecules promote cytotoxic T cells in response to the viral peptide
• MHC-I molecules promote cytotoxic T cells in response to the mutant peptides
• MHC-1 molecule binds to a viral peptide fragment produced by a virus-infected cell
• MHC-1 molecule binds to a mutant peptide fragment produced by a cancerous cell

T cells

• Cytotoxic CD8 T cells kill infected, transplanted or neoplastic cells
• The antigen of virus infected or transplanted cells binds to MHC-I molecules
• The antigen of neoplastic cells binds to MHC-I molecules

General Histology

• Chromatin
  • Euchromatin is extended and active
  • Heterochromatin is condensed and inactive
• Nucleolus
  • The nucleolus is a spherical mass without a membrane
  • The nucleolus is usually present in a single copy
  • Function: formation and assembly of rRNA for protein synthesis
• H&E staining
  • The nucleus usually stains blue (basophilic) using H&E
  • An active nucleus stains lightly basophilic
  • An inactive nucleus stains deeply basophilic and appears smaller
  • The cytoplasm typically stains pink/red (acidophilic) in H&E stain
  • Ribosomes cause basophilia in the cytoplasm

Connective Tissues

• Dense irregular connective tissue
  • Randomly interwoven collagen fiber bundles
  • Orientation provides resistance to stress from every direction
  • Found in dermis of skin, organ capsules, and submucosa
• Dense regular connective tissue
  • Parallel bundles of collagen fibers
  • Contains few fibrocytes aligned with the fibers and a small amount of ground substance