Characteristics of Blood

Lecture 2: The Characteristics of Blood

• The lecture covers the characteristics of blood as part of the Lymphoreticular System - Physiology.

Learning Objectives

• Describe physical characteristics of blood
• Describe the functions of blood
• Describe the principal components of blood

Necessity for a Circulatory System

• Rapidly transports substances over long distances in the body
• Key components include:
• Blood (fluid connective tissue)
• Heart (pump)
• Blood vessels (vascular system)

Blood's Contribution to Homeostasis

• Helps maintain relatively constant conditions internally, such as blood pH
• Transports oxygen, nutrients, hormones, carbon dioxide, nitrogenous wastes
• Regulates pH, body temperature, fluid movement across capillary walls
• Provides defense against microbes and foreign substances through white blood cells, antibodies, interferons, complement

Principal Components of Blood

• Plasma (55%): liquid portion
• 92% water
• 7% proteins
• 1% solutes (excluding proteins)
• Plasma proteins are produced by hepatocytes
• Cellular elements (45%): cells and cell fragments
• Erythrocytes (red blood cells): 99%
• Leukocytes (white blood cells) and platelets (together): 1%, called the Buffy coat
• Hematocrit: percentage of total blood volume occupied by erythrocytes

Packed Cell Volume (PCV)

• Represents 45% of blood and consists of formed elements, including:
• 99% RBCs
• <1% WBCs and platelets
• Determining hematocrit is helpful when diagnosing common blood diseases such as:
• Anemia, lower-than-normal blood volume.
• Polycythemia, higher-than-normal blood volume.

Physical Characteristics of Blood

• Color indicates saturation level of oxygen
• Bright red: oxygen-rich
• Dark red: oxygen-poor
• Hemoglobin, a color-changing pigment, causes these color variations
• More viscous than water, flows more slowly
• Plasma, at 37°C, is about 1.8 times more viscous than water
• The whole blood viscosity (relative to water) = 4.5-5.5 times
• Influenced by plasma proteins and formed elements
• Impacts blood pressure and flow

Blood Temperatures

• Slightly elevated temperature (38°C or 100.4°F) compared to normal body temperature (37°C or 98.6°F)
• Friction and resistance within blood vessels contribute to this higher temperature

Blood pH

• Average pH is 7.4, ranging from 7.35 to 7.45 in healthy individuals
• Slightly more basic (alkaline) than pure water (pH 7.0)
• Numerous buffers contribute to pH regulation

Additional Physical Characteristis of Blood

• Blood constitutes approximately 8% of adult body weight
• Adult males typically have 5 to 6 liters of blood
• Adult females average 4 to 5 liters
• Blood volume in a 70 kg male person is approximately 5.5 L
• Hematocrit calculation: Erythrocyte volume = 0.45 × 5.5 L = 2.5 L
• Plasma volume = Blood volume - Erythrocyte volume = 3.0 L

Blood Osmolarity

• Plasma osmolarity is about 300 mOsmol/L, equal to Normal Saline 0.9% NaCl (isotonic)
• Plasma oncotic pressure helps maintain this

Osmosis

• Solvents move from a region of lower solute concentration to higher solute concentration across a semi-permeable membrane
• Tonicity is the capacity of a solution to modify the fluid volume of cells

Constituents of Plasma

• Whole blood minus cells -92% water -7% plasma proteins -1% other solutes

Other Plasma Constituents: Solutes

• Electrolytes
• Organic nutrients and wastes
• Respiratory gases
• Vitamins

Functions of Plasma Proteins

• Generation of plasma colloid osmotic pressure (oncotic pressure)
• Most capillary walls are relatively impermeable to proteins in plasma
• Plasma proteins exert an osmotic force of about 25 mm Hg across the capillary wall
• Albumin is the most abundant protein in plasma (60% of plasma proteins)
• Buffering function of plasma proteins contributes to 15% of the blood's buffering capacity
• Plasma proteins function as nonspecific carriers for various hormones, solutes, and drugs, including Albumin and Globulins
• Defense: Gamma globulins are antibodies (ϒ Globulins)
• Blood clotting: β Globulins, Fibrinogen & Prothrombin contribute

Functions of Globulins

• α Globulins: Transport proteins
• ϒ Globulins: Defensive proteins, Immunoglobulins, Antibodies
• β Globulins: Coagulation factors

Serum

• Plasma minus clotting proteins
• Lacks the ability to coagulate
• When whole blood clots, the clot is removed, leaving serum, which has no coagulation factors

Blood's Cellular Elements

• Erythrocytes transport oxygen and deliver carbon dioxide to the lungs
• Leukocytes protect against pathogens (neutrophils, basophils, eosinophils, monocytes, lymphocytes)
• Platelets, cell fragments without a nucleus, promote blood clotting in damaged vessels