Comprehensive Introduction to Blood Composition, Functions, and Characteristics

Lecture Roadmap and Resource Materials

• Primary Topics Covered:

  • Composition of blood, including specific numbers and percentages.
  • Terminology and processes involved in manufacturing the different formed elements of the blood.
  • Hormones involved in the process of ‐hematoleases.‐
  • Special clinical topics: Blood doping, anemia, and blood types.
  • Hemostasis: The process of stopping bleeding, which consists of three distinct stages or phases.

• Required Resources:

  • Textbook: McGraw Hill, Chapter 18, Cardiovascular System. The instructor emphasizes that certain information (especially regarding hormones) is found in the textbook rather than the PowerPoint slides.
  • Reference Pages: Scanned page $709$ (computer page $204$). Note: Scanned page numbers are the preferred reference as they remain consistent.
  • PowerPoint: Located in common Unit 1: Blood → Readings and Multimedia → Cardiovascular System → Blood PowerPoint presentation.
  • Chapter Summary: Students are explicitly encouraged to read the chapter summaries at the end of the textbook for efficient review.

General Functions of Blood

• Transportation:

  • Gas and Nutrient Transport: Blood carries inhaled oxygen ($O_2$) and nutrients from digested food to all body tissues for growth and repair.
  • Waste Removal: Occurs at the tissue level. Once tissues use oxygen and nutrients, they generate waste. Since tissues cannot directly eliminate waste, they deposit it back into the blood on the venous side.
  • Elimination Sites: The blood transports waste to specific organs for removal:
    • Solids: Excreted as feces.
    • Liquids/Gases: Excreted as urine, sweat, or exhaled breath.

• Regulation:

  • Temperature Regulation: Blood absorbs heat from body cells, particularly muscles, which generate heat as a byproduct of use.
  • Temperature Gradient: The blood's temperature is approximately $1$ to $2$ degrees higher than general body temperature. If an oral temperature is $98^{\circ}F$, blood temperature is typically $100^{\circ}F$. In Celsius, if body temp is $37^{\circ}C$, blood is $38^{\circ}C$.
  • pH Balance: Blood maintains the body's acid-base balance. The pH scale ranges from $1$ to $14$, with $7$ being neutral. Numbers $1-6$ are acidic; $8-14$ are alkaline (basic).
  • Mechanism: Blood absorbs acids (hydrogen ions) and bases from body cells to maintain internal stability.
  • Fluid Balance: Blood regulates the level of fluids and dissolved substances in the body.

• Protection:

  • Immune Response: Blood contains a category of cells known as leukocytes involved in the immune response to fight infection.
  • Clotting: Blood contains elements that prevent excessive blood loss through clotting.

Physical Characteristics of Blood

• Color:

  • All blood is red. There is no blue blood in the human body.
  • Oxygen-Rich (Oxygenated) Blood: Bright red hue. This is typically blood that has just left the lungs or is found in arteries.
  • Oxygen-Poor (Deoxygenated) Blood: Darker red hue. Found in veins leading back to the lungs.
  • The Blue Appearance of Veins: This is an optical illusion caused by looking through subcutaneous fat (yellowish) and skin (brownish), which filters the light.

• Volume:

  • The average adult blood volume is approximately $5\,L$.
  • The general range is $4\,L$ to $6\,L$.
  • Correlation with Body Size: Volume is relative to size. A $110\,lb$ individual will have significantly less blood than a $310\,lb$ individual. This is why lighter individuals may be deferred from blood donation, as removing $0.5\,L$ (one pint) represents a larger percentage of their total volume compared to a larger person.

• Viscosity:

  • Definition: The thickness or resistance to flow of a liquid.
  • Blood vs. Water: Blood is more viscous than water because of the substances (solutes) dissolved in it.
  • Concentration: The more solute (solid) dissolved in a solvent (liquid), the more viscous and dense the solution becomes.

• Essential Normal Values:

  • Average Volume: $5\,L$.
  • Temperature: $38^{\circ}C$ or $100.4^{\circ}F$.
  • pH Range: $7.35$ to $7.45$.
  • Note: Blood is slightly alkaline because its pH is above $7.0$.

Composition of Whole Blood

• Whole Blood ($100\%$) Breakdown:

  • Plasma ($55\% \text{ of whole blood}$): The liquid portion. It is composed of approximately $90\%$ to $92\%$ water, with the remainder being dissolved substances.
  • Formed Elements ($45\% \text{ of whole blood}$): The solid portion consisting of cells and cell fragments.

• Sub-components of Formed Elements ($45\%$ total):

  • Erythrocytes (Red Blood Cells or RBCs): Make up $44\%$ of the total $45\%$ of formed elements. They are the most numerous.
  • Buffy Coat ($\le 1\% \text{ of whole blood}$): A thin layer composed of Leukocytes (White Blood Cells) and Platelets.

• Separation via Centrifuge:

  • When whole blood is placed in a centrifuge and spun, heavier solid components settle at the bottom while the liquid plasma stays at the top. A gel separator is often used in lab tubes to maintain this division.

Detailed Study of Formed Elements

• Erythrocytes (Red Blood Cells):

  • Medical Terminology: "Erythro" means red; "cyte" means cell.
  • Protein Content: Contain hemoglobin, the protein that gives blood its red color and allows the cell to carry oxygen ($O_2$).
  • Anatomy of Mature RBCs:
    • Shape: Biconcave (shaped like a dumbbell with two concave sides).
    • Anucleate: Mature RBCs lose their nucleus to make more room for transporting gases.
  • Lifespan: Approximately $120$ days ($4$ months).
  • Recycling: Old RBCs are destroyed or recycled in the liver and the spleen.

• Leukocytes (White Blood Cells):

  • Medical Terminology: "Leuco" means white; "cyte" means cell.
  • Function: Immunity and protection against foreign invaders (bacteria, viruses, fungi, dust, pollen).
  • Types: There are five distinct types of leukocytes, categorized by their different nuclei and functions (e.g., neutrophils, monocytes, lymphocytes).

• Thrombocytes (Platelets):

  • Medical Terminology: "Thrombus" means clot. These are named for their function in hemostasis.
  • Nature of Platelets: They are not actual cells but cell fragments. They are broken-off pieces of a very large cell called a "megapariosite" (megakaryocyte).
  • Function: Blood clotting.

Clinical Applications and Diagnostic Tests

• Comprehensive Metabolic Panel (CMP): Used to test substances dissolved in plasma to determine organ health:

  • Liver Function: Measured by enzymes like AST and ALT. Elevated levels indicate liver cell damage.
  • Kidney Function: Measured via Creatinine and Blood Urea Nitrogen (BUN) levels. High levels indicate the kidneys are not filtering waste properly.

• Hemoglobin A1C Test:

  • Rationale: Glucose molecules stick to the RBC cell membrane and remain there for the duration of the cell’s life.
  • Purpose: Because RBCs live for $120$ days, this test provides an average of a patient's blood sugar levels over the past three to four months, rather than a snapshot like a finger-prick test.

• Blood Smears:

  • A diagnostic technique where blood is spread thinly on a slide, dyed, and viewed under a microscope. Normal smears show numerous round, red erythrocytes, larger white leukocytes with stained nuclei, and tiny dot-like platelets.

Questions & Discussion

• Audience Question regarding Sickle Cell and Cancers: The instructor confirmed that any questions regarding blood-related diseases, such as sickle cell or cancers, as well as the effects of menstrual periods on blood counts, are welcome as they make the discussion relevant.
• Audience Question regarding Plasma Donation: Do donation requirements for plasma also depend on blood volume, similar to whole blood?
  • Response: Yes, because plasma is mostly water. If a person is dehydrated, their veins may be flat, making draws difficult. Severely dehydrated states can also cause abnormal blood test values, leading to a false reading of illness when the primary issue is simply low fluid volume.
• Audience Question regarding RBC Recycling: Do we need to know where RBCs are destroyed?
  • Response: Yes, they are destroyed and recycled in the liver and spleen. This will be covered further in the PowerPoint.
• Audience Question regarding Leukocyte Variety: Why are there so many types of white blood cells?
  • Response: Because the body must fight various types of invaders, including living biological agents (bacteria, viruses, fungi) and non-living irritants (dust, pollen). Different cells specialize in different responses.