Ch18 Blood Components

Hematocrit Calculations and Patient Plasma Analysis

• Hematocrit and Component Percentage Calculations:

  • The percentage of red blood cells in a sample is calculated using the formula:     $\text{Hematocrit Percentage} = \frac{\text{Red Blood Cell Volume}}{\text{Total Blood Volume}} \times 100$

  • Patient 1 Analysis:

  • Red blood cell volume calculation: $\frac{41}{100} = 0.41$, which yields $0.41 \times 100 = 41\%$ red blood cells.

  • Red blood cell volume measurement is recorded at approximately $28$ units or $41\%$

  • White blood cell (buffy coat) layer accounts for approximately $1\%$ to $2\%$ (or $2\%$ to $3\%$

  • Total formed elements (red blood cells + white blood cells) equal $41\% + 2\% = 43\%$

  • Plasma volume percentage is calculated as $100\% - 43\% = 57\%$ (or $57.5\%$

  • Patient 2 Analysis:

  • Plasma volume measurement equals $70$ units out of a total volume of $100$

  • Red blood cell percentage is recorded at $28\%$

  • Combined plasma and red blood cell volume equals $70 + 28 = 98$

  • White blood cell (buffy coat) percentage is determined by subtracting the combined total from overall volume: $100 - 98 = 2\%$

  • Patient 3 Analysis:

  • Plasma volume is recorded at $70$ units ($70\%$

  • Red blood cell volume is measured at $28$ units ($28\%$) or $37$ to $47$ units depending on the scale.

  • Buffy coat layer accounts for approximately $2\%$ ($2$ units).

  • White blood cell count calculation: $70 + 28 = 98$, and $100 - 98 = 2\%$ white blood cells.

  • Patient 4 Analysis:

  • Total blood sample volume equals $90$ units (instead of $100$ units).

  • Red blood cell volume equals $50$ units.

  • Red blood cell percentage calculation: $\frac{50}{90} \times 100 = 55.5\%$ (or $55.5\%$

  • Buffy coat (white blood cell) layer is slightly larger than in other samples, measured at $3$ units ($3\%$

  • Total combined formed elements equal $50 + 3 = 53$ units.

  • Plasma volume equals total volume minus formed elements: $90 - 53 = 37$ units (or $47$ units depending on total plasma reading).

  • White blood cells represent the smallest overall percentage among all blood components.

Fluid Connective Tissue Properties of Blood

• Classification:

  • Blood is classified structurally and functionally as a fluid connective tissue.

  • Unlike standard solid connective tissues, blood features a liquid/fluid matrix rather than a solid ground substance.

  • Blood lacks stationary, anchoring structural fibers such as long collagen or reticular fiber networks that anchor cells in fixed spatial positions.

• Plasma Proteins:

  • Instead of fixed structural fibers, blood plasma contains specialized colloid proteins that float freely within the circulating fluid matrix.

  • Key blood plasma proteins include:

  • Albumin: A major soluble protein dissolved in blood plasma responsible for maintaining osmotic pressure and transport.

  • Fibrinogen: A soluble plasma protein essential for blood clotting mechanisms.

  • Immunoglobulins: Specialized antibodies and autoantibodies circulating freely in the fluid matrix to provide immune protection.

Formed Elements of Blood

• Definition of Formed Elements:

  • The cellular components suspended in blood plasma are collectively termed formed elements rather than simple cells because they include cell fragments alongside true cells.

• Erythrocytes (Red Blood Cells):

  • The red-pigmented formed elements responsible for gas transport.

  • Derived from the Greek prefix erythro-, which denotes a red color or pigment.

• Leukocytes (White Blood Cells):

  • The pale or clear formed elements responsible for immune defense.

  • Derived from the Greek prefix leuko-, meaning pale, clear, or white.

  • Etymological and Ornithological Example:

  • The scientific name for the bald eagle contains the term Leukocephalus, translating directly to "white head" due to the bird's distinctive white head plumage.

  • Bird identification tools such as the Merlin Bird App can detect and differentiate up to $10$ distinct bird species singing simultaneously from audio recordings or photograph inputs.

• Platelets (Thrombocytes):

  • Platelets are non-cellular formed elements consisting of membrane-bound cytoplasmic fragments rather than intact cells.

  • Analogy: Functionally analogous to tearing off a tiny piece of a paper towel to place over a small nick or bleed caused by shaving.

  • Cellular Origin:

  • Platelets originate from massive bone marrow precursor cells called megakaryocytes.

  • Megakaryocytes reside adjacent to blood capillaries and extend cellular projections (analogous to paper towel or toilet paper rolls) directly into the capillary lumen.

  • Small cytoplasmic fragments are pinched off or pulled away from these projections directly into the circulating blood stream as needed.

Physical Characteristics and Composition of Blood Plasma

• Chemical Composition of Plasma:

  • Water Content: Liquid plasma is composed of approximately $92\%$ water.

  • Plasma Proteins: Soluble proteins (albumin, fibrinogen, immunoglobulins) floating in solution.

  • Electrolytes: Charged ions featuring either a positive charge ($+$) or negative charge ($-$).

  • Hormones: Endocrine signaling molecules circulating throughout the cardiovascular system.

  • Dissolved Gases: Includes vital dissolved gases such as Oxygen ($O_2$), Nitrogen ($N_2$), and Carbon Dioxide ($CO_2$).

  • Nutrients and Wastes: Beneficial organic nutrients alongside metabolic waste products destined for excretion.

  • Analogy: Plasma operates as a biological river transporting dissolved gases, nutrients, proteins, and chemical messages.

Physical Characteristics of Whole Blood

• Color Saturation:

  • Human blood is red, but its precise shade indicates its oxygenation status.

  • Bright Red: Indicates high oxygen content (typically represented as red vessels/arteries in anatomical diagrams and textbooks).

  • Dark Red: Indicates low oxygen content (typically represented as blue or purple vessels/veins in anatomical models and textbooks).

• Total Volume:

  • The average adult human body contains approximately $5\,L$ of blood.

  • Biological males generally possess a higher total blood volume than females.

  • Higher male blood volume and red blood cell counts are driven by higher levels of the hormone testosterone, which promotes greater muscle mass and enhanced erythropoiesis.

• Viscosity:

  • Viscosity refers to the thickness, resistance to flow, and adhesive "cling" of blood.

  • Blood viscosity is influenced by testosterone levels and total circulating cell counts, making male blood slightly more viscous on average.

Microscopic Laboratory Examination Procedures

• Microscope Settings and Procedure:

  • Laboratory slides are pre-prepared blood smears (students do not draw or smear fresh blood).

  • Objective lens settings: Toggle exclusively between low-power magnification settings (scanning red objective and low-power yellow objective).

  • High-power ($400\times$ magnification) and oil immersion lenses are strictly prohibited to prevent damage without oil application.

  • Cell estimation technique: Starting at step $3$ of the procedure, cell quantities across $3$ distinct fields of view are estimated rather than individually counted (avoiding exact counts like $473$ or $475$ cells).

  • Comparative stations include an endocrine system reference slide displaying thyroid follicle histology to compare colloid plasma appearance with circulating blood plasma.

Pathophysiology of Sickle Cell Anemia

• Microscopic Observations of Sickle Cell Blood Smears:

  • Identification of formed elements: Large leukocytes with visible nuclei (often located in slide corners), erythrocytes, and tiny extracellular platelets.

  • Predominant cell type: Erythrocytes remain the most numerous overall cell type, while leukocytes represent the largest individual cells.

  • Pathological Deviations Identified:

  • Markedly elevated platelet count relative to normal baseline smears.

  • Abnormally shaped erythrocytes: Red blood cells appear as elongated, crescent-shaped slivers rather than standard biconcave discs.

  • Decreased erythrocyte density: Overall concentration of red blood cells is sparse.

• Clinical Characteristics of Sickle Cell Anemia:

  • Defined as a combination of low red blood cell count (anemia) and abnormal sickled erythrocyte morphology.

  • Complications and Symptoms:

  • Reduced oxygen transport capacity across peripheral tissues.

  • Markedly increased risk of thrombosis, blood clotting, and severe vascular occlusion.

  • Misshapen sliver-like cells fail to roll smoothly through small vessels, causing vascular jams and blockages.

  • Associated clinical signs include severe pain crises, bouts of vomiting, and systemic organ stress.

  • Therapeutic Interventions:

  • Patients frequently require periodic blood transfusions (e.g., administered every $24\,\text{months}$ or as clinically indicated) to replenish normal functional erythrocytes and reduce vaso-occlusive events.

Laboratory Cleanup and Study Protocol

• Study Resources:

  • Practice activities are provided on page $25$ and surrounding pre-lab sections, featuring image-based exercises with typed or written answer fields for self-testing.

• Laboratory Sanitation Rules:

  • Workstations must be thoroughly cleaned and restored to pristine condition prior to departure.

  • All solid debris and laboratory scraps present on table surfaces must be wiped onto the floor so that tabletop working surfaces remain clean and clear.