Blood Anatomy and Physiology

Classification: Blood is formally considered a specialized type of connective tissue.
Primary Functions:
- Transport: Facilitates the movement of essential substances throughout the body.
- Homeostasis: Assists in maintaining a stable internal environment.

Components: A blood sample includes red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes), and plasma.
Physical Properties:
- Body Weight Contribution: Blood accounts for approximately $8\%$ of total human body weight.
- Volume:
  - Average Adult: $5\,L$ .
  - Average Female: $4-5\,L$ .
  - Average Male: $5-6\,L$ .
- Temperature: The internal temperature of blood is $38^\circ\text{C}$ ( $100.4^\circ\text{F}$ ).
- pH Level: Blood is slightly basic, with a pH range between $7.35$ and $7.45$ .
- Osmolarity: Measured at $0.9\%$ .
- Coloration:
  - Highly Oxygenated: Bright red.
  - Poorly Oxygenated: Dull red.
Hematocrit:
- Definition: The percentage of packed red blood cells in a given blood sample.
- General Average: $45\%$ .
- Female Range: $37-48\%$ .
- Male Range: $45-52\%$ .

Transport:
- Gases: Movement of Oxygen ( $O_2$ ) from the lungs to tissues and Carbon Dioxide ( $CO_2$ ) from tissues to the lungs.
- Nutrients: Delivery of glucose and amino acids.
- Waste Products: Transport of waste from protein metabolism from the tissues to the kidneys for excretion.
- Hormones: Distribution of hormones from endocrine glands to target tissues.
- Enzymes: Transport of enzymes throughout the body.
Regulation:
- Body pH: Regulated via buffers and amino acids which allow for the movement of more positive ( $+$ ) or negative ( $-$ ) ions in and out of solution.
- Body Temperature: Maintenance and distribution of body heat.
- Water Balance: Management of body fluid levels.
- Fluid Loss Prevention: Control of fluid loss through blood clotting proteins.
Protection:
- Microbial Defense: Works alongside the immune response, primarily through the actions of white blood cells.

Plasma ( $55\%$ of Blood Volume):
- Water: Constitutes $90-91\%$ (the vast majority of plasma).
- Proteins: Constitutes $7-8\%$ , much of which are clotting proteins. Specific proteins include:
  - Albumins.
  - Globulins.
  - Fibrinogen.
- Acids and Salts: Constitutes $1-2\%$ . This category includes waste, gases, hormones, glucose, nutrients, and ions.
- General Plasma List: Electrolytes, Water ( $92\%$ ), Proteins ( $7\%$ ), Wastes, Nutrients, Gases (Nitrogen $N_2$ , Oxygen $O_2$ , Carbon Dioxide $CO_2$ ), Vitamins, and Hormones.
Formed Elements ( $45\%$ of Blood Volume):
1. Erythrocytes (Red Blood Cells): Comprise $99\%$ of the formed elements.
2. Thrombocytes (Platelets): Comprise $0.6-1.0\%$ of the formed elements.
3. Leukocytes (White Blood Cells): Comprise < 0.2\% of the formed elements. Types include:
  - Neutrophils: $54-62\%$ .
  - Lymphocytes: $25-33\%$ .
  - Monocytes: $3-9\%$ .
  - Eosinophils: $1-3\%$ .
  - Basophils: < 1\%.
Measurement via Capillary Tube:
- Plasma: Top layer (approx. $55\%$ ).
- "Buffy Coat": Middle layer containing white blood cells and platelets.
- Red Cells: Bottom layer (approx. $45\%$ or Hematocrit = $45$ ).

Physical Dimensions:
- Top View: Appears as a biconcave disc.
- Diameter: $7.5\,\mu\text{m}$ .
- Thickness (Sectional View): $2.0\,\mu\text{m}$ .
Hemoglobin Molecule:
- Composition: Four polypeptide chains.
  - Polypeptide chain ( $\alpha_1$ ).
  - Polypeptide chain ( $\alpha_2$ ).
  - Polypeptide chain ( $\beta_1$ ).
  - Polypeptide chain ( $\beta_2$ ).
- Function: Contains iron-containing heme groups responsible for oxygen binding.

Historical Timeline:
- Karl Landsteiner (c. 1900): Identified different blood types and determined only certain combinations were compatible.
- Dr. Charles Drew (1941): Opened the first blood bank in New York City.
Modern Understanding: There are currently 20 different genes known to contribute to unique blood types and 30 common antigens.
ABO Blood Grouping:
- Antigen (Agglutinogen): A protein located on the red blood cell membrane.
  - Type A: Antigen A present.
  - Type B: Antigen B present.
  - Type AB: Both Antigen A and Antigen B present.
  - Type O: No antigens present.
- Antibodies (Agglutinins): Existing in the plasma to react with specific antigens.
  - Anti-B antibody: Present in Type A blood.
  - Anti-A antibody: Present in Type B blood.
  - Anti-A and Anti-B antibodies: Present in Type O blood.
  - No antibodies: Type AB blood.
- Agglutination: The clumping of red blood cells caused by the reaction between antigens and antibodies.
Genotypes and Phenotypes:
- Type A: Genotypes are homozygous dominant ( $I^AI^A$ ) or heterozygous ( $I^Ai$ ).
- Type B: Genotypes are homozygous dominant ( $I^BI^B$ ) or heterozygous ( $I^Bi$ ).
- Type AB: Genotype is $I^AI^B$ . Considered the Universal Recipient; this is a less common blood type.
- Type O: Genotype is homozygous recessive ( $ii$ ). Considered the Universal Donor; this is the most common blood type.

Rh Factor Origins: Named after the Rhesus monkey, as its blood is similar to human blood. It is caused by a different genetic antigen.
Genetics and Prevalence:
- $Rh^+$ (Dominant): On average, $85\%$ of the population is $Rh^+$ .
- $Rh^-$ (Recessive): On average, $15\%$ of the population is $Rh^-$ .
Erythroblastosis Fetalis (Hemolytic Disease of the Newborn):
- Definition: The breakage of fetal red blood cells due to maternal antibody attack.
- Scenario:
  1. First Pregnancy: An $Rh^-$ mother and an $Rh^+$ father conceive an $Rh^+$ fetus.
  2. Sensitization: During delivery, cells from the $Rh^+$ fetus enter the mother's bloodstream.
  3. Antibody Formation: The mother's immune system becomes sensitized and forms $Rh^+$ antibodies.
  4. Second Pregnancy: If the next fetus is also $Rh^+$ , the maternal antibodies cross the placenta and attack the fetal red blood cells.
- Result: This immune attack may result in miscarriage or severe hemolytic disease.
Treatment: A vaccine called RhoGam was developed in 1968 to prevent sensitization in $Rh^-$ mothers.

University of Arizona (Genes and Blood Type): http://www.biology.arizona.edu/human_bio/problem_sets/blood_types/Intro.html
University of Utah (Blood Types Tutorial): http://learn.genetics.utah.edu/content/begin/traits/blood/