Blood and Blood Components

Blood Composition

Blood consists of liquid plasma and formed elements.
Formed elements include:
- Erythrocytes (red blood cells or RBCs)
- Leukocytes (white blood cells or WBCs)
- Platelets

Refers to the percentage of packed red blood cells in the total blood volume.
Determined by centrifuging blood, which separates it into three phases:
- Plasma: Approximately 55% of whole blood.
- Buffy coat: Less than 1% of whole blood, containing leukocytes (white blood cells) and platelets.
- Erythrocytes: Approximately 45% of whole blood in males (females tend to have a slightly lower hematocrit, between 40-42%).

Color varies based on oxygen binding to hemoglobin:
- Scarlet bright red: Oxygenated blood (arterial blood).
- Darker purplish or dark red: Deoxygenated blood (venous blood).
pH ranges from 7.35 to 7.45:
- 7.35: More acidic (associated with venous blood due to CO_2 conversion to bicarbonate).
- 7.45: More alkaline (associated with arterial blood due to less CO_2).
Temperature is about 38 degrees Celsius, slightly higher than normal body temperature.
Blood accounts for about 8% of overall body weight.
Average volume is 5-6 liters for males and 4-5 liters for females.

Least dense component of blood, approximately 90% water.
Remaining 10% consists of:
- Proteins (about 7%): Albumins, globulins, clotting proteins, hormones.
- Other solutes (about 3%): Organics, electrolytes, gases.
Table 17.1 from textbook provides a detailed breakdown.

Account for 6-8% of plasma volume.
Contribute to osmotic (oncotic) pressure, maintaining water balance.
Albumin: 60% of plasma proteins, made by the liver, contributes to osmotic pressure and carries fatty acids and hormones.
Globulins: 36% of plasma proteins.
- Alpha and beta globulins: Bind and transport hydrophobic substances like lipids, metal ions, and fat-soluble vitamins.
- Gamma globulins (antibodies or immunoglobulins): Produced by plasma cells (activated B cells).
Fibrinogen: A precursor to fibrin, important for blood clotting.

Non-protein nitrogenous substances: Byproducts of cellular metabolism, including urea, uric acid, creatine, and ammonia salts.
Nutrients: Carbohydrates, amino acids, fatty acids, triglycerides, cholesterol, and vitamins.
Respiratory gases: Oxygen and carbon dioxide.
Hormones: Steroid, thyroid, and plasma protein hormones.

A blood smear stained with Wright's stain, the acidic red color stains basic parts while the basic purple color stains acidic parts. often shows donut-like erythrocytes (RBCs) with a white center (due to being enucleated) and fragmented platelets (thrombocytes).
Also contains monocytes (precursor to macrophages with kidney-shaped nuclei), lymphocytes (precursor to T cells or B cells with round nuclei), and neutrophils (multi-lobed nucleus).

Biconcave disc-like structures without a nucleus (anucleated).
Contain very few organelles.
Biconcave shape increases surface area for gas exchange.
Filled with hemoglobin (Hb), which transports oxygen and accounts for about 97% of the dry weight of RBCs.
The biconcave discs are maintained by a protein called spectrin and allow the cell to twist and squeeze throughout capillaries.
Produce ATP anaerobically.

Composed of four heme groups, each containing iron that binds oxygen.
Also contains four polypeptide chains (globins): two alpha subunits and two beta subunits.
Each hemoglobin molecule can carry four oxygen molecules.

In adults, primarily occurs in the axial skeleton and distal long bones within the red bone marrow.
Hematopoiesis: Generation of red blood cells from precursor cells.
In early embryo development, the yolk sac is the primary source.
Later, the liver and spleen become major sources.
Near birth and into adulthood, the skeleton (axial skeleton) becomes the primary source.

Starts with a hemocytoblast (stem cell).
The hemocytoblast turns into a proerythroblast (committed cell).
The Proerythroblasts then goes through 3 phases: ribosome generation, hemoglobin accumulation, and specialization.
It then transitions to an early erythroblast, then a late erythroblast, and finally a normoblast.
- Phase one: Ribosome Generation
- Phase two: Hemoglobin accumulation.
- Phase three: Ejection of the nucleus.
The end result is a Reticulocyte (no nucleus, a few organelles) which matures to form the erythrocyte.

The body is capable of producing 2-3 million RBCs per second.
Requires amino acids, lipids, and carbohydrates.
Factors such as iron, vitamin B12, and folic acid (vitamin B9) are needed.
Iron is stored in:
- Hemoglobin (65% of body’s iron).
- Liver, spleen, and bone marrow.
Iron is stabilized by:
- Ferritin and hemosiderin (intracellular).
- Transferrin (in bloodstream).
Erythropoietin (EPO): Secreted by the kidneys in response to low oxygen levels, stimulating red bone marrow to produce more RBCs.
RBCs have a lifespan of about 120 days.
Aged and damaged RBCs are taken up by macrophages in the liver, spleen, and bone marrow.
- Hemoglobin is broken down into heme and globin.
- Iron is bound to ferritin and hemosiderin.
- Heme is converted to bilirubin, secreted in urine.
- Globin is broken down into amino acids, released into the bloodstream.
- Bilirubin can be converted to stercobilin, which gives feces its brown color.
- Iron is transported by transferrin to bone marrow for reuse.

Iron deficiency anemia: Lack of iron in diet or due to blood loss.
Pernicious anemia: Deficiency of vitamin B12 due to lack of intrinsic factor (produced by parietal cells in the stomach).

Sickle cell anemia: Point mutation in the beta globin gene, substituting valine for glutamate at position six.
- Mutant hemoglobin is referred to as Hemoglobin S (HBS).
- Causes RBCs to take on a sickle shape, reducing their lifespan to about 20 days.

Normal hemoglobin (hemoglobin A) maintains cell shape in both oxygenated (arterial) and deoxygenated (venous) blood.
In sickle cell anemia, RBCs with hemoglobin S take on a normal shape when oxygenated but sickle when deoxygenated.
This sickling reduces elasticity and flexibility and causes aggregation of hemoglobin, dramatically decreasing their life expectancy.
Life Expectancy of Sickle Cells \approx 20 days
Life Expectancy of Regular Erythrocytes \approx 120 days

Refers to an increased proportion of red blood cells in blood (increased hematocrit).

There are two subtypes of Absolute Polycythemia, Primary and Secondary
Primary polycythemia (polycythemia vera): Increased red blood cell production in the bone marrow.
Secondary polycythemia: Associated with hormonal productions (elevated EPO) or blood doping (artificial increase in EPO).