4. Formed Elements

Formed Elements of Blood

Formed elements constitute approximately 45% of blood volume, while plasma makes up the remaining 55%.
Formed elements include leukocytes (white blood cells), erythrocytes (red blood cells), and platelets.
The term "formed elements" is used because not all components are complete cells with a nucleus.

Leukocytes are complete cells with a cell membrane, membrane-bound organelles, and a nucleus containing genetic material.
Make up less than 1% of total blood volume.
Crucial for immune defense against infections and foreign bodies.
Typically reside in the bloodstream until needed at a site of infection.
Exhibit leukocyte rolling, adhering to blood vessel walls and migrating into tissues.
Categorized as granulocytes or agranulocytes.
- Granulocytes: Contain visible granules (e.g., basophils, eosinophils, neutrophils).
- Agranulocytes: Lack visible granules (e.g., lymphocytes, monocytes).
Neutrophils are phagocytic.
Macrophages and monocytes also exhibit phagocytic activity.
Lymphocytes are not phagocytic; they include B cells, T cells, and natural killer cells.

Erythrocytes lack a nucleus and other organelles.
Primary role is to transport respiratory gases (oxygen and carbon dioxide).
Genetic males typically have a higher erythrocyte count (4.5 to 6.5 x 10^{12} per liter) due to higher oxygen demand, compared to genetic females.
Erythrocytes are packed with hemoglobin, a protein composed of four subunits, each containing iron.
Hemoglobin consists of globin protein and heme-iron.

Biconcave Disc Shape: Enhances surface area for gas exchange and allows flexibility to pass through capillaries.
ATP Production: Generate ATP anaerobically in the cytoplasm.
Limited Lifespan: Lack the ability to synthesize new proteins, leading to a lifespan of approximately 100-120 days.

Single red cell travels about 1,100 kilometers through the circulatory system, circulating through the heart over 300,000 times.
Aged erythrocytes undergo phagocytosis and are broken down in the liver.
Hemoglobin is processed into heme and globin components.
Globin is broken down into amino acids for recycling.
Iron from heme is stored in the spleen.
Bilirubin is processed into bile and excreted.
Requires spleen, gallbladder, and liver to work, to create new red blood cells

Erythrocytes can aggregate, forming stacks known as Rouleaux, indicating potential disease.
Rouleaux formation can occur outside the body as well.
The rate of sedimentation and stacking can indicate the presence of disease.

Occurs in the red bone marrow.
Hematopoietic stem cells differentiate into myeloid lineage cells, specifically red blood cells.
Developmental pathway takes about seven days to reach the reticulocyte stage.
Reticulocytes, formed after ejecting the nucleus, mature into erythrocytes in the bloodstream.
Requires ribosomes in order to make globin proteins, in order to do that a nucleus is needed for transcription.

Production rate should match destruction rate.
Kidneys monitor oxygen levels and release erythropoietin (EPO) in response to hypoxia.
EPO stimulates red bone marrow to increase erythrocyte production from 2.2 to 3 million per second to 30 million per second.
Increased production has a lag time of about one week.
Too many red blood cells leads to needing to decrease them, create a flowchart for that feedback.