1.3 - Formed Elements Part I

Formed elements

Erythrocytes, leukocytes, and platelets (thrombocytes); leukocytes are the only true cells with a nucleus and organelles, erythrocytes lack a nucleus and organelles, and platelets are cell fragments, not real cells

Erythrocyte

Commonly known as a red blood cell (RBC); by far the most common formed element; primary functions are to pick up inhaled oxygen from the lungs and transport it to tissues, and pick up some carbon dioxide waste at the tissues for transport to the lungs

Reticulocyte

An immature erythrocyte, present during the first day or two in circulation, that still typically contains remnants of organelles

Mature erythrocyte structure

Lacks mitochondria (relies on anaerobic respiration so it doesn't use the oxygen it's transporting) and lacks endoplasmic reticula (does not synthesize proteins); contains structural proteins that maintain shape and allow it to change shape to squeeze through capillaries

Biconcave disk shape

The shape of erythrocytes, plump at the periphery and very thin in the center; allows more interior space for hemoglobin and provides greater surface area for gas exchange relative to volume than a sphere of similar diameter

Rouleau

Stacking of erythrocytes like a roll of coins, which can occur in wider blood vessels

Red blood cells (Table 1.2)

Average abundance of 5.2 million per µL (range 4.2-6.3 million); appear as flattened, circular, red cells with no nucleus, mitochondria, or ribosomes; transport oxygen from lungs to tissues and carbon dioxide from tissues to lungs; remain in bloodstream with a 120-day life expectancy; amino acids and iron are recycled; produced in red bone marrow

Hemoglobin

A large molecule inside erythrocytes made up of proteins and iron; consists of four folded globin chains (alpha 1, alpha 2, beta 1, beta 2), each bound to a heme molecule containing an iron ion (Fe2+); each hemoglobin molecule can transport four oxygen molecules

Globin

The protein portion of hemoglobin, consisting of four folded chains designated alpha 1 and 2, and beta 1 and 2

Heme

A red pigment molecule bound to each globin chain in hemoglobin; contains an iron ion (Fe2+) that binds to one oxygen molecule

Oxyhemoglobin

Bright red, oxygenated hemoglobin formed when oxygen binds to the iron ions in the lungs

Deoxyhemoglobin

Darker red hemoglobin formed when hemoglobin releases oxygen molecules at the body tissues

Carbaminohemoglobin

The molecule formed when about 25 percent of dissolved carbon dioxide binds to the amino acids in hemoglobin (the remaining ~75 percent of CO2 dissolves in plasma or forms bicarbonate ion)

Percent saturation ("percent sat")

Indicates the proportion of hemoglobin sites carrying oxygen in the blood; measured by a pulse oximeter using red and infrared light; normal readings are 95-100%

Hypoxemia

Low blood oxygen levels, indicated by percent saturation readings below the normal 95-100% range

Anemia

A general condition of deficient RBCs or hemoglobin; more than 400 types exist; broken into three major groups: insufficient erythrocytes, low hemoglobin count, and abnormal hemoglobin

Mean corpuscular volume (MCV)

A test that measures the size of RBCs; normal-sized cells are normocytic, smaller-than-normal cells are microcytic, larger-than-normal cells are macrocytic

Mean corpuscular hemoglobin (MCH)

A test that measures the amount of hemoglobin in RBCs; normal amount is normochromic, low MCH causes hypochromic (less coloring) cells, high MCH causes hyperchromic (increased color) cells

Hemorrhagic anemia

Anemia caused by major blood loss, which may be acute (wound or trauma) or chronic (ulcers, hemorrhoids, gastritis, GI cancers, excessive menstruation, or blood loss during childbirth)

Hemolytic anemia

Anemia that occurs when RBCs rupture prematurely and RBC production does not adequately replace their destruction

Aplastic anemia

Anemia caused by deficient numbers of RBC stem cells; often inherited or triggered by radiation, medication, chemotherapy, or infection

Iron deficiency anemia

The most common type of anemia; results when insufficient iron is available to produce enough heme, impairing hemoglobin synthesis and producing microcytic, hypochromic RBCs; especially common in teens, children, vegans, and vegetarians; may also occur secondary to hemorrhagic anemia

Pernicious anemia

Anemia caused by insufficient vitamin B12, which impairs DNA synthesis and leads to inefficient cell division, producing macrocytic (larger than normal) but normochromic RBCs

Thalassemia

An inherited condition where RBC maturation does not proceed normally, typically due to an absent or faulty globin chain that does not bind properly to oxygen; RBCs may be thinner, more delicate, and shorter-lived than normal

Sickle cell anemia

A genetic disorder caused by an abnormal hemoglobin from a single amino acid substitution; delivers less oxygen to tissues and causes erythrocytes to assume a sickle/crescent shape at low oxygen concentrations, which can lodge in narrow capillaries and cause painful joints, delayed growth, blindness, and strokes; particularly found in individuals of African descent

Polycythemia

An elevated RBC count, detected via elevated hematocrit; can occur transiently with dehydration, chronically but normally in people at high altitudes, or from polycythemia vera

Polycythemia vera

A type of bone marrow cancer that causes excessive production of immature erythrocytes; can dangerously elevate blood viscosity, raising blood pressure and making it harder for the heart to pump blood

Erythrocyte production rate

Erythrocytes are produced in red bone marrow at a rate of more than 2 million cells per second, requiring nutrients (glucose, lipids, amino acids) and trace elements (iron, copper, zinc, B vitamins)

Erythrocyte lifespan

Erythrocytes live up to 120 days after release into circulation

Hemolysis

The rupture of RBCs in the bloodstream

Macrophages (in RBC life cycle)

Phagocytic cells located primarily in the bone marrow, liver, and spleen that monitor circulating RBCs and remove worn-out cells before they rupture

Globin recycling

Globin, the protein portion of hemoglobin, is broken down into amino acids that can be sent back to the bone marrow for production of new erythrocytes; unphagocytized hemoglobin breaks down in circulation, releasing alpha and beta chains removed by the kidneys

Ferritin

A form in which iron from heme may be stored in the liver or spleen

Transferrin

The protein that carries iron through the bloodstream to the red bone marrow for recycling into new erythrocytes

Biliverdin

A green pigment waste product formed from degradation of the non-iron portion of heme

Bilirubin

A yellow pigment waste product formed from further breakdown of biliverdin; binds to albumin and travels to the liver, where it is used to make bile

Bile

A compound made by the liver from bilirubin and released into the intestines to help digest dietary fats

Urobilin and stercobilin

Compounds formed when large intestine bacteria convert bilirubin from bile; some urobilins are absorbed into the bloodstream and eliminated in urine (giving urine its yellow color), while stercobilin and remaining urobilins are eliminated in feces (giving feces its yellow-brown color)

Bruise (pigment source)

Dramatic colors at an injury site produced by biliverdin from damaged RBCs

Jaundice

A yellowish tinge of the body that occurs when the liver is not functioning properly and cannot effectively remove bilirubin from circulation