Blood: Homeostasis, Components, Lab Terms, and RBC/WBC Basics
Blood and Homeostasis
Blood is central to keeping the body alive and maintaining homeostasis by transporting essential substances and regulating body conditions.
Key needs for cells discussed in the transcript:
Food (glucose) as energy source; the blood delivers glucose to cells via the digestive absorption and circulation.
Water and hydration status; the blood helps regulate water balance and is filtered by the kidneys.
Heat regulation; skin and blood vessel responses (vasodilation) help release heat to maintain body temperature.
Oxygen delivery; red blood cells (RBCs) are the oxygen transport cells; oxygen is carried to tissues and carbon dioxide is removed.
Basic idea: the blood connects nutrients, energy production, hydration, and temperature control to maintain homeostasis and pH balance (blood pH is slightly alkaline).
Blood pH and homeostasis: the blood helps maintain pH within a narrow range critical for cellular function.
Blood Components: Plasma and Formed Elements
Blood is connective tissue with two main components:
Plasma (the liquid extracellular matrix) – the liquid portion of blood.
Formed elements – the cellular components: RBCs, white blood cells (WBCs), and platelets.
Structural terms:
Formed elements = erythrocytes (RBCs), leukocytes (WBCs), thrombocytes (platelets).
Plasma = the liquid component containing dissolved substances and plasma proteins.
Centrifugation basics:
A centrifuge separates the formed elements (RBCs, WBCs, platelets) from plasma.
Hematocrit measures the proportion of blood volume occupied by RBCs.
The buffy coat (a thin middle layer) contains white blood cells and platelets.
Blood volume distribution (typical values):
Blood volume ~ 4$-$5\,
L in females; ~5$-$6\,
L in males.In the body, blood volume is roughly ~8\% of body weight.
Erythrocyte (RBC) count: ~4\times 10^6 to 6\times 10^6\,\text{cells/mm}^3 (per millimeter cubed).
Hematocrit (percentage of blood volume that is RBCs): typically around 40\%, with females slightly lower than males.
Blood Lab Basics: Tubes, CBC, and Plasma/Serum Measurements
Common blood collection tubes:
Purple top tube (EDTA) prevents clotting; used when examining whole blood and for CBC (white and red cells, platelets) under the microscope.
Red top tube (serum separator) allows the blood to clot and then separates serum from the clot; used for plasma/serum chemistry tests.
Some tubes may contain a gel at the bottom to aid separation of RBCs from plasma.
CBC (Complete Blood Count): a common initial test to evaluate RBCs, WBCs, and platelets; typically uses a purple top tube.
Blood components after centrifugation:
Red blood cells (RBCs) at the bottom.
Buffy coat (thin middle layer) containing white blood cells (WBCs) and platelets.
Plasma at the top.
Purple top tube with heparin vs EDTA:
Some purple tubes contain heparin to prevent clotting, yielding whole blood without separation of plasma; useful for certain hematology analyses.
For CBC, the purple top often used with EDTA chelating agent preserves cells for counting.
Plasma vs serum:
Plasma is the liquid component with clotting factors when blood is prevented from clotting (e.g., with heparin or EDTA or citrate).
Serum is plasma without clotting factors, obtained after coagulation.
Appendix C (in the course textbook): a detailed list of substances measured in plasma, including:
Albumin, globulins, fibrinogen (plasma proteins).
Electrolytes: sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), phosphate, etc.
Metabolic markers: glucose, cholesterol, bilirubin, carbon dioxide (CO₂), BUN (blood urea nitrogen), enzymes like amylase, liver enzymes, iron, etc.
Gases and wastes: carbon dioxide, urea, etc.
Practical clinical relevance:
A CBC provides clues about infection (elevated WBCs), anemia (low RBCs or hematocrit), or clotting issues (platelet abnormalities).
Plasma/serum values help diagnose liver, kidney, pancreas function, electrolyte imbalances, cholesterol issues, and more.
Normal ranges (e.g., thyroid hormones like T4) are used to assess health and monitor treatment.
Safety reminder:
Blood handling carries risks of pathogen transmission; standard precautions include hand washing, gloves, proper sharps disposal, and other PPE.
Red Blood Cells (Erythrocytes)
Primary role: carry oxygen to tissues via hemoglobin; remove carbon dioxide from tissues.
Key structural features:
Disc-like, biconcave shape increases surface area for gas exchange.
Anucleate (no nucleus) and lack mitochondria; cannot reproduce.
Hemoglobin contains iron in the heme group, enabling oxygen binding.
About one third of the cell’s volume is hemoglobin.
Lifespan and lifecycle:
RBCs have a lifespan of approximately 110$-$120\,\text{days} (commonly stated as ~4 months).
They travel an estimated distance of about 300\,\text{miles} during their lifespan.
They complete roughly 170{,}000\text{ circuits} through the heart and systemic circulation.
As RBCs wear out, they are broken down in the liver and spleen; materials are recycled.
Erythropoiesis (RBC production):
Red bone marrow is the site of RBC formation.
Erythropoietin (EPO), produced by the kidneys, triggers the bone marrow to increase RBC production when oxygen is low.
The trigger for EPO release is reduced blood oxygen, sensed by the kidney.
Nutritional requirements for RBC production:
Vitamin B12 (DNA synthesis in rapidly dividing cells).
Iron (central to the hemoglobin molecule).
Other vitamins and possibly folate are also important for efficient erythropoiesis.
Hemoglobin and oxygen transport:
Hemoglobin binds and carries oxygen; iron in the heme group is essential for this function.
RBC disorders (examples):
Anemia: decreased RBC count or hematocrit; insufficient oxygen transport.
Hemolytic anemia: increased RBC destruction.
Sickle cell anemia: abnormal hemoglobin causes distorted RBCs that can occlude capillaries, causing painful infarctions.
Thalassemia: abnormal hemoglobin production (discussed as a potential fatality in severe cases; needs context from clinical data).
RBC breakdown and bilirubin:
When RBCs are degraded, heme is split into iron (recycled to liver) and bilirubin (excreted via bile into the intestines).
Excess bilirubin can cause jaundice (yellowing of skin and eyes) if liver processing or RBC destruction is excessive.
Unconjugated bilirubin is transported to the liver, conjugated, and then excreted in bile.
White Blood Cells (Leukocytes) and Immune Defense
Overall role: fight infection, aid in immune defense, and participate in inflammatory processes.
Two broad groups:
Granulocytes: neutrophils, eosinophils, basophils (contain granules).
Agranulocytes: monocytes and lymphocytes (granules not prominent).
Diapedesis: leukocytes can leave blood vessels and migrate into tissues at sites of infection or injury.
Neutrophils (granulocytes): most abundant WBC; rapidly respond to bacterial infections; phagocytose bacteria.
Eosinophils (granulocytes): respond to parasitic infections and participate in allergic reactions; contain prominent granules.
Basophils (granulocytes): release histamine to promote inflammation.
Monocytes (agranulocytes): large cells that differentiate into macrophages; long-lasting responders, often elevated in chronic infection.
Lymphocytes (agranulocytes): include T cells, B cells, and natural killer (NK) cells; major players in adaptive immunity and antibody production.
Typical CBC expectations:
Leukocytes may rise (leukocytosis) with infection; decrease (leukopenia) with bone marrow suppression or certain infections.
The relative prominence of neutrophils vs lymphocytes can hint at bacterial vs viral infections, respectively (context from clinical data).
Inflammation hallmarks (inflammation mediated by WBCs): redness, heat, swelling, and pain.
Practical examples:
In bacterial abscesses, neutrophils are typically elevated and are the primary responders to clear bacteria.
Parasite infections (e.g., heartworm in dogs) may elevate eosinophils.
Leukocytes in disease contexts:
Leukocytosis indicates an ongoing immune response.
Leukopenia may indicate viral infections or bone marrow suppression.
Platelets (Thrombocytes) and Hemostasis
Platelets are small cell fragments derived from megakaryocytes in the bone marrow.
Role: participate in hemostasis to stop bleeding and form clots.
Key terms:
Thrombocytosis: elevated platelet count.
Thrombocytopenia: decreased platelet count.
Hemostasis involves platelets and clotting factors (plasma proteins) to form a stable clot.
Hemostasis, Clotting, and Tissue Events
Key plasma proteins involved in clotting: albumin, globulin, fibrinogen.
Important terms:
Thrombus: a stationary clot.
Embolus: a moving clot that travels through the bloodstream.
Infarction: tissue death due to lack of oxygen caused by blocked blood flow.
The link between bleeding control and oxygen delivery:
Stopping bleeding (hemostasis) is essential, but sustained tissue health requires intact oxygen delivery through RBCs.
RBC Breakdown, Bilirubin, and Liver Involvement
RBC degradation flow:
Old RBCs are broken down in the liver and spleen by macrophages.
Hemoglobin splits into globin (protein) and heme (iron-containing component).
Globin is recycled into amino acids.
Heme is split into iron (returned to the liver for storage or reuse) and bilirubin (a bile pigment).
Bilirubin processing:
Bilirubin is conjugated in the liver and excreted in bile into the intestines.
If bilirubin accumulates, jaundice can occur (yellowing of skin and eyes).
Liver and bile: the liver also plays a role in digestion via bile production; bilirubin processing is a key function related to RBC turnover.
Erythropoiesis: Regulation of Red Blood Cell Production
Trigger for RBC production: low blood oxygen triggers erythropoietin (EPO) release from the kidneys.
EPO signals the red bone marrow to increase RBC production.
Timeline: erythropoiesis takes some time after hypoxia is detected; in acute severe blood loss, transfusion of RBCs may be needed quickly rather than waiting for EPO-mediated production.
Stem Cells in Blood Formation
Blood-forming stem cells differentiate into three lines:
Myeloid stem line: produces erythrocytes, platelets, and granulocytes.
Lymphoid stem line: produces lymphocytes and monocytes.
Lymphocytes are specialized for immune responses and antibody production; next week’s topic will cover the lymphoid system in more detail.
The Four Basic Tissue Types and Connective Tissue Context
The four primary tissue types: connective, epithelial, muscle, nervous.
Blood is a special connective tissue; it transports vital substances, aids in gas exchange, nutrient transport, waste removal, temperature distribution, and fluid stability.
Blood volume distribution and importance of connective tissue properties in transporting substances across the body.
Safety, Real-World Relevance, and Clinical Scenarios
Real-world relevance of blood work:
CBC and blood tests are standard in diagnosing anemia, infection, and many other conditions.
Plasma tests (Appendix C) provide a wide range of measurement values (electrolytes, proteins, enzymes, waste products, hormones, etc.).
Safety considerations in clinical settings:
Handling blood requires precautions to prevent disease transmission (hand hygiene, gloves, proper disposal of sharps).
Controlled handling and timely processing of blood samples are essential for accurate laboratory results.
Practical example workflow:
A patient with weakness or dizziness may undergo a CBC to assess RBCs, WBCs, platelets, and hematocrit.
If anemia is suspected, assess iron status, B12, folate, and reticulocyte count to determine cause and treatment.
Quick Reference: Key Terms and Concepts
Erythrocyte (RBC): red blood cell; anucleate; carries oxygen via hemoglobin; lifespan ~110-120\text{ days}; produced in red bone marrow.
Leukocyte (WBC): white blood cell; immune defense; five types: neutrophils, eosinophils, basophils, monocytes, lymphocytes.
Thrombocyte (platelet): cell fragment essential for clotting.
Hematocrit: percentage of blood volume that is RBCs.
Erythropoietin (EPO): hormone from kidney that stimulates RBC production.
Hemoglobin: protein in RBCs that binds oxygen; iron-containing heme group.
Bilirubin: pigment derived from heme breakdown; processed by liver; elevated levels cause jaundice.
Hemostasis: stopping bleeding; involves platelets and clotting factors (plasma proteins like fibrinogen).
Thrombus: stationary clot; Embolus: moving clot.
Infarction: tissue death due to lack of oxygen.
Diapedesis: leukocytes moving through vessel walls into tissues.
Granulocytes vs Agranulocytes: subtypes of WBCs distinguished by granules in cytoplasm.
CBC: complete blood count; a common diagnostic test.
Plasma vs Serum: plasma contains clotting factors; serum does not.
Appendix C: reference for plasma components and measurable values (e.g., albumin, globulin, fibrinogen, sodium, potassium, calcium, glucose, bilirubin, BUN, iron, cholesterol, CO₂).
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