Overview
This lecture covers the components of blood, focusing on plasma and formed elements, especially red blood cells, their structure, function, and life cycle.
Blood Composition
- Blood consists of plasma (matrix) and formed elements (living cells).
- Plasma includes fluid (water/ground substance) and plasma proteins.
- Plasma proteins: albumin (osmotic pressure), globulins (antibodies), fibrinogen (clotting), and regulatory proteins (enzymes and some hormones).
- Plasma contains electrolytes, nutrients (carbohydrates, amino acids, lipids), and metabolic wastes (urea, uric acid, creatinine).
- Blood transports nutrients to cells and removes waste for excretion, mainly via kidneys.
Formed Elements of Blood
- Formed elements: erythrocytes (red blood cells), leukocytes (white blood cells), and platelets.
- Red blood cells make up the vast majority (high 90%) of formed elements (hematocrit).
- Erythrocytes transport oxygen and a portion of carbon dioxide.
- Leukocytes have subcategories, including various lymphocytes for immunity.
Red Blood Cell (Erythrocyte) Structure and Function
- Red blood cells are biconcave disks, increasing surface area and flexibility for capillary passage.
- Main function: carry oxygen via hemoglobin; each cell can bind up to 1 billion oxygen molecules.
- Hemoglobin binds loosely to oxygen (and some COâ‚‚), allowing release where needed.
- Mature erythrocytes lack a nucleus and most organelles, composed of about 95% hemoglobin.
- Red blood cells use glycolysis for minimal ATP, preventing oxygen consumption meant for tissues.
Red Blood Cell Life Cycle
- RBCs are produced in bone marrow, triggered by the hormone erythropoietin from kidneys.
- Lifespan is about 120 days; after that, they are broken down by macrophages in spleen, liver, or bone marrow.
- Components are recycled; iron from heme is reused, while bilirubin (from heme breakdown) is sent to the liver to be excreted in bile.
Hemoglobin Structure
- Each RBC contains ~250 million hemoglobin molecules.
- Hemoglobin is a quaternary protein with 4 subunits, each containing a heme group with an iron atom.
- Iron in heme binds oxygen reversibly, enabling effective oxygen delivery.
Key Terms & Definitions
- Plasma — The liquid matrix of blood containing water, proteins, electrolytes, nutrients, and wastes.
- Formed Elements — The living cells in blood: erythrocytes, leukocytes, and platelets.
- Albumin — Main plasma protein maintaining osmotic pressure.
- Hemoglobin — Protein in RBCs that binds and transports oxygen.
- Erythropoietin — Hormone from kidneys stimulating RBC production.
- Hematocrit — Percentage of blood volume occupied by red blood cells.
- Macrophage — White blood cell that engulfs and breaks down damaged RBCs.
- Bilirubin — Waste product from hemoglobin breakdown, excreted in bile.
Action Items / Next Steps
- Review the process of erythropoiesis and the roles of plasma proteins.
- Prepare for discussion on white blood cells and immunity in upcoming lectures.