Blood: Components, Functions, and Cellular Elements – Study Notes for Anatomy & Physiology

Components and Functions of Blood

Overview of the Cardiovascular System

The cardiovascular system is essential for transporting substances throughout the body. It consists of the heart (a pump), blood vessels (conducting hoses), and blood (fluid connective tissue).

• Heart: Pumps blood throughout the body.

• Blood Vessels: Series of tubes that carry blood.

• Blood: Specialized connective tissue containing cells suspended in a fluid matrix.

Functions of Blood

Blood performs several vital functions necessary for homeostasis and survival.

• Transport: Dissolved gases (O2, CO2), nutrients, hormones, and metabolic wastes.

• Regulation: pH and ion composition of interstitial fluids.

• Restriction: Limits fluid loss at injury sites.

• Defense: Protects against toxins and pathogens.

• Stabilization: Maintains body temperature.

Characteristics of Blood

Blood has unique physical and chemical properties.

• Temperature: 38°C (100.4°F)

• pH: Slightly alkaline (7.35–7.45)

• Volume: Approximately 7% of body weight (in kg). For a 75-kg person, about 5.25 liters.

Composition of Whole Blood

Whole Blood

Whole blood consists of plasma (fluid) and formed elements (cells and cell fragments).

• Plasma: Liquid component, makes up about 55% of blood volume.

• Formed Elements: Red blood cells, white blood cells, and platelets.

• Fractionation: Process of separating plasma from formed elements.

Plasma

Plasma is the fluid matrix of blood, primarily composed of water, proteins, and solutes.

• More than 90% water.

• Contains dissolved plasma proteins and other solutes.

• Similar in composition to interstitial fluid due to exchange across capillary walls.

Plasma Proteins

• Albumins (60%): Major contributors to plasma osmolarity; transport fatty acids, thyroid hormones, steroid hormones.

• Globulins (35%): Include antibodies (immunoglobulins) and transport globulins (hormone-binding proteins, metalloproteins, apolipoproteins, steroid-binding proteins).

• Fibrinogen (4%): Soluble protein involved in clotting; converted to insoluble fibrin during clot formation, leaving serum.

• Other Plasma Proteins (1%): Enzymes and hormones in varying concentrations.

Origins of Plasma Proteins: Most are produced in the liver; antibodies by plasma cells; peptide hormones by endocrine organs.

Formed Elements of Blood

Types of Formed Elements

• Red Blood Cells (RBCs): Erythrocytes, transport oxygen and carbon dioxide.

• White Blood Cells (WBCs): Leukocytes, involved in immune defense.

• Platelets: Cell fragments involved in clotting.

Hemopoiesis

Hemopoiesis is the process of producing formed elements, occurring primarily in red bone marrow.

Red Blood Cells (Erythrocytes)

Structure and Function

RBCs are highly specialized for oxygen transport.

• Biconcave Discs: Thin central region, thicker outer margin; increases surface area for gas exchange.

• Anucleate: Mature RBCs lack nuclei, mitochondria, and ribosomes; cannot divide or repair.

• Flexibility: Can bend and pass through capillaries as small as 4 μm.

Hemoglobin

Hemoglobin (Hb) is the protein responsible for oxygen transport.

• Structure: Quaternary protein with four globin chains, each containing a heme group with an iron ion.

• Function: Iron binds oxygen to form oxyhemoglobin ($HbO_2$); releases oxygen to form deoxyhemoglobin.

• Normal Levels: Adult male: 14–18 g/dL; adult female: 12–16 g/dL.

RBC Count and Hematocrit

• RBC Count: Number of RBCs per microliter; adult male: 4.5–6.3 million; adult female: 4.2–5.5 million.

• Hematocrit: Percentage of formed elements in blood; adult male: 46%; adult female: 42%.

RBC Life Cycle and Production

• Lifespan: About 120 days.

• Erythropoiesis: Formation of RBCs from myeloid stem cells in red bone marrow.

• Hemocytoblasts: Hematopoietic stem cells that give rise to myeloid and lymphoid stem cells.

Stages of RBC Maturation

• Myeloid stem cell → Proerythroblast → Erythroblast → Reticulocyte → Mature RBC

Regulation of Erythropoiesis

• Erythropoietin (EPO): Hormone from kidneys and liver, stimulates RBC production in response to hypoxia.

• Requirements: Amino acids, iron, folic acid, vitamins B12 and B6.

• Pernicious Anemia: Caused by lack of vitamin B12.

Hemoglobin Recycling

• Aged RBCs are engulfed by macrophages in spleen, liver, and bone marrow.

• Hemoglobin is broken down; iron is recycled, heme is converted to biliverdin (green), then bilirubin (yellow).

• Bilirubin is excreted in bile; excess causes jaundice.

• Iron is stored or transported by transferrin; excess stored in ferritin and hemosiderin.

Table: Major Components of Whole Blood

Component	Percentage	Main Function
Plasma	~55%	Transport of nutrients, hormones, waste; maintains osmotic balance
Formed Elements	~45%	Oxygen transport (RBCs), immune defense (WBCs), clotting (platelets)
Albumins	60% of plasma proteins	Osmotic pressure, transport
Globulins	35% of plasma proteins	Immune defense, transport
Fibrinogen	4% of plasma proteins	Clotting

Key Terms and Definitions

• Hemopoiesis: Formation of blood cells.

• Hematocrit: Percentage of blood volume occupied by formed elements.

• Hemoglobin: Oxygen-carrying protein in RBCs.

• Plasma: Liquid component of blood.

• Formed Elements: Cellular components of blood (RBCs, WBCs, platelets).

Additional info: These notes expand on the provided slides by including definitions, normal values, and the table summarizing blood components for clarity and exam preparation.