Blood Composition and Functions

Functions and Compositions of Blood

• Blood is a liquid connective tissue comprised of cells in a liquid matrix
• Red blood cells (erythrocytes) account for 45% of whole blood
• White blood cells (leukocytes) and platelets (thrombocytes) make up >1% of whole blood
• Plasma, consisting of water, proteins, and other solutes, constitutes 55% of blood volume
• Cellular components of blood include RBCs, WBCs, and platelets
• Blood's primary functions are transporting oxygen, carbon dioxide, nutrients, hormones, heat, and waste
• Blood regulates bodily fluids, pH, body temperature, and cellular water content to maintain homeostasis
• Blood plays crucial roles in protecting against its loss through clotting,
• It uses WBCs to combat infections

Formed Elements of Blood and Their Functions

• Red blood cells (erythrocytes) transport oxygen from the lungs to tissues
• Erythrocytes transport carbon dioxide back to the lungs
• Erythrocytes contain hemoglobin, which carries oxygen
• Erythrocytes regulate blood flow and pressure by releasing nitric oxide, causing vasodilation
• Red blood cells lack a nucleus to maximize space for myoglobin
• Erythrocytes feature a biconcave shape for increased surface area
• White blood cells (leukocytes) defend the body against infection and foreign invaders

Granular Leukocytes

• Neutrophils are first responders to bacterial infections that phagocytize pathogens
• Eosinophils combat parasitic infections and participate in allergic reactions
• Basophils release histamine, contributing to inflammatory responses

Agranular Leukocytes

• Lymphocytes include B cells that produce antibodies, T cells that attack infected cells
• Lymphocytes include natural killer cells that target abnormal cells
• Monocytes differentiate into macrophages, phagocytizing pathogens and debris

Platelets (Thrombocytes)

• Platelets are involved in blood clotting (hemostasis)
• Thrombocytes form platelet plugs to temporarily block bleeding sites
• Platelets release chemicals like serotonin and thromboxane A2 to enhance vascular spasm
• Platelets attract more platelets to injury sites

Plasma Components and Functions

• Water in plasma (~90%) acts as a solvent, carrying dissolved substances
• Plasma helps regulate temperature and also transports heat
• Plasma proteins (~7-9%) such as albumin (~60%) maintain osmotic pressure
• Albumin prevents fluid loss from blood into tissues
• Albumin acts as a transport protein for fatty acids and hormones
• Globulins (~36% of plasma proteins) transport lipids, metal ions, and fat-soluble vitamins
• Globulins include immunoglobulins (antibodies), which help defend against infection
• Fibrinogen (~4% of plasma proteins) plays a key role in blood clotting
• Fibrinogen forms fibrin threads during coagulation

Electrolytes and Blood Regulation

• Electrolytes help maintain osmotic pressure and regulate blood pH
• Electrolytes are sodium, potassium, calcium, chloride, and bicarbonate
• Nutrients are glucose, amino acids, fatty acids, and vitamins used for cell metabolism
• Waste products include urea, creatine, uric acid, and bilirubin, which the kidney/liver remove
• Gases include O2 for cellular respiration, CO2 as a waste product of metabolism, and Nitrogen
• Hormones are transported in plasma to target organs

Hematopoiesis and Stem Cells

• Hematopoiesis is the process of blood cell formation that occurs in the red marrow.
• Hematopoiesis involves differentiation into various mature blood cells from pluripotent stem cells
• Pluripotent stem cells (hemocytoblasts) are precursor cells that develop into all blood cell types
• Pluripotent stem cells differentiate into myeloid and lymphoid stem cells

Differentiation Pathways

• Myeloid stem cells give rise to RBCs (erythrocytes) through erythropoiesis, stimulated by erythropoietin (EPO), which the kidneys release in response to low O2
• Myeloid stem cells give rise to platelets (thrombocytes), which megakaryocytes produce.
• Megakaryocytes fragment into thousands of platelets
• Myeloid stem cells give rise to granular WBCs to combat bacterial infections
• Myeloid stems cells give rise to Eosinophils, which target parasites and are involved in allergic reactions
• Myeloid stem cells give rise to Basophils, which release histamine during inflammation
• Myeloid stem cells differentiate into Monocytes, which then turn into macrophages
• Lymphoid stem cells give rise to Lymphocytes, which include B cells that produce antibodies
• Lymphoid stem cells give rise to T cells, which attack infected cells
• Lymphoid stems cells give rise to natural killer cells (NK), that target and destroy virus-infected or cancerous cells

Regulation of Hematopoiesis

• Colony-stimulating factors (CSFs) and interleukins stimulate WBC proliferation and differentiation
• Thrombopoietin stimulates platelet production
• Erythropoietin (EPO) promotes RBC production

Red Blood Cell Characteristics and Functions

• Red blood cells (RBC) have biconcave discs to increase surface area for gas exchange
• Erythrocytes lack nuclei and organelles to maximize hemoglobin storage
• Flexible membrane for RBCs enables bending and squeezing through capillaries
• Spectrin is a protein in the flexible membrane of RBCs
• The lifespan of red blood cells is around 120 days
• Red blood cells have a diameter of 7.5 um, they are slightly larger than some capillaries

Functions of Erythrocytes

• RBCs transport oxygen from lungs to tissues
• Hemoglobin binds and carries O2 for delivery
• Erythrocytes transport some CO2 out from tissue to lung for exhalation
• Hemoglobin releases nitric oxide (NO), causing vasodilation to enhance blood flow/O2 delivery and regulates blood flow and pressure

Hemoglobin: Structure and Function

• Hemoglobin contains four globin chains of two alpha and two beta
• Each globin chain contains a heme group with an iron ion in the center
• Each hemoglobin molecule can bind up to 4 oxygen molecules

Hemoglobin's Role in Oxygen Transport

• In the lungs, hemoglobin binds O2 to form oxyhemoglobin, which is bright red
• In tissues, O2 is released, forming deoxyhemoglobin, which is dark red
• Around 20% of CO2 binds to hemoglobin, forming carbaminohemoglobin for CO2 transport
• Hemoglobin helps regulate pH by buffering H+ ions

RBC Component Recycling

• Macrophages in the spleen and liver phagocytize old or damaged RBCs
• Heme is split into iron (Fe2+), recycled/transported to bone marrow for new RBCs, and bilirubin
• Bilirubin ia a waste, it is excreted as bile in the liver
• Globin chains are broken down into amino acids for protein synthesis
• Erythropoiesis is the 15 day red marrow process, stimulated by EPO, maturing into erythrocytes in 1-2 days

Abnormal Red Blood Cell Values and Anemia

• Anemia is indicated by low RBC or Hb levels, which reduces oxygen delivery
• Polycythemia, a high RBC count, thickens blood and increases clot risk

Types and Causes of Anemia

• Blood loss anemia occurs from bleeding due to injury, surgery, or ulcers
• Iron-deficiency anemia stems from poor diet, blood loss, or poor iron absorption
• Pernicious anemia is caused by a lack of Vitamin B12
• Aplastic anemia is due to damaged marrow related to infection, radiation or drugs
• Hemolytic anemia results from RBC breakdown due to infection or genetic issues

Granular Leukocytes

• Neutrophils (50-70% of WBC) are multi-lobed, pale granules and act as first responders to phagocytize bacteria
• Eosinophils (2-4% of WBCs) feature a bi-lobed nucleus, orange-red granules that fights parasites and moderate allergic reactions
• Basophils (>1% of WBCs) have a bi-lobed or S-shaped nucleus, dark granules, which releases histamine to trigger inflammation

Agranular Leukocytes

• Lymphocytes (25-40% of WBCs) feature a large, round nucleus, and small cytoplasm
• B-Cells act as Lymphocytes to produce antibodies
• T-Cells act as Lymphocytes to attack infected and abnormal cells
• Natural Killer (NK) Cells act as Lymphocytes to destroy virus-infected and cancer cells
• Monocytes (3-8% of WBCs) feature a kidney shaped nucleus, large size to become macrophages and phagocytize pathogens