Blood: Structure, Function, and Disorders – ANP College Study Guide

Blood: Structure and Function

Functions of Blood

Blood is a vital connective tissue responsible for transporting substances, regulating physiological parameters, and defending the body against disease.

• Transport: Delivers oxygen (O2) and nutrients to tissues, removes carbon dioxide (CO2) and wastes, and transports hormones.

• Regulation: Maintains temperature, pH, and extracellular fluid levels.

• Protection: Clotting proteins close wounds; white blood cells defend against infection.

Characteristics of Blood

Blood exhibits specific physical and chemical properties that are essential for its function.

• pH: 7.35–7.45

• Temperature: 100.4º F

• Volume: Males: 5–6 L; Females: 4–5 L

• Color: Scarlet (high O2) to dark red (low O2)

Components of Blood

Blood consists of plasma and formed elements, each with distinct roles.

• Plasma: Fluid matrix, ~90% water, contains proteins (albumin, globulins, fibrinogen), nutrients, electrolytes, gases, hormones, and wastes.

• Formed Elements: Red blood cells (RBCs), white blood cells (WBCs), and platelets.

Hematocrit Procedure

The hematocrit is a measure of the proportion of RBCs in blood, determined by centrifuging a blood sample.

• Plasma: ~55% of blood volume

• Buffy coat: Contains WBCs and platelets (<1% of blood volume)

• RBCs: Hematocrit (Males: 47% ± 5%; Females: 42% ± 5%)

Plasma and Plasma Proteins

Composition of Plasma

Plasma is the liquid component of blood, serving as a transport medium for various substances.

• Water: 90% of plasma

• Proteins: Albumin (60%), globulins (alpha, beta, gamma), fibrinogen

• Other Components: Nitrogenous wastes, nutrients, electrolytes, respiratory gases, hormones

Albumin

Albumin is the most abundant plasma protein, crucial for maintaining osmotic pressure and transporting substances.

• Functions: Carrier protein, buffer, maintains water balance in blood

Red Blood Cells (Erythrocytes)

Structure and Function

Red blood cells are specialized for oxygen transport and exhibit unique structural features.

• Shape: Biconcave discs, increasing surface area and facilitating gas exchange

• Anucleate: Lack a nucleus

• Hemoglobin: Packed with hemoglobin for O2 transport

• No mitochondria: Do not consume the O2 they carry

Hemoglobin

Hemoglobin is the protein responsible for binding and transporting oxygen and carbon dioxide.

• Structure: 2 alpha and 2 beta chains, each with an iron (Fe) molecule

• Oxygen Binding: Each hemoglobin molecule can carry 4 O2 molecules

• RBC Content: Each RBC contains ~250 million hemoglobin molecules

RBC Vocabulary

• Oxyhemoglobin: Oxygenated hemoglobin

• Deoxyhemoglobin: Reduced hemoglobin (no O2)

• Carbaminohemoglobin: CO2 bound to hemoglobin

RBC Counts

• Women: 4.2–5.4 million cells/µL

• Men: 4.7–6.1 million cells/µL

• Viscosity: RBC count affects blood viscosity

Formation and Regulation of Blood Cells

Hematopoiesis

Hematopoiesis is the process of blood cell formation, occurring in red bone marrow.

• Location: Axial skeleton, girdles, proximal epiphyses of humerus and femur in adults

• Stem Cell: All blood elements derive from the hematopoietic stem cell (hemocytoblast)

• Production Rate: ~100 billion new RBCs/day

Erythropoiesis (RBC Formation)

Erythropoiesis is the specific process of red blood cell formation, taking about 15 days.

• Stages: Hemocytoblast → Proerythroblast → Early/Late erythroblast → Normoblast → Reticulocyte → Erythrocyte

• Reticulocyte: Immature RBC that enters circulation and matures in 1–2 days

Regulation of Erythropoiesis

Regulation is primarily controlled by the hormone erythropoietin, released by the kidneys in response to low O2.

• Triggers: Low RBC count, low hemoglobin, low O2 availability

• Negative Feedback: High O2 turns off erythropoietin production

Diet and Erythropoiesis

• Nutrients: Fats, sugars, proteins, vitamin B-12, folic acid, iron

• DNA Synthesis: B-12 and folic acid are essential for rapidly dividing cells

Aging and Destruction of RBCs

RBCs have a limited lifespan and are destroyed by macrophages, with their components recycled or excreted.

• Lifespan: 100–120 days

• Destruction: Occurs mainly in the spleen; heme is broken down to bilirubin, globin to amino acids

• Bilirubin: Released into blood, picked up by liver, secreted as bile, converted to urobilinogen and stercobilin (brown pigment)

RBC Disorders

Anemia

Anemia is a condition of low O2 carrying capacity, with various causes and symptoms.

• Symptoms: Fatigue, pallor, shortness of breath, chills

• Causes: Blood loss, RBC destruction, bone marrow failure, renal disease, iron/B12 deficiency, abnormal hemoglobin

Sickle Cell Anemia

Sickle cell anemia is an inherited disorder caused by a single amino acid substitution in the beta chain of hemoglobin.

• Mechanism: Low O2 causes hemoglobin to change shape, resulting in sickled RBCs

• Complications: Clotting, pain, stroke, infection

• Population: Common in individuals of African descent; carriers are protected from malaria

• Treatment: Transfusions, NO gas, drugs to activate fetal hemoglobin

Polycythemia

Polycythemia is a condition of excessive RBCs, increasing blood viscosity.

• Causes: Bone cancer, high altitude, blood doping, synthetic EPO

White Blood Cells (Leukocytes)

Structure and Function

White blood cells are crucial for immune defense and exhibit unique behaviors.

• Count: 4,800–10,800 WBCs/µL (<1% blood volume)

• Diapedesis: Ability to leave the bloodstream

• Amoeboid Motion: Movement outside the bloodstream

• Chemotaxis: Attracted to sites by chemicals

Types of WBCs

• Granulocytes: Neutrophils, eosinophils, basophils

• Agranulocytes: Lymphocytes, monocytes

Granulocytes

Granulocytes have lobed nuclei and granules that stain with Wright’s stain; all are phagocytic to some degree.

Neutrophils

• Percentage: 50–70% of WBCs

• Appearance: Small lilac granules, nucleus with 3–6 lobes

• Function: Phagocytize bacteria; counts increase in bacterial infection

Eosinophils

• Percentage: 2–4% of WBCs

• Appearance: Red-staining granules, nucleus with 2 lobes

• Function: Kill parasitic worms, reduce allergic reactions and asthma

Basophils

• Percentage: 0.5–1% of WBCs

• Appearance: Large purple-black granules, S or U shaped nucleus

• Function: Release histamine in inflammatory response

Agranulocytes

Agranulocytes lack membrane-bound granules.

Lymphocytes

• Percentage: ~25% of WBCs

• Appearance: Large dark purple nucleus, pale blue cytoplasm

• Function: Make antibodies, attack virus-infected and cancerous cells

Monocytes

• Percentage: 3–8% of WBCs

• Appearance: Largest WBC, U or kidney-shaped nucleus, pale blue cytoplasm

• Function: Phagocytosis; morph into macrophages in tissues

Mnemonic for WBC Order

"Never let monkeys eat bananas" helps remember the order of WBCs by number: Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils.

Leukopoiesis and WBC Disorders

Leukopoiesis

Leukopoiesis is the production of WBCs, stimulated by interleukins and colony stimulating factors (CSF).

• Lifespan: Granulocytes: hours–9 days; Agranulocytes: hours–decades

• Pathways: Hemocytoblast → Myeloid stem cell (granulocytes, monocytes) or Lymphoid stem cell (lymphocytes)

WBC Disorders

• Leukopenia: Too few WBCs; caused by drugs, diseases (HIV, lupus, influenza, malaria)

• Leukemia: Excessive, nonfunctional WBCs; marrow fails to produce RBCs and platelets

• Infectious Mononucleosis: Caused by Epstein-Barr virus; characterized by abnormal lymphocytes

Platelets and Hemostasis

Platelets

Platelets are cell fragments essential for blood clotting.

• Count: 150,000–400,000/µL

• Lifespan: ~10 days

• Function: Contain granules with clotting chemicals

Formation of Platelets

Platelet formation is stimulated by thrombopoietin and involves several developmental stages.

• Pathway: Hemocytoblast → Megakaryoblast → Promegakaryocyte → Megakaryocyte → Platelets

• Megakaryocyte: Releases platelets at the edge of sinusoid capillaries

Hemostasis

Hemostasis is the process of stopping bleeding, involving three main steps.

• Vascular Spasms: Constriction of blood vessel to restrict blood loss

• Platelet Plug Formation: Platelets adhere to exposed collagen, become sticky, and release chemicals

• Coagulation: Blood transforms from liquid to gel; involves formation of prothrombin activator, conversion of prothrombin to thrombin, and thrombin converting fibrinogen to fibrin

Fibrin: Glues platelets together, turns plasma to gel, traps formed elements

Clotting: Complete in 3–6 min; stable in 30–60 min; fibrinolysis removes clot after healing

Healthy Vessels: Produce anti-clotting chemicals (heparin); blood flow dilutes clotting chemicals

Disorders of Hemostasis

Thromboembolic Disorders

• Thrombus: Clot in unbroken vessel (e.g., coronary thrombosis)

• Embolus: Clot that breaks away and circulates

• Embolism: Clot stuck in small vessel (e.g., pulmonary, cerebral embolism)

• Treatment: Drugs to dissolve/prevent clots (aspirin, heparin, warfarin)

Bleeding Disorders

• Thrombocytopenia: Too few platelets; causes widespread hemorrhage

• Impaired Liver Function: Liver makes clotting chemicals; vitamin K deficiency or liver failure

• Hemophilia: Inherited disorder; treated with transfusions and clotting factor injections

Blood Types and Transfusions

Blood Types

Blood types are determined by the presence or absence of antigens (agglutinogens) on RBCs.

• ABO System: Type A, B, AB, O

• Antibodies: Develop against antigens not present on own RBCs

Blood Type	Antigens on RBC	Antibodies in Plasma	Blood Received
A	A	Anti-B	A, O
B	B	Anti-A	B, O
AB (universal recipient)	A, B	None	A, B, AB, O
O (universal donor)	None	Anti-A, Anti-B	O

Rh Factor

• Rh+: Antigen present

• Rh-: Antigen absent; antibodies develop after exposure

• Pregnancy: Rh- mother with Rh+ baby can develop antibodies, affecting subsequent pregnancies; prevented by RhoGAM

Blood Transfusions

• Transfusion Reaction: Wrong blood type causes clots, RBC lysis, hemoglobin release, renal failure

• Treatment: Fluids and diuretics to flush hemoglobin

Common Blood Tests

Types of Blood Tests

• Total RBC Count/Hematocrit: Used to test for anemia

• Differential WBC Count: Determines relative numbers of WBC types

• Complete Blood Count (CBC): Counts all formed elements, hematocrit, hemoglobin content, RBC size

• Complete Metabolic Profile (CMP): Provides blood chemistry, organ function, disease detection

• Prothrombin Time and Platelet Counts: Assesses clotting function

Additional info: All explanations have been expanded for academic clarity and completeness, including inferred details about blood cell development, disorders, and clinical applications.