Chapter 18: Blood – Comprehensive Study Guide

Blood: Structure, Function, and Disorders

Main Functions of Blood

Blood is a vital fluid connective tissue that performs essential functions for the body.

• Transportation: Carries oxygen (O2), carbon dioxide (CO2), nutrients, hormones, metabolic wastes, and stem cells throughout the body.

• Regulation: Maintains body pH (7.35–7.45) and regulates temperature by distributing heat.

• Protection: White blood cells (WBCs) destroy pathogens and cancer cells; platelets initiate clotting to prevent blood loss.

Blood as a Connective Tissue

Blood is classified as a fluid connective tissue due to its cellular components suspended in plasma.

Blood Cell Types and Functions

• Erythrocytes (RBCs): Transport oxygen to tissues and remove carbon dioxide.

• Leukocytes (WBCs): Defend against infectious microorganisms and other pathogens.

• Thrombocytes (Platelets): Essential for hemostasis; secrete vasoconstrictors, form platelet plugs, and promote clotting.

Plasma vs. Formed Elements

Blood consists of plasma (liquid) and formed elements (cells).

• Plasma: The liquid portion, containing proteins such as Albumin (transports materials, absorbs heat), Globulins (antibodies for immunity), and Fibrinogen (clotting).

• Formed Elements: Includes RBCs, WBCs, and platelets.

Hypoproteinemia and Kwashiorkor

• Hypoproteinemia: Deficiency of plasma proteins due to starvation, liver/kidney disease, or burns.

• Kwashiorkor: Severe protein deficiency in children, causing thin limbs and swollen abdomen (edema).

Plasma vs. Serum

• Serum: Fluid remaining after blood clots and solids are removed; lacks fibrinogen.

Hemopoiesis

Hemopoiesis is the process of blood cell production, regulated by hemopoietic growth factors.

• Location: In adults, occurs in red bone marrow; in fetus, begins in yolk sac, then bone marrow, liver, spleen, thymus.

• Precursor: All blood cells arise from pluripotent stem cells (hemopoietic stem cells).

Red Blood Cell (RBC) Characteristics

• RBCs are anucleate (lack nucleus and DNA) and lack mitochondria; use anaerobic fermentation for ATP.

• Biconcave disc shape increases oxygen-carrying capacity.

Hemoglobin (Hb)

Hemoglobin is the protein in RBCs responsible for oxygen transport.

• Each Hb molecule has 4 heme groups, each with an iron (Fe2+) atom.

• One Hb molecule can bind 4 O2 molecules.

• CO2 and CO can also bind to Hb.

• Oxyhemoglobin: Formed when Hb binds with oxygen.

RBC Lifespan and Disposal

• RBCs live about 120 days.

• Spleen and liver remove old RBCs via macrophages.

• Globin is hydrolyzed to amino acids; iron is reused or stored; heme is converted to biliverdin, then bilirubin (secreted in bile), and finally urobilinogen (excreted in feces).

RBC Regulation

• Erythropoietin (EPO): Hormone produced by kidneys; stimulates RBC production in response to hypoxia.

Bone Marrow Transplant

• Replaces cancerous or defective red bone marrow with healthy stem cells.

Diagnostic Tests and Values

Blood tests help assess health and diagnose disorders.

Test	Normal Range (Men)	Normal Range (Women)
Hematocrit	42–52%	37–48%
Hemoglobin	13–18 g/dL	12–16 g/dL
RBC Count	4.6–6.2 million/μL	4.2–5.4 million/μL

• Lower values in women due to less androgen stimulation, menstrual losses, and higher body fat.

Dietary Importance

• Iron: Required for hemoglobin synthesis.

• Folic Acid & B12: Needed for DNA synthesis and rapid cell division in erythropoiesis.

• Vitamin C & Copper: Cofactors for enzymes synthesizing hemoglobin.

RBC Diagnostic Terms

• Polycythemia: Increased RBC production.

• Anemia: Decreased RBC production or hemoglobin.

Hypoxia

• Reduced oxygen delivery to tissues; caused by high altitudes, anemia, iron/B12 deficiency, or CO poisoning.

Sickle Cell Disease

• Hereditary defect (HbS) causes RBCs to crystallize and block vessels at low oxygen levels.

Blood Typing and Compatibility

Blood typing is essential for safe transfusions.

• Agglutinogens: Antigens on RBC surface.

• Agglutinins: Antibodies in plasma.

• Blood Types: A, B, AB, O (based on A and B antigens).

• Rh Factor: "+" or "-" indicates presence or absence of Rh antigen.

Blood Type	Antigens Present	Antibodies Present
A	A	Anti-B
B	B	Anti-A
AB	A, B	None
O	None	Anti-A, Anti-B

• Universal Donor: Type O

• Universal Recipient: Type AB

• Agglutination: Clumping of RBCs when antibodies bind to foreign antigens.

Allele Functions in Blood Typing

• FUT1: Converts precursor to H substance.

• IA & IB: Add terminal sugar residues to H substance.

• i: No terminal additions (Type O).

Transfusion Compatibility Example (B+ Individual)

Donor Type	Compatibility	Reason
AB-	No	Recipient has anti-A antibodies
O+	Yes	Universal donor for antigens
B-	Yes	Compatible antigen; recipient is Rh+
A+	No	Recipient has anti-A antibodies

Rh Factor Risk in Pregnancy

• Rh-negative mother with Rh-positive fetus: Anti-Rh antibodies can cross placenta and destroy fetal RBCs in subsequent pregnancies.

Key Blood Disorders

• Anemia: Insufficient RBCs or hemoglobin.

• Leukemia: Cancer of hemopoietic tissue; high WBC counts.

• Hemophilia: Inherited bleeding disorder due to lack of clotting factors.

White Blood Cell Types

• Granulocytes: Neutrophils (phagocytize bacteria), Eosinophils (parasites/allergies), Basophils (secrete histamine/heparin).

• Agranulocytes: Monocytes (become macrophages), Lymphocytes (immunity).

• Most numerous: Neutrophils (60–70%)

• Least numerous: Basophils (0.5–1.0%)

Leukopoiesis

• Production of WBCs in red bone marrow.

WBC Migration

• Chemotaxis: Attraction to chemicals at infection sites.

• Emigration (Diapedesis): WBCs squeeze between endothelial cells.

• Selectins & Integrins: Help WBCs stick to and roll along vessel walls.

Leukocytosis vs. Leukopenia

• Leukocytosis: High WBC count (>10,000/ml).

• Leukopenia: Low WBC count (<5,000/ml).

Types of Leukemia

• Myeloid: Affects granulocytes.

• Lymphoid: Affects lymphocytes/monocytes.

• Acute: Rapid onset.

• Chronic: Slow progression.

Lymphocyte Function

• Provide long-term immunity.

• B cells: Produce antibodies.

• T cells: Kill cancerous or foreign cells.

Thrombocytes (Platelets)

• Fragments of megakaryocytes formed by thrombopoiesis, regulated by thrombopoietin.

• Function in vasoconstriction, plug formation, and initiation of clot dissolution.

Hemostasis and Coagulation

Hemostasis is the process of stopping bleeding.

• Vascular Spasm: Constriction of blood vessels.

• Platelet Plug Formation: Platelets adhere to injury site.

• Coagulation: Cascading pathway requiring calcium (Ca2+) and Vitamin K for prothrombin synthesis.

Feedback Mechanism: Clotting is a positive feedback process to seal damaged vessels quickly.

Fibrinolysis

• Dissolution of a clot by the enzyme plasmin after healing is complete.

Thrombus vs. Embolus

• Thrombus: Clot in an unbroken vessel.

• Embolus: Clot traveling in the bloodstream.

Prothrombin Time (PT)

• Test measuring how long blood takes to clot; used to monitor bleeding disorders or medication effectiveness.

Hemophilia Cause

• Caused by a faulty gene on the X chromosome resulting in deficiency of specific clotting factors.

Key Equations

• Hematocrit Calculation:

$\text{Hematocrit} = \frac{\text{Volume of RBCs}}{\text{Total Blood Volume}} \times 100\%$

• Hemoglobin Oxygen Binding:

$\text{Hb} + 4\text{O}_2 \rightarrow \text{Hb(O}_2)_4$

• Coagulation Cascade (Simplified):

$\text{Prothrombin} \xrightarrow{\text{Vitamin K, Ca^{2+}}} \text{Thrombin}$

$\text{Thrombin} + \text{Fibrinogen} \rightarrow \text{Fibrin (clot)}$

• Fibrinolysis:

$\text{Plasminogen} \xrightarrow{\text{Activators}} \text{Plasmin}$

$\text{Plasmin} + \text{Fibrin} \rightarrow \text{Fibrin fragments}$