Overview of Blood

Definition and Functions

Blood is the only fluid connective tissue in the body, essential for transporting substances and maintaining homeostasis.

• Transport: Moves nutrients, gases (O2, CO2), and wastes.

• Immune Defense: Circulates immune cells and antibodies.

• Regulation: Maintains pH, temperature, and fluid balance.

Components of Blood

• Color: Scarlet red (oxygen-rich) / Dull red (oxygen-poor)

• pH: 7.35–7.45

• Temperature: 100.4°F

Blood Plasma

Major Plasma Proteins

• Albumin: Regulates osmotic pressure

• Clotting proteins: Stop bleeding

• Antibodies: Defend against pathogens

Imbalances

• Acidosis: Blood too acidic

• Alkalosis: Blood too basic

Formed Elements of Blood

A. Erythrocytes (RBCs)

• Contain hemoglobin: 1 RBC = 250 million molecules; each binds 4 O2

• Normal hemoglobin: 12–18 g/100 mL blood

Disorders

• Anemia: Decreased oxygen-carrying ability

• Sickle Cell: Abnormal hemoglobin shape

• Polycythemia: Excess RBCs → slows blood flow

B. Leukocytes (WBCs)

• Normal Range: 4,800–10,800/mm3

• Can exit blood (diapedesis) and follow chemical signals (positive chemotaxis)

Disorders

• Leukocytosis: >11,000/mm3 → infection

• Leukopenia: Low WBC count → drugs

• Leukemia: Cancerous marrow → excess WBCs

C. Platelets (Thrombocytes)

• Derived from megakaryocytes

• Normal count: 150,000–400,000/mm3

D. Hematopoiesis

• Blood cell formation in red bone marrow

• Hemocytoblast = stem cell → differentiates into all formed elements

• Hormonal regulation:

  • Erythropoietin → RBCs

  • CSFs/interleukins → WBCs

  • Thrombopoietin → platelets

Hemostasis (Stopping Bleeding)

Phases

1. Vascular Spasms: Vasoconstriction → less blood loss

2. Platelet Plug Formation: Platelets stick to collagen, release chemicals

3. Coagulation: TF + PF3 + clotting factors + Ca2+ → thrombin → fibrin mesh

• Thrombus: Clot in unbroken vessel

• Embolus: Clot breaks free → may block vessels

Bleeding Disorders

Mnemonics

• Thrombocytopenia: "Tiny platelets = paper cuts become murder scenes."

• Hemophilia: "Royal disease—no clot, lots of drama."

• Rh- Mom + Rh+ Baby: "Mom vs. Baby Blood Battle: The Sequel."

Blood Groups and Typing

ABO System

Rh Factor

• Most Americans = Rh+

• Rh- mother + Rh+ baby = risk for hemolytic disease

• Prevent with RhoGAM

Blood Typing

• Mix RBCs with anti-A / anti-B sera → observe agglutination

• Cross-matching ensures donor-recipient compatibility

• Developmental Aspects

• Early blood formation: fetal liver & spleen

• Bone marrow takes over by 7th month

• Fetal hemoglobin: higher oxygen affinity

• Physiologic jaundice: newborn liver can't process hemoglobin fast enough

• Age-related changes: increased leukemia, anemia, clotting disorders; pernicious anemia = B12 absorption decreases

Review Quiz

Multiple Choice

1. Largest component of blood by volume?

   • a) RBCs

   • b) Buffy coat

   • c) Plasma

   • d) Platelets

2. Primary phagocyte at infection sites?

   • a) Lymphocyte

   • b) Neutrophil

   • c) Basophil

   • d) Monocyte

3. Blood component producing antibodies?

   • a) Erythrocyte

   • b) Interleukin

   • c) CSF

   • d) Lymphocyte

4. Universal donor?

   • a) AB

   • b) O

   • c) A

   • d) B

5. Phase forming platelet plug?

   • a) Vascular spasm

   • b) Coagulation

   • c) Platelet plug formation

   • d) Fibrinolysis

True/False

• Plasma is ~90% water.

• Hemoglobin carries carbon dioxide only.

• Leukocytes can move in and out of vessels.

• Basophils release histamine at inflammation sites.

• Thrombus and embolus are the same.

Matching

• Neutrophil → Phagocytizes bacteria

• Platelet → Clotting

• Erythrocyte → Transport oxygen

• Lymphocyte → Antibody production