vet 113 chapter 15

Blood: Fundamental Roles & Sample Handling

• General functions of blood

  • Supplies body tissues with required substances

  • e.g.

    • Hormones (≈ 5\% of circulating solutes mentioned in the lecture)

    • Oxygen, nutrients, regulatory molecules

  • Average whole-blood composition is an approximate value, not an exact rule every draw

  • “Think 50/50”: roughly half of a tube becomes plasma/serum and half cellular components

  • Practical lab example

    • If a test needs 1\text{ cc} of plasma, collect ≥ 2\text{ cc} of whole blood to ensure enough fluid after centrifugation

• Anticoagulant (tube) selection

  • Purple-top (EDTA = Ethylene-Diamine-Tetra-Acetate)

  • Best choice for blood smears & differential counts

  • Preserves cellular morphology; avoids platelet clumping

  • Green-top (Lithium heparin)

  • Acceptable for many chemistry tests but not ideal for morphologic evaluation (blood smears)

  • Choice must match intended testing; mis-matched anticoagulant can invalidate results

Erythrocyte (RBC) Morphology Vocabulary

• Size descriptors (cyt = cell, ‑ic = pertaining to)

  • Normocytic: normal size

  • Macrocytic / Microcytic: larger / smaller than normal

• Color (chromasia)

  • Normochromic: typical hemoglobin staining

  • Hypochromic: decreased color → less Hb or iron deficiency

  • Hyperchromic: unusually dark (rare; often artifact)

• Shape variations

  • Target cells: bull-seye pattern (dark-light-dark)

  • Rouleaux

  • RBCs stacked like coins

  • Pathologic in dogs & cats; physiologic in horses

  • Agglutination

  • Irregular clumping of RBCs

  • Suggests immune-mediated disease, some infections, or mismatched transfusion

Leukocytes (WBCs)

• Terminology

  • Leukocytes = white blood cells

  • Leukopoiesis = production of WBCs

• Five major types (differentiated by nucleus, cytoplasm color, & visible granules)

  • Neutrophils

  • Eosinophils

  • Basophils

  • Lymphocytes

  • Monocytes

• Granular vs. Agranular

  • Granulocytes: neutrophils, eosinophils, basophils (presence of cytoplasmic granules)

  • Agranulocytes: lymphocytes, monocytes (no obvious granules)

• “Basophilic” describes cells or structures that stain dark blue with basic dyes

Lymphatic System Overview

• Key functions

  • Returns excess interstitial fluid to bloodstream

  • Absorbs dietary fats & fat-soluble vitamins from intestine → transports to systemic circulation

  • Filters lymph to remove pathogens & debris

  • Provides structural sites for immune cell housing, activation, and proliferation

• Lymph formation

  • Interstitial (tissue) fluid enters blind-ended lymph capillaries ⇒ becomes lymph

• Major lymph node groups (palpable in common veterinary practice)

  • Mandibular (caudal to mandible)

  • Prescapular (cranial to shoulder)

  • Axillary (armpit)

  • Inguinal (groin)

  • Popliteal (caudal stifle)

• Clinical relevance

  • Enlarged node ⇒ active filtration of antigenic material → prompts further diagnostic search

• Tonsils

  • Masses of lymphatic tissue guarding oral & nasal entryways

• Spleen