Blood, Organs & Circulation Essentials

Blood Composition & Key Functions

• Plasma (\approx 55\%) | Formed elements (\approx 45\%)
• Major roles:
  • Transport O2, CO2, nutrients, hormones, wastes
  • Regulation: temperature, homeostasis, pH, electrolytes
  • Protection: immune defense, hemostasis (clotting)

Plasma

• (90\% water) + proteins, electrolytes, nutrients, hormones, wastes
• Liver synthesizes plasma proteins → transport & osmotic balance
• Kidneys filter plasma wastes (urea, uric acid, creatinine)

Formed Elements Overview

• Red Blood Cells (RBCs / erythrocytes) (40!–!45\%\,\text{of blood})
• White Blood Cells (WBCs / leukocytes) \approx 1\%
• Platelets (thrombocytes) — cell fragments for clotting

Hematopoiesis (Red Bone Marrow)

• Stem cell: hemocytoblast → differentiates into all blood cells
• Erythropoiesis: stimulated by erythropoietin (kidney & liver)
  • Nucleus ejected → biconcave disc maximizes O_2 carriage
• Thrombopoiesis: thrombopoietin → megakaryocyte → platelets

Red Blood Cells

• Filled with hemoglobin; no nucleus/organelles
• Function: deliver O2 to tissues, remove CO2

White Blood Cells (Defense)

• Granulocytes:
  • Neutrophils – 2!–!5-lobed nucleus, phagocytic antibacterial first responders
  • Eosinophils – bilobed, red-orange granules, antiparasitic/allergy modulation
  • Basophils – S/U nucleus, purplish granules, release histamine & heparin (inflammation)
• Agranulocytes:
  • Lymphocytes – large nucleus; B, T, NK cells for adaptive immunity
  • Monocytes – kidney-shaped nucleus; become macrophages in tissues

Platelets

• Fragments of megakaryocytes; no nucleus; granules initiate clotting

Liver & Portal Circulation

• Largest gland (1.2!–!1.6\,\text{kg}); exocrine (bile) & endocrine (metabolism, protein synthesis)
• Hepatic portal vein (~8\,\text{cm}) brings nutrient-rich blood from GI tract → sinusoids → hepatic veins → IVC
• Functional surgical segments (I–VIII) divided by portal & hepatic veins (Cantlie’s line etc.)

Kidneys & Filtration

• Retroperitoneal; size \approx 11.25\times5!–!7.5\times2.5\,\text{cm}
• Cortex, medulla (renal pyramids), pelvis
• Nephron: corpuscle (glomerulus + Bowman’s capsule) + tubules; primary site of plasma filtration

Gas Transport (Internal Respiration)

• In lungs: O_2 binds hemoglobin in RBCs
• At tissues: O2 released; CO2 diffuses into blood (in RBCs & plasma) → lungs for exhalation