Physiology Chapter 2: Blood Functions and Characteristics

Physiology (0603302) Ch.2 Blood

• Blood is a liquid connective tissue circulating through blood vessels, pumped by the heart.
• Functions:
  • Transportation:
    • Transports nutrients (amino acids, lipids, glucose), hormones, and oxygen to cells.
    • Transports wastes and carbon dioxide away from cells.
  • Regulation:
    • pH buffering (7.35-7.45): Role of hydrogen and bicarbonate ions.
    • Body temperature regulation (water and vasodilation of surface vessels).
  • Protection:
    • Clot formation: Minimizes blood loss when a vessel is damaged.
    • Protection against foreign substances (antibodies and white blood cells).

Characteristics of Blood

• Blood volume:
  • Males: 5-6 liters
  • Females: 4-5 liters
  • Varies based on size and gender of individual.
• Color:
  • Red, with arterial blood being brighter (higher oxygen content) and venous blood being darker (lower oxygen content).
• pH:
  • Arterial blood (7.35-7.45)
  • Venous blood (7.32-7.42)

Blood Composition

• Cellular portion (formed elements):
  • Lower portion in a blood sample tube (buffy coat + red blood cells).
• Fluid portion (plasma):
  • Upper portion in a blood sample tube -The average adult has a blood volume of roughly 5 liters. -The blood plasma volume totals of 2.7-3.0 liters in an average human.

Components of Blood

• Plasma (Fluid portion):
  • Water (91-92%): Transport medium for materials carried in the blood.
  • Proteins (6-8%): Maintain blood volume and blood pressure.
    • Albumin (60%): Transport protein, steroid hormones, & maintains blood volume & pressure.
    • Globulins (35%): Transport hydrophobic lipids, fat-soluble vitamins, ions and hormones; Gamma is antibodies for immunity.
    • Fibrinogen (4%): Coagulation protein.
    • Regulatory proteins (<1%): Enzymes, proenzymes and hormones.
• Other solutes (1-2%): Electrolytes, organic nutrients (ATP production, growth, maintenance of cells), organic wastes (urea, creatinine, bilirubin), dissolved gases (O2, CO2).

1. Erythrocytes (Red Blood Cells)

• Number: 4.6-6.2 million/mm³ in men, 4.5-5.1 million/mm³ in women.
• Shape: Flat, bi-concave discs lacking a nucleus and mitochondria.
• Size: 7.5 µm in diameter and 2.5 µm thick.
• Derived from precursors in bone marrow
• Importance of shape: Provides increased surface area for diffusion of O2 and CO2.
• Functions:
  • Transporting hemoglobin, which carries oxygen from lungs to tissues.
  • Contains carbonic anhydrase, catalysing the reversible reaction between carbon dioxide and water, creating carbonic acid (H2CO3).
  • Hemoglobin is responsible for most of the blood's acid-base buffering power.
• Life span: 70-150 days.
• Degradation: Macrophages in the liver and spleen phagocytose damaged RBCs; hemoglobin is broken down into heme and globin; heme breaks down to iron (recycled), biliverdin, and bilirubin (excreted in bile).

Synthesis of Erythrocytes

• Areas producing RBCs:
  • Yolk sac (early embryonic life)
  • Liver, spleen, lymph nodes (mid-gestation)
  • Bone marrow (later gestation and throughout life).

Regulation of Red Blood Cell Production

• Decreased tissue oxygenation is the most important regulator of red blood cell production.
• Other factors include low oxygen concentration, high altitude, lung diseases, and heart failure.
• Erythropoietin (EPO) is secreted by the kidney in response to low oxygen levels, stimulating erythropoiesis (RBC production) in bone marrow.

2. Leukocytes (White Blood Cells)

• Mobile units of the immune system, destroying old/abnormal cells and attacking infections like bacteria and viruses.
• Phagocytosis and antibody formation are common mechanisms.
• Types & functions:
  • Neutrophils, monocytes, eosinophils, basophils, lymphocytes (B & T cells). - Function in innate and adaptive immunity.
• Lifespan: 13–20 days.
• Location of production: Partially in bone marrow, partially in lymph tissue.

3. Thrombocytes (Platelets)

• Cellular fragments (lack nuclei) from megakaryocytes in bone marrow.
• Irregularly shaped.
• Critical for hemostasis (stopping bleeding and maintaining vascular integrity).
• Release factors to stimulate the coagulation cascade, producing fibrin to form a clot.
• Average lifespan: 7-14 days.

Blood Clotting (Hemostasis)

• Process of stopping bleeding.
  • Steps:
    • Vessel damage.
    • Vasoconstriction slows blood flow.
    • Primary hemostatic plug forms, through aggregation of platelets.
    • Secondary hemostatic plug from fibrin reinforces the primary plug.
    • Clot retracts and endothelium is repaired.

Plasma vs Serum

• Plasma is the liquid part of whole blood containing clotting factors.
• Serum is plasma without clotting factors, obtained after blood clotting in tubes without anticoagulants.

Clinical Applications of Blood

• Anemia (reduced oxygen-carrying capacity)
  • Nutritional, pernicious, aplastic
• Polycythemia (excess RBCs, occurs in high altitude or rare cases)

Clinical Applications: Assessment of Blood

• Mucous membrane color (pink=well-oxygenated, blue=poorly oxygenated).
• Capillary refill time (CRT) (normal <2 seconds; delayed CRT indicates perfusion issues).

Explore the essential functions and characteristics of blood in this quiz based on Physiology Chapter 2. Discover how blood acts as a connective tissue, its role in transportation, regulation, and protection, as well as its volume and color differences. Test your knowledge on this vital component of the human body.