Study Notes for Human Anatomy & Physiology II (PSIO202)

Human Anatomy & Physiology II (PSIO202) Study Notes

Overview of Blood Components

  • Leukocytes (White Blood Cells)
    • Have a nucleus but lack hemoglobin.
    • Two categories based on staining and presence of cytoplasmic granules:
    • Granulocytes:
      • Neutrophils
      • Eosinophils
      • Basophils
    • Agranulocytes:
      • Monocytes
      • Lymphocytes
  • Thrombocytes (Platelets)
    • Platelets are cell fragments that circulate for 5-9 days.
    • 2/3 of platelets circulate in the bloodstream; 1/3 are stored in the spleen.
    • Involved in clotting and formation of thrombus (a clot).

Learning Objectives

  1. Describe the origin and production of various white blood cells.
  2. List characteristics and functions of white blood cells.
  3. Categorize white blood cell types based on staining.
  4. Describe the anatomy, physiology, and relevance of phagocytosis.
  5. Describe the structure, function, and production of platelets.
  6. Discuss chain reactions controlling blood loss after injury.
  7. Describe events leading to platelet plug formation.
  8. Diagram and compare key elements of the extrinsic and intrinsic clotting pathways.

Hematopoiesis (Formation of Blood Cells)

  • Progenitor Cells:
    • Includes precursors known as "blasts" that lead to formed elements of circulating blood.
  • Myeloid Stem Cells produce:
    • CFU-E (Colony-forming unit-erythrocyte)
    • CFU-Meg (Colony-forming unit-megakaryocyte)
    • CFU-GM (Colony-forming unit granulocyte macrophage)
    • Various types of blood cells such as erythrocytes, platelets, and leukocytes.
  • Lymphoid Stem Cells lead to:
    • T lymphocytes (T cells) and B lymphocytes (B cells).

WBC Physiology

  • Population Details:
    • WBCs are less numerous than RBCs; approximately 1 WBC for every 700 RBCs.
    • Leukocytosis: High WBC count due to infections, strenuous exercise, or stress.
    • Leukopenia: Low WBC count due to conditions like radiation or chemotherapy.
    • Only 2% of WBCs are in circulation at any time; most reside in lymphatic tissues.

WBC Emigration

  • WBCs can travel out of blood vessels to sites of infection.
  • They roll along the endothelium due to adhesion molecules, specifically selectins, displayed near injury sites.
  • Integrins assist neutrophils in moving through vascular walls.

Phagocytosis

  • Defined as "cell eating" of pathogens.
  • Performed primarily by neutrophils and monocytes; eosinophils exhibit weaker phagocytic activity.
  • Phagocytosis involves:
    1. Chemotaxis: Attraction of phagocytic cells toward infection.
    2. Adherence: Attachment of phagocyte to pathogen’s membrane.
    3. Ingestion: Phagocyte envelops the pathogen forming a phagosome.
    4. Destruction: Phagosome fuses with lysosome creating a phagolysosome, where pathogens are digested by enzymes (lysozymes).

Fibrinolysis (Clot Breakdown)

  • Fibrinolysis is the process where blood clots are dissolved to prevent embolism.
  • Process:
    • Tissue plasminogen activator, thrombin, and plasminogen form plasmin.
    • Plasmin digests the fibrin strands, effectively breaking down the clot.

Hemostasis (Blood Stoppage)

  • Hemostasis consists of three phases:
    1. Vascular Spasm:
    • Immediate vasoconstriction in response to injury.
    • Reduces vessel diameter and stops blood flow, effective in small vessels.
    1. Platelet Plug Formation:
    • Platelets typically do not adhere to endothelial lining.
    • Upon vessel damage, they stick to exposed collagen fibers and become activated.
    • Release substances like thromboxane A2 and ADP to attract more platelets, leading to a tight platelet plug.
    1. Coagulation (Blood Clotting):
    • The transformation of blood from liquid to gel (clot).
    • Approximately 30 substances involved, with 13 clotting factors, primarily produced in the liver.
    • Clotting occurs through intrinsic (slower) and extrinsic (faster) pathways.

Clotting Pathways

  • Extrinsic Pathway:
    • Initiated by tissue factor from damaged tissues.
    • Involves calcium ions and activation of factors leading to prothrombin activation.
  • Intrinsic Pathway:
    • Initiated by damage to blood vessels and activated platelets.
  • Common Pathway:
    • Prothrombinase formation, converting prothrombin to thrombin.
    • Thrombin converts fibrinogen to fibrin and activates factor XIII, stabilizing the clot.

Clinical Application: Bone Marrow Transplant

  • Procedure:
    • Destroy diseased marrow via radiation and chemotherapy.
    • Administer samples of healthy donor marrow (can also use stem cells).
    • Techniques treat diseases such as leukemia, lymphoma, and various anemias.
    • Success depends on histocompatibility between donor and recipient.

Clotting Factors and Vitamin K

  • Clotting factors such as prothrombin and fibrinogen are synthesized in the liver.
  • Vitamin K:
    • Essential for synthesizing factors II, VII, IX, and X.
    • Deficiency leads to failure in blood clotting, resulting in bleeding disorders, such as hemophilia (lack of factor VIII).