Essentials of Human Anatomy and Physiology

Overview of Kidney Disease and Anemia

  • Many individuals with advanced kidney disease suffer from anemia due to various factors affecting the oxygen-carrying ability of blood.

    • Key Reasons for Decreased Blood Oxygen Carrying Ability:

      • Decreased RBC Count

      • Decreased Amount of Hemoglobin

      • Decreased Availability of O2

Erythropoiesis Regulation

  • The regulation of red blood cell (RBC) production (erythropoiesis) involves various steps:

    1. Stimulus: Initial condition identified as low blood O2-carrying ability.

    2. Kidneys and Liver: Release erythropoietin (EPO) hormone to stimulate RBC production.

    3. Erythropoietin's Action: Stimulates red bone marrow to enhance erythropoiesis, increasing the RBC count.

    4. Outcome: Enhanced erythropoiesis increases the ability of the blood to carry O2.

Formation of White Blood Cells and Platelets

  • The production of leukocytes (white blood cells) and platelets occurs through hormonal stimulation:

    • Colony Stimulating Factors (CSFs) and Interleukins are released in response to chemical signals (e.g., inflammatory chemicals, bacteria). They prompt bone marrow to produce leukocytes and enhance their protective functions.

    • Thrombopoietin:

      • Secreted by the liver, accelerates platelet production from megakaryocytes.

      • Limited understanding of the regulatory mechanisms involved.

Bone Marrow Biopsies

  • To assess bone marrow conditions, a biopsy is performed:

    • Involves withdrawing a small sample of red marrow from flat bones (e.g., ilium, sternum) for microscopic examination.

Hemostasis

Learning Objectives

  • Describe hemostasis or the blood-clotting process.

  • Identify factors that inhibit/enhance hemostasis.

Hemostasis Process

  • Hemostasis involves a series of reactions to stop bleeding due to blood vessel injury, characterized by:

    • Vascular Spasms: Immediate response due to blood vessel injury, causing vasoconstriction and reducing blood loss.

    • Platelet Plug Formation: Platelets adhere to exposed collagen fibers in the damaged vessel and aggregate to form a plug.

    • Coagulation:

      • Tissue factor (TF) from injured tissues and PF3 from platelets interact with calcium ions (Ca2+) and clotting factors leading to thrombin production.

      • Thrombin joins soluble fibrinogen proteins to create insoluble fibrin threads, forming a meshwork that stabilizes the clot.

    • Clot Retraction: The clot contracts to pull the blood vessel edges closer together; serum is squeezed out, promoting healing.

    • Normal clotting time is approximately 3 to 6 minutes.

Disorders of Hemostasis

Undesirable Clotting

  • Occurs in unbroken vessels, particularly in the legs, resulting in a thrombus (clot).

    • Consequences of a Thrombus: Can obstruct blood flow to cells or lead to pulmonary thrombosis, which may cause hypoxia.

    • If a thrombus dislodges and travels, it becomes an embolus, which can obstruct smaller vessels (e.g., cerebral embolus causing stroke).

    • Factors contributing to undesirable clotting include:

      • Endothelial damage (e.g., physical blows, fatty deposits).

      • Slow blood flow or pooling, especially in immobile patients.

    • Anticoagulants: Medications like aspirin, heparin, and warfarin can reduce thrombus formation.

Bleeding Disorders

  • Commonly caused by:

    • Thrombocytopenia: Reduced platelet count leading to spontaneous bleeding from small vessels (e.g., petechiae).

    • Impaired liver function affecting clotting factor synthesis.

    • Hemophilia: Hereditary disorders causing deficiency in clotting factors, leading to severe bleeding from minor injuries.

    • Vitamin K deficiency can be corrected with supplements.

Blood Groups and Transfusions

Learning Objectives

  • Understand ABO and Rh blood groups and their importance in transfusions.

Blood Loss and Transfusion Needs

  • Significant blood loss leads to pallor and weakness.

    • Over 30% blood loss can result in severe shock, potentially fatal.

  • Blood Transfusion Procedures:

    • Collect blood from donors and mix with anticoagulants for storage (e.g., refrigerated for 35 days).

ABO and Rh Blood Groups

  • ABO Blood Groups:

    • Determined by the presence of antigens A and B on RBCs:

      • Type A: A antigens, anti-B antibodies.

      • Type B: B antigens, anti-A antibodies.

      • Type AB: Both A and B antigens, no antibodies.

      • Type O: No antigens, both anti-A and anti-B antibodies.

  • Rh Blood Groups:

    • Classified based on Rh antigen (D). Rh+ individuals carry the antigen; Rh- do not produce anti-Rh antibodies unless exposed to Rh+ blood.

    • First exposure does not usually lead to hemolysis, but subsequent exposures do.

Blood Typing Process

  • Determining blood type involves:

    • Mixing blood with anti-A and anti-B serums to observe agglutination reactions.

    • Cross-matching to ensure donor and recipient compatibility.

Developmental Aspects of Blood

Learning Objectives

  • Explain physiologic jaundice in newborns.

Fetal Hemoglobin (HbF) vs. Adult Hemoglobin (HbA)

  • Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin, which is critical for oxygen transport.

  • Physiological jaundice in newborns arises from the breakdown of excessive fetal RBCs faster than the immature liver can clear the hemoglobin breakdown products.

Blood Disorders in the Elderly

  • Increased prevalence of chronic leukemias, anemias, and clotting disorders in older adults.

    • Particularly susceptible to pernicious anemia due to dietary insufficiencies from impaired absorption of vitamin B12 due to aging stomach mucosa.