Blood and Circulation & The Lymphatic System and Immunity Notes

Blood and Circulation

• Blood is a connective tissue that links all cells and organs in the body.
• Blood consists of:
  • Plasma: the fluid portion, containing water, dissolved gases, proteins, sugars, etc.
  • Formed portion: the solid portion, including red blood cells, white blood cells, and platelets.

Red Blood Cells (RBCs)

• Make up 44% of blood volume.
• Function: oxygen transport.
• Contain hemoglobin, an oxygen-binding protein.
• Lack a nucleus.
• Lifespan: 120 days.
• Anemia: a condition characterized by too few RBCs or too little hemoglobin.

White Blood Cells (WBCs) or Leukocytes

• There are approximately 700 RBCs for every 1 WBC.
• Possess a nucleus and appear colorless.
• Function: part of the body’s response to infection.
• Types of leukocytes:
  • Granulocytes: neutrophils, basophils, and eosinophils
    • Engulf and destroy foreign pathogens (e.g., bacteria, fungi, allergens, and parasites).
  • Monocytes
    • Leave the bloodstream to become macrophages.
    • Engulf and destroy bacteria.
  • Lymphocytes
    • Produce antibodies to defend against infection.

Hematopoiesis

• Multipotential hematopoietic stem cells (Hemocytoblasts) differentiate into:
  • Common myeloid progenitor:
    • Erythrocyte (Red Blood Cell)
    • Mast cell
    • Megakaryocyte → Thrombocytes (Platelets)
    • Myeloblast → Basophil, Neutrophil, Eosinophil, Monocyte → Macrophage
  • Common lymphoid progenitor:
    • Small lymphocyte → T lymphocyte, B lymphocyte → Plasma cell
    • Natural killer cell (Large granular lymphocyte)

Platelets (Thrombocytes)

• Do not contain a nucleus.
• Play a key role in blood clotting.
• Mechanism:
  • Injury to a blood vessel releases substances that attract platelets.
  • Platelets rupture, initiating a series of enzyme-catalyzed reactions.
  • Fibrin threads form a mesh around the injury, trapping blood and forming a blood clot.
  • The cascade of enzyme-catalyzed reactions is triggered by platelets, blood components, and damaged tissue.
  • Ca^{2+} is involved in the conversion of prothrombin to thrombin and fibrinogen to fibrin.
  • \text{prothrombin} \xrightarrow{Ca^{2+}} \text{thrombin}
  • \text{fibrinogen} \xrightarrow{Ca^{2+}} \text{fibrin}

Cellular Components of Blood Comparison

Plasma

• Fluid portion of blood.
• Carries blood cells and other substances.
• Transports carbon dioxide as bicarbonate ions.

Functions of Blood

• Transport
  • Nutrients, hormones, waste, gases.
• Homeostatic Regulation
  • Body temperature.
    • Vasoconstriction: blood vessels narrow to restrict blood flow to the skin and retain heat.
    • Vasodilation: blood vessels widen to increase blood flow to the skin and release heat.
    • Countercurrent heat exchange in deep arteries and veins also helps maintain a steady temperature in the body.

The Lymphatic System and Immunity

• The lymphatic system is a network of glands and vessels that carry lymph.
• Lymph is made of interstitial fluid and is similar to plasma.
• Functions:
  • Maintains the balance of fluids in the body.
  • Defends against infection.

Lymphatic System Circulation

• During blood circulation, some of the plasma leaves capillaries and enters the interstitial fluid.
• Much of this interstitial fluid is absorbed into the vessels of the lymphatic system.
• The lymphatic system is a one-way circulatory system (unlike the blood circulatory system) which transports lymph from closed-ended tubes toward the heart.

Lymph Nodes

• Protect the body against infection.
• Special white blood cells called lymphocytes mature in the lymph nodes.
• The lymph nodes also help trap and destroy bacteria in the body.

Lines of Defense Against Invaders

• There are 3 lines of defense the body uses against invaders:
  1. Barriers
  2. Non – specific defense (Macrophages)
  3. Specific defense (Antibodies)

Types of Pathogens

First Line of Defense

• Physical and chemical barriers.
• Examples: skin, eyelashes, cilia, tears, stomach acid, etc.

Second Line of Defense (Non-Specific Defense)

• Includes three types of white blood cells: macrophages, neutrophils, and monocytes.
• These cells all use phagocytosis to kill foreign particles.

Third Line of Defense (Specific Defense)

• Use of antibodies against invaders.
• Antibodies are proteins that recognize invaders and act to destroy them.
• This defense is largely aided by lymphocytes: B cells and T cells.
  • B cells – B lymphocytes; mature in the bone marrow; create antibodies.
  • T cells – T lymphocytes; mature in the thymus gland.

Antigens

• Markers on the surface of pathogens.
• T/B Cells and antibodies recognize these as invaders.

Antigen-Antibody Interaction

• Antigen – Antibody :: lock - key
• Memory B cells stay around to repeat an immune response if necessary.

Helper T-Cells

• When an invader is destroyed by phagocytosis, its antigens move to the surface of the cell that ate it (usually macrophages).
• Helper T-cells: recognize antigen and activate B and T-cells.

B-Cells

• B-cells form:
  • Plasma cells – produce antibodies to fight pathogens.
  • Memory B cells – remain in the blood to trigger a faster immune response upon 2nd infection.

T-Cells

• Killer T cells (Cytotoxic) – destroy pathogens by penetrating the cell membrane.
• Suppressor T cells – ensures normal tissue is not destroyed.
• Memory T cells – remain in the bloodstream to react immediately upon 2nd infection.

Interaction of Immune Cells

1. Bacterium enters body.
2. Macrophage engulfs the bacterium and pushes antigen markers to outer membrane of macrophage.
3. Helper T cell identifies the antigen present on the cell membrane of the macrophage.
4. The B cell identifies the blueprint of the antigen marker and begins to produce antibodies.
5. Antibodies attach to the antigens.

ABO Blood System

• Classification of human blood types based on the presence or absence of A or B antigens.
• Blood type is an inherited characteristic.
• There are four different blood types: A, B, AB, O.
• Each blood type has an antigen or marker attached to its cell membrane.
  • Blood type A - has an “A marker”.
  • Blood type B - has a “B marker”.
  • Blood type AB - has both A and B markers.
  • Blood type O - has neither.
• These markers act as antigens, and antibodies will be made to attack foreign invaders.

Blood Type Antigens and Antibodies

Blood Transfusions

• Antibodies act on the invading antigens.
• This causes agglutination - clumping of the blood; will occur when incompatible blood types are mixed.
• This is deadly.
• AB = universal recipient.
• O = universal donor.

Rh Factor

• Another group of antigens found on RBC.
  • Rh+ : Antigen is present, no antibodies.
  • Rh- : Antigen is not present, may or may not have antibodies.

Rh Factor Issues During Pregnancies

• Rh+ father and Rh- mother carrying her first Rh+ fetus.
• Rh antigens from the developing fetus can enter the mother's blood during delivery.
• In response to the fetal Rh antigens, the mother will produce anti-Rh antibodies.
• If the woman becomes pregnant with another Rh+ fetus, her anti-Rh antibodies will cross the placenta and damage fetal red blood cells.

Human Immunodeficiency Virus (HIV) and Acquired Immunodeficiency Syndrome (AIDS)

• Human immunodeficiency virus (HIV) is the cause of acquired immunodeficiency syndrome (AIDS).
• AIDS causes failure of the immune system, allowing infections and cancers to thrive.
• Transmitted through blood, semen, vaginal fluid, and breast milk.

Autoimmune Diseases

• Body attacks itself.
• T and B cells attack normal body cells.
• Examples:
  • Rheumatoid arthritis –immune response against the connective tissues of the joints.
  • Type 1 diabetes – immune reaction against the insulin-producing cells of the pancreas.
  • Multiple sclerosis – attack the myelin sheath of nerve cells.

Allergies

• When your immune system mistakes harmless antigens for harmful invaders.
• Reactions can be mild (tissue swelling) or severe (anaphylactic shock).