Untitled Flashcards Set

🫀 Cardiovascular and Immune System Study Guide (Module 6)

1. Layers of the Heart Wall

• Epicardium: Outer protective layer; contains blood vessels and nerves.

• Myocardium: Thick, muscular middle layer; responsible for heart contraction.

• Endocardium: Inner lining of the heart chambers and valves; smooth surface for blood flow.

2. Poiseuille’s Law and Blood Flow

Poiseuille’s Law:

Q = \frac{\pi \Delta P r^4}{8 \eta L}

Where:

• Q = flow rate

• \Delta P = pressure gradient

• r = radius of vessel

• \eta = viscosity

• L = length of vessel

Clinical Relevance:

• Small changes in radius = big changes in flow (radius to the 4th power).

• Vasodilation increases blood flow, vasoconstriction decreases it.

• Important in blood pressure regulation, shock, and exercise physiology.

3. Vein Valves and Retrograde Flow

• Vein valves are semilunar in shape.

• They prevent backflow of blood—especially in the legs—when muscles contract and relax.

• Work with skeletal muscle pump to return blood to the heart against gravity.

4. Endothelial Cells: Dual Roles

Anticoagulant Role

:

• Produce nitric oxide (vasodilation, anti-platelet)

• Secrete prostacyclin (inhibits platelet aggregation)

• Express thrombomodulin (activates protein C to degrade clotting factors)

Prothrombotic Role

:

• When injured, endothelial cells release:
  

  • von Willebrand Factor (vWF) from Weibel-Palade bodies → activates platelets

  • Tissue Factor (TF) → initiates coagulation cascade

5. DVT (Deep Vein Thrombosis)

• Blood clot in a deep vein (usually leg).

• Biggest risk: Pulmonary Embolism (PE) → clot travels to lungs, blocking arteries.

• Can be life-threatening; often occurs with immobility, surgery, cancer.

6. Lymphoid Tissue Types

7. T-cell Selection (Positive & Negative)

Occurs in thymus to ensure self-tolerance and functionality.

Positive Selection

(in cortex):

• T-cells must bind weakly to self-MHC on cortical thymic epithelial cells (cTECs).

• Weak binding = survive.

• No binding = apoptosis.

Negative Selection

(in medulla):

• T-cells that bind too strongly to self-antigens are eliminated.

• Mediated by medullary thymic epithelial cells (mTECs) expressing AIRE.

• Prevents autoimmune T-cells.

8. T-cell Education Pathway

1. Enter corticomedullary junction as double negative (CD4-/CD8-).

2. In subcapsular zone, T-cells proliferate.

3. Become double positive (CD4+/CD8+) in cortex.

4. Undergo positive selection via cTECs.

5. Migrate to medulla, encounter AIRE-expressing mTECs for negative selection.

6. Exit as single positive CD4+ (helper) or CD8+ (cytotoxic) T-cells.

9. Germinal Center Reactions

Located in secondary lymphoid organs (e.g., lymph nodes, spleen).

Functions:

• Affinity Maturation: B-cells mutate antibody genes → select for higher affinity.

• Class Switching: IgM switches to IgG, IgA, or IgE based on cytokine signals → functional specialization.

• Result: Stronger, more effective immune responses.

10. Splenic Venous Sinusoids

• Sinusoids: Open, leaky capillaries in the red pulp of the spleen.

• Healthy RBCs squeeze through endothelial slits.

• Old/damaged RBCs get trapped and are phagocytosed by macrophages.

• Helps maintain healthy blood cell population.

⭐️ Summary of Major Pathways

🔹

Cardiovascular Flow Regulation

• Governed by Poiseuille’s Law: radius has biggest effect.

• Endothelial cells control vasodilation (NO) and clotting (vWF, TF).

• Vein valves and muscle pump prevent blood backflow.

🔹

T-Cell Development Pathway

1. Origin in bone marrow → migrate to thymus

2. Double negative → double positive → single positive

3. Positive selection: binds self-MHC = survives.

4. Negative selection: binds self-antigen strongly = deleted.

🔹

B-Cell Activation in Germinal Centers

1. B-cells bind antigen and present it to helper T-cells.

2. Enter germinal center:
   

   • Dark zone: Proliferation and mutation.

   • Light zone: Selection for high-affinity clones.

4. Class switch recombination and exit as memory or plasma cells.