Infectious Diseases Affecting the Cardiovascular and Lymphatic Systems

Composition:
- Blood vessels: Transport blood to and from all regions.
- Heart: Pumps blood.
- Circulatory system: A closed circuit.
Functions:
- Provides oxygen and nutrients to tissues.
- Removes carbon dioxide and waste products.

Composition:
- Lymph vessels: Parallel blood vessels.
- Lymph nodes: Cluster at the groin, neck, armpit, and intestines.
- Spleen.
Function:
- Major source of immune cells and fluids.
- One-way passage: Returns fluid from tissues to the cardiovascular system.
Other lymphatic organs: gut-associated lymphoid tissue (GALT), the thymus, and the tonsils.
Direct connection between the two circulations occurs at points near the heart where large lymph ducts empty their fluid into veins.

Atria: Upper chambers.
Ventricles: Lower chambers.
Pericardium: Fibrous covering of the heart; occasional site of infection.
Wall of the heart:
- Epicardium: Outermost layer.
- Myocardium.
- Endocardium: Innermost layer, covering the heart valves and a common target for microbial infection.

Arteries: Carry oxygenated blood away from the heart under high pressure; branch into arterioles.
Veins: Start as venules in the periphery; carry deoxygenated blood back to the heart.
Capillaries: Smallest blood vessels; connect arterioles to venules; have one layer of endothelium.
Layers of blood vessels:
- Innermost layer: Endothelium; smooth surface for cell and platelet flow.
- Middle layer: Connective tissue and muscle fibers.
- Outer layer: Thin connective tissue.

Highly protected from microbial infection but vulnerable if invaded.
Infections can become systemic.
Defenses:
- 5,000 to 10,000 WBC per microliter of blood.
- Lymphocytes: Adaptive immunity.
- Phagocytes: Innate and adaptive immune responses.