Cardiovascular and Lymphatic Systems: Infectious Diseases

Composition:
- Blood vessels: Carry blood to and from all regions of the body.
- Heart: Pumps the blood.
- Closed circuit known as the circulatory system.
Functions:
- Provides tissues with oxygen and nutrients.
- Carries away carbon dioxide and waste products.

Composition:
- Lymph vessels: Roughly parallel the blood vessels.
- Lymph nodes: Cluster at body sites such as the groin, neck, armpit, and intestines.
- Spleen
Function:
- Major source of immune cells and fluids.
- One-way passage: Returns fluid from the tissues to the cardiovascular system.

The lymphatic system consists of a branching network of vessels extending into most body areas.
Higher density of lymphatic vessels in 'dead-end' areas like hands, feet, and breast, which are frequent contact points for infections.
Other lymphatic organs include lymph nodes, spleen, gut-associated lymphoid tissue (GALT), thymus, and tonsils.
Direct connection between the two circulations occurs near the heart where large lymph ducts empty their fluid into veins.

Fist-sized muscular organ that pumps blood throughout the body.
- Atria: Upper chambers.
- Ventricles: Lower chambers.
- Pericardium: Fibrous covering of the heart and occasional site of infection.
Wall of the heart has three layers:
- Epicardium (outermost).
- Myocardium.
- Endocardium (innermost): Covers the valves of the heart; common target of microbial infection.

Arteries: Carry oxygenated blood away from the heart under relatively high pressure; branch into arterioles.
Veins: Begin as venules in the periphery of the body; carry deoxygenated blood back to the heart.
Capillaries: Smallest blood vessels, connect arterioles to venules and have only one layer of endothelium.
Layers of the blood vessels:
- Innermost layer: Composed of endothelium; smooth surface encourages the flow of cells and platelets.
- Middle layer: Composed of connective tissue and muscle fibers.
- Outer layer: Thin layer of connective tissue.

The cardiovascular system is highly protected from microbial infection.
- Microbes that successfully invade the system have access to every part of the body.
- Every system has the potential to be affected.
- Bloodstream infections are considered systemic infections.
Multiple defenses against infection:
- 5,000 to 10,000 WBC per microliter of blood.
- Lymphocytes: Adaptive immunity.
- Phagocytes: Critical to innate and adaptive immune responses.

Medical conditions involving the blood have the suffix -emia:
- Viremia: Presence of viruses in the blood.
- Fungemia: Presence of fungi in the blood.
- Bacteremia: Presence of bacteria in the blood.
Septicemia (sepsis): Bacteria growing and flourishing in the blood.
Septic shock: Cascading immune responses to septicemia, resulting in decreased blood pressure, a life-threatening condition.