16

Lecture 16: The Circulatory & Lymphatic System Infections

Anatomy of the Circulatory System

  • Also known as the cardiovascular system

  • Closed network of organs and vessels

    • Moves blood around the body

  • Purpose:

    • Deliver nutrients, oxygen, and immune factors to body tissues

    • Carry away waste (such as CO2) for elimination

Chambers and Valves of the Heart

  • The heart consists of four main chambers:

    • Two at the top: right and left atria (singular: atrium)

    • Main receiving chambers

    • Two at the bottom: right and left ventricles

    • Main pumping chambers

  • The heart chambers and spaces are connected by four valves controlling one-way blood flow:

    • Tricuspid valve: between the right atrium and right ventricle

    • Bicuspid (Mitral) valve: between the left atrium and left ventricle

    • Pulmonary valve: between the right ventricle and pulmonary trunk

    • Aortic valve: between the left ventricle and aorta

Blood Vessels

  • Five types of blood vessels:

    • Arteries:

    • Thicker walls and circular lumens

    • No valves

    • Carry blood away from the heart

    • Veins:

    • Thinner walls than arteries

    • Collapsed flat lumens

    • Have valves

    • Carry blood towards the heart

    • Arterioles: Smaller than arteries

    • Venules: Smaller than veins

    • Capillaries:

    • Smallest blood vessels with the thinnest walls

    • Made of a single layer of simple squamous epithelium for gas, nutrient, and waste exchange

  • Wall Structure of Blood Vessels:

    • All blood vessels (except capillaries) have three layers:

    • Tunica externa (most superficial)

    • Tunica media

    • Tunica intima (deepest)

    • Capillaries do not follow this structure.

Structure of Blood Vessels

  • Arteries and Veins:

    • Contain tunica externa, media, and intima

    • Arteries: include smooth muscle and elastic membranes

    • Veins: also contain smooth muscle and are structured similarly but thinner

Anatomy of the Circulatory System Continued

  • Divided into two circuits:

    • Pulmonary Circuit:

    • Takes deoxygenated blood from the heart to the lungs

    • Returns oxygenated blood back to the heart (drains into the left atrium)

    • Systemic Circuit:

    • Takes oxygenated blood from the left atrium through the aorta

    • Supplies oxygen to tissues and organs

    • Returns deoxygenated blood to the heart via systemic veins (drains into the right atrium)

The Lymphatic System

  • Open network of organs, vessels, and filters that circulate a colorless fluid called lymph

    • Purpose:

    • Protect against infection

    • Maintain fluid levels

    • Filter toxins

    • Absorb fats

  • Fluid leaks from blood vessels into interstitial space (now called interstitial fluid)

    • When picked up by lymphatic capillaries, it becomes lymph, travels through vessels, filtered by lymph nodes, and returns to the bloodstream

Major Lymphatic Organs and Tissues

  • Divided into:

    • Primary Organs: Sites for lymphocyte production and maturation

    • Bone Marrow:

      • B cells are made and matured

    • Thymus Gland:

      • T cells mature

    • Secondary Organs: Sites where lymphocytes migrate to encounter pathogens

    • Lymph Nodes

    • Spleen

    • Tonsils

    • Mucosal-Associated Lymphoid Tissue (MALT)

Development of B & T Lymphocytes

  • B Cells:

    • Released from bone marrow as immature lymphocytes

    • Differentiate and mature in the bone marrow

  • T Cells:

    • Released from bone marrow, mature in thymus

    • Migration to specific compartments of lymphoid organs such as lymph nodes

Secondary Lymphoid Tissues

  • Includes tonsils, lymph nodes, and spleen

  • Structures provide organized lymphoid follicles for immune responses

Interstitial Fluid and Lymphatic Circulation

  • Process:

    • Interstitial fluid picked up by lymphatic capillaries becomes lymph circulating through the lymphatic system

    • Interaction of blood capillaries, arterioles, and lymphatic vessels leads to filtration and return of lymph to blood

Infections of the Circulatory System

  • Sterility of the Circulatory System:

    • Normally shouldn't contain microbes

    • Low risk of infection due to closed system

  • Entry Points for Microbes:

    • Breaks in the skin (wounds, needles, insect bites) can introduce pathogens

    • Once in the bloodstream, microbes face various immune defenses (antibodies, complement proteins)

Terms Describing Bloodstream Infection

  • Bacteremia: Presence of bacteria in blood

  • Septicemia: Bacteria reproducing in blood

  • Viremia: Presence of viruses in blood

  • Toxemia: Spread of microbial toxins through the circulatory system

SIRS and Sepsis

  • SIRS:

    • Severe inflammatory response to microbes or toxins

    • Can damage host tissues and organs more than the infection

  • Sepsis:

    • A life-threatening dysregulated response to infection characterized by excess cytokine production

    • Sign symptoms include fever, vasodilation, edema

    • Affects critical organs, can lead to dysfunction, increased heart rate, disorientation, shock, and death if untreated

Inflammation of the Heart and Blood Vessels

  • Infections can cause various forms of inflammation:

    • Endocarditis: Inflammation of the endocardium, may damage heart valves, could require surgery

    • Pericarditis: Inflammation of the pericardium (sac around the heart)

    • Myocarditis: Inflammation of heart muscle tissue

    • Vasculitis: Inflammation of blood vessels, can lead to tissue ischemia and necrosis, possibly requiring surgery

Infections of the Lymphatic System

  • The lymphatic system does not have normal microbiota; mainly involved in fighting infections

  • Infections can cause localized swelling and trigger inflammatory responses

  • Lymphangitis: Inflammation of lymphatic vessels leading to red streaks under the skin

  • Lymphadenitis: Inflammation of lymph nodes causing swelling (called a bubo)

Bacterial Sepsis, Septic & Toxic Shock

  • Most common pathogens causing sepsis: bacteria, particularly from pneumonia, intra-abdominal, and urinary infections

  • Common Bacterial Causes:

    • Staphylococci, Streptococci, Pseudomonas, Enterobacteriaceae

    • Initially minor infections can progress rapidly to sepsis if untreated

Puerperal Sepsis

  • Also called puerperal fever, associated with childbirth complications

  • High mortality rate before the understanding of germ theory

  • Common pathogens include Streptococcus pyogenes and others

  • Diagnosis based on fever timing and identifying causative agents

  • Prevention: Key through antiseptics during delivery and handwashing protocols

Infectious Arthritis

  • Inflammation of joint tissues, primarily caused by bacteria

  • Can be Acute or Chronic:

    • Acute: Rapid onset due to bacteremia, often involving S. aureus or Neisseria gonorrhoeae

    • Chronic: More likely in patients with pre-existing conditions, responsible for 5% of invasive arthritis cases

Diagnosis & Treatment of Infectious Arthritis

  • Diagnosis:

    • Involves aspiration of synovial fluid for analysis

  • Treatment:

    • Use of antimicrobial drugs based on susceptibility testing

Osteomyelitis

  • Inflammation of bone tissues caused by infection

  • Caused by bacteria such as S. aureus, Pseudomonas, Enterobacteriaceae

  • Symptoms: Fever, localized pain, soft tissue swelling, resulting tissue damage

  • Diagnosis: Involves imaging and bacterial culture tests

  • Treatment: Antibiotic therapy, sometimes surgical intervention

Bacterial Endocarditis

  • Infection of the heart's endocardium, causes damage and can rapidly lead to death

  • Common pathogens include Staphylococcus and Haemophilus species

  • Higher risks in those with heart damage or prosthetic devices

  • Diagnosis: Blood cultures and echocardiography

  • Treatment: High-dose IV antibiotics

Gas Gangrene

  • Infection caused by Clostridium perfringens in ischemic tissues

  • Characterized by rapidly spreading muscle tissue death (myonecrosis)

  • Symptoms: Excruciating pain, foul-smelling wound, gas-filled blisters

  • Virulence Factors: Alpha toxin (lipase), theta toxin (pore-forming)

Plague

  • Caused by Yersinia pestis, a zoonotic infection accompanied by notable pandemics

  • Forms of Plague:

    • Bubonic: Caused by flea bites, characterized by swollen lymph nodes (buboes)

    • Pneumonic: Involves lung infection; highly contagious

    • Septicemic: Direct blood infection with a high mortality rate if untreated

Lyme Disease

  • Caused by Borrelia burgdorferi, transmitted by Ixodes ticks

  • Life Cycle of Tick: Hosts needed at various stages for transmission

  • Stages of Lyme Disease:

    • Early Localized: Rash and flu-like symptoms

    • Early Disseminated: Severe neurological issues if untreated

    • Late Stage: Long-term complications may arise, such as arthritis

Burkitt Lymphoma

  • Associated with Epstein-Barr Virus (EBV), prevalent in immunocompromised individuals

    • Primarily affects B lymphocytes, leading to solid tumors

  • Symptoms: Commonly axes fever, fatigue, lymph swelling

  • Diagnosis: Biopsies and imaging to stage cancer

  • Treatment: Rapid chemotherapy initiation due to quick tumor growth

Yellow Fever

  • Caused by Yellow Fever Virus, transmitted by mosquitoes

  • Symptoms: Varying from mild to severe with possibility of organ failure

  • Diagnosis: Based on symptoms, history, and lab tests

  • Treatment: No specific treatment; prevention is key (mosquito control)

Ebola Virus Disease (EVD)

  • Highly contagious viral infection with severe symptoms

  • Transmission: Through body fluids directly or indirectly

  • Symptoms: Fever, abdominal pain, hemorrhaging leading to potential death

  • Diagnosis: Difficult initially but can use ELISA or PCR for viral detection

  • Treatment: Supportive care; currently no effective antiviral treatments

Review Questions

  1. Two top chambers of the heart: Atria

  2. Tiny filters of the lymphatic system: Lymph nodes

  3. Walls of blood capillaries are made of: Simple squamous epithelium

  4. FALSE about primary lymphatic organs: They are where actual encounters with pathogens take place

  5. Inflammation of blood vessels: Vasculitis

  6. Releases nutrients, immune factors in interstitial spaces: Capillaries

  7. Spirochete-caused disease: Lyme disease

  8. Virus causing Burkitt lymphoma: Epstein-Barr virus

  9. Pathogen causing plague: Yersinia pestis

  10. Virulence factors for gas gangrene: Alpha and theta toxins

  11. Inflammation of bone tissues this is known as: Osteomyelitis

  12. Gram-positive bacteria leading to puerperal sepsis: Streptococcus spp., Staphylococcus spp., Enterococcus spp.