Respiratory System Notes

Respiratory System Review

Structure and Function

• Upper Respiratory System (URS):

  • Nose
  • Pharynx
  • Middle ear
  • Eustachian tubes
  • Saliva: Protects mucosal surfaces.
  • Tears: Protects mucosal surfaces.
  • Parts of the larynx.

• Lower Respiratory System (LRS):

  • Trachea
  • Bronchial tubes
  • Alveoli: Site of gas exchange.
  • Ciliary escalator: Mechanism for removing particles.

Defenses of the Respiratory System

• First-line physical defense:
  • Ciliary escalator: Moves particles up and out of the body.
  • Alveolar macrophages: Immune cells that engulf microbes.
  • Respiratory mucus: Protects mucosal surfaces.

Treatment Considerations

• Lower respiratory infections are harder to treat than upper respiratory infections.

• Upper respiratory infections:

  • Treated with direct medications like nasal sprays.

• Lower respiratory infections:

  • Treated via nebulizer or inhaler: Medications must be small and aerosolized.
  • IV administration is another option.
  • Oral pills cannot directly target the lower respiratory system.

Normal Microbiota and Sterility

• Normal microbiota do not typically make us sick.
• The lower respiratory system is nearly sterile.

Microbial Diseases of the Upper Respiratory System (URS)

Common Infections

• Pharyngitis: Sore throat

• Laryngitis: Inflammation of the larynx

• Tonsillitis: Inflammation of the tonsils

• Sinusitis: Inflammation of the sinuses

• Epiglottitis: Inflammation of the epiglottis (most life-threatening)

• Suffix "-itis" denotes inflammation.

Epiglottitis

• Most life-threatening URS infection.
• Location of Epiglottis: Directs air to the lungs and food to the esophagus.
• Inflammation and swelling can obstruct the airway.
• Etiology: Haemophilus influenzae type b (opportunistic pathogen).

Streptococcal Pharyngitis (Strep Throat)

• Caused by Group A Streptococci (GAS).
• Primary agent: Streptococcus pyogenes

Virulence Factors of Streptococcus pyogenes

• Resistance to phagocytosis.
• Streptokinase: Lyses blood clots (different from coagulase).
• Streptolysins: Cytotoxic, cause local inflammation.

Diagnosis

• Visual inspection: Swollen, inflamed, red throat.
• Swab of the tonsillar area for:
  • Culture: Traditional method, takes time.
  • Rapid antigen detection test: Provides quick results.

Scarlet Fever

• Streptococcus pyogenes produces erythrogenic (reddening) toxin.
  • Toxin acquired via a virus.
• Symptoms:
  • High fever
  • Rash
  • Strawberry tongue

Diphtheria

• Caused by Corynebacterium diphtheriae.
• Gram-positive rod, pleomorphic (variable shape).

Pathophysiology

• Membrane formation in the throat: Fibrin, dead tissue, blocks air passage.
• Exotoxin: Produced when bacteria are lysed.
• Exotoxin Effects: If it circulates in the blood, the exotoxin can damage the kidneys and the heart.
• Cutaneous diphtheria: Skin ulcer with grayish coloring.

Prevention

• DTaP vaccine: The "D" stands for Diphtheria.

Otitis Media (Ear Infection)

• Pus accumulation on the eardrum.
• Eardrum Inspection: Doctors look for redness and inflammation of the eardrum.

Etiology

• Bacterial causes:
  • Streptococcus pneumoniae (strep pneumo)
  • Streptococcus pyogenes (strep pyo)
  • Moraxella catarrhalis
  • Haemophilus influenzae
• Viral causes: RSV and others.
• More common in children due to small auditory tubes.

Treatment

• Broad-spectrum antibiotics: Used since the exact cause is often unknown.
• Ineffective against viral infections.
  *Eardrum Appearance: Distended due to pus buildup.

Common Cold

• Typically caused by viruses.
• Etiology: Over 200 viruses can cause cold symptoms.
  • Rhinovirus: Thrives in lower temperatures.
  • Coronavirus
  • Enterovirus

Symptoms

• Sneezing
• Nasal congestion and secretion
• Not accompanied by fever (crucial distinction)

Treatment

• Supportive relief:
  • Cough suppressants
  • Antihistamines: Target mast cells. **