Hcb objectives 16



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HCB Objectives 16

1. Changes occurring from nose to alveoli in:



  1. Epithelium: Starts as “respiratory epithelium” in the nose (pseudostratified columnar ciliated epithelium with goblet cells) and loses its complexity to become simple squamous cells in the alveoli to allow for free gas exchange.

    1. Larynx: respiratory epithelium

      • Note: Epithelium on true vocal cords is stratified squamous for toughness to abrasion and dessication

    2. Trachea: respiratory epithelium

    3. Bronchi: respiratory epithelium

    4. Bronchioles: simple columnar to simple cuboidal ciliated

    5. Terminal bronchioles: simple cuboidal (Clara)

    6. Respiratory bronchioles: simple cuboidal (Clara)

    7. Alveolar ducts: few cuboidal and simple squamous

    8. Alveolar sacs: simple squamous

    9. Alveoli: simple squamous

  2. Smooth muscle: Important in contracting (constricting) and relaxing (dilating) the airways for increased/decreased gas exchange

    1. Larynx: skeletal muscle

    2. Trachea: trachealis (smooth) muscle in opening of C-shaped cartilage

    3. Bronchi: 4-5 layers of smooth muscle

    4. Bronchioles: 2-3 layers of smooth muscle

    5. Terminal bronchioles: 1-2 layers of smooth muscle

    6. Respiratory bronchioles: 1-2 layers of smooth muscle

    7. Alveolar ducts: 1-2 layers of smooth muscle

    8. Alveolar sacs: 1-2 layers of smooth muscle in “drumstick” extensions

    9. Alveoli: no smooth muscle

  3. Cartilage: Used for support of the upper airways where airflow can reach speeds of over 100 mph during a sneeze.

    1. Larynx: supported by hyaline cartilage rings

    2. Trachea: C-shaped hyaline cartilage rings

    3. Bronchi: incomplete plates of hyaline cartilage

    4. Bronchioles: no cartilage

    5. Terminal bronchioles: no cartilage

    6. Respiratory bronchioles: no cartilage

    7. Alveolar ducts: no cartilage

    8. Alveolar sacs: no cartilage

    9. Alveoli: no cartilage




  1. Glands: Goblet cells secrete mucus which is used to line the upper airways and prevent infections/dessication; would inhibit gas exchange in the conduction zone and are therefore not needed (macrophages live in the alveoli to kill pathogens). Seromucous glands are primarily concerned with keeping serous membranes lubricated so that potential space is maintained for regular expansion/contraction.

    1. Larynx: goblet cells and seromucous glands

    2. Trachea: goblet cells and seromucous glands

    3. Bronchi: goblet cells and seromucous glands

    4. Bronchioles: no glands

    5. Terminal bronchioles: no glands

    6. Respiratory bronchioles: no glands

    7. Alveolar ducts: no glands

    8. Alveolar sacs: no glands

    9. Alveoli: no glands

  2. Elastic fibers: Allows for expansion of respiratory tract during inspiration

    1. Pharynx: present

    2. Larynx: present

    3. Trachea: present

    4. Bronchi: present

    5. Bronchioles: present

    6. Terminal bronchioles: present

    7. Respiratory bronchioles: present

    8. Alveolar ducts: absent

    9. Alveolar sacs: absent

    10. Alveoli: absent

2. Clara cells: these cells are simple cuboidal cells found in the epithelia of interpulmonary bronchioles and terminal bronchioles. Their function is still unknown, but it is thought that they are important in detoxifying gases (by secreting CCSP).


3. Surfactant: surfactant is made by type II pneumocytes in the alveoli of the lungs. The function of surfactant is to reduce surface tension of water covering alveoli and also to keep alveoli from sticking to each other. Lack of surfactant causes respiratory distress syndrome in the newborn, the largest cause of premature birth death in the US.

  • Note: Survanta is an inhaled drug made of bovine lung extract that is used to keep surfactant on alveoli until premature babies can produce their own


4. Alveolar-capillary interface:


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