Respiratory Physiology

Lung Embryology

Lung Embryology

  • LRT (lower respiratory tract) arises from laryngotracheal diverticulum.
  • Wk 24 – resp bronchi form, respiration is possible
  • Wk 29 – type II secrete surfactant (reaches adequate levels 2 wks before birth)
  • Trachea – C-shaped cartilage
  • Left bronchus longer, narrower, greater angle; bronchi have circum rings of crtlg; pseudostrat colum epi, Goblet, neuosecr, basal, brush cells
  • Epi à lamina propria à submuc à cartilage
  • Bronchioles – no cartilage, submucosal glands
1)      membranous – smooth muscle wall; ciliated columnar cells + Clara cells
2)      respiratory – alveolar ducts, alveoli budding from wals; no musc. wall; cuboidal cells +/- cilia

 

Lung Anatomy & Histology

Alveolar histology

Alveolar Histology

Cells that make up the aveoli.

1)      Type I Pneumocytes – flat sqm cells (alveolar epithelial cells)
2)      Type II – cuboidal cells that do alveolar repair and make surfactant
3)      Macrophage – phagocytic fxn; filled w/golden-brown “smoker’s pigment” in smokers
4)      Pores of Kohn – connect adjacent alveoli, does collateral ventilation
5)      Lambert’s canals – comm. b/w airway and adj alveoli, collateral ventilation
6)      Capillary endothelial cells
7)      Reticular elastic fibers and myofibroblasts

 

Alveolar Epithelial Cells

Alveolar epithelial cells refers to Type I and Type II pneumocytes which make up an alveoli.  Type I cells compose more than 95% and are involved in gas exchange.  Type II cells make surfactant.

Type I Pneumocytes

Type I pneumocytes are flat squamous cells of alveoli that are used for gas exchange.  They cover most (more than 95%) of the surface area of an aveoli.

Lung Anatomy

Lung Anatomy

·        3 right lobes; 2 left lobes + lingula; 10 bronchopulm segments bilat w/i lobes
·        lobule – smallest gross anatomic compartment of lung (3-5 terminal bronchioles, 30 pulm acini)
·        bronchial arteries arise from intercostals and aorta; bronchial veins return to azygos and intercostals veins
·        superficial lymphatics along pleural surface; deep (intrapulm) lymph adj to bronchovasc bundle and along interlob septa; connected

 

Lung Volumes Definitions

Meanings of Lung Volumes and Capacities

  • Tidal Volume:  during each normal breath, this the volume of air that is inspired and expired.
  • Expiratory Reserve Voume:  after expiration of normal amount of air (in Tidal volume), this is the amount of air that can still be expired with more effort.
  • Inspiratory Reserve Volume:  similar to the expiratory reserve volume, this is the amount of air that can still be inspired with more effort (after taking in a normal breath of air during a tidal volume).  Think of it as the extra amount of air that you can still breathe in after a normal breath. 
  • Residual Volume:  when we breath (inspire/expire), this is the volume of air that never actually leaves the lungs (this is because the alveoli still have some air in them even after we breathe out which keeps structural integrity of the lungs). 
  • Dead space:  there are 2 types of dead spaces: anatomic and physiologic.  Both refer to air that is not involved in gas exchange.

 Lung Volumes

Calculating Ventilation Rate

Ventilation Rate

 
There are different ways to express the rate a person is breathing. In respiratory physiology, these include Minute Ventilation and Alveolar Ventilation.
Minute Ventilation
Minute ventilation is equal to the Tidal Volume times the Breaths per minute.
MV = tidal volume x Breaths/minute
 
Alveolar Ventilation
Alveolar Ventilation is equal to Tidal Volume minus Dead Space times the breaths per minute.
AV = (tidal volume – dead space) x Breaths/minute
 
Dead Space
To get the Dead Space (for using in the alveolar ventilation equation), you can use the following formula:
Dead space = Tidal Volume x (PCO2 arterial – PCO2 expired air) / PCO2 arterial
 
This formula measures the physiological dead space.