PSL301 Respiratory System Summary Notes

RESPIRATORY SYSTEM

Overview of Function and Structure
Functions
- transfer of ggases between air and blood
o O2 comes in  cellular respiration  ATP  CO2 expelled
- Regulation of body pH
o CO2 levels infuence pH of the blood
- Defence from inhaled pathogens/foreign paricles
- Vocalization
o Air needed over vocal cords

Structures that make up Respiratory System
- pharynx (where both air and food pass)
- vocal cords
- trachea  bronchus
- diaphragm (needed for letting air in and out)

Respiratory Muscles
- muscles of inspiration:
o sternocleidomastoids – attach to the top
o scalenes – attach from top and to ribs
o external intercostals – in between ribs
o diaphragm – key muscle below rib cage
- muscles of expiration
o internal intercostals – has diferent orientation as the external ones
o abdominal muscles
Lungs
- pleural sacs enclose the lungs
- two pleural membranes and pericardial cavity in between
- the double membrane structure forms the ‘sac’
Airways
- air is relatively dry and cold, thus the pathway makes it get warmer and
humidified
o air warmed to 37’C
o air humidified to 100%
o air filtered through nose and repspiratory cilia
- below larynx (voice cord) is trachea
- the trachea branches into two primary bronchi (left and right)
- primary bronchi then separates to secondary, and 22 more times terminating in a
cluster of alveoli
- filtering action of cilia – cilia beat in one direction and move the mucus to pharynx
side
- mucus layer traps inhaled particles. The particles then can be either coughed or
swallowed
o watery saline layer below mucus allow cilia to push mucus toward pharynx
- goblet cell secretes mucus
- immune cells along the epithelium also secrete antibodies to disable pathogens
o IgA
- Airway break down

, o 1st bifurcation: right and left main bronchi
o 2~4th bifurcation: lobar bronchi
 Cartilage maintains their shape (and smooth muscle)
o 5~11th bifurcation: segmental bronchi
o 12~16th bifurcation: terminal bronchioles
 stabilized by bronchiolar smooth muscles
o all the above are “conducting airways” = no gas exchange
o constitute an anatomical dead space
 air in this region does not exchange anything with cells

Lobules
- Primary Lobule (and below): region of gas exchange
- Approximately 300 million alveoli, each about 300um in diameter
- Total cross-sectional area is very large, about 180cm squared, and air velocity is
virtually zero
- Alveoli are covered with rich blood supply (from pulmonary artery and then back
to heart in pulmonary vein)
- The exchange is between single layer of endothelial
- Type I alveolar cell
o Constitute the wall of the tissue
- Type II alveolar cell
o Produce surfactants  allow lungs expand more easily
- Elastic fibers constitute as part of the connective tissue
- Alveolar macrophages
o Engulf foreign particles
- Alveolar gas exchange occurs via by passive difusion across endothelium
o Basement membranes are fused

Bloor transport to and from lungs
- 10% of the blood volume comes to lungs
- pressure is low: 25/8mmHg
- Heart (right ventricle)  pulmonary trunk  pulmonary arteries  pulmonary
arterioles  capillaries (oxygenated)  pulmonary venules  pulmonary veins 
heart (left atrium)
- Pulmonary metarteriole have many branches of capillaries coming out
o In case of embolus / blockage, others will cover and filter
o Systemic capillaries on the other hand, serve a particular area, so when
blocked, the area gets killed

Defending respiratory system
- filtering action of nose
- mucous and action of cilia lining the airways
- antibodies secreted onto respiratory surfaces
- macrophages in respiratory tract including alveoli

Lung function  must see the wave diagram
- measured by Spirometry
o clinically used often (ex. before an operation)
o person breathes into a tube