Pulmonary structure

From Iusmphysiology

• started here on 02/08/11 at 1PM.

Contents 1 Pulmonary structure 1.1 Objectives 1.2 Functions of the lung 1.3 Non-respiratory functions 1.4 Functional anatomy 1.5 Conducting zone 1.5.1 Air conditioning 1.5.2 Mucociliary escalator 1.6 Respiratory zone 1.7 Respiratory tract generations 1.8 Alveolar capillary interface 1.9 Alveolar surface 1.10 Alveolar interdependence 1.11 Emphysema (COPD) 1.12 Elastic recoil of lungs and chest wall 1.13 Transpulmonary pressure 1.14 Inspiration 1.15 Expiration 1.16 Accessory muscles of breathing 1.17 Accesory muscles of breathing 1.18 Lung volumes and capacities 1.19 Normal blood gas values 1.20 Abbreviations

Pulmonary structure

Objectives

Functions of the lung

• Pulmonary gas exchange
  • ventilation = frequency * depth of breathing
  • perfusion = cardiac output (CO) of right ventricle
    • close matching occurs between ventilation and cardiac output

• Maintenance of partial pressurs of gases in tissue

Non-respiratory functions

• Phonation
• Pulmonary defense
• Blood filter
  • They remove clots and emboli
  • They keep the venous clots from getting to the arterial side where they can cause larger problems.
• Acid-base balance
  • Use carbonic anhydrase reaction to help balance acid by breathing off CO2
• Substrate conversion
  • Have lots of ACE to help regulate blood pressure
  • Inactivates lots of things, too

Functional anatomy

• There are 23 generations of splits in the tubes
  • 1-11 have cartilage
    • Helps hold the airway open yet allows distension for esophageal distension
  • 1-16 have cilia
    • For moving mucus

Conducting zone

• this is generations 0-16
• Called deasd space because ther eis no gas exchange going on, no avleoli.
  • This protions receives blood flow from "systemic circ" = "broncheal circ"

Air conditioning

• Heated, cooled, moisturized.
  • body temp met by the endo fthe lower trachea
• Saturated with water
  • PH20 = 47 mmHg.

Mucociliary escalator

• In the first 16 generations
• Mucus on top of the cilia
• Catches particles
• Moves trapped crap up and out
• Macrophages clean up in alveoi
• In nasopharynx:
  • particles larger than 5 microns get trapped
• In bronchi (medium sized)
  • 1-5 microns settle onto mucus and are trapped
• In the small airways (the alveoli)
  • Hard to ge tup the tree so macrophages take care of them

Respiratory zone

• Generations 17-23 are for respiratory functions.
• Gas exchange!
• Pulmonary circulation supplies these generations
• Total surface area of the these generations is way bigger than the upper generations.
  • Approximately equal to a tennis court
• There are around 1000 caps per alveoli
• This is called the silent zone because degeneration in this area is largely silent.

Respiratory tract generations

• Generations 12-23 are held open by radial traction of the tissue.
  • That is, they all hold on to their neighbors and eventually some neighbor holds on to the pleural sac.
• Respiratory bronchioles start to have alveoli
• The tube with alveoli and all its alveolar sacs is the acinus.

Alveolar capillary interface

• Alveolus is very thing.
  • 0.2 to 0.5 microns
• Alveoli are connected by "something of Kahn".
• As the membrane thickens, diffusion decreases.

Alveolar surface

• Has type 1 squamous epithelial cells.
  • Cover 95% of the surface
• Type 2 alveolar cells make surfactant and regnerate type 1.
  • Much smaller than type 1
• Also, macrophages.

Alveolar interdependence

• As the chest wall expands, the alveoli expand and pull on their neighbors, etc.
• As one alveolus tries to colapse, it will expand it's neighbors.
  • So the collapsing alveolus will be held open by its neighbors.

Emphysema (COPD)

• Massive loss of alveolar interdependence.\
  • So interalveolar septum is lost and they don't hold one another open.
• As the tissue collapses, outflow is prevented.

Elastic recoil of lungs and chest wall

• How does air actually get into the lungs?
• Must have a pressure gradient.
• Lungs want to collapse, inherently.
• Chest wall wants to expand, inherently.
• To breathe in, we expand the volume in the interpleural space (become more negative in pressure).
• The balance between the force fo the chest wantting to expand and the lungs wanting to collapse generates the functional residual capacity
  • FRC = the residual volume at the end of a normal exhalation

Transpulmonary pressure

• Transpulmonary pressure = translung pressure.
• This is the difference between the pressure in the alveolus and the pressure in the pleural sac.
• Transpulmonary = PA - Ppl.
  • Ppl = pleural space pressure
  • PA = pressure in the alveolus
• This difference sets the gradient for breathing.
• The transpulmonary pressure is larger in magnitude with deeper breathing.

Inspiration

• This is the active phase of breathing meaning you have to do work and use energy.
• External intercostals move rips out and up
• Diaphragm lowers (flexes)

Expiration

• No work or energy needed
• Diaphragm relaxes (raises).
• Internal intercostals move ribs in and down

Accessory muscles of breathing

• Sternocleidomastoid and scalenes are the accessory muscles.
• Diaphragm and external intercostals can also give extra effort to help even more.

Accesory muscles of breathing

• Abdomiinal muscles will help force the diagragm up
• Internal intercostals will pull ribs down and in to help.

Lung volumes and capacities

• Just introduced now.
• This is called spirometry.
• Each tidal volume breath is 0.5L of air.
• Maximal inhalation leads to maximum lung capacity, usually around 6L
  • Transpulmonary pressure will be really high.
• Forced vital capacity is how much air an individual can move in and out of their lungs.
  • This brought us all the way down to residual volume = the volume of air in our lungs that we cannot get out.
  • Typically around 1.2L

Where does an unconscious, not breathing person sit?

• Where does one start?
  • After normal exhalation is our functional residual capcity (balance of chest wall and lung recoil; varies on size and disease, etc.); this is the start.

Normal blood gas values

• The lungs are for gas exchange.
• In the air we breath:
  • PIO2 = 102 (really high)
  • PICO2 = 0 (negligible)
• In the alveolus (PA):
  • PAO2 = 102
  • PACO2 = 40
• In the pulmonary arteries:
  • PaO2 = 40 (low b/c systemic tissues used it all up and sent it to the right heart)
    • Pa = systemic arteriole
  • PaCO2 = 46 (high b/c systemic tissues gave it all up and sent it to the right heart)
• In the pulmonary veins:
  • PVO2 = 102
  • PVCO2 = 40
  • Note that these "veins" represent what the systemic arteries will hold (once the blood gets through the left heart).

Abbreviations

• These are normal abbreviations for us to know.

• stopped here on 02/08/11 at 2PM.