Respiration Mechanics

respiratory system contains

lungs and airways

1 pair of lungs contains ___ alveoli

300 million

total alveolar surface area

1000 ft^2

function of alveoli

site of gas exchange between air and blood

bicarb equation

CO2 + H2O

4 levels of respiratory cycle

1) ventilation (exchange between lungs and atmosphere) 2) exchange between lungs and blood 3) transport of gases in blood 4) exchange between blood and cells

upper respiratory structures

nasal cavity, pharynx, tongue, larynx

lower respiratory structures

trachea, primary bronchi, lungs (smaller bronchi, brochioles, alveoli)

2 types of airway cells

ciliated epithelial cells and goblet cells

ciliated epithelial cells

epithelial cells lined with many cilia to sweep mucus and particles up the respiratory tree

goblet cells

mucus-secreting cells sandwiched between ciliated epithelial cells

conducting system

carries and distributes air through the lungs to the exchange surface (includes trachea, bronchi --> terminal bronchi)

exchange surface

aka respiratory zone; where gas exchange occurs (includes respiratory bronchi and alveoli)

location, shape, and purpose of caritlage

purely structrual; found in decreasing amounts from trachea to small bronchi, goes from C-shaped to rings to plates

alveolus diameter

300um

alveolar sacs

alveoli clump into sacs at the end of bronchioles

2 types of alveolar cells

type 1 and type 2 cells

type 1 alveolar cells

0.2um thick alveolar cells for gas exchange

type 2 alveolar cells

secrete surfactant to give lungs compliance

what type of muscles are respiratory muscles

voluntary skeletal muscles; no autonomic innervation of muscles

muscles of inspiration

muscles used to expand the chest to breathe normally; includes intercostals and diaphragm

accessory muscles of inspiration

additional muscles recruited to take an active, deep breath

muscles of active expiration

additional muscles recruited to provide force for a harder expiration

muscles of expiration

expiration is usually a passive process; muscles are only used for expiration when providing additional force (muscles of active expiration)

intercostals

open the ribcage outward during normal inspiration

diaphragm

lower the bottom of the respiratory cavity during normal inspiration

sternocleidomastoid

pulls up on the ribcage to expand more during harder inspiration

scalenus

pulls up on the ribcage to expand more during harder inspiration

internal intercostals

pull ribcage closed during forceful expiration

abdominal muscles

push chest cavity up during forceful expiration

pleural sac

visceral & parietal pleura form a fluid-filled sac around each lung

parietal pleura

outer pleural membrane attached to ribs/chest wall

visceral pleura

inner pleural membrane attached to lungs

pleural fluid creates…

negative pressure in intrapleural space due to surface tension (pulls pleura together)

residual capacity

amount of air left in lungs after a passive exhale (where Palv = Patm)

transpulmonary pressure

acts as net distending force that keeps lungs open; Ptp = Palv - Pip

typical intrapleural pressure

-4mmHg relative to atmosphere

forces on pleural sac (4)

1) outward force on visceral pleura from elastic recoil of lung 2) inward force on visceral pleura from surface tension 3) outward force on parietal pleura from elastic recoil of chest wall 4) inward force on parietal pleura from surface tension

Dalton's Law

Ptotal is the sum of partial pressures

Boyle's Law

change in volume is inversely related to change in pressure

amount of gas dissolved in a liquid depends on

partial pressure, solubility, and temperature

intraalveolar pressure

pressure inside lungs

compliance equation

compliance = (Δlung volume)/(Δtranspulmonary pressure)

surfactant

mixture of phospholipids and protein that lowers the surface tension of water on the alveolar surface

how is surfactant released?

released from type 2 alveolar cells when stretched; deep breaths increase secretion since they stretch the cells more

Law of LaPlace

if 2 bubbles have the saem srface tension, the smaller bubble has greater pressure: P = 2T/r

effect of alveolus size on amount of surfactant

smaller alveoli have more surfactant to equalize pressures (Law of LaPlace)

factors impacting airway resistance

viscosity of air sometimes affected by humidity; mainly radius of airways

how does radius change in upper airways & bronchioles

upper airways: physical obstruction by mucus; bronchioles: constriction and dilation by autonomic innervation

tidal volume

volume of air moved by 1 regular inspiration and expiration; normal ~500mL

inspiratory reserve volume

additional air that can be inhaled with maximum effort

expiratory reserve volume

additional air that can be exhaled with maximum effort

residual volume

volume of air left in lungs after maximum active expiration; normal ~1200mL

total lung capacity

total amount of air in lungs aftyer maximum inspiration; normal ~5900mL

vital capacity

total amount of air moved into/out of lungs with maximum inhale/exhale; normal ~4700mL

dead space

space in respiratory tree where air is but cannot be exchanged @ alveolar surface; typically ~150mL

minute ventilation

volume of air moved in 1 minute; tidal volume*respiration rate

elastin fibers

fibers between alveoli contributing to elastic recoil of lungs

normal breathing uses __% of energy

3%