Respiratory system

General functions of the respiratory system

Gas exchange of O2 and CO2

- metabolism

- acid-base balance

defense

filter through which different substances pass

- substances can become activated or inactivated through pulmonary circulation

upper respiratory tract

nasal passages

mouth

pharynx (throat)

larynx (voice box)

trachea (windpipe)

lower respiratory tract

right & left mainstem bronchi

bronchioles

terminal bronchioles

respiratory bronchioles

alveoli

Alveoli

are the site of gas exchange

alveolar wall composition

Type I alveolar cells and embedded in the walls are type II alveolar cells which secrete surfactant

alveolar macrophages

remove dust and foreign particles along the alveolar surface

alveolar anatomy maximizes...? how many do adults have?

surface area. Adults have approximately 300 million alveoli.

Fick's Law

V'gas \= (A x D x (deltaP)) /T

where v'gas is the rate of diffusion, A is the cross-sectional area, D is the diffusion coefficient, deltaP is the pressure gradient, and t is the thickness of the membrane

3 components of gas exchange

1) ventilation: mechanical act of moving air into and out of lungs allowing air exchange between atmosphere and alveoli

2) diffusion of O2 and CO2 between alveoli and pulmonary capillaries

3) transport of O2 and CO2 in the blood

Lung anatomy

In thoracic cavity, they sit inside a pleural sac filled with intrapleural fluid.

layers of the pleural sac

outer layer is parietal pleura

inner layer is visceral pleura

lung's natural tendency

to collapse because of elastic nature and LaPlace's Law

Surfactant

combo of lipids & proteins - functions to disrupt H-bonding between water molecules along the alveoli surface

LaPlace's Law

P \= 2T/r

P (pressure), T (surface tension), r (radius)

do smaller or larger alveoli have a greater tendency to collapse? where is surfactant more concentrated, smaller or larger alveoli?

smaller, smaller

Lung properties

chest wall wants to expand outward

lungs have a tendency to assume a collapsed state

surface tension from intrapleural fluid ensures that the lung is held to the thoracic wall

Inspiration mechanics

the diaphram contracts & descends, generating a larger thoracic cavity and more negative pressure. Lungs will also expand. Patm\>Pa and air enters lungs.

Expiration mechanics

diaphragm relaxes and ascends \= smaller thoracic cavity and higher alveolar pressure. Pa\>Patm and air exits lungs.

Pneumothorax

intrapleural and alveolar pressures equilibriate.

lung assumes collapsed state and chest wall expands.

tension pneumothorax

lung punctured but thoracic cavity sealed off, so air accumulates in the pleural cavity and puts pressure on the chest vessels & heart (decreased cardiac output).

signs of tension pneumothorax

tracheal deviation, jugular vein distension, & hypotension.

treatment for tension pneumothorax

needle aspiration or chest tube to relieve pressure.

what device can be used to meausre the volume of air being breathed in and out as a function of time

spirometer

tidal volume (TV)

volume of air inhaled or exhaled in a normal breath (500ml)

inspiratory reserve volume (IRV)

Amount of air that can be forcefully inhaled after a normal tidal volume inhalation (3,000 ml)

Inspiratory capacity (IC)

tidal volume + inspiratory reserve volume (3,500)

Expiratory Reserve Volume (ERV)

Amount of air that can be forcefully exhaled after a normal tidal volume exhalation (1,000 ml)

Residual Volume (RV)

Amount of air remaining in the lungs after a forced exhalation (1,200 ml)

Functional Residual Capacity (FRC)

ERV + RV (2,200ml)

Vital Capacity (VC)

amount of air exhaled after a maximal inspiration (4,500)

Total Lung Capacity (TLC)

total capacity of the lung (5,700ml)

obstructive lung disease

difficulty getting air out

examples of obstructive lung disease

asthma, chronic bronchitis

spirometry findings of obstructive lung disease

higher residual volumes

- increased FRC

- increased RV

- decreased VC

restrictive lung disease

difficulty getting air in

Example of restrictive lung disease

pulmonary fibrosis

spirometry findings for restrictive lung disease

decreased TLC

decreased IC

decreased VC

FEV1/FVC ratio + normal ratio

FEV1 \= forced expiratory volume in 1 sec

FVC \= forced vital capacity

decreased ratio indicates an obstruction of airflow like asthma

normal ratio is around 80%

Pulmonary ventilation rate

pulmonary ventilation \= tidal volume x respiratory rate

Anatomic dead space

not all air makes it to the alveoli for gas exchange as some remain in conducting regions of the airway. Usually comprises about 150ml of tidal volume (500ml)

Alveolar ventilation rate

alveolar ventilation \= (tidal volume - dead space volume) x respiratory rate

Gas exchange occurs via...

passive diffusion down gases respective partial pressure gradients

A sufficient pressure gradient is critical for.... *KNOW THE NUMBERS ON THE DIAGRAM

the diffusion of O2 and CO2 at the pulmonary and tissue capillaries.

ventilation (V) is adjusted through

changes in airway smooth muscle

perfusion (Q) is adjusted through

changes in pulmonary arteriolar smooth muscle

V < Q mismatch compensation?

compensation involves increasing ventilation and decreasing perfusion

V \> Q mismatch compensation

decreasing ventilation and increasing perfusion

right to left shunt

when ventilation is reduced, the alveolar partial pressures approximate those of the blood meaning no gas exchange occurs.

physiologic dead space

when perfusion is reduced, the alveolar partial pressures approximate those of inspired air, meaning that no blood is around for gas exchange.

oxygen transport + percent of oxygen dissolved

Hb + O2

oxygen not very soluble in blood (1.5% dissolved)

resting pO2 at systemic and pulmonary capillaries

40mmHg, 100mmHg

What shifts the O2-Hb curve to the right?

increased pCO2

increased H+

increased Temp

increased 2,3-Bisphosphoglycerate

Carbon dioxide transport + solubility + enzyme

10% dissolved CO2, 30% carbamino hemoglobin, 60% bicarbonate

CO2 + H2O

*catalyzed by carbonic anhydrase

Chemoreceptors

sense changes in arterial PO2, PCO2, and H+ levels & trigger compensatory mechanisms.

central chemoreceptor and peripheral chemoreceptor locations

aortic arch and carotid sinuses

Main mechanism of ventilatory control

monitering brain ECF H+ concentration which is an indicator of arterial PCO2

when arterial PO2 < 60 mmHg

non CO2 H+ control mechanism