Respiratory system Part 1

Pulmonary ventilation

The inflow and outflow of air between the alveoli and the outside environment.

Diffusion (respiratory)

The passage of $O_2$ from the alveoli to the blood and the passage of $CO_2$ from the blood to the alveoli.

Internal respiration

The phase of respiration consisting of systemic tissue gas exchange and cellular respiration.

Conducting Zone

The functional division of the respiratory system composed of rigid passageways (nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles) that transport, warm, moisten, and filter air.

Respiratory Zone

The functional division of the respiratory system where gas exchange occurs between air and blood, composed of respiratory bronchioles, alveoli, alveolar ducts, and alveolar sacs.

Pharynx

The throat passage that serves as a conduit for air leading into the trachea.

Larynx

The voice box structure where vocal cords are located.

Trachea

The windpipe that remains open and is lined with cilia to filter air before it reaches the lungs.

Bronchi

The two main branches located at the end of the trachea, each leading directly into a lung.

Bronchioles

A network of smaller branches extending from the bronchi into lung tissue that ultimately terminate at air sacs.

Inspiration

An active ventilatory process driven by diaphragmatic contraction (increasing vertical diameter) and external intercostal contraction (increasing anteroposterior diameter), dropping intrapulmonary pressure to $-1\text{ mmHg}$ to draw air into the lungs.

Expiration

A passive ventilatory process during quiet breathing in which the diaphragm relaxes upward and external intercostals relax, decreasing thoracic volume and raising intrapulmonary pressure to $+1\text{ mmHg}$ to expel air.

Boyle's Law

A gas law stating that pressure and volume are inversely proportional in a closed system at constant temperature, expressed as $P_1 \times V_1 = P_2 \times V_2$.

Pulmonary compliance

The change in lung volume that occurs when lung pressure increases or decreases by one unit.

Surfactant

A substance composed of phospholipids and proteins produced by Type II pneumocytes (septal cells) that reduces surface tension and molecular cohesion, preventing alveolar collapse during expiration.

Type II pneumocytes

Septal cells in the alveolar walls responsible for producing and secreting pulmonary surfactant.

Poiseuille's Law

A physical law stating that resistance to laminar airflow is inversely proportional to airway radius to the fourth power ($r^4$) and directly proportional to airway length, such that halving radius increases resistance 16-fold.

Laminar flow

Airflow occurring primarily in small peripheral airways where flow rate is low and driving pressure is directly proportional to gas viscosity.

Turbulent flow

Airflow occurring at high flow rates in large airways such as the trachea, where driving pressure is proportional to the square of flow and dependent on gas density.

Spirometry

A diagnostic technique used to measure the volume of air inspired and expired by the lungs.

Tidal volume ($V_T$)

The volume of air inspired or expired with each normal breath, typically equal to $0.5\text{ L}$.

Inspiratory reserve volume (IRV)

The additional volume of air that can be inspired by forceful inhalation beyond the end of a normal tidal inspiration ($2.5\text{ L}$).

Expiratory reserve volume (ERV)

The additional volume of air that can be expired by forceful exhalation beyond the end of a normal tidal expiration ($1.5\text{ L}$).

Residual volume (RV)

The volume of air remaining in the lungs after the most forceful expiration ($1.5\text{ L}$).

Inspiratory capacity (IC)

The total amount of air a person can inspire, calculated as the sum of tidal volume and inspiratory reserve volume ($V_T + \text{IRV}$).

Expiratory capacity (EC)

The total amount of air a person can expire, calculated as tidal volume plus expiratory reserve volume ($V_T + \text{ERV}$).

Vital capacity (VC)

The maximum volume of air moved into or out of the lungs during a single respiratory cycle, calculated as $\text{IRV} + V_T + \text{ERV}$.

Total lung capacity (TLC)

The maximum volume to which the lungs can be expanded after the most forceful inspiration, calculated as vital capacity plus residual volume ($\text{VC} + \text{RV}$).

4 processes of the respiratory system

1. external respiration

2. transport of gases

3. internal respiration

4. regulation of respiration

nose / nasal cavity

warms, moistens, and filters air as its inhaled

upper tract structures

1. nose

2. pharynx

3. larynx

lower tract structures

1. trachea

2. bronchi

3. bronchioles

which structure can be considered both upper and lower tract?

larynx

diaphragmatic movements

Inspiration = downward movement of the diaphragm that increases the vertical diameter of the chest cavity

Expiration = diaphragm relaces and moves upwards (passive process) causing the pulmonary pressure to increase

external intercostal muscle movements

inspiration = elevation of the ribs increases the anteroposterior diameter of the chest cavity

expiration = the intercostal muscles relax (ribs move backwards, passive process) causing the pulmonary pressure to increase

Boyles law in relation to inspiration and expiration

inspiration = increase in pulmonary volume = decrease in pulmonary pressure, therefore the pulmonary pressure is less than air pressure

expiration = decrease in pulmonary volume = increase in pulmonary pressure, therefore the pulmonary pressure is greater than air pressure

which direction does air flow (pressure wise)

areas of high pressure to areas of low pressure

what are the two types of pulmonary compliance?

1. inspiratory compliance

2. expiratory compliance

how does compliance help with ventilation?

Alveoli aren’t capable of expanding themselves, they only expand passively, therefore when inspiratory muscles contract the pleural pressure decreases, causing the pleura to pull the alveoli open and increase lung volume. Higher compliance means the lungs can expand more easily during inspiration, facilitating effective ventilation.

difference between ventilation and respiration

1. Ventilation = the process of moving air in and out of the lungs,

2. Respiration = the exchange of gases (oxygen and carbon dioxide) between the air and the bloodstream.

what prevents alveolus collapse during expiration?

1. Surfactant reduces surface tension, preventing alveolus collapse during expiration.

2. Intrapleural pressure remains negative

what creates septal cells (pneumocytes II)

formed by proteins and phospholipids

How does airflow and ventilation relate to each other?

ventilation depends on airflow

Two types of airflow

1. High airflow

2. low airflow

if the is flow is high what is called (occurs where)

turbulent airflow; occurs in larger airways (ex: trachea)

if the is flow is low what is called (occurs where)

laminar airflow; occurs in smaller airways (ex: bronchioles)