L10: Respiratory I

Respiratory functions of the respiratory system

• Gas transport for metabolism

• Move oxygen from the air into pulmonary blood

• Clearance of carbon dioxide

Non-respiratory functions of the respiratory system

• Lungs receive 100% of the cardiac output from the right heart.

• Filter blood, chemical processing, maintenance and defenses (part of the first line of defense)

• Facilitate venous return (respiratory pump)

Define respiration

Interchanges of gases between the atmosphere and the cells of the body

Define ventilation (breathing)

Air transported through the airways to and from the atmosphere to the respiratory zone of the lungs

Define gas exchange

O2/CO2 exchange between the air in the lungs and cells in the body

Define cellular respiration

oxidation of cellular molecules that produces CO2, water and ATP

Overall gas transport includes:

1. Ventilation: movement of bulk airflow, delivering air to the respiratory zone where gas exchange occurs

2. Gas exchange/Lung diffusion: gas exchange between respiratory zone and blood - O2 moves across to blood and red blood cells; reverse process for CO2

3. Circulation/Transport (Blood ⇔ tissues): Requires adequate function of the pulmonary and systemic circulations

4. Tissue diffusion: Erythrocyte/plasma ⇔ tissue cells = Passive diffusion

5. Internal respiration: metabolism using O2 and producing CO2

Airways for ventilation include:

System of tubular structures:

• Nasal and oral cavities

• Pharynx and larynx

• Trachea

• Bronchi

• Bronchioles

*Bronchioles connect to alveoli where gas exchange occurs

Main functions of airways

-Delivering gas to the respiratory zone (alveoli)

-Conditioning of the inhaled air:

• Air warmed to core body temperature (prevents temperature choc in the alveoli)

• Gas humidification: saturation with vapor to prevent dehydration of the respiratory epithelium in alveoli

• Filtration, cleansing: prevents foreign objects and microorganisms to enter the lungs (reduces risks of injury and infection)

Structure of nasal/oral cavities

• Inner surface = mucous membrane that warms and humidifies air

• Some species = hair in nostrils act as first filter

• Epithelium contains ciliated cells and mucus cells (goblet): trap foreign objects, move the mucus towards the pharynx

Structure of pharynx

Connection between nasal/oral cavity and the larynx

Structure of larynx

• Connects pharynx and the trachea: glottis and epiglottis = cartilage that prevents food to enter the trachea

• Contains the vocal cords

Structure of trachea

• Flexible tube kept open by cartilage rings

• Inner surface lined with ciliated and mucus cells

• Mucus traps particles, and coordinated cilia movements push the trash back toward the pharynx

Structure of bronchi (in the thoracic cavity)

• Possess cartilage plates to maintain the shape

• Starts with 1 tube per lung = primary bronchi

• Branches off to narrower tubes with less cartilage

• possess ciliated and mucus producing epithelial cells

Structure of bronchioles

• Lack cartilage = depend upon lung recoil to maintain potency. Possess smooth muscle

• possess ciliated and mucus producing epithelial cells

Airway cross-sectional area increases DRAMATICALLY moving from:

Trachea to respiratory zone:

• Geometric increase in number of small airways

• Reduces velocity of airflow to virtually ZERO

• Movement of gas in respiratory zone by DIFFUSION only

• Velocity (cm/sec) = flow (cm3/sec)/cross-section area (cm2)

Airway clearance

• Cilia and globlet cells work to move thin sheet of mucus from lower parts of the lungs to the throat region

• Defensins: Airway “Lysol” – destroy bacteria; first line of defense (2nd line is immune system proper)

Endoscopic View: Trachea

• Accumulation of mucus and pus in the trachea associated with inflammation of the lower airways. Turbulence is create, and more resistance to air.

• Role of the environment

Alveoli characteristics

Respiratory zone

• Clusters around terminal bronchioles

• Formed by a single layer of epithelial cells

• Adult human: covers 75-80 m2

• Directly surrounded by a capillary network

• Air separated from blood by 2 layers of cells (epithelium and endothelium): best for gas exchange

• Some epithelial cells (type 2) produce fluid = surfactant which reduces surface tension, by breaking h-bonds

• If small particles reach alveoli = “phagocytized” by macrophages (immune defense)

Thoracic cavity characteristics

Space within the thoracic cage between:

• Thoracic vertebras

• Ribs and intercostal muscles

• Sternum

• Includes the Diaphragm and Mediastinum

Diaphragm characteristics

• separate, thoracic and abdominal cavity

• sheet of skeletal muscles and tendon

Mediastinum characteristics

• Divide thoracic cage in 2 halves (from spine to sternum)

• Connective tissue containing vessels, nerves, trachea, esophagus and the heart

• Each lung fills 1 half

Pleural membranes and characteristics

• wet epithelial surfaces, attached to and covering the lungs

• parietal membrane is connected to the diaphragm which distends the lungs and also anchored around the cage

• Intrapleural space (between visceral and parietal pleura) filled with small amount of fluid = lubrication for friction free movements

Ventilation characteristics

• Follows the laws of physic: flow from high to low pressure = depends on ΔP

• Resistance to flow (R) due to friction of air particles with each others and with the ducts

• Air flow concept similar to blood flow (F = ΔP/R)

• Resistance in airways normally small → ΔP major factor

Blood flow

F (flow) = ΔP/R

• If R ↑, ΔP must ↑ to maintain air flow

• If ΔP ↓, R must ↓ to maintain air flow

What controls ΔP

Compression/expansion of the lungs by respiratory muscles

Ventilation Pump (mechanics): Inspiration

Active mechanism

• Diaphragm contracts → expands thoracic volume, creates negative pressure → lung expands → increase in alveolar volume → negative pressure gradient facilitates flow down airways from outside towards the respiratory zone

• at rest diaphragm most important muscle

• P alveolar < P atmos = propels air through the airway until P alveolar = P atmos

Ventilation Pump (mechanics): Expiration

Passive mechanism (at rest)

• End of inspiration – inspiratory muscles relax, allows lung to spontaneously recoil → increase pressure in alveoli → create pressure gradient from alveoli to atmosphere

• P alveolar > P atmos = airflow outward until equilibrium reached

Boyle’s law of gases

For a gas at a set temperature, pressure and volume are linked: P1V1 = P2V2

• If volume (V) ↑ = pressure (P) ↓

• If volume (V) ↓ = pressure (P) ↑

Special case in horses

End of expiration active → beginning of inspiration passive (recoil)

Special case: Locomotion (walking, running)

• More than just the diaphragm and intercostal muscles involved

• Muscles take active part in expiration (speeds it up)

• Galloping: synchronization with breathing

Special case: Diving mammals

• Voluntary apnea (up to 1 h)

• Strong conducting airways

• When under water, compressed gas pushed towards the air ways (no gas exchange) = prevents entry of gas in blood

• Generally, do not dive with full lungs

Factors influencing ventilation

Air ways resistance:

• Mostly in nasal cavity (diseases, obstruction)

• During exercise, animals mainly use mouth to reduce resistance (except horses: flare nostrils)

• Degree of turbulence: more turbulence = more resistance

• Diameter: reduced with branching = increase resistance. Parallel branches results in increased cross/section (surface area) which compensates for increased resistance

• Autonomic nervous system controls smooth muscle in bronchiole: Sympathetic relaxes cells = increased diameter, Parasympathetic contracts cells = reduces diameter

Lung compliance in ventilation

Ability of the lung to distend followed by the ability to recoil:

• Elastic fibers in the lung

• Muscle tissue in the intercostal muscles

• Depends on the elasticity of the tissues in the lung and the thoracic cage

• Depends on the surface tension in the alveoli

What causes alveolar surface tension

Due to hydrogen bonds in water molecules when on contact with air (gives water drops their shape)

Alveolar surface tension causes:

• Tends to reduce the surface area

• Since alveoli lined with moisture, it creates a surface tension against distension

Alveolar surface tension is reduced by the presence of..

SURFACTANT

• Mixture of phospholipids, Ca2+ and proteins

• Phopholipids reduce the surface tension between hydrogen molecules

Barker syndrome in piglets

inadequate production of surfactant = ↑ surface tension = ↑ resistance to distension = ↓ ventilation.

Pulmonary volumes: Spirometer

measure volumes of air inhaled and exhaled (Spirogram = recording)

Tidal Volume (CVT)

Volume flowing through airways

Inspiratory Reserve Volume (IRV)

It is possible to further force more air during inspiration by maximum contraction of respiratory muscles

Expiratory Reserve Volume (ERV)

After normal expiration, it is possible to force more air out

Residual Volume (RV)

After ERV forced out, there always remains air in the lungs

Vital capacity (VT)

is the maximum air that can be inhaled and exhaled

Total lung capacity =

Residual Volume (RV) + Vital capacity (VT)