RESPIRATORY SYSTEM l Physiology MCQs for dental students

RESPIRATORY SYSTEM l Physiology MCQs (multiple choice question) for dental students

 

INTRODUCTION in RESPIRATORY SYSTEM

 

The main goal of respiration is to provide O2 to the tissues and to remove CO2.

 

Respiration includes two processes:

a. External respiration: 

• the absorption of O2 and removal of CO2 from the body as a whole.

b. Internal respiration: 

• the utilization of O2 and production of CO2 by cells and the gas exchange between the cells and their fluid medium.

 

External respiration can be divided into four major steps:

1. Pulmonary ventilation,

• which means the inflow and outflow of air between the atmosphere and the lung alveoli; and distribution of air within the lungs.
• This process occurs through the breathing movements, and is regulated by respiratory centers present in the brain stem.

 

2. Diffusion:

• exchange of gases (O2 and CO2) between air in the alveoli and the blood in pulmonary capillaries.

3. Perfusion:

•    distribution of blood through the lungs.   
•    The normal volume of blood perfusing the lungs is 5-5.5 L/min. It is equal to cardiac output.

 

4. Gas transport:

• blood transports O2 from the lungs to the tissues and CO2 from the from the tissues to the lungs.

 

Structures of the respiratory system

 

I. Respiratory centers:

• located in the brain stem and connected to the respiratory muscles by respiratory nerve fibers.

 

II. Respiratory muscles:

1.    Muscles of inspiration.
2.    Muscles of expiration.

 

III. Airways:

•   The tracheobronchial tree, an arrangement of branching tubes begins at the larynx.
•   The largest airway is the trachea designated as generation 0.
•   The airway tree progressively bifurcates down to the alveolar sacs (generation 23).
•   Each generation is progressively smaller is both diameter and length.

 

Conducting zone:

•    The first 16 generations (generations 0 through 16)  
•    The larger conducting airways: made up of the trachea, bronchi and bronchioles (in succeeding generations, the number of bronchioles increases and the diameter diminishes).
•    transport air between the outside and the gas-exchanging regions of the lungs.

 

Respiratory zone:

•    The remaining 7 generations (generations 17 through 23)
•    The smaller respiratory airways: made up of respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli.
•    not only conduct air but also permit gas diffusion, which increases in significance closer to the alveoli (in the respiratory bronchioles a gradual transition in function from conduction to gas exchange occurs)

 

Functions of the conducting zone:

• The conducting zone of the respiratory system consist of the mouth, nose, pharynx, trachea, primary bronchi and all successive branching of the bronchioles up to and including the terminal bronchioles.

1. Conduction of air into the respiratory zone

2. Air conditioning

•     The mucosa of the nose, mouth and pharynx has a large surface area and a rich blood supply → this adds heat to cold air or remove heat from hot air → so when the inspired air reaches the respiratory zone, its temperature is 37° C (body temperature) regardless of the temperature of the atmosphere.
•    This function is needed to maintain a constant internal body temperature.

3. Humidification of inspired air

• Outside ambient air is dry (inspired air entering the respiratory system is rarely 100% saturated with water) → air is humidified to full saturation in moving from outside to within the airways → this function is needed to protect delicate lung tissue from desiccation.

 

4. Filtration and cleaning

• Mucus secreted by cells of the conducting zone serves to trap small particles in the inspired air and thereby perform a filtration function.
• Mucociliary escalator system:

1.    There are cilia projecting from the tops of epithelial cells that line the conducting zone (about 300 cilia per cell)
2.    Mucus is moved along at a rate of 1-2 cms per minute by cilia
3.    These cilia beat in a coordinated fashion to move mucus toward the pharynx where it can either be swallowed or expectorated (this system is termed the mucociliary escalator).
4.    Importance: particles larger than about 6 μm do not normally enter the respiratory zone of the lungs.
5.    Cilial beat may become ineffective under certain conditions such as anesthesia, smoking or prolonged dry air inspiration.

•   The alveoli themselves are normally kept clean by the action of macrophages that reside within them.

 

5. Protective reflexes

•    Irritant receptors (stimulated by irritants as smoke, allergens) located in the epithelium of airways mediate the protective responses of cough and bronchospasm.

 

6. Phonation

•    The larynx is adapted to act as a vibrator; the vibrating element is the vocal cords.
•    When air passes, across the vocal cords, it produces sound.