Breathing and Respiration

Chapter 5 

Breathing and Respiration

• Human Respiratory System

• The human respiratory system consists of:

1. The nose

2. Pharynx (throat)

3. Larynx (voice box)

4. Trachea (windpipe)

5. Bronchi

6. Lungs.

• Functions of Respiratory System:

• Respiratory system is responsible for gaseous exchange i.e. intake of 0 2 which required by body cells and elimination of Coz. which is formed as waste product by body cells.

• 1. Respiratory system also helps to regulate blood ph.

• 2. It filters inspired air, involved in production of vocal sounds (phonation).

Mechanism of Breathing and its Regulation

Respiration is the process of gaseous exchange in the body. This process is divided into three basic steps:

1. Breathing or pulmonary ventilation:

• Breathing is composed of two processes: inhalation and exhalation.

• The act of taking air in or inflow of air, is called as inhalation.

• The act of throwing air out or outflow of air is called as exhalation.

• Thus, breathing involves the exchange of air between the atmosphere and air of the lungs.

• During breathing, air flows between the atmosphere and the lungs because of alternating pressure differences created by contraction and relaxation of respiratory muscles.

Mechanism of Breathing:

• Inhalation and exhalation is dependent on pressure differences in lungs and atmosphere. The pressure difference is caused by changes in lung volume.

     The lumps must expand, for inhalation. Lung expansion increases lunp volume and thus decreases the pressure in the lungs to below atmospheric pressure.

iii. The lungs expand with the help of contraction of the main muscles of inhalation, the diaphragm (the dome-shaped skeletal muscle that forms the floor of the thoracic cavity) and external intercostals (muscles present between ribs).

• iV. Contraction of the diaphragm causes it to flatten, lowering its dome which increases the vertical diameter of the thoracic cavity. About 75% of the air that enters the lungs during quiet breathing due to contraction of diaphragm.

• V. Contraction of external intercostals elevate the ribs. As a result, there is an increase in the anteroposterior and lateral diameters of the chest cavity. About 25% of the air that enters the lungs during normal quiet breathing due to contraction of external intercostals.

• Vi. As the volume of the lump's increases in this way, the pressure inside the lungs, called the alveolar (intralumenal) pressure, drops. A pressure difference is thus established between the atmosphere and the alveoli.

• vii. Because air always flows from a region of higher pressure to a region of lower pressure, inhalation takes place. Air continues to flow into the lungs as long as a pressure difference exists.

Regulation of Respiration

• Respiratory center regulates the process of respiration. Respiratory center is widely dispersed group of neurons, located bilaterally in the medulla oblongata and pons of the brain stem.

It can be divided into three areas:

• The medullary rhythmicity area in the medulla oblongata: It controls the basic rhythm of respiration.

• i. The pneumotach The apneustic area, also in the pons: It co-ordinates the transition between inhalation and exhalation.

• area in the pons: It co-ordinates the transition between inhalation and exhalation.

Respiratory Volumes

    

• The apparatus commonly used to measure the volume of air exchanged during breathing and the respiratory rate is a spirometer or respirometer. The record is called a spirogram.

• While at rest, a healthy adult averages 12 breaths a minute, with each inhalation and exhalation moving about 500 mL of air into and out of the lungs.

• The volume of one breath is called the tidal volume (TV).

• The minute ventilation (MV): the total volume of air inhaled and exhaled each minute is respiratory rate multiplied by tidal volume:

MV = 12 breaths/min. x 500 mL/breath

= 6 liters/min.

   

• Inspiratory reserve volume: By taking a very deep breath, we can inhale a good deal more than 500 m L. This additional inhaled air, called the inspiratory reserve volume. It is about 3100 m L in an average adult male and 1900 mL in an average adult female.

• Expiratory reserve volume: If we inhale normally and then exhale as forcibly as possible, we should be able to push out considerably more air in addition to the 500 mL of tidal volume. This is called as expiratory reserve volume. It is 1200 mL in males and 700 mL in females.

• Inspiratory capacity is the sum of tidal volume and inspiratory reserve volume (500 mL + 3100 mL = 3600 mL in males and 500 mL + 1900 mL = 2400 mL in females).

• Functional residual capacity is the sum of residual volume and expiratory reserve volume (1200 mL + 1200 mL = 2400 mL in males and 1100 mL + 700 mL = 1800 mL in females).

• Vital capacity is the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume (4800 mL in males and 3100 mL in females).

• Total lung capacity is the sum of vital capacity and residual volume (4800 mL + 1200 mL = 6000 mL in males and 3100 mL + 1100 mL = 4200 mL in females).