Respiratory System In Humans Breathing Mechanism Class 10

Respiratory System In Humans: Respiration is a catabolic process, in which food materials are oxidised inside the living cells of the body to generate energy. Normally, glucose is used for this purpose. From one mole of glucose, about 686 Kcal energy is produced.Respiratory System In Humans is the system in humans that takes up oxygen and expels carbon dioxide. The function of respiratory system is to breathe in oxygen for respiration producing energy from food, and to breathe out carbon dioxide produced by respiration.

Two Steps In Respiration

Respiration is a much more complex process. It includes three main steps :

1. breathing or gaseous exchange,

2. gaseous transport through blood, and

3. oxidation of food inside the cell (or cellular respiration).

First two processes are together knows as external respiration. Organisms are adapted to various habits and habitats, therefore, breathing mechanisms (exchange of gases with the surrounding) in them are also variable. But the mechanism of cellular respiration (or internal respiration) is similar in all organisms. Since the mechanism of cellular respiration is similar in all organisms, including all plants and animals. So, we shall discuss it first.


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Cellular Respiration

Cellular respiration involves the actual oxidation (breakdown) of food material inside the cell. Due to this break-down, energy is produced. This energy is stored in the form of ATP Glucose is the most important fuel for the respiration. It is also called respiratory substrate. 

The mechanism of cellular respiration usually occurs in the presence of oxygen. But in few organisms, it occurs even in the absence of oxygen. Depending upon this, the cellular respiration may be of two types aerobic and anaerobic. 

1. Aerobic Respiration

In majority of the higher organisms, oxygen is sufficiently available inside the cell. Under such oxygen rich conditions, the pyruvate molecules enter the mitochondria and follow aerobic respiration. In aerobic respiration, pyruvate is completely oxidised into CO2 molecules. This respiration involves Kreb's cycle and ETC (electron transport chain).

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2. Anaerobic Respiration

In some organisms like Yeast, the energy is released from the food, even in the absence of oxygen This type of energy production is called anaerobic respiration. Anaerobic respiration occurs in the cytoplasm of the cells. It does not use mitochondria. During this process, the pyruvate molecules (formed in glycolysis), are not completely oxidised.

Instead, ethanol is produced as an end product. This process is also known as fermentation. Unlike aerobic respiration, this respiration is less efficient. The ATP production in this case is also very small, The overall equation for anaerobic respiration (or fermentation).

Respiratory System In Human Beings

human beings, like other land animals, are air breathers. Lungs are the main respiratory organs in human beings. The mode of respiration in human beings is called pulmonary respiration. The respiratory system in human beings consists of following parts :

1. Nostrils and Nasal Chambers

The tip of the nose has two small holes called nostrils. The nostrils lead internally into nasal cavity. The hair inside nostrils clean the air, and mucus, which is present in nasal cavity, trap the foreign particles.

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2. Pharynx (Throat)

· It is about 5 inches long, spacious chamber, which receives both, the nasal cavity and the oral (buccal) cavity.

· Pharynx leads into oesophagus and trachea. The opening of trachea is called glottis. It is guarded by a cartilaginous lid, called epiglottis.

· The glottis normally remains open but during food swallowing it gets covered by epiglottis to prevent the entry of food in trachea.

3. Larynx (Voice Box)

Larynx is a cartilaginous structure that produces sound and thus helps in speaking. It is located at the upper top of the trachea.

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4. Trachea and Bronchi

· Trachea (wind pipe) is a long tubular, hollow structure, which arises in pharynx and goes to the middle of the thoracic cavity. It serves as a passage for entry and exit of respiratory gases.

· The lower end of trachea is divided to form two branches, called primary bronchi (singular = bronchus). Each bronchus enters the lung of its side.

· Each bronchus inside the lung divides into many secondary and tertiary branches, which form bronchioles.

· Trachea and all bronchi have 'C' shaped cartilaginous rings on their outer-wall. These rings prevent trachea and bronchi from collapse, during expiration (exhalation).

5. Lungs (or Pulmonary Sacs)

· These are two, balloon like structures, which are the primary organs of respiration. These an present in the thoracic cavity, one on either side of the heart.

· Each lung is enclosed within a cover, called pleura.

· The left lung has two lobes, while the right lung has three lobes. Internally, the lungs contain many fine branches (bronchioles) and small ducts (respiratory and alveolar ducts).

· The terminal ends of these ducts open into millions of very small, delicate balloon like structures called alveoli (singular = alveolus).

· The alveoli are highly vascular (richly supplied with blood capillaries). Their wall is very thin and it forms respiratory surface for the exchange of goses.

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6. Ribs, Inter-coastal Muscles and Diaphragm

· There are 12 pairs of ribs in human beings. Ribs are bony and cartilaginous structures, that form the wall of thoracic cavity.

· One end of a rib is attached to vertebral column, while other end is attached to the sternum (breast bone). In this way, ribs form a cage like structure, called rib cage.

· Ribs protect lungs and heart.

· Ribs are provided with specialised muscles. These are called inter-coastal muscles. These a present in the space between two ribs.

· These muscles help in the outward and inward movement of ribs the bottom of the thoracie cavity. there is a large muscular flap. This is called diaphragm Normally, it is dome shaped. But during inhalation, it becomes flat.

Mechanism of Breathing

Breathing involves the intake of oxygen into the respiratory tract and elimination of CO2 The intake of oxygen is called inhalation or inspiration. The elimination of CO, 15 called exhalation or expiration.

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(a) Inhalation

· A During inhalation, the inter-coastal muscles pull the ribs outwardly and at the same time, diaphragm becomes flat.

· Due to these movements, the volume of the thoracic cavity increases but this creates a low pressure area inside the cavity.

· We know that air always moves from an area of high pressure to an erea of low pressure. So, air from outer atmosphere rushes into the thoracic cavity (lungs) through respiratory tract. This is called inhalation.

(b) Exhalation

· During exhalation, the inter-coastal muscles pull the ribs inwardly and at the same time, diaphragm again becomes dome shaped.

· Due to these movements, the volume of the thoracic cavity decreases. As a result of this a high pressure area is created inside the cavity.

· We know that air always moves from an area of high pressure to an area of low pressure. So, air from thoracic cavity (lungs), moves to the outside through respiratory tract. This is called exhalation.

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Rate of breathing

Breathing is mainly an involuntary process (that occurs automatically), but the rate of breathing is controlled by the respiratory centre of brain. Under normal conditions, rate of breathing is 15 to 18 times per minute. During vigorous exercise, the demand for oxygen increases the rate by about 20 to 25 times per minute.

In each breath, about 500 mL of air is exchanged. The cycle of inhalation and exhalation is repeated 15 to 18 times in a minute. Therefore, in 24 hours, we breathe in, about 15000 litres of air.

Breathing problems and respiratory failures occur when a person is unable to breathe normally. "Oxygen masks" are helpful in solving these problems. In serious cases, the patient is put on an equipment called "Ventilator" in which, a tube is inserted into the trachea to assist the patient in breathing.

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