RBSE Class 12 Biology Notes Chapter 23 Man-Respiratory System

Rajasthan Board RBSE Class 12 Biology Notes Chapter 23 Man-Respiratory System

General

1. Body needs energy to perform various vital activities. This energy is obtained mainly by oxidation of carbohydrates & fats.

2. Oxidation of these substance consume O₂ & release CO₂. The process of consumption of O₂ and the release of CO₂is termed as respiratory exchange.

3. According to Carter, respiration involves external respiration, internal respiration & cellular respiration. Mammals exhibit aerial respiration which needs respiratory system.

4. The respiratory system concerns with intake of O₂ and giving out of CO₂.

Types of Respiration

The respiration is of two types :

External respiration : It takes place in the lung alveoli, taking in of O₂ and giving out of CO₂ is termed as external respiration or Breathing or It is a physical process.
Internal respiration : In take of O₂ by the body cells and production of CO₂ and ATP is called internal or cellular respiration.

The internal respiration is of two types :

Aerobic respiration: Cellular respiration in presence of O₂ is called as aerobic respiration.
Anaerobic respiration : The cellular respiration in lack of O₂ is called as anaerobic respiration.

Respiratory Organs of Human beings

The respiratory passage includes following organs :

Nostrils

There is a pair of external nares ivhich are situated obliquely at the tip of the snout. This condition is called as dirhynous.
Their cavities are called as fossae or nasal passage. Both
the fossae remain separated by a nasal septum which is made up of mesethmoid cartilage.

Nasal Cavities

1. The external nares open into nasal cavities which are situated dorsally to the palate. The nasal cavities open into the naso-pharynx through a pair of internal nares or

2. Nasal cavities are formed as an invagination of the skin and it contains a turbinal bone which is a scrolled & porous bone, The projections of the turbinal bones are called as conchae.

3. The nasal cavities remain lined by pseudo-stratified epithelium which is ciliated & glandular.

4. There are Bowmann’s glands to secrete the mucous.

5. The nasal epithelium is olfactoreceptor and it is also called as Schneiderian epithelium.

Functions of nasal cavities

It filters the inspired air
It acts as olfectoreceptor
According to new researches, it is provided with pheromones receptors.
It maintance the temperature of inspired air bycooling/warming the air.
It makes the inspired air moist.

Pharynx.

It’s dorsal part is called as naso-pharynx & ventral part as oro phary nx.
Posteriorly, it has two openings viz.-gullet (dorsal) & glottis (ventral). The gullet leads into an oesophagus & the glottis opens into a larynx.
The glottis remains covered by a cartilagenous flap which is called as epiglottis. The epiglottis prevents the entry of food & water into the larynx.

Larynv

It is located in the anterior end of the throat which is formed by the modification of anterior end of trachea.
It is also called as sound producing organ.

Formation of larynx involves 4 cartilages which are of 3 types viz.—

Thyroid-one largest, C-shaped & forms ventrolateral sides.
Cricoid—one, ring-like, broad dorsally & forms base of the larynx
Arytenoid-Two small & form dorsal side.

(i) The anterior end of the arytenoid cartilage is knob-like and it is called as cartilage of Santorini.
(ii) The larynx has two pairs of elastic vocal cords which remain stretched between the thyroid and arytenoid cartilages :

Anterior or False vocal cords
Inelastic & pinkish in colour
Posterior or True vocal cords

Trachea or Windpipe

It is a simple tube which is elastic & semi-transparent.
Its length in man is of 10 cm.
It is located in the neck ventral to the oesophagus.
It is lined by pseudostratified epithelium & ciliated internally. These cilia beat constantly to force out the mucous.
The trachea is supported by tracheal rings made up of hyalin cartilage. These rings are C-shaped e. incomplete dorsally to facilitate oesophageal movements.
The posterior end of trachea bifurcates to form two These bronchii are also thin-walled & elastic but they are supported by complete cartilagenous rings. Each bronchus enters into its respective lung.

Lungs

1. Man have a pair of lungs which are situated in the thoracic cavity on both the sides of the heart.

2. The lungs are elastic, spongy, light pink, unequal & without muscles.

3. In human being, the left lung consists of two lobes viz. – left superior lobe & left inferior lobe. Whereas, the right lung includes three lobes viz.-superior lobe, middle lobe & inferior lobe.

4. Each lung is bounded by two pleural membranes –

External or Parietal pleuron
Internal or Visceral pleuron

5. Both the pleura remain closely applied to each other.

6. The space between the lung and the pleura is called as pleural cavity,

7. Each bronchus enters into the lung of own side & divide to form secondary or lobular bronchii (4 secondary bronchii in right lung & 2 secondary bronchii in left lung). Each secondary bronchus divides to form tertiary or segmental bronchii, which further divide to form intra- pulmonary bronchi

8. The ends of intra-pulmonary bronchi divide to form terminal bronchioles which further form respiratory bronchioles. These bronchioles lack cartilagenous

9. Each respiratory bronchiole gives out 2 to 11 alveolar ducts. Each alveolar duct gives out small ducts, the Each atrium forms small bag-like alveoli or air sacs which are made up of squamous epithelium. Internally, the alveolous is lined by mucous & there is network of blood capallaries outside. The alveoli provide more surface for the exchange of gases.

Inspiration

Entry of air into the lungs is called as inspiration or inhalation
It involves :
Contraction of the diaphragm muscles. As a result, it moves downwards e. the diaphragm becomes flat.
Contraction of external intercostal muscles & relaxation of internal intercostal muscles. As a result, the ribs move outward & forward i.e. antero-ventral movement of the ribs. ‘
The above changes in the factors cause an increase in the thoracic volume but the thoracic pressure is reduced. Hence, due to less pressure air enters into the lungs.

Expiration

Exit of air (CO₂) from the lungs is called as expiration or

It involves :

1. Relaxation of the muscles of the diaphragm. As a result, the diaphragm moves upwards & reasumes dome shape.
2. Contraction of internal intercostal muscles and relaxation of external intercostal muscles. As a result, the ribs move inward & backward i.e. postero-dorsal movement of the ribs.

The above changes in the factors cause a decrease in the thoracic volume but the thoracic pressure is increased. Hence, due to increased pressure air comes out of the lungs.

Note : The breathing rate in adult human beings is 12 to 20 per minute

Volumes Related to Respiration

1. Tidal Volume (TV)-The amount of air expired / inspired during one breathe is termed as tidal volume. It is 500 ml in human beings.

2. Inspiratory Reserver Volume [IRV]-The amount of air inspired over and above the normal inspiration. It is 2500 to 3000 ml in human beings.

3. Expiratory Reserve Volume [ERV]—The amount of air expired over and above the normal expiration. It is 1000 to 1100 ml in human beings.

4. Residual air [RV]-

It is the amount of air left in both the lungs after forced expiration. It is about 1100 to 1500 ml in human beings.

5. Inspiratory Capacity (IC)-The maximum inspired air is called as IC. It includes tidal volume and IRV. It is about 3500 ml in human beings.

6. Expiratory Capacity (EC)-The maximum expired air is called as EC. It includes TV + ERV. It is about 1500 to 1600 ml. in human beings.

7. Functional Residual C apacity (FRC)-The amount of air left in the lungs after normal expiration. It includes RV + ERV. It is about 2300 ml in human beings.

8. Vital Capacity (VC)—The amount of air expired maximum from both the lungs. It is IRV + TV + ERV. In human beings, it is 4600 ml.

9. Total Lung Capacity (TLC)-The total amount of air in both the lungs is called TLC. It is VC + RV. It is 5800 ml in huamn beings.

Artificial Respiration

During accidental conditions of any person such as gaseous toxicity or CO effect, electric shock etc, if breathing stops and heart beats continue then human life can be saved by giving artificial respiration.
Normally, the artificial respiration activates the respiratory centres, hence normal breathing can be restored.
Many methods of artificial respiration are known but “Mouth to Mouth technique” is most effective.

Following are the main steps for artificial respiration :

Keep the patient on hard bed in straight position. Keep one hand on the head of the patient and other hand below the head, so respiratory passage gets open.
Close the nose of patient with the hand which is on the head of patient and put mouth on the patient’s mouth in such a way that air tight position forms. The hand below the head is to be remained as such so that neck remains stretched.
Push air into the mouth of patient forcefully about 12 times of tidal volume (500 ml).
Open the nose and mouth of the pateint and allow experiation.

Respiratory disorders

Asthma

1. It is a respiratory disease. It is a condition in w⁷hich a person’s air passage becomes infiammed, narrow, swells and produces more mucus, which makes difficult to breathe.

2. The disease is caused due to pollens, dust particles, cold or smoking etc. It causes difficulty in breathing, chest pain, coughing and wheezing. The best remedy to prevent asthma is to live away from allergence.

3. Asthma can be managed with rescue inhalers to treat symptoms i.e. bronchiodiyators. Antibiotics are required to cure it.

Bronchitis

This disease involves inflammation of the timing of bronchial tubes which carry air to and fro from the lungs.
Symptoms include – swelling on the internal lining of bronchii that causes constant coughing. The bronchitis may be acute or chronic.
It may also be due to chemicals in the smoke of tobacco. Avoiding smoking is the best way to prevent asthma.

Emphysema

It is caused due to heavy smoking and air pollution. Smoking causes continuous stimulation in the lungs which destroys the alveolar walls. This results in increased air space but decrease in respiratory surface in the lungs. The lung elasticity is also reduced due to increased amount of the connective tissues. It causes difficulty in expiration.
Avoiding smoking, use of antibiotics and bronchio-dilators are helpful to get relief.

Pneumonia

It is an infectious disease which is caused by the infection of streptococcus pneumoniae
The lung alveoli get filled with dead cells (WBC) and fluid because of infection.
The patient faces breathing problems.
It is more common during childhood and old age.
Anitbiotics and bronchodilators are beneficial in curing.

Cancer of Lungs

It’s main cause is smoking. The chemicals present in the smoke of cigerettes are The smoke may cause irregular cell divisions in bronchioles and slowly cause being cancer.

Silicosis and Asbestosis

These diseases are due to air pollution.
Mainly, they occur in persons who are working at mines and factories of silica and asbestos.
The particles of silica or asbestos enter into the lungs and cause fibrosis in the upper part of the lungs.
These diseases are not curable, hence prevention is better