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Respiratio www.pucbiology.wordpress.comRevised - 2010

II PUC

Bio

Notes

Sunil StephenLecturer in biology


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Sunil Stephen / Lecturer in Biology/www.pucbiology.wordpress.com

Respiration

Structure of human respiratory system1) Draw a neat labeled diagram of human respiratory system (5 marks)

2) Briefly explain the structure of human respiratory system / explain the conducting division of respiration (5 marks).

In man, respiratory system is differentiated into two parts namely, conducting zone & respiratory zone.

Conducting Zone:Conducting zone is the region for movement of the air. It includes nasal cavity, pharynx, Larynx, trachea &

bronchi.

Trachea (Wind pipe): It is the cylindrical tube of about 12cm, located in front of the oesophagus. Trachea is

always open due to the presence of C-shaped hyaline cartilages, supporting its wall. The Trachea divided into

two branches called bronchi at the lower end. Bronchi enter into lungs.

Respiratory Zone:It is the region for the exchange of gases between body and environment. It consists of a pair of lungs.

Lungs:

Lungs are conical spongy structures present in the thoracic cavity. The lower end of the lungs is supported by a

muscular membrane called diaphragm. The left lung is bilobed and right lung is broader than left and has three

lobes.

Covering of Lungs:

The lungs are covered by a thin, double walled membrane called Pleura. The inner wall of pleura is called

Visceral Pleura and the outer wall is called parietal Pleura. The space between the two pleura is called pleural

cavity and it is filled with Pleural fluid.

Bronchial Tree:The bronchi that enter into lungs divide into secondary bronchi and further divide into many bronchioles. The

bronchioles end in the number of sacs called alveoli or air sacs.

Alveoli:Alveoli are the structural and functional unit of the respiratory system(1mark). This thin walled sac facilitates

exchange of oxygen and carbon dioxide in between blood cells and environment.


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Mechanism of breathing 5 Marks

Explain breathing or ventilation? OR What is breathing? Explain mechanism of breathing with

a neat diagram (5 m a r k s )

Breathing is the process of exchange of gases between the external atmosphere and lungs. Breathing is also

called as ventilation of lung.

The mechanism of breathing is based on the principles of diffusion and it involves two steps namely, inspirationand expiration.

a) InspirationInspiration is the process of intake of air. It is the active process involves the contraction of muscles.

1) During inspiration, the main respiratory muscles involves are diaphragm, intercostals muscles and abdominalmuscles.

2) Initially the diaphragm is dome shaped. During inspiration, it gets lowered & becomes flat. When diaphragmbecomes flat, the size of the thoracic cavity increases vertically.

3) At the same time external intercostals muscles present between ribs contract and ribs are pulled outwardsand upwards. As the result, the size of the thoracic cavity increases horizontally.

4) Both these actions increase the volume of thoracic cavity. This leads to an increase in the size of the pleuralcavity. And inter-pleural pressure decreases from 756 to 754 mm of Hg.

5) At this stage, the air present inside the lungs applies pressure on the inner wall of the lungs. Lungs expandand pressure inside the lungs (intrapulmonary pressure) decreases from 760 to 758 mm of Hg. Since theexternal atmospheric pressure is 760 mm of Hg, air rushes into lungs.

b) ExpirationExpiration is defined as process of expulsion of air from inside the lungs to the external atmosphere.

1. During expiration diaphragm relax and become dome shaped. The inter costal muscles relax and it resultsin decreasing the volume of thoracic cavity.

2. The pressure in the plural cavity increases (758mm Hg). The pressure in the lungs also increases to 762mmof Hg.

3. Since this pressure is greater than the external atmospheric pressure, air is expelled out.

Transport of Respiratory Gases

Transport of oxygen

Explain the process of transport of oxygen during respiration? (5 marks)

Oxygen in the blood is carried by two ways:

1) As a Physical solution: About 3 to 4%of oxygen in the blood gets dissolved in the plasma and carried asphysical solution.

2) As oxyhaemoglobin: About 96 to 98% of the oxygen is carried by haemoglobin. Haemoglobin is therespiratory pigment that shows high affinity to oxygen. Each haemoglobin molecule contains four atoms ofiron and it carries four molecules of oxygen. When oxygen combines with haemoglobin, oxyhaemoglobin isformed

Hb + 4O2Hb (O2)4

When blood reaches the tissues, oxyhaemoglobin dissociates give up oxygen into the cells. The haemoglobin

returns back to the lungs.


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Transport of Carbon Dioxide

Explain the process of transport CO2during respiration? (5 marks)

Carbon dioxide produced in cells during respiration is transported to lungs by blood. In the blood it is

transported both by plasma as well as the RBCs.

Carbon dioxide is transported in three forms

1. By plasma:

About 5%of CO2 combines with water of the plasma to form carbonic acid. This is transported fromthe tissues to lungs where it dissociates into carbon-dioxide and water.H2 O + CO2 H2 CO3

2. By haemoglobin

About 25%-30%of CO2 is transported by haemoglobin. Carbon dioxide combines with haemoglobinto form carbaminohaemoglobin which is an unstable compound. This is transported to the lungs byblood, where it dissociates into CO2 and haemoglobin.Hb + CO 2 Hb.CO2

3. As bicarbonates:

About 70%of CO2 is transported by blood as bicarbonates of sodium and potassium.

CO2 and water first combine to form carbonic acid in the RBCs. Carbonic acid dissociates into H+ and HCO3- in the presence of carbonic anhydrase. The bicarbonate ions from the RBC move into the plasma of blood and combine with Na+ and

K+ to form sodium bicarbonate and potassium bicarbonate.

To maintain electrical neutrality in RBC, chloride ions (Cl-) from the plasma enter into it. Thisphenomenon is known as chloride shift or Hamburgers phenomenon.

CO2 is transported to the lungs in the form of these bicarbonates, where they dissociate intobicarbonate ions, Na+, and K+.

Bicarbonate ions combine with H+ (formed due to the dissociation of H.Hb i.e., Haemoglobinicacid) to form carbonic acid.

This again dissociates into water and CO2.External Respiration It is the process of exchange of respiratory gases namely oxygen and carbon dioxide

between air in the lungs and the blood.

Chloride shift

Chloride shift is defined as the movement of Cl- from the plasma into the RBC in

response to the outward movement of HCO3- from the RBC to maintain ionic balanceduring the transportation of CO2.

Internal Respiration It is the process of exchange of oxygen and carbon dioxide between the blood and the

cells of the tissue.

Tidal Volume (TV) = 500ml It is the volume of air entering or leaving the lungs during ordinary breathing. It

is 500ml.


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Inspiratory Reserve Volume (IRV)The additional air that is inhaled after tidal volume by taking a very deep

breath is called Inspiratory Reserve Volume (IRV). It is about 3 liters in males.

Expiratory Reserve Volume (ERV) It is the additional air that can be exhaled beyond a tidal volume by

forced breathing. It is about 1 liter in male.

Residual Volume (RV)The amount of air that always remains inside the lungs is called residual volume. It is

about 1.2 liters in males.

Spirometer (Respirometer) It is the instrument used to measure volume of the air exchanged during

breathing. The rate of breathing per minute is 15-18 times per minute in a healthy person..

Respiratory disorders

1) Rhinitis (Hay Fever)Rhinitis is the inflammation of mucous membrane of the nose. It is characterized by watery secretions by

the mucous glands, continuous sneezing, watery eyes etc.,

Causes:

1. Chronic rhinitis is caused by allergens, such as house dust, air pollutants, tobacco smoke etc. Rhinitis isusually seasonal during releasing of pollen (Haying season).

2. The acute rhinitis is commonly caused by viral infection

2) AsthmaAsthma is one of the disorders of lower respiratory system involving bronchi and bronchioles characterized by

difficulty in exhaling.

Symptoms of Asthmaincludes

1. Difficulty in breathing, especially exhaling.2. Contraction of muscles of bronchi and bronchioles results in wheezing sound.3. Excessive mucus production resulting in obstruction of air passage.Causes of Asthma

1. Asthma may be caused due to allergic reaction. Allergens causing asthma includes dust mite, pollen, animalfur, fungal spores, feathers, tobacco smoke etc.,

2. Respiratory infections (viral) may also cause childhood asthma.3. In certain cases asthma is genetic.4. Emotional stress and environmental pollution can cause triggered asthma.

3) Bronchiogenic carcinoma (Lung Cancer)

It is the cancer of epithelial cells of the lungs. It results in tumor formation.

Causes of lung cancer includes mainly cigarette smoking (98%)Other causes include exposure to toxic air pollutants in the industries.

Artificial BreathingIt is the methods of forcing air into the lungs of a person who has stopped breathing.

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