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Regulation of Respiration


Table of Content

A specialised centre present in the medulla region of the brain called respiratory rhythm centre is primarily responsible for respiratory regulation. Another centre present in the pens region of the brain called pneumotaxic centre can moderate the functions of the respiratory rhythm centre. Neural signal from this centre can reduce the duration of inspiration and thereby alter the respiratory rate. 

Sagittal Section of Brain Stem

A chemosensitive area is situated adjacent to the rhythm centre which is highly sensitive to CO2 and hydrogen ions. Increase in these substances can activate this centre, which in turn can signal the rhythm centre to make necessary adjustments in the respiratory process by which these substances can be eliminated.

Receptors associated with aortic arch and carotid artery also can recognize changes in CO2 and H+ concentration and send necessary signals to the rhythm centre for remedial actions.

The role of oxygen in the regulation of respiratory rhythm is quite insignificant.

Deep OR Forced OR Voluntary Breathing

Deep or forced voluntary inspiration is caused by excessive contraction of diaphragm and muscles. Deep expiration is done by contraction of internal inter-costal muscles and relax of other muscles and diaphragm. Impulse for deep breath starts from cerebrum.

The deep breathing is referred to as thoracic breathing in contrast to the normal or quiet breathing referred to as abdominal breathing.

Sudden deep breath: Sudden deep breath is due to increased pCO2 and decreased pO2.

Breathing at high altitude: Air at mountains is thin and of low density. Residents of high altitudes are acclimatized. Visitors first suffer from Hypoxia (at 4000 m). This causes mountain sickness including high blood pressure and high breathing rate (normal rate of breathing is 12 to 18/minute). Visitor becomes normal after some days when his number of RBC, and haemoglobin percentage increases.

Breathing Rates

Respiratory Rate

Man 12 -18/min., inspiration = 2 sec. expiration = 3 sec.

In new born baby = 44/min.

Embryo = 10.

At the time of sleeping = 10/min. (Minimum).

Frog = 80/ min.

Rabbit = 38/min.

Shrew = 120/min. (Maximum).

Elephant = 6/min.

Respiratory Pigments

Haemoglobin: Found in vertebrates and in some annelids e.g. Earthworm. In annelids it dissolve in plasma. Colour of oxyhaemoglobin is Red. Colour of deoxyhaemoglobin is Purple.

Hemocyanin: In this Cu+ ions is present. It is of blue colour.

It is found in mollusc, (Octopus) Arthropoda (Prawn).

Chlorocruonin: (Fe++ ion containing green colour pigment) Found in Sabella (Annelids)

Haemoerythrin: (Fe++ containing red colour pigment)

Found in annelid plasma.

Pinaglobin: Containing brown pigment [Mn) present.

Eg. Mollusca (eg. Pinna).

Vanadium: Present in protochordates, Vanadium compound, green colour e.g. Ascidians,

Disorders of Respiratory System

Asthma is a difficulty in breathing causing wheezing due to inflammation of bronchi .and bronchioles.

Emphysema is a chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased. One of the major causes of this is Cigarette smoking.

Occupational Respiratory Disorders: In certain industries, especially those involving grinding or stone-breaking, so much dust is produced that the defense mechanism of the body cannot fully cope with the situation. Long exposure can give rise to inflammation leading to fibrosis (proliferation of fibrous tissues) and thus causing serious lung damage.

Hypoxia: Hypoxia is a condition of oxygen shortage in the tissues. It is of two types:

Artificial Hypoxia: It results from shortage of oxygen in the air as at high (over 2400 m.) altitudes. It causes mountain sickness characterised by breathlessness, headache, dizziness, nausea, vomiting, mental fatigue and bluish tinge on the skin and mucous membranes.

Anaemic Hypoxia: It results from the reduced oxygen-carrying capacity of the blood due to anaemia (decreased haemoglobin content in blood) or carbon monoxide poisoning (some haemoglobin occupied by CO). In both cases, less haemoglobin is available for carrying.

Asphyxia (Suffocation): The content of blood falls and the content rises and paralyses the respiratory centre. Breathing stops and death occurs.

Bad cold: Disease-causing microbes present in the air attack respiratory tract, producing inflammation of the mucous membrane and causes increased secretion:

Rhinitis in the nasal chambers.

Sinusitis in the sinuses.

Pharyngitis in the pharynx, often called sore throat, and is usually accompanied by tonsmitis (enlargement of tonsils).

Laryngitis in the larynx, causing hoarse voice and difficulty in speaking.

Bronchitis in the bronchioles.

Bronchitis: It is caused by the permanent swelling in bronchi, As a result of bronchitis cough is caused and thick mucus with pus cells is spitted out. Dyspnea fever develops. Dyspnea means hunger of air or deficiency of oxygen in the blood or development of hypercapnia i.e., increase of concentration in blood. This disease is accelerated by fatigue, malnutrition, cold etc. the patient experiences difficulty in breathing. Here hypertrophy and hyperplasia of bronchi takes place,

Pneumonia: During pneumonia, oxygen has difficulty in diffusing through the inflamed alveoli and the blood pO2 may be drastically reduced, Blood pCO2 usually remain normal because CO2 diffuses through the alveoli more easily than O2. In chronic patients of common cold and influenza, the lining epithelium of bronchi and lungs is inflammated. This disease is caused by Streptocoeus pneumoniae, other bacteria, fungi, protozoans, viruses and the patient feels difficulty in breathing. Its prominent symptoms are trembling, pain in chest, fever, cough etc. This disease is prevalent in either children or elderly persons in old age.

Lung cancer: It is believed that by excess smoking, lung cancer (carcinoma of lungs) is caused. The tissue increases limitlessly, which is called malignancy. This disease is fatal. The frequency of occurrence of this disease in smokers is 20% more.

Malignancy of tissues (neoplasia) causes pressure on, the cells of other tissues and destroys them. The blood capillaries are ruptured, blood starts flowing and death is caused by excessive bleeding.

Tuberculosis: This disease is also called T.B. and was considered fatal, but these days its full cure is possible. Thus, disease is called curable, these days. It is caused by bacteria Mycobacterium tuberculosis. These bacteria settle in lungs at different places and respiratory surface is decreased, the difficulty in breathing is also experienced. If the patients start taking medical advice and the medicines tight from the initial stage regularly, the patients can be fully cured of the disease. Nowadays a new therapy DOT (Direct observed treatment) is used for tuberculosis treatment, recently launched by Indian Government Many other drugs like rifampin and isoniazid are successful for the treatment of tuberculosis. Tuberculosis bacteria spreads by inhalation and exhalation.

+ Note:

In elephant false vocal cords are absent.

In hippopotamus, true vocal cords are absent.

In birds sound is produced by syrinx.

Sound of rabbit is called as Quacking

In normal respiration.

*  Frog show - 35% cutaneous respiration

9% Buccopharyrigeal respiration

56% Pulmonary respiration.

In frog sternohyal and petrohyal muscles are related with the process of respiration.

Lodwing first explained gaseous exchange in blood.

Rima glottides is the gap between the vocal cords.

The vocal cords are made up of yellow elastic tissue covered by non keratinized stratified squamous epithelium.

Rhinitis - is a chronic or acute inflammalion CO2 the mucous membrane of nose.

Orthopnea - Inability to breath in horizontal position.

Hypercapnia - Excess carbon dioxide in the, body fluid.

Haldane effect -The promodon of CO2 dissociation by oxygenation of haemoglobin is called Haldane effect.

Drinker's Respiration or Tank Respiration is an Iron lung invented by Philip Drinker, an American Engineer, in 1929.

Cyanosis - A dark bluish colour of skin and mucous membrane due to deficiency of oxygen in blood is called cyanosis

For the control of respiration following respiratory centres are found in hind brain.

Type of centre



Inspiratory centre

Medulla oblongata

Inspiration (2 second active condition).

Respiratory centre

Medulla oblongata

Expiration (3 second inactive condition)

Apneustic centre


Slow and deep inspiration.

Pneumotaxic centre


Control other centres and produce normal quite breathing

Gasping centre


Sudden and shallow respiration

Respirtory Pigments

Name of Pigment

Colour (oxidised)








Chordata (Vertebrate





Mollusca and arthropoda





Annelida, sabella, serpulids





Annelida, Sipunculoi ea, lingula




Vanadocyte in Plasma





Coelomic fluid

Echinoden ala




Coelomic fluid





Coelomic fluid






Earthworm nereis, arenicola, chironoma insecl, planorbis:






Partial Pressures (in mm Hg) of Oxygen and Carbon dioxide at Different Parts Involved in Diffusion in Comparison to those in Atmosphere

Respiratory Gas

Atmospheric Air


Blood (Deoxygenated)

Blood (Oxygenated)














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