Introduction.                                                                                                                                                         

Cells continually use oxygen (O₂) for the metabolic reactions that release energy from nutrient molecules and produce ATP. At the same time, these reactions release carbon dioxide. Since an excessive amount of CO₂ produces acidity that is toxic to cells, the excess CO₂ must be eliminated quickly and efficiently. The two systems that cooperate to supply O₂ and eliminate CO₂ are the cardiovascular system and the respiratory system. The respiratory system provides for gas exchange, intake of O₂ and elimination of CO₂, whereas the cardiovascular system transports the gases in the blood between the lungs and body cells. Failure of either system has the same effect on the body: disruption of homeostasis and rapid death of cells from oxygen starvation and buildup of waste products. In addition to functioning in gas exchange, the respiratory system also contains receptors for the sense of smell, filters inspired air, produces sounds, and helps eliminate wastes.

Respiration : Respiration is the exchange of gases between the atmosphere, blood and cells. It takes place in three basic steps :

1. Pulmonary ventilation : The first process, pulmonary (pulmo = lung) ventilation, or breathing, is the inspiration (inflow) and expiration (outflow) of air between the atmosphere and the lungs.
2. External (pulmonary) respiration : This is the exchange of gases between the air spaces of the lungs and blood in pulmonary capillaries. The blood gains O₂ and loses CO₂.
3. Internal (tissue) respiration : The exchange of gases between blood in systemic capillaries and tissue cells is known as internal (tissue) respiration. The blood loses O₂ and gains CO₂. Within cells, the metabolic reactions that consume O₂ and give off CO₂ and give off CO₂ during production of ATP are termed cellular respiration.

 Respiration.                                                                                                                                                           

Respiration is a process which involves intake of oxygen from environment and to deliver it to the cells. It

include stepwise oxidation of food in cells with incoming oxygen, elimination of

release of energy during oxidation and storing it in the form of ATP.

CO2

produced in oxidation,

1. Respiratory surface : The surface at which extend of gases (CO₂ and O₂) takes place is called respiratory surface. Respiratory surface must be vascular and have enough area for gas exchange. For example – plasma membrane in protozoa, body wall (skin) in annelids, alveocapillary membrane in men.
2. Respiratory medium : Oxygen is dissolved in air and water. Thus water and air are source of oxygen for animals and called respiratory medium. Water and air are external respiratory medium. Respiratory medium comes in contact with respiratory surface and gaseous exchange takes place between respiratory medium and blood or any other transport medium through respiratory surface by simple diffusion. Inside the body an internal respiratory medium is also found. This internal respiratory medium is tissue fluid. Cells exchange their gases with tissue fluid through plasma membrane.
3. Types of respiration : It is of two types

1. Aerobic respiration : It occurs in the presence of molecular oxygen. The oxygen completely oxidises the food to carbon dioxide and water, releasing large amount of energy. The organisms showing aerobic respiration, are called aerobes. It is found in most of animals and plants. Aerobic respiration is of two main types direct and indirect.

C6 H12 O6 + 6O2 ®

6CO2

+ 6H ₂O+ 2830 kJ

Glucose

oxygen

Carbon dioxide

Water

Energy

1. Direct respiration : It is the exchange of environmental oxygen with the carbon dioxide of the body cells without special respiratory organs and without the aid of blood. It is found in aerobic bacteria, protists, plants, sponges, coelenterates, flatworms, roundworms and most arthropods.

Protists : Amoeba proteus is about 0.25 mm. Wide and has a large surface area to volume ratio. Diffusion of gases occurs over the entire surface via cell membrane, and is enough to fulfill its metabolic requirements.

Coelenterates : In Hydra and Obelia, practically all cells are in contact with the surrounding water. Each cell can exchange gases sufficient for its own needs through the cell membrane adjacent to water.

Flatworms : Planaria can also exchange gases sufficient for its needs by diffusion over its body surface. This is facilitated by its very thin body which increases the surface area to volume ratio.

2. Indirect respiration : It involves special respiratory organs, such as skin, buccopharyngeal lining, gills and lungs, and needs the help of blood. The respiration in the skin, buccopharyngeal lining, gills and lungs is respectively called cutaneous buccopharyngeal, bronchial and pulmonary respiration. Cutaneous respiration takes place in annelids, some crustaceans, eel fish, amphibians and marine snakes. It occurs both in water and in air. Buccopharyngeal respiration is found in certain amphibians such as frog and toad. It occurs in the air. Branchial respiration is found in many annelids, most crustaceans and mollusks, some insect larvae, echinoderms, all fishes and some amphibians. It occurs in water only. Pulmonary respiration is found in snails, pila, some amphibians and in all reptiles, birds and mammals. It takes place in air only.

2. Anaerobic respiration : It occurs in the absence of molecular oxygen and is also called fermentation. In this, the food is only partially oxidised so only a part of energy (5%) is released and of energy remains trapped in the intermediate compounds. It is found in lower organisms like bacteria and yeast. It is also found in certain parasitic worms (Ascaris, Taenia) which live in deficient medium. The organism showing anaerobic respiration, are called anaerobes. These involve one of following reactions.

C6 H12O6

Glucose

¾¾In y¾eas¾ts  ®

(Fermentation of sugars)

2C₂H₅OH+ 2CO₂ + 118 kJ

Ethanol

C6 H12 O6  ¾¾^{In in}¾^test¾^inal¾^wor¾^m¾^s ® 2CH3 CHOHCOOH+ Energy

Glucose                                                        Lactic acid

Certain body tissues of even aerobes also show anaerobic metabolism e.g., during the vigorous contraction of skeletal muscle fibres. In this, the glucose is metabolised into the lactic acid in anaerobic conditions. The rapid formation and accumulation of lactic acid are responsible for muscle-fatigue. The mammalian RBCs shows anaerobic respiration as these lack the mitochondria. In lens of eye and cornea of eye respiration is anaerobic because these structures are a non vascular. Anaerobic respiration appeared first in primitive organisms because there was absence of O₂ in primitive atmosphere.

Difference between aerobic and anaerobic respiration

 Respiratory organs.                                                                                                                                         

1. Skin : Respiration by skin is called cutaneous respiration. Skin is the only respiratory organ in most annelids (earthworm and leeches) and an additional respiratory organ in amphibians (Toads and frogs). Skin should be thin, moist, naked, permeable and well vascular for respiration. For cutaneous respiration animal should have large surface area then its volume and should have relatively inactive life to minimize the use of oxygen. In earthworms, epidermis has rich network of blood capillaries and their body surface has a moist film containing secretions of epidermal mucous glands, excretory wastes and coelomic fluids. The epidermal capillaries that in turn

release the

CO₂ , take up oxygen dissolved in film of surface moisture. Some marine annelids such as sandworms

(nereis) have parapodia (locomotory appendages) for respiration. In frog 100% cutaneous respiration during hibernatin. In all marine snakes 20% respiration by skin.

2. Tracheae : In insects, peripatus centipedes and millipedes tracheae are found for respiration. Tracheae are complex system of whitish, shining, intercommunicating air tubules. Tracheae are ectodermal air tubes. In cockroaches, three pairs of longitudinal tracheal trunks are present all along the length of body which are further connected with each other with the help of transverse branches. The main tracheae give off smaller tracheae whose branch repeatedly form a network of trachioles throughout the body. Trachioles internally lined by chitinous cuticle called intima, which spirally thickened to form taenidae. Tracheae without taenidae, tracheae lined by trachein protein. From each tracheal trunk three branches come out. The dorsal branch is supplied to the dorsal muscles where as ventral one to nerve cord and ventral muscles and middle one to the alimentary canal.

Tracheae open out on body wall through ten paired lateral apertures called stigmata or spiracles or stigmatum. Stigmata are two pairs thoracic and eight pairs abdominal. Each spiracle is surrounded by an annular sclerite (peritreme) which opens into air filled cavity called atrium or tracheal chamber. Expansion of abdominal cavity allows the space inside the tracheal trunk to expand. As a result air enters through the spiracles and distributed in body cavity through tracheal system. When abdominal cavity contracts the tracheal system also contracts the pressure of air inside the tracheal systems increases causing the release of air to the outside. Most of CO₂ diffuse out by chitin. At rest, the tracheoles are filled with watery fluid, oxygen is dissolved in this fluid and diffuses to cells. During activity the fluid in the tracheoles is drawn osmotically into the tissues. Consequently more air rushes into the tracheoles. Similarity between the trachea of cockroach and rabbit is that, wall of both are non collapsible.

CHITIN OF BODY WALL

SPIRACLE

LARGE TRACHEA CHITINOUS LINING

EPITHELIUM

LUMEN

TRACHEOLE FLUID SMALL TRACHEA TRACHEOLES

TRACHEOLE CELL

MUSCLE FIBRE

MAIN TRACHEAL TRUNK TO HEAD

THORACIC SPIRACLES

ABDOMINAL SPIRACLES

LATERAL LONGITUDINAL TRACHEAL TRUNK

VENTRAL LONGITUDINAL TRACHEAL TRUNK

TRANSVERSE TRACHEAE

TRACHEAL BRANCHES TO DORSAL LONGITUDINAL TRACHEAL TRUNK

ABDOMINAL SPIRACLES

Fig. – Trachea of cockroach                                                                       Fig. – Show respiratory system of cockroach.

3. Book lungs and book gills : Spiders ticks, mites and scorpion (belongs to class arachnida) have book lungs for respiration. In scorpion 4 pairs of book lungs are present. A book lung is a chamber containing a series of thin vascular, parallel lamellae arranged like the pages of book. Book gills are found in marine king crab or horse shoe crab.
4. Gills : Aquatic animals such as prawn, unio, fishes, sea stars and tadpoles respire by gills. Respiration by gills called bronchial respiration. Gills are of two types :

1. External gills : External gills are found in arenicola (lug worm), larvae of certain insects e.g. damsel fly and some amphibians e.g. necturus, siren, proteus, frog tadpole first develop external gills which are replaced by internal gills later.
2. Internal gills : The internal gills may be phyllobranch (prawn), monopectionata (pila) eulamellibrach (unio), lameellibranch, fillibranch (pisces). In all fishes, gills are hemibranch or demibranch and holobranch. In gills, gill lamellae are found which have capillary network. Water is drawn into gills ® blood flowing in the capillaries of

gill lamellae absorb oxygen from water and release

CO2

® water containing

CO2

is thrown out from gills. The

80% of O₂ of incoming water is absorbed. Water breathing causes some problems such as

1. For indrawing the water inside the gills, animals have to make great muscular effort because water is about 800 time more denser than air.

2. Water has less uncombined the gills to fulfill the oxygen need.

O₂ than air. Therefore large quantity of water is required to be passed over

3. As the temperature rises the O₂ content of water falls and animals face problem.

5. Buccopharyngeal lining : Frog breathes by buccopharyngeal lining of buccopharyngeal cavity. This is called buccopharyngeal respiration.

 Respiratory system of human.                                                                                                                     

Human respiratory system is derived from endoderm. Human respiratory system may be divided into two components.

(i) Respiratory tract or conducting portion               (ii) Respiratory organs

(i) Respiratory tract or conducting portion : It is the passage for the air. In this part gaseous exchange does not takes place. It is also called dead air space. It is divided in following parts :

1. Nose : (Latin-Nasa) (Greek-Rhine) cavity of nose is called nasal cavity. Nasal cavity is divided into two parts by nasal septum called mesenthmoid. Each part is called nasal chamber. Each nasal chamber opens out side by external nares. Nasal septum has two part. First part is small and is made of cartilage (hyaline). Second part is major and it is bony. Vomer is the main bone. Each nasal chamber has three region.

1. Vestibular region : Vestibular region also known as vestibule, lined by non keratinized squamous epithelium, it is ectodermal in origin and have sebaceous gland, sweat gland and hair. Vestibule is also found in inner air larynx, mouth and vagina. It acts like a seive to check the entry of large dust particles and other things.
2. Respiratory region : Middle region lined by respiratory epithelium which is ciliated pseudostratified columnar epithelium. It contains mucus and serous cells. Mucus cells produce mucus and serous cells produce watery fluid. Respiratory epithelium is highly vascular and appears pink or reddish. Respiratory region acts as a air conditioner and makes the temperature of in going air nearly equal to body. It also acts as a filter not give entry to dust particles, flies or mosquitoes.
3. Olfactory region : It is upper region. It is lined by olfactory epithelium. This is also called Schneiderian epithelium. Olfactory region is the organ of smell and detect the odour of inspired air. Inspiration is stopped if odour of air is foul or offensive. According to new researches pheromone receptors are found in nasal cavities.

2. Nasal conchae : Lateral wall of nasal cavity have three shelves like structures called conchae or turbinate. 3 pairs of nasal conchae are found. Nasal conchae are covered with mucus membrane. They increase the surface of nasal chamber. Both the chambers of nasal cavity open into nasopharynx by their apertures called internal nostrils or conchae. Adjacent to internal nostril there are opening of eustachian tube. Names of these three conchae and names of the bones that form them are given below.
   1. Superior conchae : The dorsal most chochae is supported mainly by nasal bone called nasoturbinate. It is the smallest conchae.
   2. Middle conchae : Ethmoid bone called ethmoturbinate.
   3. Inferior conchae : The ventral most conchae supported by maxilla bone called maxilloturbinate. It is a separate bone itself.
3. Pharynx : It is the short vertical about 12 cm long tube. The food and air passages cross here. It can be divided in 3 parts –
   1. Nasopharynx : Nasopharynx is only respiratory upper part in which internal nares open. There are 5 opening in its wall; two internal nares, two eustachian tube opening and opening into oropharynx.
   2. Oropharynx : Middle part is called oropharynx. In this part oral cavity open known as fauces. Two pair tonsils the palatine and lingual tonsils are found in the oropharynx.
   3. Laryngopharynx or hypopharynx : Lowest part is called laryngopharynx. It leads into two tubes. One at the front is wind pipe or trachea and one at the back is food pipe or oesophagus. Both oro and laryngo pharynx is both a respiratory and a digestive pathway.

Nasopharynx lined by ciliated pseudostratified epithelia, oropharynx and laryngopharynx lined by non keratinized epithelium. Mouth serves as an alternate route for air when nasal chambers are blocked. Foramen by which pharynx opens into larynx called glottis. In general it remains open. During swallowing it is closed. It provides passage for air. Pharyns leads into the oesophagus through an aperture called gullet. In general condition it remains closed and opens at the time of swallowing. During swallowing epiglottis closes the glottis.

4. Larynx or Voice box : It is found both in frogs and rabbits. Larynx does not help in respiration. It is present on tip of trachea and is made up of 9 cartilages such as thyroid (single) has a prominence called pomum admi or adam’s apple, cricoid (single), arytenoid (paired) are piece of hyaline cartilage. While epiglottis (single), carniculate (paired) cuniform (paired), santorini are piece of elastic cartilage. Clinically, the cricoid cartilage is the landmark for making an emergency air way.

Larynx is a short tubular chamber and opens into the laryngopharynx by a slit like aperture called glottis. Glottis always remains open except during swallowing. Larynx is more prominent in men than women due to male harmone. Before puberty, the larynx is inconspicuous and similar in both sexes. Larynx is a voice producing instrument. For this purpose larynx have two types of vocal cord. In birds voice producing organ is syrinx, found at lower end of tracheae.

1. False vocal cord or vibrating fold or anterior vocal cord : These are folds of mucus membrane. Gap between them is called rema vestibuli. These are not responsible for sound production. In elephants only true vocal cords are present and are responsible for this trumpet sound.
2. True vocal cord or posterior vocal cords : They are made up of yellow elastic fibres. Gap between them is called rema glottides or peep hole. In males the length of true vocal cord is 2.25 cm and in female is 1.75 cm. The free inner rim of each vocal cord is set into vibrations as air is expelled from the lungs and the sound is produced when the cords vibrate. Pitch of the sound can be altered by contracting or relaxing the vocal cords to varying the degrees. Sound produced by rabbit is called quaking. Hippopotamus lacks true vocal cords. Vocal cords or folds in lined by non keratinized stratified squamous epithelium. Pitch is controlled by the tension of vocal folds. Lower sound produced due to decreasing muscle tension on vocal cords. Due to influence of androgens, vocal cords are usually thicker and longer in males than in females, therefore they vibrate more slowly. Thus men generally have a lower range of pitch then women. The pharynx, mouth nasal cavity act as resonating chamber. Muscle are face, tongue and lips help us enunciates words.

5. Trachea : It is a tubular structure of about 12 cm. in length and 2.5 cm in diameter. The wall of trachea is made of fibres, cartilage muscles and the mucus membrane. In middle of thorax at the level of 4^th and 5^th thoracic vertebra it divides into two branches called right and left primary bronchi. Right primary bronchus is short and broad and divides into three branches called lobes or secondary bronchi which extend separately into the three lobes of right lung. Left primary bronchus divides into two lobes or secondary bronchi that pass into two lobes of left lung. At the point of bifurcation trachea has projection of cartilage called carina. Further division of secondary bronchi is given in form of arrow diagram.

No exchange of gases (from nose to terminal bronchiole passage is a called conducting passage or dead space)

Respiratory zone

Exchange of gases takes place

Trachea

¯

Major or primary bronchi

¯

Secondary bronchi

¯

Tertiary or segmental bronchi

¯

Terminal bronchiole

¯

Respiratory bronchiole

¯

Alveolar duct

¯

Alveolar sac or atrium

¯

Air sac or alveoli (gaseous exchange)

Bronchioles are narrowest and most numerous tubes of lungs. Alveoli are not tube they are sacs like structures. Into alveolar sac 3 to 6 air sacs or alveoli open. There are 300 millions of alveoli in the two lungs. Air capillaries

replace alveoli in birds. O₂ carried in inhalation ultimately reaches in alveoli. Area of internal surface of both lungs

(alveoli) is about  70m² (750 ft ² ), about the size of a handball court. Thus provide large surface for gaseous exchange. Area of inner surface of bronchiole is 10 m² . Trachea and its branches up to alveoli are called bronchial tree.

The alveolar walls consists of two types of alveolar epithelial cells or pneumocytes. Type I alveolar (squamous pulmonary epithelial) cells are simple squamous epithelial cells that forms a continuous lining of the alveolar wall, interrupted by occasional, type II alveolar (septal) cells. Type I alveolar cells are the main site where gas exchange, takes place. Type II cuboidal alveolar cells secrete alveolar fluid. Associated with the alveolar wall are alveolar macrophages (dust cell). The thickness of alveolar-capillary membrane is 0.5mm (about ¹/₁₆ the diameter of RBC).

Pulmonary blood circulation differes from systemic circulation in two ways –

1. Pulmonary blood vessels provide less resistance to blood flow.
2. Less pressure is required to remove blood through pulmonary circulation.

In trachea about 16 – 20 c- shaped cartilagenous (hyaline) rings are found. These rings are incomplete posteriorely or incomplete dorsally. Cartilagenous rings are also found in the bronchi. In bronchioles these rings are absent. In insects trachea also find supporting rings cartilagenous rings keep trachea and bronchi open permanently even during negative pressure created by expiration. Larger bronchioles are supported by connective tissue alone which extend from the intertubular septa. Muscles of human tracheo bronchial tree are smooth and are supplied by sympathetic and parasympathetic

nerves. Contraction of these muscles

leads to narrowing of the bronchus. It is

Fig. – Bronchial tree

called bronchiospasm. Effect of bronchiospasm is remarkable on fine bronchioles where muscles are present but cartilagenous rings for support are absent. Bronchiospasm below tertiary bronchi clinically called bronchial asthma. Sympathetic nerves stimulation causes relaxation of bronchial muscles and hence drugs which causes stimulation of sympathetic nerves called sympathomimetic drugs, are given in treatment of bronchial asthma.

Wall of trachea,upper bronchi is lined by pseudostratified ciliated columnar epithelium rich in mucus secreting cells. Mucus holds the dust and bacteria which are swept by cilia toward the pharynx from where they are swallowed or thrown out. Tobacco smoke contains ciliotoxius which damages the cilia. Terminal bronchioles and beginning of respiratory bronchiole are lined by simple ciliated columnar epithelium without mucus cells. The mucus if present may block the these narrow tubules. Rest of respiratory bronchiole and alveolar duct have non ciliated cuboidal epithelium. There are 10 bronchioles in right lung and 8 bronchioles in left lung. The bronchioles contain 3 special types of cells along with normal epithelium.

1. Kultchitsky cells or argentaffin cells : They secrete serotonin and histamine. Serotonin dilate while histamine constrict the bronchioles.
2. Clara cells : They secrete a phospholipid named diapalmityl lecithin which acts as a surfactant. This surfactant prevents the collapse of bronchioles lacking cartilagenous rings. Collapsing of lungs is called atelectesis. Pottle in 1956 proved the existence of surfactant. Surfactant is formed by clara cells only at later stage of foetal life. Some times at birth some infants are devoid of surfactant so there is

great respiratory difficulty because lungs refuse to expand. In this condition death may occur. This is called respiratory distress syndrome (RDS) or hyaline membrane disease (HMD) or glassy lung disease.

3. Dust cells : They are phagocytes which eat foreign particles (dust).

(ii) Respiratory organs : In men the respiratory organ are a pair of lung. Some snakes have unpaired lungs. Respiration by lungs is called pulmonary respiration. Lungs are found in all vertebrates except fishes. In Lung fishes such as protopterus, neoceratodus and lepidosiren air bladder is found, which is modified lung. Respiration in men and rabbit is pulmonary.

SUPERIOR LOBE OF RIGHT LUNG

RIGHT MAIN BRONCHUS

MIDDLE  LOBE OF RIGHT LUNG

OBLIQUE FISSURE

LARYNX

TRACHEA CUPULA

SUPERIOR LOBE OF LEFT LUNG

LEFT MAIN BRONCHUS

CARDIAC NOTCH

(a) Lungs : Lungs lie in thoracic cavity on both side of heart in

INFERIOR LOBE

OF RIGHT LUNG

INFERIOR LOBE OF LEFT LUNG

mediasternum space. Base of lung is attached to diaphragm. Right lung

is divided into 3 lobes viz. Superior, Middle, Inferior and left lung is

Fig. –  Lungs  of  man

divided into two lobes Superior and Inferior. In rabbit, the left lung is divided into two lobes left anterior and left posterior where as the right lung has four lobes anterior azygous, right anterior, right posterior and posterior

azygous. Lungs of reptiles are more complex than those of amphibians. In birds lungs are supplemented by elastic air sacs which increase respiratory efficiency. The narrow superior partion of lung is termed the apex or cupula.

Each lung is enclosed in two membrane called pleura. Pleura are layers of peritonium of thorax. Inner membrane is called the visceral pleuron. It is firmly bound to surface of lungs. The outer membrane is called parietal pleuron. It is attacked to chest wall or wall of thoracic cavity. A narrow space exists between the two pleura. It is called pleural cavity. In pleural cavity a watery fluid is found called pleural fluid. Pleural fluid is glycoprotein in nature and secreted by pleura. Pleural fluid lubricate the pleura so that they may slide over each other without friction. This fluids reduces friction bewteen the membrane. When the lungs expand and contract in respiration. Pressure inside pleural cavity is negative – 5 mm Hg. Plurisy is inflamation of pleura and cause collection of fluid in pleural cavity. It results painful breathing (dyspnea). The surface of lung lying against the ribs, known as coastal surface. The mediastinal (medial) surface of each lung contains a region – the hilus, through which bronchi, pulmonary blood vessels, lymphatic vessels and nerve enter and exit.

 Pulmonary volumes and capacities.                                                                                                           

In clinical practice, the word respiration (ventillation) means on inspiration plus one expiration. The healthy adult averages 12 respiration’s a minute and moves above 6 litres of air into and out of the lungs while at rest. A lower-than-normal volume of air exchange is usually a sign of pulmonary mal-function. The apparatus commonly used to measure the volume of air exchanged during breathing and the rate of ventilation is a spirometer (spiro=breathe) or respirometer. The record is called a spirogram. Inspiration is recorded as an upward deflection and expiration is recorded as a downward deflection, and the recording pen usually moves from right to left.

There are 4 respiratory volumes and capacity.

Respiratory volumes :

1. Tidal volume (TV) : It is volume of air normally inspired or expired in one breath (i.e. inspiration and expiration) without any extra effort. It is about 500 ml. in normal healthy adult. In infants it is 15 ml and in fetus it is 0 ml. Tidal volume varies considerably from one person to another and in same person at different times. In an average adult, about 70% (350 ml) of tidal volumes reaches respiratory bronchioles, alveolar duct, sacs and alveoli (respiratory portion). The other 30% (150ml) remains in air spaces of nose, pharynx, larynx, trachea, bronchi, bronchioles and terminal bronchioles (conducting portion). These areas are known as anatomic dead space.

The total volume of air taken in during 1 minute is called the minute volume of respiration (MVR) or minute ventilation, It is calculated by multiplying the tidal volume by the normal breathing rate per minute. An average MVR would be 500 ml times 12 respirations per minute of 6000 ml/min. Not all of the MVR can be used in gas exchange, however, because some of it remains in the anatomic dead space. The alveolar ventilation rate (AVR) is the volume of air per minute that reaches the alveoli. In the example just given, AVR would be 350 ml times 12 respirations per minute or 4200 ml/min. Remains 3 air volumes result when one engages in strenous breathing.

2. Inspiratory reserve volume (IRV) : By taking a very deep breath, you can inspire a good deal more than 500 ml. This additional inhaled air, called IRV is about 3000 ml.
3. Expiratory reserve volume (ERV) : If you inhale normally & then exhale as forcibly as possible, you should be able to push out 1200 ml. of air in addition to 500ml. of T.V. The extra 1200 ml. is called ERV.
4. Residual volume (RV) : Even after expiratory reserve volume is expelled, considerable air remains in the lung, this volume, which can not be measured by spirometry, it is called residual volume is about 1200 ml.

5. Dead space : Portion of tracheobronchial tree where gaseous exchange does not occur called dead space.

It is also called conductive zone. Dead space is 150 ml.

6. Functional residual capacity (FRC) : It is the amount of air that remains in the lungs after a normal expiration. It is about 2300 ml.

FRC = ERV + RV

= 1100 + 1200 = 2300 ml.

7. Vital capacity (VC) : This is the maximum amount of air that can be expired forcefully from his lungs after first filling these with a maximum

deep inspiration. It is about 4600 ml.

VC = IRV + TV + ERV

= 3000+500+1100 = 4600 ml.

6, 000 ml

5, 000 ml

INSPIRATORY RESERVE

INHALATION

INSPIRATORY

VITAL

TOTAL LUNG

4, 000 ml

VOLUME

EXHALATION

CAPACITY

CAPACITY

CAPACITY