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HUMAN RESPIRATION

dr. aarifBreathingRespiration1.Intake of fresh air and removal of foul airOxidation of food to form carbon dioxide, water and energy2.Physical processBiochemical process3.No energy is released rather usedEnergy is released in the form of ATP4.Extra cellular processIntra cellular process5.No enzymes involvedLarge no of enzymes are involved6.Confined to certain organsOccurs in all the cells of the body

dr. aarifTypes of Respiration1. Anaerobic Respiration : When nutrients are oxidized without the use of O2 . In yeast glucose forms ethyl alcohol and CO2. In bacteria and muscles glucose is converted to lactic acid Endoparasites are anaerobic in nature 2. Aerobic Respiration : When nutrients are oxidized with the use of O2 either from air or from water . i) External respiration : Exchange of gases between Blood and air ii) Transport of gases to the tissues iii) Internal respiration : Exchange of gases between blood and tissues iv) Cellular respiration : Oxidation of nutrients in the cell and release of energy.

dr. aarifMechanisms of breathing vary among different groups of animals mainly on their habitats and levels of organisation.

Lower invertebrates

Sponges, coelenterates, flatworms, etc., exchange O2,by simple diffusion over their entire body surface. Earthworms use their moist cuticle and insects have a network of tubes (tracheal tubes)to transport atmospheric air within the bodySpecial vascularised structures called gills are used by most of the aquatic arthropods and molluscsVascularised bags called lungs are used by the terrestrial molluscs for the exchange of gases.

Vertebrates

Fishes use gills Reptiles, birds and mammals respire through lungs.Amphibians like frogs can respire through their moist skin also

dr. aarifHuman Respiratory SystemRespiratory pathway : a) Nostrils and Nasal chamber b) Pharynx c) Larynx d) Trachea e) Bronchi f) Bronchioles g) AlveoliRespiratory Organ : a) Lungs

dr. aarifNOSTRILS:

Nostrils are the external openings of the nose. These are also called external nares. Similarly a pair of internal openings is present. They open into pharynx. These are called internal nares NASAL CHAMBERS:

The space between the external and internal nares is known as nasal chamber. Internally, each one is lined by a mucous membrane. Ciliated epithelium is present in nasal chamber. It is divided into right and left parts by a cartilage known as mesethmoid.

Nose

dr. aarifEach nasal chamber is further divided into three regions:Vestibule: This is the anterior most part of the nasal chamber. It has hair to trap dust particles and prevent them from going inside.

Respiratory part: This is the part richly supplied with capillaries. It warms the air and makes it moist.Sensory part: This is lined by sensory epithelium for detection of smell.

dr. aarifPharynxNasal chamber opens into the pharynx.

It is a short, vertical tube measuring about 12 cm.in length.

The respiratory and the food passages cross each other in the pharynx by two separate passages.

Its upper part is known as naso-pharynx which helps in conduction of air and the lower part is called laryngo-pharynx or oro-pharynx conducting food to oesophagus.

In the pharynx, there are tonsils which are made up of lymphatic tissue. They kill bacteria trapped in the mucous

dr. aarifLarynx

It is the sound producing organ, hence also called the sound box.

In males, the larynx increases in size at the time of puberty. Hence, it is called Adam's apple and can be noticed in the neck region. From the pharynx, air enters the larynx through an opening called glottis.

The glottis is guarded by a flap called epiglottis.It prevents the entry of food particles into the respiratory passage

Along the sides of the glottis are two folds of elastic tissue called vocal cords. These are responsible for producing sound.

dr. aarifTracheaIt is also known as wind pipe. It is about 12 cm. long and 2.5 cm. wide.

It lies in front of the oesophagus and extends downward into the neck.

The wall of the trachea is made up of fibrous muscular tissue supported by 'C'- shaped cartilage rings. These are 16-20 in number. They make the trachea rigid.

The trachea is internally lined with ciliated epithelium and mucous glands.

If any foreign particle enters, it is immediately expelled out by coughing action.

Dust particles get trapped by the mucous. By ciliary movement, they are swept towards the larynx and finally they enter the oesophagus

dr. aarifBronchi & BronchiolesThe distal end of the trachea is divided into two bronchi behind the sternum. Each bronchus is supported by a complete ring of cartilage.

It enters into the lung of its respective side.

On entering the lung, each bronchus further divides into secondary and then tertiary bronchi. Tertiary bronchi divide into many minute bronchioles.

Wall of each bronchiole does not have cartilage rings.

Each bronchiole ends into a balloon-like alveolus.

These alveoli make the lungs spongy and elastic.

dr. aarifThese are the principal respiratory organs, located in the thoracic cavity.

Lungs are paired, hollow, elastic organs.

Each lung is enclosed in pleural sac.

Pleural sac is made up of two membranes ,outer parietal and inner visceral. The enclosed cavity is called the pleural cavity. It is filled with a pleural fluid, which lubricates the pleura and prevents the friction when the pleural membranes slide over each other.

Lungs are pink in colour, soft, elastic and distensible.

They are highly vascular (richly supplied with blood capillaries).

Lungs

Each sac has about twenty alveoli which look like grapes. They are covered with a network of capillaries from the pulmonary artery and vein.

The alveoli have very thin (0.0001 mm) wall composed of simple non-ciliated, squamous epithelium. It has collagen and elastin fibres. This makes the alveoli very flexible.

Each alveolus is about 0.1 mm in diameter.

The human lung has about 750 million alveoli, which increase surface area for exchange of gases. The total area covered by them is about 50 times the surface area of skin.

Alveoli are supplied by a network of pulmonary capillaries.

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Mechanism of Breathing

dr. aarifINSPIRATION :

It is an active process brought about by ribs, intercostal muscles, sternum and diaphragm.

The intercostal muscles contract, pulling the ribs outward and increase the space in the thoracic cavity. The lower part of the breast bone (sternum) is also raised.

The diaphragm contracts and becomes almost flat.Volume of the thoracic cavity is further increased, pressure on the lungs decreases. The lungs expand and their volume increases. Atmospheric air rushes into the lungs through the respiratory passage to make the pressure equal. Thus the air enters the lungs.

dr. aarifEXPIRATION: It is a passive process.

The inter-costal muscles relax pulling the ribs inwards.

The diaphragm relaxes and again becomes dome shaped.

Thus collective contraction of intercostal muscle and diaphragm reduces the volume of the thoracic cavity. The pressure on the lungs increases. The lungs get compressed and the air in the lungs, rushes out through the external nares.

Alternate inspiration and expiration together form the respiratory cycle. It occurs16-20 times per minute in man.

Breathing is under the control of the medulla oblongata of the brain

dr. aarifRESPIRATORY QUOTIENT (RQ)The ratio of the vol of CO2 / O2 used in unit time is called respiratory quotient

It varies for different substrates used for respiration

GLUCOSE has RQ = 1FAT has RQ = 0.7PROTEIN has RQ = 0.85ORGANIC ACIDS has RQ = 1.3 or 1.4

In ANAEROBIC respiration RQ = infinity

RQ is determined by means of Ganongs respirometer

dr. aarif1. External respirationIt includes the respiratory processes which take place in the lungs

O2 from the lungs diffuses in the lung capillaries and CO2 from the lung capillaries diffuses into lungs TRANSPORT OF GASESThe transport of respiratory (O2 and CO2) gases takes place in the following events:1.External respiration2.Internal respiration3.Cellular respirationExternal respiration includes three events:

a. Exchange of gasesb. Formation of oxy-haemoglobinc. Release of carbon-di-oxide:

dr. aarif1.Exchange of gases

Concentration of oxygen is higher in the inspired air than in the alveolar blood and the concentration of carbon-dioxide is higher in the alveolar blood than in the inspired air.

This results in the exchange of oxygen from the air into the blood and carbon-dioxide from blood into the air which is exhaled out.

dr. aarif2.Formation of oxy-haemoglobinThe absorbed oxygen combines with the haemoglobin of RBC's.

Haemoglobin is a respiratory protein pigment. It forms the unstable oxy-haemoglobin.Haemoglobin+ Oxygen = Oxy-Hb

Hb + 4 O2 Hb (4O2)

15 gms of Hb is present in 100 ml of blood1 gm of Hb can carry 1.34 ml of O2Thus 100 ml of blood (15 gm of Hb) can carry approx 20 ml of O2

dr. aarif3. Release of carbon-dioxideCarbon-dioxide from the blood is released outside into the air.

CO2 is brought by the blood from the tissue cells in the form of sodium and potassium bicarbonates in the blood plasma.

Some amount of CO2 is also brought by haemoglobin in the form of carbamino-haemoglobin.

CO2 brought in all these forms is released.

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dr. aarif2. Internal respirationIt includes the respiratory processes which take place in the tissue cells.

Oxygen brought by the blood is given to the tissue cells and carbon-dioxide from the tissues, is passed into the blood.

When the blood reaches the tissue cells, the unstable oxy-Haemoglobin breaks down to form haemoglobin and oxygen.

O2 Hb Dissociation Curve

dr. aarifThe ultimate purpose of respiration is to release energy. This is carried out in the cells by oxidation of food.

It results in the formation of ATP molecules. Energy is stored in this form. This energy is used to carry out vital life processes

So ,ATP is called energy currency of cell.

ATP is formed as the main product using mitochondria, while by-products are CO2 and water vapour which are transported by the blood to the lungs.

Energy released as heat to certain extent is used to maintain the body temperature.

3. Cellular respiration

dr. aarifPULMONARY AIR VOLUMES AND CAPACITIES:

The quantities of air the lungs can receive, hold or expel under different conditions are called pulmonary or lung volumes.

Pulmonary capacity refers to a combination of two or more pulmonary volumes.SPIROMETRY is the process of recording the changes in the volume of air into and out of lungs and the instrument used for this purpose is called SPIROMETER

The graph showing the changes in the pulmonary volumes and pulmonary capacities under different conditions of breathing is called a SPIROGRAM.

PULMONARY AIR VOLUMES AND CAPACITIES (TV + IRV)

(RV + ERV)(TV + IRV + ERV)

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It is the volume of air inspired or expired (both) with each normal breath (effortless). It amounts to about 500ml in the average adult man.

Of the 500ml of inspired air, only 350 ml of fresh air reaches the lung alveoli and is called alveolar volume while about 150 ml of the inspired air remains in the respiratory tract from the nasal chambers to terminal bronchioles which is often called anatomical dead space and is called dead space volume.

Physiological dead space includes anatomical dead space and the space in the non-functional alveoli. It is not useful for the gas exchange process as no gas exchange occurs in the dead space.

During exercise, tidal volume is about 4-10 times higher than normal. TIDAL VOLUME (TV)

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It is the extra volume of air which can be inspired by forced inhalation beyond the normal tidal volume. It is about 2500-3000 ml.It is the deepest possible inspiration INSPIRATORY RESERVE VOLUME (IRV)

It is the amount of air that can be expired by forceful expiration after the end of a normal tidal expiration.It is about 1000 1100 ml. EXPIRATORY RESERVE VOLUME (IRV)

It is the volume of air left behind in the lung alveoli and respiratory passage even after the most forceful expiration.It is about 1500 ml. This volume can never be expelled out by respiration. RESIDUAL VOLUME (IRV)

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It is the amount of air that a person can inhale to the maximum level.It is the sum of the inspiratory reserve volume(IRV) and the tidal volume (TV)and is about 3500 ml. (Range 3 3.5 L)IC = IRV + TV INSPIRATORY CAPACITY (IRV)

It is amount of air left in the lungs after normal expiration.It is equal to the sum of expiratory reserve volume and the residual volume.It is about 2500 ml. (2.5 Litres)FRC = ERV + RV = 1000 + 1500 = 2500 ml FUNCTIONAL RESIDUAL CAPACITY (IRV)

It is the maximum amount of air that can be expelled from the lungs by forced exhalation after a forced inhalation.It is equal to the sum of tidal volume, inspiratory reserve volume and expiratory reserve volume.Vital Capacity of lung = TV + IRV + ERV = 500 + 3000 + 1100 = 4600 mlRange of vital capacity = 3.5 4.5 Litres in a normal adult person.VC is higher in athletes, mountain dwellers, men and young onesVC is lower in non-athletes, plain dwellers, women,old and cigarette smokers VITAL CAPACITY (VC)

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It is the amount of air in the lungs and the respiratory passage after a maximum inhalation effort.It is equal to the sum of vital capacity and the residual volume.TLC= VC + RV = 3.5 4.5 L + 1.5 L = 5 6 litres (Average 5800 ml) TOTAL LUNG CAPACITY (TLC)

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Haemoglobin has about 250 times more affinity for carbon monoxide than for oxygen.

In the presence of carbon monoxide, it readily combines to form a stable compound called carboxy-haemoglobin.

The oxygen combining capacity with Hb decreases and as a result tissue suffers from oxygen starvation.

It leads to asphyxiation and in extreme cases to death.Treatment : The person needs to be administered with pure oxygen-carbon dioxide mixture to have a very high O2 level to dissociate carbon monoxide from haemoglobin.Causes:Carbon monoxide poisoning occurs often in closed room with open stove burners or furnaces or in garages having running automobile engines. CARBON MONOXIDE POISONING

dr. aarifCONTROL OF RESPIRATIONRespiration has 2 control mechanisms : Nervous and Chemical regulation

NERVOUS : The respiratory center in medulla and pons consist of 1) Dorsal respiratory group : Located in the dorsal portion of medulla Mainly causes Inspiration

2) Ventral respiratory group : Located in the ventrolateral portion of medulla Causes Inspiration or expiration

3) Pneumotaxic centre: Located in the dorsal portion of pons Mainly limits Inspiration

dr. aarifCONTROL OF RESPIRATION

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CHEMICAL : Chemoreceptors are located in the carotid and aortic bodies

Afferent nerve fibres of carotid bodies pass through Glossopharyngeal nerve to the dorsal respiratory area

Afferent nerve fibres of aortic bodies pass through vagus nerve to the dorsal respiratory area

Excess CO2 and H+ stimulate the respiratory center and accordingly alter the inspiratory and expiratory signals to the respiratory muscles

Increased CO2 lowers the pH resulting in acidosis

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dr. aarifRESPIRATORY DISORDERS- inflammatory disease of the air ways - reversible over-reactivity of the airway smooth muscle.- The mucous membrane and muscle layers of the bronchi become thickened and the mucous glands enlarge reducing airflow in the lower respiratory tract. - During an asthmatic attack, spasmodic contraction of bronchial muscle -(Bronchospasm) constricts the airway and there is excessive secretion of thick sticky mucus, which further narrows the airway. - Inspiration is normal but only partial expiration is achieved so that lungs become hyper-inflated and there is severe dyspnoea(difficulty in breathing, a.k.a. air hunger) and wheezing.- The duration of attacks usually varies from a few minutes to hours (status asthmaticus).In severe attacks the bronchi may be obstructed by mucus plugs, leading to acute respiratory failure, hypoxia (deficiency in the amount of oxygen reaching body tissues) and possibly death.Non - specific factors Cold air, Cigarette smoking, Air pollution, Upper respiratory tract infection, Emotional stress and Strenuous exercise.ASTHMA

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dr. aarifPHARYNGITIS:The inflammation of the upper respiratory tract can be caused by inhaling different micro-organisms.

Streptococcus pyogenes are common cause of inflammation of palatine tonsils and walls of pharynx.

Pharyngitis usually accompanies common cold.

dr. aarifLARYNGITIS:It is an inflammation of larynx due to viral or bacterial infection. It occurs in all the ages but more common in children.

Symptoms:The voice becomes husky initially. Severe infection may lead to aphasia. There is a feeling of rawness in the throat.Stridor may be present in children.Cough of an irritating type may be present.Cause:Vocal misuse or overuse are common causes of acute laryngitis

dr. aarifALLERGRIC RHINITIS (HAY FEVER):In this condition, atopic (immediate) hypersensitivity develops to foreign proteins (antigens) e.g. pollen, mites in pillow feathers, animal dander.

The acute inflammation of nasal mucosa and conjunction causes rhinorrhoea (excessive watery exudate from the nose), redness of the eyes and excessive secretion of tears.

Atopic hypersensitivity tends to run in families but no genetic factor has yet been identified. Other forms of atopic hypersensitivity include: Childhood onset asthma,

Eczema in infants and young children and Food allergies

dr. aarifPNEUMONIA:Infection of the alveoli. protective processes fail to prevent microbes reaching lungs.Causes:IMPAIRED COUGHING:Coughing is an effective cleaning mechanism, but if it is impaired if the person is unconscious, damage to respiratory muscles or the nerves supplying them, or painful coughing, then respiratory secretions may accumulate and become infected.

Ciliary action may be impaired or the epithelium destroyed by tobacco smoking, inhaling noxious gases, infection etc.

Depressed macrophage (W.B.Cs) activity may be caused by tobacco smoking, alcohol, and anoxia(a condition characterized by an absence of oxygen supply to an organ or a tissue).Other factors: These include reduced resistance, leucopoenia (decreased W.B.C count) and chronic diseases like cardiac failure, cancer, chronic renal failure.

dr. aarifSOME PATHOGENS ASSOCIATED WITH PNEUMONIA:Streptococcus pneumoniae:This is the commonest causative organism in pneumonia, particularly Lobar Pneumonia (acute bacterial pneumonia).Mycoplasma:It is the second commonest causative organism, and affects mainly children and young adults.Other organisms:Some viruses, protozoa and fungi may cause pneumonia in people whose general resistance is lowered or whose immune system is depressed by HIV, immunosuppressant drugs etc.

dr. aarifOCCUPATIONAL LUNG DISEASESThis group of lung diseases is caused by inhaling atmospheric pollutants at work place.To cause disease, particles must be so small that they are carried in inspired air to the level of the respiratory bronchioles and alveoli, where they can only be cleared by phagocytosis.

Larger particles are trapped by mucus in upper part of the respiratory tract and expelled by ciliary action and coughing.

Recognition of the damaging effects of these substances has led to legislation that limits workers exposure to these pollutants.

dr. aarifSILICOSIS: This may be caused by long-term exposure to dust containing silicon compounds.

High-risk industries are quarrying, granite, slate, sandstone-mining, stone masonry, sand blasting and glass and pottery work.

Inhaled silica particles accumulate in the alveoli.

The particles are ingested by macrophages, and are actively toxic to these cells.The inflammatory reaction is triggered when the macrophages destroy the particles and this result in significant fibrosis.

Silicosis appears to predispose to the development oftuberculosis, which rapidly progresses to tubercular bronchopneumonia and possibly military TB (a form varying in severity, in which minute tubercles form in different organs due to dissemination of bacilli through the body by the blood stream).

Gradual destruction of lung tissue leads to progressive reduction in pulmonary function, pulmonary hypertension and heart failure.

ASBESTOSIS: Asbestosis is caused by inhaling asbestos fibres, usually develops after 10 to 20 years exposure, but sometimes after only 2 years.

Asbestos miners and workers involved in making and using some products containing asbestos are at risk.

There are different types of asbestos, but blue asbestosis is associated with the most serious disease.

Eupnea normal breathing

Hypopnea Slow breathing

Hyperpnoea rapid breathing

Apnoea No breathing

Dyspnoea Difficult breathing

Tachypnoea Rapid shallow breathing

Orthopnoea Inability to breathe in horizontal position

Asphyxia Combination of hypoxia and hypercapnea

Hypercapnea Increased CO2 content of blood

Hypocapnea Decreased CO2 content of bloodSOME RESPIRATORY TERMS

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