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INTERMEDIATE BIOLOGY
RESPIRATORY SYSTEM
-Respiration is the oxidation of nutrients in the living cells to release energy for biological work
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RESPIRATORY ORGANS
• General body surface:
E
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lower invertebrates (sponges,coelenterates, flatworms etc)
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g
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• Tracheal tubes:
E
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insects, centipede, millipede, spider
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g
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• Lungs (Pulmonary respiration):
E
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most vertebrates
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1
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- Each terminal bronchiole gives rise to many very thin and vascularised alveoli (in lungs)
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- During swallowing, epiglottis (a thin elastic cartilaginous flap) closes glottis to prevent entry of
food into larynx
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2
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- Right lung has 3 lobes and left lung has 2 lobes
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- The pleural fluid present in between these 2 layers lubricates the surface of the lungs and
prevents friction between the membranes
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- Alveoli and their ducts form the respiratory or exchange part of the respiratory system
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STEPS OF RESPIRATION
1
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2
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3
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4
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5
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A) INSPIRATION
- Active intake of air from atmosphere into lungs
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- Contraction of external intercostal muscles (muscles found between ribs) lifts up the ribs and
sternum causing
an increase in thoracic volume in the dorso-ventral axis
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-So,lungs expand
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-So, air moves into lungs
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- During this, intercostal muscles & diaphragm relax causing a decrease in thoracic volume and
there bypulmonary volume
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- During forceful expiration, abdominal muscles and internal inter-costal muscles contract
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i
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, 60008000 ml per minute
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-It is 2500-3000 ml
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• RESIDUAL VOLUME(RV)
-Volume of air remaining in lungs
after a forcible expiration
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INSPIRATORY CAPACITY (IC)
-Total volume of air inspired
after a normal expiration (TV + IRV)
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• EXPIRATORY CAPACITY(EC)
-Total volume of air expired
after a normal inspiration (TV + ERV)
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• FUNCTIONAL RESIDUAL CAPACITY (FRC):
-Volume of air remaining in the lungs after a normal expiration (ERV +RV)
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• VITAL CAPACITY (VC)
-Volume of air that can breathe in
after a forced expiration or Volume of air that can breathe out after a forced inspiration (ERV +
TV + IRV)
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• TOTAL LUNG CAPACITY (TLC)
- Total volume of air in the
lungs after a maximum inspiration
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-It is 5000-6000 ml
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-Dead air volume is about 150 ml
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Alveoli and blood
2
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-O2& CO2 are exchanged by simple diffusion
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Respiratory gas
pO2 (in mm Hg) pCO2 (in mm Hg)

Atmospheric air
159
0
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-So O2 diffuses into capillary blood
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-So, CO2 diffusesto alveoli
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-So, the amount of CO2 that can diffuse
through the diffusion membrane per unit difference in partial pressure is higher than that of O2
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b) Endothelium of alveolar capillaries
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Its total thickness is only 0
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It enables easy gas exchange
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-It increases the gas exchange
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1
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-It occurs in 2 ways:

a
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b
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-O2 binds with haemoglobin (Hb) to form
oxyhaemoglobin
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-Hb has 4 ahaem units
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Binding of O2 depends upon pO2, pCO2, H+ ion concentration (pH) and
temperature
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- These factors are favourable for the formation of oxyhaemoglobin
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So Hb4O8
dissociates to releaseO2
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-It is used to study the effect of factors like
pCO2, H+ concentration etc
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2
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-In ti INssues, pCO2 is high due to catabolism and pO2 is low
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-This favours CO2 transport from tissues to lungs
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B) AS CARBABINOHAEMOGLOMIN
- In tissues, 20-25% of CO2
binds to Hb to form carbamino-haemoglobin
-In alveoli, CO2 dissociates from carbamino-haemoglobin
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(It is slightly present in plasma too)
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-Every 100 ml of deoxygenated blood delivers about 4 ml of CO2 to the alveoli
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B)PNEUMOTAXIC AREA
-In Pons
-It moderates functions of respiratory rhythm centre
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C)CHEMOSENSITIVE AREA
-Se

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