Class 11: Breathing and Exchange of Gases

Breathing and the exchange of gases is a crucial biological process that allows organisms to obtain oxygen (O₂) and eliminate carbon dioxide (CO₂).

1. Breathing or Pulmonary Ventilation

Breathing involves two main processes:

Inhalation (Inspiration): The process of drawing air into the lungs.
Exhalation (Expiration): The process of expelling air from the lungs.

During inhalation, the diaphragm (a dome-shaped muscle beneath the lungs) contracts and flattens, and the intercostal muscles (between the ribs) contract, causing the rib cage to expand. This increases the volume of the thoracic cavity, creating negative pressure that pulls air into the lungs. During exhalation, the diaphragm and intercostal muscles relax, decreasing the thoracic volume and pushing air out.

2. Respiratory Organs

In humans, the respiratory system includes:

Nostrils: Openings through which air enters the nasal cavity.
Nasal Cavity: Warms, moistens, and filters air.
Pharynx: A passage for air and food.
Larynx: Voice box; connects pharynx to trachea.
Trachea: Windpipe that carries air to the lungs.
Bronchi: Two main airways branching from the trachea into each lung.
Bronchioles: Smaller air passages inside the lungs.
Alveoli: Tiny air sacs where gas exchange occurs.

3. Mechanism of Breathing

Inspiration: When air enters the lungs due to a decrease in pressure inside the lungs.
Expiration: When air leaves the lungs due to an increase in pressure inside the lungs.

4. Exchange of Gases

The actual exchange of gases happens in the alveoli of the lungs:

Oxygen Diffusion: Oxygen in the inhaled air diffuses from the alveoli into the capillary blood because the partial pressure of oxygen (pO₂) is higher in the alveoli than in the blood.
Carbon Dioxide Diffusion: CO₂ diffuses from the blood (where its partial pressure is higher) into the alveoli and is expelled during exhalation.

5. Transport of Gases

Oxygen Transport: About 98.5% of oxygen is carried by hemoglobin (Hb) in red blood cells. Each hemoglobin molecule can bind to four oxygen molecules to form oxyhemoglobin.
Carbon Dioxide Transport: CO₂ is transported in three ways:
- Dissolved in plasma (about 7%).
- As bicarbonate ions (HCO₃⁻) in plasma (about 70%).
- Bound to hemoglobin (about 23%) as carbaminohemoglobin.

6. Regulation of Breathing

The rate and depth of breathing are controlled by the respiratory centers in the medulla oblongata and the pons of the brain. These centers respond to changes in CO₂ and pH levels in the blood. If CO₂ levels rise, the respiratory center increases the rate and depth of breathing to expel more CO₂.

7. Respiratory Volumes and Capacities

Tidal Volume (TV): The amount of air inhaled or exhaled during normal breathing (about 500 mL).
Vital Capacity (VC): The maximum amount of air that can be exhaled after a deep inhalation (about 4800 mL).
Total Lung Capacity (TLC): The total volume of the lungs after maximum inhalation (about 6000 mL).

8. Disorders of the Respiratory System

Asthma: Inflammation and narrowing of the airways, making it hard to breathe.
Emphysema: A condition where the alveoli are damaged, leading to reduced surface area for gas exchange.
Pneumonia: Infection causing inflammation of the lungs, usually the alveoli.
Chronic Obstructive Pulmonary Disease (COPD): A group of diseases that cause airflow blockage and breathing-related issues.

Conclusion

Breathing is the mechanical process of taking in oxygen and expelling carbon dioxide, while gas exchange ensures that oxygen is supplied to tissues and carbon dioxide is removed. This complex process is vital for cellular respiration and energy production in living organisms. Understanding the anatomy and physiology of the respiratory system helps us appreciate how our bodies maintain proper oxygenation and acid-base balance.

The process of exchange of ________________from the __________with __________ produced by cells is called breathing.
Mechanisms of breathing vary among different groups of animals depending mainly on their _____________and level of organisation.
Earthworm use their ______________for breathing.
The nasal chamber opens into the _________, a portion of which is common passage for food and air.
__________is a cartilaginous box which helps in sound production and hence called ___________ .
During swallowing, ______________ can be converted into a thin cartilaginous flap called _____________ to prevent entry of food into ________________.
Trachea is a straight tube extending up to the mid-thoracic cavity, which divides at the level of _____________ thoracic vertebra into right and left ______________ >
Humans have two lungs which are covered by a double layered ___________, with ___________ fluid between them.
The part starting with external nostrils up to ________________ constitute conducting part whereas the_________________and their ducts form respiratory or exchange part of respiratory system.
The thoracic chamber is formed dorsally by the vertebral column, ventrally by the _____________, laterally by the _________and on the lower side by dome-shaped _________.
Respiration in total involves _____________ steps.
The movement of air into and out of lungs is carried out by creating __________________ gradient between ___________ and the atmosphere.
Inspiration occur if the pressure within the lungs is ______________ than the atmospheric pressure.
Expiration takes place when intra-pulmonary pressure is ______________________________ than atmospheric pressure.
Inspiration is initiated by the contraction of diaphragm which increases the volume of thoracic chamber in the ______________ axis.
During inspiration, contraction of _____________ muscle lifts the ribs and the sternum causing an increase in the volume of thoracic chamber in ____________axis.
Humans have the ability to increase the strength of inspiration and expiration with the help of additional muscle in the ____________ .
On an average, a healthy human breathe _____________ times/minute.
The volume of air involved in breathing movements can be estimated by using a ________________ which helps in clinical assessment of pulmonary functions.
Approximately ___________ ml of air is inspired or expired during normal respiration and a healthy man can inspire or expire approximately ml of air per minute.
Inspiratory Reserve Volume averages ___________ ml whereas ERV averages ______________. .
Volume of air remaining in lungs after___________ expiration is called volume. It averages 1100 to 1200ml. _______________.
__________________ = T.V + I.R.V
Functional Residual capacity is total volume of air that will remain in lungs after ____________expiration. This includes _____________, E.R.V and _____________ .
Vital capacity is the maximum volume of air a person can breath out after a _____________ inspiration. This includes _________________, T.V and _______________
____________are the primary sites of exchage of gases.
Expiratory capacity is total volume of air a person can ______________ after normal _____________.
Pressure contributed by an individual gas in a mixture of gases is called ____________pressure and is represented as ______________ for oxygen and ____________for CO₂ .
pO₂ of deoxygenated blood is ____________ mmHg and pCO₂ in oxygenated blood is _____________mmHg.
The soulubility of CO₂ is ____________times higher than that of O₂ in blood.
The diffusion membrane is made up of three major layer – ______________________epithelium of alveoli,___________
of alveolar capillaries and_______________________ in between them.
Total thickness of diffusion membrane is ______________.
Alveolar wall of alveoli is _____________________ celled thick wall.
About _______________________ % of O₂ and ____________ % of CO₂ is transported by Hb in the blood.
____________ % of O₂ and ______________ % of CO₂ is carried in a dissolved state through plasma of blood.
O₂ bind with Hb in ____________ manner to form _________ . Each Hb molecule can carry a maximum of __________ molecules of O₂ .
A ______________ curve is obtained by plotting percentage saturation of Hb with O₂ against pO₂ . This curve is called _____________ curve.
For the formation of oxyhaemoglobin in the alveoli, favourable factors are – high pO₂ , low CO₂,_____________ H+ concentration and _____________ temperature.
Every 100ml of oxygenated blood can delive ______________ ml of O₂ to the tissue under normal physiological conditions.
CO₂ is carried by haemoglobin as _________________ .
CO2 +H2O —-> H2CO3
The above reaction is catalyzed by enzyme _____________, which is present in higher concentration in ______________ and in minute concentration in _______________ of blood.
Every 100ml of deoxygenated blood delivers approximately ______________ ml of CO₂ in alveoli.
Exchange of O₂ and CO₂ at the alveoli and tissues occur by _______________.
Respiratory rhythm is maintained bu the respiratory centre in ______________ region of brain.
A _______________ centre in pons region of brain and chemosensitive area in the medulla can alter respiratory mechanism.
The chemosensitive area in medulla is sensitive to ________________ and ___________________ .
Receptors associated with aortic arch and _____________ recognize changes in CO and H+ concentration.
________________ is a difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles.
Emphysema is a chronic disorder in which ________________ are damaged due to which respiratory surface is decreased.
Long exposure to dust, in industries involving grinding or stone-breaking, can lead to inflammation leading to______________ and thus cause serious lung damage.

1. O₂ ; atmosphere; CO₂	16. external inter-costal; dorso- ventral	31. squamous; endothelium; basement substance	46. CO ; H+ ions
2. habitat	17. abdomen	32. less than millimeter	47. carotid artery
3. moist cuticle	18. 12-16	33. one	48. asthma
4. pharynx	19. spirometer	34. 97; 20-25	49. alveolar walls
5. Larynx; sound box	20. 500; 6000-8000	35. 3; 7	50. fibrosis
6. glottis; epiglottis; larynx	21. 2500-3000; 1000-1100	36. reversible; oxyhaemoglobin ; 4
7. 5th ; primary bronchi	22. Forcible; residual	37. sigmoid; oxygen dissociation
8. pleura; pleura	23. I.C	38. lesser; lower
9. terminal bronchioles ; alveoli	24. normal; R.V	39. 5
10. sternum; ribs; diaphragm	25. Forced ; ERV ; IRV	40. carbamino-haemoglobin
11. 5	26. alveoli	41. carbonic anhydrase; RBC’s ; plasma
12. pressure; lungs	27. expire; inspiration	42. 4
13. less	28. partial; pO₂ ; pCO₂	43. diffusion
14. higher	29. 40; 40	44. medulla
15. antero-posterior	30. 20-25	45. pneumotaxic