Plus One Zoology Notes Chapter 6 Breathing and Exchange of Gases is part of Plus One Zoology Notes. Here we have given Kerala Plus One Zoology Notes Chapter 6 Breathing and Exchange of Gases.
|Text Book||NCERT Based|
|Chapter Name||Breathing and Exchange of Gases|
|Category||Kerala Plus One|
Kerala Plus One Zoology Notes Chapter 6 Breathing and Exchange of Gases
The process of exchange of O2 from the atmosphere with CO2 produced by the cells is called breathing It is commonly known as respiration.
Mechanism of breathing varies among different groups of animals depending mainly on their habitats and levels of an organization.
|Sponges||Use entire body surface|
|Spider & Scorpion||Book lungs|
Human Respiratory system
The respiratory system consists of
- Pair of Nostrils
- Nasal chambers
- External nostrils open into nasal chambers through the nasal passage.
- Nasal chamber opens into nasopharynx (Portion of the pharynx, the common passage for food and air).
- Nasopharynx opens through glottis into the trachea.
Epiglottis: Glottis covered by a thin elastic cartilaginous flap.
Function: Prevents food and other foreign particles from entering the trachea.
- The larynx is the cartilaginous box which helps in sound production and hence called the sound box.
- The trachea is a straight tube extending up to mid thoracic cavity, which divides into right and left pulmonary bronchi.
- Each bronchus undergoes repeated divisions to form secondary and tertiary bronchi and bronchiole ending up in very thin terminal bronchioles.
- Alveoli are the bag like structure arising from the terminal bronchiole. They are the functional unit of lungs.
- The branching network of bronchi, bronchiole, and alveoli comprises the lungs.
- A pair of lungs is situated in the thoracic cavity.
- It is covered by a double-layered pleura, with pleural fluid between them. It reduces friction on the lung surface. The outer layer of pleura is attached with thoracic lining.
- The inner pleural membrane is in contact with the lung surface.
- Conducting part: External nostril up to the terminal bronchiole transports the atmospheric air to the alveoli.
Respiratory part: Alveoli and their ducts, is the site of actual diffusion of O2 and CO2 and atmospheric air.
- Lungs are situated in the thoracic chamber, which is anatomically an airtight chamber.
- The thoracic chamber is formed of:
a. Vertebral column at dorsal side
b. Sternum on the ventral side
c. Ribs at the lateral side.
d. The dome-shaped diaphragm on the lower side.
Respiration involves the following steps
- Breathing (pulmonary ventilation) by which atmospheric air is drawn in and CO2 rich alveolar air is diffused out.
- Diffusion of gases(O2 and CO2) across the alveolar membrane.
- Transport of gases by the blood.
- Diffusion of O2 and CO2 between blood and tissues.
- The utilization of utilization tells for catabolic reactions and resultant release of CO2 (cellular respiration).
Mechanism of breathing
- Breathing involves two stages.
- The movement of air in and out of the lungs is carried out by creating a pressure gradient between the lungs and atmosphere.
- The pressure gradient is created by the contraction and relaxation of
- External and internal intercostal muscles.
- The process of intake of air into the alveoli of the lungs.
- It includes muscle contraction and so is an active process, consuming mechanical energy.
- Inspiration takes place when a pressure within the lungs becomes less than the atmospheric pressure, i.e., there is a negative pressure in the lungs with respect to atmospheric pressure.
- The diaphragm and a specialized set of muscles external and internal intercostals between the ribs help in the generation of such gradients.
- Contraction of the diaphragm increases the volume of the thoracic chamber.
- The contraction of intercostal muscle lifts up the ribs and sternum. This causes an increase in the volume of the thoracic chamber.
- Increase in thoracic volume causes an increase in pulmonary volume.
- When pulmonary volume increases the intrapulmonary pressure decreases resulting in the entry of air from outside into the lungs.
- The breathing out of the air from the lungs is called expiration.
- It is a passive process.
- It takes place when the intrapulmonary pressure is higher than the atmospheric pressure.
- Relaxation of the diaphragm and the intercostal muscles returns the diaphragm and sternum to the normal position.
- This reduces the thoracic volume and pulmonary volume.
- This leads to an increase in intrapulmonary pressure above the atmospheric pressure.
- This causes expulsion of air from the lungs.
♦ A healthy human breathes 12 16 times/minute
- Apparatus used to measure the rate of breathing.
- Helps in clinical assessment of pulmonary functions
Respiratory volume & capacity
|Tidal volume (TV)||♦ A volume of air inspired or expired during normal respiration.|
♦ It is approx. 500mL.
♦ A healthy man can inspire or expire approximately 6000 – 8000mL of air per minute.
|Inspiratory reserve volume (IRV)||♦ An additional volume of air that can be inspired forcibly after a normal inspiration.|
♦ This averages 2500 mL -3000 mL
|Expiratory reserve volume (ERV)||♦ An additional volume of air that can be expired forcibly after a normal expiration.|
♦ This averages 1000 mL -1100 mL
|Residual volume (RV)||♦ It is the volume of air that remains in the lungs after a forcible expiration.|
♦ This averages 1100 mL -1200 mL
|Inspiratory capacity (IC)||♦ A total volume of the air that can be inspired after normal expiration(TV+ IRV)|
|Expiratory capacity (EC)||♦ It is the total volume of air that can be expired after a normal inspiration(TV+ ERV)|
|Functional residual capacity (FRC)||♦ A volume of air that will remain in the lungs after a normal expiration (ERV+RV)|
|Vital capacity (VC)||♦ The maximum volume of air a person can breathe in after a forced expiration.|
|Total lung capacity (TLC)||♦ The total volume of air accumulated in the lungs after a forced inspiration. (RV+ERV+7V+IRV or vital capacity + residual volume)|
Exchange of gasses
- Alveoli are primary sites of gases ex-change between blood and tissues.
- O2 and CO2 are exchanged through these sites by simple diffusion based on,
- Pressure/concentration gradient.
- Solubility of gases
- Thickness of membranes
- Partial pressure of a gas is the amount of pressure contributed by an individual gas in a mixture of gases
- The partial pressure of oxygen is represented as pO2 and carbon dioxide as pCO2.
Partial pressure (in mm Hg) of CO2 and O2 at different parts involved in diffusion, in comparison to those of the atmosphere.
|Respiratory gas||Atmospheric air||Alveoli||Blood deoxygenated||Blood oxygenated||Tissues|
- Since pO2 in alveoli is more (104 mmHg) than that in the blood capillaries (40 mm Hg). O2 diffuses into capillary blood.
- Since pCO2 in deoxygenated blood is more (45 mm Hg), CO2 diffuses to the alveolus.
Diagrammatic representation of an exchange of gases at the alveolus and body tissue with blood and transport of O2 & CO2
- Since pCO2 is less(40 mm Hg) than that, of the cells (45 mm Hg), carbon dioxide diffuses from the body cells of the capillary blood via tissue fluid the blood become deoxygenated.
- Deoxygenated blood is carried to the heart and to the lungs.
- As the solubility of CO2 is 20-25 times higher than that of O2, the amount of CO2 that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher compared to that of O2.
A diagram of a section of an alveolus with a pulmonary capillary
- The diffusion membrane is made up of three layers.
- Thin squamous epithelium of alveoli
- Endothelium of alveolar capillaries
- Basement substance between them.
- However, it’s total thickness is much less than a millimeter.
Transport of Gases
- Blood is the medium of transport for respiratory gases such as O2 and CO2.
- 97% of O2 is transported by RBCs in blood.
- 3% of O2 is carried in a dissolved state through a plasma
- 20-25 % of CO2 is transported by
- About 70 % of CO2 is carried by bicarbonate.
- About 7% of CO2 is carried in a dissolved state through a plasma.
Transport of Oxygen
Blood transports oxygen in two ways.
A. In dissolved state through the plasma, Only 3% of oxygen is transported through the plasma.
B. In binding with hemoglobin
- In the RBC oxygen can bind with ’hemoglobin to form oxyhemoglobin bin. Each hemoglobin can carry a maximum of four molecules of O2.
- Partial pressures of O2 partial pres: sure of CO2, H+ concentration and temperature are the important factors which affect the binding of O2 with hemoglobin.
- A sigmoid curve is obtained when the percentage saturation of hemoglobin with O2 is plotted against the pCO2. This curve is called an oxygen dissociation curve.
Oxygen Dissociation Curve
- This curve is highly useful in studying the effect of factors like pCO2, H+ concentration etc. on the binding of O2 with hemoglobin.
i. Binding of oxygen in the alveolus
The factors favorable for the former of oxyhemoglobin in alveoli are,
- High pO2
- Low pCO2
- Lesser H+ concentration
- Lower temperature
- In the RBC, when all these factors become favorable, O2 binds with hemoglobin to form oxyhemoglobin (Hb O2). This is called oxygenation of hemoglobin.
Hb + O2 → Hb O2 (oxyhemoglobin)
ii) A release of 02 in the tissues.
The factors favorable for the dissociation of 02from the oxyhemoglobin in the tissues are,
- Low pO2
- High pCO2
- High H+ concentration
- Higher temperature
- In the tissues, when all these factors become favorable, oxyhemoglobin dissociates into hemoglobin and O2 molecule. This is called deoxygenation of hemoglobin.
- Every 100 ml of blood releases up to 5ml of oxygen to the tissues under normal physiological conditions.
Transport of carbon dioxide
i) As carbaminohemoglobin
- CO2 is carried by hemoglobin as carbaminohemoglobin (about 20 25%).
- Binding is related to the partial pressure of CO2.
- PO2 is a major factor which could affect this binding.
- When pCO2 is high and pO2 is low as in tissues, more binding of carbon dioxide occurs in tissues.
- When pCO2 is low and pO2 is high as in alveoli dissociation of CO2 from carbamino hemoglobin occurs in alveoli.
ii) As bicarbonate
- RBC contain a very high concentration of the enzyme carbonic anhydrase, minute quantities of this enzyme is present in the plasma too.
- In tissues, the pCO2 is high due to catabolism. CO2 diffuses into the blood and forms HCO3 and H+
- In the alveolus, the pCO2 is low. So the bicarbonate dissociates into CO2 and H2O.
- This CO2 is released out of lungs.
- Every 100 ml of deoxygenated blood delivers about 4 ml of CO2 to the alveoli.
Regulation of Respiration
|The region of the neural system||Functions|
|Respiratory rhythm centre (In the medulla||♦ Regulates the rhythm of respiration|
|Pneumotaxic center (pons region of the brain)||♦ Moderates the functions of the respiratory rhythm center.|
♦ It reduces the duration of inspiration and so alter the respiratory rate.
|Chemosensitive area||♦ It is highly sensitive to CO2 and hydrogen ions.|
♦ Increase in CO2 and hydrogen ions can activate this center, which signals the rhythm center.
♦ The rhythm center then makes adjustments in order to eliminate these substances.
|Receptors associated with aortic arch and carotid artery.||♦ Recognize the CO2 and hydrogen ion concentration.|
♦ Sends necessary signals to the rhythm centre for appropriate action.
Disorders of the Respiratory System
|Asthma||Inflammation of bronchi and bronchioles.||Difficulty in breathing causing wheezing, coughing and an excess amount of mucus clogs the bronchi and bronchioles.|
|Emphysema||Cigarette smoking||It is a chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased.|
|Occupational respiratory disorders||Long exposure to harmful substances like silica, asbestos, etc||The proliferation of fibrous connective tissue of the upper part of the lung causing inflammation.|
|Pneumonia||By bacteria ‘Streptococcus pneumonia’.||Alveoli acutely inflamed. Most of its space is filled with fluid and dead WBCs.|
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