for Grade XII

Respiration

Respiration can be defined as a biochemical process in which organic compounds are oxidized to liberate energy. Energy is released in a step wise process. The energy is trapped in a chemical bonds of adenosine triphosphate ATP molecules. ATP is instant sources as universal energy carriers. It is a catabolic process.

Types
1. Aerobic
It occurs in all higher forms (organisms) in this type Oxygen is necessary.
C6H12O6 + 6O2 -------- 6CO2 + 6H2O + 2880 K joule .


2. Anaerobic respiration
C6H12O6 ----------- C2H5OH(ethyl alcohol) + CO2 + 210 K joule example yeast
C6H12O6 ----------- C3H6O¬3 (lactic acid)+ energy example intestinal worms



It occurs in Yeast cells, Bacteria etc. Oxygen is not necessary. Glucose molecules are changed into ethyl alcohol and Carbon dioxide. This process is referred to fermentation.

Pulmonary respiration

All mammals whether aquatic like Dolphin, Whales etc or terrestrial have lungs as respiratory organ. The respiration by lungs is called pulmonary respiration. In man, respiratory organs are lungs and respiratory tracts which include nostrils, nasal chamber, internal nostril, nasopharynx, larynx, trachea and bronchi etc.

Nostrils are openings of nasal chamber. Nasal chambers are lined with mucous membranes which are ciliated epithelium. Nasal chambers are paired structures separated by nasal septum. Each nasal chamber has 3 parts
1. vestibular part - it is the anterior part with hairy skin which acts as filter preventing the entry of dust particles.
2. respiratory part - it is the middle part lined by glandular and vascular respiratory epithelium. It acts as air conditioner and brings the inspired air at body temperature.
3. olfactory part - it is posterior part and lined by highly sensory olfactory epithelium( Schneiderian membrane). It helps in smelling.

Functions _ filtration of air by hairs, prevent dust from entering.
_ moisten the dry air by mucous.
_ mucous traps dirt.
_ air warmed by capillary network.
_ detect smell.

Internal nostril open into nasopharynx. Little below this, is the laryngopharynx. There is presence of aperture called glottis. Glottis can be closed by leaf like cartilage epiglottis during the swallowing of food. Epiglottis prevents the entry of food into glottis. Glottis opens into larynx. Larynx is called voice box. It is cartilaginous structure. It is more developed in males than in females. It is also called Adam’s apple. It is supported by four cartilages, one cricoid, one thyroid and two arytenoids. It is lined by stratified columnar ciliated epithelium. The cilia of which beat out ward and eject the unwanted substances. There are presence of 2 pairs of vocal cords. The true pair of vocal cords set into vibrations when air is forced to go out from lungs. The vibrations produce the sound. The pitch of sound is controlled by muscles. The larynx opens into trachea.
Trachea runs through neck in front of oesophagus and extend into the thoracic cavity. It is the wind pipe about 12 cm long. It is provided with 16 to 20 dorsally incomplete c-shaped tracheal rings of cartilage. Cartilagenous rings prevents trachea from collapsing. Trachea divides into 2 primary bronchi. These are also provided with cartilaginous rings. Each primary bronchus enters into lung of its side. The right bronchus divides into 3 branches and left into 2 branches.

After entering into the lungs, primary bronchioles divide into large no. of bronchial tubes called secondary bronchioles. The secondary bronchioles further subdivides into tertiary bronchioles and then into alveolar ducts. The alveolar duct ends in alveolar sac containing 6 to 8 pocket like outgrowths called air sacs. The air sacs are about 0.1 mm in diameter. These branches make the bronchial tree.

Respiratory organs
There is a pair of spongy conical hollow bags enclosed in pleural cavities called lungs. The plural cavities are lined by tough, flexible and transparent membranes called pleura. The plura is double walled. The outer membrane is parietal and inner membrane is visceral membrane. These membranes protect lungs and stop leaking of air into thoracic cavity. The fluid secreted by pleura reduces the friction during breathing movement. The lungs are capable of great expansion. They are inflated when filled with air. These are found in either side of heart. The right lung has three lobes and left lung has two lobes. The three lobes of right lung are right superior, right inferior and middle lobe. The two lobes of left lung are left superior and left inferior. The left lung has cardiac notch at its anteromedian border to accommodate the heart. There are about 750 millions of alveoli. These large no. of alveoli provide about 100 sq meter of surface. It is about 50 times of skin surface(1.6 sq m). Alveoli are extremely thin walled and vascular structure surrounded by capillary of network. These are the site for gases exchange.

Mechanism of breathing

Breathing is simply taking in of fresh air from atmosphere and giving out of used air from lungs. Breathing renews constantly the air present in the lungs. It is accomplished through changes in the volume and air pressure of the thoracic cavity. Change in volume and air pressure is carried out by movement of ribs, internal and external intercostals muscles, diaphragm and abdominal muscles. Breathing can be divided into inhalation and exhalation.

Difference between inhalation and exhalation

Inhalation exhalation
1. Taking in of atmospheric air 1. giving out of air from lungs.
2. contraction of external intercostal 2. relaxation of external intercostals
muscle or inspiratory muscle and muscle and contraction of intercostal
relaxation of internal intercostals muscle. muscle.
3. rib cage moves forward and outward 3. rib cage moves downward and inward.
4. diaphragm contracts and becomes 4. diaphragm relaxes and become dome
flattened. shaped.
5. increase in the volume of thoracic cavity. 5. decrease in volume of thoracic cavity.
6. decease in air pressure(below atmos- 6. increase in the air pressure.
pheric pressure.
7. rushing in of air through nostril into 7. expulsion of air from lungs into atmos-
alveolar sacs causing inflation of lung. phere causing deflation of lungs.


One breath includes one inspiration or inhalation and one expiration of exhalation. The respiratory rate is the no. of breaths taken per minute. At rest, for a normal person, it is equal to 12 to 14 breaths per minute. The pulmonary air volume during breathing is measured by an apparatus called Spirometer.

Tidal volume(TV) - volume of air that is breathed in or out during effortless normal breathing. It is about 500 ml.
Inspiratory reserve volume(IRV) - it is an extra volume of air over and above the tidal volume that can be taken in during a deep breath. It is about 1500 to 2500 ml.
Expiratory reserve volume(ERV) - after a normal expiration one can still expel a large volume of air. It is known as ERV. It is about 1500 ml.
Vital capacity(VC) - it is total volume of air expired after a maximum inspiration. It is about 3.5 to 4.5 L for normal adult and about 6 L for athlete.
Total lung capacity(TLC) - it refers to amount of air present in the lung after maximum inhalation. It is equivalent to 5 to 5.5 L
Residual volume)RV) - it is the amount of air left in the lungs even after maximum expiratory effort. It can never be forced out of lungs. It is about 1500 ml.
Dead space - it is amount of air that is present in the respiratory tubes where gases exchange does not occur. With each expiration it is expelled out without undergoing any change in O2 and CO2 concentration. It is equivalent to about 150 ml. Out of tidal volume of 500 ml, 150 ml remains in the respiratory tubes as dead space and the only the rest of 350 ml is present in alveolar sacs in the lungs for exchange of gases.
Respiratory Quotient - it is the ratio of volume of CO2 produced and volume of O2 used during the respiration. It is RQ in short. For hexose sugar,

RQ = volume of CO2/volume of O2
= 6/6
= 1
for fat it is about 0.71 and for protein it is about 0.80
for mixed food it is about 0.85
RQ can show the nature of food one has taken.

Physiology of respiration

Physiology of respiration can be studied under following headings.
1. external respiration
2. transportation of O2 by blood
3. internal respiration
4. transportation of CO2 by blood.

External respiration - it is uptake of O2 and release of CO2. It takes place in the lungs called breathing.
Transport of O2 by blood - RBC of blood contain haemoglobin as respiratory pigment. Human blood contains nearly 150 gram of Hb per 100 ml. haemoglobin readily combines with and dissociates to form free Oxygen.

Hb + O2 == HbO2

Oxyhaemoglobin is unstable compound and thus can dissociate quickly.
The quantity of O2 combining with Hb depends upon pressure of Oxygen. The graph in which percentage of saturation of blood is plotted against PO2 is called Oxygen dissociaton curve. It is S shaped. It indicates that blood has high affinity for O2.
In man, arterial blood has PO2 of about 95 mm Hg and Hb is about 95 % saturated. In venous blood, PO2 is about 40 mm Hg and about 70 % haemoglobin is saturated with O2. The Oxygen and CO2 transport is closely associated. Increase in conc. of CO2 decreases the amount of O2 that can be carried in the blood at a given partial pressure of O2. This is known as Bohr’s effect. The graph shows that the increase in the PCO2 lowers the curve.

Internal respiration - it is tissue respiration. Digested food is oxidized to liberate energy.

Transport of CO2 - CO2 is product of respiration. CO2 is poisonous. It should be removed quickly. It takes place by following way.
1. By plasma in the form of carbonic acid - CO2 dissolve in water of blood plasma to form carbonic acid, about 7 % of total CO2 s carried in this way.
2. In the form of bicarbonates of Na and K - CO2 enters into the RBC to dissolve into water. It is catalysed by carbonic anhydrase enzyme. H2CO3 ionises to form bicarbonate and hydrogen. The bicarbonate ions combine with Potassium ion to form Potassium bicarbonate. Upon saturation, Potassium bicarbonate ionizes into Potassium and bicarbonate ion, These ions being at higher conc. within red cells, come out into plasma and combine with available Na ion to form Sodium bicarbonates. The loss of bicarbonate ions is balanced by chloride ions diffusing into RBC from plasma . the exchange of Cl and HCO3 between plasma and RBC is known as Chloride shift or Hamberger’s phenomenon. In the lungs, these reactions are reversed. The exchange of Cl and HCO3 is reversed. H2CO3 is formed again which break down into water and CO2. CO2 in exhaled. In this way about 70 % of CO2 is transported.
3. By RBC in the form of carbamino compounds - amino acid present in RBC get oxidized to release amino group and carboxyl group. Carbon dioxide combines with amino group to form carbamino compounds. About 23 % is transported in this form.