· The types of respiration are aerobic and anaerobic.
DIFFERENCES BETWEEN AEROBIC AND ANAEROBIC RESPIRATION
| Aerobic respiration | Anaerobic respiration |
|---|---|
| In aerobic respiration, molecular oxygen is used. | In anaerobic respiration, oxygen is not used |
| It occurs in the cytoplasm as well as in mitochondria. | It occurs in the cytoplasm only. |
| There is complete oxidation of glucose into CO2 and H2O. C66H12O6+ 6O2 → 6CO2+6H2O+ Energy |
There is incomplete oxidation of glucose into lactic acid or ethyl alcohol. C6H12O6→ 2C3H6O3 + Energy (Lactic acid) C6H12O6→ 2C2H5OH + 2CO2 (Ethyl alcohol)+ Energy |
| 38 molecules of ATP are released. | 2 molecules of ATP are released. |
· Respiration involves two processes:
a. Exchange of gases i.e. oxygen and carbon dioxide between the lungs and blood
a. Exchange of gases i.e. oxygen and carbon dioxide between the lungs and blood
b. Oxidation of foodstuffs to release energy between the blood and the tissues
· There is a special system of respiratory organs in human beings for respiration.
· On the basis of their function, they are categorized into two groups:
A. The first group
· It includes the air passages through which air travels.
· It includes nostrils, nasal passages, the larynx, pharynx, trachea, bronchi, bronchioles, alveoli of lungs and lungs are the major respiratory organs.
· The respiration through the lungs is called pulmonary respiration.
· It includes the air passages through which air travels.
· It includes nostrils, nasal passages, the larynx, pharynx, trachea, bronchi, bronchioles, alveoli of lungs and lungs are the major respiratory organs.
· The respiration through the lungs is called pulmonary respiration.
B. The second group
· It includes the mechanism of breathing i.e. changing the size of the thoracic cavity.
· It includes the mechanism of breathing i.e. changing the size of the thoracic cavity.
· It consists of ribs, rib muscles (external intercostal and internal intercostal muscles), thoracic cavity, diaphragm and abdominal muscles.
· One of the important structural characteristics of the human respiratory organs is the bony and cartilaginous structures which prevent the collapse of these organs all the time and allow the passage of air continuously. Internally all the organs are lined with the mucous membrane containing ciliated epithelium.
Air passages During breathing or Respiration
· The air after passing through the nostril travels through various air passages reaching into the alveoli of the lungs where the exchange of gases takes place.
· It includes:
· Nostrils - nasal passages or cavities - nasopharynx (upper part of the pharynx) -larynx (voice box) - trachea (windpipe) - bronchi (right and left) - small air tubes-bronchioles (small air tubes) - respiratory bronchioles (the smallest air tubes) - alveolar tubes or sacs - alveoli or air sacs
· Nostrils - nasal passages or cavities - nasopharynx (upper part of the pharynx) -larynx (voice box) - trachea (windpipe) - bronchi (right and left) - small air tubes-bronchioles (small air tubes) - respiratory bronchioles (the smallest air tubes) - alveolar tubes or sacs - alveoli or air sacs
Various air passages during Respiration or Breathing [Respiratory organs in human body]
The organs of respiration are:i. Nose and nasal cavity
ii. Pharynx
iii. Larynx
iv. Glottis
v. Epiglottis
vi. Trachea and primary bronchi
vii. Lungs
I. Nose and nasal cavity
· The nose is the first respiratory passage through which the air enters and leaves.
· The function of the nose is to begin the process by which the air is warmed, moistened and filtered.
· The outermost opening of the nose is called the nostril or external nare.
· The outermost opening of the nose is called the nostril or external nare.
· These are the paired openings that open into two nasal cavities divided by the nasal septum.
· The nose is lined by vascular ciliated columnar epithelium which contains mucus-secreting goblet cells.
· Superior, middle and inferior nasal conchae are the three bony ridges arising from the wall of each nasal cavity that increase the surface area and cause the turbulence to spread the air over the nasal surface.
· Nasal cavity posteriorly opens into the nasopharynx.
· Superior, middle and inferior nasal conchae are the three bony ridges arising from the wall of each nasal cavity that increase the surface area and cause the turbulence to spread the air over the nasal surface.
· Nasal cavity posteriorly opens into the nasopharynx.
II. Pharynx
· It is a tube of 12 to 14 cm long that extends from the base of the skull to the level of the 6th cervical vertebrae.
· It lies behind the nose, mouth and larynx.
· For the descriptive purposes, it is divided into nasopharynx, oropharynx and laryngopharynx.
· Nasopharynx is the upper part of the pharynx.
· Oropharynx is the middle part and the laryngopharynx is the lower part of the pharynx.
· The air free from the dust particles has to pass from the nasopharynx into the larynx.
· It is a tube of 12 to 14 cm long that extends from the base of the skull to the level of the 6th cervical vertebrae.
· It lies behind the nose, mouth and larynx.
· For the descriptive purposes, it is divided into nasopharynx, oropharynx and laryngopharynx.
· Nasopharynx is the upper part of the pharynx.
· Oropharynx is the middle part and the laryngopharynx is the lower part of the pharynx.
· The air free from the dust particles has to pass from the nasopharynx into the larynx.
III. Larynx (Voicebox)
· It extends from the roof of the tongue and the hyoid bone to the trachea and lies from the 3rd to 6th cervical vertebrae.
· The size of the larynx is the same until puberty for both males and females.
· Thereafter, it grows larger in males which explains the prominence of Adam’s apple.
· It consists of the following structures:
1. Cartilages of the Larynx: There are nine cartilages out of which three are single and three are paired.
(a) 1 Thyroid cartilage:
1. Cartilages of the Larynx: There are nine cartilages out of which three are single and three are paired.
(a) 1 Thyroid cartilage:
· It is the largest and the most prominent cartilage of the larynx.
· It is made up of flat pieces of hyaline cartilage with two laminae joined together forming a V-shaped notch called a thyroid notch.
(b) 2 Cricoid cartilages:
· This signet-ring like cartilage lies below the thyroid cartilage and is also composed of hyaline cartilage.
(c) 2 Arytenoid cartilages:
(c) 2 Arytenoid cartilages:
· These are a pair of pyramidal cartilages situated on the top of the cricoid cartilage.
· They are articulated with cricoid cartilage and joined with thyroid cartilage by the vocal cord.
(d) Corniculate cartilages:
· Upper ends of arytenoid cartilages contain two small conical nodules called corniculate cartilages.
· They are made up of elastic cartilage.
(e) Cuneiform cartilages:
(e) Cuneiform cartilages:
· These are a pair of rod-shaped structures of elastic cartilage that connect the epiglottis to the arytenoids cartilages.
· Calcification may occur in hyaline cartilage with advancing age, but not in elastic cartilage.
· Calcification may occur in hyaline cartilage with advancing age, but not in elastic cartilage.
IV. Glottis
· It is a slit-like aperture through which the pharynx opens into the larynx.
· It is a slit-like aperture through which the pharynx opens into the larynx.
V. Epiglottis
· It is leaf-like fibro-elastic cartilage attached to the inner surface of the anterior wall of thyroid cartilage immediately below the thyroid notch.
· It rises obliquely upwards behind the tongue and during swallowing, it closes the glottis and blocks the food.
· It is leaf-like fibro-elastic cartilage attached to the inner surface of the anterior wall of thyroid cartilage immediately below the thyroid notch.
· It rises obliquely upwards behind the tongue and during swallowing, it closes the glottis and blocks the food.
VI. Vocal cords
· They are inside the larynx.
· These are the two pairs of folds of the mucous membrane that extend into the lumen of the pharynx from the sides.
· The upper pair is called false and the lower is called the true vocal cord.
· They are thicker and longer in men than women so men have low pitch.
· Vocal cords are made up of yellow elastic tissue covered by non-keratinized stratified squamous epithelium.
· The space between the vocal cords is called the glottis.
· The vocal cords determine the size of the glottis.
· They are thicker and longer in men than women so men have low pitch.
· Vocal cords are made up of yellow elastic tissue covered by non-keratinized stratified squamous epithelium.
· The space between the vocal cords is called the glottis.
· The vocal cords determine the size of the glottis.
VII. Trachea and primary bronchi
· The trachea is a windpipe that is in continuation with the larynx and extends downwards to about the level of the 5th thoracic vertebrae where it bifurcates into a pair of primary bronchi (right and left bronchus) that enters the right and left lungs.
· It is approximately 10 to 11 cm long and lies mainly in the medial plane in front of the oesophagus.
· Its structure reveals C-shaped rings of hyaline cartilages and the incomplete ring is joined by connective tissues and smooth muscles.
· Cartilaginous rings support the walls of the trachea and prevent its collapse during inspiration.
It is lined by pseudo-stratified ciliated columnar epithelium containing mucus glands.
· The secretion of mucus glands keeps the walls of the tube moist and traps dust particles that enter the air.
· The vibratile cilia then carry the mucus containing dust particles up to the throat from where they can be spitted out.
· Each bronchus enters into their respective lungs.
· The right bronchus is shorter and wider than the left bronchus.
· The right bronchus after entering the right lung divides into three branches and the left bronchus divides into two branches called respiratory bronchioles.
· After entering into lungs, they divide and redivide into finer branches called bronchioles.
· Unlike bronchi, they are devoid of any cartilaginous rings.
VIII. Lungs
· Lungs lie in the thoracic region, each lying on either side of the heart.
· It is spongy, light pink, soft and elastic.
· Lungs lie in the thoracic region, each lying on either side of the heart.
· It is spongy, light pink, soft and elastic.
· It is covered by the inner visceral and outer parietal layers.
· Between membranes has a pleural space filled with fluid that reduces friction between the membranes when they are rubbed with each other during inspiration and expiration and also keeps lungs moist.
· Between membranes has a pleural space filled with fluid that reduces friction between the membranes when they are rubbed with each other during inspiration and expiration and also keeps lungs moist.
· Left lung is slightly smaller than the right lung.
· The left lung is divided by an oblique fissure into the larger superior and smaller inferior lobe.
· Right lung is divided into the superior, inferior and middle lobes by the oblique and horizontal fissures.
· Between the right and left lungs has a space called the mediastinum.
· Towards the posterior region of the left lung has the cardiac notch where the heart lies. Beneath the lungs has a diaphragm that separates the thoracic cavity from the abdominal cavity.
· Each lung is divided into a bronchus, bronchioles, alveolar duct, alveolar sac or air sac.
· Each bronchiole divides into smaller bronchioles and enters into a lung lobule called lobular bronchioles.
· The lobular bronchioles divide into terminal bronchioles which further sub-divide into respiratory bronchioles.
· The alveolar sac opens into several alveoli. Alveoli have very thin walls containing squamous epithelium.
· Right lung is divided into the superior, inferior and middle lobes by the oblique and horizontal fissures.
· Between the right and left lungs has a space called the mediastinum.
· Towards the posterior region of the left lung has the cardiac notch where the heart lies. Beneath the lungs has a diaphragm that separates the thoracic cavity from the abdominal cavity.
· Each lung is divided into a bronchus, bronchioles, alveolar duct, alveolar sac or air sac.
· Each bronchiole divides into smaller bronchioles and enters into a lung lobule called lobular bronchioles.
· The lobular bronchioles divide into terminal bronchioles which further sub-divide into respiratory bronchioles.
· The alveolar sac opens into several alveoli. Alveoli have very thin walls containing squamous epithelium.
Histological Structure of the Lung
· Histologically, each lung consists of several hundred-minute air-sacs called alveoli, the structural and functional units of the lung.
· They are surrounded by a network of blood capillaries where the exchange of gases takes place by diffusion.
· There are about 700 million alveoli in the lungs.
· Several alveoli unite together to form a cluster of ducts called alveolar duct forming alveolar sacs.
· It opens into the respiratory bronchiole (minute air tube).
· Several respiratory bronchioles unite together to form bronchiole and the bronchioles then unite to form a bronchus which emerges out from each lung i.e. right bronchus from the right lung and the left bronchus from the left lung.
· Each alveolus is about 0.1 mm in diameter and has a thin wall of 0.5m in thickness.
· The air-sacs (alveoli) are richly supplied with the blood capillaries having pulmonary artery and pulmonary vein.
· There are about 700 million alveoli in the lungs.
· Several alveoli unite together to form a cluster of ducts called alveolar duct forming alveolar sacs.
· It opens into the respiratory bronchiole (minute air tube).
· Several respiratory bronchioles unite together to form bronchiole and the bronchioles then unite to form a bronchus which emerges out from each lung i.e. right bronchus from the right lung and the left bronchus from the left lung.
· Each alveolus is about 0.1 mm in diameter and has a thin wall of 0.5m in thickness.
· The air-sacs (alveoli) are richly supplied with the blood capillaries having pulmonary artery and pulmonary vein.
Thoracic Cavity
· It is a hollow box rounded at the back by backbone (vertebral column), in front by sternum (breast bone) and on the sides by ribs and rib muscles.
· The two types of rib muscles are external intercostal and internal intercostal muscles.
· Eleven pairs of rib muscles are found between the twelve pairs of ribs.
· By the contraction and relaxation of these muscles, the thoracic cavity is increased and decreased during breathing (inspiration and expiration).
· It is a hollow box rounded at the back by backbone (vertebral column), in front by sternum (breast bone) and on the sides by ribs and rib muscles.
· The two types of rib muscles are external intercostal and internal intercostal muscles.
· Eleven pairs of rib muscles are found between the twelve pairs of ribs.
· By the contraction and relaxation of these muscles, the thoracic cavity is increased and decreased during breathing (inspiration and expiration).
Diaphragm
· Diaphragm is a muscular septum that separates the thorax from the abdominal cavity.
· It forms the floor of the thoracic cavity and the roof of the abdominal cavity.
· Its most important function is to aid respiration.
· Diaphragm is a muscular septum that separates the thorax from the abdominal cavity.
· It forms the floor of the thoracic cavity and the roof of the abdominal cavity.
· Its most important function is to aid respiration.
Role of the diaphragm in Respiration
· Diaphragm is a dome-shaped muscular septum that lies at the bases of the lungs.
· During inspiration, the muscles of the resting dome-shaped diaphragm contract.
· Diaphragm is a dome-shaped muscular septum that lies at the bases of the lungs.
· During inspiration, the muscles of the resting dome-shaped diaphragm contract.
· This action straightens and lowers the diaphragm and increases the size of the thoracic cavity from below.
· It increases the anteroposterior dimension of the chest.
· Due to this, the volume of the thoracic cavity, as well as lungs, is increased lowering the pressure inside the alveoli and air from the atmosphere rushes into the lungs.
· During expiration, the diaphragm relaxes and rises to attain its original position.
· It decreases the anteroposterior dimension of the chest.
· As a result, the volume of the thoracic cavity is decreased exerts pressure on the lungs.
· So, the pressure inside the lungs is greater than atmospheric pressure.
· It results in the expulsion of air from the lungs to the atmosphere.
MECHANISM OF PULMONARY RESPIRATION or BREATHING or PULMONARY VENTILATION IN MAN
· The process of intake of atmospheric air (containing Oxygen) into the lungs (inspiration) and elimination of air (containing Carbon dioxide) from the lungs (expiration) is called pulmonary respiration.
· Lungs have no muscle tissues so they cannot contract or expand of their own accord. So, breathing occurs by the combined action of the thoracic cage and the respiratory muscles.
· The thoracic cage is formed by ribs laterally, vertebrae posteriorly and sternum anteriorly.
· The respiratory muscles include the diaphragm, the intercostal muscles and other accessory muscles.
MECHANISM OF BREATHING
· Breathing is accomplished through changes in the volume and air pressure of the thoracic cavity.· It involves two steps:
(i) Inspiration
(i) Inspiration
(ii) Expiration
A. Inspiration (Inhalation)
· It is the process of taking in atmospheric air i.e. Oxygen into the lungs.
· It is an active process and involves the coordinated contraction of a number of muscles.
· It occurs when the volume of the thoracic cavity is increased and pressure is decreased.
· In order to increase the volume of the thoracic cavity, the diaphragm and external intercostal muscles of the ribs take a vital role under the influence of nerve impulses coming from the respiratory centre of the brain.
· Enlargement of the thoracic cavity consists of following movements which occur simultaneously.
(i) The external intercostal muscles of the ribs contract and pull ribs upward and outward.
(ii) The muscles of the resting dome-shaped diaphragm contract. This action straightens and lowers the diaphragm and increases the size of the thoracic cavity from below.
(iii) The abdominal muscles (serratus posterosuperior and levatore costatum) relax and allow compression of abdominal organs by the diaphragm.
· Due to such movements, the volume of the thoracic cavity is increased as a whole i.e. anteroposteriorly and transversely.
(i) The external intercostal muscles of the ribs contract and pull ribs upward and outward.
(ii) The muscles of the resting dome-shaped diaphragm contract. This action straightens and lowers the diaphragm and increases the size of the thoracic cavity from below.
(iii) The abdominal muscles (serratus posterosuperior and levatore costatum) relax and allow compression of abdominal organs by the diaphragm.
· Due to such movements, the volume of the thoracic cavity is increased as a whole i.e. anteroposteriorly and transversely.
· Since the pleural cavity contains no air, the lungs expand simultaneously with the increase in the size of the thoracic cavity.
· As the lungs expand, pressure in them drops and atmospheric air rushes into them through the air passages to balance outer and inner pressures.
· This air comes in contact with the capillaries of alveoli where the exchange of gases takes place and the blood is purified called oxygenated blood.
· It is taken into the left auricle or aorta of the heart through the capillaries of the pulmonary veins.
· From the left ventricle, it is distributed to cells and tissues for the oxidation of the foodstuffs. In this way, the inspiration is completed.
· So, inhalation (inspiration) involves a contraction of the muscles, an increase in size or volume of the thoracic cavity, an expansion of the lungs with a drop of pressure inside them and entrance of atmospheric air into the lungs through the air passages.
· So, inhalation (inspiration) involves a contraction of the muscles, an increase in size or volume of the thoracic cavity, an expansion of the lungs with a drop of pressure inside them and entrance of atmospheric air into the lungs through the air passages.
· Inhalation is followed by exhalation.
B. Expiration (Exhalation)
· The expelling of air from the lungs to the outside atmosphere occurs when the size of the thoracic cavity is reduced and pressure is increased. It is called expiration.
· The expelling of air from the lungs to the outside atmosphere occurs when the size of the thoracic cavity is reduced and pressure is increased. It is called expiration.
· It is a passive process and involves the following movements:
(i) The ribs take their original position due to contraction of the internal intercostal muscles.
(ii) The diaphragm relaxes and rises to attain its original position i.e. descends up and becomes dome-shaped.
(iii) The compressed abdominal organs push up against the diaphragm.
· As a result, the size of the thoracic cavity is decreased (anteroposteriorly and transversely), the lungs get compressed so the pressure in them rises and becomes higher than atmospheric pressure and air rushes out through the air passages.
· Hence, the entry of air (Oxygen) from the atmosphere into the lungs and the removal of the air (Carbon dioxide) from the lungs to the outside atmosphere is continued called breathing.
(i) The ribs take their original position due to contraction of the internal intercostal muscles.
(ii) The diaphragm relaxes and rises to attain its original position i.e. descends up and becomes dome-shaped.
(iii) The compressed abdominal organs push up against the diaphragm.
· As a result, the size of the thoracic cavity is decreased (anteroposteriorly and transversely), the lungs get compressed so the pressure in them rises and becomes higher than atmospheric pressure and air rushes out through the air passages.
· Hence, the entry of air (Oxygen) from the atmosphere into the lungs and the removal of the air (Carbon dioxide) from the lungs to the outside atmosphere is continued called breathing.
· It is about 16-20 times/minute in a normal adult human being.
· However, the breathing rate increases in children and during muscular exercise and in fever.
· The breathing rate also varies according to the age groups i.e. in newly born infants, it varies 40-60 times/minute and it may exceed about 70 times/minute.
· Children about 5 years – 25times/ minute; about 15 years– 20 times/ minute and adults above 25 years– 16-20 times/minute.
DIFFERENCES BETWEEN INSPIRATION AND EXPIRATION
| Inspiration | Expiration |
|---|---|
| It is the process of intake of atmospheric air into the lungs. | It is the process of giving out air from the lungs. |
| The external intercostal muscles of the ribs contract and internal intercostal muscles relax | The external intercostal muscles of ribs relax and internal intercostal muscles contract. |
| The rib cage moves forward and outward. | The rib cage moves downwards and inwards. |
| The volume of the thoracic cavity is increased and the pressure is decreased. | The volume of the thoracic cavity is decreased and the pressure is increased. |
| The diaphragm contracts and becomes flattened. | The diaphragm relaxes and becomes dome-shaped |
| Rushing of air through nostrils into the alveolar sacs causes inflation of lungs | Expulsion of air from the lungs into the atmosphere causes deflation of lungs. |
PHYSIOLOGY OF RESPIRATION IN HUMAN BEINGS
· The physiology of respiration in human being involves the following steps:i. Breathing or pulmonary ventilation
ii. External respiration
iii. Transport of oxygen
iv. Internal respiration or tissue respiration
v. Transport of carbon dioxide
I. Breathing or pulmonary ventilation
· It consists of two phases-inspiration and expiration.
· The flow of the air into the lungs is called inspiration and the movement of air out of the lungs is called expiration.
· It is accomplished through changes in the volume and air pressure of the thoracic cavity.
· When atmospheric pressure is more than the pressure inside the lungs, air flows inside the lungs and when the pressure inside the lungs is more than the atmospheric pressure, air moves out of the lungs.
· Exchange of gases takes place by simple diffusion process as gases pass from high pressure to low pressure.
· The thoracic cavity is the airtight cavity.
· On the dorsal side of this cavity lies the vertebral column, on the ventral side is the sternum and on the lateral sides ribs.
· In between each pair of ribs is a pair of muscles-external intercostal and internal intercostal muscles.
· Diaphragm is a dome-shaped structure that lies on the lower side of the thoracic cavity.
· It consists of two phases-inspiration and expiration.
· The flow of the air into the lungs is called inspiration and the movement of air out of the lungs is called expiration.
· It is accomplished through changes in the volume and air pressure of the thoracic cavity.
· When atmospheric pressure is more than the pressure inside the lungs, air flows inside the lungs and when the pressure inside the lungs is more than the atmospheric pressure, air moves out of the lungs.
· Exchange of gases takes place by simple diffusion process as gases pass from high pressure to low pressure.
· The thoracic cavity is the airtight cavity.
· On the dorsal side of this cavity lies the vertebral column, on the ventral side is the sternum and on the lateral sides ribs.
· In between each pair of ribs is a pair of muscles-external intercostal and internal intercostal muscles.
· Diaphragm is a dome-shaped structure that lies on the lower side of the thoracic cavity.
a. Inspiration (Inhalation)
· It is the energy-requiring process because it involves contraction of the diaphragm, intercostal muscles as well as accessory respiratory muscles.
· Inspiration occurs when the volume of the thoracic cavity is increased and pressure is decreased.
· In order to increase the volume of the thoracic cavity, the diaphragm and external intercostal muscles of the ribs take a vital role under the influence of nerve impulses coming from the respiratory centre of the brain.
· Enlargement of the thoracic cavity consists of following movements which occur simultaneously.
(i) The external intercostal muscles of the ribs contract and pull ribs upward and outward.
(ii) The muscles of the resting dome-shaped diaphragm contract. This action straightens and lowers the diaphragm and increases the size of the thoracic cavity from below.
(iii) The abdominal muscles relax and allow compression of abdominal organs by the diaphragm.
· Due to such movements, the volume of the thoracic cavity is increased. Since the pleural cavity contains no air, the lungs expand simultaneously with the increase in the size of the thoracic cavity. As the lungs expand, pressure in them drops and atmospheric air rushes into them through the air passages to balance outer and inner pressures.
· So, inhalation (inspiration) involves a contraction of the muscles, an increase in size or volume of the thoracic cavity, an expansion of the lungs with a drop of pressure inside them and entrance of atmospheric air into the lungs through the air passages. Inhalation is followed by exhalation.
· It is the energy-requiring process because it involves contraction of the diaphragm, intercostal muscles as well as accessory respiratory muscles.
· Inspiration occurs when the volume of the thoracic cavity is increased and pressure is decreased.
· In order to increase the volume of the thoracic cavity, the diaphragm and external intercostal muscles of the ribs take a vital role under the influence of nerve impulses coming from the respiratory centre of the brain.
· Enlargement of the thoracic cavity consists of following movements which occur simultaneously.
(i) The external intercostal muscles of the ribs contract and pull ribs upward and outward.
(ii) The muscles of the resting dome-shaped diaphragm contract. This action straightens and lowers the diaphragm and increases the size of the thoracic cavity from below.
(iii) The abdominal muscles relax and allow compression of abdominal organs by the diaphragm.
· Due to such movements, the volume of the thoracic cavity is increased. Since the pleural cavity contains no air, the lungs expand simultaneously with the increase in the size of the thoracic cavity. As the lungs expand, pressure in them drops and atmospheric air rushes into them through the air passages to balance outer and inner pressures.
· So, inhalation (inspiration) involves a contraction of the muscles, an increase in size or volume of the thoracic cavity, an expansion of the lungs with a drop of pressure inside them and entrance of atmospheric air into the lungs through the air passages. Inhalation is followed by exhalation.
b. Expiration (Exhalation)
· The expelling of air from the lungs occurs when the size of the thoracic cavity is reduced and pressure is increased. It is called expiration.
· The expelling of air from the lungs occurs when the size of the thoracic cavity is reduced and pressure is increased. It is called expiration.
· It involves the following movements:
(i) The ribs take their original position due to contraction of the internal intercostal muscles.
(ii) The diaphragm relaxes and rises to attain its original position.
(iii) The compressed abdominal organs push up against the diaphragm.
As a result, the size of the thoracic cavity is reduced, the lungs get compressed so the pressure in them rises and becomes higher than the atmospheric pressure and air rushes out through the air passages.
(i) The ribs take their original position due to contraction of the internal intercostal muscles.
(ii) The diaphragm relaxes and rises to attain its original position.
(iii) The compressed abdominal organs push up against the diaphragm.
As a result, the size of the thoracic cavity is reduced, the lungs get compressed so the pressure in them rises and becomes higher than the atmospheric pressure and air rushes out through the air passages.
II. External respiration
· It involves the exchange of gases between lung alveoli and pulmonary capillaries.
· During inspiration, oxygen enters the lungs and reaches the alveoli.
· As the alveolar membrane is extremely thin, the blood comes in close contact with air and the exchange of gases occurs by the simple diffusion method.
· The diffusion of gases occurs along the concentration gradient i.e. from higher partial pressure to lower partial pressure. The deoxygenated blood that reaches the alveolus has lower PO2 (95 mm Hg) and higher PCO2 (45 mm Hg) than the alveolar air (PO2 = 104 mm Hg, PCO2 = 40 mm Hg).
· Due to this, oxygen diffuses into the blood and carbon dioxide out of the blood into the air.
· It involves the exchange of gases between lung alveoli and pulmonary capillaries.
· During inspiration, oxygen enters the lungs and reaches the alveoli.
· As the alveolar membrane is extremely thin, the blood comes in close contact with air and the exchange of gases occurs by the simple diffusion method.
· The diffusion of gases occurs along the concentration gradient i.e. from higher partial pressure to lower partial pressure. The deoxygenated blood that reaches the alveolus has lower PO2 (95 mm Hg) and higher PCO2 (45 mm Hg) than the alveolar air (PO2 = 104 mm Hg, PCO2 = 40 mm Hg).
· Due to this, oxygen diffuses into the blood and carbon dioxide out of the blood into the air.
Internal respiration
· It involves the exchange of gases between tissue blood capillaries and tissue cells.
· The partial pressure of oxygen is higher (95 mm Hg) than that of body cells (40 mm Hg) and the partial pressure of carbon dioxide is lesser (40 mm Hg) than that of body cells (45 mm Hg).
· It involves the exchange of gases between tissue blood capillaries and tissue cells.
· The partial pressure of oxygen is higher (95 mm Hg) than that of body cells (40 mm Hg) and the partial pressure of carbon dioxide is lesser (40 mm Hg) than that of body cells (45 mm Hg).
· Due to this, oxygen diffuses from the capillary blood to the body cells and carbon dioxide diffuses from the body cells to the capillary blood.
· Now, the blood becomes deoxygenated. It is carried to the heart and hence to the lungs.
III. Transport of Gases
· Blood is the chief transporting medium as it transports oxygen and carbon dioxide.
i. Transport of oxygen
· Oxygen is carried in the blood in two forms:
(i) In the dissolved state
(ii) In the form of oxyhaemoglobin
a. In the dissolved state
· About 3% of Oxygen is carried in dissolved state in plasma and then carried to the body cells
· About 3% of Oxygen is carried in dissolved state in plasma and then carried to the body cells
b. In the form of oxyhaemoglobin
· Oxygen has a great affinity with haemoglobin present in RBCs.
· A haemoglobin molecule is formed by four polypeptide chains and four heme groups (iron pigment) each containing an iron atom.
· So, one haemoglobin molecule can carry 1-4 molecules of oxygen depending upon its percentage saturation that depends upon two factors:
i. Partial pressure of O2 (PO2) in the alveoli of lungs
ii. Partial pressure of CO2 (PCO2) in the alveoli of lungs
i. Partial pressure of O2 (PO2) in the alveoli of lungs
ii. Partial pressure of CO2 (PCO2) in the alveoli of lungs
· The maximum amount of Oxygen that the normal blood can carry is about 20 ml in 100 ml of blood.
· The oxyhaemoglobin is an unstable compound that dissociates soon into the tissues.
· About 97% of O2 is carried in the form of oxyhaemoglobin.
· About 97% of O2 is carried in the form of oxyhaemoglobin.
· One gram of haemoglobin, when fully saturated, combines with 1.34 ml of oxygen. The average haemoglobin content is 15 g per 100 ml of blood.
· So, 15 g of haemoglobin will combine 20 ml of oxygen.
· Since each molecule of haemoglobin contains four atoms of iron in the ferrous form, so, each iron atom combines with one molecule of oxygen.
· Thus, oxyhaemoglobin is formed and it is an unstable compound that dissociates to release oxygen in the tissues where the oxygen tension is low.
· Thus, oxyhaemoglobin is formed and it is an unstable compound that dissociates to release oxygen in the tissues where the oxygen tension is low.
· However, oxygen uptake is favoured in the lungs where the oxygen tension is high and gets converted into oxyhaemoglobin.
BOHR'S EFFECT
· The oxygenation of the blood in the lungs and the release of oxygen from the blood into tissues are significantly affected by changes in the concentration of Carbon dioxide in the blood.
· The oxygenation of the blood in the lungs and the release of oxygen from the blood into tissues are significantly affected by changes in the concentration of Carbon dioxide in the blood.
· It is because the dissociation of oxyhaemoglobin is directly proportional to the partial pressure of CO2 in blood. It means that dissociation of oxyhaemoglobin occurs when PCO2 is high and formation of oxyhaemoglobin occurs when PCO2 is low. It is called Bohr's effect as Christian Bohr discovered it.
· As blood passes through the lungs, CO2 easily diffuses into the alveolar air from the blood.
· As blood passes through the lungs, CO2 easily diffuses into the alveolar air from the blood.
· Due to this, partial pressure of Carbon dioxide in the blood is reduced and its pH is increased. These changes in the blood make it suitable for oxygenation of haemoglobin and so, more and more Oxygen binds with haemoglobin to form oxyhaemoglobin.
· So, the greater amount of Oxygen is transported by the blood to the tissues.
· However, at the tissue level, exactly the opposite phenomenon occurs during which Carbon dioxide enters the blood causing the decrease in blood pH.
· These changes increase the chance of dissociation of oxyhaemoglobin and therefore, more and more oxygen is supplied to tissues.
IV. INTERNAL RESPIRATION/TISSUE RESPIRATION
· Internal respiration is defined as the exchange of gases between tissue blood capillaries and tissue cells.
· It involves two steps: dissociation of oxyhaemoglobin and oxidation of foodstuffs.
A. Dissociation of oxyhaemoglobin
· Haemoglobin has a high affinity for Oxygen and that affinity is enhanced by the fall in the partial pressure of Carbon dioxide (PCO2).
· Haemoglobin has a high affinity for Oxygen and that affinity is enhanced by the fall in the partial pressure of Carbon dioxide (PCO2).
· Oxyhaemoglobin is an unstable compound that quickly dissociates in the tissues liberating into free oxygen and Hb.
· But the dissociation rate depends upon the percentage saturation of blood/Hb.
· The amount of Oxygen that Hb can carry at a particular time period is known as saturation which depends upon the partial pressure of oxygen in the alveoli i.e. PO2.
· This can be detected by a graph called the oxygen dissociation curve.
· A graphical representation to show the relationship between partial pressure of oxygen (PO2) and percentage saturation of haemoglobin with oxygen (O2) is known as the Oxygen dissociation curve which is slightly s-shaped.
· It shows that Hb has a high affinity for oxygen.
· The oxygen dissociation curve is also known as the graphical representation of the percentage of blood at a various partial pressure of O2.
· In humans, the arterial blood (oxygenated blood) has PO2 that is about 95 mm of Hg i.e. 95% of blood/Hb is saturated with O2 but in venous blood i.e. in deoxygenated blood, the PO2 is about 40 mm of Hg.
· The O2 and CO2 transport is closely related with each other i.e. the increase in PCO2 decreases the O2 combining capacity of Hb i.e. the increase in PCO2 shifts the O2 dissociation curve downwards.
· The O2 and CO2 transport is closely related with each other i.e. the increase in PCO2 decreases the O2 combining capacity of Hb i.e. the increase in PCO2 shifts the O2 dissociation curve downwards.
· This effect is called Bohr’s effect which has biological significance. It was first discovered by Christian Bohr.
· As PCO2 in the tissues is higher than that in the lungs and PO2 is less and PCO2 and PO2 lie between 10 and 40 mm of Hg.
· As PCO2 in the tissues is higher than that in the lungs and PO2 is less and PCO2 and PO2 lie between 10 and 40 mm of Hg.
· It causes the dissociation of oxygen from oxyhaemoglobin. In the active tissues, the PCO2 is high.
· It has low pH and raised body temperature.
· The oxygenated blood while passing through the inactive cells gives less O2 even if PO2 is low.
· But while passing through the active cells, it readily gives off more O2 even if PCO2 is high.
Oxidation of foodstuffs
· The Oxygen that enters into the cell cytoplasm first oxidizes glucose and the other food substances in the presence of special respiratory enzymes.
· Then it liberates energy by breaking glucose into CO2 and H2O.
C2H12O2 + 6O2 → 6CO2 + 6H2O + Energy (686 kcal)
C2H12O2 + 6O2 → 6CO2 + 6H2O + Energy (686 kcal)
V. Transport of Carbon dioxide
· Carbon dioxide is the toxic product of internal respiration so, it is essential to remove it quickly out of the body.
· Carbon dioxide is more soluble in water and transported both by RBCs and plasma.
· The transportation of CO2 from tissues to the lungs occurs in the following forms.
· Carbon dioxide is the toxic product of internal respiration so, it is essential to remove it quickly out of the body.
· Carbon dioxide is more soluble in water and transported both by RBCs and plasma.
· The transportation of CO2 from tissues to the lungs occurs in the following forms.
a. In the form of H2CO3
· Carbon dioxide is mixed with water of RBC to form an unstable compound H2CO3. This process is catalyzed by an enzyme carbonic anhydrase found in RBC.
· Carbon dioxide is mixed with water of RBC to form an unstable compound H2CO3. This process is catalyzed by an enzyme carbonic anhydrase found in RBC.
· About 5% of total CO2 is carried out in this form.
b. In the form of bicarbonate
· H2CO3 formed in RBC quickly ionizes to form bicarbonate (HCO3–) and hydrogen ions (H+).
· In the Chloride shift or Hamburger's phenomenon, there is the inflow of chloride ions into RBCs from plasma to counteract the outflow of bicarbonate ions from RBCs.
· Bicarbonate ions (HCO3–) are pumped through the RBC membrane to the plasma. HCO3– ions either combine with Na or K present in the plasma to form sodium bicarbonate (NaHCO3) or potassium bicarbonate (KHCO3) respectively.
· CO2 is transported from tissues to lungs through plasma.
· Most of the CO2 is transported in the form of sodium bicarbonate and some of the CO2 is transported in the form of potassium bicarbonate.
· In the alveolar capillaries, the CO2 concentration is low whereas in tissues it is high, the bicarbonate ions diffuse liberating CO2.
· In doing so, blood plays an important role. Hence, the blood is known as accessory respiratory pigment. About 85% of CO2 is transported in this form.
· HCO3– + Na+ → NaHCO3 (Sodium bicarbonate)
· HCO3– + Na+ → NaHCO3 (Sodium bicarbonate)
· HCO3– + K+ → KHCO3 (Potassium bicarbonate)
· These NaHCO3 and KHCO3 are carried through the plasma to the lungs where they combine with H+ ions and form H2O and CO2.
· CO2 is expelled out during expiration.
c. In the form of carbamino-haemoglobin compound
· The carbonic acid thus formed dissociates into hydrogen ion and bicarbonate ion.
· The hydrogen ion is buffered by Hb itself and forms reduced Hb.
· The CO2 then combines with an amino group of haemoglobin to form a complex carbamino haemoglobin compound. About 10% of CO2 is transported in this form.
· CO2 + Hb – NH2 → Hb – NH – COOH
· In this way, all the CO2 produced in tissue are transported to the lungs from where they are expelled out by expiration.
· In this way, all the CO2 produced in tissue are transported to the lungs from where they are expelled out by expiration.
CO2 POISONING
· Haemoglobin has much more affinity for CO than O2 (250 times more) and forms a stable compound called carboxyhaemoglobin (HbCO).
· The oxygen combining capacity of the haemoglobin decreases and the tissues or cells suffer from O2 starvation.
· The person reaches in a condition called “asphyxiation” and in extreme cases, death may occur.
· During this period, the patient is supplied with pure oxygen-carbon dioxide mixture to increase the PO2 level and to dissociate Hb from CO.
· CO poisoning even occurs in a closed room with open stoves, burners/lamps, oven/furnaces, gases etc. and even in garages running automobiles engine.
· Hb + CO → HbCO (carboxyhaemoglobin)
· Haemoglobin has much more affinity for CO than O2 (250 times more) and forms a stable compound called carboxyhaemoglobin (HbCO).
· The oxygen combining capacity of the haemoglobin decreases and the tissues or cells suffer from O2 starvation.
· The person reaches in a condition called “asphyxiation” and in extreme cases, death may occur.
· During this period, the patient is supplied with pure oxygen-carbon dioxide mixture to increase the PO2 level and to dissociate Hb from CO.
· CO poisoning even occurs in a closed room with open stoves, burners/lamps, oven/furnaces, gases etc. and even in garages running automobiles engine.
· Hb + CO → HbCO (carboxyhaemoglobin)
ARTIFICIAL RESPIRATION
· It is also known as assisted respiration.
· It is also known as assisted respiration.
· It is required when breathing is depressed/stopped.
· The depression in breathing occurs during drowning, electric shock, head and chest injuries, cardiac arrest, carbon monoxide poisoning etc.
· In such a condition, to revive the patient, artificial or assisted respiration is essential to ventilate the lungs.
· The lungs can be ventilated by mouth to mouth breathing method as the first-aid measure.
· In mouth to mouth breathing, the patient is made to lie on his back.
· The depression in breathing occurs during drowning, electric shock, head and chest injuries, cardiac arrest, carbon monoxide poisoning etc.
· In such a condition, to revive the patient, artificial or assisted respiration is essential to ventilate the lungs.
· The lungs can be ventilated by mouth to mouth breathing method as the first-aid measure.
· In mouth to mouth breathing, the patient is made to lie on his back.
· The operator lifts and extends the patient's neck by keeping a hand below it to open his airway.
· The operator then closes the patient's nostrils with fingers and applies his own mouth around the mouth of the patient and blows about 1 litre of air into it to inflate the lungs of the patient.
· Next he releases the patient's mouth to allow expiration. This procedure is repeated 10–15 times per minute. Other methods of artificial ventilation are mask and Ambu bag, automated ventilator machine etc.
· Next he releases the patient's mouth to allow expiration. This procedure is repeated 10–15 times per minute. Other methods of artificial ventilation are mask and Ambu bag, automated ventilator machine etc.
TERMINOLOGIES
· Tidal Volume (TV)· It is the volume of air that is breathed in and out during effortless normal breathing.
· It is about 500 ml in an adult normal person.
· Inspiratory Reserve Volume (IRV)
· The volume of forced inspired air in addition to normal inspired air (tidal volume) is called inspiratory reserve volume.
· It is about 2000-3000 ml.
· Expiratory Reserve Volume (ERV)
· It is the volume of air that can be expired by a forceful expiration in addition to normal tidal expiration.
· It is about 1000-1500 ml.
· Vital Capacity (VC)
· The maximum volume of air a person can breathe in after a forced expiration or the maximum volume of air a person can breathe out after a forced inspiration is called vital capacity.
· It is the sum of tidal volume, inspiratory reserve volume and expiratory reserve volume (i.e.VC = IRV + ERV +TV).
· It varies from 3400ml to 4800 ml depending upon the age, sex and height of the individual.
· Total lung capacity
· Total lung capacity is the volume of air in the lungs and respiratory passage after a maximum inspiratory effort. It is about 5000–6000 ml in adult males.
· The muscles involved in breathing are intercostal, abdominal and other accessory muscles.
· Residual volume (RV)
· The volume of air that remains in the lungs after a forceful expiration is called residual volume.
· Its value is about 1500 ml.
· Dead space (DS)
· Out of a total of 500 ml of air inspired during a normal breathe only about 350 ml of air reaches to lung alveoli for gaseous exchange, the remaining 150 ml remains in the respiratory tract which is known as dead space volume or simply dead space.
· Or, during effortless inspiration, air remains in the respiratory surface area like trachea and bronchial tubes without exchange of gases.
· It is called dead space.
· Respiration is derived from the Latin word “Respire” which means to breathe.
· Carbonic anhydrase catalyzes the formation of carbonic acid in RBCs.