Gaseous Exchange in Plants
Plants get their energy from respiration. The respiration is, therefore, also important for life of plants. Plants have no special organ or system for exchange of gases. The gaseous exchange f plants occur in cells of every part of the plant i.e. roots, stems and leaves etc according to theh' energy demands.
The conducting system (xylem & phloem) of plants for water and nutrients is not involved in the transport of gases to the plants. The air spaces present between the cells of parenchyma of leaves, stem and roots are involved in the gaseous exchange.
In the leaves and youne stems, gaseous exchange occurs through stomata and some exchange of gases also occurs through cuticle In woody stems and roots there are dead cells beneath the epidermis which lorm cork tissue. This tissue has pores called lenticels which are involved in gaseous exchange .
The aquatic plants obtain oxygen for their respiration by diffusion from the dissolved oxygen in water. Whereas the land plants get their oxygen from air directly through their stomata which are more abundant on the lower surface than the upper surface of leaves. The roots get their oxygen for gaseous exchange through diffusion from the air existing in the spaces between soil particles.
Process of Respiration The respiration in plants continues day and night. In this process, the oxygen from the airspaces in the leaves and stems diffuses into tissues and cells of the plants after getting dissolved in the film of water present over the cells. In the cells this oxygen oxidizes the carbohydrates and other organic compounds into carbon dioxide and water to produce energy.
Some of this carbon dioxide is used in photosynthesis. The rest of the carbon dioxide and some of the water (vapours) collect in the airspaces from where they pass out to the exterior through lenticels and stomata. The elimination of carbon dioxide is more evident from the parts without chlorophyll like growing seeds and buds. The water produced in this process also becomes a part of the already present water in the body of plants.
As in animals the process of oxidation (respiration) in plants consists of many enzymatic reactions. This process occurs at a faster rate in the parts of the plant having rapid growth like grov/ing seeds, buds, apical meristem of roots and shoots, because these parts require more energy to accomplish the growth process.
The gaseous exchange in plant is not very evident during the day time as the products of I respiration i.e. carbon dioxide and water are the reactants in the process of photosynthesis. So the I carbon dioxide and water produced in the respiration are utilized in photosynthesis, occuring in the ‘ day light. In the bright sunshine, because of high rate of photosynthesis the carbon dioxide produced in respiration falls short and therefore, some carbon dioxide has to be taken into the plant from outside for photosynthesis. In the day time the plants therefore, take in carbon dioxide and expel out oxygen.
The process of photosynthesis occurs in chloroplasts whereas the process of respiration takes place in cytoplasm and mitochondria. Gaseous exchange between Organisms and Environment In aerobic respiration the organisms utilize the environmental oxygen to oxidize their organic compounds as a result of which carbon dioxide is produced. The carbon dioxide is toxic to the organism and it is, therefore, necessary that the organism should expel the carbon dioxide out of its body in some way.
The aerobic organisms in the process of respiration take up oxygen from their environment and eliminate carbon dioxide from their bodies to the environment. This exchange of gases between the organisms and their environment forms the first phase of the aerobic respiration. . Gaseous exchange in animals The gaseous exchange in different animals occurs by means of different methods and organs. In small aquatic animals like the unicellular protozoa the dissolved oxygen of water diffuses directly through their cell surface into the interior of the animal and the carbon dioxide similarly diffuses out from their bodies into the external water.
This is the simplest way of gaseous exchange and it can occur only in small animals with a diameter of less than one millimeter. Such animals have greater surface area to volume ratio and have low rate of metabolism. As the animals grew in their size, their skin or external body surface became impervious to water.
Thus it made the gaseous exchange impossible through diffusion. In large animals therefore, certain organs were developed through which an efficient exchange of gases could occur. The moist vascular skin, gills, lungs and tracheoles are the respiratory organs of different animals.
These large animals have developed blood vascular system which transports oxygen from the respiratory surfaces to the deep cells and tissues in all parts of the body. The blood in all animals has some respiratory pigments which can bind oxygen and thus carry large amount of oxygen efficiently from respiratory surface to the interior cells. It is necessary that respiratory surface is thin and moist because very little diffusion of gases, if at all, can occur through the thick dry surface. In aquatic animal, it is not all difficult to keep the respiratory surfaces moist and safe.
But in land animal the respiratory surfaces are, therefore, usually situated deep down in the body and some pumping mechanism is Used to force the air to this deeply situated respiratory surface. Gaseous exchange through skin The skin is kept moist and richly supplied with blood for the dissolved oxygen to diffuse from the external water to the blood and for the carbon dioxide to diffuse from the blood to the exterior water.
In amphibia and fishes the gaseous exchange occurs through the skin besides through the gills or lungs. The frogs and tortoises breathe through the skin during their hibernation period. Gaseous exchange by gills Have you ever examined a fish closely? How will you know that the fish is fresh or not? If the colour of gills is red then it is fresh but if the colour of gills is changed, it is definitely not fresh. The red colour of the fish gills shows the presence of oxygenated blood.
The gills are very effective for gaseous exchange in aquatic animals. Some animals have external gills which project out of the body of animals. These gills have very thin and highly vascularized surfaces e.g. the dermal papillae of star fish etc. Some animals have internal gills e.g. fishes and aquatic arthropods. Gaseous exchange in fish (gill filament, gill lamella) Gaseous exchange in terrestrial animals Gaseous exchange through trachea Insects and other land dwelling arthropods (centipedes, millipedes, spiders) use tracheal tube for their gaseous exchange.
This method is very effective and simple in which air can directly reach almost every cells of the body through small and minute tubes. These animals have a network of tubes called tracheal tubes. These tubes on reaching near the cells, are divided into very If you closely observe any wasp or honeybee, you will see some changes in their body. You have noticed that their body moves again and again. When it goes forward, its inner body cavity contracts and air is released.
When its stomach moves backward, then its cavity expands and air is inhaled. In fishes the gills are present in the branchial cavity present on lateral sides of the body behind the head, this branchial cavity is covered over by an operculum. There is a counter current flow of water and blood in gills which ensures maximum exchange of oxygen and carbon dioxide between the blood and the bathing water.
Water enters through the mouth, flows over the gills and goes out of the body from the opercular aperture. minute tubes called tracheoles, whose terminal portions are filled with a fluid. The diameter of these tubes is less than a micrometer, the end of the tracheoles indent the membrane of the cells they supply. The external air enters into the large tubes of the tracheal system through spiracles.
The oxygen from this air gets dissolved in the fluid present in terminal parts of tracheoles and diffuses into the cells. The C02 from the cell diffuses out into the fluid and is thus expelled out of the body along with the outgoing air. This is a very efficient and effective system of transport without the use of oxygen carrying pigments.
Gaseous exchange through lungs In almost all the large land animals exchange of gases occurs through lungs. Some invertebrates e.g. snails, scorpions and spiders also possess lungs but in them there is no proper ventilating mechanism. In the vertebrates, the lungs are effectively and regularly ventilated. In amphibia, simple and sac-like lungs are found. The air is forced into the lungs in amphibia by the pumping action of the buccal cavity.
The lungs in reptiles, birds and mammals have become more efficient. In them the respiratory surface has increased manifold by the formation of alveoli. Mammals have highest increase in their respiratory surface. According to one estimate the respiratory area in man is from 50-90 square meters which is 50 times the surface area of the body. A man has one thousand kilometer long capillaries.
The nature has made the functioning of birds lungs very effective. In addition to lungs, birds have air sacs which are filled on breathing by 75% of the inhaled air which bypasses the lungs. The lungs first receive 25% of the fresh air with which the gaseous exchange occurs on inhaling.
As the air is exhaled, the air of the sacs which is still fresh passes through the lungs on its way to exterior and supplies oxygen to the blood and carries away carbon dioxide from the blood. Structure of Human Respiratory System A pair of lungs with associated structures and organs like nose, pharynx, larynx, trachea, bronchi and bronchioles form the respiratory system. Nose • The air enters in the nasal cavity through nostrils.
The nasal cavity is lined with hair and mucous secreting glands. This cavity is further divided into shelves, due to the presence of many small bones emerging from its walls. The beating of cilia creates a current in the mucus that carries the trapped particles towards the back of the nasal cavity. From here the mucus drips into the throat and is swallowed.
Mucus keeps the nasal chamber moist. As the air passes through the chamber on its way to the lungs, dust particles and foreign substances in the air get trapped in the hair and the mucus. The air get warmed to body temperature and is also saturated with moisture. A number of cavities called sinuses open into the nasal cavity. The sinuses are lined with mucus secreting epithelium. The opening of sinuses into the nasal cavity are very narrow.
If these apertures are closed due to cold or inflammation, the sinuses get filled up with mucus which may produce headache etc. Pharynx The thin compartment of the nasal cavity opens into the pharynx (throat) by means of two small apertures which are called internal nares. The pharynx is muscular passage way which extends from behind the nasal cavities to the opening of oesophagus and larynx.
The air goes from the pharynx into the larynx. In cases of extreme emergency when the upper air passage is blocked by a foreign object to the extent that victim cannot breathe, quick action is required to save persons life. To force such an object out of the air passage, a sudden application of pressure to the abdomen forces air out clearing respiratory passage. Larynx The upper most part of the air tube (trachea) is called the larynx.
The larynx is a box made of cartilage. Two fibrous bands called vocal cords are located in this box which on vibration by the air produce sound waves which forms the basis of human voice. This box is, therefore, also called sound boxThe air enters into glottis. This opening is guarded by a muscular flap called epiglottis which fits into this opening while the food is being swallowed into the oesophagus lying behind the tracheal tube.
This act is very important as it prevents the food from entering into the trachea and choking it. The air tube which is known as trachea is about 12 cm long by cylindrical tube which lies in front of the oesophagus. There are incomplete shaped cartilagenous rings which are regularly placed in its wall and all along its length. These rings prevents the collapsing of the tube and thus keep the air passage wide open all the time.
Trachea is also lined with ciliated mucous epithelium. Any foreign particles present in the entering air get trapped in the mucous and the clean air enters the lungs. Bronchi The trachea on entering the chest divides into two smaller tubes which are called bronchi (single bronchus) which are similar in structure to the trachea but are smaller in diameter and they have in their walls small irregular cartilageuous plates.
Each bronchus enters into the lungs of its own side. The right bronchus branches into 3 and left bronchus divides into 2 secondary bronchi which serve the 3 right and 2 left lobes of the lungs respectively. Bronchioles The secondary bronchi divide into smaller and smaller branches until they end in thousands of passage ways called respiratory bronchioles.
The bronchioles have not cartilagenous plates in their walls. Alveoli The walls of the respiratory bronchioles have clusters of tiny branches (like bunches of grapes) that along with the respiratory bronchioles are the sites of gaseous exchange, these pouches or air sacs are called alveoli (single alveolus). The alveoli are enormous in number.
Every lung has about three hundred million alveoli. Pulmonary artery carries impure blood from the heart and enters into each lung and there it divides and redivides until it forms a network of fine capillaries over the wall of each alveolus. The walls of alveoli are very thin (1/1000 mm thick) and moist and thus offer a very efficient site for gas exchange. The Lungs The masses of alveoli constitute lungs and their lobes.
The lungs and the heart lie protected in the chest box, the chest box is formed on sides and in the front by the ribs and the intercostals muscles, and by a domb shaped muscular diaphragm on its posterior. The lungs are enclosed in a double layered membrane called pleural membrane. There is a thin film of fluid in between the two layers. This watery fluid makes the movements of the lungs (expansion & contraction) easy. Mechanism of Breathing Breathing is spread over two phases
1. Inspiration
2. Expiration
Inspiration During inspiration the dome-shaped diaphragm contracts flattening somewhat and thereby lowering the floor of the thoracic cavity. The external intercostals muscles contract raising the rib cage.
A combined action of these two events expand the thoracic cavity, which in turn expands the lungs. As a result of it the air pressure within the lungs decreases. Thus air from the environment out side the body is pulled into the lungs to equalize the pressure of both sides. Expiration In expiration the external intercostals muscles relax and the internal intercostals muscles contract as a result of which ribcage drops. The diaphragm relaxes and assumes dome like shape. The combined action of these two events reduces the volume of the thoracic cavity.
The volue of lungs in turn decreases which results in an increase in the air pressure in the lungs. The air is thus forced out of the lungs. At the lungs, carbon dioxide within the blood of capillaries surrounding the alveoli and oxygen in the air of the alveoli are exchanged. The exchange of gases works by the process of diffusion. The arterial blood in the lungs has less oxygen and more carbon dioxide as compared to air entering into the lungs. In the deoxygenated blood of the lungs the pressure of carbon dioxide is greater than the pressure of carbon dioxide in the air within alveoli. Therefore, carbon dioxide diffuses out of the blood and into the alveoli.
On the other hand, the pressure of oxygen in the air within the alveoli is greater than the pressure of oxygen in the arterial blood. Therefore, oxygen diffuses out of the alveoli and into the blood. The oxygen first dissolves in the film of fluid present on inner walls of the alveoli and then diffuse into the blood through thin walls of alveoli.
The carbon dioxide of the blood diffuses out into the air of the alveoli by passing through the walls of the alveoli. In man and other animals (all vertebrates and some invertebrates) some respiratory pigments are present in blood which can transport greater amount of oxygen efficiently from lungs to the other parts of the body. If it was not for the presence of haemoglobin in the blood, the oxygen transport could have been very slow and small in amount because only a small amount of oxygen can dissolve in blood plasma. Whereas, according to an estimate one hundred mol of haemoglobin containing blood can transport about 20 ml of oxygen.
Oxygen does not combine covlently with haemoglobin. It is only loosely attached with haeme of the haemoglobin and is therefore forms oxyhaemoglobin but not haemoglobin oxide. This loose combination of oxygen with haemoglobin makes the detachment of oxygen at tissue level easy. Haemoglobin + Oxygen Oxy-haemoglobin Carbon dioxide is transported from the tissue s to the lungs mostly bonded with water in the blood which first form carbonic acid with water that quickly dissociates into HCO3 and H+ ions. A small percentage (25%) of carbon dioxide combines with haemoglobin to form carbamino compound.
Only a every small amount (6%) of carbon dioxide is simply dissolved in the blood. Effect of exercise on the rate of breathing A man breathes 16 times a minute in normal circumstances. The rate of breathing is controlled by a center in the brain which is very sensitive to the changing concentration of carbon dioxide in blood. In case of higher concentration than normal of carbon dioxide this center sends impulses directly to the diaphragm and intercostals muscle to contract at a faster rate which leads to an increase in the rate of breathing.
When you do hard work or take strenous exercise you need more energy which is provided by more and more oxidation of glucose. As a result the amount of carbon dioxide in blood increases which stimulates the carbon dioxide centre in the brain to enhance the rate of breathing so that the excess carbon dioxide from the blood can be eliminated and more oxygen can be supplied to the fastly metabolizing muscles. During it th breathing rate may increase up to 30-40 time per minute.
Plants get their energy from respiration. The respiration is, therefore, also important for life of plants. Plants have no special organ or system for exchange of gases. The gaseous exchange f plants occur in cells of every part of the plant i.e. roots, stems and leaves etc according to theh' energy demands.
The conducting system (xylem & phloem) of plants for water and nutrients is not involved in the transport of gases to the plants. The air spaces present between the cells of parenchyma of leaves, stem and roots are involved in the gaseous exchange.
In the leaves and youne stems, gaseous exchange occurs through stomata and some exchange of gases also occurs through cuticle In woody stems and roots there are dead cells beneath the epidermis which lorm cork tissue. This tissue has pores called lenticels which are involved in gaseous exchange .
The aquatic plants obtain oxygen for their respiration by diffusion from the dissolved oxygen in water. Whereas the land plants get their oxygen from air directly through their stomata which are more abundant on the lower surface than the upper surface of leaves. The roots get their oxygen for gaseous exchange through diffusion from the air existing in the spaces between soil particles.
Process of Respiration The respiration in plants continues day and night. In this process, the oxygen from the airspaces in the leaves and stems diffuses into tissues and cells of the plants after getting dissolved in the film of water present over the cells. In the cells this oxygen oxidizes the carbohydrates and other organic compounds into carbon dioxide and water to produce energy.
Some of this carbon dioxide is used in photosynthesis. The rest of the carbon dioxide and some of the water (vapours) collect in the airspaces from where they pass out to the exterior through lenticels and stomata. The elimination of carbon dioxide is more evident from the parts without chlorophyll like growing seeds and buds. The water produced in this process also becomes a part of the already present water in the body of plants.
As in animals the process of oxidation (respiration) in plants consists of many enzymatic reactions. This process occurs at a faster rate in the parts of the plant having rapid growth like grov/ing seeds, buds, apical meristem of roots and shoots, because these parts require more energy to accomplish the growth process.
The gaseous exchange in plant is not very evident during the day time as the products of I respiration i.e. carbon dioxide and water are the reactants in the process of photosynthesis. So the I carbon dioxide and water produced in the respiration are utilized in photosynthesis, occuring in the ‘ day light. In the bright sunshine, because of high rate of photosynthesis the carbon dioxide produced in respiration falls short and therefore, some carbon dioxide has to be taken into the plant from outside for photosynthesis. In the day time the plants therefore, take in carbon dioxide and expel out oxygen.
The process of photosynthesis occurs in chloroplasts whereas the process of respiration takes place in cytoplasm and mitochondria. Gaseous exchange between Organisms and Environment In aerobic respiration the organisms utilize the environmental oxygen to oxidize their organic compounds as a result of which carbon dioxide is produced. The carbon dioxide is toxic to the organism and it is, therefore, necessary that the organism should expel the carbon dioxide out of its body in some way.
The aerobic organisms in the process of respiration take up oxygen from their environment and eliminate carbon dioxide from their bodies to the environment. This exchange of gases between the organisms and their environment forms the first phase of the aerobic respiration. . Gaseous exchange in animals The gaseous exchange in different animals occurs by means of different methods and organs. In small aquatic animals like the unicellular protozoa the dissolved oxygen of water diffuses directly through their cell surface into the interior of the animal and the carbon dioxide similarly diffuses out from their bodies into the external water.
This is the simplest way of gaseous exchange and it can occur only in small animals with a diameter of less than one millimeter. Such animals have greater surface area to volume ratio and have low rate of metabolism. As the animals grew in their size, their skin or external body surface became impervious to water.
Thus it made the gaseous exchange impossible through diffusion. In large animals therefore, certain organs were developed through which an efficient exchange of gases could occur. The moist vascular skin, gills, lungs and tracheoles are the respiratory organs of different animals.
These large animals have developed blood vascular system which transports oxygen from the respiratory surfaces to the deep cells and tissues in all parts of the body. The blood in all animals has some respiratory pigments which can bind oxygen and thus carry large amount of oxygen efficiently from respiratory surface to the interior cells. It is necessary that respiratory surface is thin and moist because very little diffusion of gases, if at all, can occur through the thick dry surface. In aquatic animal, it is not all difficult to keep the respiratory surfaces moist and safe.
But in land animal the respiratory surfaces are, therefore, usually situated deep down in the body and some pumping mechanism is Used to force the air to this deeply situated respiratory surface. Gaseous exchange through skin The skin is kept moist and richly supplied with blood for the dissolved oxygen to diffuse from the external water to the blood and for the carbon dioxide to diffuse from the blood to the exterior water.
In amphibia and fishes the gaseous exchange occurs through the skin besides through the gills or lungs. The frogs and tortoises breathe through the skin during their hibernation period. Gaseous exchange by gills Have you ever examined a fish closely? How will you know that the fish is fresh or not? If the colour of gills is red then it is fresh but if the colour of gills is changed, it is definitely not fresh. The red colour of the fish gills shows the presence of oxygenated blood.
The gills are very effective for gaseous exchange in aquatic animals. Some animals have external gills which project out of the body of animals. These gills have very thin and highly vascularized surfaces e.g. the dermal papillae of star fish etc. Some animals have internal gills e.g. fishes and aquatic arthropods. Gaseous exchange in fish (gill filament, gill lamella) Gaseous exchange in terrestrial animals Gaseous exchange through trachea Insects and other land dwelling arthropods (centipedes, millipedes, spiders) use tracheal tube for their gaseous exchange.
This method is very effective and simple in which air can directly reach almost every cells of the body through small and minute tubes. These animals have a network of tubes called tracheal tubes. These tubes on reaching near the cells, are divided into very If you closely observe any wasp or honeybee, you will see some changes in their body. You have noticed that their body moves again and again. When it goes forward, its inner body cavity contracts and air is released.
When its stomach moves backward, then its cavity expands and air is inhaled. In fishes the gills are present in the branchial cavity present on lateral sides of the body behind the head, this branchial cavity is covered over by an operculum. There is a counter current flow of water and blood in gills which ensures maximum exchange of oxygen and carbon dioxide between the blood and the bathing water.
Water enters through the mouth, flows over the gills and goes out of the body from the opercular aperture. minute tubes called tracheoles, whose terminal portions are filled with a fluid. The diameter of these tubes is less than a micrometer, the end of the tracheoles indent the membrane of the cells they supply. The external air enters into the large tubes of the tracheal system through spiracles.
The oxygen from this air gets dissolved in the fluid present in terminal parts of tracheoles and diffuses into the cells. The C02 from the cell diffuses out into the fluid and is thus expelled out of the body along with the outgoing air. This is a very efficient and effective system of transport without the use of oxygen carrying pigments.
Gaseous exchange through lungs In almost all the large land animals exchange of gases occurs through lungs. Some invertebrates e.g. snails, scorpions and spiders also possess lungs but in them there is no proper ventilating mechanism. In the vertebrates, the lungs are effectively and regularly ventilated. In amphibia, simple and sac-like lungs are found. The air is forced into the lungs in amphibia by the pumping action of the buccal cavity.
The lungs in reptiles, birds and mammals have become more efficient. In them the respiratory surface has increased manifold by the formation of alveoli. Mammals have highest increase in their respiratory surface. According to one estimate the respiratory area in man is from 50-90 square meters which is 50 times the surface area of the body. A man has one thousand kilometer long capillaries.
The nature has made the functioning of birds lungs very effective. In addition to lungs, birds have air sacs which are filled on breathing by 75% of the inhaled air which bypasses the lungs. The lungs first receive 25% of the fresh air with which the gaseous exchange occurs on inhaling.
As the air is exhaled, the air of the sacs which is still fresh passes through the lungs on its way to exterior and supplies oxygen to the blood and carries away carbon dioxide from the blood. Structure of Human Respiratory System A pair of lungs with associated structures and organs like nose, pharynx, larynx, trachea, bronchi and bronchioles form the respiratory system. Nose • The air enters in the nasal cavity through nostrils.
The nasal cavity is lined with hair and mucous secreting glands. This cavity is further divided into shelves, due to the presence of many small bones emerging from its walls. The beating of cilia creates a current in the mucus that carries the trapped particles towards the back of the nasal cavity. From here the mucus drips into the throat and is swallowed.
Mucus keeps the nasal chamber moist. As the air passes through the chamber on its way to the lungs, dust particles and foreign substances in the air get trapped in the hair and the mucus. The air get warmed to body temperature and is also saturated with moisture. A number of cavities called sinuses open into the nasal cavity. The sinuses are lined with mucus secreting epithelium. The opening of sinuses into the nasal cavity are very narrow.
If these apertures are closed due to cold or inflammation, the sinuses get filled up with mucus which may produce headache etc. Pharynx The thin compartment of the nasal cavity opens into the pharynx (throat) by means of two small apertures which are called internal nares. The pharynx is muscular passage way which extends from behind the nasal cavities to the opening of oesophagus and larynx.
The air goes from the pharynx into the larynx. In cases of extreme emergency when the upper air passage is blocked by a foreign object to the extent that victim cannot breathe, quick action is required to save persons life. To force such an object out of the air passage, a sudden application of pressure to the abdomen forces air out clearing respiratory passage. Larynx The upper most part of the air tube (trachea) is called the larynx.
The larynx is a box made of cartilage. Two fibrous bands called vocal cords are located in this box which on vibration by the air produce sound waves which forms the basis of human voice. This box is, therefore, also called sound boxThe air enters into glottis. This opening is guarded by a muscular flap called epiglottis which fits into this opening while the food is being swallowed into the oesophagus lying behind the tracheal tube.
This act is very important as it prevents the food from entering into the trachea and choking it. The air tube which is known as trachea is about 12 cm long by cylindrical tube which lies in front of the oesophagus. There are incomplete shaped cartilagenous rings which are regularly placed in its wall and all along its length. These rings prevents the collapsing of the tube and thus keep the air passage wide open all the time.
Trachea is also lined with ciliated mucous epithelium. Any foreign particles present in the entering air get trapped in the mucous and the clean air enters the lungs. Bronchi The trachea on entering the chest divides into two smaller tubes which are called bronchi (single bronchus) which are similar in structure to the trachea but are smaller in diameter and they have in their walls small irregular cartilageuous plates.
Each bronchus enters into the lungs of its own side. The right bronchus branches into 3 and left bronchus divides into 2 secondary bronchi which serve the 3 right and 2 left lobes of the lungs respectively. Bronchioles The secondary bronchi divide into smaller and smaller branches until they end in thousands of passage ways called respiratory bronchioles.
The bronchioles have not cartilagenous plates in their walls. Alveoli The walls of the respiratory bronchioles have clusters of tiny branches (like bunches of grapes) that along with the respiratory bronchioles are the sites of gaseous exchange, these pouches or air sacs are called alveoli (single alveolus). The alveoli are enormous in number.
Every lung has about three hundred million alveoli. Pulmonary artery carries impure blood from the heart and enters into each lung and there it divides and redivides until it forms a network of fine capillaries over the wall of each alveolus. The walls of alveoli are very thin (1/1000 mm thick) and moist and thus offer a very efficient site for gas exchange. The Lungs The masses of alveoli constitute lungs and their lobes.
The lungs and the heart lie protected in the chest box, the chest box is formed on sides and in the front by the ribs and the intercostals muscles, and by a domb shaped muscular diaphragm on its posterior. The lungs are enclosed in a double layered membrane called pleural membrane. There is a thin film of fluid in between the two layers. This watery fluid makes the movements of the lungs (expansion & contraction) easy. Mechanism of Breathing Breathing is spread over two phases
1. Inspiration
2. Expiration
Inspiration During inspiration the dome-shaped diaphragm contracts flattening somewhat and thereby lowering the floor of the thoracic cavity. The external intercostals muscles contract raising the rib cage.
A combined action of these two events expand the thoracic cavity, which in turn expands the lungs. As a result of it the air pressure within the lungs decreases. Thus air from the environment out side the body is pulled into the lungs to equalize the pressure of both sides. Expiration In expiration the external intercostals muscles relax and the internal intercostals muscles contract as a result of which ribcage drops. The diaphragm relaxes and assumes dome like shape. The combined action of these two events reduces the volume of the thoracic cavity.
The volue of lungs in turn decreases which results in an increase in the air pressure in the lungs. The air is thus forced out of the lungs. At the lungs, carbon dioxide within the blood of capillaries surrounding the alveoli and oxygen in the air of the alveoli are exchanged. The exchange of gases works by the process of diffusion. The arterial blood in the lungs has less oxygen and more carbon dioxide as compared to air entering into the lungs. In the deoxygenated blood of the lungs the pressure of carbon dioxide is greater than the pressure of carbon dioxide in the air within alveoli. Therefore, carbon dioxide diffuses out of the blood and into the alveoli.
On the other hand, the pressure of oxygen in the air within the alveoli is greater than the pressure of oxygen in the arterial blood. Therefore, oxygen diffuses out of the alveoli and into the blood. The oxygen first dissolves in the film of fluid present on inner walls of the alveoli and then diffuse into the blood through thin walls of alveoli.
The carbon dioxide of the blood diffuses out into the air of the alveoli by passing through the walls of the alveoli. In man and other animals (all vertebrates and some invertebrates) some respiratory pigments are present in blood which can transport greater amount of oxygen efficiently from lungs to the other parts of the body. If it was not for the presence of haemoglobin in the blood, the oxygen transport could have been very slow and small in amount because only a small amount of oxygen can dissolve in blood plasma. Whereas, according to an estimate one hundred mol of haemoglobin containing blood can transport about 20 ml of oxygen.
Oxygen does not combine covlently with haemoglobin. It is only loosely attached with haeme of the haemoglobin and is therefore forms oxyhaemoglobin but not haemoglobin oxide. This loose combination of oxygen with haemoglobin makes the detachment of oxygen at tissue level easy. Haemoglobin + Oxygen Oxy-haemoglobin Carbon dioxide is transported from the tissue s to the lungs mostly bonded with water in the blood which first form carbonic acid with water that quickly dissociates into HCO3 and H+ ions. A small percentage (25%) of carbon dioxide combines with haemoglobin to form carbamino compound.
Only a every small amount (6%) of carbon dioxide is simply dissolved in the blood. Effect of exercise on the rate of breathing A man breathes 16 times a minute in normal circumstances. The rate of breathing is controlled by a center in the brain which is very sensitive to the changing concentration of carbon dioxide in blood. In case of higher concentration than normal of carbon dioxide this center sends impulses directly to the diaphragm and intercostals muscle to contract at a faster rate which leads to an increase in the rate of breathing.
When you do hard work or take strenous exercise you need more energy which is provided by more and more oxidation of glucose. As a result the amount of carbon dioxide in blood increases which stimulates the carbon dioxide centre in the brain to enhance the rate of breathing so that the excess carbon dioxide from the blood can be eliminated and more oxygen can be supplied to the fastly metabolizing muscles. During it th breathing rate may increase up to 30-40 time per minute.
Post a Comment