Gills of Fish
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.
Human Respiratory System
In humans, there is very efficient respiratory system. It consists of certain organs which are called respiratory organs these include nose, pharynx, larynx, trachea, bronchi and bronchioles.
The air enters through the external nostrils into the nasal cavity. This is lined with mucous secreting epithelium and ciliated epithelium. The nostrils are lined with hairs. The nasal cavities, located above the oral cavity and behind the nose are covered with epithelial tissue.
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 cavities moist. Bones of the nose warm up the air. Mucus moistens the air. Hair filter the air and stop the dust particles bacteria and any other foreign substance from going to next part of respiratory system. In this way air is purified and is then pushed into the pharynx.
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 is very narrow. If these openings are closed due to cold or inflammation, the sinuses get filled up with mucus this results in headache and changed voice.
The nasal cavity opens into the pharynx (throat) through two small apertures which are called internal nares or internal nostrils. The pharynx is muscular passage which extend from behind the nasal cavities to the opening of oesophagus and larynx. The air goes from the pharynx into the larynx.
The upper most part of the wind pipe (trachea) is called the larynx. The larynx is a cartilaginous box. Two fibrous bands called vocal cords are located in this box. These vibrate to produce sound. Larynx is, also called sound box or voice box. The air enters the larynx through a small aperture called glottis which is guarded by a muscular flap called epiglotis which fits into this opening while the food is being swallowed into the oesophagus. It prevents the food from entering into the trachea and choking it. During breathing epiglottis keeps the glottis open so that air goes to trachea.
The air tube (wind pipe) is known as trachea. It is about 12 cm long and lies in front of the oesophagus. It has incomplete C shaped cartilagenous rings which are regularly placed in its wall and all along its length. These rings prevent the collapsing of the tube nd thus keep the air passage wide open all the time. Trachea is also lined with ciliated mucous epithelium. Any foreign particles present in the inhaling air get trapped in the mucous that is moved out of the trachea by breathing of the cilia in the upward direction. In trachea air is further cleansed and filtered and then moved towards the lungs.
The trachea while passing the chest cavity divides into two smaller tubes which are called bronchi (single bronchus). Bronchi are similar in structure to the trachea but are smaller in diameter and they have in their walls small irregular catilageuous plates. Each bronchus enters into the lungs of its own side. The right bronchus divides into three secondary bronchi and the left bronchus divides into two secondary bronchi which serve the 3 right and 2 left lobes of the lungs respectively.
the secondary bronchi further divide into very fine branches until they end in thousands of passage ways called respiratory bronchioles. The bronchioles have not cartilaginous plates in their walls. They have smooth muscle and elastic fibers.
The walls of the respiratory bronchioles have clusters of tiny branches(like bunches of grapes) that along with the respiratory bronchioles re the sites of gaseous exchange, these pouches or air sacs are called alveoli (singular: alveolus). The alveoli are enormous in number. Each lung has about three hundred million alveoli.
Pulmonary artery brings deoxygenated blood from the heart into the lung. Here, it divides and re-divides 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. Thus, alveoli are efficient site for gaseous exchange.
There is a pair of lungs present in the chest in man. Actually, the masses of alveoli constitute lungs and their lobes. The lungs re protected by the chest box from sides and by a doem shaped muscular diaphragm from below. Chest box or ribcage is made up of ribs. Between the ribs, there are present inter-costal muscles. The diaphragm is a muscular sheet which partitions the chest and abdomen.
The two lungs re covered by 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 and contraction) easy. It also protects the lungs from external injuries.
Mechanism of Breathing
Breathing occurs in two phases:
1. During inspiration, the dome-shaped diaphragm contracts and becomes flat some what and thereby lowering the floor of the thoracic cavity.
2. The external inter-costal muscles contract raising the ribcage. A combined action of these two events expands the thoracic cavity, which in turn expands the lungs.
3. The air pressure within the lungs decreases.
4. Thus air from the environment outside the body is pulled into the lungs to equalize the pressure of both sides.
1. The diaphragm relaxes and assumes dome like shape. During expiration, the external inter-costal muscles relax and the internal inter-costal muscles contract as a result of which ribcage drops.
2. The combined action of these two event decreases the volume of the thoracic cavity which in turn decreases volume of lungs.
3. The air pressure with in the lungs increases.
4. The air is thus forced out of the lungs.
Bad Effects of Smoking on Heath
Smoking is injurious to human health. The smoke contains many chemical and gases. Dried tobacco leaves are used in cigarettes. The tobacco on burning produces a number of dangerous and toxic compounds.
Chemicals Present in Cigarette Smoke and Their Harmful Effects
1. Man is addicted to cigarette damages brain tissues.
2. Causes blood to clot more easily.
3. Harden walls of arteries.
1. Kills cells in air passages and in lungs.
2. Increases production of mucous and phlegm in lungs.
3. Causes lung cancer.
(c) Carbon Monoxide
Prevents red blood cells from combining with and transporting oxygen around the body.
promote the growth of cancerous cells in the body.
1. Irritate air passages and air sacs in the lungs.
2. Kill cells at the surface of air passages.
3. Causes smoker's cough and lung cancer.
A chemical reaction in which a substance combines with oxygen and produce heat, light and flame is called Combustion.
A process that liberates chemical energy from organic molecules when oxidized is called Respiration. It occurs in all living cells. In fact respiration is a series of complex oxidation and reduction reactions in which energy is released bit by bit.
The process in green plants by which green plants manufacture their own food by using carbon dioxide and water with the help of energy absorbed by chlorophyll from sunlight is called photosynthesis.
Relation of Combustion, Respiration and Photosynthesis
Combustion is the process of burning in which wood, coal, methane, gas etc are burnt in the presence of oxygen, producing carbon dioxide and water accompanied with the release of energy. It is an exothermic chemical reaction.
Cellular respiration can be compared to burning of fuel in which organic food (carbohydrates, fats and proteins) rich in carbon burn in the presence of oxygen producing carbon dioxide, water and energy.
Respiration like combustion is a catabolic exothermic chemical process. However, the difference between the combustion and respiration is that the combustion takes place in one go, releasing the entire energy as the heat, which may be utilized or is lost into the environment. the respiration completes in several small steps. Each step is under the control of a specific enzyme, releasing energy in small amounts which can be stored in the form of ATPs. Photosynthesis, another metabolic process, is just opposite to combustion. Combustion is a catabolic process; the photosynthesis is an anabolic process. In photosynthesis organic substance is synthesized from carbon dioxide and water in the presence of sunlight energy and chlorophyll. The molecular oxygen is evolved as the by-product combustion is exothermic and releases energy, photosynthesis is endothermic and absorbed energy.
Photosynthesis and respiration are the two metabolic reactions opposite to each other. Photosynthesis takes place only in the gree parts of the plant body having chlorophyll, whereas respiration takes place in all the living cells of plants and animals. Mitochondria are the cellular organelles where respiration takes place while the organelles for photosynthesis re chloroplasts. Photosynthesis takes place during the day time only, whereas respiration takes place day and night. In photosynthesis body weight is increased but in respiration weight is decreased. Respiration is an oxidation reaction whereas photosynthesis is a reduction reaction and can be well understood by comparing their chemical reactions.
Chemical Equation in Respiration
Glucose + Oxygen -------> Carbon dioxide + Water + Energy (In presence of mitochondria and enzymes)
Chemical Equation In Photosynthesis
Carbon dioxide + Water --------> Glucose + Oxygen (In presence of chloroplast and solar energy)
Respiratory Organs of Insects
The respiratory system of insects is called the Tracheal system. It is a network of interconnecting air filled tubes called trachea delivering air directly to the body tissue cells. Trachea open outside through pores called spiracles.
Each trachea has chitinous cuticle lining which prevents it from collapsing.
A pair of spiracles is usually located on the sides of each segment of the thorax and abdomen. Spiracles have valves to open or close them regulated by special muscles. This controls water loss from internal body tissue.
Trachea break up into numerous smaller tubes called tracheoles which ramify among the body tissues ending blindly. Tracheoles lack a chitinous lining. At rest the tracheoles are filled with watery fluid through which gaseous exchange tkes place in dissolved state.
Ventilation is brought about by contraction and relaxation of abdominal muscles which result in a rhythmic pumping of air into and out of the trachea.
Gas exchange takes place in tracheoles which are permeable to gases and are filled with a fluid in contact with the body tissue. Since oxygen diffuses directly into the tissue cells, blood of insects does not have hemoglobin so it is white. However, removal of carbon dioxide is dependent on blood plasma which takes it up for removal via spiracles.