Hey guys ! Do you know..?? All activities of living organisms require energy. They obtain this energy by the breakdown of nutrients present in their food, such as glucose, amino acids, fatty acids etc.This usually takes place in the presence of oxygen and energy is released in the process as ATP(Adenosine triphosphate). During the process of breakdown of food molecules, carbon dioxide gas (which is toxic to the body cells) is also released. So, there is a constant need of intake of oxygen from the atmosphere and removal of carbon dioxide produced by the cells out of the body to carryout bodily functions. Thus, respiration is defined as the process of oxidation of nutrients to release energy.
C6H12O6 + 6O2 ——–>6CO2 + 6H2O + 38 ATP
In the process of respiration, respiratory organs, blood and the body cells play an important role. Respiratory organs supply oxygen and remove water and carbon dioxide. Blood transports the gases from the respiratory organs to the tissue cells and vice versa. Cells of the body oxidize the food and produce energy.
Respiratory organs and modes of respiration in variation animals :-
|Respiratory organ||Mode of Respiration||Examples|
|Body surface||Body surface respiration||Almost all lower animals upto phylum – Annelida including sponges ( Leucosolenia ) and coelenterate ( Hydra ) and free – living helminthes|
|Gills||Bronchial respiration||Crustaceans ( prawn ) , cartilage and bony fish|
|Book gills||Book gill respiration||Limulus ( king crab )|
|Skin||Cutaneous respiration Tracheal respiration||Annelids ( earthworm ) and amphibians ( frog )|
|Trachea (Ectodermal tubes)||Tracheal respiration||Insects ( cockroach ) , centipedes and millipedes|
|Lungs||Pulmonary respiration||Most of tetrapod|
|Book lungs||Book lung respiration||Arachnids ( spiders and scorpion )|
Types of respiration:-
Based on the mode of oxidation of nutrients respiration is of following two types :-
- Aerobic respiration :-
It occurs when the cells utilise molecular oxygen for oxidising nutrient.It occurs in the mitochondria of the cells.It produces a lot of ATP per glucose molecule . It is done under normal circumstances by an animal , when heart rate and breathing rates are normal.
- Anaerobic respiration :-
It occurs , when nutrients are oxidised without using molecular oxygen.It is also called fermentation.It occurs in the cytoplasm of the cells.It produces less ATP per glucose molecule . It is done during oxygen deficient situations,i.e. like the first 1-2 minutes of exercise.
The exchange of oxygen and carbon dioxide by the body involves various organs for gaseous exchange , which collectively form the respiratory system . Such a well – defined respiratory system is the characteristic feature of animals only as in plants , gaseous exchange takes place through general body surface only .
The special features of mammalian respiratory system are :-
- Presence of a nose.
- Elongation of nasal passage and its complete separation from the buccal passage through palate so that internal nostrils open deep into nasopharyngeal part of pharynx.
- Long windpipe due to the presence of well – defined neck.
- Spongy and solid lungs
Respiratory system in Human:-
Respiratory system in Human includes a respiratory tract which starts from nostril and ends at alveoli.
There are two parts of respiratory tract :
Conducting part starts from external nostrils upto terminal bronchioles.
- Transport atmospheric air to the alveoli
- Humidifies air
- Removes foreign particles from air and brings the air to the body temperature. Respiratory part includes alveoli and their ducts.
Diffusion of O2 and CO2 between blood and atmospheric air.
Human respiratory system includes nostrils, nasal chambers, pharynx, larynx, trachea, bronchi, bronchioles, lungs, diaphragm and intercostal muscles.
- Nostrils and nasal chambers :
The nostrils are the external openings of the nose through which oxygen-rich air is carried inside the body and carbon dioxide air enriched with water vapor is expelled out of the body. These are also called external nares.Similarly a pair of internal openings is present.They open in the pharynx.These are called inner parts.
The space between the outer and inner nostrils as the nasal chamber. Internally, each is lined by a mucous membrane and ciliated epithelium.It is divided into right and left parts by a cartilage known as a mesathemoid.Each nasal chamber is further divided into three regions .
- Pharynx :
The nasal chamber opens into the pharynx.It is a small, vertical tube measuring about 12 cm.In length.The respiratory and the food passages cross each other in the pharynx by two separate passages.Its upper part is known as naso-pharynx which helps in conduction of air and the lower part is called laryngo-pharynx or oro-pharynx conducting food to oesophagus. In the pharynx, there are tonsils which are made up of lymphatic tissue. They kill bacteria trapped in the mucous.
- Larynx :
It is the sound producing organ. In males, the larynx increases in size at the time of puberty. Hence, it is called Adam’s apple and can be noticed in the neck region. From the pharynx, air enters the larynx through an opening called glottis. The glottis is guarded by a flap called epiglottis. It prevents the entry of food particles into the respiratory passage. Along the sides of the glottis are two folds of elastic tissue called vocal cords.These are responsible for producing sound.
It is also known as wind pipe. It is about 12 cms long and 2.5 cms wide. It lies in front of the oesophagus and extends downward into the neck. The wall of the trachea is made up of fibrous muscular tissue supported by ‘C’- shaped cartilage rings. These are 16-20 in number. They make the trachea rigid. The trachea is internally lined with ciliated epithelium and mucous glands. If any foreign particle enters, it is immediately expelled out by coughing action. Dust particles get trapped by the mucous. By ciliary movement, they are swept towards the larynx and finally they enter the oesophagus.
5.Bronchi and bronchioles :
The distal end of the trachea is divided into two bronchi behind the sternum. Each bronchus is supported by a complete ring of cartilage. It enters into the lung of its respective side. On entering the lung, each bronchus further divides into secondary and then tertiary bronchi. Tertiary bronchi divide into many minute bronchioles. Wall of each bronchiole does not have cartilage rings. Each bronchiole ends into a balloon- like alveolus. These alveoli make the lungs spongy and elastic.
These are the principal respiratory organs. Lungs are paired, hollow, elastic organs. They are located in the thoracic cavity. Each lung is enclosed in a pleural sac. It is made up of two membranes, outer parietal and inner visceral. The enclosed cavity is called the pleural cavity. It is filled with a pleural fluid, which lubricates the pleura and prevents the friction when the pleural membranes slide over each other. Lungs are pink in colour, soft, elastic and distensible. They are highly vascular (richly supplied with blood capillaries). The left lung is divided into two lobes. The right lung is divided into three lobes. Each lobe consists of bronchioles which terminate in a bunch of spherical thin walled air sacs called alveolar sacs.Each sac has about twenty alveoli which look like grapes. They are covered with a network of capillaries from the pulmonary artery and vein. Alveoli have very thin highly elastic walls. Each alveolus is about 0.1 mm in diameter. The human lung has about 750 million alveoli, which increase surface area for exchange of gases. The total area covered by them is about 50 times the surface area of skin. The outermost covering of the lungs is made up of smooth muscle fibres called visceral pleura. In the interior, there are many lobules. Each lobule contains the alveolar ducts, alveolar sacs and alveoli. The alveoli have very thin (0.0001 mm) wall composed of simple non-ciliated, squamous epithelium. It has collagen and elastin fibres. This makes the alveoli very flexible. Alveoli are supplied by a network of pulmonary capillaries.
Positive and negative pressure Lungs:-
+ve pressure lungs :
In them, the pressure inside the lungs is +ve in comparison to the atmospheric pressure at the time of inspiration.
eg. frog (hollow lungs).
-ve pressure lungs :
In them, the pressure inside the lungs is -ve as compared to atmospheric pressure at the time of inspiration.
e.g. humans (solid lungs).
Solid spongy lungs are found in case of all mammals, while amphibians like frog have hollow lungs.
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