Title Med-RM_Zoo_SP-1_Ch-4_Breathing and Exchange of Gases.pdf ✅

Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Chapter Contents The process of exchange of O2 from the atmosphere with CO2 produced by the cells is called breathing. It can also be simply defined as intake of fresh air and removal of foul air, i.e., CO2, whereas respiration is defined as an oxidation of food (glucose) to form CO2, H2O and energy. Breathing includes inspiration and expiration. Inspiration means to inhale or to breathe in and Expiration means to exhale or to breathe out. RESPIRATORY ORGANS Organs meant for respiration process are known as respiratory organs. Different animals have different respiratory organs depending upon their two main features 1. Habitat : It is the place where an animal lives. The nature of respiratory organ depends on the habitat of an animal. For example, fishes live in water, so they have gills to respire. Reptiles live on land and they respire through lungs. 2. Level of organisation : According to the level of organisation of animals, breathing mechanism varies. For example, Poriferans have cellular level of organisation. In them, no well-developed tissues, organs are present that’s why they can exchange O2 with CO2 by simple diffusion over their entire body surface. Simple diffusion means the movement of molecules from their higher concentration region to their lower concentration region. Table : Respiratory organs in different animals Animal Respiratory Organ/System Examples Lower invertebrates No well-developed respiratory organ is present. Exchange of gases by simple diffusion. Moist, thin and vascular cuticle. Tracheal system (network of tubes) Gills - plate-like or filamentous and vascularised structures. (branchial respiration) Sponges, coelenterates, flatworms. Earthworm Insects like cockroach. Aquatic arthropods like cray fish, prawn and molluscs like . Unio 1. Chapter 4 Breathing and Exchange of Gases Respiratory Organs Human Respiratory System Mechanism of Breathing Exchange of Gases Transport of Gases Regulation of Respiration Disorders of Respiratory System
114 Breathing and Exchange of Gases NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 Vertebrates Fishes Amphibians Reptiles Birds Mammals Gills Gills Moist skin , Lungs, Buccal cavity Lungs Lungs Lungs (cutaneous respiration) (pulmonary respiration) Cartilaginous and bony fishes. Tadpole larva of frog. Frogs, toads etc. Snakes, lizards etc. Pigeon, sparrow etc. Humans 2. Animal Respiratory Organ/System Examples HUMAN RESPIRATORY SYSTEM Epiglottis Larynx Trachea Primary bronchus Secondary bronchus Tertiary bronchus Pleural membranes Alveoli Pleural fluid Bronchiole Diaphragm Bronchus Cut end of rib Lung Heart Fig. : Diagrammatic view of human respiratory system (Sectional view of the left lung is also shown) It is a system consisting of respiratory passage and respiratory organs. Respiratory organs are a pair of lungs. Respiratory passage : It is a passage that takes air from outside to the respiratory surface of lungs. It consists of a pair of nostrils, nasal cavity, a pair of internal nares, pharynx, larynx, trachea, bronchi and their branches and the respiratory surface of lungs, i.e., alveoli. Structures involved in respiratory passage 1. External nostrils : A pair of external nostrils represent the first part of respiratory passage. These are the holes of our nose opening out above the upper lips. These lead into nasal chamber of nasal cavity through the nasal passage. 2. Nasal chambers : These are also two in number. The epithelial lining of cavities is known as respiratory epithelium. It has pseudostratified, ciliated, columnar, epithelium with sensory neural epithelium and goblet cells which secrete mucus. It is richly supplied with blood vessels. Functions: Mucus from goblet cells and glands makes the surface sticky for trapping dust particles present in the inspired air. Moisture from the epithelium also makes the air humid. It brings the temperature of the incoming air, upto the body temperature.
NEET Breathing and Exchange of Gases 115 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 3. Internal nares : These are the posterior openings of the nasal cavities that lead into the nasopharynx. 4. Nasopharynx : Internal nares open into a part of pharynx known as nasopharynx. It is a portion of pharynx. Only air passes through nasopharynx. It opens into the trachea through glottis of larynx region. Glottis is the opening at the upper part of larynx. Pharynx is common passage for both food and air. The pharynx opens through larynx region into trachea. 5. Larynx : It is also known as sound/voice box because it helps in the production of sound. It is made up of cartilage, present at the upper part of trachea. Its upper part has an opening, i.e., glottis. During swallowing, this glottis can be covered by epiglottis which is a leaf-shaped cartilaginous structure made up of elastic cartilage. Epiglottis is the covering or lid of glottis to prevent the entry of food into the larynx during swallowing. 6. Trachea : It is also known as wind pipe. It is a straight tube extending upto the mid-thoracic cavity, commonly called chest cavity. This tube finally divides into right and left primary bronchi at the level of 5th thoracic vertebra. It is lined by incomplete cartilaginous rings to prevent it from collapsing during inspiration. 7. Bronchi (plural), bronchus (sing.) : Each bronchus undergoes repeated divisions to form its branches. These are secondary, tertiary bronchi and bronchioles. Bronchioles are the terminal branching of bronchi. Finally, bronchioles give rise to a number of very thin, well-supplied with blood vessels, irregular walled balloon-like structures called alveoli. The walls of the bronchi and initial bronchioles are supported by incomplete cartilaginous rings. 8. Alveoli : Bronchioles open into the alveolar ducts, i.e., a tube-like structure which lead into expanded passages, the atria which open into the alveolar sacs or air sacs. There are about 300 million of alveoli in two lungs. The membrane of alveoli is very thin, irregular and richly supplied with blood vessels. Due to very close contact of blood vessels with alveoli, the exchange of gases takes place easily. Surfactant : A surface active agent - lecithin secreted by type II alveolar epithelial cells, reduces surface tension between the alveolar fluid and air. It prevents collapsing of lung alveoli. Lead to Lead to Lead to Bronchioles Alveolar ducts Atria Alveolar sacs    Lungs A pair of lungs is present in humans, lie in an air-tight chamber known as thoracic cavity or chest cavity. This cavity is formed dorsally by the vertebral column, ventrally by the sternum, laterally by the ribs. It is closed below by the diaphragm which is a dome-shaped structure made up of muscles and separates thoracic cavity from abdominal cavity.  Membranes enclose the lungs : Each lung is enclosed by two membranes known as pleura or pleural membranes. The outer pleural membrane is in close contact with the thoracic cavity whereas inner pleural membrane is in close contact with the lung surface. In between these two membranes, a narrow space is present known as pleural cavity. This pleural cavity is filled with a fluid secreted by pleural membranes known as pleural fluid.  Function of pleural fluid : It lubricates the pleural membranes so that they may slide over each other without friction during breathing. If fluid is not present, then there will be damage to the membranes which finally affects the breathing.
116 Breathing and Exchange of Gases NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456  Internal structure of lungs : The right lung is shorter by about 2.5 cm due to raised position of diaphragm on the right side to accomodate liver. The left lung is longer. It is, however, narrower than the right lung because it contains a cardiac notch for accomodating asymmetrically placed heart. Left lung is divisible by an oblique fissure into two lobes, left superior and left inferior. Right lung has two fissures, horizontal and oblique. They divide the right lung into 3 lobes – right superior, right middle and right inferior. The lobes are divided internally into segments and segments into lobules. Internally, lungs are made up of branching network of bronchi, bronchioles and alveoli. Network of bronchi include primary, secondary and tertiary bronchi. Alveoli are the main sites where actual diffusion of gases O2 and CO2 takes place between blood and atmospheric air. Fig. : Internal structure of lung Two parts of human respiratory system are : Conducting Part Exchange or Respiratory Part This part consists of external nostrils, nasal chamber, internal nares, nasopharynx, larynx, trachea, bronchi and bronchioles (upto terminal bronchioles) Functions  Conducts air from external nostrils upto bronchioles. Clears the incoming air by trapping dust particles present in it. Makes the incoming air humid by providing moisture produced by epithelium of nasal cavities. It brings the temperature of air upto the body temperature.    It includes alveoli and their ducts. Function It is the main site of human respiratory system where diffusion of gases O and CO occurs. 2 2 Steps involve in respiration : Respiration is a complex process which occurs in number of steps. These are : 1. Breathing: It is simply the inhalation of atmospheric air and exhalation of CO2 rich alveolar air. It is also known as pulmonary ventilation. 2. Diffusion of gases between alveoli and blood: Diffusion of gases O2 and CO2 takes place across the alveolar membrane to the blood capillaries surrounding it. The membrane is very thin and richly supplied with blood capillaries. 3. Transport of gases: Blood is the medium for transport of gases O2 and CO2, which transports O2 to the body cells from alveoli and CO2 from the body cells to alveoli.