Toad: Respiratory system

Respiratory system: Energy is necessary for different metabolic activities.Usable energy is produced inside cells by oxidation-reduction of glucose with the help of mitochondria. Water, C02, generally ATP (Adenosine Tri Phosphate) and heat are produced by this process. Cells can not use heat energy, so it is lost. ATP instantly supplies energy when it is needed. It should be kept in mind that in extensive heat, protoplasm gets paralyzed. For these reasons the cellular respiration process takes place step by step with the help of various type of enzymes. This process of energy generation inside cells is known as internal or cellular respiration. For this oxygen is essential. The process of collecting oxygen from the environment to every cells of the body is known as external respiration. In this process body receives oxygen enriched air and expels C02 from the body.

Cellular respiration process of metabolic activities of all organisms is same, among these the main metabolic path is Kreb's Cycle. To live in different habitats of environments, toads respire through different methods of external respiration.

To live in different environments, the toad respires in more than Generally, the

process of external respiration in toad is of four types.

1.  Cutaneous respiration

2.  Bucco- pharyngeal respiration

3.  Pulmonary respiration

4.  Gill respiration

1. Cutaneous respiration : This type of respiration takes place through theskin. The skin of toad is very thin and enriched with blood capillaries. The skin of toad contains a large number of mucus glands. Mucus is discharged from these glands; as a result the skin remains moist. For this reason, exchange of oxygen and carbon dioxide take place through skin easily in the process diffusion. During hibernation the toad respires by this process.

2. Bucco-pharyngeal respiration: The membrane of buccal cavity andpharynx of toad is very thin and there are innumerable capillaries. When air enters the buccal cavity oxygen gets into the blood of the capillaries by diffusion. This oxygenated blood flows to different parts of the body through heart and at one stage takes part in the oxidation of food inside the cell. The carbon dioxide produced as a result of oxidation of food comes out through diffusion. The toad respires this way generaly during rest.

3. Pulmonary respiration: Lungs are the main respiratory organs of toad. The toad has a pair of lungs. The lungs are pink coloured hollow sacs. Each lung is formed of innumerable smaller chambers like balloons. Each of this balloon like chambers is called air sac or alveolus. Its wall is enriched with blood vessels. When the lungs expand the air sacs become, filled with air. Exchange of oxygen andcarbon-dioxide taxes place through the air sacs. The fine air tubes with which the air sacs remain connected are called bronchioles. The two tubes which are formed one on each side by joining all the bronchioles of each lung are called bronchus: Right and left bronchi meet together and form a small trachea. Trachea and larynx or voice apparatus together form the laryngo-tracheal chamber. The lungs of each side joining with the larynx and glottis open through the nasal aperture. The adult and active living toad respires through pulmonary respiration. The pulmonary respiration is actually external respiration. External respiration is again divided into two sub stages such as, Intake of air or inspiration and Release of air or expiration.

Inspiration: At this stage oxygen along with the air enters the lungs from theenvironment. Inspiration occurs in two steps.

A. First step: At this time the nasal apertures remain open but the mouthaperture and glottis remain closed. Simultaneously the lungs contract and the floor of the buccal cavity are lowered. As a result, the volume of the buccal cavity increases. The oxygenated air from outside enters the buccal cavity. At this time exchange of oxygen and carbon-dioxide takes place in the blood of capillaries situated in the walls of the buccal cavity and pharynx.

B. Second step: At this stage the nasal apertures are closed and the floor of thebuccal cavity is raised. As a result, oxygenated air enters the alveoli of the lungs. By the diffusion process oxygen from the cavities of the alveoli enters the blood capillaries close to the walls of the alveoli. In a similar process carbon-dioxide is released.

Expiration: At this stage from the alveoli carbon-dioxide comes out of thebody. Expiration, occurs in two steps:

A. First step: At the first step of expiration the two lungs contract, externalnasal apertures and mouth aperture remain closed and the floor of the buccal cavity is lowered. As a result volume of the buccal cavity increases and carbon-di-oxide mixed air returns to the buccal cavity.

B. Second step: The floor of the buccal cavity is raised. The volume of buccalcavity reduce. At this time the glottis remains closed and the nasal apertures remain open. As a result through nasal apertures the carbon-dioxide enriched air comes outside.

Internal respiration: We have learnt earlier that internal respiratior basicallycell respiration. In this process exchange of oxygen and carbon-dioxide takes place in the blood of capillaries. At the cellular level energy produced through oxidation of glucose.

Transportation of oxygen: As a result of the entrance of air inside the lungsthe air of the lungs gets oxygen. The moist vapor that remains in this reaches to the interior part of the alveoli. Oxygen dissolves in watery drops a result the volume and pressure of oxygen increase. At this time the volt and pressure of oxygen in the blood of capillaries on the body walls of alvi remain less. As a result oxygen enters the blood through diffusion process. this time oxygen combines with the haemoglobin of blood, to form compound known as oxyhaemnglobin.

Haemoglobin + Oxygen → Oxy-haemoglobin.

This oxygen enriched blood reaches the body cells through the heart. The volume and pressure of oxygen remain less in the body cells, so breaking the oxyhaemoglobin the oxygen separates and enters the cells. This oxygen oxidizes the simple food (glucose) of the cells and produces energy.

Oxy-haemoglobin = Haemoglobin + oxygen.