Respiration

introduction

Survey of respiratory structures in animals

• In Protozoans, Porifers, Coelenterates and Helminthes there are no specialized respiratory structures, and exchange of gases occurs through general body surface.

• In Annelids respiration is either cutaneous (ex. Earthworm and Nereis) or branchial.

• In Arthropods there are various type of respiratory structures like Gills (in crustaceans),book lungs (in arachnids) and tracheal tubes (in insects).

• In Molluscs the respiratory structure are mainly Gills.• In Echinoderms the gills, body wall, respiratory tree and Tube feet (primarily

the locomotory structures) are the respiratory structures.• In Fishes the Gills are the main respiratory structures but in lung fi shes

(Dipnoi) the Gills• and Lungs both are well developed.• In Amphibians the respiratory structures are either Gills (Branchial

respiration) or Lungs• (Pulmonary respiration). In Frog the respiration is Cutaneous, Bucco-

pharyngeal as well• as Pulmonary.• In Reptiles birds and mammals the respiration is Pulmonary.

Types of Respiration• Respiration –• A process in which oxidation of organic compounds occurs in cell

and energy is released is called as respiration.• Stages of Respiration - According to scientist G.S. Carter there are

three stages in respiration-• (i) External Respiration (Ventilation) –Gaseous exchange

between environment and lung.• (ii) Internal Respiration –• (1)Gaseous exchange between lungs and blood.• (2)Gaseous exchange between blood and tissue fluid.

• (iii) Cellular Respiration – Oxidation of organic compounds in cell in which energy is released

Pathways to breakdown glucose

Human respiratory system

RESPIRATORY SYSTEM IN HUMAN

• In human the respiratory structures are Lungs which are endodermal in origin. The

• respiratory system contains following important components:

• Nasal passage• It contains hair for fi ltering out dust particles.• Bowman’s glands secrete mucus.• Turbinals (bones) warm up the air.• The sensory lining of nasal passage is called

Schneiderian membrane.

Pharynx• Pharynx• It is a common passage for gut and

respiratory tract.• The opening between Pharynx and Larynx is

called Glottis. It is closed by epiglottis• during swallowing of food. However, the

opening between Pharynx and Gut (Oesophagus) is different, and is called Gullet.

• The lateral sides of Pharynx contain openings of Eustachian canals also.

Larynx• Larynx• It is commonly called voice box or sound box.• In birds the sound box is present at the base of trachea

and is called Syrinx.• In human it contains 9 car lages− three paired and

three unpaired. The unpaired cartilages include Thyroid, Cricoid and Epiglottis while paired cartilages include Arytenoid, Corniculate and Cuneiform.

• Thyroid cartilage is collar shaped, and in males forms Adam’s apple (In frog, the thyroid cartilage is absent).

• Cricoid cartilage is ring shaped (complete).• Thyroid, Cricoid and Arytenoid are Hyaline cartilages

while Epiglottis is elastic cartilage.

Trachea

• It is commonly called wind pipe, and contains ‘C’ shaped rings of Hyaline cartilage which

• prevent its collapsing. These cartilaginous rings are dorsally incomplete.

• Tracheal lining is of Pseudo-stratifi edEpithelium

Bronchi and Bronchioles• Trachea divides into Bronchi (Sing. Bronchus)

called principal Bronchi.• These further divide into secondary bronchi and

tertiary bronchi. The cartilaginous rings are present in all Bronchi.

• Bronchi divides into Terminal Bronchioles which in turn divide into Respiratory Bronchioles. The Bronchioles do not have cartilaginous rings.

• Respiratory Bronchioles divide into Alveolar ducts forming Alveolar sacs. Each Alveolar sac is surrounded by Alveoli.

Alveoli

• Inner lining of the alveoli is simple squamousepithelium. The number of Alveoli in both the lungs is 300 million (3x108). The exchange of gases occurs mainly through alveoli.

Lungs

• Lungs in human are solid and spongy and are present in thoracic cavity.

• Le lung has 2 −lobes while right lung has 3− lobes.

• Each lung is surrounded by two membranes called pleura. The outer pleural membrane is parietal or somatic while inner pleural membrane is visceral or splanchnic in nature.

• The cavity between two pleura (pleural cavity) is filled with a fluid (perilymph) which reduces friction during breathing.

The breathing process• The breathing process includes two phases: 1. Inspiration, 2. Expiration• 1. Inspiration• It is an active process.• The External inter-costal muscles contract and the ribs move outward and

upward to• increase the volume of thoracic cavity.• The diaphragm-muscles contract and the shape of diaphragm changes from dome

to flat.• With the contraction, the lower surface of the lungs is also pulled downward.• Lungs expand and air is drawn into the lungs. The lungs in human, like other

mammals, are negative (-ve) pressure type. In frog the lungs are positive (+ve) pressure type.

• 2. Expiration• Quiet expiration is a passive process.• The diaphragm becomes dome shaped again.• The external inter-costal muscles now relax.

AIR VOLUMES• 1. Tidal volume (TV) =500 ml• The amount of air exchanged during each quiet (normal) breathing.• 2. Inspiratory reserve volume (IRV) or complementary air = 2.5 to 3 litre.• It is the maximum amount of air which can be breathed in after tidal

volume.• 3. Inspiratory capacity = 3 − 3.5 litre• Maximum amount of air which can be breathed in or inspired• Inspiratory capacity = TV + IRV• 4. Expiratory Reserve Volume (ERV) or Supplementary air = 1 to 1.2 litre• The maximum amount of air which can be breathed out after tidal volume

when inspiration is normal.• 5. Expiratory Capacity = 1.5 litre• The total amount of air which can be breathed out or expired after normal

inbreathing.• Expiratory Capacity = TV + ERV

AIR VOLUMES• 6. Vital capacity = 3.5 − 5 litre• The maximum amount of air which can be breathed out after

deepest inspiration.• Vital capacity = TV + IRV + ERV• 7. Residual Volume = 1.5 litre• The amount of air left in the lungs after breathing out vital capacity.• 8. Functional Residual Capacity = 2.5 litre• The amount of air left in the lungs after normal expiration.• Functional Residual Capacity = ERV + RV• 9. Total lungs capacity − 5 − 6 litre• The maximum amount of air that can be filled in the lungs.• 10. Dead space air = 150 ml• The amount of air present in trachea, bronchi and bronchioles,

which is not used in respiration.