Origin and phylogeny of lungs in vertebrates.pptx

Origin and phylogeny of lungs in vertebrates.pptx

1. Origin and phylogeny of lungs Dr Showkat Ahmad Wani

2. Introduction The respiratory system in vertebrates has evolved to adapt to different environments — aquatic, amphibious, and terrestrial. Among the key respiratory organs, the lung represents an adaptation for aerial respiration. Understanding the origin and phylogeny of lungs provides insights into how vertebrates transitioned from water to land.

3. Primitive Respiratory Organs Early aquatic vertebrates relied mainly on gills for respiration. However, environmental pressures such as hypoxic (oxygen-poor) waters led to the evolution of supplementary respiratory organs . These included: Skin (cutaneous respiration) Buccopharyngeal cavity Air bladders / Lungs

4. The Swim Bladder – A Related Organ The swim bladder in fishes is an outgrowth of the gut, homologous to lungs. Functions: buoyancy control, sound production, and in some species, accessory respiration. Two types: Physostomous : connected to the gut via pneumatic duct. Physoclistous : closed sac, no duct. Key point : Both lungs and swim bladders share a common embryonic origin (endodermal outpocketing of pharynx/foregut).

5. Origin of Lungs Lungs likely evolved once in vertebrate history, as paired ventral outpocketings of the pharynx. Evidence suggests that the ancestral bony fish possessed lung-like organs for air breathing. Later, in many lineages, these evolved into either: True lungs ( tetrapods , lungfishes) Swim bladders (most ray-finned fishes)

6. Phylogeny of Lungs (A) Pisces Polypterus (Bichirs) : paired ventral lungs used for aerial breathing. Dipnoi (Lungfishes) : true lungs present, highly vascular, functional in air respiration. Lepidosiren and Protopterus survive dry season by estivating and breathing via lungs. Actinopterygii (ray-finned fishes) : Primitive forms like Lepisosteus and Amia have vascularized swim bladders functioning like lungs. Advanced teleosts : swim bladder specialized for buoyancy, not respiration.

7. (B) Amphibians First true tetrapods with functional lungs. Lungs are simple, sac-like , with internal folds to increase surface area. Amphibians still rely heavily on cutaneous respiration , especially in moist environments.

8. (C) Reptiles Lungs are more compartmentalized with septa and alveoli, allowing greater efficiency. Cutaneous respiration reduced. Example: Snakes and lizards show variation — in some snakes, only one lung is functional.

9. (D) Birds Highly specialized respiratory system. Lungs are small, compact, rigid , connected to extensive air sacs . Unidirectional airflow through parabronchi ensures continuous oxygen supply — an adaptation for flight and high metabolism.

10. (E) Mammals Lungs are spongy, elastic, alveolar organs . Millions of alveoli provide enormous surface area for gas exchange. Ventilation aided by diaphragm and rib movements. Represents the most advanced stage in lung evolution.

11. 6. Comparative Summary Group Lung/Related Organ Structure Efficiency Fishes Swim bladder / lungs Simple sacs Low Amphibians Paired lungs + skin Sac-like with folds Moderate Reptiles Septate lungs More chambers Higher Birds Lungs + air sacs Parabronchi, unidirectional flow Very high Mammals Alveolar lungs Alveoli + diaphragm Highest

12. Evolutionary Significance Lungs were critical for the water-to-land transition . Allowed vertebrates to exploit terrestrial niches. Evolution shows a trend from simple sac-like structures → highly compartmentalized, efficient organs .

13. Conclusion Lungs and swim bladders share a common evolutionary origin. Primitive fishes developed lung-like organs under low oxygen conditions. Through phylogeny, lungs became increasingly complex, supporting the diversification of vertebrates into amphibians, reptiles, birds, and mammals. The evolution of lungs represents a key innovation in vertebrate history, enabling conquest of land and air.

14. Thank you