metamorphosis in amphibians (frog ) by iqra aslam

2. BY :-
IQRAASLAM
Bs zoology 5th

3. METAMORPHOSIS
 the process of transformation
 immature adult form
 two or more distinct stages.
 In an insect or amphibian

4. AMPHIBIAN METAMORPHOSIS
 amphi ("double") and bios ("life")
 aquatic terrestrial existence
 urodeles (salamanders)
 resorption of the tail fin
 destruction of the external gills
 skin structure

5. continue

6. Morphological changes
1. GROWTH OF NEW STRUCTURES
2. CELL DEATH
3. REMODELING
4. BIOCHEMICAL RESPECIFICATION

7. Conti…..
1.GROWTH OF NEW STRUCTURES
 limbs emerge
 nictitating membranes and eyelids
 Lateral eyes front eyes
 New neurons spinal cord
 Ephrin B cause ipsilateral

8. Eye migration and associated neuronal changes during metamorphosis
of the Xenopus laevis tadpole

9. 2. CELL DEATH
 the paddle-like tail
 Recent evidence ,
 Apoptosis …….. caspase-9
 Phagocytosis ……. Proteases
 Gills
 red blood cells

Shape of cells & hemoglobin

10. 3. REMODELING
 larval intestine ….. shorter
 Schrieber experiment
 metalloproteinase stromelysin-3

11. Conti…….
 optic nerve pathway
 motor neurons , tadpole jaw
 lateral line system degenerates
 ear differenciations …a brief period of deafness

12.  SKULL
 tadpole skull is primarily
neural crest-derived
cartilage……..
 adult skull is primarily
neural crest-derived bone

13. Changes in the Xenopus skull during metamorphosis.

14. 4.BIOCHEMICAL RESPECIFICATION
 Liver
 synthesize the enzymes
 Ammonotelic……. ureotelic

15. Hormonal control
 1912 by Gudernatsch
 fed powdered horse thyroid glands
 Allen (1916
 destroyed the thyroid
 threshold model
low concentration ……..development of limbs
increasing amounts ….. resorption of the tail

16. Metabolism of (T4) and
(T3).

17.  Hormone receptor
 (TRa)………….. all tissues , before thyroid gland
 (TRB)…………. activated by thyroid hormones.

18.  Stages of metamorphosis
1.premetamorphosis
 CRH….. (TSH), …..T4…… low amounts of T3.
 High levels of deiodinase II before secretion of t4….T3
 limb rudiments

19.  Metamorphic climax stage
 concentration of T4 rises
 TRB levels peak inside the cells
 deiodinase II is expressed as tail resorption, gill
resorption, and intestinal remodeling

20. Regionally specific developmental programs

21. Thank you