Definition of atresia in English:
 atresia
noun əˈtriːʃəəˈtriːziəəˈtrēZH(ē)ə
mass noun1Medicine 
Absence or abnormal narrowing of an opening or passage in the body.
 Example sentencesExamples
-  The main objective of our study was to identify chromosomal regions possibly containing putative disease loci involved in the etiology of anal atresia.
 -  An X-ray revealed she had a condition called trachea oesophageal fistula and atresia, where the oesophagus and windpipe have not split properly.
 -  The Foundation is of vital importance to Sarah and her family because her youngest daughter, Carol, was diagnosed last year with a rare liver disease called biliary atresia.
 -  Mary has pulmonary atresia, a condition that means the heart and the main blood vessel to the lungs have failed to develop properly.
 -  Cheryl was diagnosed with pulmonary atresia as a baby, and underwent two heart operations when she was six-months-old and five.
 
2Physiology 
The degeneration of those ovarian follicles which do not ovulate during the menstrual cycle.
 Example sentencesExamples
-  The process by which follicles degenerate and disappear is little understood and is termed follicular atresia.
 -  These structures form through a process of follicular atresia accompanied by hypertrophy of the follicular cells.
 -  Furthermore, they may cause premature depletion of the follicle pool by induction of follicular atresia or oocyte apoptosis and, thereby, lead to reduced fertility.
 -  Mammalian females have a fixed number of oocytes at birth, which decreases dramatically with advancing age due to follicular atresia.
 -  This results in atresia of the dominant follicle and re-initiation of follicular recruitment.
 
Origin
  
Early 19th century: from a-1 'without' + Greek trēsis 'perforation' + -ia1.