214 



Tn poPHYSIS AND rxONADOTROPHIC HORMONES 



' A 



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lri"«X 



cm 



Fi(i.3.25. l^lcriron microjir.'il'ii sliowin^ a jionioii ot an aci(loi>iul irom rhc a(lonohy]loplly^ 

 of a rat. Part of the nucleus (AO is present above and a segment of the cell membrane (cw) 

 crosses the field below. A few dense ovoid secretory granules {gr) are scattereti throughout the 

 field. Several mitochorndia (w) are also seen. They show double-layered limiting membranes 

 and internal crests {cr) or "cristae mitochondriales" of Palade (1952) which are characteristic 

 features of all mitochondria. 



The endoplasmic reticulum (er) is seen in the lower portion of the cell. This cytoplasmic 

 component occurs here in the form of parallel rows of long, membrane-limited sacs. When 

 reconstructed in three dimensions the sacs are continuous with one another at the ends, and 

 the membranes thus enclose a broad flat cavity. These appearances represent just one or- 

 ganizational variant of this highly complicated system (Palade and Porter, 1954). 



A number of tiny dense particles {hji) (ca. lOOA) are distributed throughout the cytoplasm, 

 but are porticularly concentrated along the membrane surfaces of the endoplasmic reticulum. 

 These particles are generally considered to be the site of localization of cytoplasmic ribonu- 

 cleoprotein (Palade, 1955). 



Components of the Golgi apparatus can also ])<> identified in tlic cytoplasm. In electron 

 micrographs the Golgi "complex" may be resohed into 3 coniiionents: relatively empty- 

 ajipearing vacuoles (t'oc) of varying sizes (Dalton and Felix. 1954; Sjiistrand and Hanzon, 

 1954; Farquhar, 1956); paired membranes (Gm) (ca. 7 m^ each) (Palade, 1952) ; small gran- 

 ules or vesicles (Gu) (ca. 40 m^) (Palade and Porter, 1954). X 31,500. 



