Golgi Apparatus

It is a natural reticular apparatus and is a differentiated portion of the endomembrane system usually found in all animal cells except in mammalian RBC.

Morphology:

The shape of Golgi is quite variable according to functional stages. It occurs as dense reticulum of anastomosing trabeculae or as an irregular fenestrated plaque or as a ring hollow sphere united together. In nerve cells it occurs as a reticulum of wide meshes around the nucleus. It is small in muscle cells and karge in nerve and gland cells. Their number is also variable from single to hundreds per cell.

It has a definite structure consisting of dictyosome units made of three components i.e cisternae, tubules and vesicles. The cisternae or sacciles are similar to the smooth endoplasmic reticulum and appear as stacks of closely spaced membrane delimited sacs. The peripheral regions of cisternae show tubules which branch anastomose to produce the fenestrated system. Small vesicles arise by budding of pinching off the ends of the tubules.

Functions:

• Cell secretion: The secretory materials are concentrated and packed into vesicles and vacuoles which often contain mixture of complexes of components. The secretion may be either continuous, i.e the secretory product is discharged without storage or may be discontinuous i.e first stored in secretory or zymogen granules and are then released out.
• Formation of Lysosome: They are involved in the formation of primary lysosomes. Since most lysosomal enzymes are glycoproteins, Golgi is been implicited in their glycosidation.
• Glycosidation of Lipids and Proteins: It is involved in producing glycolipids and glycoproteins by glycosidation of lipids and proteins.
• Sulfation of Carbohydrates: Carbohydrates and proteoglycans are sulfated in the Golgi complex.
• Functioning of contractile vacuole: It assists in functioning of contractile vacuoles in certain protozoans.
• Formation of acrosome during Spermiogenesis: During the maturation of the sperm the Golgi plays a role in the formation of acrosome. In the early stages the Golgi appears as spherical body comprising cisternae arranged in parallel stacks and numerous small vesicles. As development proceeds the Golgi becomes regular in shape and large vacuoles are formed by dilations of cisternal sacs. In centre of these large granules a dense granule the proacrosomal granule is present. this continues to grow by a process called accretion and approaches the anterior pole of the nuclear membrane constituting the acrosomal granule. It spreads and finally collapses with the nuclear membrane forming the cap material. It becomes acrosome which lies at the apex of the nucleus and apparently comprises some enzymes involved in the process of fertilization.