Lysosomes

 Lysosomes

Def: >>-The digestive system of the cell >>-Formed at mature surface of G.A >>-Contain about 40 different hydrolytic enz. [phospholipases, proteases, nucleases,….] >>-Numerous in phagocytic cells [WBCs] 

L.M: -Not stained by H & E -Stained by special histochemical stain [acid phosphates] for enzymes inside 

E.M: -Electron-dense appearance -2 Types are distinguished

1ry lysosomes: -Newly formed -Small homogenous vesicles

2ry lysosomes: -Fusion of 1ry Lysosomes + intracellular macromolecules >>-Heterogeneous vesicles

Types of Secondary lysosomes: >>1-Heterolysosomes: Fusion of 1ry lysosome + Phagosome containing solid food or bacteria >>2-Multivesicular bodies: Fusion of 1ry lysosome + Pinocytic vesicle containing fluid droplets >>3-Autolysosomes: Fusion of 1ry lysosome + autophagic vacuole containing destroyed old organelles [as dead mitochondria, rER, …..], the process is called Autophagy >>4-Residual bodies: 2ry lysosomes containing indigestible remnants

Fate of Residual Bodies: >>1-Exocytosis of their content [Cytostool] >>2-Converted to lipofuscin pigment in long-lived cells [Heart muscles, neurones,……]

Important Notes Cytosolic components are protected from lysosomal enzymes by: >>1-The membrane surrounding lysosomes >>2-The pH of cytosol (~7.2) which is not optimal for enzymes activity

 The optimum pH for enz. activity is (~5.0). So, leakage of lysosomal enzymes isn’t harmful to the cell

Functions of Lysosomes n Digestion of: >>1-Nutrients in cytoplasm >>2-Solid particle (phagocytic vesicles): bacteria & viruses → Immune function >>3-Fluid droplets (Pinocytic vesicles) >>4-Old organelles >>5-Dead cells (autolysis after death)