Histology Lecture (2) Cell Structure (2) PDF

Histology lecture (2) Cell structure (2) Histology Endoplasmic reticulum (ER) Definition Membranous organelle, Formed of a network (reticulum) that extends from the nuclear membrane to the cell membrane. Formed of intercommunicating chann...

Histology lecture (2) Cell structure (2) Histology Endoplasmic reticulum (ER) Definition Membranous organelle, Formed of a network (reticulum) that extends from the nuclear membrane to the cell membrane. Formed of intercommunicating channels called cisternae (reservoirs). Types Rough endoplasmic  The cisternae are covered by ribosomes and polysomes reticulum (RER) → rough or granular surface (RER). Smooth endoplasmic  No attached ribosomes. reticulum (SER) N.B. Both types are continuous with each other. Histology Rough endoplasmic reticulum (RER) Smooth endoplasmic reticulum (SER)  Membranous organelle, concerned with  Endoplasmic reticulum Cisternae with no Definition synthesis of protein, mostly to be secreted attached ribosomes. outside the cell.  It is continuous with RER.  Cells specialized for protein secretion, as:  Cells specialized for lipid biosynthesis, as cells Prominent 1. Fibroblasts (synthesize collagen). of adrenal glands, testis and ovary. in 2. Plasma cells (synthesize antibodies).  Liver cells.  Muscle cells (named sarcoplasmic reticulum). L/M Basophilic due to the attached ribosomes. They are not basophilic  Parallel cisternae continuous with the outer  The cisternae are either tubular or vesicular in nuclear membrane. shape (not flattened).  The cisternae are flattened in shape.  Smooth surface: no attached ribosomes.  Have attached ribosomes & polyribosomes. E/M Histology 1. Segregation of protein synthesized by the 1. Synthesize phospholipids of cell membrane. attached ribosomes. 2. In the liver cells: 2. Initial glycosylation of proteins (addition of  Glycogen metabolism. carbohydrates to the synthesized protein).  Detoxification of certain drugs and toxic substances such as alcohol. 3. In the adrenal glands, testis and ovary: Functions  Lipid biosynthesis (eg synthesis of steroid hormones eg cortisone, male & female hormones). 4. In the muscle cells:  Sarcoplasmic reticulum releases calcium ions during contraction and reuptakes it during relaxation. 1. Transported to the Golgi apparatus for secretion outside the cell. 2. Form primary lysosomes. 3. Form the Integral proteins of cell membrane. Histology Golgi apparatus Definition A membranous organelle, Concerned with secretion of protein which is synthesized by RER. FUNCTIONS 1. Concentration, packaging & storage of protein to be secreted. 2. Glycosylation of proteins: Glycosylation of proteins begins in the RER and is completed in Golgi saccules. 3. Forms primary lysosomes. 4. Synthesis of many glycosaminoglycans (GAGs) that form the extracellular matrix (ECM) of connective tissue. L/M H. & E. Silver  Unstained area near the nucleus  Appears dark brown. (negative Golgi image). Histology E/M  4-10 saccules forming a stack.  Each stack has 2 surfaces: 1. Golgi Cis face Trans face saccules Immature face (convex) Mature face (concave) Receives transfer vesicles Releases secretory vesicles carrying proteins from RER. outside the cell. 2. Transfer  Small, carry proteins from RER to the immature face of Golgi. vesicles  Large, arise from the mature face. 3. Secretory  Either: vesicles a) Secreted outside the cell (exocytosis) OR b) Remain in the cytoplasm as primary lysosomes. Histology Lysosomes DEfiNitioN Membranous organelles which contain about 40 hydrolytic enzymes (acid hydrolases). They are called suicide bags. Acid hydrolases optimal  at acidic pH (~5.0). eg proteases & phosphatases. activity  Synthesized & segregated in the RER. Formation  Transferred to the Golgi apparatus→ primary lysosomes. Site Present in the cytoplasm of all cells. More abundant in cells with great phagocytic activity (macrophages). L/M Enzyme histochemistry: demonstration of acid phosphatase enzyme activity (the marker of Lysosomes). Histology E/M Primary lysosomes Secondary lysosomes Freshly synthesized Start intracytoplasmic digestion. Shape Spherical Irregular Size Small Larger Homogenous moderate electron Heterogenous because of the EM dense granular core. digested materials. Types of 2ry lysosomes Heterolysosomes Multivesicular body Autophagic vacuole Primary lysosomes Primary lysosomes Primary lysosomes phagocytosed solid phagocytosed fluid phagocytosed a dead or foreign particles. particles. worn out cell organelle. Histology Functions 1. The lysosomal enzymes digest phagocytosed particles to simple molecules. 2. The remaining undigested portion is called Residual body:  Residual bodies will be expelled outside the cell by exocytosis.  In some long-lived cells (eg, neurons, cardiac muscle), residual bodies can accumulate over time as Lipofuscin Pigments.