Histology Lecture 4 PDF

Histology lecture (4) Nucleus & cell inclusions Histology Nucleus Definition Rounded or elongated structure found in all cells. Controls all cellular metabolic activities & plays important role in cell division - he...

Histology lecture (4) Nucleus & cell inclusions Histology Nucleus Definition Rounded or elongated structure found in all cells. Controls all cellular metabolic activities & plays important role in cell division - heredity. Sites It is essential for life, present in all cells except mature RBCs and blood platelets. Number Mononucleated Binucleated Multinucleated One nucleus Two nuclei More than 2 nuclei Liver cells and top cells Osteoclast and skeletal Most of body cells. of transitional epithelium. muscle fibres. Size Small. Medium sized. Large, may reach 25 μm in ovum & some ganglion cells. Histology Shape Rounded Oval Flattened Rod shaped Bent rod Horse shoe shaped Kidney shaped Bilobed Segmented Lobulated. Position The nucleus usually occupies the widest part of the cell. Central Eccentric Peripheral Basal Histology L/M In H&E : nucleus appears basophilic due to its content of nucleic acids. The nucleus may be: Vesicular (open-face) nucleus Condensed nucleus Lightly stained. Deeply stained nucleus. Looks like a vesicle, its details could be Its details could not be identified. identified. Contains a large amount of nuclear sap. Contains a small amount of nuclear sap. In metabolically active cells e.g. nuclei of In metabolically inactive cells e.g. small nerve cells and lymphocyte. E/M Consists of four components: 1. Nuclear membrane (nuclear envelope). 2. Chromatin. 3. Nucleolus. 4. Nuclear sap. Histology 1 Nuclear membrane (nuclear envelope) Def Membrane which encloses nucleus and separates it from cytoplasm. Single basophilic line surrounding the nucleus LM Its basophilia is due to the presence of peripheral surface. Two membranes: A. Outer membrane:  Has many ribosomes on its surface.  Continuous with the membranes of rough endoplasmic reticulum. B. Inner membrane: EM  Has chromatin granules attached to its inner surface (peripheral chromatin).  Supported by nuclear lamina formed of intermediate filament (lamins) The nuclear envelope is interrupted by many nuclear pores. Separates the nucleus from the surrounding cytoplasm. Functions Exchange of materials between the nucleus and the surrounding cytoplasm through the nuclear pores. Hutchinson-Gilford Progeria Syndrome Clinical  Childhood disorder caused by mutation in gene responsible for synthesis point of lamin → children accelerated aging, slow growth and characteristic features. Histology 2 Chromatin Definition Basophilic material from which chromosomes are formed. Structure It is a nucleoprotein, formed of DNA+ Histone protein. Types Euchromatin Heterochromatin Extended chromatin or active Condensed chromatin or inactive Other name chromatin chromatin  Extended parts of chromosomal  Coiled parts of chromosomal Structure threads threads Activity  Carries active genes  Carries inactive genes Function  Directs protein synthesis  Doesn’t direct protein synthesis  Appears as clear areas by (too thin  Fine or coarse basophilic chromatin LM to be seen). granules  Could be seen by with high  Appears as electron dense EM magnification and appears as granules shades of grey  Occupies the more central regions  Peripheral chromatin. Distribution of nucleus.  Nucleolus associated chromatin.  Chromatin islands. Histology 3 Nucleolus Def one or more rounded basophilic bodies present in the interphase nuclei. Size: up to 1μm in diameter, they are prominent in cells actively synthesizing protein. Not surrounded by a membrane LM Staining: basophilic due to 1. The surrounding nucleolar associated chromatin. 2. Its ribonucleic acid (RNA) content. 1. Synthesis of ribosomal RNA (rRNA): The nucleolus is the only part of the nucleus where rRNA is transcribed. 2. The genes that code for rRNA are known as nucleolar genes (Nucleolar Functions organizers) which present on satellite chromosomes (13, 14, 15, 21, 22). 3. r RNA is conjugated with protein and migrates through the nuclear pores to reach the cytoplasm as ribosome subunits. Tumor cells in high-grade malignancies commonly have multiple nucleoli that are larger and more irregular in shape than in normal cells. Clinical point Histology 4 Nuclear sap Definition Semifluid colloidal clear solution in which chromatin and nucleoli are suspended. Nuclear changes indicating cell death Pyknosis  The nucleus is Homogenous, smaller, darker & eccentric. Karyorrhexis  The nucleus is broken into small fragments. Karyolysis  The nucleus dissolves and finally disappears. Histology Cell Inclusions Definition Non-living materials in the cytoplasm. Include 1. Crystals. 2. Stored food : Carbohydrates Lipids Stored in the cell as glycogen granules. Stored as: Site: Liver cells & Muscle fibers. a) Small droplets in liver cells. b) Large globules in CT fat cell. 3. Pigments : colored substances that can be seen in cell without staining. Endogenous pigments Exogenous pigments 1. Hemoglobin. 1. Lipochrome pigments: e.g. carotene. 2. Hemoglobin derivatives e.g. bilirubin. 2. Dust: Small dust particles are continuously 3. Melanin. inhaled and entering respiratory system. 4. Lipofuscin pigment: (golden brown). They are phagocytosed by macrophages in the lung and cause black pigmentation. 3. Minerals. 4. Tattoo marks. Lipofuscin pigment: (goLden brown): Present in cardiac muscle fibers, nerve cells and hepatocytes. Considered as wear and tear pigment or as residual bodies that are not hydrolyzed by lysosomal enzymes. They increase with age.