L5 The Nucleus Histo (1) PDF

# Faculty of Medicine, Delta University for Science and Technology ## Level 1, Semester 1 - Module (Basic science) ## The Nucleus - Contact: Prof. Dr. Samar Asker - Department: Histology - Official email: [email protected] - Academic hours: - AM: 00:00-00:00 - AM: 00:00-00:00 -...

# Faculty of Medicine, Delta University for Science and Technology ## Level 1, Semester 1 - Module (Basic science) ## The Nucleus - Contact: Prof. Dr. Samar Asker - Department: Histology - Official email: [email protected] - Academic hours: - AM: 00:00-00:00 - AM: 00:00-00:00 - AM: 00:00-00:00 ## Learning Outcomes By the end of the lecture, the students will be able to: 1. Identify the histological structure of the nucleus. 2. Recognize the functional significance of the nucleus. 3. Correlate the structure of the nucleus with its function. ## LM - **Shape:** Rounded, oval, flattened, rod-shaped, horseshoe-shaped, kidney-shaped, bilobed, segmented or lobulated. - **Position:** The nucleus tends to occupy the widest part of the cell. It may be central, eccentric or basal. - **Staining:** The nucleus is basophilic, it stains blue with haematoxylin. Its basophilia is due to its content of nucleic acids. ## Appearance - **Vesicular (or Open-face) nuclei:** - Pale-stained nuclei. - Details of their components could be seen. - Active cells as nuclei of nerve cells and liver cells. - **Condensed (or deeply stained) nuclei:** - They are deeply basophilic nuclei. - No details could be seen inside. - In metabolically inactive cells e.g. nuclei of small lymphocytes. ## EM <start_of_image> magnification 1- Nuclear membrane (nuclear envelope). 2- Chromatin. 3- Nucleolus. 4- Nuclear sap. ## Nuclear membrane (nuclear envelope). - Encloses the nucleus and separates it from the surrounding cytoplasm. - **LM:** Single basophilic due to the presence of peripheral chromatin on its inner surface and the ribosomes on its outer surface. - **EM:** Double walled membrane separated by a perinuclear space. - Nuclear pores are present at intervals where the two layers are fused together and they are covered by diaphragm to allow substances to pass from and to the nucleus. ## Nuclear Chromatin Consists of DNA + Nucleoprotein & forms chromosomes of the cell. **LM:** Basophilic granules called chromatin granules. The basophilia is due to the phosphoric acid component of the nucleic acid. **Two types of chromatin according to activity:** | Structure | The condensed chromatin: Heterochromatin = inactive chromatin | The Extended Chromatin: Euchromatin = Active Chromatin | | ----------------- | ----------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------- | | LM. | Fine or coarse basophilic granules | Not visible (It appears as clear areas) | | EM. | electron-dense granules | Only with high magnification | | Activity | Contains inactive genes i.e. they do not direct protein synthesis. | The genes are active i.e. they direct protein synthesis. | | Distribution | It is distributed within the nucleus as: -Peripheral Chromatin: adherent to the inner nuclear membrane. -Nucleolus-Associated Chromatin: aggregated around the nucleolus. -Chromatin islands: aggregated as clumps of chromatin granules in the nuclear sap. | It occupies the more central region of the nucleus. | ## <start_of_image> - Nucleolus One or more dark basophilic bodies present in the nuclei. The number varies according to nucleus activity. The nucleolus is not surrounded by a membrane. Staining Nucleoli are basophilic due to: - The surrounding nucleolar associated chromatin. - Its ribonucleic acid (RNA) content. ## EM - The light material: spaces filled with nuclear sap. - The dark material is composed of: - Fibrillar center: five pairs of satellite chromosomes (DNA) site of rRNA transcription. - Pars fibrosa: fine filaments represents newly formed rRNA strands. - Pars granulosa: (rRNA) conjugated with protein = ribosome subunits in various stages of formation. ## Function of the Nucleus - Cell division as it contains the chromosomes which carry the genetic information. - Control the vital processes within the cell, as protein formation. - It forms the different types of RNA (mRNA, rRNA & tRNA). ## It’s MCQ Time 1. Which one of the following statements describe the nucleolus? a) It is the site of complete ribosomal assembly and maturation. b) It is of uniform size and number in different cells. c) It contains an organizer composed of DNA. d) It synthesizes the ribosomal protein. 2. Why the Vesicular nuclei are more active than condensed ones? a) They contain more nuclear sap. b) They are larger in size. c) They have more amount of extended chromatin. d) Their nuclear envelope has more numerous nuclear pores. 3. Which of the following causes the basophilia of the nuclear membrane? a) Nucleolus associated chromatins. b) Peripheral chromatin. c) Chromatin island. d) The ribosomes attached to inner surface. ## Practical **Vesicular (open-face) nucleus** - Image of a microscopic slide showing a nucleus with multiple nucleoli and dispersed chromatin. **Nuclear membrane** - Image of a transmission electron microscope (TEM) image of a nuclear membrane. - The image shows two layers of membrane separated by a perinuclear space. - It also highlights small pores within the membrane. **Euchromatic nucleus** - Image of a TEM image of a nucleus. - The image shows the nucleus membrane and nucleolus, and dispersed chromatin. **A nucleus showing chromatin distribution** - Image of a TEM image of a nucleus. - The image shows the nucleus membrane and nucleolus, and three different types of chromatin: peripheral chromatin, nucleolus-associated chromatin and chromatin islands. ## References - Ross MH &Pawlina W. (2011). *Histology. A Text and Atlas*. - Junqueira LC and Carneiro J. (2003). *Basic Histology. A Text and Atlas*. - https://youtu.be/Nh53tsrxr7g ## Thank You