L3: Nucleus Flashcards
What is the nucleus?
It is a rounded or elongated structure which is responsible for all the cellular activities and plays an important role in cell division and hereditary.
what is the site of the nucleus?
It is found in nearly all cells except RBCs and blood platelets.
what is the number of nuclei?
mono: In most of the body cells.
bi: in liver cells and the top cells of the transitional layer of epithelium
multi: in cells like osteoclast and skeletal muscle fibres
what is the size of the nucleus?
It may be small, medium-sized, or large. It may reach 25 um like in the ovum and some ganglion cells
what is the shape of the nucleus?
it differs according to the type of the cell as it may be rounded, elongated, rod-shaped, bent rod, bilobed, segmented, kidney shaped.
what is the position of the nucleus?
it occupies the widest area of the cell and it may be central, eccentric, peripheral, or basal.
how does the nucleus appear under LM?
-it appears as a basophilic structure due to its content of nucleic acids.
-appears in two shapes: vesicular (open face) or condensed
Describe the vesicular (open face) nucleus
-lightly stained
-its content can be seen
-in highly metabolic cells like liver and nerve cells
Describe the condensed nucleus
-Heavily stained
-Its details cant be identified
-in low metabolic cells like small lymphocytes
How does the nucleus appear under EM?
consists of 4 parts:-
nucleolus
chromatin
nuclear sap
nuclear membrane
what is the nuclear envelope?
It is a double membraned membrane that surrounds the nucleus and separates it from the cytoplasm.
how is the nuclear membrane seen under LM?
-It is seen as a monolayer membrane as it is basophilic due to the chromatin associated with it.
how is the nuclear membrane seen under EM?
-It is seen as a double membranes membrane that consists of inner and outer layers and is interrupted by nuclear pores.
what is the function of the nuclear envelope?
- it separates the nucleus from the cytoplasm
-it allows the passage of certain substances in and out of the nucleus.
what is chromatin?
it is a basophilic material from which chromosomes are formed.
what is the structure of chromatin?
it is formed of nucleoprotein
what are the types of chromatin?
-extended chromatin and condensed chromatin
extended chromatin
(structure-activity-function-LM-EM-distribution)
-Extended parts of chromosomal threads.
-Carries active genes.
-Directs protein synthesis.
-Appears as clear areas (too thin to be seen).
-Could be seen with high magnification and appears as shades of grey.
-Occupies the more central regions of the nucleus.
condensed chromatin
(structure-activity-function-LM-EM-distribution)
-Coiled parts of chromosomal threads
-Carries inactive genes
-Doesn’t direct protein synthesis
-Fine or coarse basophilic chromatin granules
-Appears as electron-dense granules
-Peripheral chromatin, Nucleolus associated chromatin. and Chromatin islands.
what is the nucleolus?
one or more rounded basophilic bodies present in the interphase nuclei.
How is the nucleolus seen under LM?
-its size may reach up to 1um and it is mostly present in protein synthesizing cells.
-not surrounded by a membrane.
-It is basophilic as it contains RNA and chromatin attached to it
what is the function of the nucleolus?
- Synthesis of ribosomal RNA (rRNA).
- rRNA is conjugated with protein and migrates through the nuclear pores to reach the cytoplasm as ribosome subunits.
what are the nuclear changes indicating the death of the cell?
- Pyknosis: the nucleus becomes homogenous, smaller in size, darker in staining, and eccentric in position.
- Karyorrhexis: the nucleus is broken into small fragments.
- Karyolysis: the nucleus dissolves and finally disappears.
