Cytology 2 l General Histology & Biology MCQ for dental students

Cytology 2 (Cell membrane structure) l General Histology & Biology MCQ (multiple choice question) for dental students 

 

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NUCLEUS

DEF:

• rounded or elongated structure found in all cells and controls all cellular metabolic activities and plays important role in cell division and heredity

 

SITE:

• it is present in all cells except mature RBCs and blood platelets

 

NUMBER

• Mononucleated: 1 nucleus ,e.g. most of body cells
• Binucleated : 2 nuclei ,e.g. liver cells and top cells transitional epithelium
• Multinucleated : > 2 nuclei ,e.g. osteoclast and skeletal muscle fibers

SIZE:

• small , medium sized or large .

 

SHAPE:

• the shape of nucleus differs in the different types of cells
• may be rounded, oval, flattened, kidney shaped, bilobed, segmented or lobulated.

POSITION

• the nucleus usually occupies the widest part of the cell
• it may be central , eccentric , peripherally or basal

 

nuclear membrane (nuclear envelope)

DEF:

• the membrane which encloses the nucleus and separates it from the surrounding cytoplasm

LM:

• Appears as a single basophilic line surrounding the nucleus.
• basophilia due to ribosome outside & chromatin inside  

EM:

• Formed of two membranes :
• inner & outer nuclear membranes separated by perinuclear space (25mm wide)

   The outer membrane is continuous with the membranes of rER & has attached ribosomes.
   The inner membrane has chromatin granules attached to its inner surface.

• The nuclear envelope is interrupted by many nuclear pores
• Each covered by a diaphragm → regulates the exchange of molecules between nucleus & cytoplasm.

FUNCTION:

1. Separates the nucleus from the surrounding cytoplasm.
2. Allows the exchange of materials between the nucleus and the surrounding cytoplasm through the nuclear pores

nuclear sap

Def

• is a semifluid colloidal clear solution in which chromatin and nucleoli are suspended

L/M

• appears as clear or empty areas in the nucleus .

E/M

1. Appears electron lucent
2. Vesicular nucleus : large amount of nuclear sap                                                      
3. Condensed nucleus : contains small amount of nuclear sap
4. Function : act as medium through which RNA moves towards the nuclear pores

 

Nuclear changes indicating cell death:

1-pyknosis:

• the nucleus becomes  homogenous, smaller in size, darker in staining and eccentric in position.

2- Karyorrhexis:

• the nucleus is broken into small fragments.

3- Karyolysis:

• the nucleus dissolves and finally disappears

Cell cycle

Definition  :

• The cell cycle is the series of events that take place in a cell leading to its division and duplication of its DNA (DNA replication) to produce two daughter cells , It includes interphase & Cell division

Types :

1. Amitosis (direct division):_

• in lower animals like amoeba.                                                    
• Simple fission of nucleus & cytoplasm into two daughter cells.

2. Mitosis (indirect cell division): 

• in somatic cells.
• Gives two daughter cells, each has the same diploid No. of chromosomes

3. Meiosis (reduction cell division):_

• In gem cells of testis & ovary.
• Gives four cells, each has half number of chromosomes  (haploid number)