Qu'est-ce que la cytologie?

• Cytology is the study of cells.

General Information

• All living things are made up of units called cells, invisible to the naked eye.
• The cell is the smallest fundamental, structural, and functional unit of a living organism.
• Cells can nourish themselves, grow, develop and reproduce.
• Organisms can be composed of unicellular or multicellular cells.
• Unicellular organisms, such as amoebas, are living beings made up of a single cell.
• Multicellular organisms, such as animals and plants, are living things made up of several cells.

The Eukaryotic Cell

• A eukaryotic cell is one that has a true nucleus, limited by a nuclear envelope containing genetic material in the form of DNA.
• It contains a highly structured cytoplasm containing many specific organelles.
• It is limited by a plasma membrane which separates it from the external environment, and which limits the cytoplasm.

Morphological Specificities of Eukaryotic Cells

• Eukaryotic cells have different shapes and sizes, even within the same organism.
• They can be free, like erythrocytes, or associated in tissues.
• Intestinal, gastric, and hepatic cells are between 30 and 50µm in size.

Components of Eukaryotic Cells

• The eukaryotic cell is delimited by a plasma membrane and contains a nucleus and cytoplasmic organelles.
• Protoplasm represents the content of a living cell including the nucleus and cytoplasm (grouping the hyaloplasm and the organelles).
• Hyaloplasm is a transparent structure, which supports the organelles. It includes the cytosol and the cytoskeleton.
• The cytosol is a solution rich in water, proteins, sugars and ions, it has a homogeneous and transparent appearance.

Plasma Membrane

• The plasma membrane is made up of a double lipid layer, proteins and carbohydrates, and constitutes a selective fluid barrier, while at the same time being waterproof, isolating the cell from the external environment.

The Nucleus

• The nucleus is the most visible organelle under the microscope, more or less rounded and delimited by a double envelope called the nuclear envelope. It contains most of the cell's genetic material (DNA).

Endoplasmic Reticulum

• The endoplasmic reticulum is a membrane system composed of flattened cavities communicating with each other and sometimes carrying ribosomes.
• The rough endoplasmic reticulum is characterized by the presence of ribosomes, attached to the external face of the reticular membrane.
• The smooth endoplasmic reticulum has no ribosomes on its surface.
• The two types perform several physiological functions such as the synthesis of proteins and lipids, the detoxification of drugs, and the storage of calcium.

Golgi Apparatus

• The Golgi apparatus is a membrane system formed by a stack of flattened saccules.
• By receiving vesicles from the rough endoplasmic reticulum containing proteins, it modifies its structure by adding carbohydrates (for example N-glycosylation), thus playing an essential role in protein synthesis.

The Cytoskeleton

• The cytoskeleton is a network composed of 3 types of protein fibers: microtubules, intermediate filaments and actin microfilaments. All three play fundamental roles in the structure and movement of the cell and its organelles.

Lysosomes

• Lysosomes are organelles limited by a membrane and containing enzymes necessary for cellular digestion.

Peroxisomes

• Peroxisomes are more or less spherical organelles whose role is cellular detoxification.

Mitochondria

• The mitochondrion is a rod-shaped organelle, delimited by two membranes, one external and smooth and the other internal forming crests. In addition to the fact that it contains mitochondrial DNA, it plays an essential role in the production of ATP.