Cytology Overview by Dr. Esam El-Shwihy

Study Notes

Cytology is the study of cells, which are the fundamental units of structure and function in organisms.
Cells consist of a cell membrane (plasmalemma) and protoplasm, which includes cytoplasm and nucleus.

Cell Membrane Functions:
- Maintains cell integrity
- Controls substance exchange (selective permeability)
- Recognizes antigens and foreign cells
Protoplasm Components:
- Cytoplasm: Contains cytosol, organelles, and inclusions
  - Cytosol: Semifluid matrix
  - Organelles: Active structures crucial for cell function
  - Inclusions: Nutrient storage, not essential for life
- Nucleus Components:
  - Nuclear envelope, nucleolus, chromatin, nuclear matrix

Light Microscope:
- Ordinary stains highlight cell features (e.g., hematoxylin for basophilia, eosin for acidophilia).
Electron Microscope:
- Provides greater detail; distinguishes electron-dense (dark) and electron-light (lucent) structures.

Molecular Structure:
- Fluid-mosaic model includes phospholipid bilayer, cholesterol, and proteins
Phospholipids:
- Form double layers with polar (hydrophilic) heads and non-polar (hydrophobic) tails.
Membrane Proteins:
- Integral Proteins: Embedded in the lipid bilayer
- Peripheral Proteins: Associate with the bilayer's surface

Passive Transport:
- Moves substances based on concentration gradient without energy
Active Transport:
- Moves substances against concentration gradient; requires energy (e.g., sodium-potassium pump)
Vesicle-Mediated Transport:
- Endocytosis:
  - Cell intake of substances (e.g., phagocytosis for solids, pinocytosis for fluids)
- Exocytosis:
  - Release of substances from the cell

Membranous organelles crucial for energy production
Found in all cells except mature red blood cells
Composed of:
- Outer Membrane: Smooth, no selective permeability
- Inner Membrane: Folded into cristae; site of ATP production via oxidative phosphorylation
- Matrix: Contains enzymes, ribosomes, RNA, DNA, and Ca²⁺ ions.
Functions:
- ATP synthesis
- Calcium regulation and detoxification

Non-membranous organelles key for protein synthesis
Present in all cells except mature erythrocytes
Types:
- Free Ribosomes: Scattered in cytoplasm, synthesize internal proteins
- Attached Ribosomes: Bound to rough endoplasmic reticulum (rER), synthesize secretory proteins
Structure contains rRNA and proteins; visible only under EM as small particles.

Two types:
- Smooth ER (sER): Lacks ribosomes, involved in lipid synthesis, detoxification, and calcium regulation
- Rough ER (rER): Studded with ribosomes; synthesizes secretory and membrane proteins
Continuous network essential for cellular functions.

Membranous organelle involved in protein processing
Consists of stacks of flattened cisternae
Functions include:
- Protein modification (glycosylation, sulfation)
- Concentrating and packaging proteins and lysosomes
- Membrane recycling with the plasma membrane

Membranous organelles containing hydrolytic enzymes
Classified into:
- Primary Lysosomes: Newly formed, homogeneous contents
- Secondary Lysosomes: Heterogeneous contents formed from fusion with vesicles (e.g., phagosomes, autophagosomes)
Act as intracellular digestive systems; release contents via exocytosis.