6 topics with concise breakdowns: definitions, key facts, and class questions.
The cell is the elemental structural unit of living matter, but the human body does not consist exclusively of cells. In this section, we examine the fundamentals of cytology and the tenets of the cell theory, as well as the morphology of non-cellular structures (symplasts, syncytia, and extracellular matrix), which are essential for understanding tissue organization.
Special attention is paid to the cell boundary — the plasmalemma. You will study the molecular structure and functions of cell membranes, mechanisms of substance transport (passive, active, vesicular), and specialized structures of the apical surface (microvilli, stereocilia, cilia).
What is most frequently asked in class? Instructors love to focus on the classification and structure of intercellular junctions (tight junctions, adhesion junctions, desmosomes, gap junctions). Colloquia will also invariably feature questions on how the fluid mosaic model of the membrane ensures its selective permeability and receptor function.
Can isolated organelles function as independent organisms?
No. According to cell theory, isolated organelles (nucleus, mitochondria) cannot independently maintain homeostasis. The minimal structure possessing all attributes of life is only an intact cell.
Why are erythrocytes not considered true cells?
In histology, mature erythrocytes are classified as post-cellular structures because they have adapted to gas transport by completely losing their nucleus and most organelles.
What structures form the resting potential?
The generation of the resting potential involves the sodium-potassium pump (actively exchanging $Na^+$ for $K^+$) and potassium channels, which provide partial efflux of $K^+$ down its gradient.
What is the difference between simple and facilitated diffusion?
Simple diffusion occurs directly through the lipid bilayer of the membrane, whereas facilitated diffusion requires the participation of specialized carrier proteins (translocases). Both processes occur down the concentration gradient without ATP expenditure.
What is the main difference between a desmosome and an adherens junction?
The differences lie in their shape and molecular composition. A desmosome is a punctate "spot" with desmoplakins and intermediate filaments, whereas an adherens junction is a continuous ribbon around the cell with vinculin and actin filaments.
What is the difference between villi and microvilli?
Villi are projections of the entire mucosa (tissue level), whereas microvilli are tiny cytoplasmic protrusions of a single individual epithelial cell (cellular level).
Master the entire topic in the "Histology" course
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