Introduction to Histology and Cytology

Flashcards covering the fundamentals of cytology, the structural components of the cell, and the detailed molecular structure and function of the plasma membrane.

Histology

The branch of science focused on explaining and clarifying the histological structure of cells, their origin, reproduction methods, functional behavior, and the interrelationships between them.

Cytology

The study of cells, focused on looking at, understanding, and interpreting cellular structures.

Prokaryotic cells

Cells that lack a nucleus or membrane-bound organelles, such as bacteria.

Eukaryotic cells

Cells that contain a nucleus and membrane-bound organelles, such as animal cells.

Cell

A mass of protoplasm surrounded by a membrane and containing a nucleus and organelles; it is considered the fundamental unit of life.

Plasmalemma

Another name for the Cell (Plasma) Membrane.

L.M. Appearance of Cell Membrane

The membrane cannot be seen directly under a light microscope but can be inferred due to the deposition of dyes.

E.M. Appearance of Cell Membrane

Appears as two electron-dense bands separated by one electron-lucent band, forming a trilaminar membrane or unit membrane.

Unit Membrane Thickness

$$7.5\,nm$$

Cell Membrane Composition (Lipids)

Comprise $35\%$ of the molecular structure, specifically phospholipids and cholesterol.

Cell Membrane Composition (Proteins)

Comprise $60\%$ of the molecular structure.

Cell Membrane Composition (Carbohydrates)

Comprise $5\%$ of the molecular structure.

Integral proteins

Proteins strongly embedded within the lipid bilayer that are difficult to remove without detergents, including transmembrane proteins like ion channels.

Peripheral proteins

Proteins loosely attached to the lipid bilayer that can be extracted by changing the pH or mixing with salt solutions.

Glycocalyx

Also known as the cell coat; it is formed by oligosaccharides in the form of glycoproteins and glycolipids projecting on the outer cell surface.

PAS

A stain used to identify the glycocalyx or cell coat.

Fluid mosaic model

A model describing the cell membrane where the bilayer is fluid at body temperature, allowing lipid molecules and other components to move, rotate, and exchange places.

Passive diffusion

Movement of substances across the cell membrane that needs no energy, including simple diffusion (e.g., $O_2$, $CO_2$) and osmosis (e.g., water).

Active transport

Energy-requiring movement of substances like fatty acids, amino acids, and ions across the membrane.

Na and K pump

An active transport mechanism that moves $3\,Na$ to the outside and $2\,K$ to the inside while consuming $1\,ATP$ molecule.

Facilitated diffusion

The movement of substances like sugar through water-filled protein pores.

Selective transport

Transport involving cell receptors where specific substances like drugs, bacteria, or hormones only affect target cells.

Endocytosis

The process of bringing substances into the cell, categorized into pinocytosis (cell drinking) and phagocytosis (cell eating).

Exocytosis

The process of moving substances out of the cell.

Cell junctions

Structures that regulate cell-to-cell interaction.