5/28/25 Cytology

Cytology Review

Objectives

• Summarize general cell organization, composition, & structure.
• Describe functions of typical cellular components: membrane, cytoplasm, nucleus, & intracellular organelles.
• Organelles: Endoplasmic reticulum (ER; smooth/rough), golgi apparatus (GA), lysosomes, secretory vesicles, peroxisomes, mitochondria, cytoskeleton (filaments & tubular structures).

Why is Review Important?

• Knowledge of cellular biology supports PT understanding of how the body (especially nerve & muscle fibers) functions & the underlying pathophysiology of disorders (most disease processes initiate at the cellular level).
• Factors (disease, meds, age, environmental exposures, etc.) impact cellular replication & function = impact on overall health

"Typical Cell" Organization

• 3 major components:
  • Cell membrane
  • Cytoplasm (organelles)
  • Nucleus with nuclear membrane

"Typical Cell" Composition: (Varies depending on cell type)

• Water: 75\%
• Proteins: 20\%
  • Structural & functional
• Lipids: 2\%
• Carbohydrates: 1\%
• Ions: <1\%
• Nucleic acids: <1\%
  • DNA
  • RNA

Cell Structure

• Intracellular organelles
  • Highly organized physical structures critical for cell function
• Most organelles have their own membranes:
  • Nucleus, endoplasmic reticulum (ER), mitochondria, lysosomes, golgi apparatus (GA)

Review: Components of the "Typical Cell"

Cell Membrane: Overview

• Semipermeable – helps regulate what comes in/out of the cell
• Receptors for hormones and biologically active substances
• Participates in muscle & nerve cell electrical events
• Aids in cell growth and proliferation

Cell Membrane: Lipid Barrier

• Lipid molecules form a phospholipid bilayer
  • Inner – hydrophobic; outer – hydrophilic
  • ~100\% lipids & proteins
• Dynamic, fluid system: thin, pliable structures
• Function: Impedes penetration of water-soluble substances

Cell Membrane Lipid Barrier: Large Glycoproteins

• Two Types: integral & peripheral
  1. Integral
     • Transmembrane
     • Channels: Ions, H2O/H2O soluble, etc.
     • Carrier proteins: active transport
     • Serve as receptor/ligand channels & activate intercellular proteins
     • G protein-coupled receptors

Movement Across the Cell Membrane

• Diffusion – simple
  • Molecule must be lipid soluble or must move through a protein channel
  • Facilitated
    • Specific to size, shape, charge of ion/molecule
  • Channels may be gated
• Active transport - requires energy (carrier proteins)
  • Most common: Na^+/K^+ pump (more in muscle & nerve!)

Movement Across the Cell Membrane

• Ion Channels
  • Mechanically-gated: open in response to deformation of membrane surface
  • Temperature-gated: open in response to heat or cold
  • Ligand-gated: open in response to chemical messenger attaching to receptor (Ligand – chemical messenger released by 1 cell to itself or to another cell)
  • Voltage-gated: open in response to change in membrane potential
  • G-protein coupled receptors: ligand binding activates G-protein complex, activates/inhibits cellular proteins = slower, longer lasting, modulatory action
    • Often a target for meds

Cell Membrane Lipid Barrier: Large Glycoproteins

2. Peripheral
   • Often attached to integral proteins
   • Not transmembrane
   • Attachment points for cytoskeletal structures
   • Act as enzymes or controllers of transportation thru the membrane

Cell Membrane Lipid Barrier: Glycocalyx

• Loose carbohydrate (glycoproteins, glycolipids, & proteoglycans) coating (fuzzy) on the outside surface of cells
• Functions:
  • Negative charge, repels other (-) charged surrounding cells
  • Cell-to-cell recognition & adhesion
  • May act as receptor substances, binding hormones (e.g., insulin)
  • Functions in immune response - recognizes antigens & antibodies

Cell Membrane: Key Points

• Semipermeable
  • Small, lipid-soluble, nonpolar molecules can pass freely through the cell membrane
• Transmembrane glycoproteins cross the membrane
  • Significant role in movement of ions & molecules across the cell membrane
• Peripheral glycoproteins do not extend into lipid bilayer
  • Role in intracellular messaging & cytoskeleton
• Glycocalyx
  • Repel/bind cells together, receptors for hormones, recognize antigens/antibodies

Cytoplasm

• Contains organelles (little organs), inclusions, & cytoskeleton
• Organelles are distinct structures
  • Membrane systems of the cell - metabolism, energy requiring, energy generating
  • Nonmembranous structural components
• Inclusions - storage components in cytoplasm
  • May/may not be surrounded by a membrane
• Cytosol = jelly-like fluid portion of cytoplasm

Nucleus

• Control center
• Cell grow & maturity
• Cell replicate (mitosis)
• Die (apoptosis)
• Largest membrane bound structure in the cell
• Large amount of DNA, which comprise the genes
• Genes determine cell proteins, intercellular enzymes, & cytoplasmic & nuclear activities
• Inheritance – information from generation to generation

Nucleus

• Nuclear membrane = nuclear envelope
  • Large pores
• Nucleolus – Non-membranous; simple accumulation of large amounts of RNA & proteins as found in ribosomes
• RNA transported through the nuclear membrane pores and into the cell cytoplasm to form ribosomes
• Ribosomes – sites of protein synthesis

Transcription/Translation

• Transcription (in the nucleus)
  • Copying genetic sequence (message) - DNA to mRNA
  • mRNA leaves via nuclear pores – into cytoplasm
• Translation (in cytoplasm)
  • Translation of message (mRNA) by ribosomes to synthesize proteins

Intracellular Organelles: Endoplasmic Reticulum (ER)

• Membrane limited
• Processes & transports substances made inside the cell
• Rough (RER) - ribosomes attached
  • Synthesize protein
• Smooth (SER) - synthesizes lipids
  • Provides various enzymes that control glycogen breakdown & detoxify substances that might cause cell damage

Organelles: Golgi Apparatus (GA)

• Membrane limited
• Stacks of thin, flat vesicles/sacs
• Functions in association w/ER
• ER vesicles fuse w/GA
• GA - process & package proteins forming
  • Lysosomes
    • Intercellular digestion
    • Hydrolytic enzymes - proteins to amino acids, glycogen to glucose, lipids to fatty acids
  • Secretory granules
    • Storage containers
    • Transport substances out of the cell

Organelles: Peroxisomes

• Membrane limited
• Similar to lysosomes, but smaller
• Contain oxidases - breakdown poisons
• ~1/2 of alcohol you drink is detoxified by liver peroxisomes
• Self-replication or bud off of SER

Organelles: Mitochondria

• Membrane limited (inner & outer membranes)
• “Powerhouse of the cell”
• Number (self-replicating) & size vary depending on cell energy needs
• Cardiac muscle, skeletal muscle with long-term exercise
• Cristae (infoldings)
• Oxidation of nutrients = ATP, CO2, H2O
• ATP transported into the cell
• ATP: 3 key functions
  1. Transport substances
  2. Synthesis of chemical compounds
  3. Mechanical work (e.g., muscle)

Organelles: Cytoskeleton

• Non-membranous; provides physical structure/support for the cell
• Rigid structure, “tracklike” system that directs organelle movement within the cell (“conveyor belts”)
  • Facilitates endocytosis/exocytosis
• Filaments: cellular movement/contraction, cell locomotion (e.g., white blood cells)
  • Microfilaments – cell structure & support for cell membrane, thin microfilaments involved in muscle contraction (actin)
  • Microtubules - movement, cell elongation & migration, genesis & beating of cilia
  • Centrioles: organized microtubules in dividing cells

Cell Components: Key Points

• Nucleus: Control center, houses DNA
• RER: protein synthesis - ribosomes synthesize protein (translate mRNA into protein)
• SER: synthesizes lipids
• GA: processes & packages proteins
• Mitochondria: powerhouse (generate ATP)
• Cytoskeleton (microtubules & microfilaments): cell structural framework & promotes cell movement