Cell Biology, Histology & Human Systems – Comprehensive Exam Notes

Lysosomes

  • Membrane-bound, spherical/oval organelles present in eukaryotic cells.
  • Contain a diverse set of acid hydrolase enzymes that function optimally at low pH (≈ 5).
  • Roles
    • Intracellular digestion (“suicide sacs”): break down worn-out organelles, macromolecules, or pathogens taken in by endocytosis.
    • Extracellular digestion: can release enzymes outside the cell (e.g.
      osteoclasts resorbing bone).
    • Important in apoptosis and autophagy.

Microtubules (Cytoskeleton)

  • Long, hollow, tubular polymers made from the protein tubulin (α- and β-subunits).
  • Key functions
    • Structural: scaffold that resists compression; help maintain overall cell shape.
    • Force generation/motility: form the core of cilia and flagella; interact with motor proteins (kinesin, dynein) for vesicle/organelle transport.
    • Spindle apparatus: separate chromosomes during mitosis and meiosis.
    • Organization: emanate from centrosomes/centrioles to define cell polarity.

Cell Division Overview

  • Two fundamental processes that create new cells:
    1. Mitosis → somatic (body) cells.
    2. Meiosis → gametes (sperm or egg; fancy term = gametes).
  • Both start after interphase, during which DNA is replicated.
    • Diploid starting cell = 2N2N (two complete chromosome sets).
    • Humans: 2N=462N = 46 chromosomes (23 maternal + 23 paternal).
    • After S phase replication: still "46 chromosomes" (because sisters are attached at centromere) but 92 chromatids.
  • Helpful acronym for stages: PMAT (Prophase → Metaphase → Anaphase → Telophase) followed by Cytokinesis.

Mitosis (Left-side of split screen)

  • Purpose: growth, repair, replacement; produces two genetically identical diploid daughter cells.
  • Phases & key events
    • Prophase
    • Chromosomes condense (become visible, thicken).
    • Mitotic spindle begins to form; nuclear envelope breaks down.
    • Metaphase – “M for Middle”
    • Chromosomes line up single-file at metaphase plate.
    • Anaphase – “A for Away”
    • Sister chromatids separate and are pulled toward opposite poles.
    • Telophase
    • Chromatids (now chromosomes) reach poles; nuclear envelopes re-form.
    • Chromosomes de-condense.
    • Cytokinesis
    • Contractile ring (actin/myosin) pinches cytoplasm → two identical 2N2N cells (46 chromosomes each in humans).

Meiosis (Right-side of split screen)

  • Purpose: sexual reproduction; generates genetic diversity; produces four haploid (non-identical) cells.
  • Occurs in two successive divisions: Meiosis I and Meiosis II.
Meiosis I (“reductional division”)
  • Prophase I
    • Homologous chromosomes pair → tetrads.
    • Crossing over (genetic recombination) occurs at chiasmata, generating recombinant chromatids.
  • Metaphase I – paired homologs line up in pairs, not single-file.
  • Anaphase I – homologous chromosomes (not chromatids) pulled apart.
  • Telophase I / Cytokinesis – two haploid (but duplicated) nuclei; chromosomes still consist of sister chromatids.
Meiosis II (“equational division”)
  • Prophase II – chromosomes re-condense in each haploid cell; no synapsis/crossing over.
  • Metaphase II – chromosomes line up single-file (like mitosis).
  • Anaphase II – sister chromatids finally separate.
  • Telophase II / Cytokinesis – produces four haploid (NN) gametes.
  • Humans: each gamete contains 2323 chromosomes.
Significance & Connections
  • Fertilization: sperm(N=23)+egg(N=23)  ⟶  zygote(2N=46)\text{sperm} (N{=}23) + \text{egg} (N{=}23) \;\longrightarrow\; \text{zygote} (2N{=}46).
  • Zygote undergoes many rounds of mitosis to develop an organism.
  • Crossing over + independent assortment produce enormous genetic variation.
    • Example: some insects (e.g.
      mosquitoes) have 6 chromosomes; diagrams often use 6 for clarity.

Histology & Microscopy

  • Histology = study of tissues; relies on microscopy.
  • Historical milestones
    • 1590s: Hans & Zacharias Janssen invent primitive compound microscope.
    • 1670s: Anton van Leeuwenhoek builds high-power (∼270×\sim270\times) lenses → sees bacteria, spermatozoa; credited “Father of Microbiology.”
    • 1850s: Joseph von Gerlach pioneers carmine (insect-derived red dye) histological staining.
  • Standard prep steps: fix → embed → section (ultrathin) → stain.
  • Stains differentiate structures (e.g.
    nuclei, cytoplasm) by chemical affinity → critical for identifying tissue types.

The Four Primary Tissue Types

  1. Epithelial Tissue
    • Sheets of tightly packed cells; little ECM.
    • Functions: protection, absorption, filtration, secretion.
    • Sub-types by layers & shape
      • Simple squamous (alveoli) – gas exchange.
      • Simple cuboidal (glands, renal tubules) – secretion/absorption.
      • Simple columnar (intestinal lining) – nutrient absorption.
      • Stratified squamous (epidermis) – protection.
  2. Connective Tissue
    • Components: cells + extracellular matrix (ECM) (fibers + ground substance).
    • Fiber types: collagen (tensile), elastin (elastic recoil), reticular.
    • ECM density defines subtype:
      • Fluid → blood.
      • Semi-solid (loose/areolar, adipose) → cushioning, energy storage.
      • Dense/rigid → dense regular (ligaments, tendons), cartilage, bone.
  3. Muscle Tissue – specialized for contraction.
    • Skeletal
      • Long, cylindrical, multinucleate, obvious striations.
      • Voluntary; attaches to bones → body movement.
    • Cardiac
      • Branched cells, single nucleus; striated; intercalated discs (gap + adhering junctions).
      • Involuntary; walls of heart → pump blood.
    • Smooth
      • Spindle-shaped, uninucleate, non-striated; forms sheets.
      • Involuntary; walls of hollow organs (intestines, vessels, uterus) → peristalsis, vasoconstriction.
    • Lab ID tips
      • Striations & multinuclei → skeletal.
      • Striations + branching + discs → cardiac.
      • No striations, tapered cells → smooth.
  4. Nervous Tissue
    • Cell types
      • Neurons – generate/conduct electro-chemical impulses.
      – Parts: dendrites (input), soma, axon (output).
      • Glial cells – support, insulate, protect neurons; anchor to vasculature.
    • Functions: sensation, integration, control of muscles/glands.

From Cells → Tissues → Organs → Systems

  • Cells (≈ 30×101230{\times}10^{12} in body) belong to ~200200 specialized cell types.
  • Similar cells form tissues → two or more tissues form organs (kidney, liver).
  • Organs collaborating form organ systems.

Eleven Major Human Body Systems (Quick Review)

  1. Integumentary – skin barrier, temperature regulation, sensory.
  2. Skeletal – bones, ligaments; support, protection, mineral storage.
  3. Muscular – movement (skeletal, smooth, cardiac).
  4. Urinary – kidneys filter blood, produce urine, regulate water & electrolytes.
  5. Respiratory – lungs exchange O<em>2O<em>2/CO</em>2CO</em>2 with atmosphere.
  6. Digestive – ingest, break down, absorb nutrients; eliminate waste.
  7. Endocrine – glands secrete hormones (e.g.
    adrenaline) for long-distance communication.
  8. Reproductive – produce gametes; enable offspring.
  9. Lymphatic/Immune – returns interstitial fluid (lymph) to blood; houses immune cells.
  10. Nervous – rapid electrical signaling (CNS + PNS).
  11. Circulatory/Cardiovascular – heart pumps blood through arteries, veins, capillaries.
  • Systems are highly interdependent (e.g.
    muscular + skeletal for locomotion; endocrine + nervous for regulation).

Study Strategies Noted by Speakers (Minor Points)

  • Write tasks/goals in planners to avoid double-booking.
  • Use auditory reinforcement: say info aloud or teach concepts to others.
  • Visual comparison (e.g.
    split-screen mitosis vs meiosis) aids pattern recognition.

Miscellaneous Examples & Fun Facts

  • Amoebas perform all life functions within a single cell – contrast to human multicellularity & specialization.
  • Mosquitoes possess six chromosomes – convenient for simplified diagrams.
  • Histological stains originally derived from natural sources (e.g.
    saffron, cochineal insects).

Key Numerical References & Equations

  • Diploid: 2N=462N = 46 (humans). Haploid: N=23N = 23.
  • Post-S-phase chromatids: 9292 in human cell.
  • Leeuwenhoek scope magnification: ≈270×\approx 270\times.
  • Human cell count: 3.0×10133.0 \times 10^{13}.
  • Cell type count: ≈200\approx 200.

Practical / Ethical / Real-World Connections

  • Understanding meiosis underpins genetic counseling, fertility treatments, and inheritance studies.
  • Histology is essential for pathology diagnoses (cancer, tissue damage).
  • Knowledge of tissue response to staining techniques informs lab safety and environmentally ethical dye sourcing.