Lab 2: Cell and Homeostasis

Levels of Organization

• From small to big: $\text{Atoms} \rightarrow \text{Molecules} \rightarrow \text{Organelle} \rightarrow \text{Cells} \rightarrow \text{Tissues} \rightarrow \text{Organs} \rightarrow \text{Organ Systems} \rightarrow \text{Organism}$

• Concept: increasing complexity but interdependence of components.

Atoms, Molecules, Ions, and Water

• Atomic structure: $\text{nucleus} \; + \; \text{electron shells}$

• Stability: electroneutrality and the $\text{octet rule}$ as foundation for molecule/ion formation

• Bonding and polarity: $\text{Polar vs Non-polar molecules}$ ; hydrogen bonding and water

• Ions: $\mathrm{H^+}, \ \mathrm{Na^+}, \ \mathrm{Cl^-}, \ \mathrm{Ca^{2+}}$

• Biological molecules: $\text{Water}, \ \text{Protein}, \ \text{Nucleic Acids}, \ \text{Fats}, \ \text{Carbohydrates}$

• Water structure: H–O–H with covalent bonds; each H shares electrons with O; O completes with 8 electrons in outer shell

  • Example: $\text{H outer shell} = 2, \ \text{O outer shell} = 8$

Ions, Electrolytes, and Homeostasis

• Ions: atoms/molecules with a charge due to electron loss/gain

• Cations vs Anions with examples: $\mathrm{H^+}, \mathrm{Na^+}, \mathrm{K^+}, \mathrm{Ca^{2+}}$ vs $\mathrm{F^-}, \mathrm{Cl^-}, \mathrm{O^{2-}}, \mathrm{PO_4^{3-}}$

• Electrolytes: inorganic ions that conduct electricity in solution; imbalances disturb functions (e.g., low $\mathrm{K^+}$; sodium conduction issues)

• Clinical note: diuretics like Lasix can alter fluid/electrolyte balance

• Negative Feedback

  • Conserve water if blood water volume is low, etc

• Positive Feedback

  • Only two: Blood clotting and childbirth

  • Does not stop until reaching homeostasis

The Cell Membrane and Hydrophobic/Hydrophilic Environments

• Cell membrane = phospholipid bilayer; hydrophilic heads face aqueous environments; hydrophobic tails form interior

• Amphipathic: both hydrophilic and hydrophobic regions present

• Membrane contains transport proteins, carbohydrates, and lipids; semipermeable barrier

• Outside vs inside of cell: extracellular fluid (often interstitial fluid) vs cytosol

The Cell and Organelles (Structure and Function, high-level)

• Cytoplasm: cytosol + organelles; organelles can be membranous or nonmembranous

• Nucleus: control center; stores genetic information; nucleolus (RNA synthesis) and chromatin

• Centrosome with centrioles: organizing microtubules (9+0 triplets in each centriole)

• Cytoskeleton: microfilaments, intermediate filaments, microtubules; provides shape and movement

• Microvilli: increase surface area for absorption

• Cilia: motile or sensor; move materials over cell surfaces

• Ribosomes: protein synthesis; free ribosomes and those on rough ER

• Endoplasmic Reticulum (ER): rough ER (protein synthesis, ribosome association); smooth ER (lipid and carbohydrate synthesis)

• Golgi apparatus: processing, packaging, and shipping of secretory products

• Mitochondria: double membrane; cristae; produce ~all ATP required by the cell

• Peroxisomes: breakdown of fatty acids; detoxify harmful substances

• Lysosomes: intracellular digestion of damaged organelles and pathogens

• Proteasomes: degradation of damaged or abnormal proteins

• Vesicles: intracellular transport and secretion

Homeostasis and Feedback Systems

• Homeostasis: maintenance of stable internal conditions

• Feedback components: Receptor (sensor) → Center/Comparator (set-point) → Effector (target) → Change in controlled variable

• Negative feedback: counteracts a change to return to set-point (common in homeostasis)

• Positive feedback: enhances a change (less common; e.g., processes that amplify)

• Example: Thermoregulation

  • Normal body set-point maintained by hypothalamus

  • If temperature deviates, effectors (shivering, sweating) prompt corrective responses

• Terms to know: hypothermia, hyperthermia, pyretic, set-point, effector, comparator, range

• Lab example: dehydration and ADH release

  • Hypothalamus detects low blood water

  • Pituitary releases ADH

  • Kidneys conserve water; urine becomes more concentrated

Osmosis, Diffusion, and Tonicity

• Osmosis: diffusion of water across a selectively permeable membrane from high solvent (water) to low solvent (water) concentration

  • Requires semipermeable membrane

  • Define: diffusion; selective semipermeable membrane

• Membrane transport types:

  • Simple diffusion: small nonpolar molecules diffuse directly through the phospholipid bilayer

  • Facilitated diffusion: large or polar molecules diffuse via transport proteins

• Tonicity concepts: hypotonic, isotonic, hypertonic

• RBC examples in solutions:

  • Isotonic: normal cells; no net water movement

  • Hypotonic: water moves into cells → swelling and potential lysis

  • Hypertonic: water moves out of cells → crenation

• Osmosis in context of body fluids and hydrostatic pressure; net water movement impacts cell volume

• Solvent = water

• Solute = particles (Ions, Glucose, Salt)

Summary of Key Terms to Memorize

• Set-point, Comparator, Receptor, Effector, Range

• Hypothermia, Hyperthermia, Pyretic

• Hypotonic, Isotonic, Hypertonic

• Hydrophobic vs Hydrophilic; Amphipathic

• Membranous vs Nonmembranous organelles

• ATP, Cristae, Oxidative phosphorylation (implied by mitochondria)

• Osmosis, Diffusion, Facilitated diffusion