Biology: Organismal Level Functions

Organismal Function and Life Processes

• Organ systems collaborate to sustain life; failure of any system can result in death.

• Maintaining boundaries:

  • Cellular level: Plasma membrane regulates entry and exit of substances.
  • Organismal level: Integumentary system (skin) protects against pathogens and toxins.

• Movement:

  • Involves skeletal and muscular systems for voluntary (skeletal muscle) and involuntary (smooth and cardiac muscles) actions.
  • Examples include chewing (skeletal) and digestive function (smooth).

• Responsiveness:

  • The nervous system detects stimuli and triggers responses via neurons.
  • Reflex action demonstrated by touch reaction to a hot surface.

• Digestion:

  • Macromolecules are broken down into smaller units for absorption into the bloodstream.

• Metabolism:

  • Encompasses all chemical reactions within the body.
  • Catabolism breaks down larger molecules, while anabolism builds them up.
  • Cellular respiration converts these reactions into ATP energy.

Plasma Membrane Structure

• Fluid Mosaic Model depicts the plasma membrane as a phospholipid bilayer with embedded proteins.
• Selectively impermeable to water-soluble molecules, separates intracellular fluid (ICF) from extracellular fluid (ECF).

Chemical Composition of Cell Membranes

• Lipids:

  • Phospholipids form the membrane's core structure with:
    • Hydrophilic phosphate head facing fluids.
    • Nonpolar fatty acid tails forming a barrier.
  • Cholesterol enhances membrane stability and flexibility.

• Proteins:

  • Integral proteins cross the membrane, serving various roles including transporting substances.
  • Peripheral proteins assist in enzymatic and structural functions.

• Carbohydrates:

  • Form glycoproteins and glycolipids on the extracellular surface contributing to cell recognition and identity.

Cell Junctions

• Types of cell junctions include:
  • Tight junctions: prevent leakage between adjacent cells.
  • Anchoring junctions: connect cells to one another or to extracellular matrix.

Osmosis and Tonicity

• Osmosis is the diffusion of water across a selectively permeable membrane, moving from low to high solute concentration.
• Osmolarity measures solute concentration; higher osmolarity means more solute particles.
• Tonicity influences cell shape:
  • Isotonic: no net water movement; cell remains unchanged.
  • Hypertonic: cell loses water and shrinks; high external solute concentration.
  • Hypotonic: cell gains water and may burst; low external solute concentration.

Active Transport Mechanisms

• Requires energy (ATP) to move substances against concentration gradients.

• Types include:

  • Primary active transport: ATP directly alters protein shape to transport molecules (e.g., sodium-potassium pump).
  • Secondary active transport: uses established gradients to move additional molecules (e.g., sodium-glucose co-transport).

• Vesicular transport:

  • Endocytosis: Engulfing substances into the cell.
    • Phagocytosis: Engulfs large particles, forming a vesicle; fuses with lysosome for digestion.
    • Pinocytosis: Cell takes in extracellular fluid with dissolved solutes.

Key Functions and Processes

• Active forms of transport are essential for maintaining cellular function and homeostasis.
• Concentration gradients created by active transport affect nutrient uptake and cellular signaling.
• Understanding cell membrane dynamics is crucial for grasping broader physiological concepts.### Exocrine and Endocrine Glands
• Exocrine Glands: Secrete substances onto surfaces or into cavities using ducts. Examples include sweat glands, pancreas, salivary glands, oil glands.
• Endocrine Glands: Ductless, secrete hormones directly into the bloodstream. Can form compact multicellular organs or diffuse systems, mainly multicellular.
• Secretion Methods:
  • Unicellular exocrine glands are rare; consist of single cells (e.g., goblet and mucous cells).
  • Multicellular exocrine glands have two main components: acinus (secretory unit) and duct (pathway for secretion).
• Classification of Multicellular Exocrine Glands:
  • By structure:
    • Simple (unbranched duct).
    • Compound (branched duct).
    • Acinus shapes: tubular, alveolar, tubuloalveolar.
  • By mode of secretion:
    • Merocrine: Secretion via exocytosis without cell change.
    • Holocrine: Cell ruptures to release secretion (e.g., sebaceous glands).
    • Apocrine: Cells fill until they tear, leaking secretion with minimal damage.

Connective Tissue

• Most abundant tissue type, present in all organs and organ systems, excluding the nervous system.
• Functions include support, protection, insulation, storage, and transport.
• Extracellular Matrix (ECM): Nonliving matrix separating living cells; essential for connective tissue.
• All connective tissues derive from mesenchyme, embryonic tissue.

Components of Connective Tissue

• Ground Substance: Fills spaces, comprising:
  • Interstitial fluid (allows nutrient transport).
  • Cell adhesion proteins (act as glue).
  • Proteoglycans (determine consistency; more = thicker).
• Fibers: Provide structural support, classified as:
  • Collagen Fibers: Strong, flexible; resist pulling forces; found in skin, tendons, ligaments.
  • Elastic Fibers: Stretch easily, return to original shape; prevalent in skin and lungs.
  • Reticular Fibers: Form networks; hold tissues in place, common where connective tissue meets other tissues.

Homeostasis and Connective Tissue

• Marfan Syndrome: Genetic disorder affecting connective tissue due to FBN1 gene mutation.
• Most common cancers: skin, colon, lung, breast, prostate; treatments include chemotherapy and radiation.

Skin Functions

• Protection:
  • Chemical: Sweat and oils kill bacteria; melanin protects from UV damage.
  • Physical: Acts as a barrier against bacterial entry.
  • Biological: Dendritic cells and macrophages digest and clear pathogens.
• Temperature Regulation:
  • Insensible perspiration: Constant, unnoticeable sweat aids in minor temperature adjustments.
  • Sensible perspiration: Noticeable sweating in response to heat.
  • Vasoconstriction in cold conditions preserves internal body heat by directing blood to deep tissues.
• Sensation:
  • Exteroceptors are responsive cutaneous sensory receptors detecting external stimuli.
  • Mechanoreceptors respond to touch and pressure.