Physiology: Homeostasis and Feedback Mechanisms

Homeostasis

• The body continuously monitors and adjusts various physiological parameters: temperature, blood pH, blood sugar levels, and blood pressure.
• Loss of homeostasis can lead to various pathologies and diseases.
• Key focus in physiology is understanding body responses and regulatory mechanisms.

Feedback Mechanisms

• Negative Feedback

  • Detects adverse changes and initiates processes to reverse them.
  • Primary method for maintaining homeostasis.
  • Example: When body temperature rises, vasodilation and sweating occur, leading to heat loss and normalization of temperature.

• Positive Feedback

  • Detects changes and triggers greater responses in the same direction.
  • Less common but plays critical roles, such as in childbirth.
  • Example: Baby pressure against cervix leads to increased contractions, enhancing the birthing process.

Chemical Reactions

• Billions of chemical reactions occur within the body, essential for functions like seeing, hearing, breathing, and thinking.
• Tryptophan, an amino acid, is produced through specific chemical reactions in the body.

Atomic Structure

• Electrons possess a negative charge, protons a positive charge, and neutrons have no charge.
• An atom becomes an ion when it has unequal numbers of protons and electrons.
• Cations are positively charged ions, while anions are negatively charged ions.

Polarity of Molecules

• Bonding between atoms can result in non-polar molecules (equal electron sharing) or polar molecules (unequal sharing).
• Polar molecules have distinct charge distributions, with one end being positive and the other negative.

Types of Chemical Bonds

• Hydrogen Bonds

  • Weak bonds crucial for biological processes.

• Ionic Bonds

  • Form through the attraction of cations and anions; relatively weak and easily broken.

• Covalent Bonds

  • Strong bonds formed through the sharing of electrons; not easily broken.

Osmosis and Cell Membrane Transport

• A solution is a mixture of solute (particulate matter) and solvent (liquid).
• Osmosis: Diffusion of water from low to high solute concentration.
• Cell membranes are selectively permeable, allowing free passage for certain substances while restricting others.

Tonicity

• Hypertonic: Higher solute concentration outside the cell.
• Isotonic: Equal solute concentration inside and outside the cell.
• Hypotonic: Lower solute concentration outside the cell.
• Water moves to equalize solute concentrations, impacting cell shape and function.

Cellular Structures

• Ribosomes: Complexes of protein and RNA found in the nucleolus, rough ER, and cytoplasm, translating RNA into proteins.

• Lysosomes: Membrane-bound vesicles containing enzymes that degrade fats, proteins, and nucleic acids; utilized by white blood cells.

• Peroxisomes: Similar to lysosomes, containing oxidative enzymes for metabolizing organic compounds.

• Golgi Apparatus: Synthesizes carbohydrates, modifies proteins from the rough ER, and packages them for transport.

Genetics and Alleles

• Dominant Alleles: Expressed in phenotype and can mask recessive alleles.

• Recessive Alleles: Expressed only when both alleles are recessive.

• Example: Mutation in CFTR gene can cause cystic fibrosis; carriers have one dominant and one recessive allele.

• Codominance: Two different dominant alleles are expressed simultaneously (e.g., blood types A and B).

• Incomplete Dominance: Results in a blended phenotype (e.g., pink flowers from red and white parents).

• Polygenic Inheritance: Multiple genes contribute to traits like eye color and conditions such as heart disease or cancer.