Principles of Human Physiology: Exam 1 Study Guide

Introduction to Physiology and Homeostasis

What is Physiology?

Physiology is the scientific study of the functions and mechanisms in a living system. It explains how organisms, organ systems, organs, cells, and biomolecules carry out the chemical and physical functions that exist in a living system.

• Physiology focuses on how the body maintains life and responds to internal and external changes.

Homeostasis

Homeostasis is the maintenance of a stable internal environment despite changes in the external environment.

• Negative feedback loops: Mechanisms that reverse a change to keep a variable within a normal range (e.g., body temperature regulation).

• Positive feedback loops: Mechanisms that amplify a change (e.g., blood clotting, childbirth contractions).

• Antagonistic effectors: Systems that have opposing effects to maintain balance (e.g., insulin and glucagon in blood glucose regulation).

• Not all variables are regulated identically; some have tighter control than others.

Chemical Nature of the Body

Atomic Structure and Chemical Bonds

Atoms are composed of protons, neutrons, and electrons. Chemical bonds form when atoms share or transfer electrons to achieve stability.

• Ionic bonds: Transfer of electrons between atoms.

• Covalent bonds: Sharing of electrons between atoms.

• Hydrogen bonds: Weak attractions between polar molecules.

Isotopes

• Isotopes are atoms of the same element with different numbers of neutrons.

• Some isotopes are radioactive and used in medical imaging.

Acids, Bases, and the pH Scale

• Acids release H+ ions in solution; bases accept H+ ions.

• The pH scale measures hydrogen ion concentration: $\mathrm{pH} = -\log_{10}[\mathrm{H}^+]$

• pH 7 is neutral; below 7 is acidic, above 7 is basic.

Organic Molecules and Macromolecules

• All organic molecules have a carbon backbone and functional groups that determine their properties.

• Four major macromolecules:

  • Carbohydrates: Sugars and starches; energy source; building block is the monosaccharide.

  • Lipids: Fats, oils, steroids; energy storage, membrane structure; building block is the fatty acid.

  • Proteins: Enzymes, structural components; building block is the amino acid.

  • Nucleic acids: DNA and RNA; genetic information; building block is the nucleotide.

• Dehydration synthesis joins monomers by removing water; hydrolysis breaks polymers by adding water.

• Polymerization is essential for storage and function of macromolecules.

Life and Death of Cells

Cytoskeletal Components and Functions

• Microfilaments: Actin filaments; cell movement and shape.

• Intermediate filaments: Structural support.

• Microtubules: Tubulin; cell division, intracellular transport.

Cell Organelles

• Nucleus: Contains DNA; control center.

• Mitochondria: ATP production.

• Endoplasmic reticulum: Protein and lipid synthesis.

• Golgi apparatus: Modifies, sorts, and packages proteins.

• Lysosomes: Digestion of macromolecules.

Cell Division and Differentiation

• Cells divide in response to signals (growth factors, cell cycle checkpoints).

• Differentiation: Cells become specialized based on gene expression.

Cell Death

• Apoptosis: Programmed cell death; orderly and beneficial.

• Necrosis: Uncontrolled cell death; often due to injury.

Hallmarks of Cancer

• Uncontrolled cell division, evasion of apoptosis, sustained angiogenesis, tissue invasion, and metastasis.

Nuclear Processes

Molecules of Inheritance

• DNA is the hereditary material; proven by experiments (e.g., Avery, Hershey-Chase).

• Nucleotides are the building blocks of DNA and RNA.

DNA Replication

• Process by which DNA makes a copy of itself during cell division.

• Key enzymes: DNA polymerase, helicase, ligase.

Transcription and Translation

• Transcription: DNA to mRNA in the nucleus.

• Translation: mRNA to protein at the ribosome.

• Requires mRNA, tRNA, ribosomes, amino acids.

Mutations

• Changes in DNA sequence; can be point mutations, insertions, deletions.

• May result in altered proteins or loss of function.

• Caused by errors in replication, chemicals, radiation.

Differential Gene Expression

• Cells control which genes are expressed to perform specialized functions.

Enzymes and Energy

Forms of Energy and Thermodynamics

• Kinetic energy: Energy of motion.

• Potential energy: Stored energy.

• First law of thermodynamics: Energy cannot be created or destroyed.

• Second law of thermodynamics: Entropy (disorder) increases in a closed system.

Endergonic vs. Exergonic Reactions

• Endergonic: Require energy input (e.g., synthesis of macromolecules).

• Exergonic: Release energy (e.g., breakdown of glucose).

Enzyme Function and Regulation

• Enzyme: Biological catalyst that speeds up reactions by lowering activation energy.

• Substrate: Molecule upon which an enzyme acts.

• Product: Result of the enzymatic reaction.

• Active site: Region on enzyme where substrate binds.

• Affinity: Strength of substrate binding.

• Cofactors and coenzymes: Non-protein helpers for enzyme activity.

• Enzyme activity is affected by temperature, pH, substrate concentration, and inhibitors.

• Up-regulation: Increase in enzyme production; down-regulation: decrease in enzyme production.

• Competitive inhibitors: Bind to active site; noncompetitive inhibitors: Bind elsewhere, changing enzyme shape.

• Michaelis-Menten kinetics describe enzyme activity: $V = \frac{V_{max}[S]}{K_m + [S]}$

Cellular Metabolism

Basal Metabolic Rate (BMR)

• BMR is the rate of energy expenditure at rest, necessary to maintain vital body functions.

Energy Storage in the Body

• Energy is stored as glycogen (short-term) and fat (long-term).

ATP and Energy Transfer

• ATP hydrolysis: $\mathrm{ATP} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{ADP} + \mathrm{P_i} + \text{energy}$

• Phosphorylation: Addition of phosphate group to a molecule.

Electron Carriers and Redox Reactions

• Electron carriers (NAD+, FAD) transport electrons during cellular respiration.

• Redox reactions: Transfer of electrons between molecules.

Cellular Respiration Pathways

• Glycolysis: Glucose to pyruvate; produces ATP and NADH.

• Citric acid cycle: Acetyl-CoA to CO2; produces NADH, FADH2, ATP.

• Electron transport chain (ETC): Uses NADH/FADH2 to generate ATP via oxidative phosphorylation.

• Chemiosmosis theory: ATP synthesis driven by proton gradient across mitochondrial membrane.

• Fermentation: Occurs when oxygen is limited; regenerates NAD+ for glycolysis.

Membranes and Membrane Transport

Membrane Structure and Function

• Composed of phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Functions: barrier, transport, communication, cell recognition.

Membrane Transport Processes

• Passive diffusion: Movement down concentration gradient; no energy required.

• Facilitated diffusion: Uses transport proteins; still passive.

• Osmosis: Diffusion of water across a semipermeable membrane.

• Active transport: Moves substances against gradient; requires energy.

  • Primary active transport: Direct use of ATP (e.g., Na+/K+ pump).

  • Secondary active transport: Uses energy from another gradient.

• Carrier-mediated transport: Involves specific transport proteins; shows saturation kinetics.

• Endocytosis: Uptake of materials via vesicles.

• Exocytosis: Release of materials via vesicles.

• Pinocytosis: "Cell drinking"; uptake of fluid.

• Gradients (concentration, electrical) power many transport mechanisms.

Laboratory Material

The Scientific Method and Experimentation

• Steps: Observation, hypothesis, experiment, data collection, analysis, conclusion.

Serum Analysis and Spectrophotometry

• Serum analysis measures levels of macromolecules (glucose, protein, cholesterol).

• Beer's Law: Absorbance is proportional to concentration: $A = \varepsilon l c$

• Standard curves are constructed to determine unknown concentrations.

• Spectrophotometers measure absorbance of light by solutions.

Enzyme Function in the Lab

• Enzyme activity is measured by reaction rate and substrate conversion.

• Energy of activation is the energy required to start a reaction.

Osmolarity, Tonicity, and Solution Preparation

• Osmolarity: Total solute concentration in a solution.

• Tonicity: Effect of a solution on cell volume (isotonic, hypertonic, hypotonic).

• Penetrating solutes can cross membranes; non-penetrating solutes cannot.

• Solutions are prepared by dissolving solutes to a desired concentration.

Table: Comparison of Membrane Transport Mechanisms

Transport Type	Energy Required?	Direction	Carrier Protein?	Example
Passive Diffusion	No	Down gradient	No	O2 across membrane
Facilitated Diffusion	No	Down gradient	Yes	Glucose transport
Active Transport	Yes	Against gradient	Yes	Na+/K+ pump
Osmosis	No	Water down gradient	No	Water movement
Endocytosis/Exocytosis	Yes	Bulk transport	No	Neurotransmitter release