BackMini-Textbook Study Notes: Physiology, Membrane Dynamics, Signal Transduction, pH & Buffers, Hearing, and Neurons
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Chapter 1: Introduction to Physiology
Definition and Structure-Function Relationship
Physiology is the study of the normal functions of living organisms and their parts. Anatomy is the study of the structure of organisms. The relationship between structure and function is fundamental: the form of a biological structure enables its function.
Structure and Function: Closely related; e.g., the shape of red blood cells allows them to carry oxygen efficiently.
Four Major Themes in Physiology:
Structure and function are closely related.
Living organisms need energy for processes such as growth, repair, and maintenance.
Information flow coordinates body function (e.g., nervous and endocrine signaling).
Homeostasis maintains internal stability despite external changes.
Homeostasis
Homeostasis is the maintenance of a stable internal environment. Failure of homeostasis can lead to disease.
Regulated Variables: Body temperature, blood glucose, pH, etc.
Law of Mass Balance: To maintain homeostasis, input must equal output.
Reflex Control Pathways
Reflex pathways regulate homeostasis via feedback mechanisms.
Components: Stimulus → Sensor (receptor) → Input signal → Integrating center → Output signal → Target (effector) → Response
Example: High blood glucose (stimulus) → Beta cells of pancreas (sensor) → Insulin secretion (output signal) → Body/liver cells (target) take up glucose (response)
Feedback Mechanisms
Negative Feedback: Returns variable to set point; maintains homeostasis. Example: Regulation of blood glucose.
Positive Feedback: Amplifies change; does not maintain homeostasis. Example: Childbirth (oxytocin release).
Clinical Scenario: In type 2 diabetes, negative feedback is disrupted, leading to elevated blood glucose.
Levels of Organization
Hierarchy: Chemical → Cellular → Tissue → Organ → Organ system → Organism
Chapter 5: Membrane Dynamics & Lab 1
Transport Mechanisms
Cells use various mechanisms to move substances across membranes.
Simple Diffusion: Passive; no protein required; for small hydrophobic molecules.
Facilitated Diffusion: Passive; requires channel or carrier protein; moves down concentration gradient.
Active Transport: Requires energy (ATP); moves molecules against concentration gradient.
Vesicular Transport: Includes phagocytosis, endocytosis, exocytosis.
Fick's Law of Diffusion
Predicts diffusion rate based on several factors:
Equation:
Where: J = rate of diffusion, D = diffusion coefficient, A = surface area, ΔC = concentration gradient, ΔX = membrane thickness.
Osmolarity and Tonicity
Osmolarity: Total number of solute particles per liter of solution.
Tonicity: Effect of a solution on cell volume.
Types:
Isotonic: No net water movement; cell remains normal.
Hypotonic: Water enters cell; cell swells (hemolysis).
Hypertonic: Water leaves cell; cell shrinks (crenation).
Carrier Proteins
Uniport: Transports one substance.
Symport: Transports two substances in same direction.
Antiport: Transports two substances in opposite directions.
Examples: GLUT (uniport), SGLT (symport), Na+-K+ ATPase (antiport).
Secondary Active Transport: Uses electrochemical gradient established by primary active transport.
Protein-Mediated Transport Characteristics
Specificity: Transporter recognizes specific molecules.
Competition: Similar molecules compete for transporter.
Saturation: Transport rate reaches maximum when all transporters are occupied.
Competitive Inhibitor: Molecule that binds transporter, blocking normal substrate.
Chemical and Electrical Disequilibrium
Osmotic Equilibrium: ICF and ECF have same osmolarity.
Chemical Disequilibrium: Unequal ion distribution.
Electrical Disequilibrium: Cell interior is more negative than exterior.
Factors: Unequal ion concentrations ("salty banana"), selective permeability (leak K+ channels).
Resting Membrane Potential: –65 to –70 mV.
Membrane Potential Changes
Depolarization: Membrane potential becomes less negative.
Hyperpolarization: Membrane potential becomes more negative.
Repolarization: Return to resting potential.
Lab 2: pH and Buffers
pH Scale and Homeostasis
pH measures hydrogen ion concentration; crucial for normal body function.
Relationship: Lower pH = higher H+ concentration = more acidic.
Physiological pH: Blood pH is tightly regulated (7.35–7.45).
Conjugate Pairs and Equilibrium
Conjugate Pair: Weak acid and its conjugate base.
Equilibrium Shift: Adding acid shifts equilibrium toward base; adding base shifts toward acid.
Buffers
Definition: Weak acid/base pair that minimizes pH changes by absorbing or releasing H+.
Buffering Region: Flat region near pKa on titration curve indicates good buffering.
Body Buffers
Buffer | Location |
|---|---|
Bicarbonate | Extracellular fluid (blood plasma) |
Hemoglobin | Red blood cells |
Phosphate | Intracellular fluid, urine |
Protein Buffers | Cells and plasma |
Lab 3: Hearing
Physiology of Hearing
Hearing involves detection of sound waves and their interpretation by the brain.
Sound Waves: Compression and expansion of air molecules.
Pathway: Outer ear canal → Tympanic membrane → Middle ear bones → Cochlea (hair cells) → Auditory nerve → Cerebrum.
Hair Cells: Sensory receptors for hearing.
Sound Localization
Mechanism: Brain compares signals from both ears to determine location.
Hearing Pathways and Deafness
Air Conduction: Normal hearing through middle ear.
Bone Conduction: Vibrations through skull.
Types of Deafness:
Conductive Deafness: Problem in outer/middle ear.
Sensorineural Deafness: Problem in inner ear or nerve.
Self-Perception of Voice
Bone conduction causes you to hear your own voice differently than others do.
Chapter 6: Signal Transduction
Cell Communication
Cells communicate via local and long-distance signaling.
Local Communication:
Gap junctions (direct cytoplasmic connections)
Paracrine signals (affect nearby cells)
Autocrine signals (affect same cell that secreted them)
Long-Distance Communication:
Endocrine system (hormones via blood)
Nervous system (electrical signals and neurotransmitters)
Endocrine vs. Nervous System
Feature | Endocrine | Nervous |
|---|---|---|
Signal Type | Hormones (chemical) | Electrical + neurotransmitters |
Target Specificity | Broad (any cell with receptor) | Specific (targeted synapses) |
Speed | Slow (seconds to days) | Fast (milliseconds) |
Duration | Long-lasting | Short-lived |
Lipophilic vs. Lipophobic Signal Molecules
Lipophilic: Cross cell membrane; receptors inside cell; slow response. Example: Steroid hormones.
Lipophobic: Cannot cross membrane; receptors on cell surface; fast response. Example: Peptide hormones.
Signal Transduction Steps (Lipophobic Molecules)
Membrane Receptor: Binds extracellular ligand (first messenger).
Transduction: Converts extracellular signal to intracellular signal (second messenger).
Amplification: Amplifier enzyme increases signal strength.
Types of Membrane Receptors
Type | Characteristics | Example |
|---|---|---|
Receptor-Channel | Fast; ion flow | Acetylcholine nicotinic receptor |
GPCR | Slower; signal amplification | Acetylcholine muscarinic receptor |
Receptor-Enzyme | Enzyme activity | Insulin receptor |
Integrin Receptor | Cell adhesion/signaling | Integrins |
Acetylcholine: Can produce opposite responses depending on receptor type (e.g., stimulates muscle contraction via nicotinic receptor, slows heart rate via muscarinic receptor).
Receptor-Ligand Principles
Specificity: Receptors bind specific ligands.
Competition: Multiple ligands compete for same receptor.
Saturation: All receptors occupied; maximum response.
Agonists and Antagonists
Agonist: Ligand that activates receptor.
Antagonist: Ligand that blocks receptor.
Up-Regulation and Down-Regulation
Up-Regulation: Increase in receptor number; enhances response.
Down-Regulation: Decrease in receptor number; reduces response.
Example: Chronic exposure to high hormone levels may cause down-regulation.
Chapter 8: Neurons
Nervous System Hierarchy
Hierarchy: Central (brain, spinal cord) and Peripheral (sensory/afferent, efferent)
Efferent: Somatic motor (skeletal muscle), Autonomic (cardiac, smooth muscle; sympathetic, parasympathetic)
Cell Types: Neurons (signal transmission), Glial cells (support)
Graded Potentials and Action Potentials
Graded Potentials: Occur in dendrites/cell body; vary in amplitude; can be depolarizing (EPSP) or hyperpolarizing (IPSP).
Action Potentials: Occur in axon; all-or-none; generated when graded potentials reach threshold via temporal/spatial summation.
Action Potential Graph and Ion Permeability
Resting State: Voltage-gated Na+ and K+ channels closed.
Rising Phase: Na+ channels open; Na+ influx.
Falling Phase: K+ channels open; K+ efflux.
Hyperpolarization: K+ channels remain open briefly.
Action Potential Conduction
One Direction: Due to absolute refractory period (Na+ channels inactivated).
Relative Refractory Period: Requires stronger stimulus.
Myelination
Role: Increases speed and efficiency of conduction.
Clinical Example: Multiple sclerosis (loss of myelin slows conduction).
Synaptic Transmission
Steps:
Action potential arrives at axon terminal.
Voltage-gated Ca2+ channels open.
Ca2+ triggers synaptic vesicle fusion.
Neurotransmitter released into synaptic cleft.
Neurotransmitter binds receptors on postsynaptic cell.
Removal: Neurotransmitter must be cleared for proper signaling.
Clinical/Experimental Changes: Removal of Ca2+ inhibits release; receptor inhibition blocks response; termination blockage prolongs signal.
Stimulus Strength: Increases frequency, not amplitude, of action potentials.
Convergence and Divergence
Convergence: Multiple presynaptic neurons synapse onto one postsynaptic neuron.
Divergence: One presynaptic neuron synapses onto multiple postsynaptic neurons.
