MV

Exam 1 Study Notes: Chapters 1-5

Chapter 1 – Introduction to Physiology

  • Four cell/tissue types
    • Neurons / nervous tissue
    • Muscle cells / muscle tissue
    • Epithelial cells / epithelial tissue
    • Connective cells / connective tissue
  • Organs
    • Composed of at least two tissue types
    • Performs specific functions
  • Organ systems
    • Collection of organs performing a particular task
  • Internal vs external environment
    • Internal environment
    • Immediate environment of most cells
    • Includes plasma and tissue fluid
    • External environment
    • External side of the epithelial body barrier
    • Includes: surroundings outside the skin, air in the lungs, food in the stomach, urine in the bladder
  • Homeostasis (Chapter 2 reference; core concept)
    • Homeostasis – ability to maintain a relatively constant internal environment
    • Regulated variable – aspect maintained (e.g., ext{blood glucose}, ext{ temperature}, etc.)
    • Set point – expected value of a regulated variable
    • Negative feedback – the effector works opposite the factor
    • If a regulated variable decreases, the system responds to make it increase, and vice versa
    • Positive feedback – effector pushes the factor farther away from set point
    • Receptors – sensors that detect stimuli
    • Integrating center – receives signals from receptors; orchestrates an appropriate response; often in brain or endocrine gland; relays signals (output) to effectors
    • Effectors – receive signals from integrating center; responsible for body responses
  • Difference between negative and positive feedback
    • Negative feedback opposes the change to maintain stability
    • Positive feedback drives the system away from the set point (less common in homeostasis)
  • Components of a homeostatic control mechanism
    • Receptors (sensors)
    • Integrating center (processing/decision making)
    • Effectors (elicit response)
    • Communication pathways (e.g., neural, endocrine) to relay signals

Chapter 2 – The Cell

  • Four types of biological molecules
    • Carbohydrates
    • Lipids
    • Proteins
    • Nucleic acids
  • Plasma membrane (cell membrane) – basics
    • Found in ALL CELLS
    • Barrier between cell and external environment
    • Components
    • Phospholipid bilayer
    • Cholesterol
    • Membrane proteins
    • Membrane carbohydrates
  • Nucleus
    • Structure
    • Nuclear envelope – double phospholipid bilayer
    • Nuclear pores
    • Nucleolus – site of ribosomal RNA (rRNA) synthesis
    • Function
    • Transmission and expression of genetic information
    • Contains DNA: stores genetic code
    • DNA transcribed to RNA: necessary to express the genetic code
  • Cytoplasm
    • Cytosol (fluid) and organelles
    • Functions
    • Location of specific chemical reactions
    • Fat and carbohydrates stored in masses called inclusions
    • Storage of secretory vesicles
  • Endoplasmic reticulum (ER)
    • Rough ER
    • Flattened sacs with granules (ribosomes) on surface
    • Functions in synthesis of proteins to be packaged into vesicles
    • Smooth ER
    • Tubules; smooth appearance
    • Functions in lipid synthesis; stores calcium
  • Golgi apparatus
    • Functions
    • Post-translational processing of proteins
    • Packaging of proteins and other molecules into vesicles and directing them to the target
  • Mitochondria
    • Structure
    • Double membrane (outer membrane and inner membrane)
    • Intermembrane space
    • Inner membrane folded into cristae
    • Matrix (inner space)
    • Functions
    • Site of aerobic cellular respiration which makes ATP
  • Lysosomes
    • Membrane-bound vesicles containing digestive enzymes
    • Function – break down cellular or extracellular debris
  • Peroxisomes
    • Membrane-bound
    • Function – degrade certain waste molecules; by-product is hydrogen peroxide (H₂O₂)
    • Contain catalase which breaks down H₂O₂
  • Ribosomes
    • Made of rRNA and proteins; no membrane; very small (~25 nm)
    • Made of two subunits
    • Function – protein synthesis
    • Locations
    • Fixed – attached to rough endoplasmic reticulum
    • Free – loose in cytosol
  • Centrioles
    • Paired cylindrical structures; bundles of protein filaments; perpendicular to each other
    • Function – development of the mitotic spindle
  • Cytoskeleton
    • Made of protein filaments: microfilaments, intermediate filaments, microtubules
    • Functions
    • Mechanical support and structure
    • Intracellular transport of materials
    • Suspension of organelles
    • Formation of adhesions with other cells
    • Contraction and movement
  • Intercellular junctions
    • Tight junctions
    • Common in epithelial tissue; specialized for molecular transport
    • Form a nearly impermeable barrier
    • Force transepithelial transport
    • Desmosomes
    • Filamentous junction between cells
    • Binds cells together for strength; found in tissue subject to mechanical stress
    • Cadherins cross into extracellular space; linked to intracellular filaments at the plaque
    • Gap junctions
    • Composed of membrane proteins
    • Link the cytosol of two adjacent cells
    • Ions and molecules moving between cells act as signals; enable direct communication

Chapter 3 – Metabolism

  • Definition of metabolism
    • Metabolism – all chemical reactions occurring in a cell
  • Types of metabolic reactions
    • Hydrolysis – breaks down large molecules
    • Condensation – joins smaller molecules together
    • Phosphorylation – requires energy
    • Dephosphorylation – releases energy
    • Oxidation – removal of electrons and H⁺
    • Reduction – addition of electrons and H⁺
  • Energy concepts
    • Kinetic energy – associated with motion (e.g., thermal, radiant, electromagnetic, electrical)
    • Potential energy – stored energy (e.g., chemical, mechanical, nuclear, gravitational)
  • Laws of Thermodynamics
    • First Law (conservation of energy)
    • Energy cannot be created nor destroyed; energy can change form; the total energy in a closed system is constant
    • The human body is an open system
    • Second Law
    • Processes move in the direction that tends to spread out energy
    • Example: breaking a large molecule into smaller molecules; movement from high to low concentration
  • Exergonic vs endergonic reactions
    • Exergonic (catabolic)
    • Break down large molecules into smaller ones
    • Proceeds spontaneously
    • Releases energy
    • Endergonic (anabolic)
    • Build complex molecules from smaller ones
    • Does not proceed spontaneously
    • Requires energy input
  • Activation energy
    • Activation energy – energy necessary for a reaction to proceed
  • Enzymes
    • Proteins that catalyze (increase the rate of) chemical reactions
    • Decrease activation energy needed
    • Substrate – reactant that binds to an enzyme at the active site
    • Enzymes are specific for one set of substrates or a group of similar substrates
    • Enzymes are not changed in the reaction; are not consumed
    • Enzymes are identified by the suffix -ase
  • Factors affecting rates of enzyme-catalyzed reactions
    • Enzyme catalytic rate (kcat): how many molecules produced per unit time
    • Substrate concentration
    • Enzyme concentration
    • Affinity of enzyme for substrate (Km reflects affinity)
    • Temperature and pH
  • Adenosine triphosphate (ATP)
    • Primary energy source for cellular work
  • Aerobic cellular respiration (glucose oxidation) – stages (order from first to last)
    • Glycolysis
    • Breakdown of glucose to two pyruvate molecules
    • Location: cytosol
    • Net gain: 2 ATP
    • 2 NAD⁺ reduced to 2 NADH
    • No O₂ consumed, no CO₂ produced
    • Linking step (pyruvate oxidation to acetyl CoA)
    • Pyruvate converted to acetyl CoA
    • One NADH produced per pyruvate molecule ⇒ total 2 NADH per ONE glucose
    • One CO₂ produced per pyruvate molecule ⇒ total 2 CO₂ per ONE glucose
    • Krebs cycle (citric acid cycle)
    • Per acetyl CoA: initial substrate is acetyl CoA
    • Production per acetyl CoA
      • 1 ext{ GTP} = 1 ext{ ATP}
      • 3 ext{ NADH} + 3 ext{ H}^+ and 1 ext{ FADH}_2
      • Waste: 2 ext{ CO}_2
    • Since each glucose yields two acetyl CoA, the cycle turns twice per glucose
    • Net yield per glucose (from Krebs via two turns): 2 ext{ ATP}
    • Oxidative phosphorylation / Electron transport chain (ETC)
    • Bulk of ATP formed by oxidative phosphorylation
    • Electron transport system: chain of molecules in the inner mitochondrial membrane
    • NADH and FADH₂ donate electrons; redox reactions move electrons to oxygen
    • Last electron acceptor: ext{O}_2
    • Proton pumping: Energy released pumps H^+ against its gradient into the intermembrane space
    • Chemiosmosis: H^+ diffuse back through ATP synthase to synthesize ATP
    • Net yield from oxidative phosphorylation: ext{~28 ATP} per glucose
  • Overall yield
    • Total ATP produced from one glucose molecule: 38 ATP
  • Chapter summary
    • Glucose oxidation in aerobic respiration yields energy in stages with a total of 38 ATP per glucose, via glycolysis, linking step, Krebs cycle, and oxidative phosphorylation

Chapter 4 – Membrane Transport

  • Basics of membrane transport
    • Membranes separate intracellular fluid (ICF) from extracellular fluid (ECF)
    • They allow exchange of material between ICF and ECF
  • Why transport is important
    • Obtain O₂ and nutrients
    • Remove waste products
  • Membranes are selectively permeable
    • Allow some molecules to pass; others are restricted
    • Nonpolar (lipid-soluble) molecules pass easily
    • Polar molecules and ions usually require assistance
  • Passive transport (no cellular energy required)
    • Movement down the concentration gradient (downhill)
    • Types of passive transport
    • Simple diffusion – through phospholipid bilayer
      • Rate factors
      • Magnitude of driving force (concentration gradient) – larger gradient = larger net flux
      • Membrane surface area
      • Membrane permeability
        • Lipid solubility of diffusing substance
        • Hydrophobic substances diffuse faster
      • Size and shape of diffusing particle
      • Temperature – higher temperature → faster diffusion
      • Thickness of membrane (affects permeability)
    • Facilitated diffusion – passive, via carrier or channel
    • Osmosis – diffusion of water through a membrane
      • Characteristics
      • Unaffected by membrane potentials
      • Driven by water gradient
      • Osmolarity – total solute concentration of a solution
      • Tonicity – comparative term for osmotically active solutes
      • Isotonic solution – no net water movement; solute concentrations equal across membrane
      • Hypertonic solution – higher solute outside → water leaves cell
      • Hypotonic solution – lower solute outside → water enters cell
    • Rate factors for diffusion and osmosis
    • Driving gradient magnitude (osmotic gradient for water)
    • Membrane permeability and surface area
  • Active transport (requires energy)
    • Nonspontaneous; moves material against the gradient (uphill)
    • Involves a pump (membrane protein)
    • Pump characteristics
    • Membrane protein; transporter and enzyme; can harness energy
    • Has specific binding sites
    • Can become saturated
    • Primary vs secondary active transport
    • Primary active transport – energy from ATP
    • Secondary active transport – energy released from ion diffusion (coupled transport)
  • Transport of macromolecules
    • Endocytosis – movement into the cell
    • Phagocytosis – engulfing large particles
    • Pinocytosis – uptake of dissolved particles
    • Receptor-mediated endocytosis – ligand binds receptors on membrane
    • Exocytosis – movement out of the cell
  • Transport across epithelium (specialized transport across two membranes)
    • Epithelial structure
    • Tight junctions – limit paracellular passage; create barrier
    • Basolateral membrane – blood-facing; rests on basement membrane; cytosolic side of epithelial cells
    • Apical membrane – lumen-facing
    • Na⁺/K⁺ pump (primary active transport)
    • Transports Na⁺ out of the cell and K⁺ into the cell
    • K⁺ channel – allows K⁺ to leak out down electrochemical gradient
    • Glucose carrier – passive exit from the cell via a carrier protein
    • Apical membrane specific components
    • Na⁺ channel – Na⁺ leaks into cell from lumen
    • Na⁺-linked glucose pump – inward movement of Na⁺ coupled with inward movement of glucose
    • TheNa⁺ electrochemical gradient provides energy that drives secondary active transport of glucose

Chapter 5 – Chemical Messengers

  • Definition of chemical messengers
    • The messenger is produced by the source cell
    • The messenger is released, often by secretion
    • The messenger travels to the target cell
    • The target cell has receptors for the messenger
    • Binding of the messenger to the receptor triggers a target cell response
    • Communication is indirect (via receptors and signaling pathways)
  • Classifications of chemical messengers
    • By function
    • By chemical properties (solubility) – lipophobic vs lipophilic; chemical class
  • Functional classifications and subclassifications
    • Paracrine chemical messenger – signals nearby cells
    • Autocrine chemical messenger – a subclass of paracrines; signals the same cell that secreted it
    • Neurotransmitter – messenger produced by neurons; released into the extracellular fluid of the synaptic cleft
    • Hormone – messenger produced by endocrine cells; secreted into the blood via interstitial fluid
    • Neurohormone – messenger produced by neurons; secreted into the blood
  • Lipophobic vs lipophilic ligands
    • Lipophobic (water-soluble; not lipid soluble)
    • Receptors on the cell membrane
    • Generally cause enzyme activation or changes in membrane permeability
    • Examples: amino acids, amines, peptide and protein messengers
    • Lipophilic (lipid soluble; not water soluble)
    • Usually intracellular receptors (cytosol or nucleus)
    • General target response via gene activation
    • Examples: steroid ligands, eicosanoids
  • Storage vs synthesis on demand
    • Lipophobic ligands: stored in vesicles; released by exocytosis
    • Lipophilic ligands: synthesized on demand; cannot be stored in vesicles
  • Transport of messengers
    • Diffusion through interstitial fluid (local signaling)
    • Source and target are close; ligand degrades quickly
    • Bloodborne transport (distance signaling)
    • Lipophobic ligands dissolve in plasma
    • Lipophilic ligands bind to carrier proteins
  • Receptor binding and signal transduction
    • Receptor binding
    • Specificity – generally binds one messenger or a class
    • One messenger may bind to many receptor types
    • Receptors may have different affinities (binding strength)
    • One target cell may have receptors for many messengers
    • Binding is brief and reversible
    • Affinity – strength of binding
    • Location of binding
      • Lipophobic ligands – receptors on the cell membrane
      • Lipophilic ligands – receptors inside the cell (cytosol or nucleus)
    • Cellular response and factors that influence response
    • Strength depends on: concentration of messenger, number of receptors per cell, receptor affinity
  • Up-regulation vs down-regulation
    • Up-regulation – receptor number increases on the target; occurs when messenger concentrations are low for a prolonged period; cells become more responsive
    • Down-regulation – receptor number decreases on the target; occurs when messenger concentrations are high for a prolonged period; cells become less responsive (tolerance)
  • Agonists and antagonists
    • Agonist – binds to receptor and mimics normal response
    • Antagonist – binds to receptor but does not trigger a response; competes with normal ligand; response is opposite of an agonist
  • Types of receptors and signal transduction mechanisms
    • Signal transduction can be intracellular-mediated or membrane-bound
    • Intracellular-mediated responses (lipophilic ligands; except thyroid hormones)
    • Receptors located in cytosol or nucleus
    • Cell response often via gene activation
    • Membrane-bound receptor-mediated responses
    • Receptor activation leads to: movement of ions or phosphorylation of enzymes
  • Receptor classifications (channel-linked, enzyme-linked, GPCRs)
    • Channel-linked receptors (fast ligand-gated channels)
    • Usually highly specific; receptor and channel are same protein
    • Ligand binding causes channel opening/closing; ions diffuse across the membrane
    • Action is direct
    • Enzyme-linked receptors
    • Receptor and enzyme are the same protein
    • Ligand binding activates the enzyme; activated enzyme causes the target response
    • G protein–coupled receptors (GPCRs)
    • Receptors activate G proteins on the intracellular side of the membrane
    • Messenger binds to receptor → receptor activates G protein
    • G proteins link messenger to slow ligand-gated channels and/or second messengers
  • Quick recall phrases
    • Lipophobic ligands require membrane receptors and rapid, direct signaling
    • Lipophilic ligands use intracellular receptors and modulate gene expression
    • GPCR signaling often involves second messengers (e.g., cAMP, Ca²⁺) to relay the signal
  • Practical implications and examples to remember
    • Hormones like insulin (lipophobic) act via membrane receptors leading to rapid cellular responses
    • Steroid hormones (lipophilic) pass through membranes and affect gene transcription
    • Neurotransmitters like acetylcholine can act at nicotinic (ion channel) receptors or muscarinic (GPCR) receptors depending on subtype