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
- 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