Anatomy & Physiology Study Guide: Cell Types, Organ Systems, Metabolism, and Membrane Transport (Chapters 1-5)

Chapter 1 – Introduction to Physiology

Cell and Tissue Types

Cells are the basic units of life, and tissues are groups of similar cells performing specific functions. There are four primary types of cells/tissues in the human body:

• Neurons/Nervous tissue: Specialized for communication via electrical and chemical signals.

• Muscle cells/tissue: Responsible for movement and force generation.

• Epithelial cells/tissue: Form protective barriers and are involved in absorption, secretion, and transport.

• Connective cells/tissue: Provide structural support, connect tissues, and store energy.

Organs and Organ Systems

Organs and organ systems are hierarchical levels of organization in the body:

• Organs

  • Composed of at least two tissue types.

  • Perform specific functions (e.g., heart pumps blood).

• Organ system

  • Collection of organs performing a particular task (e.g., digestive system).

Internal vs. External Environment

The body maintains distinct internal and external environments:

• Internal environment

  • Immediate environment of most cells.

  • Includes plasma and tissue fluid.

• External environment

  • External side of the epithelial body barrier.

  • Includes surroundings external to the skin, air in the lungs, food in the stomach, urine in the bladder.

Homeostasis

Homeostasis is the ability to maintain a relatively constant internal environment.

• Regulated variable: The aspect that is maintained (e.g., blood glucose, temperature).

• Set point: Expected value of a regulated variable.

Feedback Mechanisms

• 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: The effector pushes the factor farther away from the set point.

Homeostatic Control Mechanism Components

• Receptors: Sensors that detect stimuli and relay signals to the integrating center.

• Integrating center: Receives signals from receptors, orchestrates an appropriate response, often in the brain or endocrine gland, and relays signals to effectors.

• Effectors: Receive signals from the integrating center and are responsible for body responses.

Chapter 2 – The Cell

Biological Molecules

Cells are composed of four major types of biological (organic) molecules:

• Carbohydrates

• Lipids

• Proteins

• Nucleic acids

Cell Components

• Plasma membrane

  • 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 synthesis)

  • Function:

    • Transmission and expression of genetic information

    • Contains DNA (stores genetic code)

    • DNA transcribed to RNA (necessary to express genetic code)

• Cytoplasm

  • Cytosol (fluid) and organelles

  • Location of specific chemical reactions

  • Fat and carbohydrates stored in masses called inclusions

  • Storage of secretory vesicles

• Endoplasmic reticulum (ER)

  • Rough ER: Flattened sacs; functions in synthesis of proteins to be packaged into vesicles.

  • Smooth ER: Tubules, smooth appearance; functions in lipid synthesis and stores calcium.

• Golgi apparatus

  • Post-translational processing of proteins

  • Packaging of proteins and other molecules into vesicles and directing them to the target

• Mitochondria

  • Double membrane; area between outer and inner membrane is intermembrane space

  • Inner membrane folded into cristae; inner space is the matrix

  • 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; degrade certain waste molecules

  • By-product is hydrogen peroxide (H2O2); contain catalase which breaks down H2O2

• Ribosomes

  • No membrane; very small (25 nm); made of two subunits

  • Function: Protein synthesis

  • Fixed (attached to rough ER) or free (loose in cytosol)

• Centrioles

  • Paired cylindrical structures; contain bundles of protein filaments perpendicular to each other

  • Function in development of the mitotic spindle

• Cytoskeleton

  • Made of protein filaments: Microfilaments, Intermediate filaments, Microtubules

  • Functions: Mechanical support and structure, intracellular transport, suspension of organelles, formation of adhesions, contraction, movement

Intercellular Junctions

• Tight junctions: Common in epithelial tissue specialized for molecular transport; form a nearly impermeable barrier; force transepithelial transport.

• Desmosomes: Filamentous junctions between cells; bind cells together for strength; found in tissue subject to mechanical stress; use cadherins.

• Gap junctions: Composed of membrane proteins; link the cytosol of two adjacent cells; ions and molecules move between cells as signals; communication is direct.

Chapter 3 – Metabolism

Definition of Metabolism

Metabolism refers to all chemical reactions occurring in a cell.

Types of Metabolic Reactions

• Hydrolysis: Breaks down large molecules.

• Condensation: Joins smaller molecules together.

• Phosphorylation: Requires energy; addition of phosphate group.

• Dephosphorylation: Releases energy; removal of phosphate group.

• Oxidation: Removal of electrons and H+.

• Reduction: Addition of electrons and H+.

Kinetic vs. Potential Energy

• Kinetic energy: Associated with motion (thermal, radiant, electromagnetic, electrical).

• Potential energy: Stored energy (chemical, mechanical, nuclear, gravitational).

Laws of Thermodynamics

• First Law: Energy cannot be created nor destroyed; energy can change form; energy in the universe (a closed system) is constant. The human body is an open system.

• Second Law: Processes move in the direction that spreads out energy (breaking a large molecule to smaller molecules; movement of molecules from high to low concentration).

Exergonic vs. Endergonic Reactions

• Exergonic reaction: Catabolic; break down large molecules into smaller ones; proceeds spontaneously; releases energy.

• Endergonic reaction: Anabolic; build complex molecules from smaller ones; does not proceed spontaneously; requires an input of energy.

Activation Energy

Activation energy is the 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 identified by the suffix -ase.

Factors Affecting Enzyme-Catalyzed Reaction Rates

• Enzyme's catalytic rate: How many molecules are generated per unit time.

• Substrate concentration.

• Enzyme concentration.

• Affinity of enzyme for substrate.

• Temperature and pH.

Adenosine Triphosphate (ATP)

• ATP is the primary energy source for cellular work.

Stages of Aerobic Cellular Respiration

• Glycolysis

  • Breakdown of glucose to two pyruvate molecules.

  • Takes place in the cytosol.

  • Net gain of 2 ATP molecules.

  • 2 NAD+ molecules reduced to 2 NADH molecules.

  • No O2 consumed; no CO2 produced.

• Linking Step

  • Pyruvate converted to acetyl CoA.

  • One NADH molecule produced per pyruvate molecule.

  • One CO2 molecule per pyruvate molecule.

• Krebs Cycle

  • Production per acetyl CoA:

    • 1 GTP produced = 1 ATP

    • 3 NADH + 3 H+ and 1 FADH2

  • Waste produced per acetyl CoA: 2 CO2

  • As glucose generates two acetyl CoA molecules, the cycle turns twice.

  • 2 ATP per initial glucose molecule.

• Oxidative Phosphorylation/Electron Transport Chain

  • Bulk of ATP is formed by oxidative phosphorylation.

  • Electron transport system: Chain of molecules in the inner mitochondrial membrane.

  • NADH and FADH2 (from previous steps) donate electrons.

  • Molecules undergo oxidation-reduction reactions, going from high to low energy.

  • Last electron acceptor = O2.

  • Energy released is used to pump H+ ions against their concentration gradient into intermembrane space.

  • H+ ions diffuse back through ATP synthase.

  • ATP is synthesized by oxidative phosphorylation.

  • Produces 28 ATP.

• Total ATP produced from 1 glucose molecule: 38 ATP

Chapter 4 – Membrane Transport

Basics of Membrane Transport

Membranes separate intracellular fluid from extracellular fluid and allow exchange of material between these compartments.

• Transport is important for obtaining O2 and nutrients.

Types of Membrane Transport

• Passive transport

  • Spontaneous; no cellular energy required.

  • Movement down the concentration gradient.

  • Types:

    • Simple diffusion: Transport through phospholipid bilayer.

    • Facilitated diffusion: Transport through protein channels or carriers.

    • Osmosis: Diffusion of water through membrane.

• Active transport

  • Movement against the concentration gradient ("uphill").

  • Requires energy and membrane "pump" proteins.

  • Types:

    • Primary active transport: Energy comes from a high-energy compound, usually ATP.

    • Secondary active transport: Energy released from one diffusion drives another transport.

• Transport of macromolecules

  • Uses membrane-bound compartments.

  • Includes endocytosis (movement into the cell) and exocytosis (movement out of the cell).

  • Types of endocytosis:

    • Phagocytosis: Plasma membrane engulfs large particles.

    • Pinocytosis: Engulfing fluid and dissolved substances.

    • Receptor-mediated endocytosis: Substance binds to receptors on cell membrane.

Osmolarity and Tonicity

• Osmolarity: Total solute concentration of a solution.

• Tonicity: Comparative term; caused by impermeant solutes; determines the behavior of a cell placed into the solution.

• Types of solutions:

  • Isotonic solution: Solute concentration is the same inside and outside the cell.

  • Hypertonic solution: Higher solute concentration outside the cell; water leaves the cell.

  • Hypotonic solution: Lower solute concentration outside the cell; water enters the cell.

Membrane Specializations

• Tight junctions: Limit passage of materials through spaces between cells (paracellular spaces).

• Basement membrane: Anchors and supports epithelial cells.

• Na+ pump: Transports Na+ out of the cell.

• K+ transport: Allows K+ to leave the cell down its electrochemical gradient.

• Glucose transport: Glucose passes into the cell through carrier proteins.

• Apical membrane: Membrane on lumen side of cell; Na+ ions pass into the cell.

• Linked glucose pump: Inward movement of Na+ coupled with inward movement of glucose; Na+ electrochemical gradient provides energy for secondary active transport of glucose.

Chapter 5 – Chemical Messengers

Chemical Messengers and Cell Communication

Chemical messengers travel to target cells, which have specific receptors for the messenger. Binding initiates communication and cellular response.

Classification of Chemical Messengers

• By function:

  • Paracrine: Signals nearby cells.

  • Autocrine: Signals the same cell that secreted it.

  • Neurotransmitter: Messenger produced by neurons; released into the ECF of the synaptic cleft.

  • Hormone: Messenger produced by endocrine cells; secreted into the blood.

  • Neurohormone: Messenger produced by neurons; secreted into the blood.

• By chemical properties:

  • Lipophobic ligand: Water soluble, not lipid soluble; does not cross the cell membrane; acts on membrane-bound receptors.

  • Lipophilic ligand: Lipid soluble, not water soluble; easily crosses the cell membrane; acts on intracellular receptors.

Synthesis and Release of Chemical Messengers

• Lipophobic ligands: Synthesis is independent of demand; stored in vesicles until needed; released by exocytosis.

• Lipophilic ligands: Cannot be stored in vesicles; synthesized and released immediately from source.

Transport of Chemical Messengers

• Lipophobic ligands: Quickly degraded; act locally.

• Lipophilic ligands: Transported in blood bound to carrier proteins; act at a distance.

Signal Transduction and Receptor Binding

• Messenger binds to receptor, producing a cellular response.

• Specificity: Receptors generally bind one messenger or a set of similar messengers.

• One messenger may bind to many receptor types; one target cell may have receptors for many messengers.

• Affinity: Strength of binding between receptor and messenger.

• Location of binding:

  • Lipophobic ligands: Cell membrane receptors.

  • Lipophilic ligands: Intracellular receptors.

• Strength of response depends on messenger concentration, number of receptors, and receptor affinity.

Regulation of Receptors

• Up-regulation: Receptor number increases on target cell; occurs with low messenger concentrations for a prolonged period; cells become more responsive.

• Down-regulation: Receptor number decreases; occurs with high messenger concentrations for a prolonged period; cells become less responsive (tolerance develops).

Agonists and Antagonists

• Agonist: Chemical that binds to a receptor and mimics the normal response.

• Antagonist: Chemical that binds to a receptor but does not result in a response; competes with the normal ligand; response is the opposite of an agonist.

Types of Receptors and Signal Transduction

• Intracellular receptors: For lipophilic ligands (except thyroid hormones); found in cytosol or nucleus; response via gene activation.

• Membrane-bound receptor-mediated responses:

  • Movement of ions

  • Phosphorylation reactions

• Fast ligand-gated channels: Receptor and channel are the same protein; binding of ligand opens the channel; ions diffuse across the membrane.

• Enzyme-linked receptors: Receptor and enzyme are the same protein; ligand binding activates the enzyme, causing a cellular response.

• G protein-coupled receptors (GPCRs): Activate regulatory proteins on the intracellular side of the membrane; messenger binds to receptor, activating the G protein, which links the messenger to:

  • Slow ligand-gated channels

  • Second messengers