Cell Structure, Membrane Transport, and Tissue Organization: Study Notes for Anatomy & Physiology

Chapter 3: Cellular Structure and Function

Plasma Membrane Structure and Passive Transport

The plasma membrane is a selectively permeable barrier that regulates the movement of substances into and out of the cell. Its structure is crucial for various passive transport processes.

• Phospholipid bilayer: Composed of hydrophilic heads and hydrophobic tails, forming a semi-permeable boundary.

• Passive transport: Movement of substances across the membrane without energy input, including diffusion and osmosis.

• Example: Oxygen and carbon dioxide diffuse directly through the lipid bilayer.

Types of Diffusion and Osmosis

Cells utilize different mechanisms to transport substances based on their properties and concentration gradients.

• Simple diffusion: Movement of small, nonpolar molecules (e.g., O2, CO2) directly through the membrane.

• Facilitated diffusion: Movement of larger or polar molecules via membrane proteins (channels or carriers).

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Direction: All move substances down their concentration gradients.

• Mechanism: Simple diffusion is direct; facilitated diffusion uses proteins; osmosis involves aquaporins.

Active Transport: Primary vs. Secondary

Active transport moves substances against their concentration gradients, requiring energy.

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

• Secondary active transport: Uses energy from the movement of another substance down its gradient (e.g., glucose transport coupled to Na+ influx).

Endocytosis and Exocytosis

Cells use vesicular transport to move large particles or volumes across the membrane.

• Endocytosis: Uptake of substances into the cell via vesicle formation.

• Exocytosis: Release of substances from the cell by vesicle fusion with the membrane.

• Direction: Endocytosis is inward; exocytosis is outward.

Types of Endocytosis

Endocytosis can be classified based on the nature of the material taken in.

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

• Phagocytosis: "Cell eating"; engulfment of large particles or cells.

• Receptor-mediated endocytosis: Specific uptake of molecules via receptor binding.

Membrane Potential

The membrane potential is the voltage difference across the plasma membrane, essential for cell signaling.

• Resting membrane potential: Established by ion gradients, mainly Na+ and K+.

• Maintenance: Na+/K+ ATPase pump maintains gradients.

• Equation: $V_m = rac{RT}{F} imes ext{ln} rac{[K^+]_ ext{out}}{[K^+]_ ext{in}}$ (Nernst equation for K+)

Membrane Receptors

Membrane receptors mediate communication between the cell and its environment.

• Roles: Signal transduction, cell recognition, and transport.

• G protein-coupled receptors (GPCRs): Initiate intracellular signaling cascades upon ligand binding.

Cytosol Composition

The cytosol is the fluid component of the cytoplasm, containing water, ions, proteins, and nutrients.

• Functions: Site of many metabolic reactions.

Mitochondria Structure and Function

Mitochondria are double-membraned organelles responsible for ATP production.

• Structure: Outer membrane, inner membrane with cristae, and matrix.

• Function: Cellular respiration and energy production.

Ribosomes, Endoplasmic Reticulum, and Golgi Apparatus

These organelles are involved in protein synthesis and processing.

• Ribosomes: Sites of protein synthesis; can be free or bound to ER.

• Endoplasmic reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids and detoxifies.

• Golgi apparatus: Modifies, sorts, and packages proteins and lipids for secretion or use within the cell.

• Interrelationships: Proteins synthesized in the ER are processed in the Golgi and transported via vesicles.

Lysosomes and Peroxisomes

Both are membrane-bound organelles with distinct functions.

• Lysosomes: Contain digestive enzymes for breaking down waste and cellular debris.

• Peroxisomes: Contain enzymes for oxidation reactions, including breakdown of fatty acids and detoxification of hydrogen peroxide.

Centrioles, Cilia, and Flagella

Centrioles are involved in cell division and formation of cell extensions.

• Role: Organize microtubules in mitosis and form basal bodies for cilia and flagella.

• Cilia: Short, hair-like structures for movement of substances across cell surfaces.

• Flagella: Longer, whip-like structures for cell motility (e.g., sperm).

• Microvilli: Finger-like extensions that increase surface area for absorption.

Cytoskeletal Elements

The cytoskeleton provides structural support and facilitates movement.

• Microfilaments: Actin filaments for cell shape and movement.

• Intermediate filaments: Provide mechanical strength.

• Microtubules: Tubulin polymers for intracellular transport and cell division.

Nuclear Envelope, Nucleolus, and Chromatin

The nucleus contains genetic material and is surrounded by a double membrane.

• Nuclear envelope: Double membrane with nuclear pores for transport.

• Nucleolus: Site of ribosomal RNA synthesis.

• Chromatin: DNA-protein complex; condenses to form chromosomes during cell division.

Cell Cycle Phases

The cell cycle consists of distinct phases for cell growth and division.

• G1 phase: Cell growth.

• S phase: DNA replication.

• G2 phase: Preparation for mitosis.

• M phase: Mitosis and cytokinesis.

DNA Replication

DNA replication ensures genetic continuity during cell division.

• Process: DNA unwinds, and each strand serves as a template for synthesis of a new complementary strand.

• Enzymes: DNA polymerase, helicase, ligase.

Genes and Genetic Code

Genes are segments of DNA that code for proteins; the genetic code is the set of rules by which nucleotide sequences are translated into amino acids.

• Function: Genes determine cell structure and function by directing protein synthesis.

Transcription and Translation

These processes convert genetic information into functional proteins.

• Transcription: DNA is used to synthesize messenger RNA (mRNA).

• Translation: mRNA is decoded by ribosomes to assemble amino acids into proteins.

Chemical Composition of Plasma Membrane

The plasma membrane is composed of lipids, proteins, and carbohydrates, each contributing to its function.

• Lipids: Phospholipids, cholesterol (fluidity), glycolipids.

• Proteins: Integral and peripheral; involved in transport, signaling, and structural support.

• Carbohydrates: Glycoproteins and glycolipids for cell recognition.

Cell Junctions

Cell junctions connect adjacent cells and regulate communication and permeability.

• Tight junctions: Prevent leakage between cells.

• Desmosomes: Provide mechanical strength.

• Gap junctions: Allow direct communication via ion and molecule passage.

Chapter 4: Tissue Organization

Structural and Functional Characteristics of Epithelial Tissue

Epithelial tissue covers body surfaces, lines cavities, and forms glands.

• Characteristics: Cellularity, polarity, attachment, avascularity, regeneration.

• Functions: Protection, absorption, secretion, filtration.

Types of Epithelia: Classification, Function, and Location

Epithelia are classified by cell shape and number of layers.

• Simple epithelium: Single layer; absorption and filtration (e.g., alveoli).

• Stratified epithelium: Multiple layers; protection (e.g., skin).

• Squamous, cuboidal, columnar: Cell shapes with specific functions and locations.

Glands: Definition and Types

Glands are specialized epithelial structures that secrete substances.

• Exocrine glands: Secrete into ducts (e.g., sweat glands).

• Endocrine glands: Secrete hormones directly into blood.

• Unicellular glands: Single cells (e.g., goblet cells).

• Multicellular glands: Composed of multiple cells; classified by structure and function.

Connective Tissue: Characteristics and Elements

Connective tissue supports, binds, and protects organs.

• Common characteristics: Extracellular matrix, varying vascularity.

• Structural elements: Cells (fibroblasts, adipocytes), fibers (collagen, elastic, reticular), ground substance.

Types of Connective Tissue and Functions

Connective tissues are classified based on their structure and function.

• Loose connective tissue: Areolar, adipose, reticular; support and cushioning.

• Dense connective tissue: Regular, irregular, elastic; strength and flexibility.

• Specialized connective tissue: Cartilage, bone, blood.

Muscle Tissue: Structure and Location

Muscle tissue is responsible for movement and force generation.

• Skeletal muscle: Voluntary, striated; attached to bones.

• Cardiac muscle: Involuntary, striated; found in heart.

• Smooth muscle: Involuntary, non-striated; walls of hollow organs.

Nervous Tissue: General Characteristics

Nervous tissue is specialized for communication via electrical and chemical signals.

• Components: Neurons (signal transmission), neuroglia (support).

• Functions: Sensory input, integration, motor output.

Additional info:

• Some details, such as specific examples of cell types and tissue locations, were inferred based on standard Anatomy & Physiology curriculum.