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

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Chapter 3: Cell Structure and Membrane Transport

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 barrier to most water-soluble substances.
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 Passive Transport: Simple Diffusion, Facilitated Diffusion, and Osmosis

Passive transport mechanisms differ in the substances they move and their mechanisms.

Simple Diffusion: Movement of small, nonpolar molecules (e.g., O2, CO2) directly through the membrane down their concentration gradient.
Facilitated Diffusion: Movement of larger or polar molecules (e.g., glucose, ions) via protein channels or carriers.
Osmosis: Diffusion of water across a selectively permeable membrane through aquaporins.
Direction: All move substances from areas of higher to lower concentration.

Active Transport: Primary vs. Secondary

Active transport requires energy to move substances against their concentration gradients.

Primary Active Transport: Direct use of ATP to transport molecules (e.g., Na+/K+ pump).
Secondary Active Transport: Uses energy from the movement of one substance down its gradient to drive another substance against its gradient.

Endocytosis and Exocytosis

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

Endocytosis: Uptake of materials into the cell via vesicles (e.g., phagocytosis, pinocytosis).
Exocytosis: Release of substances from the cell via vesicle fusion with the plasma membrane.
Direction: Endocytosis brings substances in; exocytosis expels substances out.

Types of Endocytosis: Pinocytosis, Phagocytosis, Receptor-Mediated Endocytosis

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 electrical potential difference across the plasma membrane.

Resting Membrane Potential: Established by the unequal distribution of ions, mainly Na+ and K+, and maintained by the Na+/K+ pump.
Equation:

Membrane Receptors and G Protein-Coupled Receptors

Membrane Receptors: Proteins that bind signaling molecules and initiate cellular responses.
G Protein-Coupled Receptors (GPCRs): Activate intracellular signaling cascades via G proteins.

Cytosol Composition

Cytosol: The fluid portion of the cytoplasm, containing water, ions, proteins, and nutrients.

Mitochondria: Structure and Function

Structure: Double membrane, inner folds (cristae).
Function: ATP production via cellular respiration.

Ribosomes, Endoplasmic Reticulum, and Golgi Apparatus

Ribosomes: Sites of protein synthesis; free or bound to rough 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 in the cell.
Interrelationships: Proteins made in rough ER are sent to Golgi for processing.

Lysosomes and Peroxisomes

Lysosomes: Contain digestive enzymes for breaking down waste and cellular debris.
Peroxisomes: Contain enzymes for breaking down fatty acids and detoxifying harmful substances.

Centrioles, Cilia, and Flagella

Centrioles: Organize microtubules; essential for cell division and formation of cilia/flagella.
Cilia: Short, hair-like extensions for movement of substances across cell surfaces.
Flagella: Long, whip-like extensions for cell movement (e.g., sperm).

Microvilli vs. Cilia

Microvilli: Increase surface area for absorption; found in intestinal cells.
Cilia: Move substances over cell surfaces; found in respiratory tract.

Cytoskeletal Elements

Microfilaments: Actin filaments for cell shape and movement.
Intermediate Filaments: Provide mechanical support.
Microtubules: Tubulin structures for cell shape, transport, and division.

Nuclear Envelope, Nucleolus, and Chromatin

Nuclear Envelope: Double membrane with pores for transport.
Nucleolus: Site of ribosome synthesis.
Chromatin: DNA and associated proteins; condenses to form chromosomes during cell division.

Cell Cycle Phases

Interphase: Cell growth and DNA replication.
Prophase: Chromatin condenses, spindle forms.
Metaphase: Chromosomes align at cell equator.
Anaphase: Sister chromatids separate.
Telophase: Nuclear envelopes reform.
Cytokinesis: Division of cytoplasm.

DNA Replication

Process: DNA unwinds, each strand serves as a template for a new strand.
Equation:

Gene and Genetic Code

Gene: Segment of DNA coding for a protein.
Genetic Code: Sequence of nucleotides specifying amino acids.

Transcription and Translation

Transcription: DNA is used to synthesize mRNA.
Translation: mRNA is used to assemble amino acids into proteins.
Equation:

Chemical Composition of Plasma Membrane

Components: Phospholipids, cholesterol, proteins, carbohydrates.
Functions: Barrier, communication, transport, cell recognition.

Cell Junctions: Tight Junctions, Desmosomes, Gap Junctions

Tight Junctions: Seal cells together, prevent leakage.
Desmosomes: Anchor cells together, provide mechanical strength.
Gap Junctions: Allow communication via channels between cells.

Chapter 4: Tissue Types and Characteristics

Structural and Functional Characteristics of Epithelial Tissue

Characteristics: Cellularity, polarity, attachment, avascularity, regeneration.
Functions: Protection, absorption, secretion, sensation.

Types of Epithelia: Classification, Functions, and Locations

Simple Squamous: Single layer, flat cells; found in alveoli, blood vessels.
Simple Cuboidal: Single layer, cube-shaped; found in kidney tubules.
Simple Columnar: Single layer, tall cells; found in digestive tract.
Stratified Squamous: Multiple layers, flat cells; found in skin, mouth.
Transitional: Multiple layers, can stretch; found in urinary bladder.

Glands: Definition and Types

Gland: Structure that secretes substances.
Exocrine Glands: Secrete into ducts (e.g., sweat glands).
Endocrine Glands: Secrete hormones into blood (e.g., thyroid gland).
Unicellular vs. Multicellular: Single cell (e.g., goblet cell) vs. many cells (e.g., salivary gland).

Classification of Multicellular Exocrine Glands

Structural: Simple (unbranched ducts) or compound (branched ducts).
Functional: Merocrine (exocytosis), apocrine (part of cell lost), holocrine (entire cell ruptures).

Connective Tissue: Characteristics and Elements

Common Features: Cells, fibers, ground substance (matrix).
Structural Elements: Fibroblasts, collagen fibers, elastic fibers, reticular fibers.

Types of Connective Tissue and Functions

Loose Connective Tissue: Areolar, adipose, reticular; supports and binds tissues.
Dense Connective Tissue: Regular, irregular, elastic; provides strength and flexibility.
Cartilage: Hyaline, elastic, fibrocartilage; supports and cushions.
Bone: Rigid support and protection.
Blood: Transport of nutrients, gases, and waste.

Muscle Tissue: Structure and Location

Skeletal Muscle: Striated, voluntary; attached to bones.
Cardiac Muscle: Striated, involuntary; found in heart.
Smooth Muscle: Non-striated, involuntary; found in walls of hollow organs.

Nervous Tissue: General Characteristics

Components: Neurons and neuroglia.
Functions: Transmit electrical signals, support and protect neurons.

Table: Comparison of Cell Junctions

Junction Type	Structure	Function	Location
Tight Junction	Interlocking proteins	Seal between cells	Intestinal lining
Desmosome	Protein plaques, intermediate filaments	Mechanical strength	Skin, heart
Gap Junction	Connexon channels	Cell communication	Cardiac muscle

Table: Types of Epithelial Tissue

Type	Structure	Function	Location
Simple Squamous	Single layer, flat cells	Diffusion, filtration	Alveoli, capillaries
Simple Cuboidal	Single layer, cube-shaped	Secretion, absorption	Kidney tubules
Simple Columnar	Single layer, tall cells	Absorption, secretion	Digestive tract
Stratified Squamous	Multiple layers, flat cells	Protection	Skin, mouth
Transitional	Multiple layers, can stretch	Stretching	Urinary bladder

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