Chapter 3: Cells, Membranes, and Tissues – Key Concepts in Anatomy & Physiology

Chapter 3: Cells, Membranes, and Tissues

Cell Types and Major Differences

This section introduces the fundamental differences between eukaryotic and prokaryotic cells, which are the two main categories of cells found in living organisms.

• Eukaryotic cells: Contain a true nucleus and membrane-bound organelles. Examples include animal and plant cells.

• Prokaryotic cells: Lack a true nucleus and membrane-bound organelles. Example: bacteria.

• Key differences: Eukaryotes are generally larger, have complex internal structures, and can be multicellular; prokaryotes are simpler and usually unicellular.

• Example: Escherichia coli (prokaryote) vs. human skin cell (eukaryote).

Body Compartments: Cavities, Body Fluids, and Membranes

The human body is organized into various compartments separated by membranes, containing different types of fluids.

• Body cavities: Spaces within the body that house organs (e.g., thoracic, abdominal cavities).

• Body fluids:

  • Intracellular fluid (ICF): Fluid inside cells.

  • Extracellular fluid (ECF): Fluid outside cells, including interstitial fluid and plasma.

• Membranes: Thin layers of tissue that cover surfaces, line cavities, and separate spaces or organs.

Concept of Lumen

The lumen refers to the inside space of a tubular structure, such as a blood vessel or the intestine.

• Example: The lumen of the small intestine is where digestion and absorption occur.

Biological Membranes: Composition and Functions

Biological membranes are essential for compartmentalization and regulation of substances entering or leaving the cell.

• Main components: Phospholipid bilayer, proteins, carbohydrates, and cholesterol.

• Functions:

  • Selective permeability

  • Cell signaling

  • Structural support

  • Cell recognition

Cell Anatomy: Major Organelles

Cells contain specialized structures called organelles that perform distinct functions.

• Nucleus: Contains genetic material (DNA); controls cell activities.

• Mitochondria: Site of ATP (energy) production.

• Endoplasmic reticulum (ER): Synthesizes proteins (rough ER) and lipids (smooth ER).

• Golgi apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes for waste breakdown.

• Subcellular localization: Refers to the specific location of organelles within the cell.

Cytoskeleton: Structure and Functions

The cytoskeleton is a network of protein fibers that provides structural support and facilitates movement within the cell.

• Main proteins: Microtubules, microfilaments (actin), and intermediate filaments.

• Functions:

  • Maintains cell shape

  • Enables intracellular transport

  • Facilitates cell division and movement

Tissues of the Body

The human body is composed of four primary tissue types, each with distinct characteristics and functions.

Tissue Type	Characteristics	Location/Function
Epithelial	Cells closely packed, form sheets	Lines surfaces, forms glands
Connective	Cells scattered in extracellular matrix	Supports, binds, protects organs
Muscle	Elongated cells (fibers), contractile	Movement, posture, heat production
Nervous	Neurons and supporting cells	Receives, processes, transmits information

Extracellular Matrix (ECM): Concept and Role

The extracellular matrix is a complex network of proteins and carbohydrates outside cells, providing structural and biochemical support.

• Main components: Collagen, elastin, proteoglycans, glycoproteins.

• Functions:

  • Anchors cells

  • Regulates cell behavior

  • Facilitates tissue repair

Cell Junctions

Cell junctions are specialized structures that connect adjacent cells, allowing communication and maintaining tissue integrity.

• Tight junctions: Seal cells together, preventing leakage.

• Desmosomes: Provide mechanical strength by anchoring cells.

• Gap junctions: Allow direct communication between cells via channels.

Summary Table: Key Concepts

Concept	Definition	Example/Application
Cell Type	Eukaryotic vs. Prokaryotic	Human cell vs. Bacterial cell
Body Fluid	ICF and ECF	Plasma, cytoplasm
Membrane	Phospholipid bilayer	Cell membrane
Tissue Type	Epithelial, Connective, Muscle, Nervous	Skin, bone, muscle, brain

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.