Chapter 3: Compartmentation: Cells and Tissues

Functional Compartments of the Body

• The body is organized into three major cavities:

  • Cranial cavity: Contains the brain.

  • Thoracic cavity: Encloses the heart and lungs.

  • Abdominopelvic cavity: Contains digestive organs and reproductive organs.

• Fluid-filled compartments also exist within the body:

  • Circulatory system: Includes blood.

  • Eyes: Have aqueous humor.

  • Cerebrospinal fluid (CSF): Surrounds the brain and spinal cord.

  • Pleural and pericardial sacs: Surrounds the lungs and heart respectively.

• Lumen of Organs:

  • Refers to the interior of any hollow organ.

  • Organs with lumen include:

  • Heart

  • Lungs

  • Blood vessels

  • Intestines

  • The lumen may be filled with air or fluid and sometimes connects to the external environment.

• Fluid Compartments in the body functionally include:

  • Extracellular fluid (ECF): Divided into two components.

  • Plasma: Liquid component of blood.

  • Interstitial fluid: Fluid that surrounds cells.

  • Intracellular fluid (ICF): Fluid found within cells.

Biological Membranes

• The cell membrane serves several critical functions:

  • Physical isolation: Separates the interior of the cell from the external environment.

  • Regulation of exchange: Controls the movement of substances in and out of the cell.

  • Communication: Facilitates signaling and communication between the cell and its environment.

  • Structural support: Maintains cell shape and integrity.

  • Secretion: Cells can release substances into the extracellular space.

• Cell membranes are primarily composed of:

  • Lipids (primarily phospholipids), proteins, and carbohydrates.

  • The fluid mosaic model describes the dynamic nature of cell membranes where components move fluidly within the lipid bilayer.

Membrane Composition

• Table 3.1 Composition of Selected Membranes:

  • Red blood cell membrane: 49% protein, 43% lipid, 8% carbohydrate

  • Myelin membrane around nerve cells: 18% protein, 79% lipid, 3% carbohydrate

  • Inner mitochondrial membrane: 76% protein, 24% lipid, 0% carbohydrate

Membrane Lipids

• Hydrophobic barrier: Lipids form a barrier that is resistant to water-soluble substances.

• Types of lipids include:

  • Phospholipids

  • Sphingolipids

  • Cholesterol

• Phospholipids can form several structures in aqueous solutions:

  • Bilayer

  • Micelle

  • Liposome

• Membrane Proteins:

  • Can be loosely or tightly attached, categorized into:

  • Integral vs. Peripheral

  • Transmembrane proteins: Span the membrane.

  • Lipid-anchored proteins: Attached to lipids in the membrane (e.g., GPI anchor).

  • Lipid rafts: Specialized domains within the membrane composed primarily of sphingolipids and lipid-anchored proteins.

Membrane Carbohydrates

• Glycocalyx:

  • A protective layer on the external surface of the cell, formed from:

  • Glycolipids

  • Glycoproteins

Intracellular Compartments

• Differentiation leads to specialized function in cells, depending on active genes.

• Cells consist of the following compartments:

  • Cell Membrane: Outer boundary of the cell.

  • Cytoplasm: Internal environment, including:

  • Cytosol: Fluid portion of cytoplasm.

  • Inclusions: Non-membrane-bound structures (e.g., glycogen granules).

  • Cytoskeleton: Insoluble protein fibers.

  • Organelles: Membrane-bound compartments (e.g., nucleus, mitochondria).

Inclusions in Cytosol

• Inclusions are found in direct contact with cytosol; they lack membranes and serve various functions:

  • Nutrient storage:

  • Glycogen granules

  • Lipid droplets

  • Non-nutrient storage:

  • Ribosomes: Composed of RNA and protein, they are involved in protein synthesis (Includes fixed and free ribosomes, and polyribosomes).

Cytoplasmic Protein Fibers

• Differ in size and function:

  • Microfilaments: Composed of actin fibers; involved in cell movement.

  • Intermediate filaments: Include keratin and neurofilaments; provide structural support.

  • Microtubules: Made of tubulin; involved in cell structure and motility.

  • Accessory proteins associated with the cytoskeleton assist with movement and support.

Organelles

• Organelles are specialized compartments surrounded by membranes, including:

  • Mitochondria: Responsible for ATP production; possess their own DNA and double lipid bilayer.

  • Endoplasmic reticulum (ER):

  • Rough ER (RER): Studded with ribosomes, involved in protein synthesis.

  • Smooth ER (SER): Lacks ribosomes, involved in lipid synthesis and calcium ion storage.

  • Golgi apparatus: Modifies, sorts, and packages proteins into vesicles.

  • Vesicles: Two types tracked include lysosomes (break down waste) and peroxisomes (break down fatty acids).

Nucleus

• The nucleus serves as the control center of the cell.

  • Nuclear envelope: Comprises two membranes with nuclear pore complexes for substance exchange.

  • Chromatin: Organizes DNA and contains proteins for protection.

  • Nucleoli: Site for ribosomal RNA synthesis.

Tissues of the Body

• Histology: The study of tissue structure and function.

• Extracellular matrix (ECM): Produced by cells, varying in composition across different tissues.

  • Proteoglycans: Large molecules that provide cushioning and support.

  • Fibers: Include collagen, fibronectin, and laminin.

Cell Junctions

• Cell-adhesion molecules (CAMs): Membrane-spanning proteins that facilitate cell adhesion.

  • Types of Cell Junctions:

  • Gap junctions: Allow communication between cells.

  • Tight junctions: Prevent leakage between cells.

  • Anchoring junctions: Stabilize tissue structure (includes adherens junctions and desmosomes).

Tissue Types

• Four main tissue types:

  • Epithelial tissue: Covers body surfaces and lines cavities.

  • Connective tissue: Supports and binds other tissues.

  • Muscle tissue: Facilitates movement (includes cardiac, smooth, and skeletal).

  • Neural tissue: Transmits electrical signals via neurons and supports cells (glial cells).

Epithelial Tissues

• Epithelia provide protection and regulate exchange.

  • Structures include:

  • Layers of epithelial cells.

  • Basal lamina: Separates epithelium from underlying connective tissue.

Types of Epithelia

• Classified based on structure:

  • Simple: One layer of cells.

  • Stratified: Multiple layers of cells.

  • Shapes:

  • Squamous: Flattened cells.

  • Cuboidal: Cube-shaped cells.

  • Columnar: Column-shaped cells.

Exchange Epithelium

• Characteristics: Very thin, flattened cells for gas exchange.

  • Found in lungs and blood vessels; referred to as endothelium in blood vessels.

Transporting Epithelium

• Characteristics: Cell shapes are cuboidal or columnar with specific membrane modifications.

  • Properties vary depending on tissue function and can be regulated.

Ciliated and Protective Epithelia

• Ciliated epithelia: Move fluid and particles (e.g., in the respiratory tract).

• Protective epithelia: Prevent exchange, protecting against mechanical and chemical stress.

Secretory Epithelia

• Produce and secrete substances into extracellular space (e.g., exocrine and endocrine glands).

  • Exocrine glands: Release secretions externally (e.g., via ducts).

  • Endocrine glands: Release hormones directly into the bloodstream.

Characteristics of Tissue Types

• Epithelial: Minimal matrix, no direct blood supply, various arrangements (simple to stratified).

• Connective: Extensive matrix, with variable components and functions.

• Muscle: Minimal matrix, specialized for contraction.

• Nerve: Minimal matrix, excitable cells for signaling.

Tissue Remodeling

• Cell death:

  • Necrosis: Death due to injury.

  • Apoptosis: Programmed cell death.

• Stem Cells:

  • Undergo mitosis and possess totipotent, pluripotent, and multipotent potential.

  • Exhibit plasticity: Ability to change shape and function.

Organs

• Definition: Groups of tissues that work together to perform related functions.

• Example: Skin incorporates all four tissue types and performs multiple functions.