HISTOLOGY

Wall of Channel Formation by Nexins

  • Description of a cell's structure involved in communication junctions.

  • Components include:

    • Nexins

    • Cell membrane

    • Intercellular gap

    • Organelles (Nucleus, Golgi complex, Mitochondria, etc.)

Endoplasmic Reticulum (ER)

  • Description of the endoplasmic reticulum as a membranous network within the cell.

  • Divided into two types:

    1. Smooth Endoplasmic Reticulum (SER):

    • Involved in lipid metabolism and calcium storage.

    • Synthesizes lipids, particularly membrane phospholipids.

    • Located near the cell's periphery and processes proteins from RER.

    1. Rough Endoplasmic Reticulum (RER):

    • Site of protein synthesis.

    • Ribosomes give it a rough appearance.

    • The lumen of RER continuous with the perinuclear space and lumen of SER.

  • Cytoplasm is divided into:

    • Vacuoplasm (inside channels)

    • Hyaloplasm (outside channels)

Ribosomes

  • Sites of protein synthesis in both connection with RER and free in cytoplasm.

  • Can exist as monosomes (single ribosomes) or polysomes (groups of ribosomes).

  • Structure:

    • Approximately 15 nm in diameter, made of proteins and RNA.

Mitochondria

  • Double-membraned organelle known as the cell's powerhouse (produces ATP).

  • Number varies with metabolic activity of the cell (0.5-2 μm).

  • Structure includes:

    • Outer membrane (smooth)

    • Inner membrane (folded into cristae)

    • Matrix containing enzymes, RNA, and DNA (maternal origin).

  • Functions:

    • Produces ATP, stocks calcium and mediates cell growth and death.

Golgi Complex

  • Also known as the Golgi body, involved in secretion and intracellular transport.

  • Structure:

    • Composed of flattened sacs called cisternae (around 4-8 cisternae in most cells).

    • Two extremes labeled as:

    • Cis face (facing the ER)

    • Trans face (farther from ER)

  • Involved in the following processes:

    • Phosphorylation of proteins.

    • Glycosylation of proteins to form glycoproteins.

    • Packaging substances into vesicles (secretory vesicles, lysosomes, etc).

Lysosomes

  • Vesicles containing hydrolytic enzymes.

  • Role:

    • Digestion of unwanted materials in the cell (e.g., bacteria, worn-out organelles).

  • Formation:

    • Enzymes synthesized in ER are packed into vesicles at the Golgi, forming primary lysosomes.

    • Fuse with endosomes to form secondary lysosomes where active digestion happens.

Peroxisomes

  • Membrane-bound vesicles containing enzymes involved in the oxidation of fatty acids and detoxification processes.

  • Contain enzymes that catabolize hydrogen peroxide.

  • Commonly found in liver and renal tubule cells.

Cytoskeleton

  • Found throughout the cytoplasm; provides structural support, shape, and organization of organelles.

  • Composed of:

    • Microfilaments (actin, 7 nm): Involved in cell motility, muscle contraction, and cytoplasmic streaming.

    • Microtubules (tubulin, 25 nm): Structure, transport, and mitotic spindle formation.

    • Intermediate filaments (10 nm): Provide tensile strength connecting cells to one another.

Centrioles

  • Small structures composed of microtubules, vital for cell division (mitosis).

  • Arranged in a cylinder at right angles to one another within a structure called a centrosome.

Nucleus

  • The control center of the cell, layered compactly within the cell.

  • Its functions include:

    • Storage of genetic material (DNA)

    • Regulation of cellular activities such as growth, metabolism, and reproduction.

Cell Junctions

  • Intercellular connections that pass signals between adjacent cells. Classification includes:

    1. Anchoring junctions - Bind cells together under potential mechanical stress (e.g. desmosomes).

    2. Occluding junctions - Tight junctions that limit the movement of molecules (e.g. intestinal epithelium).

    3. Communicating junctions - Gap junctions facilitate direct transport of substances between cells (e.g. cardiac muscle).

Cell Organelles

  • Summary of organelle function, roles include energy production, protein sorting, secretion, digestion, metabolic cycling, etc.

  • Importance of organelles in maintaining cell integrity and function.

Histology Cross-Sections

  • Diagrams depicting organelles in cells under various magnifications (Figures 2.13-2.21).