Body structure and organ system

Primary Components of Human Cells

• Plasma Membrane

  Selectively permeable membrane composed of a phospholipid bilayer with embedded proteins. It encases the entire cell and plays a critical role in cellular homeostasis by regulating what enters and exits the cell.

  • Functions:

    • Separates the intracellular environment from the extracellular environment.

    • Facilitates communication with other cells through protein receptors.

    • Essential for maintaining the proper concentration of ions and nutrients necessary for cellular functions.

• Cytoplas

  A viscous, gel-like fluid that fills the interior of the cell, primarily composed of water, electrolytes, and a mixture of organic molecules. It serves as the site where many cellular processes occur.

  • Functions:

    • Houses organelles and provides a medium for biochemical reactions.

    • Supports and maintains cell structure through its viscosity.

• Nucleus

  A large, spherical organelle positioned near the center of the cell, containing the cell's genetic material organized into chromatin.

  • Functions:

    • Acts as the control center, regulating gene expression and cell activity.

    • Houses chromosomes during cell division and direct formation of ribosomes in the nucleolus.

• Nuclear Membrane

  A double-layered, porous membrane that encases the nucleus and contains nuclear pores that control the movement of substances in and out of the nucleus.

  • Functions:

    • Protects genetic material.

    • Facilitates selective transport, allowing RNA and proteins to pass while preventing DNA from leaking out.

• Nucleolus

  A prominent, dense structure within the nucleus, without a surrounding membrane, where ribosomal RNA (rRNA) is synthesized.

  • Functions:

    • Produces ribosomes, which are essential for protein synthesis.

• Mitochondria

  Elongated, rod-shaped organelles often referred to as the “powerhouses” of the cell due to their role in energy production, containing their own DNA and protein synthesis machinery.

  • Functions:

    • Convert nutrients such as glucose and fats into adenosine triphosphate (ATP), the energy currency of the cell.

    • Play a role in cellular respiration and metabolism.

• Ribosomes

  Small, complex structures made of ribosomal RNA and protein, found either floating freely in the cytoplasm or attached to the rough endoplasmic reticulum.

  • Functions:

    • Site of protein synthesis, where messenger RNA (mRNA) is translated into polypeptides to form proteins.

    • Critical for both intracellular protein synthesis and for proteins meant for secretion or incorporation into the cell membrane.

• Endoplasmic Reticulum

  A vast network of membranous tubules and sacs that can be categorized into rough (RER) and smooth (SER) endoplasmic reticulum, connected to the nuclear membrane and extending throughout the cytoplasm.

  • Functions:

    • RER: Studded with ribosomes; plays a key role in synthesizing and transporting proteins.

    • SER: Lacks ribosomes; involved in lipid synthesis, detoxification processes, and calcium ion storage.

• Golgi Apparatus

  Composed of a series of flattened membranous sacs, playing a pivotal role in modifying, sorting, and packaging proteins and lipids produced in the endoplasmic reticulum.

  • Functions:

    • Processes and packages proteins for secretion or delivery to other organelles.

    • Forms lysosomes and produces secretory vesicles containing materials for export.

• Lysosomes

  Membrane-bound organelles filled with enzymes capable of breaking down various biomolecules.

  • Functions:

    • Digest cellular waste, damaged organelles, and other unwanted materials through hydrolytic enzymes, recycling cellular components and maintaining homeostasis.

• Cytoskeleton

  A dynamic network composed of protein filaments and tubules that provides structural support, shape, and organization to the cell.

  • Functions:

    • Maintains cell shape and mechanical resistance to deformation.

    • Facilitates intracellular transport and cell motility through the movement of organelles and vesicles.

• Centrioles

  Cylindrical structures found in pairs, composed of microtubules, located near the nucleus and involved in cell division.

  • Functions:

    • Play a vital role in organizing the mitotic spindle during cell division and guiding the movement of chromosomes to daughter cells.

• Cilia

  Short, hair-like projections extending from the cell surface, covered by the plasma membrane and