Cell Structure and Function: An Overview for Anatomy & Physiology

Cells: Introduction and Overview

Learning Outcomes

• Outline and define the major structural components of a cell.

• Name the fluids inside and outside a cell.

• State the size range of human cells and explain why cell size is limited.

Types of Cells in the Human Body

The human body contains over 200 different types of cells, each specialized for particular functions. These include:

• Nerve cells (neurons): Specialized for communication via electrical and chemical signals.

• Muscle cells: Responsible for movement; includes striated (voluntary), smooth (involuntary), and cardiac muscle cells.

• Bone cells: Involved in bone formation and maintenance.

• Gland cells: Secrete substances such as hormones or enzymes.

• Blood cells: Includes red blood cells (oxygen transport), white blood cells (immune defense), lymphocytes, monocytes, neutrophils, eosinophils, and basophils.

• Reproductive cells: Sperm and ovum, responsible for sexual reproduction.

Additional info: Each cell type has a unique structure that supports its specific function in the body.

Major Structural Components of a Cell

Plasma Membrane (Cell Membrane)

The plasma membrane is a phospholipid bilayer that forms the boundary of the cell, separating the internal environment from the external environment.

• Phospholipid bilayer: Composed of hydrophilic (water-attracting) phosphate heads and hydrophobic (water-repelling) fatty acid tails.

• Functions: Regulates entry and exit of substances, facilitates communication with other cells, and maintains chemical composition differences between intracellular and extracellular fluids.

Cytoplasm

The cytoplasm is the region between the plasma membrane and the nucleus, containing cytosol and organelles.

• Cytosol: The clear, gel-like fluid that embeds the cell's organelles; also called intracellular fluid (ICF).

• Organelles: Specialized structures that perform distinct cellular functions.

Fluids:

• Intracellular Fluid (ICF): Fluid within the cell (cytosol).

• Extracellular Fluid (ECF): Fluid outside the cell, found in tissues (interstitial fluid), blood plasma, and lymph.

Nucleus

The nucleus contains the cell's genetic material (DNA) and acts as the control center for cellular activities.

• Functions: Stores genetic information, directs protein synthesis, and regulates cell growth and reproduction.

Structure of a Generalized Cell

Key Organelles and Their Functions

• Nucleus: Contains DNA; site of ribosome synthesis (nucleolus).

• Mitochondria: "Powerhouse" of the cell; site of ATP (energy) production. Surrounded by a double membrane with inner folds called cristae.

• Endoplasmic Reticulum (ER):

  • Rough ER (RER): Studded with ribosomes; synthesizes and processes proteins.

  • Smooth ER (SER): Lacks ribosomes; synthesizes lipids and detoxifies chemicals.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosomes: Contain digestive enzymes; break down waste, cellular debris, and foreign materials.

• Peroxisomes: Break down fatty acids and detoxify harmful substances.

• Ribosomes: Sites of protein synthesis; can be free in cytoplasm or attached to RER.

• Cytoskeleton: Network of protein filaments (microfilaments, intermediate filaments, microtubules) that provide structural support and facilitate movement.

Additional info: The structure of a generalized cell is often depicted in diagrams to illustrate the spatial relationships among organelles.