Chapter 3: The Cell – Structure and Function in Human Anatomy & Physiology

Basic Processes of Cells

Introduction to Cellular Functions

Cells are the fundamental units of life, performing essential processes to maintain homeostasis and support the organism. The main processes include metabolism, substance transport, communication, and reproduction.

• Cell Metabolism: The sum of all chemical reactions in a cell, necessary for maintaining life. This includes anabolic (building up), catabolic (breaking down), and oxidation-reduction reactions.

• Substance Transport: The movement of compounds into, out of, or within the cell, essential for nutrient uptake and waste removal.

• Communication: Cells interact with their environment and other cells through signaling mechanisms.

• Reproduction: Many cells undergo cell division to produce new cells for growth, repair, or reproduction.

Overview of Cell Structure

Major Components of Animal Cells

Animal cells share three primary structural components, each with specialized functions.

• Plasma Membrane: The outer boundary that separates the cell from its environment.

• Cytoplasm: The region between the plasma membrane and the nucleus, containing:

  • Cytosol: Also called intracellular fluid (ICF), a watery gel with proteins, dissolved solutes, and RNA. It is the site of many metabolic reactions and may contain inclusions (storage bodies).

  • Organelles: Specialized structures ("molecular machines") that perform and compartmentalize specific cellular functions (e.g., mitochondria, endoplasmic reticulum).

  • Cytoskeleton: A network of protein filaments that supports the cell, maintains its shape, holds organelles in place, and provides tracks for intracellular transport.

• Nucleus: The control center of the cell, surrounded by a nuclear envelope. It contains most of the cell's DNA and is the site for RNA production, which together regulate protein synthesis and cellular activities.

Functions of the Plasma Membrane

• Physically isolates the cell from its surroundings, providing a selective barrier.

• Provides structural support and mediates communication with other cells.

• Regulates the transport of substances into and out of the cell.

• Identifies the cell to other cells and the immune system.

The plasma membrane also defines two main fluid compartments:

• Intracellular Space: Contains intracellular fluid (cytosol) within the cell.

• Extracellular Space: Contains extracellular fluid (ECF) outside the cell.

Cell Size and Diversity

Cells vary greatly in size, shape, and function, allowing for specialization. For example, nerve cells are long and thin for signal transmission, while red blood cells are biconcave for gas exchange.