What is a Cell? The Foundation of Life

Cells are the fundamental units of life, forming the structural and functional basis of all living organisms. In the human body, they are highly specialised, working collectively to maintain homeostasis, metabolism, communication, and survival.

When cells are exposed to physiological stress — such as dehydration, heat, or reduced oxygen availability — their ability to maintain normal function can be compromised. Understanding how cells are structured and how they function provides a foundation for understanding disease, and for the physiology, pathology, and pharmacology you will encounter throughout the course.

Each cell contains key organelles, each with distinct roles essential for function and coordination.

📌 Core Cellular Components & Their Roles

🧬 Nucleus – The Genetic Control Center

• Houses DNA, which encodes instructions for protein synthesis and cellular function
• Coordinates gene expression, determining cell differentiation and specialisation
• Contains the nucleolus, responsible for ribosome production

⚡ Mitochondria – Energy production and cell survival

• Generate ATP through oxidative phosphorylation, providing energy for cellular processes
• Regulate cellular metabolism, including lipid and carbohydrate utilisation
• Play a role in regulating cell survival and programmed cell death (apoptosis)

📦 Golgi Apparatus – Protein processing and distribution

• Modifies, sorts, and packages proteins for transport within and outside the cell
• Facilitates glycosylation, influencing protein stability and function
• Works closely with the endoplasmic reticulum via vesicular transport

🔗 Endoplasmic Reticulum (ER) – Synthesis and Transport Network

• Rough ER: Studded with ribosomes and responsible for protein synthesis
• Smooth ER: Involved in lipid metabolism, detoxification, and calcium storage
• Acts as an internal transport and processing network within the cell

🛡️ Cell Membrane – A Dynamic and Selective Barrier

• Composed of a phospholipid bilayer that maintains cellular structure
• Embedded with proteins, channels, and receptors that enable transport and signalling
• Regulates osmotic balance, ion exchange, and intercellular communication

🧩 Other Important Cellular Components

• Ribosomes – Sites of protein synthesis (free vs membrane-bound determines protein destination)
• Lysosomes – Intracellular digestion and recycling; important in immune function and genetic storage diseases
• Peroxisomes – Fatty acid metabolism and detoxification
• Cytoskeleton – Provides structure, intracellular transport, and enables cell movement

🔬 Cells Work Together to Form Tissues and Organ Systems

Cells do not function in isolation. They organise into tissues, organs, and systems, allowing the body to perform complex physiological tasks:

• Neurons transmit electrical signals for sensation, movement, and cognition
• Muscle cells contract through actin–myosin interactions, enabling movement
• Epithelial cells form protective barriers and regulate absorption and secretion
• Immune cells (leukocytes) defend against pathogens through antigen recognition

Cells continuously adapt to their environment through growth, division, and programmed death.  Disruption at the cellular level can therefore affect whole organs and systems, contributing to clinical illness.

Coordination between cells occurs through chemical signalling, electrical activity, and direct cell–cell connections, allowing rapid and precise physiological responses.

💡 Key Takeaway

Cells are dynamic, specialised units, each playing a vital role in sustaining life. Whether coordinating metabolism, signalling, defence, or structural support, they ensure organism survival at every level.

💭 Reflection

What type of cell do you find most interesting, and why?

Consider:

• What structural features stand out?
• How do these features enable its function?
• What might happen if that cell failed?