Chapter 3: Cells – The Living Unit (Anatomy & Physiology Study Notes)

Cells: The Living Unit

Introduction

Cells are the fundamental units of life in all living organisms. Understanding their structure and function is essential for the study of anatomy and physiology, as all body processes depend on cellular activity.

Cell Theory

Principles of Cell Theory

• The cell is the smallest structural and functional living unit. All living things are composed of cells, which are the basic units of life.

• Organismal functions depend on individual and collective cell functions. The activities of an organism are the sum of the activities of its cells.

• Biochemical activities of cells are dictated by their specific subcellular structures. The structure of each cell determines its function.

Additional info: Modern cell theory also states that all cells arise from pre-existing cells by cell division.

Cell Diversity

Types and Characteristics of Human Cells

There are over 200 different types of human cells, each specialized for particular functions. These cells vary in size, shape, subcellular components, and roles within the body.

• Fibroblasts: Cells that connect body parts, form linings, or transport gases.

• Erythrocytes (Red Blood Cells): Specialized for oxygen transport.

• Epithelial Cells: Form linings and coverings of organs and body surfaces.

• Skeletal Muscle Cells: Move body parts by contracting.

• Smooth Muscle Cells: Move organs and body parts, especially in internal organs.

• Fat Cells (Adipocytes): Store nutrients in the form of fat.

• Macrophages: Immune cells that fight disease by engulfing pathogens.

• Nerve Cells (Neurons): Gather information and control body functions by transmitting electrical signals.

• Sperm Cells: Specialized for reproduction.

Additional info: The diversity in cell structure reflects the diversity in cell function throughout the human body.

Generalized Cell Structure

Common Features of Human Cells

Despite their diversity, all human cells share certain structural features that are essential for their function.

• Plasma Membrane: A flexible outer boundary that separates the cell from its environment and regulates the movement of substances in and out of the cell.

• Cytoplasm: The intracellular fluid that contains organelles and is the site of most cellular activities.

• Nucleus: The control center of the cell, containing genetic material (DNA) and directing cellular activities.

Additional info: The cytoplasm includes both the cytosol (fluid portion) and the organelles (specialized structures with specific functions).