Cell Structure and Function: An Overview for Anatomy & Physiology

3 - Cells

Learning Outcomes

This section introduces the foundational concepts of cell structure and function in human anatomy and physiology. Students should be able to:

• 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.

Overview of Cell Types

Diversity of Human Cells

The human body contains over 200 distinct cell types, each specialized for particular functions. Understanding these cell types is essential for grasping tissue and organ function.

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

• Muscle cells: Include striated (voluntary/skeletal), smooth (involuntary), and cardiac muscle cells, responsible for movement and force generation.

• Bone cells: Involved in bone formation and maintenance.

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

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

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

Additional info: Each cell type has unique structural features and functions that contribute to the overall physiology of the human body.

Cytology: Components of a Cell

Major Structural Components

Cells are the basic units of life, and their structure reflects their function. The main components include:

• Plasma membrane (cell membrane): A phospholipid bilayer that forms the cell's surface boundary, controlling entry and exit of substances.

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

  • Cytosol: The clear gel-like fluid embedding other components; also called intracellular fluid (ICF).

  • Extracellular fluid (ECF): Fluid found outside the cell, such as blood plasma and interstitial fluid.

• Organelles: Diverse structures performing specialized tasks for the cell (e.g., mitochondria, endoplasmic reticulum).

• Nucleus: Contains the genetic code (DNA) and controls cellular activities.

Structure of a Generalized Cell

The generalized cell model illustrates the arrangement of key organelles and structures:

• Microvilli: Increase surface area for absorption.

• Microfilaments and microtubules: Provide structural support and facilitate movement.

• Golgi apparatus: Modifies, sorts, and packages proteins and lipids.

• Endoplasmic reticulum (rough and smooth): Synthesizes proteins and lipids.

• Mitochondria: Produce ATP, the cell's energy currency.

• Lysosomes and peroxisomes: Digest and detoxify cellular waste.

• Nucleus: Houses DNA and nucleolus (site of ribosome synthesis).

Additional info: The arrangement and abundance of organelles vary depending on cell type and function.

Table: Major Human Cell Types and Their Functions

Cell Type	Main Function	Example Location
Nerve Cell	Transmit electrical signals	Brain, spinal cord
Muscle Cell	Contract for movement	Skeletal muscles, heart
Bone Cell	Form and maintain bone	Bones
Gland Cell	Secrete hormones/enzymes	Endocrine glands
Blood Cell	Transport gases, immune defense	Bloodstream
Reproductive Cell	Fertilization	Ovaries, testes

Additional info: This table summarizes the main cell types depicted in the provided diagram.

Key Terms and Definitions

• Phospholipid bilayer: The fundamental structure of the plasma membrane, composed of hydrophilic heads and hydrophobic tails.

• Organelles: Specialized structures within the cell that perform distinct functions.

• Cytosol: The fluid portion of the cytoplasm.

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

• Extracellular fluid (ECF): Fluid outside the cell.

• Nucleus: Organelle containing genetic material (DNA).

Summary

Cells are the building blocks of the human body, with specialized structures and functions that support life. Understanding the diversity of cell types and their components is essential for further study in anatomy and physiology.