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

Cells: The Living Units

Introduction to Cells

Cells are the fundamental structural and functional units of life. All living organisms are composed of cells, which carry out essential processes necessary for survival. Human bodies contain over 250 different types of cells, each specialized for particular functions.

• Cell Theory: States that all living things are made of cells, and cells are the basic units of structure and function in organisms.

• Diversity: Human cells vary in size (mostly in the micrometer range), shape, and subcellular components, leading to differences in function.

• Examples: Muscle cells (movement), nerve cells (communication), red blood cells (oxygen transport), macrophages (defense), and reproductive cells.

Basic Parts of a Human Cell

Most human cells share three main structural features:

• Plasma Membrane: A flexible outer boundary that separates the cell's internal environment from the external environment.

• Cytoplasm: The intracellular fluid containing organelles and other cell structures.

• Nucleus: The DNA-containing control center that regulates cellular activities.

Additional info: The cytoplasm includes cytosol (fluid), organelles (specialized structures), and inclusions (stored nutrients or pigments).

Extracellular Materials

Types and Functions

Extracellular materials are substances found outside cells and play important roles in tissue structure and function.

• Extracellular Fluids:

  • Interstitial Fluid: Bathes and surrounds cells.

  • Blood Plasma: Fluid component of blood.

  • Cerebrospinal Fluid: Surrounds nervous system organs.

• Cellular Secretions: Includes substances like saliva and mucus, which aid in lubrication, protection, and digestion.

• Extracellular Matrix: A network of proteins and polysaccharides that acts as a glue to hold cells together and provides structural support.

Additional info: The extracellular matrix is especially important in connective tissues, providing both strength and elasticity.

Learning Objectives Overview

Key Concepts for Study

• Understand the general size and diversity of human cells.

• Identify examples of extracellular materials and their functions.

• Describe the structure of the plasma membrane, including the phospholipid bilayer, proteins, and cholesterol.

• Explain the three types of cell junctions: tight junctions, desmosomes, and gap junctions.

• Distinguish between passive and active transport mechanisms across the plasma membrane:

  • Passive Transport: Simple diffusion, facilitated diffusion, osmosis.

  • Active Transport: Primary and secondary active transport, endocytosis, exocytosis.

• Predict cell behavior in hypertonic, isotonic, and hypotonic solutions.

• Describe the structure and function of major organelles: mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, cytoskeleton, centrosomes, centrioles.

• Identify external features of the cell: cilia, flagella, microvilli.

• Explain the structure and packaging of DNA, including chromatin and chromosomes.

• Describe the stages of the cell cycle, especially interphase and mitosis.

• Summarize DNA replication and the enzymes involved.

• Understand transcription and translation, including initiation, elongation, and termination steps.

• Discuss cell clean-up processes: apoptosis, autophagy, proteasome function.

• Describe cell aging and the role of telomeres.

Additional info: These objectives guide the study of cell structure, function, and life cycle in Anatomy & Physiology.