Cellular Level of Organization: Anatomy & Physiology Study Notes

Introduction to Cells

Cell Theory and Cellular Homeostasis

The cell is the smallest living unit in the human body and serves as the fundamental building block of all organisms. Understanding cell theory is essential for grasping the principles of anatomy and physiology.

• Cell Theory:

  • Cells are the building blocks of all organisms.

  • All cells arise from the division of preexisting cells.

  • Cells are the smallest units that carry out life's essential physiological functions.

  • Each cell maintains homeostasis at the cellular level.

  • Homeostasis at higher levels (tissue, organ, organ system, organism) results from the combined feedback of many cells.

Types of Cells in the Human Body

Cells in the human body are classified based on their function and role in reproduction.

• Sex Cells (Germ Cells or Reproductive Cells):

  • Enable reproduction.

  • Male: sperm

  • Female: oocyte

• Somatic Cells: All body cells except sex cells.

Cytology is the study of the structure (anatomy) of cells and is a branch of cell biology.

Cell Anatomy

Overview of a Model Cell

A typical cell contains various organelles, each with specific functions necessary for cellular operation and survival.

• Nonmembranous Organelles:

  • Microvilli: Extensions that increase surface area for absorption.

  • Centrioles: Organize spindle fibers during cell division.

  • Cytoskeleton: Provides structural support and shape.

  • Cilia: Move substances across the cell surface.

  • Ribosomes: Synthesize proteins.

• Membranous Organelles: (not shown in the provided image, but typically include mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes)

Key Nonmembranous Organelles (as shown in Figure 3-1)

• Microvilli: Increase cell surface area for absorption.

• Centrioles: Essential for cell division.

• Cytoskeleton: Network of protein filaments for cell shape and movement.

• Cilia: Motile structures that move fluids over the cell surface.

• Ribosomes: Sites of protein synthesis, found free in cytoplasm or attached to rough ER.

Example: Epithelial Cell Structure

In epithelial cells, microvilli are abundant to maximize absorption, while cilia help move mucus and trapped particles out of the respiratory tract.

Additional info: Membranous organelles such as mitochondria (energy production), endoplasmic reticulum (protein and lipid synthesis), and Golgi apparatus (modification and packaging of proteins) are also critical for cell function but are not detailed in the provided images.