Cell Theory and Stem Cell Concepts

Cell Theory and Stem Cell Theory

• Cells originate from other cells, inheriting the same genetic information.
• Stem cells have two defining characteristics: self-renewal and differentiation.
• Self-renewal allows stem cells to replicate, creating identical copies.
• Differentiation involves epigenetic changes, leading to specialized behaviors in stem cells.
• Embryonic stem cells are the only truly totipotent stem cells, meaning they can differentiate into any cell type.
• Differentiation progresses to pluripotent stem cells, such as mesenchymal and hematopoietic, which have more limited differentiation potentials.

Embryological Origin of Cell Types

• The three primary germ layers formed during early development are ectoderm, mesoderm, and endoderm.
• These germ layers give rise to different cell types and organs.
• Trans-differentiation, the transformation of one cell type into another across germ layers, is not a naturally occurring process but a subject of active research.

Tissue Types

• Epithelial tissue: Composed of closely packed cells with minimal extracellular matrix.
• Functions: Lining of surfaces, body cavities, glandular secretion.
• Connective tissue: Contains various fixed and wandering cells embedded in an abundant extracellular matrix.
• Functions: Support and protection of tissues and organs.
• Muscle tissue: Contains elongated, contractile cells with moderate extracellular matrix.
• Functions: Strong contraction, body movements.
• Nervous tissue: Composed of elongated cells with extremely fine processes and very minimal extracellular matrix.
• Functions: Transmission of nerve impulses.

Levels of Organization

• The term "tissue" can refer to both simple (histological) and compound tissues.
• Organs are distinct groups of tissues that work together to perform a specific function.
• Organs integrate simple tissue functions to create complex, higher-level functions.

Organ Function from Organization

• The intestine is an example of how multiple tissues work together.
• Ciliated columnar epithelium separates the food compartment and facilitates absorption.
• Connective tissue provides shape, structure, and space within the intestine.
• Smooth muscle tissue enables food motility.
• Vascular tissues are responsible for nutrient transport.

Physical Properties of Tissues

• Strength: Maximum stress a tissue can withstand before failure (tearing).
• Toughness: Ability to absorb energy and prevent fracture.
• Elasticity: Ability and force to return to its original shape.